Hydrogen Evolution Reaction Research Articles

Novel Gel method MXene-Supported Dual-Site PtNi-NiO for Electrocatalytic Water Reduction and Urea Oxidation.

Compared to the traditional oxygen evolution reaction (OER), the urea oxidation reaction (UOR) generally exhibits a lower overpotential during the electrolytic process, which is conducive to the hydrogen evolution reaction (HER) at the cathode. The superior structure and abundant sites play a crucial role in promoting the adsorption and cleavage of urea molecules. Therefore, this paper introduces a simple metal cation-induced gelation method to prepare an electrocatalyst with PtNi alloy-NiO dual sites supported on Ti3C2Tx, which simultaneously exhibits excellent UOR and HER performance. PtNi-NiOx/Ti3C2Tx demonstrates good catalytic activity for the urea oxidation reaction, requiring only 1.364V (overpotential of 0.994V) to achieve a current density of 100mAcm-2 in UOR, and also exhibits remarkable catalytic activity in the hydrogen evolution reaction, with PtNi-NiOx/Ti3C2Tx achieving a current density of 10mAcm-2 in HER with only 24mV of overpotential. In the UOR//HER two-electrode electrolysis cell, it requires only 1.361 and 1.538V to reach current densities of 10 and 100mAcm-2, respectively. According to density functional theory (DFT) calculations, the dual active sites can intelligently adsorb the electron-donating/electron-withdrawing groups in urea molecules, activate chemical bonds, and thereby initiate urea decomposition.

Sustained hydrogen production through alkaline water electrolysis using Bridgman–Stockbarger derived indium-impregnated copper chromium selenospinel

The depletion of conventional fossil fuels necessitates the development of sustainable energy alternatives, with electrochemical water splitting for hydrogen (H2) production being a promising solution. However, large-scale hydrogen generation is hindered by the scarcity of cost-effective electrocatalysts to replace noble metals such as Pt and RuO2 in the Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER). In this study, we report the synthesis of CuCr2-xInxSe4 (x = 0, 0.2, 0.4) using a dual approach combining the Bridgman-Stockbarger method and ball milling. Among the synthesized materials, CuCr1.8In0.2Se4 demonstrates outstanding HER activity in 1.0 M KOH, achieving a potential of −0.16 V vs. RHE at a current density of 10 mA cm−2. Moreover, the material shows remarkable durability during a three-electrode accelerated degradation test in an alkaline medium, maintaining its performance over 24 h at a constant current density of −200 mA cm−2, with a stable potential of −0.57 V vs. RHE. Additionally, CuCr1.8In0.2Se4 was tested in a two-electrode configuration alongside CoFe LDH, achieving a benchmark of 1.7 V for overall water splitting. It sustained a current density of 400 mA cm−2 for 24 h in an accelerated degradation test, exhibiting a minimal loss of 0.1 V after the testing period. These results highlight CuCr1.8In0.2Se4 as a promising non-noble metal catalyst for HER, demonstrating its potential to reduce reliance on noble materials for large-scale hydrogen production.

Laser-Regulated Iridium-Diffused Nitrogen-Carbon Sites for Enhanced Hydrazine-Assisted Alkaline Seawater Splitting and Zinc-Hydrazine Batteries.

The current study presents a quick and simple method for synthesizing Ir nanoclusters decorated on an N-doped carbon (NC) matrix via pulsed laser ablation in liquid, followed by pyrolysis. The resulting Ir-NC material acts as a dual-functional electrocatalyst, efficiently facilitating hydrogen generation through the hydrazine oxidation reaction (HzOR) and the hydrogen evolution reaction (HER) in alkaline seawater. The optimized Ir-NC-2 catalyst exhibits a low operating potential of 23mV versus the reversible hydrogen electrode for HzOR and a remarkably low overpotential of 24mV for HER, achieving a current density of 10mAcm-2 in alkaline seawater, surpassing the performance of the Pt/C catalyst. Notably, the Ir-NC-2 catalyst also demonstrates superior dual-functionality in overall hydrazine-assisted seawater splitting, requiring only 0.1V at 10mAcm-2 while maintaining stability. Moreover, density functional theory calculations reveal that the strong electronic interaction between the Ir nanoclusters and the NC matrix enhances mass transfer and electron conductivity, significantly boosting HER activity and accelerating the kinetics of hydrazine dehydrogenation. Consequently, the Ir-NC-2 catalyst performs efficiently in a Zn-hydrazine battery, achieving high energy efficiency of 95.5% and demonstrating excellent stability for 120h (360 cycles), indicating its potential for practical applications.

Structure-Driven Performance Enhancement in Palladium-Graphene Oxide Catalysts for Electrochemical Hydrogen Evolution.

Graphene oxide (GO) has recently gained significant attention in electrocatalysis as a promising electrode material owing to its unique physiochemical properties such as enhanced electron transfers due to a conjugated π-electron system, high surface area, and stable support for loading electroactive species, including metal nanoparticles. However, only a few studies have been directed toward the structural characteristics of GO, elaborating on the roles of oxygen-containing functional groups, the presence of defects, interlayer spacing between the layered structure, and nonuniformity in the carbon skeleton along with their influence on electrochemical performance. In this work, we aim to understand these properties in various GO materials derived from different graphitic sources. Both physiochemical and electrochemical characterization were employed to correlate the above-mentioned features and explore the effect of the location of the palladium nanoparticles (Pd NPs) on various GO supports for the hydrogen evolution reaction (HER). The interaction of the functional groups has a crucial role in the Pd dispersion and its electrochemical performance. Among the different GO samples, Pd supported on GO derived from graphene nanoplate (GNP), Pd/GO-GNP, exhibits superior HER performance; this could be attributed to the optimal balance among particle size, defect density, less in-plane functionalities, and higher electrochemical surface area. This study, thus, helps to identify the optimal conditions that lead to the best performance of Pd-loaded GO, contributing to the design of more effective HER electrocatalysts.

Engineering the Coordination Environment in the Silver(I)- and Ruthenium(II)-N-Heterocyclic Carbene Complexes in Instigating the Electrocatalytic Hydrogen Evolution Reaction.

The quest for cost-efficient and high-performance electrocatalysts towards electrocatalytic water splitting is a key and an interdisciplinary area of study. Considerable progress is being driven by developments in the field of energy research. In a fundamental study, we have synthesized NHC precursors (6 and 7) and corresponding metal-NHC complexes of silver(I)- (8 and 9) and ruthenium(II)- (10 and 11) of a N-heterocyclic carbene-based ligand type incorporating coumarins. These NHC precursors and metal-NHC complexes were characterized through various analytical and spectral techniques. The silver(I)-NHC complexes 8 and 9 displayed a linear coordination geometry with a center of inversion, which is evidenced by the single-crystal X-ray diffraction technique. Both the series of complexes were assessed for their efficacies in the hydrogen evolution reaction (HER). The results demonstrated that attributed to its peculiar coordination geometry, high electrical conductivity the silver(I)- and ruthenium(II)-NHC complexes exhibited exemplary electrocatalytic activity. Activities of the hydrogen evolution reaction on two differently modified electrode substrates with metal-NHC complexes have been studied. To attain the benchmark HER current density of 10 mA cm-2, in 1.0 M KOH, an overpotential of -375 to -527 mV vs RHE was required for the metal-NHC complexes. Based on the analysis of the Tafel slope values, the rate-determining step was the adsorption of hydrogen as investigated in the potential window. The molecular electrocatalyst 10 presented a superior stability and maintained the electrocatalytic activity for a duration of 18 h with complex 8 and 24 h with respect to complex 10 in 1.0 M KOH. Apace with these studies, hydrogen oxidation studies were examined in 0.5 M H2SO4 by a substantial current density at the platinum ring electrode. This research offers feasible guidance for developing organometallic-based molecular electrocatalysts with good electrocatalytic performance.

Application of ZrO2 and Ni modified carbon nanotube composites as bifunctional water electrolysis catalysts

By using carbon nanotube (CNT) as the carrier, Ni as the active center and ZrO2 as the modifier, an efficient electrocatalytic material (ZrO2-Ni/CNT) is designed and synthesized in this paper. The structure and properties of the catalyst are characterized by various instrumental analysis methods such as SEM, TEM, XRD and XPS. The electrochemical test results show that the addition of ZrO2 can significantly improve the catalytic performance of this catalyst in the electrochemical water splitting. In an alkaline solution, ZrO2-Ni/CNT catalyst displays an exceedingly low overpotential of 169 mV and 249 mV at the current density of 10 mA cm−2 towards hydrogen evolution reaction and oxygen evolution reaction, respectively. This work shows that the modification of ZrO2 can improve the electrocatalytic activity of Ni-based materials, and the modification strategy can be applied to improve the electrocatalytic activity of commercial Ni-based electrode materials.

Impact of Side Chains in 1-n-Alkylimidazolium Ionomers on Cu-Catalyzed Electrochemical CO2 Reduction.

This study presents the impact of the side chains in 1-n-alkylimidazolium ionomers with varying side chain lengths (CnH2n+1 where n = 1, 4, 10, 16) on Cu-catalyzed electrochemical CO2 reduction reaction (CO2RR). Longer side chains suppress the H2 and CH4 formation, with the n-hexadecyl ionomer (n = 16) showing the greatest reduction in kinetics by up to 56.5% and 60.0%, respectively. On the other hand, C2H4 production demonstrates optimal Faradaic efficiency with the n-decyl ionomer (n = 10), a substantial increase of 59.9% compared to its methyl analog (n = 1). Through a combination of density functional theory calculations and material characterization, it is revealed that the engineering of the side chains effectively modulates the thermodynamic stability of key intermediates, thus influencing the selectivity of both CO2RR and hydrogen evolution reaction. Moreover, ionomer engineering enables industrially relevant partial current density of -209.5 mA cm-2 and a Faradaic efficiency of 52.4% for C2H4 production at 3.95 V, even with a moderately active Cu catalyst, outperforming previous benchmarks and allowing for further improvement through catalyst engineering. This study underscores the critical role of ionomers in CO2RR, providing insights into their optimal design for sustainable chemicalsynthesis.

High-Entropy Multiple-Anion Aqueous Electrolytes for Long-Life Zn-Metal Anodes.

Aqueous zinc-ion batteries (AZIBs) hold great promise for large-scale energy storage applications, however, their practical use is significantly hindered by issues such as zinc dendrite growth and hydrogen evolution. To address these challenges, we propose a high-entropy (HE) electrolyte design strategy that incorporates multiple zinc salts, aimed at enhancing ion kinetics and improving the electrochemical stability of the electrolyte. The interactions between multiple anions and Zn2+ increase the complexity of the solvation structure, resulting in smaller ion clusters while maintaining weakly anion-rich solvation structures. This leads to improved ion mobility and the formation of robust interphase layers on the electrode-electrolyte interface. Moreover, the HE electrolyte effectively suppresses hydrogen evolution and corrosion side reactions while facilitating uniform and reversible Zn plating/stripping processes. Impressively, the optimized electrolyte enables dendrite-free Zn plating/stripping for over 3000 h in symmetric cells and achieves a high Coulombic efficiency of 99.5% at 10 mA cm-2 in asymmetric cells. Inspiringly, full cells paired with Ca-VO2 cathodes demonstrate excellent performance, retaining 81.5% of the initial capacity over 1800 cycles at 5 A g-1. These significant findings highlight the potential of this electrolyte design strategy to improve the performance and lifespan of Zn-metal anodes in AZIBs.

Electrodeposition of Thin Film Cu-Zn-Sn Alloy for Water Splitting Application

An energy transition to renewable energy sources is necessary due to the scarcity of fossil fuels and their detrimental effects on the environment. Water splitting process is one of the practical and effective way that does not occur spontaneously. This study investigates catalytic activity of Cu-Zn-Sn (CZT) photocatalyst in hydrogen evolution and oxygen evolution reaction. The CZT deposited with varied electrolyte’s pH of 6 and 9 on indium tin oxide substrate at the room temperature for 600 seconds. According to the X-ray diffraction patterns, there were Cu6Sn5, Cu5Zn8, and Sn metal phases with monoclinic, cubic, and cubic crystal systems. The scanning electron microscopy technique results of all CZT alloy sample showed a dense, non-uniform, and polycrystalline surface structure. The CZT alloys were found to have an average particle size of 0.35 μm. CZT alloys can produce a photocurrent density of 0.19 mA/cm² at a potential of 1.29 V vs RHE. the charge transfer resistance of CZT synthesized at pH 6 is lower (21.48 Ω) compared to pH 9 (28.36 Ω). The Tafel slope of HER for pH 9 CZT was -133 mV/dec, which was lower than that of pH 6 CZT (-88 mV/dec), indicating faster H2 production and corrosion resistance on pH 9 CZT.

Ruthenium Phosphide Nanoclusters Dispersed on Zeolitic Imidazolate Framework-8 and Encapsulated in N,P-Codoped Carbon as Electrocatalysts for the Hydrogen Evolution Reaction

Ruthenium Phosphide Nanoclusters Dispersed on Zeolitic Imidazolate Framework-8 and Encapsulated in N,P-Codoped Carbon as Electrocatalysts for the Hydrogen Evolution Reaction

Photocarrier Dynamics of Two-Dimensional Aza-Fused Covalent Organic Frameworks as Bifunctional Photocatalysts toward Overall Water Splitting.

Designing high-efficiency bifunctional photocatalysts toward photoinduced overall water splitting is one of the most promising and challenging research directions for clean energy generation. By employing static electronic structure calculation and nonadiabatic molecular dynamics (NAMD) simulation, we herein established a recently synthesized two-dimensional (2D) aza-fused covalent organic framework (aza-COF) as a potential bifunctional photocatalyst toward overall water splitting reactions. Our calculated results reveal that the overpotentials for hydrogen evolution reaction and oxygen evolution reaction are only 0.06 and 0.31 V, respectively, at pH = 4. The dynamics of photoexcited charge carriers studied through NAMD simulation predicts the electron-hole recombination time (25.15 ns), and this confirms that the photogenerated electron and hole carriers migrate to the active sites for the occurrence of reaction before they recombine. Therefore, our results suggest that the 2D aza-COFs exhibit great potential as metal-free and single-material photocatalysts toward overall water splitting under visible light.

The Interfacial Ni/Fe─O─Y Bonds Contribute to High-Efficiency Water Splitting.

Developing economical and efficient electrocatalysts is critical for hydrogen energy industrialization through water electrolysis. Herein, a novel dual-site synergistic NiFe/Y2O3 hybrid with abundant interfacial Ni/Fe─O─Y bonds is designed by density functional theory (DFT) simulations. In situ Raman spectra combined with DFT calculations reveal that the interfacial Ni/Fe─O─Y units greatly promote H2O dissociation and optimize the adsorption of both H* and oxygen species, achieving excellent activity and durability for hydrogen evolution reaction. As expected, NiFe/Y2O3 exhibits a low overpotential of 27 mV at 10 mA cm-2 and robust stability of over 200 h at 1000 mA cm-2, and also outstanding water splitting performance with a low cell voltage of 1.64 V at 100 mA cm-2, showing significant potential for real-world applications.

Polyaniline prepared by Fe3O4 catalysed eco-friendly synthesis as electrocatalyst for efficient water electrolysis

Preparing cost-effective and highly active catalysts for electrocatalytic hydrogen evolution reaction is crucial for developing hydrogen-based technologies. Hence, four conductive polyanilines, prepared by the environmentally-friendly approach using Fe3O4 nanoparticles/H2O2 as the catalyst/main oxidant system (PANI/Fe3O4), were investi¬gated for the first time as electrocatalysts for hydrogen evolution reaction (HER) in acidic media (0.1 M H2SO4) by using voltammetry and chronoamperometry. PANI/Fe3O4 electrodes exhibited Tafel slope values in the -171 to -246 mV dec-1 range depending on the synthesis conditions ‒ Fe3O4/aniline mass ratio and polymerization time. The sample PANI/Fe3O4-II(3) prepared with shorter reaction time and higher Fe3O4/aniline mass ratio showed the best electrocatalytic behaviour reflected in the lowest onset potential (-0.286 V), the lowest overpotential to reach a current density of -10 mA cm-2, the highest current density, the lowest HER activation energy (10 kJ mol-1), and the lowest charge-transfer resistance (5.3 Ω) under HER conditions. Materials were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photo¬electron spectroscopy and electrochemical impedance spectroscopy, and differences in their electrocatalytic HER performance were explained by differences in their content of Fe3O4, surface and electrical properties. Moreover, the possibility of using PANI/Fe3O4-II(3) as HER electrocatalyst in a wider range of pH (i.e. in alkaline media as well) and as a bifunc¬tional electrocatalyst, i.e., for oxygen evolution reaction beside HER, was also examined.

High-Density Atomic Level Defect Engineering of 2D Fe-Based Metal-Organic Frameworks Boosts Oxygen and Hydrogen Evolution Reactions.

Electrocatalysts based on metal-organic frameworks (MOFs) attracted significant attention for water splitting, while the transition between MOFs and metal oxyhydroxide poses a great challenge in identifying authentic active sites and long-term stability. Herein, we employ on-purpose defect engineering to create high-density atomic level defects on two-dimensional Fe-MOFs. The coordination number of Fe changes from 6 to 4.46, and over 28% of unsaturated Fe sites are formed in the optimized Fe-MOF. In situ characterizations of the most optimized Fe-MOF0.3 electrocatalyst during the oxygen evolution reaction (OER) process using Fourier transform infrared and Raman spectroscopy have revealed that some Fe unsaturated sites become oxidized with a concomitant dissociation of water molecules, causing generation of the crucial *OH intermediates and Fe oxyhydroxide. Moreover, the presence of Fe oxyhydroxide is compatible with the Volmer and Heyrovsky steps during the hydrogen evolution reaction (HER) process, which lower its energy barrier and accelerate the kinetics. As a result, the optimized Fe-MOF electrodes delivered remarkable OER (259 mV at 10 mA cm-2) and HER (36 mV at 10 mA cm-2) performance. Our study offers comprehensive understanding of the effect of phase transformation on the electrocatalytic process of MOF-based materials.

Multidentate Chelating Ligands Enable High-Performance Zinc-Bromine Flow Batteries.

Zinc bromine flow battery (ZBFB) is a promising battery technology for stationary energy storage. However, challenges specific to zinc anodes must be resolved, including zinc dendritic growth, hydrogen evolution reaction, and the occurrence of "dead zinc". Traditional additives suppress side reactions and zinc dendrite formation by altering the solvation structure of Zn2+ and adsorbing onto the zinc surface through only a limited number of zincophilic sites, resulting in weak adsorption on zinc metal and potential inability to simultaneously optimize the solvation structure of zinc ions. Obviously, increasing the number of potential zincophilic sites in the additive can significantly enhance the interaction with zinc. Herein, we propose a strong chelate, ethylenediamine tetramethylene phosphonic acid (EDTMPA) as the additive, which boasts six potent zincophilic sites, not only promotes the formation of the water-deficient inner Helmholtz plane but also plays a crucial role in restructuring the solvation environment of Zn2+. As a result, the zinc symmetric flow battery with EDTMPA exhibited exceptional coulombic efficiency of 99.4% over 800 cycles, surpassing the previous studies by a significant margin. Furthermore, the assembled ZBFB has showcased a dendrite-free and enduring cycling over 400 cycles at 80 mA cm-2.

Multidentate Chelating Ligands Enable High‐Performance Zinc‐Bromine Flow Batteries

Zinc bromine flow battery (ZBFB) is a promising battery technology for stationary energy storage. However, challenges specific to zinc anodes must be resolved, including zinc dendritic growth, hydrogen evolution reaction, and the occurrence of "dead zinc". Traditional additives suppress side reactions and zinc dendrite formation by altering the solvation structure of Zn2+ and adsorbing onto the zinc surface through only a limited number of zincophilic sites, resulting in weak adsorption on zinc metal and potential inability to simultaneously optimize the solvation structure of zinc ions. Obviously, increasing the number of potential zincophilic sites in the additive can significantly enhance the interaction with zinc. Herein, we propose a strong chelate, ethylenediamine tetramethylene phosphonic acid (EDTMPA) as the additive, which boasts six potent zincophilic sites, not only promotes the formation of the water‐deficient inner Helmholtz plane but also plays a crucial role in restructuring the solvation environment of Zn2+. As a result, the zinc symmetric flow battery with EDTMPA exhibited exceptional coulombic efficiency of 99.4% over 800 cycles, surpassing the previous studies by a significant margin. Furthermore, the assembled ZBFB has showcased a dendrite‐free and enduring cycling over 400 cycles at 80 mA cm−2.

Enhancing Hydrogen Evolution Reaction through the Improved Mass Transfer and Charge Transfer by Bimetal Nodes.

The high cost of hydrogen production by water electrolysis severely challenges its commercial application. It is highly desirable to develop efficient electrocatalysts and innovative electrolytic cells. Introducing additional metal nodes to form bimetallic metal-organic framework (MOF) is a simple, feasible strategy to overcome the poor electrocatalytic performance of single-metal MOF. In this study, the hydrothermal method is used to synthesize bimetallic NixCoy-BTC. It is found that for hydrogen evolution reaction (HER), Ni0.8Co0.2-BTC merely requires a potential of -0.203 V (vs reverse hydrogen electrode, RHE) to achieve 10 mA cm-2, which is significantly lower than that of Ni-BTC (-0.341 V vs RHE). Notably, electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analysis indicate that NixCoy-BTC has improved charge transfer and mass transfer process, compared with Ni-BTC. Electron paramagnetic resonance (EPR) confirms that Ni0.8Co0.2-BTC has more unpaired electrons than Ni-BTC. Density functional theory (DFT) calculations show that compared with Ni-BTC, NixCoy-BTC is more thermodynamically favorable for the adsorption of H+, OH-, and H2O. It demonstrates that the change of mass transfer caused by bimetallic nodes and the delicate variation of MOF surface play an important role in the electrochemical process. Moreover, a novel electrolytic cell was developed using a methanol oxidation reaction (MOR) to replace oxygen evolution reaction (OER). In this MOR-based electrolytic cell, a current density of 50 mA cm-2 can be achieved at only a cell voltage of 1.85 V, which is lower than the 2.22 V of OER-based electrolytic cell, suggesting that 16.7% electric energy can be saved. At the same time, the Faraday efficiency (FE, 98.2%) of the MOR-based cell is higher than that (94.5%) of the OER-based cell. This research offers a promising strategy for low-cost hydrogen production.

Modulating Electrolyte Solvation Structure for High‐Voltage and Low‐Temperature Magnesium‐ion Supercapacitors

Aqueous electrolytes supercapacitors have great potential in energy storage devices due to their high‐power density and safety. However, due to the water hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the electrochemical stabilization window of aqueous electrolytes needs to be widened. Moreover, the application of aqueous electrolyte at low temperature is often limited by the freezing point of water. In this paper, we modulate the solvation structure of aqueous magnesium‐ion supercapacitors by using sulfolane as a co‐solvent. The modulated low salt concentration hybrid electrolyte extends the electrochemical stability window of the electrolyte to 2.9V and enhances the stability of the electrolyte at extreme temperatures, as well as provides safe and non‐flammable properties. Based on the hybrid electrolyte, the water‐organic hybrid magnesium‐ion supercapacitors (HMSCs) are able to operate within an enlarged voltage range of 0 – 2.2 V at a low temperature of ‐30°C. The HMSC shows a specific capacitance of up to 58 F/g at room temperature and retains a specific capacitance of 39 F/g at a current density of 15 A/g. Furthermore, it has an outstanding cycling performance at ‐30 °C, maintaining a specific capacitance of more than 92% after 20,000 cycles.

Screening of Silver‐Based Single‐Atom Alloy Catalysts for NO Electroreduction to NH3 by DFT Calculations and Machine Learning

AbstractExploring NO reduction reaction (NORR) electrocatalysts with high activity and selectivity toward NH3 is essential for both NO removal and NH3 synthesis. Due to their superior electrocatalytic activities, single‐atom alloy (SAA) catalysts have attracted considerable attention. However, the exploration of SAAs is hindered by a lack of fast yet reliable prediction of catalytic performance. To address this problem, we comprehensively screened a series of transition‐metal atom doped Ag‐based SAAs. This screening process involves regression machine learning (ML) algorithms and a compressed‐sensing data‐analytics approach parameterized with density‐functional inputs. The results demonstrate that Cu/Ag and Zn/Ag can efficiently activate and hydrogenate NO with small Φmax(η), a grand‐canonical adaptation of the Gmax(η) descriptor, and exhibit higher affinity to NO over H adatoms to suppress the competing hydrogen evolution reaction. The NH3 selectivity is mainly determined by the s orbitals of the doped single‐atom near the Fermi level. The catalytic activity of SAAs is highly correlated with the local environment of the active site. We further quantified the relationship between the intrinsic features of these active sites and Φmax(η). Our work clarifies the mechanism of NORR to NH3 and offers a design principle to guide the screen of highly active SAA catalysts.

Comprehensive theoretical study of the effects of facet, oxygen vacancies, and surface strain on iron and cobalt impurities in different surfaces of anatase TiO2.

We report the results of systematic ab initio modelling of various configurations of iron and cobalt impurities embedded in the (110), (101), and (100) surfaces of anatase TiO2, with and without oxygen vacancies. The simulation results demonstrate that incorporation into interstitial voids at the surface level is significantly more favourable than other configurations for both iron and cobalt. The calculations also demonstrate the crucial effect of the facet as well as the lesser effects of other factors, such as vacancies and strain on the energetics of defect incorporation, magnetic moment, bandgap, and catalytic performance. It is further shown that there is no tendency towards the segregation or clustering of impurities on the surface. The calculated free energies of the hydrogen evolution reaction in acidic media predict that iron impurities embedded in the (101) surface of anatase TiO2 can be a competitive catalyst for this reaction.