The 100 most-cited articles in The Journal of Physical Chemistry C, 2021

The crystal orbital bond index (COBI) is a new and intuitive method for quantifying covalent bonding in solid-state materials.COBI is based on the bond index by Wiberg and Mayer and extends their ideas to the case of translationally invariant objects, that is, crystalline matter.COBI's qualitative interpretation resembles the well-established crystal orbital overlap population and crystal orbital Hamilton population methods but should be more familiar to chemists since it directly relates to the classical bond order.In contrast to the aforementioned descriptors, COBI also allows for examining multicenter interactions within a local-orbital framework.As an additional bonding indicator, we refer to the Ewald sum for electrostatic lattice potentials, thereby enabling the calculation of electrostatic lattice energies as well as site potentials from quantum-mechanical charges as directly derived from the wave function, not from the density.

As a general-purpose force field for molecular simulations of layered materials and their fluid interfaces, Clayff continues to see broad usage in atomistic computational modeling for numerous geoscience and materials science applications due to its (1) success in predicting properties of bulk nanoporous materials and their interfaces, (2) transferability to a range of layered and nanoporous materials, and (3) simple functional form which facilitates incorporation into a variety of simulation codes. Here, we review applications of Clayff to model bulk phases and interfaces not included in the original parameter set and recent modifications for modeling surface terminations such as hydroxylated nanoparticle edges. We conclude with a discussion of expectations for future developments.

Hybrid perovskites have been widely used in solar cells and light-emitting diode applications due to superior optoelectronic properties. However, ion migration in these materials causes photo- and thermal instability. On the other hand, mixed electronic–ionic conduction could be advantageous in electrochemical energy storage applications. We have fabricated porous electrodes from three-dimensional (3D) bulk and 2D layered perovskite single crystals and demonstrated that the ion migration could play a significant role in determining the overall performance of the electrochemical supercapacitor. The areal capacitance (∼58 mF cm –2 ), specific capacitance (∼36.82 F g –1 ), and energy density (∼9 W h kg –1 ) calculated at a current density of 0.6 mA cm –2 are higher in 3D perovskite-based supercapacitors, while the maximum power density (∼400 W kg –1 ) is significantly higher in 2D perovskite-based supercapacitors due to faster intercalation/deintercalation of the electrolyte ions into the porous electrode. We have also estimated the amount of diffusion-controlled charge storage to that…

Lithium metal batteries (LMB) are recognized as the most promising high-energy-density energy storage devices. However, its large-scale commercial applications are seriously hampered by the poor cycling stability and potential safety issues. Solid electrolyte interphase (SEI) acts a dominant role in influencing the regulation of Li deposition and overall performance of LMBs, but the composition as well as the evolution of SEI remain quite elusive. Advanced characterization methods and operando monitoring techniques are urgently required. Herein, in this perspective, we first briefly introduce the development history of SEI research and the SEI formation mechanisms as well as the common known components of SEI. Then, we focus on several recent advanced technologies for SEI characterization and monitoring, and the corresponding study cases will be presented. In the end, perspectives including the future investigation directions, the in situ characterization methods, and the component-performance associated model are proposed. We believe that this timely review will help to give a…

A wide range of inorganic nanomaterials with many fascinating properties and application potentials in widespread fields may be synthesized by wet chemical synthetic routes. To achieve scientific and commercial viability of nanomaterials with uniformity and scalability, it is necessary to develop efficient and cost-effective, preferably sustainable, methods. The molten salt synthesis (MSS) method is one such bottom-up technique to fabricate a wide variety of inorganic nanomaterials with tunable size, morphology, and surface characteristics. It is also environmentally friendly, cost-effective, simple to operate, easy to scale, and generalizable, etc. This review gives a critical overview on this emerging and rapidly developing method for making defect free nanomaterials in well-defined texture, surface, and morphology at a relatively low formation temperature. We have discussed its different aspects, including the role of molten salts, the choice of molten salts, the electrochemical aspects, some advanced modifications of the conventional MSS technique, and their implications. To…

Electrochemical impedance spectroscopy, photoelectron spectroscopy, and Kelvin probe measurements on various TiO 2 single-crystal surfaces show that the position of the Fermi level and the conduction band minimum depend significantly on the sample environment (vacuum, air, water vapor, and aqueous or aprotic electrolyte solutions). In most cases, the conduction-band minimum increases in the series: anatase < rutile < brookite. The offset between anatase and rutile indicates a type II staggered alignment if the environment is vacuum, air, water vapor, or aprotic electrolyte solution, but a type IV aligned configuration is found in an aqueous electrolyte solution. The photoelectron spectra in water vapor reveal a strong upshift of the conduction band, which is nearly reversible in the early stages of water/titania interactions. Our results rationalize various earlier contradictions and highlight the need for proper analytical techniques and experimental conditions for investigation of the band energetics, which is relevant to practical applications of titania materials.

High Resolution Image Download MS PowerPoint Slide “Anode-free” batteries present a significant advantage due to their substantially higher energy density and ease of assembly in a dry air atmosphere. However, issues involving lithium dendrite growth and low cycling Coulombic efficiencies during operation remain to be solved. Solid electrolyte interphase (SEI) formation on Cu and its effect on Li plating are studied here to understand the interplay between the Cu current collector surface chemistry and plated Li morphology. A native interphase layer (N-SEI) on the Cu current collector was observed with solid-state nuclear magnetic resonance spectroscopy (ssNMR) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry (CV) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies showed that the nature of the N-SEI is affected by the copper interface composition. An X-ray photoelectron spectroscopy (XPS) study identified a relationship between the applied voltage and SEI composition. In addition to the typical SEI components, the SEI contains copper oxides (Cu…

Gallium-based liquid metals have gained plenty of attention in the scientific community due to their extraordinary properties. The most intriguing properties of liquid metals are high surface tension, density anomaly, high electrical and thermal conductivity, phase transition, and their temperature and low viscosity in combination with their low toxicity. Though there are many reports of the physical properties of gallium-based liquid metals, some of these are highly scattered and inconsistent. Therefore, we compile literature data of these aspects of gallium-based liquid metals, point out general relationships of these physical parameters, and unravel inconsistencies in the literature. Subsequently, we state reasons for the observed scatter and recommend science-based values researchers should employ. Furthermore, we discuss important dependencies between the physical parameters, introduce methods to alter the physical parameters, and introduce selected applications based on changing the physical properties. Finally, we point out open questions concerned with the physical…

This Perspective Letter discusses the characterization by infrared spectroscopy of CO adsorbed of isolated metal atoms, also referred to as single atom catalysts (SAC).The main difficulties encountered during the analysis are briefly discussed, e.g.band assignment, sample structural evolution, spectral corrections and signal enhancement.Theoretical investigations by DFT stressed the high number of surface structures that may be considered for the support (e.g., crystal termination, partial reduction or not) and isolated metal atom (e.g., adsorbed or substituted, oxidized or not), still making site identification a challenge.In addition, most DFT models do not incorporate surface hydroxyls, carbonates or other adsorbates that are present on real materials.Cases regarding Rh, Pd and Pt-based catalysts are presented in which IR has genuinely proven conclusive, in complement to other techniques, in terms of the nature of the metal phases present.Finally, recent contributions in which the exact nature of the phase present is still open or questionable are discussed, the aim of the…

Noncovalent interactions at electrified interfaces are key to improving activity for the oxygen evolution reaction (OER). Here, we showed that on RuO 2 (110) in alkaline solutions, OER activity is cation-dependent, being largest in 0.1 M KOH compared to LiOH and NaOH. Using crystal truncation rod analysis, −O is detected on the coordinatively unsaturated site at 1.5 V RHE in 0.1 M KOH, suggesting that the rate-determining step is −O + OH – → -OOH + e –, which is different from that in acid involving the final deprotonation of −OOH. The ordering of interfacial water in base was found to decrease with increasing potential and independent of cations. Using surface-enhanced infrared spectroscopy, the density of isolated water molecules (zero H-bonds) was found to increase, and the density of icelike water molecules (four H-bonds) decreases from Li + to K + at OER potentials. The higher activity of more isolated interfacial OH – ions in the case of K + and the lesser stabilization of −O intermediates by hydration water of K + compared to Na + and Li + can result in higher OER activity…

Abstract The aim of this work was to investigate the influence of morphology on its electrochemical properties by comparing ZnO nanostructures in the forms of tetrapods of different sizes, nanorods, and nanoparticles. ZnO tetrapods were prepared by the combustion method and separated into two fractions by size, ruling out the influence of synthesis conditions. Structural and morphological properties of different ZnO nanostructure morphologies were identified by using various characterization techniques: scanning and transmission electron microscopies (SEM and TEM), X-ray powder diffraction (XRD), nitrogen adsorption/desorption measurements at 77 K, and UV–vis spectroscopy (UV–vis). Analysis of electrochemical properties showed the highest active surface area of 0.095 cm2 and the lowest peak separation value of 61.7 mV for large ZnO tetrapods, which are close to the theoretical values. The correlation between the pore size in different ZnO nanostructures because of packing and their electrochemical properties is established. We expect that the detailed analysis of ZnO nanostructures…

Ionic liquids (ILs) have become highly popular solvents over the last two decades in a range of fields, especially in electrochemistry. Their intrinsic properties include high chemical and thermal stability, wide electrochemical windows, good conductivity, high polarity, tunability, and good solvation properties, making them ideal as solvents for different electrochemical applications. At charged surfaces such as electrodes, an electrical double layer (EDL) forms when exposed to a fluid. IL ions form denser EDL structures compared to conventional solvent/electrolyte systems, which can cause differences in the behavior for electrochemical applications. This Perspective discusses some recent work (over the last three years) where the structure of the EDL in ILs has been examined and found to influence the behavior of supercapacitors, batteries, sensors, and lubrication systems that employ IL solvents. More fundamental work is expected to continue in this area, which will inform the design of solvents for use in these applications and beyond.

Cu-doped TiO 2 photocatalysts [Cu-(1 to 10) atom %] synthesized by the sol–gel method and thoroughly characterized using several techniques were evaluated for photocatalytic reduction of CO 2 under ambient conditions. These photocatalysts converted the reactant mixture of CO 2 and moisture selectively into methane and oxygen under visible irradiation without the use of any sacrificial agent. The Cu dopant considerably lowered the bandgap of TiO 2, thereby making it feasible for doped TiO 2 to absorb light in the visible region. Beyond 1% Cu doping the Cu-doped TiO 2 materials were far superior as compared to anatase TiO 2 for the reduction of CO 2 to CH 4, and the lowest doping (Cu-1%) concentration in TiO 2 lattice shows the maximum production of CH 4 (1081 μL/h/g), whereas the highest doping (Cu-10%) shows the least activity (200 μL/h/g). The photoreduction activity was found to decrease with increasing Cu concentration; under similar conditions without use of any cocatalysts. X-ray photoelectron spectroscopy (XPS) results along with cyclic voltammetry data (CV) indicate that the…

The chlorine evolution reaction (CER) has practical applications in the chlor-alkali industry and electrochemical wastewater treatment. Efficient, stable, and cost-effective electrodes are critical for energy efficient chlorine production, water disinfection, and wastewater treatment. These practical applications require an in-depth understanding of the catalytic mechanism of chlorine evolution, the need for lower-cost electrode materials, and improvements in electrode design at the atomic scale. Herein, we examine factors controlling activity, selectivity, and stability of alternative CER electrodes and provide mechanistic insights for achieving improvements in performance and durability. Steric effects of crystal structure and intermetallic electron polarization provide insights for understanding and tuning the electrode activity and selectivity. Additional insight into electrode deactivation mechanisms was gained by employing model material systems under controlled conditions. Herein, we explore viable strategies for the development of more efficient noble-metal-free CER…

Theoretical assessment of potential-dependent activation energies of electrochemical reactions is of critical importance but remains challenging. In this work, we present two computational tools to tackle this long-standing challenge. First, we implement a general computational framework for constant-potential saddle searches including both atomic positions and number of electrons as variables. Second, we develop a novel correction method to determine potential-dependent activation energies based on conventional zero-charge calculations. Different from existing capacitance-only schemes, our correction method takes into account the potential-dependent structural relaxation. This correction allows a significant reduction in computational overhead, but is still quite accurate, supplementing the direct constant-potential simulation. With these tools, we study the O–O bond formation reaction on the RuO 2 (110) surface. A number of new mechanistic insights are developed from the constant-potential calculations. The proton-coupled electron transfer pathway for the O–O bond formation has…

NiOOH is one of the most promising catalysts for electrooxidation of water and organic molecules. Accompanying the long experimental practice to optimize the catalyst, atomic simulations, mainly based on density functional theory (DFT) calculations, have been performed in recent years to reveal the atomic structure of NiOOH and the reaction mechanism in catalysis. Due to both the structural complexity and the difficulty in computing the electronic structure, there are great concerns over the accuracy of first-principles methods and the validity of the structure models. This Perspective serves to overview the current status of atomic simulation on the structure and catalysis of NiOOH. We first present NiOOH phases and structures obtained by the latest global optimization methods in combination with machine learning potentials. The electronic structures of NiOOH are then described by comparing the performance of different theoretical levels, in particular, those based on PBE+U and hybrid functionals in DFT calculations. Finally, taking the oxygen evolution reaction of water splitting…

The excited state charge transfer (CT) characteristics of nonfullerene acceptors play an important role in determining the photo excited CT mechanisms and performance for organic solar cells (OSCs). Here, we systematically investigated the structure–property relationship and excited state CT characteristics based on A–D–A and A–DA′D–A type acceptors by density functional theory (DFT) and time-dependent DFT (TD-DFT). Comparing to the A–D–A type acceptors IT-4F and DTPC-DFIC, the A–DA′D–A type acceptor Y6 exhibits distinct structural and electronic characteristics, such as featuring larger Mulliken electronegativity, molecular polarity index (MPI), and electrostatic potential (ESP). Besides this, the larger hole and electron delocalization index (HDI, EDI) proves more effective charge separation for Y6. Their excited state CT characteristics are all mainly from the intermediate cores to the terminal units, while the CT in the opposite direction of Y6 is stronger than that of IT-4F and DTPC-DFIC, which provides theoretical support for the formation of multielectron transport channels…

The effect of La-doping on the crystallographic structure and the Raman line-shape of CeO 2 has been investigated. X-ray diffraction analysis suggests that the lattice parameter and the Ce/La–O bond length gradually increase with La-doping. The Williamson–Hall plot method has been used to investigate structural coherency and lattice strain. Scanning electron microscopy and energy-dispersive X-ray spectroscopy have been carried out to study the particle size distribution and weight percentage doping of La in CeO 2, respectively. Intrinsic and extrinsic oxygen vacancies have been understood in terms of ionic radii mismatch and the mixed oxidation state of the host and dopant. Furthermore, Raman spectroscopy results indicate the appearance of red-shift, peak broadening, and asymmetry with an antiresonance dip in the Raman line-shape (F 2g ). The observed changes in the Raman line-shape have been explained, considering electron–phonon-coupling-induced Fano scattering and phonon confinement effects.

The kinetics of aqueous outer-sphere electron-transfer (ET) reactions are determined in large part by noncovalent electrostatic interactions that originate from the surrounding electrolyte solution. In this work, we examine the role of spectator cations in modifying the rate of heterogeneous ET for an [Fe(CN) 6 ] 3– /[Fe(CN) 6 ] 4– redox pair. We combine the results of electrochemical measurement, in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), classical molecular dynamics simulation, and theoretical modeling to demonstrate how changing the identity of the spectator cation species over a series that includes Li +, Na +, K +, Rb + to Cs + influences the solvation properties and ET kinetics of the redox species. By analyzing the results in the context of the Marcus–Hush–Chidsey (MHC) theory, we find that the solvent reorganization energy increases systematically as the cationic radius decreases. The trend can be attributed to cation-dependent coordination environments of the redox species, whereby more cations of less charge density such as Cs + than Li + are…

The partial replacement of Portland cement by aluminosilicate-rich supplementary cementitious materials (SCMs) represents a valuable approach to lower the CO 2 footprint of concrete. However, SCMs alter the composition and structure of the principal binding component, calcium-alumino-silicate-hydrate (C-(A)-S-H), a less-crystalline aluminum-substituted calcium silicate hydrate. The uptake and structural impact of alkalis and aluminum are investigated for synthesized C-(A)-S-H phases with different Ca/Si and Al/Si ratios and alkali (Na + ) contents, using solid-state 23 Na, 27 Al, and 29 Si NMR as principal analytical tools. 29 Si{ 1 H} CP/MAS NMR data propose that the −87 ppm resonance originates from a second type of Q 2 pairing sites most likely in the middle of octameric or longer silicate units. This assignment along with constraints induced by the silicate dreierketten structure results in reliable simulations of the 29 Si NMR spectra. A quantitative 1:1 relation between the Al/Si ratios from 29 Si NMR and the content of fourfold-coordinated Al from 27 Al NMR is observed, which…

The two-dimensional (2D)/three-dimensional (3D) heterojunction perovskite solar cell (PSC) has recently been recognized as a promising photovoltaic structure for achieving high efficiency and long-term stability. Rational design of the 2D spacer cation is important to achieve a win–win situation for defects’ passivation and photogenerated carrier extraction. Herein, we carry out first-principles calculation to analyze the dipole moment of phenethylamine-type molecules and their resulting 2D/3D perovskites. Based on the results of theoretical calculation, the dipole moment of 2D cations can be well tuned by varying the number of fluorine atoms on the para-position of the benzene ring, which further determines the interfacial dipole across the 2D/3D heterojunction interface. A high dipole 2D perovskite layer at the interface between the 3D perovskite and hole-transporting material is found to promote charge transport and suppress charge trapping efficiently. As a result, our 2D/3D PSCs exhibit a champion power conversion efficiency over 22% and a fill factor over 83%. Moreover, our…

2D electronic spectroscopy (2DES) techniques have gained particular interest given their capability of following ultrafast coherent and noncoherent processes in real-time. Although the fame of 2DES is still majorly linked to the investigation of energy and charge transport in biological light-harvesting complexes, 2DES is now starting to be recognized as a particularly valuable tool for studying transport processes in artificial nanomaterials and nanodevices. Particularly meaningful is the possibility of assessing coherent mechanisms active in the transport of excitation energy in these materials toward possible quantum technology applications. The diverse nature of these new target samples poses significant challenges and calls for a critical rethinking of the technique and its different realizations. With the confluence of promising new applications and rapidly developing technical capabilities, the enormous potential of 2DES techniques to impact the field of nanosystems, quantum technologies, and quantum devices is here delineated.

The reliable programmability of DNA origami makes it an extremely attractive tool for bottom-up self-assembly of complex nanostructures. Utilizing this property for the tuned arrangement of plasmonic nanoparticles holds great promise particularly in the field of biosensing. Plasmonic particles are beneficial for sensing in multiple ways, from enhancing fluorescence to enabling a visualization of the nanoscale dynamic actuation via chiral rearrangements. In this Perspective, we discuss the recent developments and possible future directions of DNA origami-enabled plasmonic sensing systems. We start by discussing recent advancements in the area of fluorescence-based plasmonic sensing using DNA origami. We then move on to surface-enhanced Raman spectroscopy sensors followed by chiral sensing, both utilizing DNA origami nanostructures. We conclude by providing our own views on the future prospects for plasmonic biosensors enabled using DNA origami.

The room-temperature sodium–sulfur (Na–S) batteries have attracted remarkable attention because of their promise to deliver high-capacity and low-cost earth-abundant sodium and sulfur. However, the practical development of Na–S batteries is hindered due to multiple challenges, including rapid capacity fading stems from the dissolution of intermediate sodium polysulfides (Na 2 S n ) and slow kinetics of electrochemical conversion reactions. In this study, we introduced novel transition-metal single-atom catalysts (SACs) on nitrogen-doped graphene (NG) to impede the dissolution of higher-order Na 2 S n and improve otherwise sluggish kinetics of short-chain polysulfides. The density functional theory (DFT) calculations are used to elucidate the detailed interactions of the polysulfides on the SACs. The pristine and nitrogen-doped graphenes are also considered and found to provide ineffective anchoring for trapping polysulfides. However, the SACs embedded via monodispersed transition-metal atoms in NG (TM-NG where TM = Cr, Fe, and Co) exhibit adequate binding strength toward Na 2 S n…

Catalytic transformation of CO 2 into chemicals in large demand such as ethanol has attracted much research attention under the background of establishing carbon-neutral societies. Supported Rh catalysts are promising candidates for the hydrogenation of CO 2 to ethanol but suffer from low ethanol productivity and poor catalyst stability. Here, we report that zeolite silicalite-1 embedded Na-promoted Rh nanoparticles (Na-Rh@S-1) demonstrate high productivity and stability for CO 2 hydrogenation to ethanol. The ethanol selectivity of 24% was attained at a CO 2 conversion of 10%, and the space-time yield of ethanol reached 72 mmol g Rh –1 h –1, which outperformed most of the Rh-based catalysts reported to date. While a reference catalyst prepared by impregnation underwent deactivation, the Na-Rh@S-1 catalyst was stable for at least for 100 h owing to the confinement effect. The Na + modifier played crucial roles in enhancing the CO 2 conversion and ethanol selectivity by suppressing methane formation. The characterizations suggest that the presence of Na + enables the coexistence of Rh…

Vibrational strong coupling offers newfound potential to affect chemical processes and represents a wholly new approach to catalysis. While this presents extraordinary opportunities in the areas of product-selective synthesis, pharmaceutical design and yield, energy generation and storage, and unique optical devices, there are a number of important obstacles, including a lack of mechanistic understanding, unconventional or misleading spectroscopic interpretations, and a shortage of corroborating evidence. Here, we present our perspective on opportunities, obstacles, and the most pressing work to be completed in order to establish the significant but challenging new field of quantum optical chemistry.

Two-dimensional (2D) transition-metal monochalcogenides have been recently predicted to be potential photo(electro)catalysts for water splitting and photoelectrochemical (PEC) reactions.Differently from the most established InSe, GaSe, GeSe, and many other monochalcogenides, bulk GaS has a large band gap of ∼2.5 eV, which increases up to more than 3.0 eV with decreasing its thickness due to quantum confinement effects.Therefore, 2D GaS fills the void between 2D small-band-gap semiconductors and insulators, resulting of interest for the realization of van der Waals type-I heterojunctions in photocatalysis, as well as the development of UV light-emitting diodes, quantum wells, and other optoelectronic devices.Based on theoretical calculations of the electronic structure of GaS as a function of layer number reported in the literature, we experimentally demonstrate, for the first time, the PEC properties of liquid-phase exfoliated GaS nanoflakes.Our results indicate that solution-processed 2D GaS-based PEC-type photodetectors outperform the corresponding solid-state photodetectors.In…

Limited by the intrinsic semiconductor behavior and the number of active sites, the application of MoS 2 as an electrocatalyst is hindered. Doping is an easiest strategy to improve its properties. In addition, it is found that the interlayer-regulatory can be used as another strategy to improve the catalytic properties of MoS 2 . Therefore, we apply the first-principles method to systematically study the effect of interlayer doping on the catalytic properties of MoS 2 disulfide. Furthermore, we investigate the influence of the interlayer-doped systems on the catalytic hydrogen evolution of MoS 2 . The results show that the interlayer doping strengthens the interaction between the monolayer of MoS 2, which is beneficial to improve the structural stability. Importantly, interlayer doping promotes local hybridization at the Fermi level inducing the interlayer-doped MoS 2 to show a degree of metallic behavior. As a result, it is obviously beneficial to improve the catalytic hydrogen evolution effect of MoS 2 . Finally, it is found that hydrogenated C-doped MoS 2, with excellent…

A major challenge toward the practical application of lithium–sulfur (Li–S) batteries is the lithium polysulphide (LiPS) shuttling, caused by the rapid LiPS migration in the electrolyte and slow reaction kinetics. Single-atom catalyst (SAC) materials hold the promise of strong LiPS binding to the cathode and improved reaction kinetics in Li–S batteries. In this study, we examine the electrocatalytic properties of four SAC materials with TM–N 4 –C (TM = Co, Fe, V, and W) formation, from simulations based on the density functional theory. We study for the first time a W-based SAC as the Li–S cathode host and calculate the adsorption energy of five LiPS intermediates (Li 2 S n, n = 1, 2, 4, 6, and 8). We explore the mechanism for the conversion of Li 2 S 2 to Li 2 S and present the energy profiles based on the Gibbs free energy for the LiPS reaction pathway from S 8 to Li 2 S. V- and W-based SACs provide high LiPS binding, of up to 6.0 times of pristine graphene, and largely improved reaction kinetics by lowering the S dissociation barrier of the Li 2 S 2 decomposition by ∼2.5 times…

High Resolution Image Download MS PowerPoint Slide Alkali-activated materials are promising low-carbon alternatives to Portland cement; however, there remains an absence of a fundamental understanding of the effect of different activator types on their reaction products at the atomic scale. Solid-state 27 Al and 29 Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and 1 H– 29 Si cross-polarization MAS NMR spectroscopy are used to reveal the effect of the activator anion on the nanostructure, cross-linking, and local hydration of aged alkali-activated slag cements. The main reaction product identified is a mixed cross-linked/non-cross-linked sodium-substituted calcium aluminosilicate hydrate (C–(N)–A–S–H) gel with a structure comparable to tobermorite 11 Å. Analysis of cross-polarization kinetics revealed that a higher content of soluble silicate in the activator promoted the incorporation of Al into the aluminosilicate chains of C–(N)–A–S–H gels, charge-balanced preferentially by protons within the gel interlayer. In sodium carbonate-activated slag cements,…

Lead-free all-inorganic perovskites have been widely investigated as alternative materials to replace organic lead-based perovskites in solar cells. Although thousands of studies have been reported, several questions remain in debate, e.g., the role of structural phases and octahedra distortions in the optoelectronic and excitonic properties. Here, we report a theoretical investigation of those effects in the CsGeX 3 (X = Cl, Br, I) perovskites by the combination of hybrid density functional theory calculations, spin–orbit coupling for the valence states, maximally localized Wannier functions tight-binding framework, and solution of the Bethe–Salpeter equation (BSE). In contrast to CsGeCl 3 and CsGeBr 3, which has an energetic preference for distorted cubic structures, hexagonal phases yield the lowest energy for CsGeI 3, i.e., the X atomic radius plays an important role in the relative stability. Our results show that octahedra distortion lowers the total energy and increases the energy band gap substantially (above 1.0 eV), which can be explained by volume increasing and…

The Frenkel exciton dissociation efficiency and the subsequent free charge carrier migration rate mainly determine the photocatalytic property of polymeric carbon nitride (PCN). Herein, by postcalcination of heptazine-based PCN in molten salts at mild temperature (673 K), we are able to design a series of crystalline PCNs with a promising triazine–heptazine hybrid structure. The molecular triazine–heptazine junctions promote the exciton splitting, while the ordered in-plane packing structure facilitates the hot charge carrier migration. Accordingly, the optimal triazine–heptazine-based PCN exhibits a dramatically enhanced activity toward one-step excitation photocatalytic overall water splitting to generate H 2 and O 2 with visible light over heptazine-based pristine PCN, by a factor of ∼34 times.

The recently synthesized two-dimensional (2D) MoSi 2 N 4 material with a proper band gap and excellent environmental stability promises potential optoelectronic applications. On the basis of first-principles calculations and electron–phonon interaction theory, we systematically analyze the structural, optical, carrier distribution and transport, and photocatalytic water-splitting properties of pristine and strained MoSi 2 N 4 monolayers. They are all found to be dynamically stable. Their optical absorption efficiencies are very high for photon energy larger than the respective band gap. Surprisingly, the optical absorption coefficient of tensile MoSi 2 N 4 is as large as 10 6 cm –1 across 300–880 nm. To the best of our knowledge, this is the best among optoelectronic materials in the visible region. In addition, compressive strain results in spatial separation of photogenerated electrons and holes, which is beneficial for increasing their separation rates. Transport properties indicate that the lifetime and mean free path (MFP) of photogenerated electrons and holes are,…

Fixing the greenhouse gas CO 2 via cycloaddition reactions to value-added cyclic carbonates or photocatalytic reduction of CO 2 to produce desirable fuels is the most coveted, although challenging, energy-efficient valorization technique owing to the chemical and thermodynamic stability of CO 2 . Therefore, catalytic materials with an optimum amount of surface porosity and Lewis acidity and basicity play an instrumental and crucial role in CO 2 activation in the CO 2 fixation reaction. On the other hand, the efficacy of the photocatalytic reduction of CO 2 depends on the appropriate band alignment of the catalytic materials and the competitive H 2 evolution reaction. Here, we have synthesized Ce-MOFs with and without amine functionalization and compared both MOFs for CO 2 fixation with epoxides and photocatalytic reduction of CO 2 . The amine-functionalized MOF, Ce-BDC-NH 2, not only exhibited efficient CO 2 fixation to produce cyclic carbonate at room temperature and pressure but also demonstrated effective photoreduction of CO 2 with high selectivity toward CH 3 OH and HCO 2 H.…

Metal–water interactions are investigated using ab initio molecular dynamics simulations performed on water-interfaced Pt(111) and Au(111) as model systems, aiming at understanding the mechanism of interface water molecules to regulate the potential of zero charge (PZC) of metal electrodes in aqueous solutions. Several metal–water interactions are distinguished, and their effects on the metal work function (WF) are quantified through carefully correlating the interfacial atomic and electronic structures. The first layer of interface water molecules possesses an O-down configuration and significantly lowers the metal WF by increasing the near-surface electron density through Pauli repulsion, coordination bonding, and subordinate dipole orientation. In contrast, the H-down-configured water molecules in the second solvation layer increase the metal WF due to the metal–hydrogen bonding interaction and dipole orientation. Involved in the second layer are also water molecules that have no preferred orientation and merely act as hydrogen bond linkers. They negligibly affect the electronic…

High Resolution Image Download MS PowerPoint Slide The interfacial capacitance of a metal electrode in contact with a dilute electrolyte is generally expected to follow the behavior predicted by the Gouy–Chapman–Stern model. Recent experiments [ Angew. Chem. Int. Ed. 2020, 59, 711], however, have shown that a deviation from the Gouy–Chapman behavior is observed even in dilute electrolytes on platinum and gold single-crystal electrodes. Such deviations are usually attributed to an interaction between the surface and the electrolyte ions. However, a quantitative model showing that the strong deviations from the Gouy–Champan behavior observed for Pt can be ascribed to such an effect is still lacking, particularly as other experimental observables do not indicate a strong ion adsorption. Here, we propose a double-layer model that is capable of reproducing the main experimental findings in a simple and (in parts) analytical way. The analytical model thereby includes the attractive ion–surface interaction via an additional capacitive element connected in parallel to the Gouy–Chapman…

Photocatalytic CO 2 reduction into renewable fuels by sustainable and clean solar energy can be considered as an ideal option to decrease the atmospheric CO 2 level and fulfill the energy requirements. Layered double hydroxides (LDHs) with high surface area, tunable composition as well as exposed active sites have received enormous attention for photocatalytic CO 2 reduction. Herein, a novel NiAl-LDH/Ti 3 C 2 T x nanosheet (NiAl-LDH/TNS) with a core–shell structure was synthesized via an in situ hydrothermal method, and 2D NiAl-LDH coupled with the 2D Ti 3 C 2 T x nanosheet to form a Schottky junction can suppress the back-diffusion of electrons and facilitate the transfer of charge carriers. Benefiting from the feature, the optimized sample with the additive Ti 3 C 2 T x amount of 75 mg (NiAl-LDH/TNS-75) has the photocatalytic CO 2 reduction conversion rate of CO (2128.46 μmol h –1 g –1 ) with the selectivity of CO (90.2%) under visible-light irradiation, which is about 8.6 times higher than that of pristine NiAl-LDH. This work provides a new insight into the construction of novel…

Following on the heels of the remarkable lead halide perovskite optoelectronic materials, interest in lead-free halide perovskites has grown rapidly in the past decade. Double perovskite halides with the general formula A 2 M I M III X 6 (where A is a large monovalent cation in the perovskite A site, M I is a univalent metal, M III is a trivalent metal, and X is a halide) represent one of the promising classes of such materials, and of these, the iodides are particularly interesting since their band gaps are expected to be similar to those found in the iconic lead-containing phases, A PbI 3 . However, the successful synthesis of A 2 M I M III I 6 iodides appears to have been elusive. In this work, we examine the likelihood that double perovskite halides will form using a combination of the Goldschmidt tolerance factor and the radius ratio of the trivalent metals, M III, and rationalize the rarity of double perovskite iodides in terms of these descriptors. Using this model as the formability criterion, we predict the possible existence of more than 300 hitherto unknown double…

The behavior of the trion and exciton photoluminescence (PL) under various laser excitation conditions, that is, energy and power, is studied in monolayer and few-layer (FL) chemical vapor deposition (CVD)-MoS 2 flakes grown on SiO 2 /Si. The room-temperature μ-PL spectroscopy of the flakes shows that the A exciton at 1.86 eV is overlapped by the trion component. First, the thickness-dependent characterization of the flakes has been carried out. The trion spectral weight and dissociation energy are observed to increase with the number of layers, which is correlated with an increase in nonequilibrium electron density. We propose the presence of many-body effects explaining this unusual dependence in CVD-MoS 2 on n-type SiO 2 /Si. In the power-dependent μ-PL measurements, the deconvolution of spectra for the exciton and trion bands shows a faster intensification of the trion component compared to the A exciton with increasing laser power. The trion binding (dissociation) energy varied from 28 to 33 meV in the monolayer and from 32 to 46 meV in FL MoS 2, when increasing the power of…

High Resolution Image Download MS PowerPoint Slide We have investigated the doping-induced local structural and electronic effects in the recently developed low band gap room temperature ferroelectric Mn–Nb co-doped BaTiO 3 . Experimental and theoretical Raman spectroscopies are utilized to quantify the Ti off-centering, identified to be the intrinsic origin of ferroelectricity in these systems. Mn and Nb exhibit contrasting doping behaviors that have remarkable effects on BaTiO 3 functionality. Jahn–Teller distorted Mn 3+ is primarily associated with lowering of the bulk band gap, while charge-compensating Nb 5+ off-centers within the O 6 octahedra, creating a polar mode that stabilizes the ferroelectric ground state. The charge neutral aliovalent Mn 3+ –Nb 5+ pair effectively couples to the inherent ferroelectric instability of the BaTiO 3 lattice, restoring some spontaneous polarization lost by doping Mn 3+ (d 4 ) ions at Ti 4+ (d 0 ) sites.

High Resolution Image Download MS PowerPoint Slide Although using supported noble-metal catalysts for CO 2 hydrogenation is an effective solution due to their excellent catalytic properties, metal oxide supports themselves can exhibit good activity being more economically feasible. This work focuses on investigating the complexity of the Co 3 O 4 system during the CO 2 methanation reaction, which is usually accompanied by the formation of unstable dispersions of cobalt oxide and metallic Co. Herein, we have tested different types of Co 3 O 4: synthetically prepared mesoporous m-Co 3 O 4 (BET surface area, 95 m 2 /g) and commercial c-Co 3 O 4 (BET surface area, 15 m 2 /g; purchased from Merck) in the CO 2 methanation reaction under different reduction temperatures (273–673 K). The reduction temperature was adjusted to 573 K for both the catalysts to reach the optimal Co/cobalt oxide ratio and consequently the best catalytic performance. m-Co 3 O 4 is more active (CO 2 conversion 95%) and stable at higher temperatures compared to c-Co 3 O 4 (CO 2 conversion 63%) due to its…

Persistent luminescence and photochromism are two fascinating optical properties that involve charge trapping via defects and their release due to an external stimulation. In both processes, it is possible to define “1” (or “on”) and “0” (or “off”) optical states. Consequently, materials with one of these phenomena find major interest in view of designing smart, anticounterfeiting, and optical information storage devices. Combining both processes within a single material can lead to a new generation of information storage phosphors, in which it may be possible to obtain three different optical states by playing on the external stimulations applied on the material. For that purpose, the elaboration of nickel-doped ZnGa 2 O 4 spinel transparent nano-glass-ceramics is presented in this work. The short-wave infrared (SWIR) emission, a broad band located at ca. 1275 nm, arises from Ni 2+ cations located in gallium octahedral sites. SWIR persistent luminescence, arising from the same doping ion transition, can also be monitored after UV charging. Interestingly, UV irradiation not only…

The modern society is confronted with severe problems of energy consumption, climatic variation, and environmental pollution. A series of electrocatalysis reactions, including oxygen evolution reaction (OER), hydrogen evolution reaction (HER), CO 2 reduction reaction (CO 2 RR), N 2 or nitrate reduction reaction (NRR or NO x RR), and methanol or ethanol oxidation reaction (MOR or EOR), have become promising ways to solve these serious issues and realize sustainable development. However, the limited understanding of the dynamic process of electrocatalysis still hinders the rational design of these electrocatalysts. Combining infrared spectroscopy with electrocatalysis, in situ electrochemical infrared spectroscopy ( in situ EIRS) is a mighty tool to acquire deep insight of dynamic electrocatalytic reaction process at molecule level. Moreover, the surface sensitive in situ EIRS could acquire information about the adsorbates and the key intermediate, making it broad prospects in the study of electrocatalytic dynamic process. In this short review, we summarize recent progress of in situ…

Nanoceria have been widely applied in biosystems because of their peroxidase- and oxidase-like catalytic activities. However, the atomistic mechanisms of these activities are still open questions. Using density functional theory calculations, we propose the mechanisms for these catalytic processes. The results suggest that oxygen vacancies present in nanoceria play vital roles in the catalysis. Specifically, oxygen vacancies located in the third layer are essential to form the kinetically feasible catalytic cycles. In contrast, nanoceria without oxygen vacancies are predicted to have the weak activities because of its weak affinity for H 2 O 2 and O 2 . Instead, the O v -free nanoceria can directly oxidize protonated TMB under an acidic condition. The intermediate formed by the one-electron reduction of O 2 during the oxidase-like catalysis is active to produce the electron paramagnetic resonance signal of O 2 •– . The results provide atomistic level insight into the enzyme-like catalytic activities of nanoceria, which explains the experimental findings and may help the future…

Understanding the plasma etching mechanism of diamond is of great significance to promote diamond applications; however, insights into the atomic-scale etching mechanisms are hidden by the complex chemical reactions during the etching process due to the lack of an in situ characterization technique into the etching process. Herein, we conducted an etching simulation of diamond using the reactive molecular dynamics simulation method to comparatively investigate the different etching mechanisms of diamond by oxygen and hydrogen plasma with different incident energies. In the case of oxygen etching, at all tested incident energies, C–C bonds on the diamond surface are dissociated by the irradiated oxygen, and carbon atoms of diamond are etched away via the generation and desorption of gaseous carbon monoxide and carbon dioxide molecules. In the case of hydrogen etching, at low incident energies, we revealed that the carbon atoms are etched through the desorption of gaseous hydrocarbon molecules similar to the oxygen etching mechanism, while with increasing the incident energies, we…

The synthesis of high-quality WS2 and more so of MoS2 (multiwall) nanotubes in substantial amounts from oxide precursors is a very challenging and important undertaking. While progress has been offered by a recent report, the present work presents another step forward in the synthesis of MoS2 nanotubes with a narrow size distribution and better crystallinity than before. Williamson–Hall analysis of the X-ray diffraction data is used to analyze the crystallinity and strain in the nanotubes. This analysis shows that the crystallinity and average diameter of the WS2 and MoS2 nanotubes reported here (type II) are better than those obtained according to the previous methods (type I). Size selection by centrifugation reported by others is used here to prepare several fractions of WS2 and MoS2 nanotubes according to their average diameter. The high refractive index of WS2 and more so MoS2 enables the nanotubes to trap light by total internal reflection, turning them into nanocylindrical resonators and thereby supporting cavity-mode resonances. The extinction, net absorption, and transient…

Lithium phosphorus oxynitride (LiPON) has paved the way for thin film solid-state battery technology development and has shown application in a large range of fields since its first reported synthesis in 1993. The term LiPON describes the family of materials with the general formula of Li x PO y N z offering a great range of stoichiometries with varying properties. Understanding how the properties of LiPON are affected by different preparation methods is important for tuning this material to fit the required application. It is also useful to understand the LiPON relation between the amorphous structure and ionic conductivity, as well as the electrochemically degradation in contact with electrode materials. This review summarizes various methods of synthesizing LiPON and evaluates them on the basis of multiple properties of the resulting material. Structure–property relationships are identified to categorize the various LiPON stoichiometries that have been synthesized. Possible lithium ion conduction pathways and electrochemical degradation mechanism in LiPON are discussed.…

The local pH near the surface of a CO 2 reduction electrocatalyst strongly impacts catalytic selectivity and activity. Here, confocal fluorescence microscopy was used to map the electrolyte pH near a copper gas diffusion electrode during CO 2 reduction with micron spatial resolution in three dimensions. We observed that the local pH increased from pH 6.8 to greater than pH 10 as the current density was increased from 0 to 28 mA/cm 2 in a 100 mM KHCO 3 electrolyte. Variations in the pH across the surface indicate areas of locally increased activity. Within deep trenches of the active layer, the local pH increases as trench width decreases. Computational models confirm these experimental results and also showed that the catalyst found within narrow trenches is more active than that found at the surface of the electrode. This study suggests that the overpotential required to perform selective CO 2 reduction can be reduced by increasing the density of narrow trench regions in the microporous layer.

In the electrochemical CO 2 reduction reaction (CO 2 RR), single atom catalysts (SACs) supported on carbon materials have exhibited high activity and selectivity. However, the carbon supports are mainly graphene and carbon nanotubes, which are composed of sp 2 -hybridized carbon. Graphdiyne with sp-hybridization has been investigated as a promising carbon material for various catalytic reactions. In this study, the effect of sp-hybridization on graphdiyne was investigated using density functional theoretical (DFT) calculations for the CO 2 RR reactivity of Mn, Fe, Co, Ni, Cu, and Zn SACs supported on graphdiyne (M–graphdiyne). Among them, Co–graphdiyne exhibits a high activity and selectivity for CH 3 OH product, with remarkably low free energy barrier of 0.31 eV, which is superior to SACs supported on graphene with sp 2 -hybridization. The d-band center and atomic number of the metal atom, and the charge redistribution on sp-hybridization exert significant influence to the energy of intermediates, which are key to understanding the activity and selectivity of SACs in CO 2 RR.

A room-temperature zero-gap, KOH anolyte CO 2 electrolyzer demonstrating 40% energetic conversion efficiency (EE) for CO 2 to CO using AEMION anion-exchange membranes is achieved at an industrially relevant current density of 200 mA cm –2 . The concentration and volume of the anolyte are found to be critical to the determination of EE as carbonate ion crossover is shown to cause a significant increase in E Cell during continuous operation. Using thicker and/or lower ion-exchange capacity variant membranes results in an approximately 20% reduction in carbonate ion crossover, which is critical for the economic viability of direct CO 2 electrolysis systems. It is proposed that future membrane designs must reduce carbonate crossover without compromising the electrolyzer efficiency and stability.

The defect control of polycrystalline perovskite films is essential for achieving an efficient and stable perovskite solar cell (PSC). However, existing methods of reducing defects suffer from their complex processes, low durability, and limited effects by using molecular materials in terms of passivation mechanisms. Herein, a hybrid film composed of SnO 2 nanoparticles/Ti 3 C 2 T x MXene nanoflakes is used as the electron transport layer (ETL) in a planar regular-structure PSC. The results indicate that by changing the Ti 3 C 2 T x /SnO 2 ratios (0–2.2 wt %) in ETLs, the film qualities of top perovskite layers are controllable, including the compactness, crystal size, surface roughness, crystallinity, optical absorption, defect density, and so forth. The defect density in perovskite films is substantially reduced from 5.65 × 10 15 to 2.25 × 10 15 cm –3 using an optimized hybrid ETL (1.4 wt %) compared with the pristine SnO 2, while the electrical conductivity of the hybrid ETL is decreased probably due to the geometric factor of the incorporated MXene. As a result, the power…

The performance of lithium-ion batteries (LIB) using organic electrolytes strongly depends on the formation of a stable solid electrolyte interphase (SEI) film. Elucidating the dynamic evolution and spatial composition of the SEI can be very useful to study the stability of SEI components and help optimize the formation cycles of LIB. We propose a classical molecular dynamics simulation protocol for predicting the first stages of SEI formation using a reaction method involving the decomposition of EC and LiPF 6 molecules in the electrolyte. We accelerate the formation of SEI components near the anode surface by increasing the probability of reactions, implemented through a geometry matching scheme, followed by a force-field reconfiguration. We observe the formation of gases (C 2 H 4 ), inorganic (Li 2 CO 3 and LiF) and organic (LEDC) components. This protocol shows promise to be able to evaluate the effects of varying electrolyte compositions and additives on SEI layer structure and composition.

Exciton binding energy ( E b ) plays an essential role in organic electronics. For organic solar cells, the existence of E b necessitates interfacial energy level offsets to drive exciton dissociation into free charge carriers at the donor/acceptor interfaces, which results in an extra energy loss with respect to inorganic and perovskite solar cells. Thus, it is highly desirable to reduce the E b for improving the performance of organic photovoltaics. In this perspective, we summarize our recent advances on theoretical studies of the E b in A–D–A small-molecule acceptors for organic photovoltaics. We highlight the importance of the polarization effect on decreasing the E b by stabilizing charge carriers. Moreover, the polarization energies of charge carriers are found to be greatly influenced by different molecular packing structures. Remarkably, an extremely weak E b is achieved in the state-of-the-art A–D–A acceptor of Y6 with a three-dimensional compact molecular packing, thus enabling direct photogeneration of free charge carriers even without the assistance of the…

Lack of efficient hydrogen storage method is one of the technical bottlenecks for the implementation of hydrogen energy. Liquid organic hydrogen carriers (LOHCs), especially N-heterocycles, have been considered as potential candidates for both on-board and off-board hydrogen storage owing to their low cost, high gravimetric hydrogen storage capacity, reversibility, and compatibility with the existing infrastructures with minimal modification. LOHCs however encounter severe kinetic barriers in the hydrogen uptake and release processes, and thus efficient catalysts are critically needed. Much attention has been given to the design and development of catalysts for the reversible hydrogenation and dehydrogenation of N-heterocycles. In this Mini-Review Article, we summarize recent activities in advancing those compounds for hydrogen storage through thermo-, photo-, and electrocatalysis, aiming to provide a guidance for rational catalyst design. At the end of the Mini-Review Article, challenges and future research directions of the catalyst design in the LOHCs field are discussed.

High Resolution Image Download MS PowerPoint Slide Copper (Cu) is a unique electrocatalyst, which is able to efficiently oxidize CO at very low overpotentials and reduce CO 2 to valuable fuels with reasonable Faradaic efficiencies. Yet, knowledge of its electrochemical properties at the solid/liquid interface is still scarce. Here, we present the first two-stranded correlation of the potential of zero free charge (pzfc) of Cu(111) in alkaline electrolyte at different pH values through application of nanosecond laser pulses and the corresponding interfacial structure changes by in situ electrochemical scanning tunneling microscopy imaging. The pzfc of Cu(111) at pH 13 is identified at −0.73 V SHE in the apparent double layer region, prior to the onset of hydroxide adsorption. It shifts by (88 ± 4) mV to more positive potentials per decreasing pH unit. At the pzfc, Cu(111) shows structural dynamics at both pH 13 and pH 11, which can be understood as the onset of surface restructuring. At higher potentials, full reconstruction and electric field dependent OH adsorption occurs, which…

The synthesis of single-atom catalysts (SACs) is one of the main challenges in heterogeneous catalysis and electrocatalysis since it requires substrates with high thermal/chemical stability on which metal atoms can be stabilized without sintering. The present study introduces MXenes, a new class of two-dimensional materials involving transition-metal carbides, as feasible substrates for anchoring single-metal atoms. Using first-principles calculations based on the density functional theory, a systematic screening is performed including ten bare metal atoms of the 3d series and nine bare MXene surfaces with M 2 C stoichiometry (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W). The results show that all 3 d metal atoms interact exothermically with the MXene substrates and that the properties of the resulting [email protected] can be tuned by appropriately choosing the each of the two components. The analysis of the results indicates that it is possible not only to have atomically dispersed atoms at an MXene surface but also to control its charge (partially oxidized or partially reduced)…

In the present study, alkaline earth metal scheelite-type ABO4 compounds (A = Ca, Sr, and Ba; B = Mo and W) synthesized by a hydrothermal method were systematically studied. The as-obtained photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, UV–vis diffuse reflectance (DR/UV–vis) spectroscopy, photoluminescence, and thermoluminescence (TL) spectroscopy together with charge carrier lifetime measurements, electron paramagnetic resonance (EPR) spectroscopy, and electrochemical impedance spectroscopy (EIS). The photocatalytic activity was studied in the reaction of phenol degradation under simulated solar light. The obtained tungstates and molybdates revealed excellent photocatalytic activity despite the low surface area and wide bandgap typical for insulators. The mechanism of phenol degradation proceeded through hydroquinone and catechol formation in the presence of hydroxyl and superoxide radicals. The presence of electron traps allowed absorption of light with lower energy than…

With rising CO 2 levels, it is important to develop new methods to capture CO 2 directly from air. Currently, most direct air capture (DAC) adsorbents, such as amines, rely on chemisorption. However, finding materials with weaker, reversible adsorption could improve the regenerability of these adsorbents. The low concentration of CO 2 relative to other components of air and the presence of humidity limit the effectiveness of physisorbent materials for DAC. In this work, we screened the 2014 computation-ready, experimental metal–organic framework (CoRE MOF) database along with silica zeolites, aluminophosphate (AlPO) zeolites, and gallophosphate (GaPO) zeolites for DAC under humid conditions based on heat of adsorption criteria. After the initial assessment, AlPO and GaPO zeolites appeared to be promising adsorbents for DAC. To assess the accuracy of these initial predictions, we compared adsorbate–adsorbent interaction energies predicted by the force field used in screening (UFF) and dispersion-corrected density functional theory. To improve the accuracy of these predictions,…

The use of additives in the transport layer can affect film formation, passivate the defects in the bulk or at the surface, and tune the direct bandgap, which promotes the performance of perovskite photodetectors. In this work, the incorporation of Mg into NiO anode interlayers which are used as hole transporting layers (HTLs) in organic–inorganic hybrid perovskite photodetectors is investigated. The device configuration is indium tin oxide (ITO)/NiO or Mg-doped NiO/CH 3 NH 3 PbI 3 /C 60 /bathocuproine (BCP)/Cu. Mg-doped NiO as the HTL for perovskite photodetectors improves the electrical conductivity and the crystallinity of perovskite thin films, which also helps promote energy level matching with the perovskite layer. These can greatly improve hole transport and extraction abilities as well as reduce carrier recombination. The performance of the perovskite photodetector is confirmed by analyzing the current density–voltage characteristics as well as dynamic and transient photocurrent response characteristics. The device with the Mg-doped NiO layer presents a high specific…

Nickel-rich cathode materials have the advantages of high specific energy, high discharging voltage, and low cost. However, harmful phase transitions, Li + /Ni 2+ cation mixing, and lattice oxygen precipitation limit the battery performance. In the present work, to address these issues, Mg- and Al-doped LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM) materials were synthesized by a hydrothermal method, which were used as cathodes of lithium ion batteries. Compared with NCM without doping, the Al-doped NCM (NCM-Al) exhibited improved electrochemical behavior, and the Mg-doped NCM (NCM-Mg) showed declined performance. The difference in battery behavior is further investigated. It was found that Al doping expanded the layer spacing of NCM and thus improved the ion diffusion mobility, while Mg doping reduced the layer spacing and was accompanied by drastic structural change during the charging/discharging process, leading to poor cycling stability. The present work provides an experimental reference for boosting performance of lithium ion batteries by elemental doping.

We report the results of modeling CO 2 reduction (CO 2 R) to CO over Ag(110) and Cu(211) surfaces at different applied potentials using grand-canonical density functional theory (GC-DFT), a method specifically designed to accurately model electrochemical systems. In addition to demonstrating GC-DFT’s ability to accurately model electrochemical processes, we also compare it with the computational hydrogen electrode (CHE) approach. GC-DFT predicts that the geometries of these reacting systems strongly depend on the applied potential, and the Helmholtz free energies vary nonlinearly with the applied potential, which contradicts a central assumption of the CHE approach. The CHE approach neglects the change in the number of electrons on the electrode surface at different applied potentials, which reduces its accuracy as the potential changes from the potential of zero charge. Our results further demonstrate that the grand free energies of the reaction intermediates not only depend on the value of the applied potential but also on the metal surface type, adsorption site, and adsorbate.…

Inorganic–organic hybrid halide perovskite MAPbI 3 (MA = CH 3 NH 3 ) has attracted much attention because of its suitable band gap and strong visible-light absorption ability. However, intrinsic Pb toxicity and poor stability have hindered its further application in photovoltaic devices. Recently, Cs-based inorganic double perovskites with good stability and prominent light absorption have drawn substantial interest. Here, we have systematically investigated the electronic and optical properties of lead-free double perovskite Cs 2 MM′Br 6 (M = Cu, Ag, and Au; M′ = Ga, In, Sb, and Bi) from first-principles calculations. Our results indicate that candidates have high stability against decomposition. The absorption coefficient of all double perovskites in the visible-light region can reach ∼10 5 cm –1 . Direct band gaps (∼1.47 eV of Cs 2 AgInBr 6 and ∼1.37 eV of Cs 2 AgGaBr 6 ) are close to the optimal value (1.34 eV) requested by the Shockley–Queisser limit. The spectroscopic limited maximum efficiency (∼31.9% of Cs 2 AgInBr 6 and ∼32.45% of Cs 2 AgGaBr 6 ) can be obtained at the…

Graphitic carbon nitride (g-C 3 N 4 )/WO 3 /WS 2 ternary heterojunctions were fabricated for the first time via in situ growing WO 3 and WS 2 on superior thin g-C 3 N 4 nanosheets. A mechanic chemical prereaction plays an important role in the formation of S-scheme heterojunctions. Namely, the heterostructured photocatalyst prepared by optimized preparation conditions revealed enhanced photodegrading activity (∼8.6 times of pure g-C 3 N 4 ) for organic pollutants in the visible light region. Compared with g-C 3 N 4 nanosheets, the rate of hydrogen generation increased to ∼7.8 times higher, in which the apparent quantum efficiency at 420 nm reached 8.9%. Particularly, the as-prepared ternary photocatalyst exhibited a hydrogen generation rate of 29 μmol g –1 h –1 even without Pt loaded. The matched energy band structure, band bending effect, and intimate interface contact of the 2D/2D g-C 3 N 4 /WO 3 heterojunction together determined the S-scheme electron transfer path. Photogenerated electrons and holes with high redox capacities were reserved to participate in the photocatalytic…

Potassium poly (heptazine imide) (K-PHI), a crystalline two-dimensional carbon-nitride material, is an active photocatalyst for water splitting. The potassium ions in K-PHI can be exchanged with other ions to change the properties of the material and eventually to design the catalysts. We report here the electronic structures of several ion-exchanged salts of K-PHI (K, H, Au, Ru, and Mg) and their feasibility as water splitting photocatalysts, which were determined by density functional theory (DFT) calculations. The DFT results are complemented by experiments where the performances in the photocatalytic hydrogen evolution reaction (HER) were recorded. We show that due to its narrow band gap, Ru-PHI is not a suitable photocatalyst. The water oxidation potentials are straddled between the band edge potentials of H-PHI, Au-PHI, and Mg-PHI; thus, these are active photocatalysts for both the oxygen and hydrogen evolution reactions, whereas K-PHI is active only for the HER. The experimental data show that these are active HER photocatalysts, in agreement with the DFT results.…

The propane dehydrogenation (PDH) reaction converts cheap propane to value-added propene. Pt-based catalysts show high performance in PDH, but suffer from coke formation and deactivation. Therefore, promoter, that is, a second metal component, is required to enhance its stability. Our previous study has constructed Pt/Cu single atom alloy (SAA) catalysts and achieved high PDH selectivity and anticoke ability. However, the nature of its high performance in PDH still remains to be revealed. This paper describes the origin of catalytic performance for Pt/Cu SAA in PDH via density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations. We constructed a complex reaction network with 54 reversible reaction steps, including adsorption, desorption, C–H bond breaking, and C–C bond cracking processes on the Pt/Cu SAA catalyst. The high selectivity of propene has been demonstrated because of the higher occurrence of propene formation and, simultaneously, the high energy barriers for deep dehydrogenation of propene. The lower coverages of the coke species origin from the…

Hexagonal boron nitride (h-BN) holds great potential for applications due to its unique electronic properties and high chemical stability. Practical applications of h-BN, however, rely on the growth of large-scale, high-quality samples, for which an adequate understanding of the growth mechanism is critically important. In this work, we study the nucleation of h-BN on the Ni(111) surface by density functional theoretical calculations. Our results reveal a novel structural crossover from a chain-like BN cluster to an sp 2 -bonded honeycomb network at the very beginning of growth. This structural transition occurs in clusters with a critical size of 8 BN pairs, beyond which the honeycomb structure is energetically preferred. After that, the growth proceeds in a downhill manner till a full coverage of h-BN on the Ni surface, driven by continuous reduction in energy of the BN clusters with feeding BN pairs. The critical size can be controlled by tuning chemical potentials. Our results also present that lattice defects, such as 4- and 5-membered rings, are higher in energy and, thus,…

High Resolution Image Download MS PowerPoint Slide Sb 2 Se 3 thin films have received increasing interest for their applications in optoelectronics. However, technological intervention demands a material-specific understanding of the reactivity to different environments. Both thermal annealing and laser irradiation carried out in an ambient atmosphere are expected to induce changes in the pristine crystallographic phase of Sb 2 Se 3, causing the creation of additional secondary phases. Here, we investigate by means of Raman spectroscopy the effect of thermal annealing and laser irradiation at different fluencies on the structural and vibrational properties of Sb 2 Se 3 thin films. The vacuum-annealed Sb 2 Se 3 thin films at 290 °C and subjected to laser excitation power above 2 mW exhibit a secondary phase, revealing the occurrence of selenization. Further, in situ X-ray diffraction over a broad range of annealing temperatures in N 2 and ambient atmospheres was employed to study the structural properties of the Sb 2 Se 3 thin films. In situ XRD performed in a N 2 atmosphere does not…

Defect engineering for metal–organic frameworks is a promising process that can modulate their electronic structure, surface chemical properties, and porosity. In this study, we demonstrate that defect engineering using an acetic acid modulator on a zirconium-based metal–organic framework (UiO-66-NH 2 ) is an effective approach to enhance the photocatalytic performance in hydrogen peroxide (H 2 O 2 ) production. The amount of missing-linker defects introduced into the UiO-66-NH 2 structure was varied by changing the acetic acid concentration. A higher H 2 O 2 concentration was produced when defective UiO-66-NH 2 was used under light irradiation compared with pristine UiO-66-NH 2 . It was demonstrated that the efficient excited carrier consumption during the photocatalytic reaction originated from promoting the linker-to-cluster charge transfer (LCCT) process, and the suppression of H 2 O 2 decomposition was due to hydrophobization of the samples by introducing missing-linker defects with acetate ligands. This study provides new insight into design strategies for developing MOF…

Chiral gold nanoparticles (Au NPs) have attracted considerable attention in the fields of asymmetric catalysis, optical materials, and biosensing, owing to their chiroptical plasmonic properties. The chiroptical plasmonic property of Au NPs is determined by their chiral morphologies. However, synthetic methods capable of tuning the chiral morphologies are still rare. Herein, we report a seed-mediated method for regulating the chiral morphology of Au nano-octopods by adjusting the degree of oligomerization of glutathione (GSH). The small and relatively higher amount of GSH oligomers directed evolution in propeller-like chiral NPs and flower-like chiral NPs, respectively. Moreover, the GSH oligomers complexed with Au in advance can improve the quality of chiral NPs. This study provides guidelines for the rational design of chiral plasmonic NPs with diverse morphologies.

Metal diborides are a class of ceramic materials with crystal structures consisting of hexagonal sheets of boron atoms alternating with planes of metal atoms held together with mixed character ionic/covalent bonds. Many of the metal diborides are ultrahigh-temperature ceramics such as HfB 2, TaB 2, and ZrB 2, which have melting points above 3000 °C, high mechanical hardness and strength at high temperatures, and high chemical resistance, while MgB 2 is a superconductor with a transition temperature of 39 K. Here, we demonstrate that this diverse family of non-van der Waals (vdW) materials can be processed into stable dispersions of quasi-two-dimensional (2D) nanosheets using ultrasonication-assisted exfoliation. We generate quasi-2D nanosheets of the metal diborides AlB 2, CrB 2, HfB 2, MgB 2, NbB 2, TaB 2, TiB 2, and ZrB 2 and use electron and scanning probe microscopy techniques to characterize their structures, morphologies, and compositions. The exfoliated layers have a distribution of lateral dimensions from tens of nanometers up to several micrometers and a distribution of…

High Resolution Image Download MS PowerPoint Slide Magnetic nanocomposites (NCs) are extremely appealing for a wide range of energy-related technological applications, specifically as building blocks for next-generation permanent magnets. The design of such nanostructures requires precise chemical synthesis methods, which will permit the fine-tuning of the magnetic properties. Here we present an in-depth structural, morphological and magnetic characterization of ferrite-based nanostructures obtained through a bottom-up sol–gel approach. The combination of the high coercivity of a hard phase SrFe 12 O 19 (SFO) and the high saturation magnetization of a soft phase, CoFe 2 O 4 (CFO), allowed us to develop exchange-coupled bimagnetic NCs. A symbiotic effect is observed in a SFO/CFO nanocomposite, as the unique oriented growth of SFO prevents grain growth of the CFO, thus restricting the crystallite size of both. Through X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and magnetic measurements we clarify the relationship between the distribution and size of…

In this study, we garnered three important factors simultaneously, namely, wormhole mesoporosity of TiO 2 with well-designed interfaces for effective charge transfers, precise loading of MoS 2 for plasmon induction, and increased surface area with exposed surface atoms and active sites. The controlled loading of MoS 2 on porous TiO 2 (MPT) forms a heterojunction that effectively modulates the interface engineering and thereby greatly enhances hydrogen evolution. The synthesis of a photocatalyst is based on a simple hydrothermal process that is well characterized. The resulting composite materials were tested for hydrogen evolution reactions. At optimum loading, MPT 10 induced a maximum hydrogen evolution rate of 1376 μmol h –1 g –1 with 2.28% apparent quantum yield (AQY), which was 10-fold higher compared to the MCT 10 (MoS 2 -commercial TiO 2 ) H 2 evolution rate of 138 μmol h –1 g –1 with 0.23% AQY under similar reaction conditions. The shorter decay component, lower emission intensity, and higher estimated lifetime of MPT 10 suggest its superiority over other materials. Density…

The mechanism for the dehydration of Mg(OH) 2 and hydration of MgO was investigated by near-infrared (NIR) spectroscopy. Mg(OH) 2 showed three absorption bands in the NIR region at 7339, 7306, and 7157 cm –1, due to the different hydroxyl groups (7339 cm –1: OH( e ) and OH( c ) located on the edge and corner of the Mg(OH) 2 sheet, 7306 cm –1: OH( t ) located on the terrace of Mg(OH) 2 sheet, 7157 cm –1: OH( i ) located on the interlayer of Mg(OH) 2 sheets). During the phase transition from Mg(OH) 2 to MgO at approximately 400 °C, the interlayer OH( i ) of Mg(OH) 2 disappeared by a dehydration reaction and the OH( t ) on the (001) plane of Mg(OH) 2 was converted to the hydrogen-bonded hydroxyl groups on the (111) plane of MgO (7309 cm –1 ). Furthermore, when MgO was in contact with water vapor at 85 and 50 °C (RH 85%), the isolated hydroxyl groups of the MgO surface (7360 cm –1 ) were easily hydrated to form hydrogen-bonded ones (7309 cm –1 ). When a monolayer Mg(OH) 2 sheet was formed on the MgO surface, OH( e ), OH( c ), and OH( t ) were observed at 7345 and 7309 cm –1 . As the…

Superconductivity under pressure is a very important research path for finding new superconductors, and electrides have been shown to present superconductivity under pressure. In the present work, using density functional theory (DFT) in association with the particle swarm search method (PSO), we discovered a remarkable electride superconductor Li 5 C with P 6/ mmm symmetry. This newly predicted material has stability in the range from 50 to 210 GPa, confirmed by phonon analysis and ab initio molecular dynamics. This electride has a two-dimensional (2D) hexagonal anionic electron topology, creating connected electronic channels in the interstitial sites of the crystal. We also show that Li 5 C has a significant conventional electron–phonon coupling with superconducting critical temperatures ( T c ) estimated up to 48.3 K at 210 GPa, which is the highest T c value already reported for lithium–carbon compounds and one of the highest known transition temperatures predicted for electrides. Even at moderate pressure (50 GPa), this material shows a relatively high T c value (14.2 K).

Separation of xylene isomers is an important process in the chemical industry and there has been considerable interest in developing advanced materials for xylene separation. In this study, we synergize computational screening and machine learning to explore the selective adsorption of p -xylene over o - and m -xylene in metal–organic frameworks (MOFs). First, a large set (4764) of computation-ready experimental MOFs is screened by geometric analysis and molecular simulation. The relationships between MOF structural descriptors (void fraction, volumetric surface area, and largest cavity diameter) and separation performance metrics (adsorption capacity of p -xylene N p -xylene and selectivity of p -xylene over o - and m -xylene S p /( m + o ) ) are established. Then two machine-learning methods (back-propagation neural network and decision tree), as well as particle swarm optimization, are utilized to analyze and optimize N p -xylene and S p /( m + o ) . The importance of each descriptor for separation is evaluated in six different MOF data sets. In the 100 top-performing MOFs, the…

A deep understanding of hot carrier (HC) dynamics is important to improve the performance of optoelectronic devices by reducing the thermalization losses. Here, we investigate the hot hole cooling and transfer dynamics of CsPbBr 3 nanocrystals (NCs) using 5,10,15,20-tetra(4pyridyl) porphyrin (TpyP) molecules. Density functional theory (DFT) is used to elucidate the mechanism underlying charge extraction as well as the HC transfer process in the CsPbBr 3 –TpyP system. It is noted that the hot hole states are localized around the top surface of CsPbBr 3, while the hot electron states are delocalized away from its top surface, indicating easy extraction of hot holes from the CsPbBr 3 by TpyP molecules, as compared to the hot electrons. The significant drop of initial hot carrier temperature from 1140 to 638 K at 400 nm excitation confirms the hot hole transfer from CsPbBr 3 NCs to TpyP molecules, which is dependent on the excitation energy, and the maximum transfer efficiency is found to be 42% (for 0.85 eV above band edge photoexcitation). In addition, the hot hole transfer rate is…

Single-atom catalysts have expanded the design paradigm for oxygen reduction reaction (ORR) relying on nonplatinum group metals (non-PGM). Here, density functional theory calculations were performed on a variety of dual-metal active centers, consisting of both PGM (Pt and Pd) and non-PGM (Fe, Co, Ni, and Cu) metals, embedded in a monolayer of graphene and coordinated by six pyridinic nitrogen atoms. The dual-metal site stability, OH ligand effect, and electronic structures relevant to ORR were investigated. The ORR reactivities can be depicted in terms of a volcano diagram divided into multiple potential limiting regimes based on a wide range of Δ G OH* values. In addition to OH removal and free molecular O 2 protonation as the potential-limiting steps, the protonation of adsorbed O 2 and O also emerge as likely potential-limiting steps due to strong O 2 adsorptions at certain dual-metal active sites. Among the systems investigated, Fe–Co(OH) s exhibits the highest activity. Moreover, other PGM-free dual-metal sites such as Fe–Fe(OH), Fe–Cu(OH), and Co–Co(OH) also appear to be…

Safe and effective storage of hydrogen fuel is a step toward a hydrogen economy. As a model storage media, magnesium hydride (MgH 2 ) experiences sluggish dehydrogenation dynamics, although its storage capacity is excellent. This computational work investigated MgH 2 /graphene heterojunction, focusing on the effect of graphene dopants on hydrogen release from MgH 2 . It is demonstrated that dopants in graphene can improve MgH 2 dehydrogenation, reducing both reaction barrier and reaction energy. It is further predicted that excellent dehydrogenation thermodynamics and kinetics can be obtained with the use of B/P codoped graphene (BP@graphene). Given that graphene codoping has been experimentally studied for years, the proposed MgH 2 /BP@graphene heterojunction is approachable and recommended for experimental validation.

Recently, Cu(I)-based metal halides have gained great attention due to their fascinating structures and optoelectronic properties. Here, we report the synthesis, crystal structure, and photophysical properties of zero-dimensional (0D) organic copper bromide hybrid, where the isolated [CuBr 2 ] − units are encircled by the organic cation of TBA + (TBA + = tetrabutylammonium cation), forming the bulk assembly of periodic 0D blocks. Moreover, this 0D structure enables strong electron–phonon interaction to promote the formation of a self-trapped excited state that shows a bright broadband cyan emission with a photoluminescence quantum yield (PLQY) of 55% for (TBA)CuBr 2 single crystals (SCs). Particularly, the as-synthesized compound shows extraordinary antiwater stability, and its PL intensity remains above 99.1% after soaking in water for 24 h. This work illustrates that the water-sensitive Cu(I) can also be used as a high antiwater stability luminescent material by introducing appropriate multifunctional organic ligands, thus opening up a new route for high antiwater materials based…

Graphene oxide (GO) and reduced GO (RGO) have attracted interest as economical alternatives for pristine graphene with controllable properties spanning their applications in many fields. Abundant lattice defects present in GO and RGO have made their physical and chemical properties largely diverse from that of pristine graphene. This makes their identification and characterization ambiguous as the rules applied for pristine graphene may not be practical for GO and RGO. Here, we report a new insight into the characterization of GO and thermally reduced GO monolayer flakes deposited on different commonly used Si-based substrates by Raman spectroscopy along with optical visualization to address this uncertainty. It was found that the dielectric substrates with a lower reflectance in the visible range give a better optical contrast under normal white light illumination and intense Raman signals owing to the multiple reflection and interference at the interfaces of the multilayer system. Accordingly, a Si substrate with a 90 nm SiO 2 layer gives the highest I G′ / I G ratio along with a…

High-entropy alloys (HEAs) have intriguing material properties, but their potential as catalysts has not been widely explored. Based on a concise theoretical model, we predict that the surface of a quaternary HEA of base metals, CoCrFeNi, should go from being nearly fully oxidized except for pure Ni sites when exposed to O to being partially oxidized in an acidic solution under cathodic bias, and that such a partially oxidized surface should be more active for the electrochemical hydrogen evolution reaction (HER) in acidic solutions than all the component metals. These predictions are confirmed by electrochemical and surface science experiments: the Ni in the HEA is found to be most resistant to oxidation, and when deployed in 0.5 M HSO, the HEA exhibits an overpotential of only 60 mV relative to Pt for the HER at a current density of 1 mA/cm.

We designed MoS 2 /M 2 CS 2 (M = Ti, V) heterostructures and investigated their electrochemical performances to evaluate their possibility to serve as anode materials for metal (Li/Na/K/Mg)-ion batteries (LIBs/NIBs/KIBs/MIBs) by the first-principles method. The results show that the two heterostructures are stable and exhibit metallic properties before or after adsorption of metal ions. The low diffusion barriers (below 0.4 eV) indicate that the two heterostructures have excellent rate performances for the four batteries. The theoretical capacities of heterostructures for NIBs (about 400 mAh/g) or LIBs (about 320 mAh/g) are all much higher than those for KIBs or MIBs. This demonstrates that MoS 2 /M 2 CS 2 are suitable as anode materials for NIBs/LIBs instead of KIBs/MIBs. Furthermore, the average open-circuit voltages of MoS 2 /M 2 CS 2 for NIBs are both lower than those for LIBs, and they show higher capacities for NIBs than LIBs, which further manifest that the MoS 2 /M 2 CS 2 heterostructures are more promising candidates for NIBs.

Electromagnetic interference originated from communication equipment and portable electronic devices and has become a potential threat to human health and the environment. In this experiment, we successfully prepared a novel two-dimensional (2D) Ti 3 C 2 T x /Fe 3 O 4 nanoparticle composite with a simple solvothermal reaction. The magnetic Fe 3 O 4 nanoparticles are homogeneously distributed on both the surface and interlayers of Ti 3 C 2 T x, forming a typical hierarchical structure. The dielectric loss of the as-synthesized 2D nanocomposites can be attributed to the strong magnetic loss caused by Fe 3 O 4 nanoparticles as well as the conductive loss originated from Ti 3 C 2 MXene. The achieved excellent electromagnetic wave absorption performance was −50.18 dB at 10.18 GHz with an absorber thickness of only 1.7 mm. Meanwhile, the effective absorption bandwidth of the composite with 30 wt % Fe 3 O 4 loading reached at 3.2 GHz (1.3 mm). We believe that the outstanding microwave absorption performance of Ti 3 C 2 T x /Fe 3 O 4 composites with the wide-band and thin-thickness…

Short-pulse laser irradiation of a colloidal solution of nanoparticles is an effective method for fragmenting the nanoparticles and producing a population of smaller nanoparticles and atomic clusters with properties desired in various fields of applications, including biology, medicine, and catalysis. To investigate the mechanisms involved in the fragmentation, we develop a computational model capable of realistic treatment of a variety of interrelated processes occurring on different time and length scales, from the electronic excitation by the laser pulse, to the electron–phonon energy transfer and an explosive phase decomposition of the superheated nanoparticle, and to the generation and collapse of a nanobubble in a liquid environment. The application of the model to simulation of laser fragmentation of a Au nanoparticle in water has revealed two distinct channels of the formation of the fragmentation products. The first channel involves the direct injection of compact nanodroplets propelled by the phase explosion of the irradiated nanoparticle deep into the water environment.…

Double perovskites are proposed as a Pb-free substitution of toxic lead-halide perovskite photovoltaic materials. Unfortunately, they are usually either unstable or have an undesirable electronic structure. In this study, we start from a stable double perovskite, Cs 2 AgBiX 6 (X = Cl, Br), which has a large and indirect band gap. Based on first-principles calculations, we find that a transition from indirect to direct band gap can be realized via doping Sn 2+ (Ge 2+ ) with occupied 5s (4s) orbitals. At the same time, the band gap decreases to a value suitable for photovoltaic applications. The optical absorption is largely enhanced, and the exciton binding energy is also significantly reduced upon doping. These effects lead to high power conversion efficiencies. For example, the efficiency of Ge–Te-codoped Cs 2 AgBiCl 6 is 31.4%, which is the highest among all known nontoxic stable halide perovskite materials. The results presented here open a new avenue for photovoltaic material design.

The soft, dynamic lattice of inorganic lead halide perovskite CsPbX 3 (X = Cl –, Br –, I – ) leads to the emergence of many interesting photophysical and optoelectronic phenomena. However, probing their lattice dynamics with vibrational spectroscopy remains challenging. The influence of the fundamental octahedral building block in the perovskite lattice can be better resolved in zero-dimensional (0D) vacancy-ordered double perovskites of form A 2 BX 6 . Here we study Cs 2 TeX 6 (X = Cl –, Br –, I – ) single crystals to yield detailed insight into the fundamental octahedral building block and to explore the effect that its isolation in the crystal structure has on structural and electronic properties. The isolated [TeX 6 ] 2– octahedral units serve as the vibrational, absorbing, and emitting centers within the crystal. Serving as the vibrational centers, the isolated octahedra inform the likelihood of a random distribution of 10 octahedral symmetries within the mixed-halide spaces, as well as the presence of strong exciton–phonon coupling and anharmonic lattice dynamics. Serving as…

Significant challenges remain for developing efficient catalysts in an electrochemical multielectron CO 2 reduction reaction (CO 2 RR), which usually suffers from poor activity and selectivity. Motivated by the recent experimental progress in fabricating dual-metal atom catalysts (DMACs) in N-doped graphene materials (graphene-N6V4; N: nitrogen and V: vacancy), we sampled eight types of homonuclear (N6V4-M 2, M = Cr, Mn, Fe, Co, Ni, Cu, Pd, and Ag) catalysts and 28 types of heteronuclear (N6V4-M1M2) catalysts to study CO 2 RR activity via first-principles high-throughput screening. Using stability, activity, and selectivity as indicators along with the broken conventional scaling relationship, N6V4-AgCr was selected as a promising candidate for deep CO 2 reduction to methane with a low overpotential of 0.55 V after two screening rounds. Further analysis showed that a frustrated Lewis pair, formed between metal and the para-N, owing to the difference in the electronic arrangement of the d orbitals of various transition metals, caused a difference in the spin polarization of the…

The nature and spectroscopic expression of external surface sites of zeolites, in particular ZSM-5, is a long-debated question. Herein, we use three cutting-edge techniques: Fourier-transform infrared spectroscopy (FTIR) with Fourier self-deconvolution (FSD), high magnetic field proton NMR spectroscopy under fast magic-angle spinning (MAS) and periodic boundary Density Functional Theory (DFT) calculations to study external surface models and analyze the effect of crystallite size. This provides an unequaled description of the various kinds of hydroxyl groups and of their proximities. The hydrogen-bond donor, acceptor or isolated nature of the hydroxyls results in distinct signals both in FTIR and NMR spectra, but the peak assignment is not the same from one technique to the other when the chemical nature of the hydroxyl changes. Bridging Si–(OH)–Al groups and Al–(H 2 O) lead to overlapping signals in one-dimensional 1 H MAS NMR, whereas their contributions are strongly different in FTIR spectra. However, quantification and proximity assessment could only be obtained by 1 H MAS NMR.…

Rational construction of self-template catalysts for efficient electrolytic water splitting reactions is being a challenging prospect in sustainable energy production. For the first time, owing to these aims, we report a self-template representation of self-assembled iron-modulated cobalt-nickel phosphide (Fe-CoNiP) grown on 3D-nickel foam (NF) using a facile amine hydrolysis-approached synergetic phosphorylation strategy. Due to its unique vertically standing self-template hierarchical nanoarrays and atomic modulated multicomponent system, these Fe-CoNiP nanoarchitectures exhibit excellent electrocatalytic hydrogen and oxygen evolution reactions with very low applied overpotentials of 110 and 280 mV to obtain 10 mA cm –2, respectively, and an overpotential value of 390 mV ( J 10 ) obtained for overall water splitting overtakes most precious-metal/phosphide-based electrocatalysts in an alkaline medium. Moreover, the rationally cocrystallized Fe-CoNiP binder-free electrocatalyst as a multifunctional electrode has robust physicochemical stability above 2 days with very little…

Lead-free halide perovskites, as environment-friendly materials, have received critical interest in photovoltaic applications. In this regard, the bismuth halide perovskites demonstrate better stability under ambient conditions than lead halide perovskites and consequently remain one of the critical areas for the development of lead-free absorber materials. The steady-state optical properties are widely investigated in these bismuth halide perovskites, but excited-state charge carrier dynamics such as hot carrier relaxation remain elusive. However, it is crucial to investigate the rapid relaxation of above band gap “hot” carriers as it restricts the fundamental efficiency limit in the perovskite solar cells. Here, we demonstrate the cation-dependent hot carrier cooling in the lead-free A 3 Bi 2 I 9 [A = FA (formamidinium), MA (methylammonium), and Cs (cesium)] perovskite by using femtosecond transient absorption spectroscopy. These lead-free perovskites were fabricated from gamma-butyrolactone (γ-GBL) solvent to ensure uniformity and continuity of the as-grown film and were well…

Since ABX 3 halide perovskites exhibit intrinsic instability, their A 2 BX 6 variants have been examined as potential alternatives for optoelectronic applications. The better stability of A 2 BX 6 variants compared to that of ABX 3 halide perovskites was previously attributed to simply the better valence stability of B 4+ compared to that of B 2+, as exemplified by Sn 4+ and Sn 2+ . However, the atomic origin of the stability difference between ABX 3 and A 2 BX 6 remains unclear. In this work, taking CsSnCl 3 and Cs 2 SnCl 6 as examples, we provide a general first-principles understanding of the stability difference between ABX 3 and A 2 BX 6 . We find that Cs 2 SnCl 6 exhibits stronger Sn–Cl bonds, a larger chemical window, and a lower density of defects than CsSnCl 3 . Owing to its unique crystal structure, Cs 2 SnCl 6 possesses a more stable (111) surface without dangling Sn–Cl bonds; thus, the adsorption and diffusion of water are more difficult. We conclude that the stronger bonds and the more stable surfaces are the primary enablers of the better stability of A 2 BX 6 compared…

ZnIn 2 S 4 (ZIS) has shown great potential in photocatalytic solar-energy conversion. However, it is still suffering from severe charge recombination and poor surface area. Nonmetal heteroatom doping is considered as an effective strategy for improving its photocatalytic performance. Herein, phosphorus-doped ZIS (P-ZIS) nanosheets were prepared by a simple hydrothermal treatment of ZIS using NaH 2 PO 4 as a precursor. The effect of P doping on the crystal structure, band structure, and the photocatalytic CO 2 reduction activity of ZIS under visible light were investigated. It was found that P doping in the lattice of ZIS plays a key role in tuning its electronic properties. The ratio of ZIS to NaH 2 PO 4 influences the photocatalytic performance of P-ZIS, and the optimum ratio is 1:15. Optimized P-ZIS exhibits a remarkable visible-light photocatalytic CO production rate of 18.8 μmol/30 min, 2.5-folds higher than that of the pure ZIS. The ultrathin nanosheets feature and an upward shift of CB edge result in the enhancement of CO 2 photoreduction efficiency of P-ZIS. This work…

MXene is widely used for electrode materials. However, the interfacial resistance between metal and semiconductor affects the device performance. The strain has become an effective strategy to improve interfacial properties. With the aim of revealing the interface mechanism and improving device performance, we use the first-principles calculation to investigate the electronic properties of Ti 3 C 2 T 2 /MoS 2 (T = F, O, OH) junctions and the effect of strain on the interfaces. The calculations show weak forces between Ti 3 C 2 T 2 and MoS 2 monolayer, and the interfacial interaction decreases in the order of Ti 3 C 2 (OH) 2 /MoS 2, Ti 3 C 2 F 2 /MoS 2, and Ti 3 C 2 O 2 /MoS 2 . Ti 3 C 2 F 2 /MoS 2 exhibits a p-type Schottky barrier with 0.51 eV and Ti 3 C 2 O 2 /MoS 2 shows a p-type Schottky barrier with 0.12 eV, whereas an n-type ohmic contact occurs in Ti 3 C 2 (OH) 2 /MoS 2 . Interestingly, the contact types and Schottky barrier height in the Ti 3 C 2 F 2 /MoS 2 and Ti 3 C 2 O 2 /MoS 2 junctions can be tuned by biaxial strain in plane, which shows a transition from a p-type…

Swelling clays are known to exhibit crystalline swelling at the layer scale (∼nm): X-ray diffraction (XRD) identifies discrete jumps in interlayer spacing upon a change in relative humidity (RH) corresponding to the thickness of a water layer. Continuum theories are not adapted to describe systems at the scale of a few water molecules, and much effort has been dedicated to understand and predict crystalline swelling from molecular simulations. Grand canonical (GC) molecular simulations combined with thermodynamic stability analysis are one of the most appropriate techniques to predict swelling as a function of RH from atomistic simulations. Yet, the usual GC Monte Carlo is quite inefficient, and improved algorithms are needed to reach reasonable accuracy. In this work, we report results of configurational bias GC molecular simulations of Na-montmorillonite, one of the most studied swelling clays. This data set covers a wide range of relative fugacities above and below vapor saturation and a wide range of spacings, encompassing all hydration states. This makes it possible to derive a…

Defects are pervasive in electrochemical systems across multiple length scales. The defect chemistry largely differs from the bulk behavior and often dictates the rate performance for battery materials. However, the impact of material defects on Li kinetics remains elusive because of their complex nature and the sensitivity of the reaction kinetics on the local atomic environment. Here we focus on the grain boundaries (GBs) in layered-oxide cathodes and address their role in Li transport using the first-principles theoretical approach. We construct the coincidence site lattices of ∑2(11̅04̅), ∑3(1̅102̅), ∑5(11̅01̅), and ∑9(1̅104̅) GBs. The energy profiles for Li migration across and along the grain planes are plotted. We discuss in detail how the atomistic features associated with various grain structures such as the local structural distortion and charge redistribution determine the Li transport kinetics. Specifically, the coherent ∑2 GBs facilitate Li migration with 1–2 orders of magnitude increased diffusivity than the bulk diffusion, the asymmetric ∑3 GBs significantly impede Li…

High Resolution Image Download MS PowerPoint Slide The enhancing effect of extraframework Al (EFAl) species on the acidity of bridging hydroxyl groups in a steam-calcined faujasite zeolite (ultrastabilized Y, USY) was investigated by in situ monitoring the H/D exchange reaction between benzene and deuterated zeolites by 1 H MAS NMR spectroscopy. This exchange reaction involves Brønsted acid sites (BAS) located in sodalite cages and supercages. In a reference faujasite zeolite free from EFAl, both populations of BAS are equally and relatively slowly reactive toward C 6 H 6 . In USY, in stark contrast, the H/D exchange of sodalite hydroxyl groups is significantly faster than that of hydroxyl groups located in the faujasite supercages, even though benzene has only access to the supercages. This evidences selective enhancement of BAS near Lewis acidic EFAl species, which according to the NMR findings are located in the faujasite sodalite cages.

We construct here a highly active and stable Co 9 S 8 @CdIn 2 S 4 heterostructure for photocatalytic H 2 evolution under visible light. In a hierarchical hollow construction with closely connected heterogeneous shells, two photoactive sulfide semiconductors are incorporated rationally. This unique architecture can efficiently allow photoinduced charges to be separated and transferred and provide a broad surface area and exposure of rich sites for photocatalytic redox reactions. The Co 9 S 8 @CdIn 2 S 4 hierarchical hollow heterostructure shows enhanced light-harvesting ability and remarkable catalytic activity because of its distinctive structural and compositional advantages. The photocatalyst shows a high hydrogen evolution rate of 4604 μmol h –1 g –1 without any noble metal as a cocatalyst under 1.5 AM simulated light irradiation. In this work, using the two-dimensional ultrathin subunits with distinct structural and compositional benefits, we show how this material can be interfaced successfully to give intriguing photophysical properties.

An electrochemical dinitrogen (N 2 ) reduction reaction (NRR) under mild conditions has been considered as a promising and sustainable alternative to the conventional Haber–Bosch method. However, searching for an efficient, stable, and low-cost electrocatalyst is still challenging and attractive. Here, based on density functional theory, a single B atom adsorbed on a series of carbon phosphide monolayers [B/PC x single-atom catalysts (SACs), x = 2, 3, 5, and 6] was constructed as metal-free catalysts and their NRR catalytic activities were systematically investigated. Consequently, among the investigated systems, the B/PC 6 SAC is identified as the most promising candidate, on which the N 2 molecule can only be sufficiently activated through the enzymatic pathway with a limiting potential of −0.37 V, and importantly, it remains as a stable structure after ab initio molecular dynamics simulations at 300 K. It can be found from the electronic property calculations that the p-orbitals of the B atom have a good degree matching with the p-orbitals of the adsorbed N 2 species, favoring…

High Resolution Image Download MS PowerPoint Slide Auxetic materials (negative Poisson’s ratio) are of exceptional importance for nanomechanical applications. Using first-principles calculations, we propose two-dimensional δ-phase carbon monochalcogenides (δ-CS, δ-CSe, and δ-CTe) with very strong auxeticity. In contrast to the known two-dimensional materials, we find that Poisson’s ratio is negative in all crystal directions. In addition, the δ-phase carbon monochalcogenides turn out to be direct or quasi-direct bandgap semiconductors with impressive absorption of solar radiation.

Single wall carbon nanotubes (SWCNT) fluoresce in the near infrared (NIR) and have been assembled with biopolymers such as DNA to form highly sensitive molecular sensors. They change their fluorescence when they interact with analytes. Despite the progress in engineering of these sensors the underlying mechanisms are still not understood. Here, we identify processes and rate constants that explain the photophysical signal transduction by exploiting sp3 quantum defects in the sp2 carbon lattice of SWCNTs. As a model system we use ssDNA coated (6,5)-SWCNTs, which increase their NIR emission (E11, 990 nm) up to + 250 % in response to the important neurotransmitter dopamine. In contrast, SWCNTs coated with DNA but with a low number of NO2-Aryl sp3 quantum defects decrease both their E11 (-35%) and defect related E11* emission (- 50%) at 1130 nm. Consequently, the interaction with the analyte does not change the radiative exciton decay pathway alone. Furthermore, the fluorescence response of pristine SWCNTs increases with SWCNT length, suggesting that exciton diffusion is affected. The…