The 100 most-cited articles in The Journal of Physical Chemistry C, 2022

The description of the band gap of halide perovskites at the level of density functional theory (DFT) has been subject of several studies but still presents significant problems and deviations from experimental values.Various approaches have been proposed, including the use of system-specific hybrid functionals with a variable amount of exact exchange or the explicit inclusion of spin-orbit coupling (SOC) effects.In this work, we present a pragmatic recipe to compute the band gap of halide perovskites with a minimum average error.The recipe is tested on a set of 36 halide perovskites of the type ABX 3 [A = Cs, methyl-ammonium (MA), and formamidinium (FA); B = Ge, Sn, and Pb; and X = Cl, Br, and I] for which experimental estimates of the band gap have been reported in the literature.Upon assessment of the accuracy of commonly used DFT functionals and the analysis of their performances based on error and statistical analysis, we suggest a strategy to compute band gaps in halide perovskites with a single functional.This is based on the use of the hybrid HSE06 functional where SOC is…

Step-scheme (S-scheme) heterojunctions comprising two semiconductors having two sets of charge carriers at different sites with an outstanding redox capability have emerged as a prospective tactic for H 2 O 2 production and antibiotic remediation. Herein, 0D/2D Fe 2 O 3 QD/B-g-C 3 N 4 (F-BN) was successfully fabricated via in situ nucleation of Fe 2 O 3 quantum dots (FQDs) over boron-doped g-C 3 N 4 (BCN) sheets for H 2 O 2 production and photo-Fenton amoxicillin (AMX) degradation. Empirical results demonstrate that the F-BN composite shows a superior catalytic activity compared to the parent material and the optimized 3F-BN attains the best activity for H 2 O 2 generation (729 μmol and solar-to-chemical conversion efficiency (SCC) of 0.12%) and photo-Fenton AMX degradation (93%) with a “ k ” of 0.0891 min –1, which is 3.34 and 7.01 times higher than those of the pristine materials. The outstanding activity could be attributed to effective separation and utilization of excitons through the S-scheme transfer pathway. Moreover, charge transfer through the S-scheme transfer corridor…

Polymer composites filled with conductive fillers can demonstrate ultrahigh effective dielectric permittivity, which is generally attributed to an enhanced Maxwell–Wagner–Sillars interfacial polarization associated with the formation of microcapacitor networks. Here, we explore a composite of the ethylene–propylene–diene elastomer with carbon-black (CB) nanofillers and investigate its dielectric response over wide ranges of temperature and frequency. The dielectric relaxation exhibits atypical (counter-Arrhenius) temperature dependence, contradicting the widely assumed interfacial polarization mechanisms. It is shown that the relaxation/polarization is actually determined by electron displacement─primarily via e-conduction and tunneling within CB clusters─and that the composites’ dielectric response can be quantitatively correlated with the CB cluster morphology via a set of scaling laws. Considering the selected composite as a paradigmatic system, the physical origins of the dielectric relaxation and the associated scaling relations seem to be generally applicable and expected to…

Phosphor-converted white-light-emitting diodes (pc-WLEDs) are a commercially successful product for energy-efficient illumination. A large number of reported phosphors exhibit high photoluminescence efficiency but struggle in pc-WLED applications. So what kind of phosphors are required to upgrade the existing pc-WLED? An answer to this question is provided here. The industry is moving toward high-power pc-WLED. For that, issues of thermal instability (at ∼200 °C) and luminescence saturation of phosphors, along with the efficiency drop of the InGaN chip, need to be addressed. Another research direction is to reduce excessive blue light from the present commercial pc-WLED, by replacing the blue-emitting InGaN chip with an ultraviolet (UV)-violet chip. Designing phosphors for high-power pc-WLED with UV-violet chip still remains a challenge. This Perspective highlights the present challenges and provides insights to address them in the future.

High Resolution Image Download MS PowerPoint Slide Reactive magnesium oxide (MgO)-based cement (RMC) can play a key role in carbon capture processes. However, knowledge on the driving forces that control the degree of carbonation and hydration and rate of reactions in this system remains limited. In this work, density functional theory-based simulations are used to investigate the physical nature of the reactions taking place during the fabrication of RMCs under ambient conditions. Parametric indicators such as adsorption energies, charge transfer, electron localization function, adsorption/dissociation energy barriers, and the mechanisms of interaction of H 2 O and CO 2 molecules with MgO and brucite (Mg(OH) 2 ) clusters are considered. The following hydration and carbonation interactions relevant to RMCs are evaluated: (i) carbonation of MgO, (ii) hydration of MgO, carbonation of hydrated MgO, (iii) carbonation of Mg(OH) 2, (iv) hydration of Mg(OH) 2, and (v) hydration of carbonated Mg(OH) 2 . A comparison of the energy barriers and reaction pathways of these mechanisms shows that…

Abstract The challenges afflicting cesium lead halide perovskite nanocrystals (PNCs) are long-term stability and deterioration of photoluminescence (PL) properties with time, hindering its commercialization applicability. The presence of surface defects on cesium lead bromide (CsPbBr3) PNCs commonly lead to the degradation of PL properties via ligand loss. In this work, we explored benzoic acid post-treatment to improve the PL and long-term stability of green-emitting CsPbBr3 PNCs. The surface defects are passivated via co-ordination of carboxyl group with under coordinated surface lead atoms. The photoluminescence quantum yield is in unity with benzoic acid (BA) post-treatment, also reflected in PL decay profiles. The BA-CsPbBr3 PNCs exhibit excellent stability for more than a year. Thirty-six percent of the initial PL intensity is preserved for BA-CsPbBr3 PNCs, while the PL is completely quenched for untreated CsPbBr3 PNCs within 24 h of continuous UV illumination (λex = 365 nm). Nearly 21% of the PL is preserved for BA-CsPbBr3 PNCs, whereas the PL is quenched instantly for…

, respectively, enabling the band alignment of the series to be established. Finally, the valence band measurements are compared with the calculated density of states which shows the role of p-d hybridization in these materials. Down the group, an increase in the p-d hybridization from the sulfide to the telluride is observed, explained by the configuration energy of the chalcogen p orbitals becoming closer to that of the valence Mo 4d orbitals. This pushes the valence band maximum closer to the vacuum level, explaining the decreasing IP down the series. High-resolution SXPS and HAXPES core-level spectra address the shortcomings of the XPS analysis in the literature. Furthermore, the experimentally determined band alignment can be used to inform future device work.

The complexation and decomplexation of CO2 with a series of quinones of different basicity during electrochemical cycling in dimethylformamide solutions were studied systematically by cyclic voltammetry. In the absence of CO2, all quinones exhibited two well-separated reduction waves. For weakly complexing quinones, a positive shift in the second reduction wave was observed in the presence of CO2, corresponding to the dianion quinone-CO2 complex formation. The peak position and peak height of the first re-duction wave were unchanged, indicating no formation of complexes between the semiquinones and CO2. The relative heights of both reduction waves remained constant. In the case of strongly complexing quinones, the second reduction wave disappeared while the peak height of the first reduction wave approximately doubled, indicating that the two electrons transferred simultaneously at this potential. The observed voltammograms were rationalized through several equilibrium arguments. Both weakly and strongly complexing quinones underwent either stepwise or concerted mechanisms of…

Abstract Defects in powder photocatalysts determine the photocatalytic activity. The addition of defects sometimes enhances the activity, but sometimes decreases it. However, the factors determining the difference between these cases have not been fully elucidated yet. Herein, we investigated the effects of oxygen vacancies on photocarrier dynamics in WO3 powder using broadband transient absorption spectroscopy. It was found that the decay of deeply trapped electrons was accelerated when the number of oxygen vacancies was increased by H2 reduction. This result suggests that oxygen vacancies in WO3 mainly act as recombination centers. This is in contrast to many other photocatalysts such as TiO2 and SrTiO3, where the carrier lifetime increases with increasing oxygen vacancy concentration. These differences can be attributed to the difference in the distance between oxygen vacancies. When defects are dispersed, trapped electrons need to travel over long distances by repeatedly hopping and tunneling between defects to combine with holes, resulting in decelerated recombination. In…

Understanding hydrogen evolution reaction (HER) behaviors over two-dimensional transition-metal dichalcogenides (2D-TMDs) is critical for the development of nonprecious HER electrocatalysts with better activity. In this work, by combining density functional theory calculations with microkinetic modeling, we thoroughly investigated the HER mechanism on 2D-TMDs. We find an important dependence of simulated cell size on the calculated hydrogen adsorption energy and the activation barrier for MoS 2 . Distinct from previous “H migration” mechanisms proposed for the Heyrovsky reaction, the rate-determining step for MoS 2, we propose that the Mo site only serves as the stabilized transition state rather than H adsorption. In comparison to transition-metal electrocatalysts, we find that the activation barrier of the Heyrovsky reaction on 2D-TMDs scales with the hydrogen adsorption energy exactly as for transition metals except that all activation energies are displaced upward by ca. 0.4 eV. This higher Heyrovsky activation barrier is responsible for the substantially lower activity of…

Integrating multiple metals to form high-entropy materials is an efficient strategy to bring about fantastic physicochemical and electrocatalytic properties. Herein, a high-entropy metal–organic framework (HE-MOF) with five metals (Ni, Co, Fe, Zn, and Mo) has been rationally synthesized via a mild solvothermal method. The HE-MOF brings a two-dimensional array structure, which could not only enhance the electrical conductivity but also promote rgw mass transport of reactants, intermediates, and products. Therefore, the electrocatalyst displays excellent electrocatalytic oxygen evolution reaction (OER) activity (requiring the overpotential of 254 mV to achieve a current density of 50 mA cm –2 ) and long-term stability up to 100 h. Further mechanistic study highlights MO 6 /MOOH (M = metals) intermediates as the active centers, and the synergy of different metals contrubites to entropy increase effects that drive efficient oxygen evolution. Our strategy could give a broad prospect of engineering cost-effective high-entropy metallic catalysts for broad applications.

The development of anode materials with good stability, high capacity, and excellent electrical conductivity is an important challenge for high-performance Li-ion batteries. Herein, the feasibility of BeB 2 and MgB 2 monolayers as Li-ion batteries anode materials has been theoretically investigated. The simulation results reveal that the BeB 2 and MgB 2 monolayers maintain good electrical conductivity throughout the lithiation process. Meanwhile, the Li–BeB 2 and Li–MgB 2 systems exhibit small changes in lattice (−1.66 and 1.75%) during the lithiation/delithiation process showing good cycle stability. The BeB 2 and MgB 2 monolayers exhibit high energy density for Li adsorption due to the high storage capacities (1749.8 and 1750.9 mAh g –1 ) and low average open-circuit voltage (0.333 and 0.697 V). The Li storage capacities of BeB 2 and MgB 2 are 4.5 times higher than that of the commercial anode material graphite. These results demonstrate that BeB 2 and MgB 2 monolayers can be used as promising alternative anode materials with high energy density for Li-ion batteries.

High Resolution Image Download MS PowerPoint Slide Nuclear magnetic resonance (NMR) chemical shifts are a direct probe of local atomic environments and can be used to determine the structure of solid materials. However, the substantial computational cost required to predict accurate chemical shifts is a key bottleneck for NMR crystallography. We recently introduced ShiftML, a machine-learning model of chemical shifts in molecular solids, trained on minimum-energy geometries of materials composed of C, H, N, O, and S that provides rapid chemical shift predictions with density functional theory (DFT) accuracy. Here, we extend the capabilities of ShiftML to predict chemical shifts for both finite temperature structures and more chemically diverse compounds, while retaining the same speed and accuracy. For a benchmark set of 13 molecular solids, we find a root-mean-squared error of 0.47 ppm with respect to experiment for 1 H shift predictions (compared to 0.35 ppm for explicit DFT calculations), while reducing the computational cost by over four orders of magnitude.

A combined experimental and density functional theory (DFT) study of metal–organic framework-5 (MOF-5) and its doped variants (M@MOF-5, M = Co, Fe, Ni, and Mn) has been performed to elucidate changes in electronic properties. The in situ doping of transition metals in MOF-5 has remained an unexplored area. All MOFs are synthesized using the hydrothermal method and characterized by X-ray, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, fluorescence spectroscopy, thermogravimetric analysis (TGA), and diffuse reflectance spectroscopy. TGA indicates that the structure of MOF-5 and doped MOF-5 is stable up to 450 °C; however, the Ni-doped MOF is less stable. The band gap is calculated by the Kubelka–Munk method. Doping remarkably decreases the band gap from 3.8 eV of pristine MOF-5 to 3.7, 3.6, 3.3, and 2.6 eV of Ni-, Mn-, Co-, and Fe-doped MOF-5s, respectively. DFT/time-dependent DFT computations reveal changes in electronic properties for 25–75% dopant substitutions in the secondary building unit for each…

High Resolution Image Download MS PowerPoint Slide Metal halide perovskite (MHP) devices often show different types of hysteresis in separate voltage domains. At low voltage, the impedance response is capacitive, and the cell gives regular hysteresis. At high voltage, the hysteresis is inverted, corresponding to an inductive response that causes a negative capacitance feature. We calculate the hysteresis current due to a chemical inductor model, and we show that the current is inversely proportional to the voltage scan rate. We formulate a general dynamical model for the solar cell response in the style of neuronal models for the action potential, based on a few differential equations. The model allows us to track the transition from capacitive to inductive properties, both by impedance spectroscopy and current–voltage measurements at different voltage sweep rates. We obtain a correlation of the time constants for the capacitor and the inductor. We interpret the origin of the low-frequency features in terms of ion-controlled surface recombination. This explains the strong…

Using single-atom catalysts for the electrochemical reduction of carbon dioxide is a promising method for excess renewable electricity as chemical energy in fuels. In this study, we have investigated single non-noble metal atoms supported on nitrogen-doped graphene (M-N 4 @Gr, where M = Fe, Co, Ni) as catalysts for the electrocatalytic reduction of CO 2 using first-principles density functional theory and the computational hydrogen electrode model. The results show that HCOOH is the preferred product of CO 2 reduction on the Ni-N 4 @Gr catalyst with an overpotential of 1.511 V, while Fe-N 4 @Gr and Co-N 4 @Gr prefer to reduce CO 2 to CH 4 with the overpotential of 0.877 and 0.687 V, respectively. The computational results revealed that the coordination environment affects d orbital occupations, leading to a difference in the spin polarization of the systems and thus affecting the performance and selectivity of catalysts. Our work may pave the way for extending single non-noble atom catalysts, which consist of earth-abundant elements, toward electrocatalytic CO 2 reduction reaction…

Electrochemical carbon dioxide capture has recently emerged as a promising alternative approach to conventional energy-intensive carbon capture methods. The most common electrochemical capture approach is to employ redox-active molecules such as quinones. Upon electrochemical reduction, quinones become activated for the chemical capture of CO2. The main disadvantage of this method is the possibility of side-reactions with oxygen, which is present in almost all gas mixtures of interest for carbon capture. This issue can potentially be mitigated by fine-tuning redox potentials through the introduction of electron-withdrawing groups on the quinone ring. In this article, we investigate the thermodynamics of the electron transfer and chemical steps of CO2 capture in different anthraquinone derivatives with a range of substituents. By combining density functional theory calculations and cyclic voltammetry experiments, we discover a trade-off between redox potentials and the strength of CO2 capture. We show that redox potentials can readily be tuned to more positive values to impart…

High Resolution Image Download MS PowerPoint Slide The beneficial effects on ZnO and TiO 2 photocatalytic activity resulting from a suitable combination of doping and heterojunctions were proposed and investigated by a synergistic experimental and theoretical study. In detail, the ZnO/N-doped TiO 2 heterojunction was synthesized and tested in the photocatalytic degradation of atrazine under UV and visible light. Wide-angle X-ray diffraction (WAXD) analysis reveals the presence of both ZnO and TiO 2 crystalline phases in the heterojunction. UV–vis DRS analysis shows that the simultaneous presence of ZnO and N-doped TiO 2 in the heterojunction results in a slight increase in the band gap value in the UV region, while the shoulder in the visible region typically of bare N-doped TiO 2 is preserved. On the basis of these experimental observations, density functional theory (DFT) calculations were carried out to model both the N-doped TiO 2 structure and to rationalize the experimental decrease in the band gap energy. The DFT modeling of band alignment of the ZnO/N-doped TiO 2…

Coupling photocatalytic hydrogen (H 2 ) evolution with selective organic synthesis in one redox cycle showcases great potential for the coinstantaneous utilization of photoexcited electrons and holes toward sustainable production of value-added fuels and chemicals. Herein, we construct one-dimensional/two-dimensional (1D/2D) WO 3 /ZnIn 2 S 4 (WO 3 /ZIS) hierarchical Z-scheme composites for bifunctional integrated light-driven H 2 production and biomass-derived aromatic alcohol conversion. The superior photoactivity and selectivity over WO 3 /ZIS composites compared with that over bare WO 3 nanorods (NRs) and ZIS nanosheets (NSs) can be attributed to the assembly of the Z-scheme heterostructure. The construction of WO 3 /ZIS direct Z-scheme composites not only facilitates the charge separation dynamics by transporting photoinduced electrons and holes to spatially separated redox sites but also steers the selectivity of targeted products by tuning the energy band potentials to endow electrons and holes with stronger reduction and oxidation abilities. The mechanistic studies combining…

High Resolution Image Download MS PowerPoint Slide Rutile RuO 2 is a prime catalyst for the oxygen evolution reaction (OER) in water splitting. Whereas RuO 2 is typically considered to be non-magnetic (NM), it has recently been established as being anti-ferromagnetic (AFM) at room temperature. The presence of magnetic moments on the Ru atoms signals an electronic configuration that is markedly different from what is commonly assumed, the effect of which on the OER is unknown. We use density functional theory (DFT) calculations within the DFT+ U approach to model the OER process on NM and AFM RuO 2 (110) surfaces. In addition, we model the thermodynamic stability of possible O versus OH terminations of the RuO 2 (110) surface and their effect on the free energies of the OER steps. We find that the AFM RuO 2 (110) surface gives a consistently low overpotential in the range 0.4–0.5 V, irrespective of the O versus OH coverage, with the exception of a 100% OH-covered surface, which is, however, unlikely to be present under typical OER conditions. In contrast, the NM RuO 2 (110) surface…

High Resolution Image Download MS PowerPoint Slide Guest molecules in layered double hydroxides (LDHs) may be located both on the surface and in the interlayer gallery. In this work, a comparative study of various IR spectroscopic methods coupled with X-ray diffraction (XRD) is presented, which makes it possible to distinguish between the two possibilities. During the experimental work, first, CaAl-LDHs intercalated with nitrate/carbonate ions were transformed to d -gluconate- and benzoate-containing solids. Depending on the initial interlayer ion, the organic molecules may end up between the layers and/or on the surface of the LDH. The IR spectra of the specimens were recorded by using four different techniques, which are different in their penetration depth (photoacoustic spectroscopy (PAS), attenuated total reflectance (ATR), diffuse reflectance IR spectroscopy (DRIFTS), and wide angle diffuse reflectance (WA-DRIFTS)). By comparing the spectra obtained, the anionic species that are surface adsorbed to LDHs were proven to be distinguishable from those intercalated in the…

CO 2 hydrogenation to methanol has attracted much attention. The mechanism, the factors affecting selectivity, and the rate-determining step of the reaction have not been clearly concluded. Here, the reaction mechanism on the Cu/ZnO/Al 2 O 3, the Pd/ZnO, and the ZnZrO x catalysts was studied by in situ infrared spectroscopy and HCOOH temperature-programmed surface reaction (HCOOH-TPSR) experiment. It is shown that the HCOO* mechanism is a feasible mechanism, and the more stable HCOO* on the catalysts is, the higher the selectivity of methanol accompanied with the less CO produced via the decomposition of HCOO*. H 2 –D 2 isotope exchange reaction is inhibited in the presence of CO 2, which indicates that H 2 activation and H* migration are inhibited by CO 2 adsorbed on the catalysts. As for CO 2 hydrogenation to methanol, the reaction orders of H 2 and CO 2 are close to 0.5 and 0, respectively, indicating that activated H* on the catalysts is insufficient. Comparing CO 2 hydrogenation to methanol reaction and H 2 –D 2 isotope exchange reaction, their H 2 reaction orders are both 0.5…

The electrochemical reduction of CO 2 (CO 2 RR) is a promising alternative to achieve carbon neutrality and the sustainable development of human civilization. Rational design of electrocatalysts for CO 2 RR requires thorough understanding of catalytically active sites and corresponding reaction mechanisms from the atomic level, where theoretical computations and simulations are indispensable. In this perspective, we summarize the recent progress in simulating CO 2 RR from both thermodynamic and kinetic aspects, including different methods for describing solvent–ion effects and applied potentials. In addition, a brief overview of applications of machine learning (ML) to the design of CO 2 RR catalysts is presented, and the simulation of electrocatalytic processes is also discussed, considering the solvent model under a constant potential by ML. Finally, an outlook is provided for the future development of computational models and their applications to CO 2 RR.

calculations revealed that magnetic impurities do not affect the magnetic ordering observed in the pure phases, and thus, in general in these systems, ferromagnetism may not be easily induced by such a kind of elemental doping. However, unlike for the hosts, the first and second (dopant-host) exchange couplings are of similar order of magnitude. This leads to frustration in the case of antiferromagnetic coupling and may be one of the reasons of the observed lower magnetic ordering temperature of the doped systems.

High Resolution Image Download MS PowerPoint Slide Carbon nanotube (CNT) films have excellent conductivity and suitable flexibility for chemical sensing and touch screen devices. Understanding the pathways of charge transport within the network is crucial to develop new functional materials and improve existing devices. Here, we study the electrical conductivity of networks of CNTs containing Group 11 metals (Au, Ag, and Cu), s–p metals (K, Ca, and Al), AuCl 3, AuCl 4, and Cl using quantum mechanical methods and semiclassical Boltzmann transport theory. The conductivity is characterized along the nanotubes and across the intersecting junction. The conductivity is much weaker across the junction than along the nanotubes and could be strengthened in all directions using dopants. The largest increase in conductivity is induced by Al along the nanotubes and by Cu across the intersection [389-fold and 14-fold relative to the pristine (8,0) network, respectively]. Additionally, Ag dopants activate charge transport along the semiconducting nanotube in heterogeneous networks of mixed metal…

Abstract Electrochromic windows that dynamically absorb incident solar irradiation are envisioned as smart technology devices that can reduce power consumption in buildings and accelerate progress toward sustainable development. While regulating the visible light in interior spaces to suite the comfort of occupants, electrochromic windows can also offer thermal control by controlling the flux of solar energy, including infrared radiation. The ability to selectively modulate visible and infrared solar transmittance is denoted as dual-band electrochromism. Dual-band control can be achieved by employing materials that absorb light in different spectral regions when electrochemically charged, with light absorption due to either a polaronic or a plasmonic mechanism, depending on the charging conditions. In this Perspective, we discuss how adopting a plasmonic or a polaronic approach can affect the performance of an electrochromic device in terms of different quantitative figures-of-merit and the challenges and opportunities for designing better dual-band electrochromic devices in the…

Amorphous titania (am.-TiO2) has gained wide interest in the field of photocatalysis, thanks to exceptional disorder-mediated optical and electrical properties compared to crystalline TiO2. Here, we study the effects of intrinsic Ti3+ and nitrogen defects in am.-TiO2 thin films via the atomic layer deposition (ALD) chemistry of tetrakis(dimethylamido)titanium(IV) (TDMAT) and H2O precursors at growth temperatures of 100-200 °C. X-ray photoelectron spectroscopy (XPS) and computational analysis allow us to identify structural disorder-induced penta- and heptacoordinated Ti4+ ions (Ti5/7c4+), which are related to the formation of Ti3+ defects in am.-TiO2. The Ti3+-rich ALD-grown am.-TiO2 has stoichiometric composition, which is explained by the formation of interstitial peroxo species with oxygen vacancies. The occupation of Ti3+ 3d in-gap states increases with the ALD growth temperature, inducing both visible-light absorption and electrical conductivity via the polaron hopping mechanism. At 200 °C, the in-gap states become fully occupied extending the lifetime of photoexcited charge…

= 0.43 eV. Detailed insights into the process of transient bulk diffusion are obtained from kinetic Monte Carlo simulations.

Electrochemical dinitrogen (N 2 ) reduction reaction (NRR) provides a green method for low-temperature ammonia (NH 3 ) synthesis, but this process is still hampered by high overpotential and poor Faradaic efficiency. Based on density functional theory, the NRR catalytic performances of 29 transition metal atoms anchored on the ternary B 3 C 2 P 3 monolayer (M/B 3 C 2 P 3 SACs) were systematically evaluated to screen eligible electrocatalysts. Combining the intrinsic physical properties of the metal atom and its coordinated atoms, Ψ is selected from multi-level descriptors. The structure–activity relation of the SACs is clearly revealed, and the V/B 3 C 2 P 3 SAC stands near the top of the volcano plot with a small negative limiting potential of −0.30 V and a high theoretical selectivity of 87.4%. Moreover, all hydrogenation steps of the NRR process on the V/B 3 C 2 P 3 SAC exhibit surmountable barriers under room temperature with a large rate constant of 3.42 × 10 –2 s –1, exhibiting a promising catalytic activity. Besides, the SAC structure remains well with no bond breaking under…

Implementation of vapor/phase dosing of small molecule inhibitors (SMIs) in advanced atomic layer deposition (ALD) cycles is currently being considered for bottom-up fabrication by area-selective ALD. When SMIs are used, it can be challenging to completely block precursor adsorption due to the inhibitor size and the relatively short vapor/phase exposures. Two strategies for precursor blocking are explored: (i) physically covering precursor adsorption sites, i.e., steric shielding, and (ii) eliminating precursor adsorption sites from the surface, i.e., chemical passivation. In this work, it is determined whether steric shielding is enough for effective precursor blocking during area-selective ALD or whether chemical passivation is required as well. At the same time, we address why some ALD precursors are more difficult to block than others. To this end, the blocking of the Al precursor molecules trimethylaluminum (TMA), dimethylaluminum isopropoxide (DMAI), and tris(dimethylamino)aluminum (TDMAA) was studied by using acetylacetone (Hacac) as inhibitor. It was found that DMAI and…

Materials that sustain localized surface plasmon resonances have a broad technology potential as attractive platforms for surface-enhanced spectroscopies, chemical and biological sensing, light-driven catalysis, hyperthermal cancer therapy, waveguides, and so on. Most plasmonic nanoparticles studied to date are composed of either Ag or Au, for which a vast array of synthetic approaches are available, leading to controllable size and shape. However, recently, alternative materials capable of generating plasmonically enhanced light-matter interactions have gained prominence, notably Cu, Al, In, and Mg. In this Perspective, we give an overview of the attributes of plasmonic nanostructures that lead to their potential use and how their performance is dictated by the choice of plasmonic material, emphasizing the similarities and differences between traditional and emerging plasmonic compositions. First, we discuss the materials limitation encapsulated by the dielectric function. Then, we evaluate how size and shape maneuver localized surface plasmon resonance (LSPR) energy and field…

Ammonia (NH 3 ) is a valuable chemical for fertilizer production and for use as an effective hydrogen carrier. Electrocatalytic nitrate reduction has recently received great attention as an alternative for NH 3 synthesis due to its kinetically favorable reaction. However, this promising strategy suffers from low Faradaic efficiency (FE) at large current density (>100 mA cm –2 ) and low nitrate concentrations because of the competing hydrogen evolution reaction. Herein, we report a catalyst consisting of earth-abundant cobalt–copper (Co 1– x Cu x ) nanoparticles supported on a three-dimensional substrate for efficient and selective NH 3 synthesis via electrocatalytic nitrate reduction. Typically, the optimized Co 0.5 Cu 0.5 catalyst performs at a high NH 3 Faradaic efficiency (FE) of over 95% at −0.03 V with NH 3 partial current density of ∼176 mA cm –2 at 50 mM nitrate, which is 7.3- and 1.7-fold higher than that of pure Co and Cu counterparts. Importantly, replacing Co with Cu enables the tuning of onset potential on Co catalyst maintaining high selectivity toward NH 3 . A…

High Resolution Image Download MS PowerPoint Slide Three-dimensional lead halide perovskites are promising materials for optoelectronic applications. The most famous representative comprise methylammonium (MA + ) and formamidinium (FA + ) cations, but recently, this group was enlarged by methylhydrazinium (MHy + ) analogues that crystallize in polar structures at room-temperature. Properties of three-dimensional (3D) perovskites can be tuned by mixing of molecular cations or halide anions. Here, we report synthesis and physicochemical characterization of mixed-halide MHyPbBr x Cl 3– x ( x = 0.40, 0.58, 0.85, 1.33, 1.95, 2.25, and 2.55) and MHyPbBr 2.8 I 0.2 perovskites. X-ray diffraction data show that all materials feature a polar monoclinic P 2 1 symmetry at room temperature. With the temperature increase, all MHyPbBr x Cl 3– x perovskites undergo a displacive phase transition to another polar orthorhombic Pb 2 1 m phase at T 2 ≥ 318 K. The bromine rich crystals ( x ≥ 1.33) exhibit an additional order–disorder phase transition to the archetypal cubic Pm 3̅ m phase at T 1 ≥ 409 K.…

Designing van der Waals (vdW) heterostructures has been considered to be a promising strategy for fabricating high-performance nanosized optoelectronic devices. Based on the first-principles calculations within density functional theory (DFT), we have demonstrated that a BP/MoSi 2 P 4 vdW heterostructure possesses a direct band gap with a typical type-II band alignment, which can facilitate the effective separation of photogenerated electron–hole pairs. Compared with a MoSi 2 P 4 monolayer, not only the hole carrier mobility but also the optical absorption intensity of the BP/MoSi 2 P 4 heterostructure can be enhanced significantly. The predicted photoelectric conversion efficiency (PCE) for the BP/MoSi 2 P 4 heterostructure can reach up to 22.2%, which is competitive with other existing two-dimensional (2D) heterostructures studied previously. Our findings indicate that the 2D BP/MoSi 2 P 4 heterostructure can be a good candidate for new optoelectronic nanodevices.

Negative permittivity of materials can be obtained by plasma oscillation or dielectric resonance, but the relationship between these two negative permittivity behaviors has been neglected. Combining the advantages of two negative permittivity behaviors, the negative permittivity can be more tunable and is expected to realize epsilon-near-zero behavior. In this work, percolative bismuth ferrite/silver composites with different contents of Ag were successfully fabricated by a simple solid-state sintering method. With the addition of Ag, the Lorentz-like and Drude-like negative permittivity behaviors were successively observed in bismuth ferrite/silver composites. The reasons for the two types of negative permittivity behaviors are dielectric resonance and plasma oscillation, respectively. Further investigation revealed that the synergistic effect of dipole resonance and free electrons led to a change of resonance frequency, a decrease of magnitude, and a transition of two negative permittivity behaviors. Moreover, with the addition of Ag in percolative bismuth ferrite/silver…

High Resolution Image Download MS PowerPoint Slide Li 3 YX 6 (X = Cl, Br) materials are Li-ion conductors that can be used as solid electrolytes in all solid-state batteries. Solid electrolytes ideally have high ionic conductivity and (electro)chemical compatibility with the electrodes. It was proven that introducing Br to Li 3 YCl 6 increases ionic conductivity but, according to thermodynamic calculations, should also reduce oxidative stability. In this paper, the trade-off between ionic conductivity and electrochemical stability in Li 3 YBr x Cl 6– x halogen-substituted compounds is investigated. The compositions of Li 3 YBr 1.5 Cl 4.5 and Li 3 YBr 4.5 Cl 1.5 are reported for the first time, along with a consistent analysis of the whole Li 3 YBr x Cl 6– x ( x = 0–6) tie-line. The results show that, while Br-rich materials are more conductive (5.36 × 10 –3 S/cm at 30 °C for x = 4.5), the oxidative stability is lower (∼3 V compared to ∼3.5 V). Small Br content ( x = 1.5) does not affect oxidative stability but substantially increases ionic conductivity compared to pristine Li 3 YCl…

One of the potential strategies to solve renewable energy shortage is to design low-cost efficient photocatalysts for water splitting to aid hydrogen and oxygen evolution reactions (HER and OER). Two-dimensional (2D) materials like MXenes and transition metal dichalcogenides (TMDs) have caught special attention owing to their unique optical, electrical, and mechanical properties, but come with issues like photocorrosion and poor charge separation. Bilayer vdW heterojunctions of suitable constitutive monolayers are coming up as a potential solution to these hazards, accredited to their tunable band gap and efficient charge separation. In this paper, we have investigated the possibility of Ti 2 CO 2 –WX 2 (X = S, Se, Te) vdW heterostructures to perform as Z -scheme photocatalysts by employing first-principle density functional calculations, and thereby, the Ti 2 CO–WSe 2 heterostructure has emerged as the most promising material for Z -scheme photocatalysis. Further, excited-state dynamics simulation reveals that the timescales of electron transfer and hole transfer are greater (1.13…

Carbon dots (CDs) that simultaneously exhibit full-color and wide-range lifetime-tunable room-temperature phosphorescence (RTP) are of particular interest for potential applications in encryption and information security. However, achieving such CDs remains a great challenge thus far. This work reports on the development of a straightforward host–guest approach, where a metal–organic framework (MOF) host acts as an RTP activator of fluorescent CDs, with the RTP color dependent on the fluorescent component. The developed CDs@MOF composites exhibited RTP with a tunable emission wavelength from blue (478 nm) to red (631 nm), while the lifetime was tunable from 85.67 to 1064.21 ms. As far as is known, this is the report of CD-based RTP materials with simultaneous full-color and wide-range lifetime-tunable properties for the first time. In comparison to conventional 3D coding applications of CDs, the wide-range lifetime-tunable property allows for the creation of an additional dimension in encryption. Thus, the developed RTP CDs@MOF composites have potential as writable security inks for…

Photothermal conversion with high efficiency depends on not only absorption but also on the process and the speed of the photothermal conversion. Herein, we report the combination of carbon fibers (CFs) and metal nanoparticles (NPs) with a localized surface plasma resonance (LSPR) effect. On investigating their optical properties and the photothermal conversion in water evolution, we observe that all of the metal NPs/CFs perform better than the CFs. The rate of water evolution on Au NPs/CFs is up to 9.9 ± 0.2 kg·m –2 ·h –1 and those of Ag NP/CFs and Cu NPs/CFs are 8.6 ± 0.1 and 7.1 ± 0.2 kg·m –2 ·h –1, respectively, which are higher than that of the CFs (7.0 ± 0.3 kg·m –2 ·h –1 ). Heat localization and the LSPR effect of metal nanoparticles are considered the main reasons for the enhanced photothermal conversion. The mechanism of the LSPR effect enhancing the photothermal conversion is that the metal NP loading provides more paths for energy conversion and accelerates the photothermal conversion.

Transition metal dichalcogenides, such as molybdenum disulfide (MoS 2 ), have unique electronic and optoelectronic properties that are often altered by environmental effects, particularly substrate or contact materials. Understanding these effects is important for device design and engineering. There is limited information concerning how MoS 2 interacts with 3D semiconductors such as metal oxides. This work demonstrates the influence of substrate material and MoS 2 layer thickness on the work function of exfoliated MoS 2 flakes. Kelvin probe force microscopy is used to probe the work function of MoS 2 on titanium oxide (TiO x ), molybdenum oxide (MoO x ), and gold (Au). We find that TiO x based substrates yield a lower MoS 2 work function than MoO x and Au for various MoS 2 thicknesses, and that the screening lengths for each substrate are larger than 5 nm. By reporting the work function variation of MoS 2 on these substrates, this study aims to provide important insights into device design and contact engineering.

Lead-free copper halide scintillators have shown tremendous potential applications in X-ray detection and imaging. However, the imaging resolution is still rather limited due to the lack of a scintillation waveguide, especially for the solution-processed nanocrystal scintillators. Here, we report a solution synthesis route for Cs 3 Cu 2 I 5 nanowire (NW) arrays via an anodized aluminum oxide (AAO) template-assisted in situ growth. As the NWs grow, the precursor concentration directly affects the length and uniformity of the Cs 3 Cu 2 I 5 NWs among the various factors. The as-synthesized Cs 3 Cu 2 I 5 NW array scintillators achieve a high spatial resolution of 20 lp mm –1, which is so far the highest value for this emerging copper halide scintillators. The present study provides a convenient and facile method to synthesize Cs 3 Cu 2 I 5 NW arrays for high-resolution X-ray imaging.

Superconductivity allows electric conductance with no energy losses when the ambient temperature drops below a critical value ( T c ). Currently, the machine learning (ML)-based prediction of potential superconductors has been limited to chemical formulas without explicit treatment of material structures. Herein, we implement an efficient structural descriptor, the smooth overlap of atomic position (SOAP), into the ML models to predict the T c values with explicit atomic structural information. Using a data set containing 5713 compounds, our ML models with the SOAP descriptor achieved a 92.9% prediction accuracy of coefficient of determination ( R 2 ) score via rigorous multialgorithm cross-verification procedures, exceeding the 86.3% accuracy record without atomic structure information. Several new high-temperature superconductors with T c values over 90 K were predicted using the SOAP-assisted ML model. This study provides insights into the structure–property relationship of high-temperature superconductors.

Cu/SSZ-13 is the current state-of-the-art catalyst for selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) in diesel after-treatment systems. Recent investigations under in situ or operando conditions yielded rich molecular level understanding about dynamic transformations of Cu sites during reactions. However, in situ investigations aiming at the distinction of the two SCR-active Cu species in this catalyst, that is, Z 2 Cu II and ZCu II OH, are still scarce. Herein, we apply in situ UV–vis spectroscopic studies combined with theoretical calculations to investigate the two Cu sites under SCR-relevant conditions at low temperatures. We demonstrate that in the presence of O 2, two isolated ZCu II OH sites readily transform into a double O-bridged dicopper species with a Cu–Cu distance of 3.37 Å, whereas Z 2 Cu II species cannot undergo such a transformation. In addition, ZCu II OH displays stronger activity than Z 2 Cu II during both reduction by NH 3 and NO oxidation to bidentate nitrates. Despite these differences, Z 2 Cu II and ZCu II OH sites exhibit similar spectroscopic…

The presence of excimers, as revealed by broad, structureless, and red-shifted emission, is quite common in a great many organic solution- and solid-phase systems. A fundamental theoretical account of excimer creation and relaxation has generated enormous interest over the years. Here, a model based on a Holstein–Peierls Hamiltonian is presented to account for absorption and photoluminescence in molecular dimers. The model extends the Frenkel-charge transfer (CT)-Holstein model in order to account for both local and nonlocal coupling to a slow inter molecular vibrational mode. The model shows that excimer emission can be induced either through (1) local inter molecular coupling to the dimer CT states or through (2) the nonlocal Frenkel-CT coupling terms. Finally, by incorporating both the local and nonlocal inter molecular coupling, the measured absorption and excimer emission spectra for a set of two different bis(perylene diimide) covalently linked dimers are successfully reproduced. The evolution from structured to unstructured excimer emission likely occurs via an increase in…

Zero-dimensional (0D) organic–inorganic metal halides (OIMHs) have attracted tremendous attention due to their fascinating optoelectronic properties. Herein, we report an antimony(III)-based 0D OIMH of [PPh 3 H] 2 [SbCl 5 ] comprising discrete [SbCl 5 ] 2– pyramids and protonated triphenylphosphine (PPh 3 H) cations with a low charge density. Abundant supramolecular interactions including C–H···Cl and rare P–H···Cl hydrogen bonds and C–H···Π and anion···Π interactions lead to a three-dimensional (3D) supramolecular framework structure of [PPh 3 H] 2 [SbCl 5 ]. Photophysical characterizations indicate that [PPh 3 H] 2 [SbCl 5 ] has singlet/triplet dual-band emission. The intersystem crossing between the single and triplet states is tunable upon changing the temperature. Analyses of the Huang–Rhys factor ( S ), exciton activation energy ( E a ), and electron–phonon coupling energy (Γ op ) verify that the soft lattice and strong electron–phonon coupling result in the broad emission of [PPh 3 H] 2 [SbCl 5 ], while the excited-state reorganization of the [SbCl 5 ] 2– pyramid leads to a…

Great influences of the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of the analyte and their alignments compared to the Fermi level of the substrate on the charge transfer (CT) process, and consequently, on the surface-enhanced Raman scattering (SERS) phenomenon have been described via theoretical calculations. To provide experimental evidence, in this study, two antibiotics, chloramphenicol (CAP) and amoxicillin (AMX), were investigated as analytes in SERS sensors based on electrochemically synthesized colloidal silver nanoparticles (e-AgNPs) as the substrate. Despite the same experimental condition, similarities in analyte structure, and in the ability of absorbing onto e-AgNPs, the detection of the two antibiotics showed obvious distinction. While CAP was able to be detected using e-AgNP-based SERS sensors at concentrations down to 1.2 × 10 –9 M, there were no characteristic peaks observed in the SERS spectra of AMX even at a high concentration of 10 –3 M. The LUMO and HOMO energy levels of the two analytes were measured…

High Resolution Image Download MS PowerPoint Slide Selective CO 2 capture and electrochemical conversion are important tools in the fight against climate change. Industrially, CO 2 is captured using a variety of aprotic solvents due to their high CO 2 solubility. However, most research efforts on electrochemical CO 2 conversion use aqueous media and are plagued by competing hydrogen evolution reaction (HER) from water breakdown. Fortunately, aprotic solvents can circumvent HER, making it important to develop strategies that enable integrated CO 2 capture and conversion. However, the influence of ion solvation and solvent selection within nonaqueous electrolytes for efficient and selective CO 2 reduction is unclear. In this work, we show that the bulk solvation behavior within the nonaqueous electrolyte can control the CO 2 reduction reaction and product distribution occurring at the catalyst–electrolyte interface. We study different tetrabutylammonium (TBA) salts in two electrolyte systems with glyme ethers (e.g., 1,2 dimethoxyethane or DME) and dimethyl sulfoxide (DMSO) as a low…

Promoting carrier separation and migration is the key factor to improve photocatalytic performance. In this work, we proposed a novel WSi 2 N 4 /MoSi 2 N 4 heterostructure including six different stacking configurations, in which the AB stacking configuration is thermodynamically most stable and can satisfy the requirement of overall water splitting. The presence of an internal electric field owing to the symmetry breaking will promote the carrier separation to different layers, and the low exciton (e–h pairs) binding energy (0.12 eV) and high carrier mobility further boost the separation and migration of electrons and holes; these results demonstrate that heterojunctions have high carrier activity and good photocatalytic performance. The high light absorption coefficient (∼10 5 cm –1 ) and enhanced visible light absorption also further support our theoretical predictions. Moreover, the research of nonadiabatic molecular dynamics provides a deeper understanding that the time of carrier transfer is much longer than e–h recombination (2420 fs for electrons, 67 ns for e–h…

High Resolution Image Download MS PowerPoint Slide We investigate the pH-dependent surface chemistry of three relevant and widely used oxides, MgO, TiO 2, and γ-Al 2 O 3, from ab initio molecular dynamics simulations at the level of density functional theory (DFT). We studied the MgO (001), anatase TiO 2 (101), and γ-Al 2 O 3 (001) low-index surfaces and considered solvation effects by explicitly simulating the solid/water interfaces. The analysis of the MgO/H 2 O, TiO 2 /H 2 O, γ-Al 2 O 3 /H 2 O interfaces allowed us to access atomistic details of the structure and the effects induced by water on these surfaces. We also investigated the pH dependence by means of the Grand Canonical formulation of species in solution. This allowed us to evaluate acid–base equilibrium constants and the point-of-zero charge (pH PZC ) values. The calculated pH PZC values compare well with available experimental measurements. Based on the above result, we also predicted the fraction of charged species (H + and OH – ) and neutral molecules (H 2 O) present on the surface as a function of pH, a fundamental…

The lead-free Cs 2 AgBiBr 6 double perovskites have recently emerged as promising candidates for optoelectronic applications due to their less toxicity and high stability. Although the photophysical study of Cs 2 AgBiBr 6 has been extensively explored, the same for dielectric relaxation and carrier conduction remains elusive. Here, we uncover the dielectric relaxation and charge conduction mechanism in the Cs 2 AgBiBr 6 single crystals using temperature-dependent electrochemical impedance spectroscopy in correlation with modulus spectroscopy. We found that the ionic displacement and space charge polarization are mainly responsible for the dielectric response. A sharp transition frequency as ∼191 Hz for 0 °C to ∼492 Hz for 90 °C was observed in the dielectric constant (ε′) versus temperature study, where dε′/d T exhibits a positive and negative coefficient below and above the transition frequency, respectively. Stevels model analysis suggests that the contribution of traps reduces with the increase in temperature and therefore conduction enhances. This model also confirms the…

The search for an efficient electrode material based on 2D materials for Li/Na-ion rechargable batteries is an emerging field of research in the recent times. By employing density functional theory (DFT) based calculations, we herein proposed a porous boron phosphide (p-BP) monolayer having superior electronic conductivity and enough thermodynamic stability as an excellent cathode material for Li/Na-ion batteries. We have analyzed the structure, stability, electronic structure of p-BP monolayer and addressed the adsorption of Li/Na atoms over the monolayer followed by the charge transfer and the chemical interaction between the alkali metal atom and the p-BP monolayer. The calculated diffusion energy barriers, are within the range of 0.031 to 0.495 eV. We have also measured the open circuit voltages of the studied systems that vary from 1.92 to 5.48 V, which supports the plausibility of an efficient cathode material. Finally, the Li storage capacity is found to be in between 689.4 and 931.96 mAh/g, while that of Na is in between 1378.8 to 1659.66 mAh/g. All these calculated results…

Metal–organic frameworks (MOFs) are an emerging class of materials possessing significant potential in separation and storage applications. Identifying optimal candidates from tens of thousands of MOFs that have been reported is a challenging task. To this end, machine learning (ML) represents a promising approach to facilitate the selection of best-performing MOFs. In this study, we propose a scheme to develop chemistry-encoded convolutional neural network (CNN) models to predict gaseous adsorption properties, i.e., Henry’s constants of adsorption and adsorption selectivity, in chemically diverse MOFs. To train CNN models, the MOF structures are represented by their atomic locations coupled with associated chemical information of each framework atom including the 6–12 Lennard-Jones parameters (i.e., σ and ε) and point-charge values (i.e., q ). Henry’s constants of CH 4 and CO 2 in approximately 10 000 MOF structures computed via molecular simulations are used for training and testing. Our developed CNN models show a superior prediction accuracy. Models for zeolites are also…

High Resolution Image Download MS PowerPoint Slide DFT + U with occupation matrix control (OMC) is applied to study computationally bulk UO 2 and PuO 2, the latter for the first time. Using the PBESol functional in conjunction with OMC locates AFM and NM ground states for UO 2 and PuO 2, respectively, in agreement with experimental findings. By simulating the lattice parameter, magnetic moment, band gap, and densities of states, U = 4.0 eV is recommended for AFM UO 2, yielding data close to experiments for all considered properties. U = 4.5 and 4.0 eV are recommended for NM and AFM PuO 2, respectively, though much larger U values (c. 10 eV) are required to yield the most recently reported PuO 2 band gap. For both oxides, several excited states have similar properties to the ground state, reinforcing the need to employ OMC wherever possible.

The detection of broadband spectroscopy is a huge challenge for modern optoelectronics, especially for extremely high- or low-energy photons. For metal halide perovskites significant progress has been made in high-energy photons such as X-rays, but there is little exploration of the perovskites in the high-performance detection of low-energy photons, especially mid- or far-infrared photons. Most infrared photodetectors suffer large dark currents, and perovskite photodetectors’ performances are significantly limited by ion migration. Here, a facile solution evaporation method is developed to grow a centimeter-scale zero-dimensional (0D), lead-free perovskite Cs 3 Bi 2 I 9 single crystal for high-performance mid-infrared photodetectors with ultralow dark current drifts. The 0D Cs 3 Bi 2 I 9 perovskite single crystal (PSC) photodetector shows an ultralow dark current drift (1.67 × 10 –17 A cm –2 V –1 s –1, 9 orders of magnitude smaller than that of MAPbI 3 ) and ultralow power consumption (smaller than 1 pA at 1 V bias) for greatly inhibited ion migration. The photodetector achieves…

A simple and effective photocatalytic system has always been the goal of photocatalytic research. In this study, Ag/Ag 2 O was grown in situ on a CeO 2 substrate by a one-step method to form a Ag/Ag 2 O/CeO 2 photocatalyst. The close combination of the two made the composite catalyst have more effective hydrogen evolution sites. The Ag/Ag 2 O/CeO 2 composite catalyst has a wide light absorption wavelength, low overpotential, and small electrochemical impedance, which are favorable for the development of a photocatalytic system. CeO 2 and Eosin Y continue to provide photogenerated electrons as electron donors, while the heterostructure of the Ag/Ag 2 O/CeO 2 system enables the separation of electrons on the conduction band of CeO 2 . The ingenious coordination of the two can effectively isolate the photogenerated electron–hole pairs, thus supporting the continuous progress of photocatalytic hydrogen evolution. Importantly, Ag/Ag 2 O/CeO 2 has excellent photocatalytic performance for hydrogen production; in particular, Ag/Ag 2 O/CeO 2 -30 has the highest hydrogen production…

High Resolution Image Download MS PowerPoint Slide One of the major hurdles in the utilization of metallic lithium anodes is understanding the Li + transfer kinetics through the solid electrolyte interface (SEI) in addition to Li oxidation. Electrochemical impedance spectroscopy (EIS) combined with temperature variation provides deeper comprehension and reveals kinetic parameters of individual processes separately. In this study, we report temperature-dependent EIS analysis of metallic Li anodes to shed light on the kinetics of anodic/interfacial processes at different states of charge and wide temperature ranges (−25 to 75 °C), utilizing lithium thionyl chloride (Li/SOCl 2 ) and lithium manganese dioxide (Li/MnO 2 ) primary batteries as model systems. We found in both batteries that the impedance of the SEI processes is highly temperature-dependent with non-Arrhenius behavior at temperatures greater than 35 °C. Conversely, the kinetics of the anodic process showed small temperature dependence that is explained by the Arrhenius equation throughout the temperature range studied. The…

The use of machine learning for the prediction of physical and chemical properties of crystals based on their structure alone is currently an area of intense research in computational materials science. In this work, we studied the possibility of using machine-learning-trained algorithms in order to calculate the thermal properties of siliceous zeolite frameworks. We used as training data the thermal properties of 120 zeolites, calculated at the DFT level, in the quasi-harmonic approximation. We compared the statistical accuracy of trained models (based on the gradient-boosting regression technique) using different types of descriptors, including ad hoc geometrical features, topology, pore space, and general geometric descriptors. While geometric descriptors were found to perform best, we also identified limitations on the accuracy of the predictions, especially for a small group of materials with very highly negative thermal expansion coefficients. We then studied the generalizability of the technique, demonstrating that the predictions were not sensitive to the refinement of…

The stability and dissolution of rutile oxides such as RuO 2 and IrO 2 which are used as electrocatalysts for water splitting have long been the Achilles’ heel in the long-term operation of electrolyzers for sustainable production of hydrogen from water. In this study, using a combination of ab initio steered molecular dynamics, enhanced sampling, and ab initio thermodynamics, we investigate the surface stability and dissolution of three prominent electro(photo)catalysts for water splitting: RuO 2, IrO 2, and TiO 2 in the rutile phase. We provide an atomistic understanding of the dissolution process and establish possible dissolution paths for different oxides using the (110) surface as a prototype. Interestingly, we identify a distinct surface site specificity in the dissolution of the RuO 2 (110) surface, with the coordinately undersaturated sites more prone to dissolution, whereas no such surface site specificity exists for the IrO 2 (110) surface. In addition, our investigation of more complex dissolution mechanisms involving codissolution of the different surface sites on the…

Metal halide perovskites (MHPs) have attracted extensive attention due to their excellent optoelectronic properties. Among them, layered two-dimensional (2D) metal halide materials with special structures have attracted extensive attention due to their superior stability and optoelectronic properties. Here, we report the 2D Ruddlesden–Popper (RP) phase Cs 3 Cd 2 Cl 7 synthesized by a solvothermal method, and the photoluminescence quantum yields (PLQYs) of the pristine Cs 3 Cd 2 Cl 7 sample (PLQY ∼ 10%) can be increased to 68 ± 5% through appropriate Sb 3+ doping. This should be the highest PLQY of all reported all-inorganic RP-phase Cd-based perovskites so far. Our results indicate that the highly efficient cyan emission can be attributed to the common self-trapped exciton (STE) emission of the triplet states of Cd 2+ and Sb 3+ induced by strong electron–phonon coupling, and Sb 3+:Cs 3 Cd 2 Cl 7 has excellent structural and spectral stability. This new material should be a promising candidate for optoelectronic applications in the future.

High Resolution Image Download MS PowerPoint Slide The local structural changes associated with the ZIF-8 framework flexibility upon nitrogen gas adsorption have been studied by in situ X-ray absorption spectroscopy (XAS) and high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy. Different thermodynamic conditions (isobar and isotherm) have been used to explore the so-called “gate opening” transition in which the hexagonal pore windows of the sodalite cage open, increasing the accessible volume for gas adsorption. To elucidate the source of the spectral changes in the XANES region of the absorption spectra observed along the gas adsorption and through the transition from the closed to the open pore configuration, ab initio calculations have been performed. Our results demonstrate that the transition from the closed to the open pore configurations involves not only the rotation of the MeIM ligand but also a further bend of the Me group away from the plane defined by the IM ring. Additionally, the contribution of the N 2 molecules…

The potential of zero charge (U_PZC) is an important quantity of metal-water interfaces that are central in many electrochemical applications. In this work, we use ab initio molecular dynamics (AIMD) simulations to study a large number of (111), (100), (0001) and (211) and overlayers of transition metal-water interfaces in order to identify simple descriptors to predict their U_PZC. We find a good correlation between water coverage and the work function reduction Δφ which is defined by the difference of the work function in vacuum and in the presence of water. Furthermore, we determine the vacuum binding energies of H2O and *OH species as good descriptors for the prediction of water coverage and thereby of ∆φ. Our insights unify different facet geometries and mixed metal surfaces and thereby generalize recent observations. We further present a scheme to predict U_PZC based only on the *OH binding and the vacuum work function estimated from static DFT calculations. This formalism is applicable to all investigated metals and mixed metal surfaces including terrace and step geometries…

Most electrolyte additives can improve lithium-ion batteries’ performance by forming a solid electrolyte interphase (SEI) layer on the electrode surface. However, the influences of such additives on the lithium-ion (Li + ) solvation structure, particularly on the Li + desolvation process and its relationship with the attained electrode performance, are mostly overlooked. Herein, we designed a novel ether-based electrolyte to stabilize the alloying anode (e.g., Sb, antimony) by introducing LiNO 3 as an additive, where a new interfacial model was constructed to show the additive effect on the kinetic and thermodynamic properties of Li + –solvent–anion complex in the electrolyte. We find that the NO 3 – anion can weaken the Li + –solvent interaction, promote the Li + desolvation, particularly mitigate electrolyte decomposition by tuning the location of the Li + –solvent–anion complex on the electrode surface, and then improve electrolyte stability. This is the first time to show that the LiNO 3 additive can contribute to a far distance of the Li + –solvent–anion complex from the Sb…

The electrochemical CO 2 reduction reaction (CO 2 RR) is important for a sustainable future.Key insights into the reaction pathways have been obtained by density functional theory (DFT) analysis, but so far, DFT has been unable to give an overall understanding of selectivity trends without important caveats.We show that an unconsidered parameter in DFT models of electrocatalysts�the surface coverage of reacting species�is crucial for understanding the CO 2 RR selectivities for different surfaces.Surface coverage is a parameter that must be assumed in most DFT studies of CO 2 RR electrocatalysts, but so far, only the coverage of nonreacting adsorbates has been treated.Explicitly treating the surface coverage of reacting adsorbates allows for an investigation that can more closely mimic operating conditions.Furthermore, and of more immediate importance, the use of surface coverage-dependent adsorption energies allows for the extraction of ratios of adsorption energies of CO 2 RR intermediates (COOH ads and HCOO ads ) that are shown to be predictive of selectivity and are not…

We report on the tunable dielectric properties achieved in cation-substituted nickel ferrite (NiFe 2 O 4; NFO) by selectively engineering the crystallographic site occupation of the dopant cation in the NFO ceramics. The NFO, Mg-substituted NFO (NiMg 0.2 Fe 1.8 O 4; NMFO), and In-substituted NFO (NiIn 0.2 Fe 1.8 O 4; NIFO) nanocrystals were synthesized by employing a tartrate-gel chemical route, followed by calcination at 500 °C. High-resolution transmission electron microscopy (HRTEM) analyses indicate the crystal quality of NFO, NMFO, and NIFO nanomaterials. The HRTEM data revealed that all of the ferrite materials were nanocrystalline with sizes in the range of 15–25 nm. Coupled with HRTEM analyses, X-ray diffraction analyses indicate the formation of single-phase spinel-structured NFO, NMFO, and NIFO materials without any detectable impurities. Chemical analysis performed using Mossbauer spectroscopy indicates that Mg 2+ occupies the octahedral site, while In 3+ preferably occupies the tetrahedral site of the spinel-structured NFO. The Fourier transform infrared (FTIR)…

Selective removal of ∼1% acetylene impurity from ethylene is an essential process to prevent the poisoning of the Ziegler–Natta catalyst in polyethylene production. Developing an earth-abundant catalyst to replace Pd and a new approach to reduce energy consumption represents an immense challenge in this field. Herein, we present an atomic understanding of the trend in electrocatalytic acetylene semi-hydrogenation over 12 transition metals with systematic density functional theory calculations and the computational hydrogen electrode model. Copper stands out and is theoretically identified as the ideal metal for electrocatalytic acetylene conversion to ethylene with a suppressed hydrogen evolution reaction. Our theoretically predicted Cu catalyst has been successfully synthesized and tested to be superior for selective alkyne semi-hydrogenation experimentally, which greatly validates our computational framework for the rational design of the catalyst. This work not only illustrates the key factors determining the activity and selectivity but also provides new suggestions for further…

To study the promoting effect of strong metal–support interactions (SMSIs) on the catalytic oxidation of ethyl acetate, a series of Pd/CeO 2 catalysts with different CeO 2 support morphologies of nanocubes (NC), spindles (SP), and nanospheres (NS) were prepared for the catalytic oxidation of ethyl acetate. The study indicated that the catalytic activity of Pd/CeO 2 catalysts possessed a significant structure–activity relationship. A series of characterization results revealed that the SMSIs between Pd nanoparticles (NPs) and the CeO 2 support optimized surface chemical states, promoted the formation of surface oxygen vacancies, activated the surface oxygen species, and improved the low-temperature reducibility. Among all of these catalysts, Pd/CeO 2 -SP exhibited the best catalytic activity for ethyl acetate oxidation ( T 90 = 180 °C, WHSV = 60 000 mL g –1 h –1 ), which was attributed to the SMSIs between Pd NPs and the CeO 2 -SP support.

The Fe–N–C materials are promising noble-free alternatives to Pt-based oxygen reduction reaction (ORR) electrocatalysts. Identifying the actual active structure of FeN 4 -based moieties is helpful for the regulation and design of high-performance electrocatalysts. However, the current theoretical researches were mostly based on the charge-neutral model (CNM), which cannot accurately describe the electrochemical interface. Herein, we employed the constant potential based grand canonical density functional theory (GC-DFT) computations to study the ORR mechanism of axially decorated FeN 4 electrocatalysts. We studied around ten types of axial ligands, and the constant potential energetics and microkinetic modeling demonstrated that the Fe center can exhibit excellent activity for boosting the four-electron ORR via covalently linked −NH 2 ligand. The lowering of the antibonding d z 2 –p z orbital is responsible for weakening the adsorption of oxygen in FeN 4 –Ls to promote ORR activity, and the −NH 2 decoration led to the lowest antibonding orbital energy. In particular, the adsorption…

High Resolution Image Download MS PowerPoint Slide Plasmonic red shifts of nanoparticles are commonly used in imaging technologies to probe the character of local environments, and the understanding of their dependence on size, shape, and surrounding media has therefore become an important target for research. The red shift of plasmon resonances changes character at about 8–10 nm of size for spherical gold nanoparticles─above this value, the red shift progresses linearly with particle size, while below this size, the red shift changes nonlinearly and more strongly with size. Using an atomistic discrete interaction model, we have studied the special properties of the nanoparticle surface layers and discovered its importance for ultrafine plasmonic nanoparticles and their red shifts. We find that the physical origin for the specific properties inherent to the surface layer of atoms near the nanoparticle boundary is related to the anisotropy of the local environment of atoms in this layer by other atoms. The anisotropy changes the conditions for light-induced nonlocal interactions of…

The kinetics of the thermal decomposition of CaCO 3 is significantly influenced by atmospheric and self-generated CO 2 due to the reversibility of the reaction. More detailed understanding of this well-known phenomenon is desired for establishing an effective Ca-looping in the CaO–CaCO 3 system for energy storage and CO 2 capture. This article shows the universal kinetics of the thermal decomposition of CaCO 3 over different temperatures and partial pressures of CO 2 ( p (CO 2 )) with the aid of an accommodation function (AF) composed of p (CO 2 ) and equilibrium pressure. An analytical form of AF with exponents ( a, b ) was derived based on the kinetic considerations for the consecutive elementary steps of the surface nucleation and interfacial reaction. The overall kinetics of the thermal decomposition of CaCO 3 were described universally over different temperatures and p (CO 2 ) values by introducing the AF, in views of the isoconversional and isothermal kinetic relationships using the extended Friedman and experimental master plots, respectively. The universal kinetic…

In energetic materials, the localization of energy into “hotspots” is known to dictate the initiation of chemical reactions and detonation. Recent all-atom simulations have shown that more energy is localized as internal potential energy (PE) than can be inferred from the kinetic energy (KE) alone. The mechanisms associated with pore collapse and hotspot formation are known to depend on pore geometry and dynamic material response such as plasticity. Therefore, we use molecular dynamics (MD) simulations to characterize shock-induced pore collapse and the subsequent formation of hotspots in 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a highly anisotropic molecular crystal, for various defect shapes, shock strengths, and crystallographic orientations. We find that the localization of energy as PE is consistently larger than the KE in cases with significant plastic deformation. An analysis of MD trajectories reveals the underlying molecular- and crystal-level processes that govern the effect of orientation and pore shape on PE localization. We find that the regions of highest PE relate…

Aggregation-induced emission (AIE) has been significantly explored to enhance luminescence properties. Here, we synthesized bimetallic AuCu nanoclusters (NCs) and studied their AIE by reconstructing the surface motif from −S–Au(I)–S– Au(I)–S– to −S–Au(I)–S–Cu(I)–S–, as evident from X-ray photoelectron spectroscopy (XPS) and microscopy studies. A significant blue shift in the emission band of Au NCs is observed with the change of the Au/Cu molar ratio. We observed enormous emission enhancement with decreasing temperature due to suppression of the intramolecular motion of surface ligands. A 200-fold emission enhancement occurs due to the aggregation of ultrasmall-sized AuCu NCs in a less polar medium of the water–ethanol mixture. An increase in the radiative rate supports the effect of the Au(I)–Cu(I) metallophilic interaction. A decrease in the nonradiative rate confirms the restriction of ligand motions in the aggregated state. Metal cluster-based AIE-type materials pave the way to design highly luminescent materials for potential applications in sensing, biolabeling, light-emitting…

Chalcogenide perovskite materials have received extensive attention in the field of thermoelectrics (TEs) due to their inherent large Seebeck coefficient and ultra-low thermal conductivity. Herein, we demonstrate that the orthorhombic CaZrS 3 perovskite is a promising TE material by using first-principles calculations combined with the semiclassical Boltzmann transport theory. The anisotropic property has been observed clearly on the electronic properties and TE performances of CaZrS 3 along a, b, and c directions. The orthorhombic CaZrS 3 shows excellent thermal stability, which leads to superior performance of electric and thermal conductivities simultaneously; thus it possesses outstanding power factor and ultra-low thermal conductivity and yields impressive ZT values of n-4.06 and p-2.62. This study provides a guideline for chemical doping and provides inspiration for the promotion of related experimental investigations.

Abstract The unique chemical and physical properties of metal–organic frameworks (MOFs) endow them with promising applications in the electrochemical sensing field. Herein, a novel label-free electrochemical sensing strategy for cardiac troponin I (cTnI) has been constructed on the basis of immunoaffinity-induced depression of the electrochemical signal of Cu-MOF-74. The electrochemical assay shows that the immunoaffinity reaction between cTnI and anti-cTnI on the electrode surface can effectively inhibit the electrochemical signal of electrode-confined Cu-MOF-74, suggesting that the Cu-MOF-74-based interface may find application in the label-free analysis of cTnI. Thus, Cu-MOF-74 acts as a bifunctional material in this strategy, namely, the immobilization matrix of probe molecules and the signal source of the sensing analysis. In addition, the reason for the electrochemical signal depression of Cu-MOF-74 induced by immunoaffinity reaction is attributed to the increase in the insulation layer and the blocking of the electrolyte diffusion from the bulk solution to the electrode…

High Resolution Image Download MS PowerPoint Slide A theoretical analysis of reversible and quasireversible electrode reactions of a dissolved redox couple under conditions of the novel technique of differential square-wave voltammetry (DSWV) is presented. The technique is recently introduced as a hybrid form between differential pulse voltammetry (DPV) and square-wave voltammetry (SWV) as the two most advanced and competitive pulse-form voltammetric techniques for a purpose of unifying their advantages and further advancing both techniques in terms of analytical performances, mechanistic analysis, and electrode kinetics. The potential modulation of DSWV consists of potential steps and pulses providing a plethora of voltammetric curves, which enable in-depth characterization of the electrode reaction with a minimal set of measurements. Based on numerical simulations, a set of criteria for characterization and differentiation between reversible and quasireversible electrode reactions are established.

Pd ion exchanged zeolites emerged as promising materials for the adsorption and oxidation of air pollutants. For low-temperature vehicle exhaust, dispersed Pd ions are able to adsorb NOx even in H2O-rich exhaust in the presence of carbon monoxide. In order to understand this phenomenon, changes in Pd ligand environment have to be monitored in-situ. Herein, we directly observe the activation of hydrated Pd ion shielded by H2O into a carbonyl-nitrosyl complex Pd2+(NO)(CO) in SSZ-13 zeolite. The subsequent thermal desorption of ligands on Pd2+(NO)(CO) complex proceeds to nitrosyl Pd2+ rather than to carbonyl Pd2+ under various conditions. Thus, CO molecules act as additional ligands to provide alternative pathway through Pd2+(NO)(CO) complex with lower energy barrier for accelerating NO adsorption on hydrated Pd2+ ion, which is kinetically limited in the absence of CO. We further demonstrate that hydration of Pd ions in the zeolite is a prerequisite for CO-induced reduction of Pd ions to metallic Pd. The reduction of Pd ions by CO is limited under dry conditions even at a high…

Graphene-like graphite (GLG), a carbon material synthesized by heat treatment of graphite oxide, can be charged at a high rate without deposition of lithium metal even when the potential of the GLG anode is stepped below the Li deposition potential. However, the factors contributing to this outstanding rapid chargeability of GLG have been unclear until now. In this study, to clarify the factors, the charge-transfer resistance and diffusion resistance of GLG were quantitatively evaluated by the electrochemical impedance method using GLG thin films as model electrodes. The activation energy of lithium-ion transfer at the GLG/electrolyte interface was found to be almost the same as that reported for graphite, and it was clear that this process was as slow as that in graphite. On the other hand, the lithium-ion diffusion coefficient in GLG calculated from the Warburg impedance was several orders higher than that of graphite, which clearly shows that this contributed greatly to the fast-charging characteristics of GLG. In addition, in the comparison among GLGs with different structural…

Abstract Many attempts have been made to improve the energy density of supercapacitors toward their large-scale applications in storing renewable energy. Herein, the surface wettability effect is unraveled with the combination of static and dynamic density functional theories through which the energy densities and power densities of electrochemical supercapacitors are analyzed with different sets of pore sizes, surface voltages, and bulk ion concentrations. We demonstrate that tuning the surface wettability of electrodes may improve the energy density but simultaneously reduce the power density, and an optimal energy density with a relatively small cost of power density can be achieved by adopting highly confined pores. In addition, increasing ion bulk concentration and/or surface voltage can enhance both the energy density and power density. This work provides a complementary dynamic insight into the surface wettability effect on the performance of supercapacitors.

Recently, low-dimensional metal halides (LDMHs) have attracted tremendous attention due to their fascinating optoelectronic properties. Here, we report an organic–inorganic hybrid Cu(I)-based metal halide of (TPA)CuCl 2 (TPA + = tetrapropylammonium cation), where the isolated [CuCl 2 ] − units are surrounded by TPA +, thus forming a zero-dimensional block. Moreover, the as-synthesized compound shows a broad green emission with a photoluminescence (PL) quantum efficiency of 91.8% and a large Stokes shift of 230 nm, stemming from the self-trapped exciton (STE) transition. Variable-temperature Raman spectra reveal that there is a strong anharmonic electron–phonon coupling in (TPA)CuCl 2, which provides clear evidence for the formation of STEs, and this is also supported by the temperature-dependent PL spectra of (TPA)CuCl 2 . Moreover, it was found that TPA + not only works as a ligand but also participates in the STE emission. Our results provide a clear statement that the formation of the STE is related not only to the low-frequency phonon of [CuCl 2 ] − clusters but also to the…

Searching for high-efficiency photocatalysts for overall water splitting is a promising strategy to solve the energy crisis and environmental problems. Among many kinds of photocatalysts, direct Z-scheme systems have attracted much attention. Here, we propose two-dimensional arsenene/ZrS 2 (HfS 2 ) heterostructures as potential direct Z-scheme photocatalysts based on density functional theory simulations. Our calculations demonstrate that arsenene/ZrS 2 (HfS 2 ) heterostructures have type-II band alignments with small band gaps, facilitating spatial separation of photo-generated carriers and enhancing sunlight absorption ability. Meanwhile, interlayer charge transfer induces a built-in electric field, resulting in the band edge positions bending at the interface region. Combined with the closed band edge positions and small interlayer band gaps, the direct Z-scheme charge transfer pathway is confirmed for them. Additionally, both heterostructures show energic, dynamical, and thermal stability based on the calculated results. What is more, under solar irradiation, the hydrogen…

Electrosynthesis of ammonia under mild conditions has been impeded by the lack of high-performance electrocatalysts. Inspired by the high activity and selectivity of single-atom catalysts (SACs) with maximum atom utilization, we systematically explored a new class of two-dimensional SACs formed by embedding 30 types of transition metals (TMs) in two-dimensional (2D) parallel patterning of tetracyanoethylene (TCNE) networks (labeled as p-TM[TCNE], p means parallel) for the nitrogen reduction reaction (NRR) through the combination of high-throughput screening and density functional theory calculations. Three p-TM[TCNE] (TM = Mo, Nb, Ti) catalysts stand out with high catalytic activity and selectivity. The full reaction path search demonstrates that these three catalysts prefer the distal mechanism, among which p-Mo[TCNE] has the lowest limiting potential of −0.36 V. The origin of high activity might be ascribed to the joint effects from exposed active sites in 2D planar structures, high stability and metallic properties of catalysts, and efficient charge transfer between adsorbed N 2…

High Resolution Image Download MS PowerPoint Slide The physicochemical properties of titanium dioxide (TiO 2 ) depend strongly on the crystal structure. Compared to anatase, rutile TiO 2 has a smaller bandgap, a higher dielectric constant, and a higher refractive index, which are desired properties for TiO 2 thin films in many photonic applications. Unfortunately, the fabrication of rutile thin films usually requires temperatures that are too high (>400 °C, often even 600–800 °C) for applications involving, e.g., temperature-sensitive substrate materials. Here, we demonstrate atomic layer deposition (ALD)-based fabrication of anatase and rutile TiO 2 thin films mediated by precursor traces and oxide defects, which are controlled by the ALD growth temperature when using tetrakis(dimethylamido)titanium(IV) (TDMAT) and water as precursors. Nitrogen traces within amorphous titania grown at 100 °C inhibit the crystal nucleation until 375 °C and stabilize the anatase phase. In contrast, a higher growth temperature (200 °C) leads to a low nitrogen concentration, a high degree of oxide…

In lithium-ion batteries (LIBs), the quality of a solid electrolyte interphase (SEI) that forms at the electrode/electrolyte interface substantially affects the stability and lifetime of the devices. One of the major determinants of the morphology and properties of SEI is the surface structure and composition of the graphitic anode used. The presence of oxygenated surface groups at the graphitic anode facilitates the formation of SEI at the interface that stabilizes LIBs. A series of DFT calculations reveal that at typical operating conditions (temperature, pH) of LIBs, the (1120) edge facet of graphite anode will be fully oxygenated, while the basal sites remain unsaturated. The oxygen functional groups at the edge sites are comprised of mostly hydroxyl and ketonic groups, with carboxyl and carbonyl groups are present in small amounts. Furthermore, we observe transformation of carbonyl group into ketonic group in the presence of empty surface carbon sites, which further stabilize the graphite surface. Meanwhile, carboxyl groups are more stable when all surface sites within a…

Chlorine gas plays a paramount role in modern industrial chemistry and is one of the most basic chemicals produced by the electrolysis of brine solution. In the past decades, the dimensionally stable anode (DSA) made of RuO 2 is the benchmark catalyst for the chlorine evolution reaction (CER) with high activity. However, the drawbacks of the DSA, such as high cost and inferior selectivity, demand the development of low-cost and efficient electrocatalysts for CER. Herein, three low-dimensional Fe/Co/Ni-dithiolene metal–organic frameworks (MOFs) were systematically investigated using the density functional theory. Our calculation results predict that Ni-based dithiolene MOF can efficiently catalyze the CER with a low thermodynamic overpotential of 0.049 V via the Cl* intermediate. The electronic resonance structure of [Ni 2+ (L •– )(L 2– )] − in the Ni-based dithiolene MOF leads to the electron transfer first from S atoms in ligands to Ni cations to achieve a stable electronic configuration, which leads to the most desirable Ni–Cl interaction strength for CER. Moreover, the…

High Resolution Image Download MS PowerPoint Slide The influence of the phase of the ZrO 2 support (monoclinic, tetragonal, and amorphous, referred to as m-, t-, and am-, respectively) on the nature of the surface species involved in methanol synthesis and the rates of their formation on ZrO 2 -supported, In-based catalysts for CO 2 hydrogenation has been investigated. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at 300 °C and 20 bar (H 2:CO 2:N 2 = 3:1:1 volume ratio) on m-ZrO 2:In, In 2 O 3 /t-ZrO 2, and In 2 O 3 /am-ZrO 2 catalysts (m-ZrO 2:In is a solid solution) shows that formate species (HCOO*) appear prior to methoxy species (*OCH 3 ), and both intermediates form faster on the more active m-ZrO 2:In catalyst. Only formate bands are detected for the In 2 O 3 /t-ZrO 2 catalyst. For these materials, indium sites are essential for the formation of HCOO* and *OCH 3 species as only carbonate species are observed on m-, t-, and am-ZrO 2 supports under CO 2 hydrogenation conditions. The nature of the reaction intermediates is confirmed by ex situ…

This work presents spectroscopic investigations of methylammonium lead iodide, MAPbI 3, a perovskite thin film, with a focus on elucidating the exciton binding energy of the semiconductor via various approaches in modeling of absorption and photoluminescence spectroscopic data collected in the 150–293 K temperature range. These include the application of modified versions of Elliott’s formula to reconstruct steady-state absorption of the semiconductor in the spectral range of the bandgap edge, validated by conjunction with outcomes from transient absorption spectroscopy, and application of numerous variations of the Arrhenius equation to model temperature-induced broadening of the excitonic absorption band and temperature-dependent changes in intensity of photoluminescence emission spectra. All these approaches were simultaneously applied on the spectroscopic data acquired on the same MAPbI 3 sample and provide a more comprehensive image of how the value of exciton binding energy depends on the determination methodology. This work demonstrates that after excluding outliers…

Both high-entropy materials and metal–organic frameworks (MOFs) can be used as efficient catalysts for oxygen evolution, but it remains a challenge to combine their advantages to further improve the oxygen evolution reaction (OER). Herein, MOFs are served as precursors to prepare the high-entropy metal sulfide (HEMS) (MnFeCoNiCu)S 2 nanoparticles based on the maximized configurational entropy theory, exhibiting ultra-efficient OER performance. The strong synergistic effect among Mn, Fe, Co, Ni, and Cu builds a stable electronic structure and provides a favorable local coordination environment, which enhance the catalytic performance greatly. In addition, the appropriate doping of sulfur source contributes to modulate the electronic structure, which promotes the formation of single-phase HEMS nanoparticles with the dimeter of sub-3 nm. The (MnFeCoNiCu)S 2 nanoparticles display the best OER performance (a low overpotential of 221 mV at 10 mA cm –2 in 1 M KOH solution) and good stability (remains to be 97.6% after 12 h by chronoamperometry). This work provides a potential application…

High Resolution Image Download MS PowerPoint Slide Dopamine (DA) adsorption and electron-transfer kinetics are strongly sensitive to the structure and composition of carbon electrodes. Activation of carbon surfaces is a popular method to improve DA detection, but the role of carbon structural features on DA behavior remains uncertain. Herein, we use scanning electrochemical cell microscopy (SECCM) for local anodization of glassy carbon (GC) electrodes in acid media followed by electrochemical imaging of DA adsorption and electrochemistry covering both unmodified and anodized GC regions of the same electrode. Electrochemical measurements of adsorbed DA involve the delivery of DA from the SECCM meniscus (30 μM) for 1 s periods followed by voltammetric analysis at a reasonable sweep rate (47 V s –1 ). This general approach reduces effects from interelectrode variability and allows for considerable numbers of measurements and statistical analysis of electrochemical data sets. Localized electrode activity is correlated to surface structure and chemistry by a range of characterization…

Ion migration has been widely investigated in the lead halide perovskites, which severely deteriorates the performance of solar cells. However, the impacts of ion migration on photodetection have been rarely studied so far. In the current work, ion migration in the all-inorganic perovskite CsPbBr 3 and its impacts on photodetection have been investigated in detail. Electrical property studies showed that ion migration has occurred under an external electric field poling, which led to the formation of a pn-junction within the CsPbBr 3 single crystals. Density function theory calculations have shown that vacancy-assisted Br-ion migration dominated the ion transportation processes. Accordingly, the Au/CsPbBr 3 /Au metal–semiconductor–metal structured photodetectors showed a decreased performance in terms of a decreased on–off ratio and decreased detectivity through a long-term operation under a bias voltage, although the photoresponsivity slightly increased simultaneously. The results provided in this work verify the negative effects of ion migration in the all-inorganic perovskite…

Scalable and stable deployment of water electrolyzers requires the development of in operando analyses to monitor changes in the cell operation due to differing materials or conditions. Here, we present a comprehensive analysis of Nafion-based water electrolysis in membrane electrode assemblies (MEA) under vapor-fed and liquid-fed operation (<200 mA cm –2 ) using electrochemical impedance spectroscopy (EIS) and distribution of relaxation times analysis. These analyses are used to determine the different processes influencing cell operation and are correlated to in situ methods (Tafel analyses, open-circuit measurements) and morphological analyses to develop an equivalent circuit model for MEA operation. The proposed model can extract the anode ionic conductivity, the Tafel slope and exchange current for the oxygen evolution reaction, electrode capacitance, and mass transport losses from a single EIS spectrum. Further, a contact impedance is observed between the anode catalyst layer and the porous transport layer that is dependent on the porous transport layer identity and cell…

Pt catalyst particles on reducible oxide supports often change their activity significantly at elevated temperatures due to the strong metal–support interaction (SMSI), which induces the formation of an encapsulation layer around the noble metal particles. However, the impact of oxidizing and reducing treatments at elevated pressures on this encapsulation layer remains controversial, partly due to the “pressure gap” between surface science studies and applied catalysis. In the present work, we employ synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect of O 2 and H 2 on the SMSI-state of well-defined Pt/TiO 2 (110) catalysts at pressures of up to 0.1 Torr. By tuning the O 2 pressure, we can either selectively oxidize the TiO 2 support or both the support and the Pt particles. Catalyzed by metallic Pt, the encapsulating oxide overlayer grows rapidly in 1 × 10 –5 Torr O 2, but orders of magnitude less effectively at higher O 2 pressures, where Pt is in an oxidic state. While the oxidation/reduction of Pt particles is reversible, they…

Poly(vinylidene fluoride) (PVDF) is a well-known polymer with a (−CH 2 –CF 2 −) n chemical formula that is used, in particular, in electronic devices. The spatial arrangements of −CH 2 – and −CF 2 – units and the spatial alignment of PVDF chains determine the ferroelectricity, pyroelectricity, and piezoelectricity of condensed-phase PVDF. PVDF can be fabricated with Al metal as an energetic composite for rocket propellants. To better understand how PVDF molecular structures affect the properties in the condensed phase and the chemical reaction mechanisms with Al, we have developed a C/H/O/Al/F ReaxFF force field through parameterization against data from quantum mechanical (QM) calculations and experiments. This ReaxFF force field demonstrates good transferability in both low-temperature regimes, dominated by nonreactive conformational changes, and high-temperature regimes, dominated by PVDF chemical conversion. In the low-temperature regime, we investigated the α → β crystalline phase transition kinetics induced by a poling electric field or mechanical deformation. The molecular…

Sulfones are polar molecules that can be used as thermally stable electrolyte solvents for Li-ion batteries (LIBs). Li salts form stoichiometric solvates with sulfones in the electrolytes. The melting points of the solvates tend to be higher than room temperature, thereby limiting the operating temperature range of the batteries. In this study, the applicability of ternary eutectic mixtures of LiN(SO 2 F) 2 (LiFSA), sulfolane (SL), and dimethyl sulfone (DMS) as LIB electrolytes was assessed. Relative to the binary LiFSA–sulfone electrolytes, the ternary eutectic electrolytes remained liquid over a wide temperature range due to the increased entropy of mixing. Sulfone-bridged Li + –sulfone–Li + and anion-bridged Li + –FSA – –Li + network structures were formed in the eutectic electrolyte with a composition of [LiFSA]/[SL]/[DMS] = 1/1.5/1.5. Pulsed-field gradient NMR measurements revealed that the Li + ion dynamically exchanges sulfones and anions and diffuses more rapidly than these ligands, resulting in the relatively high Li + transference number of the electrolyte. Highly…

There is an increasing interest in the amorphous states of metal–organic frameworks (MOFs) and porous coordination polymers, which can be produced by pressure-induced amorphization, temperature-induced amorphization, melt–quenching, ball milling, irradiation, etc. They can exhibit useful physical and chemical properties, distinct from those achievable in the crystalline states, along with greater ease of processing, and intrinsic advantages over crystals and powders, such as high transparency and mechanical robustness. However, these amorphous states are particularly challenging to characterize, and the determination of their framework structure at the microscopic scale is difficult, with only indirect structural information available from diffraction experiments. In this Perspective, we review and compare the existing methodologies available for the determination of microscopic models of amorphous MOFs, based on both experimental data and simulation methods. In particular, we present the atomistic models that can be obtained using Reverse Monte Carlo (RMC) methods, Continuous…

In general, the activities for H 2 evolution are dependent on the morphologies and exposed facet of semiconductor-based photocatalysts. Here, we reported that CdS with the (002) crystal facet and a small capacitance was vital for enhancing photocatalytic H 2 evolution. After loading CoP as a co-catalyst, the H 2 evolution activity of CoP/CdS-P (particle-like, dominant (002) facet) increased remarkably to 24 600 μmol/(h g), which was 1.28 times that of CoP/CdS-L (leaflike), 2.09 times that of CoP/CdS-R (rodlike), and 5.67 times that of CoP/CdS-S (spherelike). Electrochemical tests and surface photovoltage spectra demonstrated that CdS-P with a large proportion of the (002) facet and the smallest capacitance of 4.31 F/cm 2 leads to the highest separation and transportation of photoexcited electrons. This study reveals the superiority of CdS with the (002) facet and gives an idea to design efficient semiconductor-based photocatalysts with a small capacitance.

Nowadays, ozone (O 3 ) has become a worldwide pollutant, and it is challenging to prepare monolithic O 3 decomposition catalysts substituting the conventional complicated process of adhering catalyst powders onto porous substrates. Herein, monolithic Cu 2 O–CuO/Cu catalysts are obtained facilely by in situ thermal oxidizing–reducing copper foam. After optimization, the CuO nanowires (NWs) are first produced by annealing Cu foam in O 2 at 400 °C for 2 h and then the NW surface is reduced into Cu 2 O by annealing in Ar/H 2 at 350 °C for 2 h. The obtained Cu 2 O–CuO/Cu monolithic catalyst exhibits high catalytic activity to 20 ppm O 3, maintaining 100% at a space velocity of 11,000 h –1 and even about 94% at 38,000 h –1 . The catalytic ability toward O 3 can be attributed to the generated Cu + /Cu 2+ redox couples, the donor/acceptor-type point defects, and the Cu 2 O–CuO p–p heterojunction. This demonstrates the successful and convenient preparation of the monolithic catalyst for rapid, controllable, and productive O 3 removal applications.

Extinction at 400 nm is a convenient, cheap, and fast method for in situ determination of Au concentration in colloids with good accuracy even in the presence of Au(+3) ions and other interference factors. However, these possibilities have been validated only with common citrate gold nanospheres and, in part, with gold nanorods. Here, we demonstrate the universality of the UV–vis extinction method with six experimental and theoretical models: (1) CTAC-stabilized gold nanospheres; (2) small and large nanosphere clusters; (3) gold nanorods with plasmon resonances (PRs) ranging from 670 to 980 nm; (4) 2D nanotriangles and (5) 2D nanoplates with PRs from 600 to 775 nm; and (6) gold nanostars with PRs from 680 to 820 nm. In total, we fabricated 34 samples with different nanoparticle sizes, shapes, morphologies, and Au concentrations. From COMSOL, T-matrix, and generalized multiparticle Mie simulations, we derived a universal relation between the extinction cross section and the particle or cluster volume V: C ext (nm 2 ) = 0.51 × V (nm 3 ), 10 2 ≤ V (nm 3 ) ≤ 10 5, which gives a…

High Resolution Image Download MS PowerPoint Slide It is a general notion in interfacial electrochemistry that the stability of adsorbate phases that only contain hydrogen atoms should be independent of the pH value of the electrolyte on the scale of the reversible hydrogen electrode, whereas the stability of adsorbate phases that do not contain any hydrogen should be independent of the pH value on the scale of the standard hydrogen electrode. In this Perspective, it will be argued on the basis of a grand-canonical approach that such a Nernstian behavior can only be reproduced if the free energy of the adsorbate phase is independent of the electrochemical control parameters. In general, this should not be true, so that the Nernstian behavior should be the exception rather than the rule. Still, structural and chemical factors will be discussed that might lead to a Nernstian behavior. This requires an analysis of the electrochemical electrolyte/electrode interface on the atomistic level. At the same time, this analysis also provides a guideline for the validity of grand-canonical…

In recent years, many efforts have been devoted to investigating the interaction of nanoparticles (NPs) with lipid biomimetic interfaces, both from a fundamental perspective aimed at understanding relevant phenomena occurring at the nanobio interface and from an application standpoint for the design of novel lipid-nanoparticle hybrid materials. In this area, recent reports have revealed that citrate-capped gold nanoparticles (AuNPs) spontaneously associate with synthetic phospholipid liposomes and, in some cases, self-assemble on the lipid bilayer. However, the mechanistic and kinetic aspects of this phenomenon are not yet completely understood. In this study, we address the kinetics of interaction of citrate-capped AuNP with lipid vesicles of different rigidities (gel-phase rigid membranes on one side and liquid-crystalline-phase soft membranes on the other). The formation of AuNP-lipid vesicle hybrids was monitored over different time and length scales, combining experiments and simulation. The very first AuNP-membrane contact was addressed through molecular dynamics simulations,…

Continuous flow synthesis of semiconductor quantum dots (QDs) holds the promise of being highly reproducible, being scalable, and providing precise control of all reaction parameters. Here, we applied this technique to the aqueous synthesis of the Ag–In–S (AIS) core and AIS/ZnS core/shell QDs and optimized several parameters comprising reaction temperature, pressure, time, nature, and the ratio of precursors. Photoluminescence quantum yield (PLQY) values of 32%/44% (average/best) for the core and 77%/83% for the core/shell system have been obtained in short reaction times (8–15 min). We demonstrate by means of combined structural and optical studies that the high PLQY originates from donor–acceptor pair recombination processes, involving essentially [In Ag 2+ + 2V Ag – ] defect complexes whose formation is favored by the large excess of indium used (In:Ag ratio of 4:1), and the low reaction temperature (100–120 °C). The structural disorder is further enhanced during ZnS shell growth, which in addition to surface passivation and removal of nonradiative decay channels leads to the…

In this work, we present extensive electronic structure simulations on the oxygen evolution reaction (OER) mechanism and the influence of Fe substitution in cobalt(oxy)hydroxide under OER conditions. The study employs cluster models with an explicit treatment of the electrochemical potential via charges, an inclusion of the pH via protonation/deprotonation, and an implicit treatment of solvation. Our results suggest that early oxidation of Fe(III) to Fe(IV) promotes the electrophilic character in the reaction center, reducing the proton affinity of the surface-bound hydroxyl moieties. Computed energy profiles with explicit inclusion of the electrochemical potential imply that the Fe center of the Fe–OH site after its deprotonation acts as the active center for water nucleophilic attack. For the pristine cobalt(oxy)hydroxide system, Co(IV) promotes the efficient formation of an active O radical intermediate followed by intramolecular O–O coupling under OER conditions. In a detailed study of different computational approaches, it is demonstrated that the explicit inclusion of the…