The 100 most-cited articles in Journal of the American Chemical Society, 2020

The exact role of a defect structure on transition metal compounds for electrocatalytic oxygen evolution reaction (OER), which is a very dynamic process, remains unclear. Studying the structure–activity relationship of defective electrocatalysts under operando conditions is crucial for understanding their intrinsic reaction mechanism and dynamic behavior of defect sites. Co 3 O 4 with rich oxygen vacancy (V O ) has been reported to efficiently catalyze OER. Herein, we constructed pure spinel Co 3 O 4 and V O -rich Co 3 O 4 as catalyst models to study the defect mechanism and investigate the dynamic behavior of defect sites during the electrocatalytic OER process by various operando characterizations. Operando electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) implied that the V O could facilitate the pre-oxidation of the low-valence Co (Co 2+, part of which was induced by the V O to balance the charge) at a relatively lower applied potential. This observation confirmed that the V O could initialize the surface reconstruction of V O –Co 3 O 4 prior to the…

Aqueous Zn batteries are promising energy storage devices for large-scale energy-storage due to low cost and high energy density. However, their lifespan is limited by the water decomposition and Zn dendrite growth. Here, we suppress water reduction and Zn dendrite growth in dilute aqueous electrolyte by adding dimethyl sulfoxide (DMSO) into ZnCl 2 –H 2 O, in which DMSO replaces the H 2 O in Zn 2+ solvation sheath due to a higher Gutmann donor number (29.8) of DMSO than that (18) of H 2 O. The preferential solvation of DMSO with Zn 2+ and strong H 2 O–DMSO interaction inhibit the decomposition of solvated H 2 O. In addition, the decomposition of solvated DMSO forms Zn 12 (SO 4 ) 3 Cl 3 (OH) 15 ·5H 2 O, ZnSO 3, and ZnS enriched-solid electrolyte interphase (SEI) preventing Zn dendrite and further suppressing water decomposition. The ZnCl 2 –H 2 O–DMSO electrolyte enables Zn anodes in Zn||Ti half-cell to achieve a high average Coulombic efficiency of 99.5% for 400 cycles (400 h), and the Zn||MnO 2 full cell with a low capacity ratio of Zn:MnO 2 at 2:1 to deliver a high energy density…

Electrochemical conversion of nitrate (NO 3 – ) into ammonia (NH 3 ) recycles nitrogen and offers a route to the production of NH 3, which is more valuable than dinitrogen gas. However, today’s development of NO 3 – electroreduction remains hindered by the lack of a mechanistic picture of how catalyst structure may be tuned to enhance catalytic activity. Here we demonstrate enhanced NO 3 – reduction reaction (NO 3 – RR) performance on Cu 50 Ni 50 alloy catalysts, including a 0.12 V upshift in the half-wave potential and a 6-fold increase in activity compared to those obtained with pure Cu at 0 V vs reversible hydrogen electrode (RHE). Ni alloying enables tuning of the Cu d- band center and modulates the adsorption energies of intermediates such as *NO 3 –, *NO 2, and *NH 2 . Using density functional theory calculations, we identify a NO 3 – RR-to-NH 3 pathway and offer an adsorption energy–activity relationship for the CuNi alloy system. This correlation between catalyst electronic structure and NO 3 – RR activity offers a design platform for further development of NO 3 – RR…

The association of an electron-rich substrate with an electron-accepting molecule can generate a new molecular aggregate in the ground state, called an electron donor-acceptor (EDA) complex. Even when the two precursors do not absorb visible light, the resulting EDA complex often does. In 1952, Mulliken proposed a quantum-mechanical theory to rationalize the formation of such colored EDA complexes. However, and besides a few pioneering studies in the 20th century, it is only in the past few years that the EDA complex photochemistry has been recognized as a powerful strategy for expanding the potential of visible-light-driven radical synthetic chemistry. Here, we explain why this photochemical synthetic approach was overlooked for so long. We critically discuss the historical context, scientific reasons, serendipitous observations, and landmark discoveries that were essential for progress in the field. We also outline future directions and identify the key advances that are needed to fully exploit the potential of the EDA complex photochemistry.

Developing efficient catalysts for nitrogen fixation is becoming increasingly important but is still challenging due to the lack of robust design criteria for tackling the activity and selectivity problems, especially for electrochemical nitrogen reduction reaction (NRR). Herein, by means of large-scale density functional theory (DFT) computations, we reported a descriptor-based design principle to explore the large composition space of two-dimensional (2D) biatom catalysts (BACs), namely, metal dimers supported on 2D expanded phthalocyanine (M 2 -Pc or MM′-Pc), toward the NRR at the acid conditions. We sampled both homonuclear (M 2 -Pc) and heteronuclear (MM′-Pc) BACs and constructed the activity map of BACs by using N 2 H* adsorption energy as the activity descriptor, which reduces the number of promising catalyst candidates from over 900 to less than 100. This strategy allowed us to readily identify 3 homonuclear and 28 heteronuclear BACs, which could break the metal-based activity benchmark toward the efficient NRR. Particularly, using the free energy difference of H* and N 2 H*…

The limitations of the Haber–Bosch reaction, particularly high-temperature operation, have ignited new interests in low-temperature ammonia-synthesis scenarios. Ambient N 2 electroreduction is a compelling alternative but is impeded by a low ammonia production rate (mostly <10 mmol g cat –1 h –1 ), a small partial current density (<1 mA cm –2 ), and a high-selectivity hydrogen-evolving side reaction. Herein, we report that room-temperature nitrate electroreduction catalyzed by strained ruthenium nanoclusters generates ammonia at a higher rate (5.56 mol g cat –1 h –1 ) than the Haber–Bosch process. The primary contributor to such performance is hydrogen radicals, which are generated by suppressing hydrogen–hydrogen dimerization during water splitting enabled by the tensile lattice strains. The radicals expedite nitrate-to-ammonia conversion by hydrogenating intermediates of the rate-limiting steps at lower kinetic barriers. The strained nanostructures can maintain nearly 100% ammonia-evolving selectivity at >120 mA cm –2 current densities for 100 h due to the robust subsurface Ru–O…

Atomically dispersed transition metal active sites have emerged as one of the most important fields of study because they display promising performance in catalysis and have the potential to serve as ideal models for fundamental understanding. However, both the preparation and determination of such active sites remain a challenge. The structural engineering of carbon- and nitrogen-coordinated metal sites (M-N-C, M = Fe, Co, Ni, Mn, Cu, etc.) via employing new heteroatoms, e.g., P and S, remains challenging. In this study, carbon nanosheets embedded with nitrogen and phosphorus dual-coordinated iron active sites (denoted as Fe-N/P-C) were developed and determined using cutting edge techniques. Both experimental and theoretical results suggested that the N and P dual-coordinated iron sites were favorable for oxygen intermediate adsorption/desorption, resulting in accelerated reaction kinetics and promising catalytic oxygen reduction activity. This work not only provides efficient way to prepare well-defined single-atom active sites to boost catalytic performance but also paves the way…

Fluorescence imaging has become a fundamental tool for biomedical applications; nevertheless, its intravital imaging capacity in the conventional wavelength range (400-950 nm) has been restricted by its extremely limited tissue penetration. To tackle this challenge, a novel imaging approach using the fluorescence in the second near-infrared window (NIR-II, 1000-1700 nm) has been developed in the past decade to achieve deep penetration and high-fidelity imaging, and thus significant biomedical applications have begun to emerge. In this Perspective, we first examine recent discoveries and challenges in the development of novel NIR-II fluorophores and compatible imaging apparatuses. Subsequently, the recent advances in bioimaging, biosensing, and therapy using such a cutting-edge imaging technique are highlighted. Finally, based on the achievement in the representative studies, we elucidate the main concerns regarding this imaging technique and give some advice and prospects for the development of NIR-II imaging for future biomedical applications.

The oxygen evolution reaction (OER) is the performance-limiting half reaction of water splitting, which can be used to produce hydrogen fuel using renewable energies. Whereas a number of transition metal oxides and oxyhydroxides have been developed as promising OER catalysts in alkaline medium, the mechanisms of OER on these catalysts are not well understood. Here we combine electrochemical and in situ spectroscopic methods, particularly operando X-ray absorption and Raman spectroscopy, to study the mechanism of OER on cobalt oxyhydroxide (CoOOH), an archetypical unary OER catalyst. We find the dominating resting state of the catalyst as a Co(IV) species CoO 2 . Through oxygen isotope exchange experiments, we discover a cobalt superoxide species as an active intermediate in the OER. This intermediate is formed concurrently to the oxidation of CoOOH to CoO 2 . Combing spectroscopic and electrokinetic data, we identify the rate-determining step of the OER as the release of dioxygen from the superoxide intermediate. The work provides important experimental fingerprints and new…

Defect engineering is widely applied in transition metal dichalcogenides (TMDs) to achieve electrical, optical, magnetic, and catalytic regulation. Vacancies, regarded as a type of extremely delicate defect, are acknowledged to be effective and flexible in general catalytic modulation. However, the influence of vacancy states in addition to concentration on catalysis still remains vague. Thus, via high throughput calculations, the optimized sulfur vacancy (S-vacancy) state in terms of both concentration and distribution is initially figured out among a series of MoS 2 models for the hydrogen evolution reaction (HER). In order to realize it, a facile and mild H 2 O 2 chemical etching strategy is implemented to introduce homogeneously distributed single S-vacancies onto the MoS 2 nanosheet surface. By systematic tuning of the etching duration, etching temperature, and etching solution concentration, comprehensive modulation of the S-vacancy state is achieved. The optimal HER performance reaches a Tafel slope of 48 mV dec –1 and an overpotential of 131 mV at a current density of 10 mA…

Herein, we demonstrate that the strategic implementation of electron-accepting tricoordinate boron and electron-donating carbazole subunits into polycyclic aromatic hydrocarbons (PAHs) produces a family of attractive full-color luminophores that can emit narrowband and efficient thermally activated delayed fluorescence (TADF). A versatile modular design for these boron- and carbazole-embedded PAHs can facilitate the systematic modulation of their photophysical and optoelectronic properties. Organic light-emitting diodes that utilize these PAHs as TADF emitters demonstrate narrowband electroluminescence from blue to red, achieving high maximum external quantum efficiencies of 29.3%, 31.8%, and 22.0% for blue, green, and red, respectively.

As a novel class of porous crystalline materials, hydrogen-bonded organic frameworks (HOFs), self-assembled from organic or metal-organic building blocks through intermolecular hydrogen-bonding interactions, have attracted more and more attention. Over the past decade, a number of porous HOFs have been constructed through judicious selection of H-bonding motifs, which are further enforced by other weak intermolecular interactions such as π-π stacking and van der Waals forces and framework interpenetration. Since the H-bonds are weaker than coordinate and covalent bonds used for the construction of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), HOFs have some unique features such as mild synthesis condition, solution processability, easy healing, and regeneration. These features enable HOFs to be a tunable platform for the construction of functional materials. Here, we review the H-bonding motifs used for constructing porous HOFs and highlight some of their applications, including gas separation and storage, chiral separation and structure determination,…

Photocatalytic reduction of CO 2 to value-added fuels is a promising route to reduce global warming and enhance energy supply. However, poor selectivity and low efficiency of catalysts are usually the limiting factor of their applicability. Herein, a photoinduction method was developed to achieve the formation of Cu single atoms on a UiO-66-NH 2 support (Cu SAs/UiO-66-NH 2 ) that could significantly boost the photoreduction of CO 2 to liquid fuels. Notably, the developed Cu SAs/UiO-66-NH 2 achieved the solar-driven conversion of CO 2 to methanol and ethanol with an evolution rate of 5.33 and 4.22 μmol h –1 g –1, respectively. These yields were much higher than those of pristine UiO-66-NH 2 and Cu nanoparticles/UiO-66-NH 2 composites. Theoretical calculations revealed that the introduction of the Cu SAs on the UiO-66-NH 2 greatly facilitates the conversion of CO 2 to CHO* and CO* intermediates, leading to excellent selectivity toward methanol and ethanol. This study provides new insights for designing high-performance catalyst for photocatalytic reduction of CO 2 at the atomic scale.

Selective and efficient catalytic conversion of carbon dioxide (CO 2 ) into value-added fuels and feedstocks provides an ideal avenue to high-density renewable energy storage. An impediment to enabling deep CO 2 reduction to oxygenates and hydrocarbons (e.g., C 2+ compounds) is the difficulty of coupling carbon–carbon bonds efficiently. Copper in the +1 oxidation state has been thought to be active for catalyzing C 2+ formation, whereas it is prone to being reduced to Cu 0 at cathodic potentials. Here we report that catalysts with nanocavities can confine carbon intermediates formed in situ, which in turn covers the local catalyst surface and thereby stabilizes Cu + species. Experimental measurements on multihollow cuprous oxide catalyst exhibit a C 2+ Faradaic efficiency of 75.2 ± 2.7% at a C 2+ partial current density of 267 ± 13 mA cm –2 and a large C 2+ -to-C 1 ratio of ∼7.2. Operando Raman spectra, in conjunction with X-ray absorption studies, confirm that Cu + species in the as-designed catalyst are well retained during CO 2 reduction, which leads to the marked C 2+…

Abstract Photocatalytic reduction of molecular oxygen is a promising route toward sustainable production of hydrogen peroxide (H2O2). This challenging process requires photoactive semiconductors enabling solar energy driven generation and separation of electrons and holes with high charge transfer kinetics. Covalent organic frameworks (COFs) are an emerging class of photoactive semiconductors, tunable at a molecular level for high charge carrier generation and transfer. Herein, we report two newly designed two-dimensional COFs based on a (diarylamino)benzene linker that form a Kagome (kgm) lattice and show strong visible light absorption. Their high crystallinity and large surface areas (up to 1165 m2·g–1) allow efficient charge transfer and diffusion. The diarylamine (donor) unit promotes strong reduction properties, enabling these COFs to efficiently reduce oxygen to form H2O2. Overall, the use of a metal-free, recyclable photocatalytic system allows efficient photocatalytic solar transformations.

Excitonic effects caused by Coulomb interactions between electrons and holes play subtle and significant roles on photocatalysis, yet have been long ignored. Herein, porphyrinic covalent organic frameworks (COFs, specifically DhaTph-M), in the absence or presence of different metals in porphyrin centers, have been shown as ideal models to regulate excitonic effects. Remarkably, the incorporation of Zn 2+ in the COF facilitates the conversion of singlet to triplet excitons, whereas the Ni 2+ introduction promotes the dissociation of excitons to hot carriers under photoexcitation. Accordingly, the discriminative excitonic behavior of DhaTph-Zn and DhaTph-Ni enables the activation of O 2 to 1 O 2 and O 2 •–, respectively, under visible light irradiation, resulting in distinctly different activity and selectivity in photocatalytic terpinene oxidation. Benefiting from these results, DhaTph-Ni exhibits excellent photocatalytic activity in O 2 •– -engaged hydroxylation of boronic acid, while DhaTph-Zn possesses superior performance in 1 O 2 -mediated selective oxidation of organic…

Engineering single-atom electrocatalysts with high-loading amount holds great promise in energy conversion and storage application. Herein, we report a facile and economical approach to achieve an unprecedented high loading of single Ir atoms, up to ∼18 wt %, on the nickel oxide (NiO) matrix as the electrocatalyst for oxygen evolution reaction (OER). It exhibits an overpotential of 215 mV at 10 mA cm –2 and a remarkable OER current density in alkaline electrolyte, surpassing NiO and IrO 2 by 57 times and 46 times at 1.49 V vs RHE, respectively. Systematic characterizations, including X-ray absorption spectroscopy and aberration-corrected Z-contrast imaging, demonstrate that the Ir atoms are atomically dispersed at the outermost surface of NiO and are stabilized by covalent Ir–O bonding, which induces the isolated Ir atoms to form a favorable ∼4+ oxidation state. Density functional theory calculations reveal that the substituted single Ir atom not only serves as the active site for OER but also activates the surface reactivity of NiO, which thus leads to the dramatically improved OER…

Passivating surface and bulk defects of perovskite films has been proven to be an effective way to minimize nonradiative recombination losses in perovskite solar cells (PVSCs). The lattice interference and perturbation of atomic periodicity at the perovskite surfaces often significantly affect the material properties and device efficiencies. By tailoring the terminal groups on the perovskite surface and modifying the surface chemical environment, the defects can be reduced to enhance the photovoltaic performance and stability of derived PVSCs. Here, we report a rationally designed bifunctional molecule, piperazinium iodide ( PI ), containing both R 2 NH and R 2 NH 2 + groups on the same six-membered ring, behaving both as an electron donor and an electron acceptor to react with different surface-terminating ends on perovskite films. The resulting perovskite films after defect passivation show released surface residual stress, suppressed nonradiative recombination loss, and more n -type characteristics for sufficient energy transfer. Consequently, charge recombination is…

(CO2RR) to CO. However, the concomitant hydrogen evolution reaction (HER) remains unavoidable under aqueous conditions. In this work, a rotating ring disk electrode (RRDE) setup has been developed to study quantitatively the role of mass transport in the competition between these two reactions on the Au surface in 0.1 M bicarbonate electrolyte. Interestingly, while the faradaic selectivity for CO formation was found to increase with enhanced mass transport (from 67% to 83%), this effect is not due to an enhancement of the CO2RR rate. Remarkably, the inhibition of the competing HER from water reduction with increasing disk rotation rate is responsible for the enhanced CO2RR selectivity. This can be explained by the observation that, on the Au electrode, water reduction improves with more alkaline pH. As a result, the decrease in the local alkalinity near the electrode surface with enhanced mass transport suppresses HER due to the water reduction. Our study shows that controlling the local pH by mass transport conditions can tune the HER rate, in turn regulating the CO2RR and HER…

Understanding the role of the oxidation state of the Cu surface and surface-adsorbed intermediate species in electrochemical CO 2 reduction is crucial for the development of selective CO 2 -to-fuel electrocatalysts. In this study, the electrochemical CO 2 reduction mechanism over the Cu catalysts with various oxidation states was studied by using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), in situ soft X-ray absorption spectroscopy (Cu L-edge), and online gas chromatography measurements. The atop-adsorbed CO (CO atop ) intermediate is obtained on the electrodeposited Cu surface which primarily has the oxidation state of Cu(I). CO atop is further reduced, followed by the formation of C 1 product such as CH 4 . The residual bridge-adsorbed CO (CO bridge ) is formed on the as-prepared Cu surface with Cu(0) which inhibits hydrocarbon formation. In contrast, the CV-treated Cu electrode prepared by oxidizing the as-prepared Cu surface contains different amounts of Cu(I) and Cu(0) states. The major theme of this work is that in situ SEIRAS results show the…

While catalysis is highly dependent on the electronic structure of the catalyst, the understanding of catalytic performance affected by electron spin regulation remains challenging and rare. Herein, we have developed a facile strategy to the manipulation of the cobalt spin state over covalent organic frameworks (COFs), COF-367-Co, by simply changing the oxidation state of Co centered in the porphyrin. Density functional theory (DFT) calculations together with experimental results confirm that Co II and Co III are embedded in COF-367 with S = 1/2 and 0 spin ground states, respectively. Remarkably, photocatalytic CO 2 reduction results indicate that COF-367-Co III exhibits favorable activity and significantly enhanced selectivity to HCOOH, accordingly much reduced activity and selectivity to CO and CH 4, in sharp contrast to COF-367-Co II . The results highlight that the spin-state transition of cobalt greatly regulates photocatalytic performance. Theoretical calculations further disclose that the presence of Co III in COF-367-Co is preferable to the formation of HCOOH but detrimental…

Ferroelectric materials have a variety of technological applications, as transducers, capacitors, sensors, etc. Great interest in molecular ferroelectrics has emerged because of their structural flexibility, tunability, and homochirality. However, the discoveries of molecular ferroelectrics are not abundant. The lack of chemical design is the main challenge in realizing new molecular ferroelectrics. Consequently, chemical design approaches, including the ideas of introducing quasi-spherical theory, homochirality, and H/F substitution, have been developed recently. Through these advanced methodologies, a wide range of ferroelectrics were successfully synthesized, changing the blind search into a targeted chemical design. In this Perspective, we aim to provide insight into the fundamental chemistry and physics of molecular ferroelectrics and propose the concept of "ferroelectrochemistry", concerned with the targeted design and performance optimization of molecular ferroelectrics from the chemical point of view. We start with the basic theories used in the modification of chemical…

The insufficient intracellular H 2 O 2 level in tumor cells is closely associated with the limited efficacy of chemodynamic therapy (CDT). Despite tremendous efforts, engineering CDT agents with a straightforward and secure H 2 O 2 supplying ability remains a great challenge. Inspired by the balance of H 2 O 2 generation and elimination in cancer cells, herein, a nanozyme-based H 2 O 2 homeostasis disruptor is fabricated to elevate the intracellular H 2 O 2 level through facilitating H 2 O 2 production and restraining H 2 O 2 elimination for enhanced CDT. In the formulation, the disruptor with superoxide dismutase-mimicking activity can convert O 2 •– to H 2 O 2, promoting the production of H 2 O 2 . Simultaneously, the suppression of catalase activity and depletion of glutathione by the disruptor weaken the transformation of H 2 O 2 to H 2 O. Thus, the well-defined system could perturb the H 2 O 2 balance and give rise to the accumulation of H 2 O 2 in cancer cells. The raised H 2 O 2 level would ultimately amplify the Fenton-like reaction-based CDT efficiency. Our work not only…

The enabling of high energy density of all-solid-state lithium batteries (ASSLBs) requires the development of highly Li + -conductive solid-state electrolytes (SSEs) with good chemical and electrochemical stability. Recently, halide SSEs based on different material design principles have opened new opportunities for ASSLBs. Here, we discovered a series of Li x ScCl 3+ x SSEs ( x = 2.5, 3, 3.5, and 4) based on the cubic close-packed anion sublattice with room-temperature ionic conductivities up to 3 × 10 –3 S cm –1 . Owing to the low eutectic temperature between LiCl and ScCl 3, Li x ScCl 3+ x SSEs can be synthesized by a simple co-melting strategy. Preferred orientation is observed for all the samples. The influence of the value of x in Li x ScCl 3+ x on the structure and Li + diffusivity were systematically explored. With increasing x value, higher Li +, lower vacancy concentration, and less blocking effects from Sc ions are achieved, enabling the ability to tune the Li + migration. The electrochemical performance shows that Li 3 ScCl 6 possesses a wide electrochemical window of…

Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of electrocatalysis oxygen evolution reaction (OER) in acid. Herein, we report a novel strategy to prepare iridium single-atoms (Ir-SAs) on ultrathin NiCo 2 O 4 porous nanosheets (Ir–NiCo 2 O 4 NSs) by the co-electrodeposition method. The surface-exposed Ir-SAs couplings with oxygen vacancies (V O ) exhibit boosting the catalysts OER activity and stability in acid media. They display superior OER performance with an ultralow overpotential of 240 mV at j = 10 mA cm –2 and long-term stability of 70 h in acid media. The TOFs of 1.13 and 6.70 s –1 at an overpotential of 300 and 370 mV also confirm their remarkable performance. Density functional theory (DFT) calculations reveal that the prominent OER performance arises from the surface electronic exchange-and-transfer activities contributed by atomic Ir incorporation on the intrinsic V O existed NiCo 2 O 4 surface. The atomic Ir sites substantially elevate the electronic activity of surface lower…

The development of highly active and durable catalysts for electrochemical reduction of CO 2 (ERC) to CH 4 in aqueous media is an efficient and environmentally friendly solution to address global problems in energy and sustainability. In this work, an electrocatalyst consisting of single Zn atoms supported on microporous N-doped carbon was designed to enable multielectron transfer for catalyzing ERC to CH 4 in 1 M KHCO 3 solution. This catalyst exhibits a high Faradaic efficiency (FE) of 85%, a partial current density of −31.8 mA cm –2 at a potential of −1.8 V versus saturated calomel electrode, and remarkable stability, with neither an obvious current drop nor large FE fluctuation observed during 35 h of ERC, indicating a far superior performance than that of dominant Cu-based catalysts for ERC to CH 4 . Theoretical calculations reveal that single Zn atoms largely block CO generation and instead facilitate the production of CH 4 .

Despite the extensive studies of the nanozymes showing their superior properties compared to natural enzymes and traditional artificial enzymes, the development of highly specific nanozymes is still a challenge. The catechol oxidase specifically catalyzing the oxidations of o -diphenol to the corresponding o -quinone is important to the biosynthesis of melanin and other polyphenolic natural products. In this study, we first propose that MOF-818, containing trinuclear copper centers mimicking the active sites of natural catechol oxidase, shows efficient catechol oxidase activity with good specificity and no peroxidase-like characteristics. MOF-818 has good specificity and high catalytic activity as a novel catechol oxidase nanozyme.

Ultrasound (US)-triggered sonodynamic therapy (SDT) that enables noninvasive treatment of large internal tumors has attracted widespread interest. For improvement in the therapeutic responses to SDT, more effective and stable sonosensitizers are still required. Herein, ultrafine titanium monoxide nanorods (TiO 1+ x NRs) with greatly improved sono-sensitization and Fenton-like catalytic activity were fabricated and used for enhanced SDT. TiO 1+ x NRs with an ultrafine rodlike structure were successfully prepared and then modified with polyethylene glycol (PEG). Compared to the conventional sonosensitizer, TiO 2 nanoparticles, the PEG–TiO 1+ x NRs resulted in much more efficient US-induced generation of reactive oxygen species (ROS) because of the oxygen-deficient structure of TiO 1+ x NR, which predominantly serves as the charge trap to limit the recombination of US-triggered electron–hole pairs. Interestingly, PEG–TiO 1+ x NRs also exhibit horseradish-peroxidase-like nanozyme activity and can produce hydroxyl radicals ( • OH) from endogenous H 2 O 2 in the tumor to enable…

The platinum-group metals (PGMs) are six neighboring elements in the periodic table of the elements. Each PGM can efficiently promote unique reactions, and therefore, alloying PGMs would create ideal catalysts for complex or multistep reactions that involve several reactants and intermediates. Thus, high-entropy-alloy (HEA) nanoparticles (NPs) of all six PGMs (denoted as PGM-HEA ) having a great variety of adsorption sites on their surfaces could be ideal candidates to catalyze complex reactions. Here, we report for the first time PGM-HEA and demonstrate that PGM-HEA efficiently promotes the ethanol oxidation reaction (EOR) with complex 12-electron/12-proton transfer processes. PGM-HEA shows 2.5 (3.2), 6.1 (9.7), and 12.8 (3.4) times higher activity than the commercial Pd/C, Pd black and Pt/C catalysts in terms of intrinsic (mass) activity, respectively. Remarkably, it records more than 1.5 times higher mass activity than the most active catalyst to date. Our findings pave the way for promoting complex or multistep reactions that are seldom realized by mono- or bimetallic catalysts.

Covalent organic frameworks (COFs) are excellent platforms with tailored functionalities in photocatalysis. There are still challenges in increasing the photochemical performance of COFs. Therefore, we designed and prepared a series of COFs for photocatalytic hydrogen generation. Varying different ratios of β-ketoenamine to imine moieties in the linkages could differ the ordered structure, visible light harvesting, and bandgap. Overall, β-ketoenamine-linked COFs exhibited much better photocatalytic activity than those COFs having both β-ketoenamine and imine moieties on account of a nonquenched excited state and more favorable HOMO level in the photoinduced oxidation reaction from the former. Specifically, after in situ growth of β-ketoenamine-linked COFs onto NH 2 –Ti 3 C 2 T x MXene via covalent connection, the heterohybrid showed an obvious improvement in photocatalytic H 2 evolution because of strong covalent coupling, electrical conductivity, and efficient charge transfer. This integrated linkage evolution and covalent hybridization approach advances the development of…

Covalent organic frameworks (COFs) are a promising category of porous materials possessing extensive chemical tunability, high porosity, ordered arrangements at a molecular level, and considerable chemical stability. Despite these advantages, the application of COFs as membrane materials for gas separation is limited by their relatively large pore apertures (typically >0.5 nm), which exceed the sieving requirements for most gases whose kinetic diameters are less than 0.4 nm. Herein, we report the fabrication of ultrathin two-dimensional (2D) membranes through layer-by-layer (LbL) assembly of two kinds of ionic covalent organic nanosheets (iCONs) with different pore sizes and opposite charges. Because of the staggered packing of iCONs with strong electrostatic interactions, the resultant membranes exhibit features of reduced aperture size, optimized stacking pattern, and compact dense structure without sacrificing thickness control, which are suitable for molecular sieving gas separation. One of the hybrid membranes, TpEBr@TpPa-SO 3 Na with a thickness of 41 nm, shows a H 2 permeance…

Adsorptive separation of acetylene (C 2 H 2 ) from carbon dioxide (CO 2 ) promises a practical way to produce high-purity C 2 H 2 required for industrial applications. However, challenges exist in the pore environment engineering of porous materials to recognize two molecules due to their similar molecular sizes and physical properties. Herein, we report a strategy to optimize pore environments of multivariate metal–organic frameworks (MOFs) for efficient C 2 H 2 /CO 2 separation by tuning metal components, functionalized linkers, and terminal ligands. The optimized material UPC-200(Al)-F-BIM, constructed from Al 3+ clusters, fluorine-functionalized organic linkers, and benzimidazole terminal ligands, demonstrated the highest separation efficiency (C 2 H 2 /CO 2 uptake ratio of 2.6) and highest C 2 H 2 productivity among UPC-200 systems. Experimental and computational studies revealed the contribution of small pore size and polar functional groups on the C 2 H 2 /CO 2 selectivity and indicated the practical C 2 H 2 /CO 2 separation of UPC-200(Al)-F-BIM.

Bulk-heterojunction organic photovoltaic devices with nonfullerene acceptors (NFAs) exhibit efficient hole transfer with small interfacial energy offset, which results in power conversion efficiencies above 17% in single junction devices using the high-performance NFA of Y6. However, the underlying mechanism responsible for the hole transfer channel in the polymer/Y6 blends remains poorly understood. Herein, we report that the hole transfer channel of photocharge generation is mediated by an intra-moiety excited state in a blend of donor polymer PM6 and NFA Y6 using broadband transient absorption (TA) spectroscopy. By comparing the TA data recorded from the solution and film Y6 samples, we identify the ultrafast formation of an intra-moiety excimer state together with the conversion from the primary local excitation on a time scale of ∼0.2 ps in the Y6 film. The intra-moiety excimer state acts as the intermediate for the hole transfer channel, which dissociates into free polarons on a time scale of ∼15 ps in the PM6/Y6 blend at room temperature. The intra-moiety intermediate state,…

The recombination of electron–hole pairs severely detracts from the efficiency of photocatalysts. This issue could be addressed in metal–organic frameworks (MOFs) through optimization of the charge-transfer kinetics via rational design of structures at atomic level. Herein, a pyrazolyl porphyrinic Ni-MOF (PCN-601), integrating light harvesters, active catalytic sites, and high surface areas, has been demonstrated as a superior and durable photocatalyst for visible-light-driven overall CO 2 reduction with H 2 O vapor at room temperature. Kinetic studies reveal that the robust coordination spheres of pyrazolyl groups and Ni-oxo clusters endow PCN-601 with proper energy band alignment and ultrafast ligand-to-node electron transfer. Consequently, the CO 2 -to-CH 4 production rate of PCN-601 far exceeds those of the analogous MOFs based on carboxylate porphyrin and the classic Pt/CdS photocatalyst by more than 3- and 20-fold, respectively. The reaction avoids the use of hole scavengers and proceeds in a gaseous phase which can take full advantage of the high gas uptake of MOFs. This work…

Photocatalytic nitrogen fixation represents a green alternative to the conventional Haber–Bosch process in the conversion of nitrogen to ammonia. In this study, a series of Bi 5 O 7 Br nanostructures were synthesized via a facile, low-temperature thermal treatment procedure, and their photocatalytic activity toward nitrogen fixation was evaluated and compared. Spectroscopic measurements showed that the tubular Bi 5 O 7 Br sample prepared at 40 °C (Bi 5 O 7 Br-40) exhibited the highest electron-transfer rate among the series, producing a large number of O 2 .– radicals and oxygen vacancies under visible-light photoirradiation and reaching a rate of photocatalytic nitrogen fixation of 12.72 mM·g –1 ·h –1 after 30 min of photoirradiation. The reaction dynamics was also monitored by in situ infrared measurements with a synchrotron radiation light source, where the transient difference between signals in the dark and under photoirradiation was analyzed and the reaction pathway of nitrogen fixation was identified. This was further supported by results from density functional theory…

The electrochemical synthesis of chemicals from carbon dioxide, which is an easily available and renewable carbon resource, is of great importance. However, to achieve high product selectivity for desirable C 2 products like ethylene is a big challenge. Here we design Cu nanosheets with nanoscaled defects (2–14 nm) for the electrochemical production of ethylene from carbon dioxide. A high ethylene Faradaic efficiency of 83.2% is achieved. It is proved that the nanoscaled defects can enrich the reaction intermediates and hydroxyl ions on the electrocatalyst, thus promoting C–C coupling for ethylene formation.

Abstract Layered Na-based oxides with the general composition of NaxTMO2 (TM: transition metal) have attracted significant attention for their high compositional diversity that provides tunable electrochemical performance for electrodes in sodium-ion batteries. The various compositions bring forward complex structural chemistry that is decisive for the layered stacking structure, Na-ion conductivity, and the redox activity, potentially promising new avenues in functional material properties. In this work, we have explored the maximum Na content in P2-type layered oxides and discovered that the high-content Na in the host enhances the structural stability; moreover, it promotes the oxidation of low-valent cations to their high oxidation states (in this case Ni2+). This can be rationalized by the increased hybridization of the O(2p)-TM(3d-eg*) states, affecting both the local TM environment as well as the interactions between the NaO2 and TMO2 layers. These properties are highly beneficial for the Na storage capabilities as required for cathode materials in sodium-ion batteries. It…

The mitigation of decomposition reactions of lithium-ion battery electrolyte solutions is of critical importance in controlling device lifetime and performance. However, due to the complexity of the system, exacerbated by the diverse set of electrolyte compositions, electrode materials, and operating parameters, a clear understanding of the key chemical mechanisms remains elusive. In this work, operando pressure measurements, solution NMR, and electrochemical methods were combined to study electrolyte oxidation and reduction at multiple cell voltages. Two-compartment LiCoO 2 /Li cells were cycled with a lithium-ion conducting glass-ceramic separator so that the species formed at each electrode could be identified separately and further reactions of these species at the opposite electrode prevented. One principal finding is that chemical oxidation (with an onset voltage of ~4.7 V vs Li/Li + for LiCoO 2 ), rather than electrochemical reaction, is the dominant decomposition process at the positive electrode surface in this system. This is ascribed to the well-known release of reactive…

The grain boundary in copper-based electrocatalysts has been demonstrated to improve the selectivity of solar-driven electrochemical CO 2 reduction toward multicarbon products. However, the approach to form grain boundaries in copper is still limited. This paper describes a controllable grain growth of copper electrodeposition via poly(vinylpyrrolidone) used as an additive. A grain-boundary-rich metallic copper could be obtained to convert CO 2 into ethylene and ethanol with a high selectivity of 70% over a wide potential range. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy unveils that the existence of grain boundaries enhances the adsorption of the key intermediate (*CO) on the copper surface to boost the further CO 2 reduction. When coupling with a commercially available Si solar cell, the device achieves a remarkable solar-to-C2-products conversion efficiency of 3.88% at a large current density of 52 mA·cm –2 . This low-cost and efficient device is promising for large-scale application of solar-driven CO 2 reduction.

Typical organic photovoltaic materials show high Urbach energies (ca. 25-50 meV), which is considerably higher than those of their inorganic counterparts and limits further improvement in the device efficiency of organic solar cells (OSCs). In this study, we introduce a facile method of selenium substitution to reduce the Urbach energy of organic photovoltaic materials to 20.4 meV (Y6Se), which is the lowest value reported for high-performance organic photovoltaic materials and very close to those (ca. 15 meV) of typical inorganic/hybrid semiconductors, such as crystalline silicon, gallium nitride, and lead-halide perovskite. Next, OSCs based on Y6Se showed 17.7% efficiency, which is among the best results for OSCs and the record efficiency of as-cast single junction OSCs to date.

The anticipated shift in the focal point of interest of solid-state chemists, crystal engineers, and crystallographers from structure to properties to function parallels the need to apply our accumulated understanding of the intricacies of crystal structure to explaining the related properties, with the ultimate goal of harnessing that knowledge in applications that require soft, lightweight, or biocompatible organic solids. In these developments, the adaptive molecular crystals warrant particular attention as an alternative choice of materials for light, flexible, and environmentally benign devices, primarily memories, capacitors, sensors, and actuators. Some of the outstanding requirements for the application of these dynamic materials as high-efficiency energy-storage devices are strongly induced polarization, a high switching field, and narrow hysteresis in the case of reversible dynamic processes. However, having been studied almost exclusively by chemists, molecular crystals still lack the appropriate investigations that reliably evaluate their reproducibility, scalability,…

We describe a new electrophotocatalytic strategy that harnesses the power of light and electricity to generate an excited radical anion with a reducing potential of –3.2 V vs. SCE, which can be used to activate substrates with very high reduction potentials (Ered ~ –1.9 to –2.9 V). The resultant aryl radicals can be engaged in various synthetically useful transformations to furnish arylboronate, arylstannane, and biaryl products.

Developing algorithmic approaches for the rational design and discovery of materials can enable us to systematically find novel materials, which can have huge technological and social impact. However, such rational design requires a holistic perspective over the full multistage design process, which involves exploring immense materials spaces, their properties, and process design and engineering as well as a techno-economic assessment. The complexity of exploring all of these options using conventional scientific approaches seems intractable. Instead, novel tools from the field of machine learning can potentially solve some of our challenges on the way to rational materials design. Here we review some of the chief advancements of these methods and their applications in rational materials design, followed by a discussion on some of the main challenges and opportunities we currently face together with our perspective on the future of rational materials design and discovery.

Incorporating chiral organic molecules into organic/inorganic hybrid 2D metal-halide perovskites results in a novel family of chiral hybrid semiconductors with unique spin-dependent properties. The embedded chiral organic moieties induce a chiroptical response from the inorganic metal–halide sublattice. However, the structural interplay between the chiral organic molecules and the inorganic sublattice, as well as their synergic effect on the resulting electronic band structure need to be explored in a broader material scope. Here we present three new layered tin iodide perovskites templated by chiral ( R / S -)methylbenzylammonium ( R/S -MBA), i.e., ( R -/ S -MBA) 2 SnI 4, and their racemic phase ( rac -MBA) 2 SnI 4 . These MBA 2 SnI 4 compounds exhibit the largest level of octahedral bond distortion compared to any other reported layered tin iodide perovskite. The incorporation of chiral MBA cations leads to circularly polarized absorption from the inorganic Sn–I sublattice, displaying chiroptical activity in the 300–500 nm wavelength range. The bandgap and chiroptical activity are…

Alloying is a long-established strategy to tailor properties of metals for specific applications, thus retaining or enhancing the principal elemental characteristics while offering additional functionality from the added elements. We propose a similar approach to the control of properties of two-dimensional transition metal carbides known as MXenes. MXenes (M n +1 X n ) have two sites for compositional variation: elemental substitution on both the metal (M) and carbon/nitrogen (X) sites presents promising routes for tailoring the chemical, optical, electronic, or mechanical properties of MXenes. Herein, we systematically investigated three interrelated binary solid-solution MXene systems based on Ti, Nb, and/or V at the M-site in a M 2 XT x structure (Ti 2-y Nb y CT x, Ti 2-y V y CT x, and V 2-y Nb y CT x, where T x stands for surface terminations) showing the evolution of electronic and optical properties as a function of composition. All three MXene systems show unlimited solubility and random distribution of metal elements in the metal sublattice. Optically, the MXene systems are…

Achieving efficient charge transfer at small frontier molecular orbital offsets between donor and acceptor is crucial for high performance polymer solar cells (PSCs). Here we synthesize a new wide band gap polymer donor, PTQ11, and a new low band gap acceptor, TPT10, and report a high power conversion efficiency (PCE) PSC (PCE = 16.32%) based on PTQ11–TPT10 with zero HOMO (the highest occupied molecular orbital) offset (Δ E HOMO(D–A) ). TPT10 is a derivative of Y6 with monobromine instead of bifluorine substitution, and possesses upshifted lowest unoccupied molecular orbital energy level ( E LUMO ) of −3.99 eV and E HOMO of −5.52 eV than Y6. PTQ11 is a derivative of low cost polymer donor PTQ10 with methyl substituent on its quinoxaline unit and shows upshifted E HOMO of −5.52 eV, stronger molecular crystallization, and better hole transport capability in comparison with PTQ10. The PSC based on PTQ11–TPT10 shows highly efficient exciton dissociation and hole transfer, so that it demonstrates a high PCE of 16.32% with a higher V oc of 0.88 V, a large J sc of 24.79 mA cm –2, and a…

Hybrid manganese halides have attracted widespread attention because of their highly emissive optical properties. To understand the underlying structural factors that dictate the photoluminescence quantum yield (PLQY) of these materials, we report five new hybrid manganese bromides with the general formula A m MnBr 4 [ m = 1 or 2, A = dimethylammonium (DMA), 3-methylpiperidinium (3MP), 3-aminomethylpiperidinium (3AMP), heptamethylenimine (HEP), and trimethylphenylammonium (TMPEA)]. By studying the crystal structures and optical properties of these materials and combining our results with the findings from previously reported analogs, we have found a direct correlation between Mn···Mn distance and the PLQY, where high PLQYs are associated with long Mn···Mn distances. This effect can be viewed as a manifestation of the concentration-quenching effect, except these are in stoichiometric compounds with precise interatomic distances rather than random alloys. To gain better separation of the Mn centers and prevent energy transfer, a bulky singly protonated cation that avoids H-bonding is…

The engineering coordination environment offers great opportunity in performance tunability of isolated metal single-atom catalysts. For the most popular metal–N x (MN x ) structure, the replacement of N atoms by some other atoms with relatively weak electronegativity has been regarded as a promising strategy for optimizing the coordination environment of an active metal center and promoting its catalytic performance, which is still a challenge. Herein, we proposed a new synthetic strategy of an in situ phosphatizing of triphenylphosphine encapsulated within metal–organic frameworks for designing atomic Co 1 –P 1 N 3 interfacial structure, where a cobalt single atom is costabilized by one P atom and three N atoms (denoted as Co-SA/P-in situ). In the acidic media, the Co-SA/P-in situ catalyst with Co 1 –P 1 N 3 interfacial structure exhibits excellent activity and durability for the hydrogen evolution reaction (HER) with a low overpotential of 98 mV at 10 mA cm –2 and a small Tafel slope of 47 mV dec –1, which are greatly superior to those of catalyst with Co 1 –N 4 interfacial…

Increasing battery energy density is greatly desired for applications such as portable electronics and transportation. However, many next-generation batteries are limited by electrolyte selection because high ionic conductivity and poor electrochemical stability are typically observed in most electrolytes. For example, ether-based electrolytes have high ionic conductivity but are oxidatively unstable above 4 V, which prevents the use of high-voltage cathodes that promise higher energy densities. In contrast, hydrofluoroethers (HFEs) have high oxidative stability but do not dissolve lithium salt. In this work, we synthesize a new class of fluorinated ether electrolytes that combine the oxidative stability of HFEs with the ionic conductivity of ethers in a single compound. We show that conductivities of up to 2.7 × 10 – 4 S/cm (at 30 °C) can be obtained with oxidative stability up to 5.6 V. The compounds also show higher lithium transference numbers compared to typical ethers. Furthermore, we use nuclear magnetic resonance (NMR) and molecular dynamics (MD) to study their ionic…

Metal-organic frameworks (MOFs) have shown great potential as nanophotosensitizers (nPSs) for photodynamic therapy (PDT). The use of such MOFs in PDT, however, is limited by the shallow depth of tissue penetration of short-wavelength light and the oxygen-dependent mechanism that renders it inadequate for hypoxic tumors. Here, to combat such limitations, we rationally designed core-shell upconversion nanoparticle@porphyrinic MOFs (UCSs) for combinational therapy against hypoxic tumors. The UCSs were synthesized in high yield through the conditional surface engineering of UCNPs and subsequent seed-mediated growth strategy. The heterostructure allows efficient energy transfer from the UCNP core to the MOF shell, which enables the near-infrared (NIR) light-triggered production of cytotoxic reactive oxygen species. A hypoxia-activated prodrug tirapazamine (TPZ) was encapsulated in nanopores of the MOF shell of the heterostructures to yield the final construct TPZ/UCSs. We demonstrated that TPZ/UCSs represent a promising system for achieving improved cancer treatment in vitro and in vivo…

Exploitation of room temperature (RT) photochromism and photomagnetism to induce single-molecule magnet (SMM) behavior has potential applications toward optical switches and magnetic memories, and remains a tremendous challenge in the development of new bulk magnets. Herein, a series of chain complexes [Ln 3 (H–HEDP) 3 (H 2 –HEDP) 3 ]·2H 3 –TPT·H 4 –HEDP·10H 2 O ( QDU-1; Ln = Dy ( QDU-1(Dy) ), Gd ( QDU-1(Gd) ), and Y ( QDU-1(Y) ); HEDP = hydroxyethylidene diphosphonate; TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine) were synthesized by solvothermal reactions. All the compounds exhibited reversible photochromic and photomagnetic behaviors via UV light irradiation at RT, induced by the photogenerated radicals via a photoinduced electron transfer (PET) mechanism. More importantly, the PET process induced significant variations in magnetic interactions for the Dy(III) congener. Strong ferromagnetic coupling with remarkably slow magnetic relaxation without applied dc fields was observed between Dy III ions and photogenerated O • radicals, showing SMM behavior after RT illumination. For the…

Selective oxidation of alcohols to their corresponding aldehyde or carboxylic acid is one of the most important classes of organic synthesis reactions. In addition, electrochemical alcohol oxidation is considered a viable anode reaction that can be paired with H 2 evolution or other reductive fuel production reactions in electrochemical and photoelectrochemical cells. NiOOH, a material that has been extensively studied as an oxygen evolution catalyst, is among the most promising electrocatalysts for selective alcohol oxidation. Electrochemical alcohol oxidation by NiOOH has been understood since the 1970s to proceed through a hydrogen atom transfer to NiOOH. In this study, we establish that there is a second, more dominant general alcohol oxidation pathway on NiOOH enabled at more positive potentials. Using a three-step electrochemical procedure we developed, we deconvoluted the currents corresponding to these two pathways for various alcohols and aldehydes. The results show that alcohols and aldehydes have a distinct difference in their respective preferences for the two oxidation…

Oxygen-bearing copper (OBC) has been widely studied for enabling the C–C coupling of the electrocatalytic CO 2 reduction reaction (CO 2 RR) since this is a distinctive hallmark of strongly correlated OBC systems and may benefit many other Cu-based catalytic processes. Unresolved problems, however, include the instability of and limited knowledge regarding OBC under realistic operating conditions, raising doubts about its role in CO 2 RR. Here, an atypical and stable OBC catalyst with a hierarchical pore and nanograin-boundary structure was constructed and was found to exhibit efficient CO 2 RR for the production of ethylene with a Faradaic efficiency of 45% at a partial current density of 44.7 mA cm –2 in neutral media, and the ethylene partial current density is nearly 26 and 116 times that of oxygen-free copper (OFC) and commercial Cu foam, respectively. More importantly, the structure–activity relationship in CO 2 RR was explored through a comprehensive analysis of experimental data and computational techniques, thus increasing the fundamental understanding of CO 2 RR. A…

Rechargeable aqueous Zn-ion energy storage devices are promising candidates for next-generation energy storage technologies. However, the lack of highly reversible Zn 2+ -storage anode materials with low potential windows remains a primary concern. Here, we report a two-dimensional polyarylimide covalent organic framework (PI-COF) anode with high-kinetics Zn 2+ -storage capability. The well-organized pore channels of PI-COF allow the high accessibility of the build-in redox-active carbonyl groups and efficient ion diffusion with a low energy barrier. The constructed PI-COF anode exhibits a specific capacity (332 C g –1 or 92 mAh g –1 at 0.7 A g –1 ), a high rate capability (79.8% at 7 A g –1 ), and a long cycle life (85% over 4000 cycles). In situ Raman investigation and first-principle calculations clarify the two-step Zn 2+ -storage mechanism, in which imide carbonyl groups reversibly form negatively charged enolates. Dendrite-free full Zn-ion devices are fabricated by coupling PI-COF anodes with MnO 2 cathodes, delivering excellent energy densities (23.9 ∼ 66.5 Wh kg –1 ) and…

Modulating lattice oxygen in metal oxides that conducts partial oxidation of methane in balancing C–H activation and syngas selectivity remains challenging. This paper describes the discovery of distorting FeO 6 octahedra in La 1– x Ce x FeO 3 ( x = 0, 0.25 0.5, 0.75, 1) orthorhombic perovskites for the promotion of lattice oxygen activation. By combined electrical conductivity relaxation measurements and density functional theory calculations studies, this paper describes the enhancement of FeO 6 octahedral distortion in La 1– x Ce x FeO 3 promoting their bulk oxygen mobility and surface oxygen exchange capability. Consequently, La 0.5 Ce 0.5 FeO 3 with the highest FeO 6 distortion achieves exceptional syngas productivity of ∼3 and 8 times higher than LaFeO 3 and CeFeO 3, respectively, in CH 4 partial oxidation step with simultaneous high CO 2 conversion (92%) in the CO 2 -splitting step at 850 °C. The results exemplify the feasibility to tailor the active lattice oxygen of perovskite by modulating the distortion of BO 6 in ABO 3, which ultimately influences their reaction…

Exploring efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) in alkaline media is critical for developing anion exchange membrane electrolyzers. The key to a rational catalyst design is understanding the descriptors that govern the alkaline HER activity. Unfortunately, the principles that govern the alkaline HER performance remain unclear and are still under debate. By studying the alkaline HER at a series of NiCu bimetallic surfaces, where the electronic structure is modulated by the ligand effect, we demonstrate that alkaline HER activity can be correlated with either the calculated or the experimental-measured d band center (an indicator of hydrogen binding energy) via a volcano-type relationship. Such correlation indicates the descriptor role of the d band center, and this hypothesis is further supported by the evidence that combining Ni and Cu produces a variety of adsorption sites, which possess near-optimal hydrogen binding energy. Our finding broadens the applicability of d band theory to activity prediction of metal electrocatalysts and may offer…

Liquid-liquid phase separation plays an important role in cellular organization. Many subcellular condensed bodies are hierarchically organized into multiple coexisting domains or layers. However, our molecular understanding of the assembly and internal organization of these multicomponent droplets is still incomplete, and rules for the coexistence of condensed phases are lacking. Here, we show that the formation of hierarchically organized multiphase droplets with up to three coexisting layers is a generic phenomenon in mixtures of complex coacervates, which serve as models of charge-driven liquid-liquid phase separated systems. We present simple theoretical guidelines to explain both the hierarchical arrangement and the demixing transition in multiphase droplets using the interfacial tensions and critical salt concentration as inputs. Multiple coacervates can coexist if they differ sufficiently in macromolecular density, and we show that the associated differences in critical salt concentration can be used to predict multiphase droplet formation. We also show that the coexisting…

Defective or heteroatom-doped metal-free carbon materials (MFCMs) have been regarded as efficient oxygen reduction reaction (ORR) catalysts in the past decade. However, the active centers for ORR in MFCMs are hard to confirm precisely and synthesize controllably through common methods such as high-temperature pyrolysis or heteroatom doping. To verify the precise structure acting as the active center for the ORR, we first report two crystalline metal-free thiophene-sulfur covalent organic frameworks (MFTS-COFs) as ORR catalysts. The MFTS-COFs show more positive catalytic capability than the thiophene-free COF, indicating that pentacyclic thiophene-sulfur building blocks act as active centers to induce ORR catalytic activity. MFTS-COFs with higher contents of thiophene-sulfur exhibit better ORR performance. The experimental identification is supported by density functional theory calculations. These results thus demonstrate that rational design and precise synthesis of metal-free crystalline organic materials can promote the development of new ORR catalysts.

Incorporating a dipole interlayer has been one of the most crucial interfacial engineering strategies in organic and perovskite solar cells. An interfacial dipole brings steep shifts in electronic band structure across interfaces and thus effectively tunes charge carrier transport. However, the origin of the interfacial dipole and its effects on device performance are not entirely clear; they are even controversial in some cases. We devote this Perspective to identifying the electric dipole of various interlayers and correlating the interfacial dipole with device performance on the basis of classical semiconductor device theory. It is important to further consider the chemical nature of interlayers beyond the simplified model of an interfacial dipole to develop a full understanding of interfacial structure, energy bands, and device operation mechanism. Researchers are encouraged to integrate in situ and in operando characterizations with numerical simulations in future studies.

Tumor hypoxia has proven to be the major bottleneck of photodynamic therapy (PDT) to clinical transformation. Different from traditional O 2 delivery approaches, here we describe an innovative binary photodynamic O 2 -economizer (PDOE) tactic to reverse hypoxia-driven resistance by designing a superoxide radical (O 2 •– ) generator targeting mitochondria respiration, termed SORgenTAM. This PDOE system is able to block intracellular O 2 consumption and down-regulate HIF-1α expression, which successfully rescues cancer cells from becoming hypoxic and relieves the intrinsic hypoxia burden of tumors in vivo, thereby sparing sufficient endogenous O 2 for the PDT process. Photosensitization mechanism studies demonstrate that SORgenTAM has an ideal intersystem crossing rate and triplet excited state lifetime for generating O 2 •– through type-I photochemistry, and the generated O 2 •– can further trigger a biocascade to reduce the PDT’s demand for O 2 in an O 2 -recycble manner. Furthermore, SORgenTAM also serves to activate the AMPK metabolism signaling pathway to inhibit cell repair and…

Metal oxides are widely employed in heterogeneous catalysis, but it remains challenging to determine their exact structure and understand the reaction mechanisms at the molecular level due to their structural complexity, in particular for binary oxides. This paper describes the observation of the strong electronic interaction between In 2 O 3 and monoclinic ZrO 2 (m-ZrO 2 ) by quasi-in-situ XPS experiments combined with theoretical studies, which leads to support-dependent methanol selectivity. In 2 O 3 /m-ZrO 2 exhibits methanol selectivity up to 84.6% with a CO 2 conversion of 12.1%. Moreover, at a wide range of temperatures, the methanol yield of In 2 O 3 /m-ZrO 2 is much higher than that of In 2 O 3 /t-ZrO 2 (t-: tetragonal), which is due to the high dispersion of the In–O–In structure over m-ZrO 2 as determined by in situ Raman spectra. The electron transfer from m-ZrO 2 to In 2 O 3 is confirmed by XPS and DFT calculations and improves the electron density of In 2 O 3, which promotes H 2 dissociation and hydrogenation of formate intermediates to methanol. The concept of the…

We describe a new catalytic strategy to transcend the energetic limitations of visible light by electrochemically priming a photocatalyst prior to excitation. This new catalytic system is able to productively engage aryl chlorides with reduction potentials hundreds of millivolts beyond the potential of Na 0 in productive radical coupling reactions. The aryl radicals produced via this strategy can be leveraged for both carbon–carbon and carbon–heteroatom bond-forming reactions. Through direct comparison, we illustrate the reactivity and selectivity advantages of this approach relative to electrolysis and photoredox catalysis.

Aqueous rechargeable zinc batteries (ZBs) have received considerable attention recently for large-scale energy storage systems in terms of rate performance, cost, and safety. Nevertheless, these ZBs still remain a subject for investigation, as researchers search for cathode materials enabling high performance. Among the various candidate cathode materials for ZBs, quinone compounds stand out as candidates because of their high specific capacity, sustainability, and low cost. Quinone-based cathodes, however, suffer from the critical limitation of undergoing dissolution during battery cycling, leading to a deterioration in battery life. To address this problem, we have introduced a redox-active triangular phenanthrenequinone-based macrocycle ( PQ-Δ ) with a rigid geometry and layered superstructure. Notably, we have confirmed that Zn 2+ ions, together with H 2 O molecules, can be inserted into the PQ-Δ organic cathode, and, as a consequence, the interfacial resistance between the cathode and electrolytes is decreased effectively. Density functional theory calculations have revealed…

Lithium metal batteries are vital devices for high-energy-density energy storage, but the Li metal anode is highly reactive with electrolyte and forms uncontrolled dendrite that can cause undesirable parasitic reactions and, thus, poor cycling stability and raise safety concerns. Despite remarkable progress to partially solve these issues, the Li metal still plates at the electrode/electrolyte interface where the parasitic reactions and dendrite formation invariably occur. Here, we demonstrate the inward-growth plating of Li atoms into a metal foil of thickness of tens of micrometers while avoiding surface deposition, which is driven by the reversible solid–solution-based alloy phase change. Lithiation of the solid–solution alloy phase allows the freshly generated Li atoms at the surface to sink into the metal foil, while the reversible alloy phase change is companied by the dealloying reaction during delithiation, which extracts Li atoms from inside of the metal foil. The yielded dendrite free Li anode produces an enhanced Coulombic efficiency of 99.5 ± 0.2% with a reversible…

High-entropy perovskite fluorides (HEPFs) have great potential in electrocatalysis that has not been realized because of the limitation of a high-temperature synthetic route and the limited understanding of high-entropy materials. The use of HEPFs in effective oxygen evolution catalysis and a feasible synthesis route for HEPFs in a boiled solution by combining a hydrothermal method with mechanochemistry are first reported here. These HEPFs consisting of cost-effective elements dramatically gave excellent catalytic activity for the oxygen evolution reaction in an alkaline media.

We report on the continuous fine-scale tuning of band gaps over 0.4 eV and of the electrical conductivity of over 4 orders of magnitude in a series of highly crystalline binary alloys of two-dimensional electrically conducting metal–organic frameworks M 3 (HITP) 2 (M = Co, Ni, Cu; HITP = 2,3,6,7,10,11-hexaiminotriphenylene). The isostructurality in the M 3 (HITP) 2 series permits the direct synthesis of binary alloys (M x M′ 3– x )(HITP) 2 (MM′ = CuNi, CoNi, and CoCu) with metal compositions precisely controlled by precursor ratios. We attribute the continuous tuning of both band gaps and electrical conductivity to changes in free-carrier concentrations and to subtle differences in the interlayer displacement or spacing, both of which are defined by metal substitution. The activation energy of (Co x Ni 3– x )(HITP) 2 alloys scales inversely with an increasing Ni percentage, confirming thermally activated bulk transport.

Enzyme immobilization has been demonstrated to be a favorable protocol to promote industrialization of biomacromolecules. Despite tremendous efforts to develop new strategies and materials to realize this process, maintaining enzyme activity is still a formidable challenge. Herein we created a sacrificial templating method, using metal-organic frameworks (MOFs) as sacrificial templates to construct hollow covalent organic framework (COF) capsules for enzyme encapsulation. This strategy can provide a capacious microenvironment to unleash enzyme molecules. The improved conformational freedom of enzymes, enhanced mass transfer, and protective effect against the external environment ultimately boosted the enzymatic activities. We also found that this strategy possesses high versatility that is suitable for diverse biomacromolecules, MOF templates, and COF capsules. Moreover, the dimensions, pore sizes, and shell thickness of COF capsules can be conveniently tuned, allowing for customizing bioreactors for specific functions. For example, coencapsulation of different enzymes with…

Abstract The ability to differentiate between highly similar C–H bonds in a given molecule remains a fundamental challenge in organic chemistry. In particular, the lack of sufficient steric and electronic differences between C–H bonds located distal to functional groups has prevented the development of site-selective catalysts with broad scope. An emerging approach to circumvent this obstacle is to utilize the distance between a target C–H bond and a coordinating functional group, along with the geometry of the cyclic transition state in directed C–H activation, as core molecular recognition parameters to differentiate between multiple C–H bonds. In this Perspective, we discuss the advent and recent advances of this concept. We cover a wide range of transition-metal-catalyzed, template-directed remote C–H activation reactions of alcohols, carboxylic acids, sulfonates, phosphonates, and amines. Additionally, we review eminent examples which take advantage of non-covalent interactions to achieve regiocontrol. Continued advancement of this distance- and geometry-based differentiation…

The rational design of multifunctional catalysts that use non-noble metals to facilitate the interconversion between H 2, O 2, and H 2 O is an intense area of investigation. Bimetallic nanosystems with highly tunable electronic, structural, and catalytic properties that depend on their composition, structure, and size have attracted considerable attention. Herein, we report the synthesis of bimetallic nickel–copper (NiCu) alloy nanoparticles confined in a sp 2 carbon framework that exhibits trifunctional catalytic properties toward hydrogen evolution (HER), oxygen reduction (ORR), and oxygen evolution (OER) reactions. The electrocatalytic functions of the NiCu nanoalloys were experimentally and theoretically correlated with the composition-dependent local structural distortion of the bimetallic lattice at the nanoparticle surfaces. Our study demonstrated a downshift of the d-band of the catalysts that adjusts the binding energies of the intermediate catalytic species. XPS analysis revealed that the binding energy for Ni 2p 3/2 band of the Ni 0.25 Cu 0.75 /C nanoparticles was shifted…

This Perspective discusses oriented external-electric-fields (OEEF), and other electric-field types, as “smart reagents”, which enable in principle control over wide-ranging aspects of reactivity and structure. We discuss the potential of OEEFs to control nonredox reactions and impart rate-enhancement and selectivity. An OEEF along the “reaction axis”, which is the direction whereby electronic reorganization converts reactants’ to products’ bonding, will accelerate reactions, control regioselectivity, induce spin-state selectivity, and elicit mechanistic crossovers . Simply flipping the direction of the OEEF will lead to inhibition . Orienting the OEEF off the reaction axis enables control over stereoselectivity, enantioselectivity, and product selectivity . For polar/polarizable reactants, the OEEF itself will act as tweezers, which orient the reactants and drive their reaction. OEEFs also affect bond-dissociation energies and dissociation modes (covalent vs ionic), as well as alteration of molecular geometries and supramolecular aggregation. The “key” to gaining access to this…

Oxide-/hydroxide-derived copper electrodes exhibit excellent selectivity toward C 2+ products during the electrocatalytic CO 2 reduction reaction (CO 2 RR). However, the origin of such enhanced selectivity remains controversial. Here, we prepared two Cu-based electrodes with mixed oxidation states, namely, HQ-Cu (containing Cu, Cu 2 O, CuO) and AN-Cu (containing Cu, Cu(OH) 2 ). We extracted an ultrathin specimen from the electrodes using a focused ion beam to investigate the distribution and evolution of various Cu species by electron microscopy and electron energy loss spectroscopy. We found that at the steady stage of the CO 2 RR, the electrodes have all been reduced to Cu 0, regardless of the initial states, suggesting that the high C 2+ selectivities are not associated with specific oxidation states of Cu. We verified this conclusion by control experiments in which HQ-Cu and AN-Cu were pretreated to fully reduce oxides/hydroxides to Cu 0, and the pretreated electrodes showed even higher C 2+ selectivity compared with their unpretreated counterparts. We observed that the…

Understanding the molecular structure and self-assembly of thiadiazole-derived non-fullerene acceptors (NFAs) is very critical for elucidating the origin of their extraordinary charge generation and transport properties that enable high power conversion efficiencies to be achieved in these systems. A comprehensive crystallographic study on a state-of-the-art NFA, Y6, and its selenium analog, CH1007, has been conducted which revealed that the face-to-face π-core interaction induced by benzo[2,1,3]thiadiazole S–N-containing moieties plays a significant role in governing the molecular geometries and unique packing of Y6 and CH1007 to ensure their superior charge-transport properties. Moreover, benefitting from the red-shifted optical absorption via selenium substitution, photovoltaic devices based on a PM6: CH1007:PC 71 BM ternary blend delivered an exceptionally high short-circuit current of 27.48 mA/cm 2 and a power conversion efficiency of 17.08%.

The electrochemical CO 2 reduction reaction (CO 2 RR) using Cu-based catalysts holds great potential for producing valuable multi-carbon products from renewable energy. However, the chemical and structural state of Cu catalyst surfaces during the CO 2 RR remains a matter of debate. Here, we show the structural evolution of the near-surface region of polycrystalline Cu electrodes under in situ conditions through a combination of grazing incidence X-ray absorption spectroscopy (GIXAS) and X-ray diffraction (GIXRD). The in situ GIXAS reveals that the surface oxide layer is fully reduced to metallic Cu before the onset potential for CO 2 RR, and the catalyst maintains the metallic state across the potentials relevant to the CO 2 RR. We also find a preferential surface reconstruction of the polycrystalline Cu surface toward (100) facets in the presence of CO 2 . Quantitative analysis of the reconstruction profiles reveals that the degree of reconstruction increases with increasingly negative applied potentials, and it persists when the applied potential returns to more positive values.…

The origins of the pH-dependent kinetics of hydrogen evolution and oxidation reactions on Pt surfaces are unsolved dilemmas that have lasted for over half a century. In this study, surface-enhanced infrared absorption spectroscopy is applied to directly monitor the vibrational behaviors of adsorbed hydrogen atoms and interfacial water molecules on Pt surfaces in a wide pH window from 1.1 to 12.9. For the first time, we successfully measure the pH-dependent changes of hydrogen and water binding strength according to their vibrational wavenumbers, which are both monotonously weakened as the solution pH increases. Their changes are the net results of altered electrochemical interface environments and are important contributions to the pH-dependent hydrogen reaction kinetics. Our results add significant new insights into the role of interfacial environments on electrocatalysis.

Boron-containing polymers have many applications resulting from their prominent properties. Organoboron species with reversible B-O bonds have been successfully employed for the fabrication of various self-healing/healable and reprocessable polymers. However, the application of the polymers containing boronic ester or boroxine linkages is limited because of their instability to water. Herein, we report the hydrolytic stability and dynamic covalent chemistry of the nitrogen-coordinating cyclic boronic diester (NCB) linkages, and a new class of vitrimers based on NCB linkages is developed through the chemical reactions of reactive hydrogen with isocyanate. Thermodynamic and kinetic studies demonstrated that NCB linkages exhibit enhanced water and heat resistance, whereas the exchange reactions between NCB linkages can take place upon heating without any catalyst. The model compounds of NCBC-X1 and NCBC-X2 containing a urethane group and urea group, respectively, also showed higher hydrolytic stability compared to that of conventional boronic esters. Polyurethane vitrimers and…

A microporous three-dimensional (3D) hydrogen-bonded organic framework (HOF-20) has been constructed from an aromatic-rich tetratopic carboxylic acid, 5-(2,6-bis(4-carboxyphenyl)pyridin-4-yl)isophthalic acid (H 4 BCPIA). The activated HOF-20a has a moderately high Brunauer–Emmett–Teller (BET) surface area of 1323 m 2 g –1 and excellent stability in water and HCl aqueous solution. HOF-20 exhibits highly efficient turn-up fluorescent sensing of aniline in water with a detection limit of 2.24 μM and is selective toward aniline in the presence of aromatic interferents, owing to the hydrogen bonding and edge-to-face π–π stacking interactions between the HOF-20 host and the guest aniline molecules, as demonstrated in the single-crystal X-ray structure of HOF-20⊃aniline. Density functional theory (DFT) calculations further demonstrate that the recognition of aniline molecules by HOF-20 could restrict the rotation of the aromatic rings in H 4 BCPIA linkers, reducing the nonradiative decay pathways upon photoexcitation and subsequently enhancing the fluorescence intensity.

Two-dimensional (2D) covalent organic frameworks (COFs) are promising metal-free materials for photocatalytic water splitting because of their high surface area and predictability to assemble various molecules with tunable electronic properties. Unfortunately, 2D COFs capable of visible-light-driven photocatalytic overall water splitting are rare, partly due to rigorous requirements to their band alignments and coexistence of catalytic sites for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, 12 2D nitrogen-linked COFs are designed based on first-principles calculations and topological assembly of molecular segments with catalytic activities toward either HER or OER, respectively. The electronic band structures calculated with HSE06 method indicate that 2D COFs are semiconductors with a widely tunable bandgap ranging from 1.92 to 3.23 eV. The positions of both conduction and valence band edges of nine 2D COFs match well with the chemical reaction potential of H 2 /H + and O 2 /H 2 O, which are capable of photocatalytic overall water splitting. Of…

Ruthenium pyrochlores, that is, oxides of composition A 2 Ru 2 O 7−δ, have emerged recently as state-of-the-art catalysts for the oxygen evolution reaction (OER) in acidic conditions. Here, we demonstrate that the A-site substituent in yttrium ruthenium pyrochlores Y 1.8 M 0.2 Ru 2 O 7−δ (M = Cu, Co, Ni, Fe, Y) controls the concentration of surface oxygen vacancies (V O ) in these materials whereby an increased concentration of V O sites correlates with a superior OER activity. DFT calculations rationalize these experimental trends demonstrating that the higher OER activity and V O surface density originate from a weakened strength of the M–O bond, scaling with the formation enthalpy of the respective MO x phases and the coupling between the M d states and O 2 p states. Our work introduces a novel catalyst with improved OER performance, Y 1.8 Cu 0.2 Ru 2 O 7−δ, and provides general guidelines for the design of active electrocatalysts.

Aqueous Al-ion batteries (AAIBs) are the subject of great interest due to the inherent safety and high theoretical capacity of aluminum. The high abundancy and easy accessibility of aluminum raw materials further make AAIBs appealing for grid-scale energy storage. However, the passivating oxide film formation and hydrogen side reactions at the aluminum anode as well as limited availability of the cathode lead to low discharge voltage and poor cycling stability. Here, we proposed a new AAIB system consisting of an Al x MnO 2 cathode, a zinc substrate-supported Zn–Al alloy anode, and an Al(OTF) 3 aqueous electrolyte. Through the in situ electrochemical activation of MnO, the cathode was synthesized to incorporate a two-electron reaction, thus enabling its high theoretical capacity. The anode was realized by a simple deposition process of Al 3+ onto Zn foil substrate. The featured alloy interface layer can effectively alleviate the passivation and suppress the dendrite growth, ensuring ultralong-term stable aluminum stripping/plating. The architected cell delivers a record-high…

All-inorganic lead halide perovskite nanocrystals (NCs) are potential candidates for fabricating high-performance light-emitting diodes (LEDs) owing to their precisely tunable bandgaps, high photoluminescence (PL) efficiency, and excellent color purities. However, the performance of pure red (630–640 nm) all-inorganic perovskite LEDs is still limited by the halide segregation-induced instability of the electroluminescence (EL) of mixed halide CsPbI 3- x Br x NCs. Herein, we report an effective approach to improving the EL stability of pure red all-inorganic CsPbI 3- x Br x NC-based LEDs via the passivation of potassium bromide on NCs. By adding potassium oleate to the reaction system, we obtained potassium bromide surface-passivated (KBr-passivated) CsPbI 3- x Br x NCs with pure red PL emission and a photoluminescence quantum yield (PLQY) exceeding 90%. We determine that most potassium ions present on the surface of NCs bind with bromide ions and thus demonstrate that potassium bromide surface passivation of NCs can both improve the PL stability and inhibit the halide segregation of…

The successful use of electrochemiluminescence (ECL) in immunoassay for clinical diagnosis requires development of novel ECL signal probes. Herein, we report lanthanide (Ln) metal–organic frameworks (LMOFs) as ECL signal emitters in the ECL immunoassay. The LMOFs were prepared from precursors containing Eu (III) ions and 5-boronoisophthalic acid (5-bop), which could be utilized to adjust optical properties. Investigations of ECL emission mechanisms revealed that 5-bop was excited with ultraviolet photons to generate a triplet-state, which then triggered Eu (III) ions for red emission. The electron-deficient boric acid decreased the energy-transfer efficiency from the triplet-state of 5-bop to Eu (III) ions; consequently, both were excited with high-efficiency at single excitation. In addition, by progressively tailoring the atomic ratios of Ni/Fe, NiFe composites (Ni/Fe 1:1) were synthesized with more available active sites, enhanced stability, and excellent conductivity. As a result, the self-luminescent europium LMOFs displayed excellent performance characteristics in an ECL…

Photocatalysis provides an intriguing approach for the conversion of methane to multicarbon (C 2+ ) compounds under mild conditions; however, with methyl radicals as the sole reaction intermediate, the current C 2+ products are dominated by ethane, with a negligible selectivity toward ethylene, which, as a key chemical feedstock, possesses higher added value than ethane. Herein, we report a direct photocatalytic methane-to-ethylene conversion pathway involving the formation and dehydrogenation of alkoxy (i.e., methoxy and ethoxy) intermediates over a Pd-modified ZnO–Au hybrid catalyst. On the basis of various in situ characterizations, it is revealed that the Pd-induced dehydrogenation capability of the catalyst holds the key to turning on the pathway. During the reaction, methane molecules are first dissociated into methoxy on the surface of ZnO under the assistance of Pd. Then these methoxy intermediates are further dehydrogenated and coupled with methyl radical into ethoxy, which can be subsequently converted into ethylene through dehydrogenation. As a result, the optimized…

Abstract In this article we investigate the electrochemical reduction of CO2 at gold electrodes under mildly acidic conditions. Differential electrochemical mass spectroscopy (DEMS) is used to quantify the amounts of formed hydrogen and carbon monoxide as well as the consumed amount of CO2. We investigate how the Faradaic efficiency of CO formation is affected by the CO2 partial pressure (0.1–0.5 bar) and the proton concentration (1–0.25 mM). Increasing the former enhances the rate of CO2 reduction and suppresses hydrogen evolution from proton reduction, leading to Faradaic efficiencies close to 100%. Hydrogen evolution is suppressed by CO2 reduction as all protons at the electrode surfaces are used to support the formation of water (CO2 + 2H+ + 2e– → CO + H2O). Under conditions of slow mass transport, this leaves no protons to support hydrogen evolution. On the basis of our results, we derive a general design principle for acid CO2 electrolyzers to suppress hydrogen evolution from proton reduction: the rate of CO/OH– formation must be high enough to match/compensate the mass…

Emerging nonfullerene acceptors (NFAs) with crystalline domains enable high-performance bulk heterojunction (BHJ) solar cells. Thermal annealing is known to enhance the BHJ photoactive layer morphology and performance. However, the microscopic mechanism of annealing-induced performance enhancement is poorly understood in emerging NFAs, especially regarding competing factors. Here, optimized thermal annealing of model system PBDB-TF:Y6 ( Y6 = 2,2′-((2 Z,2′ Z )-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4- e ]thieno[2″,3′’:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]-thieno[3,2- b ]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1 H -indene-2,1-diylidene))dimalononitrile) decreases the open circuit voltage ( V OC ) but increases the short circuit current ( J SC ) and fill factor (FF) such that the resulting power conversion efficiency (PCE) increases from 14 to 15% in the ambient environment. Here we systematically investigate these thermal annealing effects through in-depth characterizations of carrier mobility, film…

The incorporation of molecular switches in organic structures is of great interest in the chemical design of stimuli-responsive materials that mimic the complex functions of living systems. Merocyanine dyes that convert to spiropyran moieties upon exposure to visible light have been extensively studied as they can be incorporated in hydrated covalent networks that will expel water when this conversion occurs and induce a volumetric shrinkage. We report here on a sulfonate-based water-soluble photoswitch that, in contrast to the well-known systems, triggers a volumetric expansion in hydrogels upon exposure to photons. Contraction is in turn observed under dark conditions in a highly reversible manner. The novel behavior of the photoswitch incorporated in the covalent network was predicted by coarse-grained simulations of the system's chemical structure. Using pH control and polymeric structures that differ in lower critical solution temperature, we were able to develop hydrogels with highly tunable volumetric expansion. The novel molecular function of the systems developed here led…

In this study, we propose a new concept of vertically aligned 2D covalent organic framework (COF) layers forming a membrane for efficient gas separation on the basis of precise size exclusion. Gas transport takes place through the COF interlayer space (typically 0.3–0.4 nm) rather than through the nanometer-sized pore apertures. Construction of such a unique membrane architecture was implemented via in situ oriented growth of 2D COFs inside a skeleton of vertically aligned CoAl-layered double hydroxide (LDH) nanosheets. The resultant vertical COF-LZU1 membrane exhibits a high H 2 permeance of ∼3600 GPU together with a desirable separation selectivity for gas mixtures such as H 2 /CO 2 (31.6) and H 2 /CH 4 (29.5), thus surpassing the 2008 Robeson upper bounds. The universality of this approach was demonstrated by successfully producing two types of high-quality vertical COF membranes with superior performance as well as outstanding running stability.

Nonaqueous rechargeable lithium–oxygen batteries (LOBs) are one of the most promising candidates for future electric vehicles and wearable/flexible electronics. However, their development is severely hindered by the sluggish kinetics of the ORR and OER during the discharge and charge processes. Here, we employ MOF-assisted spatial confinement and ionic substitution strategies to synthesize Ru single atoms riveted with nitrogen-doped porous carbon (Ru SAs-NC) as the electrocatalytic material. By using the optimized Ru 0.3 SAs-NC as electrocatalyst in the oxygen-breathing electrodes, the developed LOB can deliver the lowest overpotential of only 0.55 V at 0.02 mA cm –2 . Moreover, in-situ DEMS results quantify that the e – /O 2 ratio of LOBs in a full cycle is only 2.14, indicating a superior electrocatalytic performance in LOB applications. Theoretical calculations reveal that the Ru–N 4 serves as the driving force center, and the amount of this configuration can significantly affect the internal affinity of intermediate species. The rate-limiting step of the ORR on the catalyst…

Materials with circularly polarized luminescence (CPL) activity have immense potential applications in molecular switches, optical sensors, information storage, asymmetric photosynthesis, 3D optical displays, biological probe, and spintronic devices. However, the achiral architectures of most of the luminophores severely limit their practical needs. Within this context, molecular ferroelectrics with striking chemical variability and structure–property flexibility bring light to the assembly of CPL-active ferroelectric materials. Herein, we report organic–inorganic perovskite enantiomorphic ferroelectrics, ( R )- and ( S )-3-(fluoropyrrolidinium)MnBr 3, undergoing a 222F2-type ferroelectric phase transition at 273 K. Their mirror relationships are verified by both single-crystal X-ray diffraction and vibrational circular dichroism (VCD). Furthermore, the corresponding Cotton effect for two chiral crystals was captured by mirror CPL activity. This may be assigned to the inducing interaction between the achiral luminescent perovskite framework and chiral organic components. As far as…

Atmospheric moisture is a ubiquitous water resource available at any time and any place, making it attractive to develop materials for harvesting water from air to address the imminent water shortage crisis. In this context, we have been exploring the applicability of covalent organic frameworks (COFs) for water harvesting and report here a new porous, two-dimensional imine-linked COF with a voided square grid topology, termed COF-432. Unlike other reported COFs, COF-432 meets the requirements desired for water harvesting from air in that it exhibits an S-shaped water sorption isotherm with a steep pore-filling step at low relative humidity and without hysteretic behavior-properties essential for energy-efficient uptake and release of water. Further, it can be regenerated at ultra-low temperatures and displays exceptional hydrolytic stability, as demonstrated by the retention of its working capacity after 300 water adsorption-desorption cycles.

The unclear Li + local environment and Li + conduction mechanism in solid polymer electrolytes, especially in a ceramic/polymer composite electrolyte, hinder the design and development of a new composite electrolyte. Moreover, both the low room-temperature Li + conductivity and large interfacial resistance with a metallic lithium anode of a polymer membrane limit its application below a relatively high temperature. Here we have identified the Li + distribution and Li + transport mechanism in a composite polymer electrolyte by investigating a new solid poly(ethylene oxide) (PEO)-based NASICON–LiZr 2 (PO 4 ) 3 composite with 7 Li relaxation time and 6 Li → 7 Li trace-exchange NMR measurements. The Li + population of the two local environments in the composite electrolytes depends on the Li-salt concentration and the amount of ceramic filler. A composite electrolyte with a [EO]/[Li + ] ratio n = 10 and 25 wt % LZP filler has a high Li + conductivity of 1.2 × 10 –4 S cm –1 at 30 °C and a low activation energy owing to the additional Li + in the mobile A2 environment. Moreover, an in…

Abstract Three-dimensional (3D) covalent organic frameworks (COFs) are rare because there is a limited choice of organic building blocks that offer multiple reactive sites in a polyhedral geometry. Here, we synthesized an organic cage molecule (Cage-6-NH2) that was used as a triangular prism node to yield the first cage-based 3D COF, 3D-CageCOF-1. This COF adopts an unreported 2-fold interpenetrated acs topology and exhibits reversible dynamic behavior, switching between a small-pore (sp) structure and a large-pore (lp) structure. It also shows high CO2 uptake and captures water at low humidity (<40%). This demonstrates the potential for expanding the structural complexity of 3D COFs by using organic cages as the building units.

State-of-the-art, high-performance perovskite solar cells (PSCs) contain a large amount of iodine to realize smaller bandgaps. However, the presence of numerous iodine vacancies at the surface of the film formed by their evaporation during the thermal annealing process has been broadly shown to induce deep-level defects, incur nonradiative charge recombination, and induce photocurrent hysteresis, all of which limit the efficiency and stability of PSCs. In this work, modifying the defective surface of perovskite films with cadmium iodide (CdI 2 ) effectively reduces the degree of surface iodine deficiency and stabilizes iodine ions via the formation of strong Cd–I ionic bonds. This largely reduces the interfacial charge recombination loss, yielding a high efficiency of 21.9% for blade-coated PSCs with an open-circuit voltage of 1.20 V, corresponding to a record small voltage deficit of 0.31 V. The CdI 2 surface treatment also improves the operational stability of the PSCs, retaining 92% efficiency after constant illumination at 1 sun intensity for 1000 h. This work provides a…

An ideal material for C 2 H 6 /C 2 H 4 separation would simultaneously have the highest C 2 H 6 uptake capacity and the highest C 2 H 6 /C 2 H 4 selectivity. But such material is elusive. A benchmark material for ethane-selective C 2 H 6 /C 2 H 4 separation is peroxo-functionalized MOF-74-Fe that exhibits the best known separation performance due to its high C 2 H 6 /C 2 H 4 selectivity (4.4), although its C 2 H 6 uptake capacity is moderate (74.3 cm 3 /g). Here, we report a family of pore-space-partitioned crystalline porous materials (CPMs) with exceptional C 2 H 6 uptake capacity and C 2 H 6 /C 2 H 4 separation potential (i.e., C 2 H 4 recovered from the mixture) despite their moderate C 2 H 6 /C 2 H 4 selectivity (up to 1.75). The ethane uptake capacity as high as 166.8 cm 3 /g at 1 atm and 298 K, more than twice that of peroxo-MOF-74-Fe, has been achieved even though the isosteric heat of adsorption (21.9–30.4 kJ/mol) for these CPMs is as low as about one-third of that for peroxo-MOF-74-Fe (66.8 kJ/mol). While the overall C 2 H 6 /C 2 H 4 separation potentials have not yet…

Methanol–water reforming is a promising solution for H 2 production/transportation in stationary and mobile hydrogen applications. Developing inexpensive catalysts with sufficiently high activity, selectivity, and stability remains challenging. In this paper, nickel-supported over face-centered cubic (fcc) phase α-MoC has been discovered to exhibit extraordinary hydrogen production activity in the aqueous-phase methanol reforming reaction. Under optimized condition, the hydrogen production rate of 2% Ni/α-MoC is about 6 times higher than that of conventional noble metal 2% Pt/Al 2 O 3 catalyst. We demonstrate that Ni is atomically dispersed over α-MoC via carbon bridge bonds, forming a Ni 1 –C x motif on the carbide surface. Such Ni 1 –C x motifs can effectively stabilize the isolated Ni 1 sites over the α-MoC substrate, rendering maximized active site density and high structural stability. In addition, the synergy between Ni 1 –C x motif and α-MoC produces an active interfacial structure for water dissociation, methanol activation, and successive reforming processes with compatible…

Abstract Capacity retention in lithium metal batteries needs to be improved if they are to be commercially viable, the low cycling stability and Li corrosion during storage of lithium metal batteries being even more problematic when there is no excess lithium in the cell. Herein, we develop in situ NMR metrology to study “anode-free” lithium metal batteries where lithium is plated directly onto a bare copper current collector from a LiFePO4 cathode. The methodology allows inactive or “dead lithium” formation during plating and stripping of lithium in a full-cell lithium metal battery to be tracked: dead lithium and SEI formation can be quantified by NMR and their relative rates of formation are here compared in carbonate and ether-electrolytes. Little-to-no dead Li was observed when FEC is used as an additive. The bulk magnetic susceptibility effects arising from the paramagnetic lithium metal were used to distinguish between different surface coverages of lithium deposits. The amount of lithium metal was monitored during rest periods, and lithium metal dissolution (corrosion) was…

This work describes a strategy to produce circularly polarized thermally activated delayed fluorescence (CP-TADF). A set of two structurally similar organic emitters SFST and SFOT are constructed, whose spiro architectures containing asymmetric donors result in chirality. Upon grafting within the spiro frameworks, the donor and acceptor are fixed proximally in a face-to-face manner. This orientation allows intramolecular through-space charge transfer (TSCT) to occur in both emitters, leading to TADF properties. The donor units in SFST and SFOT have a sulfur and oxygen atom, respectively; such a subtle difference has great impacts on their photophysical, chiroptical, and electroluminescence (EL) properties. SFOT exhibits greatly enhanced EL performance in doped organic light-emitting diodes, with external quantum efficiency (EQE) up to 23.1%, owing to the concurrent manipulation of highly photoluminescent quantum efficiency (PLQY, ∼90%) and high exciton utilization. As a comparison, the relatively larger sulfur atom in SFST introduces heavy atom effects and leads to distortion of the…

Understanding the dynamic structural reconstruction/transformation of catalysts during electrochemical CO 2 reduction reaction (CO 2 RR) is highly desired for developing more efficient and selective catalysts, yet still lacks in-depth realization. Herein, we study a model system of copper nanowires with various degrees of silver modifications as electrocatalysts for CO 2 RR. Among them, the Cu 68 Ag 32 nanowire catalyst achieves the highest activity and selectivity toward methane with an extremely high faradaic efficiency of ∼60%, about 3 times higher than that of primitive Cu nanowires, and even surpasses the most efficient catalysts for producing methane. By using in situ grazing-angle X-ray scattering/diffraction, X-ray absorption spectroscopy, and Raman techniques, we found that the Cu 68 Ag 32 nanowires underwent an irreversible structural reconstruction and well-stabilized chemical state of Cu on the catalyst surface under the working CO 2 RR conditions, which greatly facilitates the CO 2 to methane conversion. Further analysis reveals that the restructuring phenomenon can be…

Abstract Encapsulation of metal nanocatalysts by support-derived materials is well known as a classical strong metal–support interaction (SMSI) effect that occurs almost exclusively with active oxide supports and often blocks metal-catalyzed surface reactions. In the present work this classical SMSI process has been surprisingly observed between metal nanoparticles, e.g., Ni, Fe, Co, and Ru, and inert hexagonal boron nitride (h-BN) nanosheets. We find that weak oxidizing gases such as CO2 and H2O induce the encapsulation of nickel (Ni) nanoparticles by ultrathin boron oxide (BOx) overlayers derived from the h-BN support (Ni@BOx/h-BN) during the dry reforming of methane (DRM) reaction. In-situ surface characterization and theory calculations reveal that surface B–O and B–OH sites in the formed BOx encapsulation overlayers work synergistically with surface Ni sites to promote the DRM process rather than blocking the surface reactions.

A single nickel atom embedded in graphene is one of the most representative single-atom catalysts, and it has a high activity and selectivity for electrochemical CO 2 reduction (CO 2 R) to CO. However, the catalytic origin, especially the coordination structure of Ni, remains highly puzzling, as previous density functional theory (DFT) calculations showed that all the possible structures should be inactive and/or nonselective. Here, using ab initio molecular dynamics (AIMD) and a “slow-growth” sampling approach to evaluate the reaction kinetic barriers, we show that the charge capacity (of the site) and hydrogen bonding (with the intermediates), which were neglected/oversimplified in previous DFT calculations, play crucial roles, and including their effects can resolve the catalytic origin. Particularly, a high charge capacity allows the catalytic site to carry more charges than required for the electrochemical step, lowering the electrochemical barrier, and hydrogen bonding promotes the reaction that produces polar intermediates by stabilizing the intermediates and facilitating the…

Highly selective adsorptive separation of olefin/paraffin through porous materials can produce high purity olefins in a much more energy-efficient way than the traditional cryogenic distillation. Here we report an ultramicroporous cobalt gallate metal–organic framework (Co-gallate) for the highly selective sieving separation of propylene/propane at ambient conditions. This material possesses optimal pore structure for the exact confinement of propylene molecules while excluding the slightly large propane molecules, as clearly demonstrated in the neutron diffraction crystal structure of Co-gallate⊃0.38C 3 D 6 . Its high separation performance has been confirmed by the gas sorption isotherms and column breakthrough experiments to produce the high purity of propylene (97.7%) with a high dynamic separation productivity of 36.4 cm 3 cm –3 under ambient conditions. The gas adsorption measurement, pore size distribution, and crystallographic and modeling studies comprehensively support the high sieving C 3 H 6 /C 3 H 8 separation in this MOF material. It is stable under different…