Interfacial Structure of Water as a New Descriptor of the Hydrogen Evolution Reaction

PtO nanoclusters on ultra-thin 2D Mo2C enhance hydrated cation interaction for superior alkaline hydrogen evolution reaction

Platinum oxide (PtO) is regarded as an effective catalyst beyond platinum metal for the hydrogen evolution reaction (HER). However, slow kinetics and structural instability limit its wide application as alkaline electrocatalyst. Herein, PtO nanoclusters decorated ultrathin two-dimensional (2D) Mo2C with a Pt concentration of 0.98 wt% (Mo2C-PtO) is designed and prepared to overcome these hurdles. The Mo2C-PtO catalyst shows significant interfacial charge reconstruction and strong electrostatic interaction with hydrated ions and exhibits remarkable HER performance with an ultra-low overpotential of 5, 64 and 329 mV at 10, 100 and 1000 mA cm-2 and a small Tafel slope of 25 mV dec-1 in alkaline solution, as well as the long-term durability of hydrogen production at 500 mA cm-2. In situ Raman scattering and theoretical calculation reveal the fast migration and dissociation of cationic hydration water at interface, which accelerates Volmer reaction. The key intermediates of OH* and H* transfer rapidly from the interface to Mo2C and PtO, respectively, which increases the availability of interfacial sites and facilitates the fast Volmer-Tafel mechanism. This study highlights the potential of carbide-supported PtO nanoclusters as highly efficient catalysts for alkaline hydrogen production and offers insights into the interfacial water evolution mechanism.

Single-Atom Sb-Doped RuSbOx Bifunctional Catalysts for Ultra-Stable PEM Water Electrolyzers

Developing highly efficient and stable Pt/Ir-free bifunctional catalysts is very urgent for lowering the catalyst cost of proton exchange membrane water electrolyzer (PEMWE). Herein, a single-atom Sb-doped RuSbOx bifunctional catalyst is developed for ultra-stable PEMWE. RuSbOx exhibits excellent stability with a long-term operation of 150 h for oxygen evolution reaction (OER) and 300 h for hydrogen evolution reaction (HER) at 100 mA cm-2 in acidic media, respectively. Impressively, the PEMWE with RuSbOx as bifunctional catalysts only needs 1.72 to reach 1.0 A cm-2, and can maintain stable operation for 200 h at 200 mA cm-2. The in situ Raman and molecular probe methods reveal that the single-atom Sb doping can reconstruct the interfacial water structure on the surface of RuSbOx, resulting in an enriched supply of free water, accelerating the deprotonation process and reducing the local acidity of the catalyst surface, thereby improving the acidic OER activity and stability. Density functional theory calculations further confirm the above experimental results. In short, this work reveals that Sb is an outstanding structural stabilizer, and single-atom Sb-doping can maximize the OER stability of Ru-based catalysts in acid, which provides a useful strategy for designing ultra-stable electrocatalysts for PEMWE.

Electric-Double-Layer Mechanism of Surface Oxophilicity in Regulating the Alkaline Hydrogen Electrocatalytic Kinetics

Regulating the surface oxophilicity of the electrocatalyst is known as an efficient strategy to mitigate the order-of-magnitude kinetic slowdown of hydrogen electrocatalysis in a base, which is of great scientific and technological significance. So far, its mechanistic origin remains mainly ascribed to the bifunctional or electronic effects that revolve around the catalyst-intermediate interactions and is under extensive debate. In addition, the understanding from the perspective of interfacial electric-double-layer (EDL) structures, which should also strongly depend on the electrode property, is still lacking. Here, by decorating a Pt electrode with Mo, Ru, Rh, and Au metal atoms to tune surface oxophilicity and systematically combining electrochemical activity tests, in situ surface-enhanced infrared absorption spectroscopy, density functional theory calculation, and ab initio molecular dynamics simulation, we found that there exist consistent volcano-type relationships between *OH adsorption strength and alkaline hydrogen evolution activity, the stretching/bending vibration information on interfacial water, and the potential of zero charge (PZC) of the electrode. This demonstrates that the origin of surface oxophilicity in impacting the alkaline hydrogen electrocatalytic activity lies in its modification toward the electrode PZC, which thereby dictates the electric field strength, rigidity, and hydrogen bonding network structure in EDL and ultimately governs the interfacial proton transfer kinetics. These findings emphasize the importance of focusing on electrocatalytic interface structures to understand electrode property-dependent reaction kinetics.

N-Heterocyclic Carbene Polymer-Stabilized Au Nanowires for Selective and Stable Reduction of CO2

The structural stability of nanocatalysts during electrochemical CO2 reduction (CO2RR) is crucial for practical applications. However, highly active nanocatalysts often reconstruct under reductive conditions, requiring stabilization strategies to maintain activity. Here, we demonstrate that the N-heterocyclic carbene (NHC) polymer stabilizes Au nanowire (NW) catalysts for selective CO2 reduction to CO over a broad potential range, enabling coupling with Cu NWs for one-step tandem conversion of CO2 to C2H4. By combining the hydrophobicity of the polystyrene chain and the strong binding of NHC to Au, the polymer stabilizes Au NWs and promotes CO2RR to CO with excellent selectivity (>90%) across -0.4 V to -1.0 V (vs RHE), a significantly broader range than unmodified Au NWs (-0.5 V to -0.7 V). Stable CO2RR at negative potentials yields a high jCO of 142 A/g Au at -1.0 V. In situ ATR-IR analysis indicates that the NHC polymer regulates the water microenvironment and suppresses hydrogen evolution at high overpotential. Moreover, NHC-Au NWs maintain excellent stability during 10 h of CO2RR testing, preserving the NW morphology and catalytic performance, while unmodified NWs degrade into nanoparticles with reduced activity and selectivity. NHC-Au NWs can be coupled with Cu NWs in a flow cell to catalyze CO2RR to C2H4 with 58% efficiency and a partial current density of 70 mA/cm2 (overall C2 product efficiency of 65%). This study presents an adaptable strategy to enhance the catalyst microenvironment, ensure stability, and enable efficient tandem CO2 conversion into value-added hydrocarbons.

Interfacial-Free-Water-Enhanced Mass Transfer to Boost Current Density of Hydrogen Evolution

The advancement of water electrolysis highlights the growing importance of electrolyzers capable of operating at high current densities, where mass transfer dynamics plays a crucial role. In the electrode reactions, the interfacial water is a key factor in regulating these dynamics. However, the potential of utilizing interfacial-free water (IFW) to modulate electrode behavior remains underexplored. Herein, we investigate the effect of interfacial water structure on hydrogen evolution reaction (HER) performance across different current density ranges, using designed platinum-coated nickel hydroxide on nickel foam (Pt@Ni(OH)2-NF) electrodes. We reveal that with increasing current density, changes in interfacial water structure alter the rate-determining step of the HER. Pt@Ni(OH)2-NF exhibited excellent performance in alkaline electrolytes, achieving 1000 mA cm-2 at 114 mV overpotential. This study provides a novel approach to optimizing alkaline water electrolysis dynamics by enhancing mass transfer, further paving the way for more efficient and energy-saving hydrogen production.

Simultaneous modulation of Ni single atoms and NiOx clusters on TiO2 for solar-driven CO2 and H2O conversion to CH4

Construction of the photocatalysts with synergistic active sites holds great significance in enhancing the direct CO2 reduction coupled with H2O oxidation under solar irradiation. This work demonstrates the fabrication of a dual-active-site catalyst (NiSA-NiOx/TiO2) through in-situ formation and simultaneous modulation of Ni single atoms (NiSA) and NiOx clusters on porous TiO2. Both NiSA and NiOx are characterized by X-ray absorption fine structure (XAFS) analyses and diffuse reflectance infrared Fourier transform spectroscopy using CO as a probe molecule (CO-DRIFTS). The optimized NiSA-NiOx/TiO2 photocatalyst exhibits enhanced performance in the reduction of CO2 to CH4 using H2O as a hydrogen source. The deliberate modulation of NiSA and NiOx on TiO2 provides active sites for efficient activation of CO2 and H2O, synchronously promoting the two half-reactions of CO2 reduction and H2O oxidation. The photocatalytic mechanism is elucidated based on a series of control experiments and in situ characterizations. The results reveal that NiSA sites play a crucial role in CO2 adsorption and activation, while NiOx clusters facilitate H2O oxidation for proton provision. The synergistic effect of NiSA and NiOx greatly enhances the photocatalytic conversion of CO2 and H2O to CH4. This work showcases the rational design of semiconductor photocatalysts featuring synergistic active sites for efficient conversion of CO2 and H2O into hydrocarbons by utilizing solar energy.

Negative-Valent Platinum Stabilized by Pt─Ni Electron Bridges on Oxygen-Deficient NiFe-LDH for Enhanced Electrocatalytic Hydrogen Evolution

The unique hydrogen adsorption characteristics of negatively charged platinum play a crucial role in enhancing the electrocatalytic hydrogen evolution reaction. However, atomically dispersed Pt atoms are typically anchored to the support through non-metallic atom bonds, resulting in a high oxidation state. Here, atomically dispersed Pt atoms are anchored in oxygen-deficient NiFe-LDH. Electron transfer between Pt and NiFe-LDH occurs primarily through Pt─Ni bonds rather than the conventional Pt─O bonds. Oxygen vacancies in the NiFe-LDH promote additional electron transfer from Ni to Pt, thereby reducing the valence state of Pt and enhancing hydrogen adsorption. Meanwhile, the elevated valence state of Ni increases the catalyst's hydrophilicity and reduces the energy barrier for hydrolysis dissociation. This catalyst demonstrates remarkably low overpotentials of 4 and 9 mV at 10 mA cm-2 in 1 m KOH and 1 m KPi, respectively. Additionally, its mass activity is 51.5 and 23.7 times higher that of Pt/C, respectively. This study presents a novel strategy for enhancing electrocatalytic performance through the rational design of coordination environments and electronic structures in supported metal catalysts.

Defect-Induced Electron Localization Promotes D2O Dissociation and Nitrile Adsorption for Deuterated Amines

Electrochemical reductive deuteration of nitriles is a promising strategy for synthesizing deuterated amines with D2O as the deuterated source. However, this reaction suffers from high overpotentials owing to the sluggish D2O dissociation kinetics and high thermodynamic stability of the C≡N triple bond. Here, low-coordinated copper (LC-Cu) is designed to decrease the overpotential for the electrosynthesis of the precursor of Melatonin-d4, 5-methoxytryptamine-d4, by 100 mV with a 68 % yield (Faradaic efficiency), which is 4 times greater than that of high-coordinated copper (HC-Cu). The low coordinated sites induced an enrichment of electrons to concentrate K+ ions hydrated deuterium water (K⋅D2O) and decrease the energy of the Volmer step via the polarization effect, leading to a continuous supplementation of *D for the reductive deuteration of nitriles. Moreover, the enhanced local electric field changes the adsorption configuration of nitriles from a semibridge model to a flat model, leading to faster reduction kinetics of nitriles with a high reaction rate at lower potentials. High deuterium incorporation, a wide substrate scope, and easy gram-scale synthesis over LC-Cu at 300 mA rationalize the design concept. Furthermore, the enhanced antitumor and antioxidation effects of Melatonin-d4 highlight the great promise of deuterated drugs.

Defect-Driven hydrogen Evolution: Enhanced hydrogen spillover on Pt-MoS2 interface via sulfur vacancies

The hydrogen spillover is considered a powerful strategy for improving the kinetics of hydrogen evolution reaction (HER) due to the decoupling of hydrogen adsorption and desorption. However, the hydrogen spillover rate strongly depends on the metal-support interfaces, and the Fermi levels (Ef) difference between metal and support hinders the occurrence of hydrogen spillover. Here, we prepared platinum (Pt) doped on molybdenum disulfide (MoS2) with sulfur vacancies (Sv) catalyst (Pt/Sv-MoS2) and investigated the internal relationship between metal-support interfaces and hydrogen spillover mechanism. The experimental and theoretical results show that sulfur (S) vacancies reduce the work function (ΔΦ) at the metal-support interface, thus accelerating the migration rate of hydrogen from Pt to Sv-MoS2. Meanwhile, the introduction of S vacancies promotes the high dispersion of Pt nanoparticles (Pt NPs) and weakens the electron supply from Pt to MoS2, facilitating active hydrogen (*H) adsorption step and thus increasing the hydrogen coverage on the Pt sites. Consequently, the prepared Pt/Sv-MoS2 catalyst exhibited significantly enhanced HER activity, achieving an overpotential of 26 mV at 10 mA·cm-2 and a Tafel slope of only 28 mV·dec-1, which is superior to commercial 20 % Pt/C.

Engineering Heteronuclear Dual-Metal Active Sites in Ordered Macroporous Architectures for Enhanced C2H4 Production from CO2 Photoreduction

Photocatalytic C2H4 synthesis from CO2 and H2O by utilizing solar energy represents a promising sustainable process, yet its efficiency remains significantly limited. Herein, we proposed a dual-engineered strategy integrating 3D ordered macroporous (3DOM) architectures with heteronuclear dual-metal active sites to synergistically promote the photocatalytic C2H4 production. As an example, the Cu/3DOM-In2O3 photocatalyst was synthesized by in situ incorporating Cu single atoms (Cu SAs) into 3DOM In2O3 through a template-assisted pyrolysis process. The strong interaction between Cu SAs and In2O3 resulted in the formation of charge-polarized Cu─In active sites along with abundant oxygen vacancies (OVs). 3DOM architectures serving as special nanoreactors displayed significant advantages in promoting CO2 enrichment and confining key intermediates, thereby increasing *CO coverage. Meanwhile, the charge-polarized Cu─In active sites effectively mitigated electrostatic repulsion and promoted the formation of *CO + *CHO intermediates, resulting in a thermodynamically spontaneous C─C coupling step. Therefore, the Cu/3DOM-In2O3 photocatalyst exhibited robust CO2 reduction to C2H4, achieving high C2H4 evolution rates under various CO2 concentrations, including pure CO2, 10% CO2 in Ar (simulated flue gas), and 0.04% CO2 in Ar (simulated air). This work offers a novel strategy for the construction of photocatalysts with tailored microstructures and specific active sites to promote the conversion of CO2 and H2O into multicarbon products.

Disentangling Multiple pH-Dependent Factors on the Hydrogen Evolution Reaction at Au(111)

Understanding how the electrolyte pH affects electrocatalytic activity is a topic of crucial importance in a large variety of systems. However, unraveling the origin of the pH effects is complicated often by the fact that both the reaction driving forces and reactant concentrations in the electric double layer (EDL) change simultaneously with the pH value. Herein, we employ the hydrogen evolution reaction (HER) at Au(111)-aqueous solution interfaces as a model system to disentangle different pH-dependent factors. In 0.1 M NaOH, the HER current density at Au(111) in the potential range of -0.4 V < E RHE < 0 V is up to 60 times smaller than that in 0.1 M HClO4. A reaction model with proper consideration of the local reaction conditions within the EDL is developed. After correcting for the EDL effects, the rate constant for HER is only weakly pH-dependent. Our analysis unambiguously reveals that the observed pH effects are mainly due to the pH-dependent reorganization free energy, which depends on the electrostatic potential and the local reaction conditions within the EDL. Possible origins of the pH and temperature dependence of the activation energy and the electron transfer coefficients are discussed. This work suggests that factors influencing the intrinsic pH-dependent kinetics are easier to understand after proper corrections of EDL effects.

Regulating Interfacial H2O Activity and H2 Bubbles by Core/Shell Nanoarrays for 800 h Stable Alkaline Seawater Electrolysis

The catalytic activity and stability under high current densities for hydrogen evolution reactions (HER) are impeded by firm adherence and coverage of H2 bubbles to the catalytic sites. Herein, we systematically synthesize core/shell nanoarrays to engineer bubble transport channels, which further remarkably regulate interfacial H2O activity, and swift H2 bubble generation and release. The self-supported catalyst holds uniform ultra-low Ru active sites of 0.38 wt% and promotes the rapid formation of plentiful small H2 bubbles, which are rapidly released by the upright channels, mitigating the blockage of active sites and avoiding surface damage from bubble movements. As a result, these core/shell nanoarrays achieve ultralow overpotentials of 18 and 24 mV to reach 10 mA cm-2 for HER in 1 M KOH freshwater and seawater, respectively. Additionally, the assembled electrolyzer demonstrates stable durability over 800 hours with a high current density of 2 A cm-2 in 1 M KOH seawater. The techno-economic analysis (TEA) indicates that the unit cost of the hydrogen production system is nearly half of the DOE's (Department of Energy) 2026 target. Our work addresses the stability challenges of HER and highlights its potential as a sustainable and economically feasible solution for large-scale hydrogen production of seawater.

Self-activated oxophilic surface of porous molybdenum carbide nanosheets promotes hydrogen evolution activity in alkaline environment

Molybdenum carbides are promising alternatives to Pt-based catalysts for the hydrogen evolution reaction (HER) due to their similar d-band electronic configuration. Notably, MoxC exhibits superior HER kinetics in alkaline media compared to acidic conditions, contrasting with Pt-based catalysts. Herein, we present 3D porous β-Mo2C nanosheets, achieving an overpotential of 111 mV at 10 mA cm-2 in 1 M KOH, significantly lower than in acidic environments. Simulations on pristine Mo2C surface reveal that water dissociation poses a higher energy barrier in alkaline media, suggesting that crystal structure alone does not dictate kinetics. Operando attenuated total reflection surface-enhanced infrared absorption spectroscopy shows that Mo2C activates interfacial water, generating liquid-like and free water, and facilitates hydroxyl species adsorption, reducing activation energy to below 38.43 ± 0.19 kJ/mol. Our findings on the self-activation effect offer insights into the HER mechanism of Mo-based electrocatalysts and guide the design of highly active HER catalysts.

High-Performance FeRu Alloy Electrocatalyst Integrated with a Mo Substrate for Hydrogen Evolution Reaction in Seawater

The production of hydrogen from seawater offers a potential pathway to accomplish sustainable energy solutions. However, this process is impeded by the sluggish kinetics of the hydrogen evolution reaction (HER) and the corrosive nature of seawater. In this work, an FeRu alloy electrocatalyst integrated with a Mo substrate (FeRu/MoO2@Mo) is developed, specifically designed for HER in both alkaline and seawater environments. The FeRu/MoO2@Mo catalyst demonstrated remarkable performance, achieving overpotentials of only 22, 42, and 65 mV in alkaline solution, simulated seawater, and real seawater at 10 mA cm-2. Moreover, the FeRu/MoO2@Mo electrocatalyst exhibited long-term stability for HER, maintaining its activity for at least 400 h under conditions of 1m KOH. In situ Raman spectroscopy and theoretical calculations revealed incorporation of Fe reduces the density of states near the Fermi level of Ru, thereby optimizing hydrogen adsorption-desorption behavior and enhancing the HER activity. This work offers a scalable and cost-effective strategy for the development of efficient non-platinum catalysts.

Electrochemical N-N Oxidatively Coupled Dehydrogenation of 3,5-Diamino-1H-1,2,4-triazole for Value-Added Chemicals and Bipolar Hydrogen Production

Electrochemical H2 production from water favors low-voltage molecular oxidation to replace the oxygen evolution reaction as an energy-saving and value-added approach. However, there exists a mismatch between the high demand for H2 and slow anodic reactions, restricting practical applications of such hybrid systems. Here, we propose a bipolar H2 production approach, with anodic H2 generation from the N-N oxidatively coupled dehydrogenation (OCD) of 3,5-diamino-1H-1,2,4-triazole (DAT), in addition to the cathodic H2 generation. The system requires relatively low oxidation potentials of 0.872 and 1.108 V vs RHE to reach 10 and 500 mA cm-2, respectively. The bipolar H2 production in an H-type electrolyzer requires only 0.946 and 1.129 V to deliver 10 and 100 mA cm-2, respectively, with the electricity consumption (1.3 kWh per m3 H2) reduced by 68%, compared with conventional water splitting. Moreover, the process is highly appealing due to the absence of traditional hazardous synthetic conditions of azo compounds at the anode and crossover/mixing of H2/O2 in the electrolyzer. A flow-type electrolyzer operates stably at 500 mA cm-2 for 300 h. Mechanistic studies reveal that the Pt single atom and nanoparticle (Pt1,n) optimize the adsorption of the S active sites for H2 production over the Pt1,n@VS2 cathodic catalysts. At the anode, the stepwise dehydrogenation of -NH2 in DAT and then oxidative coupling of -N-N- predominantly form azo compounds while generating H2. The present report paves a new way for atom-economical bipolar H2 production from N-N oxidative coupling of aminotriazole and green electrosynthesis of value-added azo chemicals.

Dynamic surface reconstruction engineers interfacial water structure for efficient alkaline hydrogen oxidation

Investigating the dynamic evolution of the catalyst and regulating the structure of interfacial water molecules participating in the hydrogen oxidation reaction (HOR) are essential for developing highly efficient electrocatalysts toward the practical application of anion exchange membrane fuel cells. Herein, we report an efficient strategy to activate hexagonal close-packed PtSe catalyst through in situ reconstruction that undergoes dynamic Se leaching and phase transition during linear sweep voltammetry cycles. The obtained Pt-Se catalyst presents as a surface Se atom-modified face-centered-cubic Pt-based nanocatalyst, and it exhibited remarkable catalytic performance in the alkaline HOR, showing an intrinsic activity of 0.552 mA cm-2 (j 0,s) and a mass activity of 1.084 mA μg-1 (j k,m @ 50 mV). The experimental results, including in situ surface-enhanced infrared absorption spectroscopy and density functional theory calculations suggest that the accumulated electrons on the surface-decorated Se of Pt-Se can induce the regulation of the interfacial water structure between the electrode and electrolyte surface in the electric double-layer region. Consequently, the migration of OH- species from the electrolyte to the catalyst surface can be apparently accelerated within this disordered water network, which together with the optimized intermediate thermodynamic binding energies, contribute to the enhanced alkaline HOR activity.

Electrochemical Lithiation Regulates the Active Hydrogen Supply on Ru-Sn Nanowires for Hydrogen Evolution Toward the High-Performing Anion Exchange Membrane Water Electrolyzer

Designing a rational electrocatalyst/electrolyte interface with superb active hydrogen supply is of significant importance for the alkaline hydrogen evolution reaction (HER) and anion exchange membrane water electrolyzers (AEMWEs). Here, we propose a strategy to tune the interfacial active hydrogen supply via inducing dissoluble cation into electrocatalysts to boost HER in alkali, with electrochemical lithiated sub-2 nm RuSn0.8 nanowires (NWs) as a proof of concept. It is found that a part of Li+ could dissolve in situ from lithiated RuSn0.8 NWs during HER, which tends to affect the interfacial structure and facilitate the proton transport. Among all the Li-Ru-Sn and Ru-Sn NWs, the best-performing Li3.0RuSn0.8 NWs exhibit the lowest initial overpotential of 66 mV at 100 mA cm-2 in 1.0 M KOH, which could be further reduced to 38 mV after the 30 000 cycles accelerated stability test (AST). In situ Raman spectroscopy and operando X-ray adsorption spectroscopy indicate that the pristine Li3.0RuSn0.8 NWs are highly active toward water dissociation and the dissolved Li+ during AST could further enhance the flexibility of the hydrogen bond network for proton transportation. Ab initio molecular dynamics simulations and density functional theory calculations disclose that the incorporation of Li into the Ru-Sn lattice is beneficial to lower the water dissociation barrier, while dissolved Li+ at the interface significantly increases the population of interfacial water molecules, thereby providing sufficient active hydrogens for H2 production. The AEMWE equipped with the Li3.0RuSn0.8 NWs cathode delivers an extremely low cell voltage (1.689 V) at an industrial-scale current density (1 A cm-2) and outstanding stability (56 μV h-1 loss at 1 A cm-2 after 1000 h galvanostatic test), representing one of the best alkaline HER electrocatalysts ever reported.

Tailoring Lewis Acidity of Metal Oxides on Nickel to Boost Electrocatalytic Hydrogen Evolution in Neutral Electrolyte

Neutral-pH water splitting for hydrogen production features a benign environment that could alleviate catalyst and electrolyzer corrosion but calls for the corresponding high-efficiency and earth-abundant hydrogen evolution reaction (HER) catalysts. Herein, we first designed a series of metal oxides decorated on Ni as the model catalysts and found a volcano-shaped relationship between the Lewis acidity of Ni/metal oxides and HER activity in neutral media. The Ni/ZnO with the optimum Lewis acidity could balance water dissociation and hydroxyl desorption, thereby greatly boosting the HER. On the basis of this finding, we further in situ grew the Ni/ZnO heterostructure on a three-dimensional conductive support. The resulting catalyst requires overpotentials of merely 34 and 194 mV to deliver the current densities of 10 and 200 mA cm-2, respectively, and can stably operate at these current densities for 2000 h in 1 M phosphate buffer solution (pH 7), representing the most active and durable HER catalyst in neutral electrolyte reported thus far. Our work provides an effective design scheme for low-cost and high-performance neutral HER catalysts.

Steering the Electronic Microenvironment of Ruthenium Sites via Boron Buffering Enables Enhanced Hydrogen Evolution under a Universal pH Range

Optimizing the microenvironment of active sites is crucial for enhancing the catalytic activity of the hydrogen evolution reaction (HER) across various pH conditions. Here, guided by theoretical predictions of boron (B)-doping's electronic buffering effect on ruthenium (Ru) at the atomic scale, a highly efficient and universal-pH Ru-based HER electrocatalyst (Ru-NBC) by introducing B and nitrogen (N) into a carbon (C) matrix was designed. The Ru-NBC catalyst demonstrated exceptional HER activity, requiring overpotentials of 27, 40, and 68 mV in 1 M KOH, 0.5 M H2SO4, and 1 M phosphate buffer solution (PBS), respectively, to achieve a current density of 10 mA cm-2. In situ Raman spectroscopy, ambient-pressure X-ray photoelectron spectroscopy, and potential of zero charge measurements revealed that B-doping modulates the local Ru microenvironment, restructuring the distribution balance of the interfacial water hydrogen-bond network within the electrochemical double layer and thereby facilitating water adsorption and dissociation. Density functional theory calculations further verified that the electronic buffering effect of B optimizes hydrogen adsorption in acidic media and water activation in alkaline conditions, resultantly contributing to the universal-pH HER performance. This study could provide guidance for the design of advanced electrocatalysts through modulation of the local microenvironment of active sites for energy storage and conversion.

Synergistic Catalysis in Fe─In Diatomic Sites Anchored on Nitrogen-Doped Carbon for Enhanced CO2 Electroreduction

Diatomic catalysts are promising for the electrochemical CO2 reduction reaction (CO2RR) due to their maximum atom utilization and the presence of multiple active sites. However, the atomic-scale design of diatomic catalysts and the elucidation of synergistic catalytic mechanisms between multiple active centers remain challenging. In this study, heteronuclear Fe─In diatomic sites anchored on nitrogen-doped carbon (FeIn DA/NC) are constructed. The FeIn DA/NC electrocatalyst achieves a CO Faradaic efficiency exceeding 90% across a wide range of applied potentials from -0.4 to -0.7 V, with a peak efficiency of 99.1% at -0.5 V versus the reversible hydrogen electrode. In situ, attenuated total reflection surface-enhanced infrared absorption spectroscopy and density functional theory calculations reveal that the synergistic interaction between Fe and In diatomic sites induce an asymmetric charge distribution, which promote the adsorption of CO2 at the Fe site and lowered the energy barrier for the formation of *COOH. Moreover, the unique Fe─In diatomic site structure increase the adsorption energy of *OH through a bridging interaction, which decrease the energy barrier for water dissociation and further promoted CO2RR activity.

Platinum/(Carbon-Nanotube) Electrocatalyst Boosts Hydrogen Evolution Reaction in Acidic, Neutral and Alkaline Solutions

Widely used catalysts for electrocatalytic hydrogen (H2) evolution reaction (HER) have high platinum (Pt) contents and show low efficiencies in neutral and alkaline solutions. Herein, a carbon nanotube (CNT) supported Pt catalyst (Pt/CNT45) with 1 wt.% Pt is fabricated. For HER, the mass activity of Pt/CNT45 in acidic (18.76 A mgPt -1), neutral (3.92 A mgPt -1), and alkaline (3.88 A mgPt -1) solutions is respectively much higher than those on commercial Pt/C catalyst with 20 wt.% Pt (acidic: 0.31 A mgPt -1, neutral: 0.03 A mgPt -1, alkaline: 0.07 A mgPt -1). Thus, Pt/CNT45 enhances HER not only in acidic solutions but also in neutral and alkaline solutions. Ptδ+ at Pt-CNT interface on Pt/CNT45 promotes water (H2O) dissociation and hydroxyl (OH) desorption from Pt/CNT45, thus enhancing HER. This work opens a new way for enhancing HER in a wider pH range by catalyst with low Pt content, and helpful for commercialization.

Short-Path Hydrogen Spillover on CeO2-Supported PtPd Nanoclusters for Efficient Hydrogen Evolution in Acidic Media

Hydrogen spillover in supported metal electrocatalysts has garnered significant research attention for its potential to enhance the hydrogen evolution reaction (HER) efficiency. However, challenges remain in facilitating hydrogen spillover and reducing the associated energy barriers. Herein, PtPd alloy clusters are anchored to the CeO2 surface, enabling short-path hydrogen spillover and lowering the reaction energy barrier in acidic environments. During HER, hydrogen is initially adsorbed on the noble metal surface and subsequently migrates to the interface, rather than precipitating directly on the CeO2 surface. This interface exhibits a near-zero Gibbs free energy of hydrogen adsorption (0.023 eV). Consequently, the catalyst demonstrates an exceptionally low overpotential of only 5.7 mV at 10 mA cm-2 in acidic media, along with remarkable long-term stability. These findings provide valuable insights into designing highly efficient HER electrocatalysts for acidic environments based on hydrogen spillover mechanisms.

Proton Relay in Hydrogen-Bond Networks Promotes Alkaline Hydrogen Evolution Electrocatalysis

Common O-/H-down orientation of H2O molecules on electrocatalysts brings favorable OH/H delivery; however, adverse H/OH delivery in their dissociation process hampers the H2O dissociation kinetics of the alkaline hydrogen evolution reaction (HER). To overcome this challenge, we raised a synergetic H2O dissociation concept of metal-supported electrocatalysts involving efficient OH delivery from O-down H2O to the metal, timely proton relay from O-down H2O on the metal to H-down H2O on the support through the hydrogen-bond network, and prompt H delivery from H-down H2O to the support. After theoretically profiling that a high work function difference between the metal and the support (ΔΦ) induces a strong electric field at the metal-support interface that increases hydrogen-bond connectivity to promote proton relay, we practiced this concept over cobalt phosphide-supported ruthenium (Ru/CoP) catalysts with a high ΔΦ = 0.4 eV, achieving a record-high Ru utilization HER activity of 66.1 A mgRu-1 at -0.1 V vs RHE. The insights into this synergetic H2O dissociation mechanism provide opportunity for the design of bicomponent alkaline HER electrocatalysts.

Facilitating alkaline hydrogen evolution kinetics via interfacial modulation of hydrogen-bond networks by porous amine cages

The electrode-electrolyte interface is pivotal in the electrochemical kinetics. However, modulating the electrochemical interface at the atomic or molecular level is challenging due to the lack of efficient interfacial regulators. Here, we employ a porous amine cage as an interfacial modifier to Pt cluster in a confining configuration, largely enhancing alkaline HER kinetics by facilitating charge transfer. In situ electrochemical surface-enhanced Raman spectra, in combination with the ab initio molecular dynamics simulation, elucidates that the interaction between water and the -NH- moiety of cage frame softens the H-bonds net of interfacial water, making it more flexible for charge transfer. Moreover, our investigation pinpointed that the -NH- moiety acted as a pump for charge transfer by Grotthuss mechanism, lowering the kinetic barrier for hydrogen adsorption. Our findings highlight the strategy of establishing a soft-confining interfacial modifier by porous cage, offering opportunities to optimize electrochemical interfaces and promote reaction kinetics in a targeted way.

Kinetic cation effect in alkaline hydrogen electrocatalysis and double layer proton transfer

Unveiling the so far ambiguous mechanism of the significant dependence on the identity of alkali metal cation would prompt opportunities to solve the more than two orders of magnitude slowdown of hydrogen electrocatalytic kinetics in base relative to acid, which has hampered the effort to reduce the precious metal usage in fuel cells by using the hydroxide exchange membrane. Herein, we present atomic-scale evidences from ab-initio molecular dynamics simulation and in-situ surface-enhanced infrared absorption spectroscopy which show that it is the apparent discrepancies in the electric double-layer structures induced by differently sized cations that lead to largely different interfacial proton transfer barriers and therefore hydrogen electrocatalytic kinetics in base. Concretely, severe accumulation of larger cation in electric double-layer causes more discontinuous interfacial water distribution and H-bond network, thus rendering the proton transfer from bulk to interface more obstructed. Such notion is strikingly different from the previously envisioned impact of cation-intermediate interactions on the energetics of surface steps, providing a unique interfacial perspective for understanding the ubiquitous cation specificity in electrocatalysis.

Tuning Proton Affinity on Co-N-C Atomic Interface to Disentangle Activity-Selectivity Trade-off in Acidic Oxygen Reduction to H2O2

In oxygen reduction reaction to H2O2 via two-electron pathway (2e- ORR), adsorption strength of oxygen-containing intermediates determines both catalytic activity and selectivity. However, it also causes activity-selectivity trade-off. Herein, we propose a novel strategy through modulating the interaction between protons and *OOH intermediates to break the activity-selectivity trade-off for highly active and selective 2e- ORR. Taking the typical cobalt-nitrogen-carbon single-atom catalyst as an example, boron heteroatoms doped into second coordination sphere of CoN4 (Co1-NBC) increase proton affinity on catalyst surface, facilitating proton attack on the former oxygen of *OOH and thereby promoting H2O2 formation. As a result, Co1-NBC simultaneously achieves prominent 2e- ORR activity and selectivity in acid with onset potential of 0.724 V vs. RHE and H2O2 selectivity of 94 %, surpassing most reported catalysts. Furthermore, Co1-NBC exhibits a remarkable H2O2 productivity of 202.7 mg cm-2 h-1 and a remarkable stability of 60 h at 200 mA cm-2 in flow cell. This work provides new insights into resolving activity-selectivity trade-off in electrocatalysis.

Interfacial Water Regulation for Nitrate Electroreduction to Ammonia at Ultralow Overpotentials

Nitrate electroreduction is promising for achieving effluent waste-water treatment and ammonia production with respect to the global nitrogen balance. However, due to the impeded hydrogenation process, high overpotentials need to be surmounted during nitrate electroreduction, causing intensive energy consumption. Herein, a hydroxide regulation strategy is developed to optimize the interfacial H2O behavior for accelerating the hydrogenation conversion of nitrate to ammonia at ultralow overpotentials. The well-designed Ru─Ni(OH)2 electrocatalyst shows a remarkable energy efficiency of 44.6% at +0.1 V versus RHE and a nearly 100% Faradaic efficiency for NH3 synthesis at 0 V versus RHE. In situ characterizations and theoretical calculations indicate that Ni(OH)2 can regulate the interfacial H2O structure with a promoted H2O dissociation process and contribute to the spontaneous hydrogen spillover process for boosting NO3 - electroreduction to NH3 at Ru sites. Furthermore, the assembled rechargeable Zn-NO3 -/ethanol battery system exhibits an outstanding long-term cycling stability during the charge-discharge tests with the production of high-value-added ammonium acetate, showing great potential for simultaneously achieving nitrate removal, energy conversion, and chemical synthesis. This work can not only provide a guidance for interfacial H2O regulation in extensive hydrogenation reactions but also inspire the design of a novel hybrid flow battery with multiple functions.

Identifying the Bifunctional Mechanism in Alkaline Water Electrolysis by Lewis Pairs at the Single-Atom Scale

The bifunctional mechanism, involving multiactive compositions to simultaneously dissociate water molecules and optimize intermediate adsorption, has been widely used in the design of catalysts to boost water electrolysis for sustainable hydrogen energy production but remains debatable due to difficulties in accurately identifying the reaction process. Here, we proposed the concept of well-defined Lewis pairs in single-atom catalysts, with a unique acid-base nature, to comprehensively understand the exact role of multiactive compositions in an alkaline hydrogen evolution reaction. By facilely adjusting active moieties, the induced synergistic effect between Lewis pairs (M-P/S/Cr pairs, M = Ru, Ir, Pt) can significantly facilitate the cleavage of the H-OH bond and accelerate the removal of intermediates, thereby switching the rate-determining step from the Volmer step to the Heyrovsky step. Moreover, the representative Ru-P Lewis pairs deliver an impressive 266 h durability at a high industrial current density of 2 A cm-2 without activity decay in anion-exchange membrane water electrolysis, and the concept can be extended to modify commercial noble-metal-based catalysts for performance enhancement. This work not only sheds light on the important effect of the bifunctional mechanism in alkaline water electrolysis at the single-atom scale but also offers a universal descriptor for the rational design of advanced catalysts.

Ultrafast Synthesis of IrB1.15 Nanocrystals for Efficient Chlorine and Hydrogen Evolution Reactions in Saline Water

The production of storable hydrogen fuel through water electrolysis powered by renewable energy sources such as solar, marine, geothermal, and wind energy presents a promising pathway toward achieving energy sustainability. Nevertheless, state-of-the-art electrolysis requires support from ancillary processes which often incur financial and energy costs. Developing electrolysers capable of directly operating with water that contains impurities can circumvent these processes. Herein, we demonstrate the efficient and durable electrolysis of saline water to produce chlorine gas (Cl2) and hydrogen using structurally ordered IrB1.15, synthesized through ultrafast joule heating. IrB1.15 exhibits remarkable performance, achieving overpotentials of 75 mV for the chlorine evolution reaction (CER) and 12 mV for hydrogen evolution reactions (HER) at current densities of 10 mA cm-2. Moreover, IrB1.15 displays a durability of over 90 h towards both CER and HER. Density functional theory reveals that IrB1.15 has adsorption energies significantly closer to 0 eV for Cl and H, compared to IrO2 and Pt/C. Furthermore, in situ Raman investigations reveal that Ir in IrB1.15 serves as the active center for CER, while the introduction of B atoms to Ir lattices mitigates the formation of absorbed hydrogen species on the Ir surface, thereby enhancing the performance of IrB1.15 in HER.

Probing the Electric Double-Layer Capacitance to Understand the Reaction Environment in Conditions of Electrochemical Amination of Acetone

To elucidate interfacial dynamics during electrocatalytic reactions, it is crucial to understand the adsorption behavior of organic molecules on catalytic electrodes within the electric double layer (EDL). However, the EDL structure in aqueous environments remains intricate when it comes to the electrochemical amination of acetone, using methylamine as a nitrogen source. Specifically, the interactions of acetone and methylamine with the copper electrode in water remain unclear, posing challenges in the prediction and optimization of reaction outcomes. In this study, initial investigations employed impedance spectroscopy at the potential of zero charge to explore the surface preconfiguration. Here, the capacitance of the EDL was utilized as a primary descriptor to analyze the adsorption tendencies of both acetone and methylamine. Acetone shows an increase in the EDL capacitance, while methylamine shows a decrease. Experiments are interpreted using combined grand canonical density functional theory and ab initio molecular dynamics to delve into the microscopic configurations, focusing on their capacitance and polarizability. Methylamine and acetone have larger molecular polarizability than water. Acetone shows a partial hydrophobic character due to the methyl groups, forming a distinct adlayer at the interface and increasing the polarizability of the liquid interface component. In contrast, methylamine interacts more strongly with water due to its ability to both donate and accept hydrogen bonds, leading to a more significant disruption of the hydrogen bond network. This disruption of the hydrogen network decreases the local polarizability of the interface and decreases the effective capacitance. Our findings underscore the pivotal role of EDL capacitance and polarizability in determining the local reaction environment, shedding light on the fundamental processes important for electro-catalysis.

Boosting the oxygen reduction activity on metal surfaces by fine-tuning interfacial water with midinfrared stimulation

Heterogeneous catalysis at the metal surface generally involves the transport of molecules through the interfacial water layer to access the surface, which is a rate-determining step at the nanoscale. In this study, taking the oxygen reduction reaction on a metal electrode in aqueous solution as an example, using accurate molecular dynamic simulations, we propose a novel long-range regulation strategy in which midinfrared stimulation (MIRS) with a frequency of approximately 1,000 cm-1 is applied to nonthermally induce the structural transition of interfacial water from an ordered to disordered state, facilitating the access of oxygen molecules to metal surfaces at room temperature and increasing the oxygen reduction activity 50-fold. Impressively, the theoretical prediction is confirmed by the experimental observation of a significant discharge voltage increase in zinc-air batteries under MIRS. This MIRS approach can be seamlessly integrated into existing strategies, offering a new approach for accelerating heterogeneous reactions and gas sensing within the interfacial water system.

Unveiling the Structure and Dissociation of Interfacial Water on RuO2 for Efficient Acidic Oxygen Evolution Reaction

Understanding the structure and dynamic process of interfacial water molecules at the catalyst-electrolyte interface on acidic oxygen evolution reaction (OER) kinetics is highly desirable for the development of proton exchange membrane water electrolyzers. Herein, we construct a series of p-block metal elements (Ga, In, Sn) doped RuO2 catalysts with manipulated electronic structure and Ru-O covalency to investigate the effect of electrochemical interfacial engineering on the improvement of acidic OER activity. Associated with operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy measurements and theoretical analysis, we uncover the free-H2O enriched local environment and dynamic evolution from 4-coordinated hydrogen-bonded water and 2-coordinated hydrogen-bonded water to free-H2O on the surface of Ga-RuO2, are responsible for the optimized connectivity of hydrogen bonding network in the electrical double layer by promoting solvent reorganization. In addition, the structurally ordered interfacial water molecules facilitate high-efficiency proton-coupled electron transfer across the interface, leading to reduced energy barrier of the follow-up dissociation process and enhanced acidic OER performance. This work highlights the key role of structure and dynamic process of interfacial water for acidic OER, and demonstrates the electrochemical interfacial engineering as an efficient strategy to design high-performance electrocatalysts.

Rechargeable Hydrogen Gas Batteries: Fundamentals, Principles, Materials, and Applications

The growing demand for renewable energy sources has accelerated a boom in research on new battery chemistries. Despite decades of development for various battery types, including lithium-ion batteries, their suitability for grid-scale energy storage applications remains imperfect. In recent years, rechargeable hydrogen gas batteries (HGBs), utilizing hydrogen catalytic electrode as anode, have attracted extensive academic and industrial attention. HGBs, facilitated by appropriate catalysts, demonstrate notable attributes such as high power density, high capacity, excellent low-temperature performance, and ultralong cycle life. This review presents a comprehensive overview of four key aspects pertaining to HGBs: fundamentals, principles, materials, and applications. First, detailed insights are provided into hydrogen electrodes, encompassing electrochemical principles, hydrogen catalytic mechanisms, advancements in hydrogen catalytic materials, and structural considerations in hydrogen electrode design. Second, an examination and future prospects of cathode material compatibility, encompassing both current and potential materials, are summarized. Third, other components and engineering considerations of HGBs are elaborated, including cell stack design and pressure vessel design. Finally, a techno-economic analysis and outlook offers an overview of the current status and future prospects of HGBs, indicating their orientation for further research and application advancements.

Ultrafast H-Spillover in Intermetallic PtZn Induced by the Local Disorder for Excellent Electrocatalytic Hydrogen Evolution Performance

Ordered intermetallic Platinum-Zinc (PtZn) shows potential in hydrogen evolution reaction (HER), but faces a huge challenge in activity enhancement due to the H-repulsion properties of Zinc (Zn). Here, local disorder in ordered intermetallic PtZn nanoparticles confined in N-doped porous carbon (I-PtZn@NPC) via a confinement-high-temperature pyrolysis strategy is realized to boost the HER performance. Experiments and calculations demonstrate that the local substitution of Pt atoms for Zn atoms creates an ultra-short H-spillover channel (Pt site→Pt-Zn bridge site →Zn site). Benefiting from such an ultra-fast H-migration from Pt site to Zn site, I-PtZn@NPC exhibits enhanced intrinsic activity with an ultralow overpotential (η10: 2.3 mV, η100: 24 mV) than commercial Pt black catalyst. Furthermore, a 25 cm2 commercial proton exchange membrane (PEM) electrolyzer equipped with I-PtZn@NPC achieved stable operation at 1.60 Vcell for 200 h at a current density of 1 A cm⁻2. This design of local Zn disorder in the ordered intermetallic PtZn sheds new light on the rational development of efficient Zn-based alloy HER electrocatalysts.

Insight Into Intermediate Behaviors and Design Strategies of Platinum Group Metal-Based Alkaline Hydrogen Oxidation Catalysts

Hydrogen oxidation reaction (HOR) can effectively convert the hydrogen energy through the hydrogen fuel cells, which plays an increasingly important role in the renewable hydrogen cycle. Nevertheless, when the electrolyte pH changes from acid to base, even with platinum group metal (PGM) catalysts, the HOR kinetics declines with several orders of magnitude. More critically, the pivotal role of reaction intermediates and interfacial environment during intermediate behaviors on alkaline HOR remains controversial. Therefore, exploring the exceptional PGM-based alkaline HOR electrocatalysts and identifying the reaction mechanism are indispensable for promoting the commercial development of hydrogen fuel cells. Consequently, the fundamental understanding of the HOR mechanism is first introduced, with emphases on the adsorption/desorption process of distinct reactive intermediates and the interfacial structure during catalytic process. Subsequently, with the guidance of reaction mechanism, the latest advances in the rational design of advanced PGM-based (Pt, Pd, Ir, Ru, Rh-based) alkaline HOR catalysts are discussed, focusing on the correlation between the intermediate behaviors and the electrocatalytic performance. Finally, given that the challenges standing in the development of the alkaline HOR, the prospect for the rational catalysts design and thorough mechanism investigation towards alkaline HOR are emphatically proposed.

Stable selenium nickel-iron electrocatalyst for oxygen evolution reaction in alkaline and natural seawater

The development of efficient and stable catalysts for oxygen evolution reaction (OER) in seawater presents a major challenge for hydrogen production through water electrolysis. In this work, we present a stable NiFe foam catalyst with a Se-doped Ni/Fe oxide surface prepared through a combination of chemical vapor deposition and electrochemical exfoliation. This method effectively modifies the surface of the commercial NiFe foam to a rough and stable Se-doped Ni/Fe oxide surface, displaying exceptional OER performance in both freshwater and seawater with more than 54 days stability in natural seawater. Characterizations reveal Ni-Se doped Fe oxide surface, with subsurface layers consisting of Ni alloyed with a moderate concentration of Fe, optimizes the adsorption free energy of oxygen-containing intermediates. Our results demonstrate a surface engineering approach to activate NiFe foam as a robust OER catalyst for seawater electrolysis, which is beneficial for the hydrogen economy and for the environment.

Water-Driven Stacking Structure Transformation of Ultrathin Ru Nanosheets for Efficient Hydrogen Evolution Reaction

Ultrathin crystalline materials are a class of popular materials that can potentially exhibit fascinating physical and chemical properties dictated by their unique stacking freedom. However, it is challenging to achieve the controllable synthesis over their stacking structure for ultrathin crystalline materials. Herein, water is employed as a key regulatory factor to realize phase engineering in ultrathin nanosheets (NSs), thereby altering stacking faults to achieve distinct stacking arrangements. Ruthenium (Ru) NSs with consistent specific surface areas but different stacking manners are fabricated through the systematic regulation of water. Based on this, it is demonstrated that the hydrogen evolution reaction (HER) performance can be significantly influenced by their stacking structures. Further in-depth investigations reveal that the distinct stacking structures of Ru NSs, featuring a limited area of side facets, will influence the energy barrier of sluggish Volmer step in HER. Ru NSs with ABC stacking exhibit an accelerated Volmer process with outstanding catalytic activity, demonstrating a remarkably low overpotential (25 mV at 10 mA cm-2) and Tafel slope (29 mV dec-1) than most of the reported HER catalysts. The work will advance the understanding of controllable synthesis methods and illuminate the structure-activity relationships in ultrathin crystalline nanomaterials.

Alkaline Hydrogen Evolution Reaction Electrocatalysts for Anion Exchange Membrane Water Electrolyzers: Progress and Perspective

For the aim of achieving the carbon-free energy scenario, green hydrogen (H2) with non-CO2 emission and high energy density is regarded as a potential alternative to traditional fossil fuels. Over the last decades, significant breakthroughs have been realized on the alkaline hydrogen evolution reaction (HER), which is a fundamental advancement and efficient process to generate high-purity H2 in the laboratory. Based on this, the development of the practical industry-oriented anion exchange membrane water electrolyzer (AEMWE) is on the rise, showing competitiveness with the incumbent megawatt-scale H2 production technologies. Still, great challenges lie in exploring the electrocatalysts with remarkable activity and stability for alkaline HER, as well as bridging the gap of performance difference between the three-electrode cell and AEMWE devices. In this perspective, we systematically discuss the in-depth mechanisms for activating alkaline HER electrocatalysts, including electronic modification, defect construction, morphology control, synergistic function, field effect, etc. In addition, the current status of AEMWE is reviewed, and the underlying bottlenecks that impede the application of HER electrocatalysts in AEMWE are summarized. Finally, we share our thoughts regarding the future development directions of electrocatalysts toward both alkaline HER and AEMWE, in the hope of advancing the commercialization of water electrolysis technology for green H2 production.

Vanadium-Doped Heterointerfaced Ni3N-MoOx Nanosheets with Optimized H and H2O Adsorption for Effective Alkaline Hydrogen Electrocatalysis

Nickel (Ni)-based materials represent a compelling avenue as platinum alternatives in the realm of alkaline hydrogen electrocatalysis. However, conventional nickel nitrides (Ni3N) have long been hindered by sluggish hydrogen evolution kinetics in alkaline environments, owing to inadequate adsorption strengths of both hydrogen and water molecules. Herein, a novel approach is presented involving the design of vanadium (V)-doped Ni3N/MoOx heterogeneous nanosheets (V-Ni3N@MoOx), engineered to achieve optimized adsorption strengths for hydrogen evolution and oxidation reactions (HER/HOR). Theoretical insights underscore the superior catalytic performance of this composite, attributed to a synergistic interplay between unique V doping and the heterointerfaced structure. This synergistic effect not only fine-tunes the electronic structure, establishing an optimal d band center to mitigate proton over-bonding, but also ameliorates the energy barrier through enhanced H2O dissociation capability. Consequently, V-Ni3N@MoOx manifests remarkable catalytic activities, evincing an overpotential of 56 mV at 10 mA cm-2 for HER and an exchange current density of 1.91 mA cm-2 for HOR in alkaline media. Notably, the stability assessment reveals the enduring performance of V-Ni3N@MoOx for HER/HOR, exhibiting no activity decay over extended operational durations. This study underscores the efficacy of heterogeneous interface modulation as a transformative strategy in designing Ni-based materials for alkaline hydrogen electrocatalysis.

Roles of copper(I) in water-promoted CO2 electrolysis to multi-carbon compounds

The membrane electrode assembly (MEA) is promising for practical applications of the electrocatalytic CO2 reduction reaction (CO2RR) to multi-carbon (C2+) compounds. Water management is crucial in the MEA electrolyser without catholyte, but few studies have clarified whether the co-feeding water in cathode can enhance C2+ formation. Here, we report our discovery of pivotal roles of a suitable nanocomposite electrocatalyst with abundant Cu2O-Cu0 interfaces in accomplishing water-promoting effect on C2+ formation, achieving a current density of 1.0 A cm-2 and a 19% single-pass C2+ yield at 80% C2+ Faradaic efficiency in MEA. The operando characterizations confirm the co-existence of Cu+ with Cu0 during CO2RR at ampere-level current densities. Our studies reveal that Cu+ works for water activation and aids C‒C coupling by enhancing formations of adsorbed CO and CHO species. This work offers a strategy to boost CO2RR to C2+ compounds in industrial-relevant MEA by combining water management and electrocatalyst design.

Insights into the pH effect on hydrogen electrocatalysis

Hydrogen electrocatalytic reactions, including the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR), play a crucial role in a wide range of energy conversion and storage technologies. However, the HER and HOR display anomalous non-Nernstian pH dependent kinetics, showing two to three orders of magnitude sluggish kinetics in alkaline media compared to that in acidic media. Fundamental understanding of the origins of the intrinsic pH effect has attracted substantial interest from the electrocatalysis community. More critically, a fundamental molecular level understanding of this effect is still debatable, but is essential for developing active, stable, and affordable fuel cells and water electrolysis technologies. Against this backdrop, in this review, we provide a comprehensive overview of the intrinsic pH effect on hydrogen electrocatalysis, covering the experimental observations, underlying principles, and strategies for catalyst design. We discuss the strengths and shortcomings of various activity descriptors, including hydrogen binding energy (HBE) theory, bifunctional theory, potential of zero free charge (pzfc) theory, 2B theory and other theories, across different electrolytes and catalyst surfaces, and outline their interrelations where possible. Additionally, we highlight the design principles and research progress in improving the alkaline HER/HOR kinetics by catalyst design and electrolyte optimization employing the aforementioned theories. Finally, the remaining controversies about the pH effects on HER/HOR kinetics as well as the challenges and possible research directions in this field are also put forward. This review aims to provide researchers with a comprehensive understanding of the intrinsic pH effect and inspire the development of more cost-effective and durable alkaline water electrolyzers (AWEs) and anion exchange membrane fuel cells (AMFCs) for a sustainable energy future.

Manipulating the interfacial water structure by electron redistribution for the hydrogen evolution reaction

The sluggish dissociation of water in alkaline electrolytes significantly hinders the kinetics of the hydrogen evolution reaction (HER), particularly on surfaces of Ru-based catalysts. The structure of water at the water-catalyst interface influences this dissociation process, yet controlling the configuration of water molecules is challenging due to their random distribution. In this study, a NiRu alloy supported on nitrogen-doped carbon (NiRu/NC) is selected as a model catalyst to investigate the electron distribution of the catalyst manipulating the adsorption configuration and orientation of water molecules. The introduction of Ni leads to charge transfer from Ni to Ru atoms within the NiRu alloy, causing a notable redistribution of charge that strengthens the local electric fields surrounding the NiRu alloy. These electron-rich Ru sites attract K+ cations to the surface, resulting in an increased presence of K+ cation-hydrated water molecules, which is an H-down configuration with a reduced Ru-H distance. This phenomenon is confirmed by in situ Raman spectroscopy. Consequently, NiRu/NC exhibits outstanding HER performance, achieving low overpotentials of 16 and 344 mV at current densities of 10 and 1000 mA cm-2, respectively.

Osmolyte-Induced Modulation of Hofmeister Series

Natural selection has driven the convergence toward a selected set of osmolytes, endowing them with the necessary efficiency to manage stress arising from salt diversity. This study combines atomistic simulations and experiments to investigate how two osmolytes, glycine and betaine, individually modulate the Hofmeister ion ordering of alkali metal salts (LiCl, KCl, and CsCl) near a charged silica interface. Both osmolytes are found to prevent salt-induced aggregation of the charged entities, yet their mode and degree of relative modulation depend on their intricate interplay with specific salt cations. Betaine's ion-mediated surface interaction maintains Hofmeister ion ordering, whereas glycine alters the relative Hofmeister order of the cation by salt-specific ion desorption from the surface. Experimental validation through surface-enhanced Raman spectroscopy supports these findings, elucidating osmolyte-mediated alterations in interfacial water structures. These observations based on an inorganic interface are reciprocated in amyloid beta 40 dimerization dynamics, highlighting osmolytes' efficacy in mitigating salt-induced aggregation. A molecular analysis suggests that the differential modes of interaction, as found here for glycine and betaine, are prevalent across classes of zwitterionic osmolytes.

Beyond Traditional Synthesis: Electrochemical Approaches to Amine Oxidation for Nitriles and Imines

The electrochemical oxidation of amines to nitriles and imines represents a critical frontier in organic electrochemistry, offering a sustainable pathway to these valuable compounds. Nitriles and amines are pivotal in various industrial applications, including pharmaceuticals, agrochemicals, and materials science. This review encapsulates the recent advancements in the electrooxidation process, emphasizing mechanistic understanding, electrode material innovations, optimization of reaction conditions, and exploration of solvent and electrolyte systems. Additionally, the review addresses the operational parameters that significantly affect the electrooxidation process, such as current density, temperature, and electrode surface, offering insights into their optimization for enhanced performance. By providing a comprehensive view of the current state and prospects of amine electrooxidation to nitriles and imines, this review aims to inspire further development, innovation, and research in this promising area of green chemistry.

Electrolyte-Assisted Structure Reconstruction Optimization of Sn-Zn Hybrid Oxide Boosts the Electrochemical CO2-to-HCOO- Conversion

Electrolyte plays crucial roles in electrochemical CO2 reduction reaction (e-CO2RR), yet how it affects the e-CO2RR performance still being unclarified. In this work, it is reported that Sn-Zn hybrid oxide enables excellent CO2-to-HCOO- conversion in KHCO3 with a HCOO- Faraday efficiency ≈89%, a yield rate ≈0.58 mmol cm-2 h-1 and a stability up to ≈60 h at -0.93 V, which are higher than those in NaHCO3 and K2SO4. Systematical characterizations unveil that the surface reconstruction on Sn-Zn greatly depends on the electrolyte using: the Sn-SnO2/ZnO, the ZnO encapsulated Sn-SnO2/ZnO and the Sn-SnO2/Zn-ZnO are reconstructed on the surface by KHCO3, NaHCO3 and K2SO4, respectively. The improved CO2-to-HCOO- performance in KHCO3 is highly attributed to the reconstructed Sn-SnO2/ZnO, which can enhance the charge transportation, promote the CO2 adsorption and optimize the adsorption configuration, accumulate the protons by enhancing water adsorption/cleavage and limit the hydrogen evolution. The findings may provide insightful understanding on the relationship between electrolyte and surface reconstruction in e-CO2RR and guide the design of novel electrocatalyst for effective CO2 reduction.

Compressive strain in Cu catalysts: Enhancing generation of C2+ products in electrochemical CO2 reduction

Elastic strain in Cu catalysts enhances their selectivity for the electrochemical CO2 reduction reaction (eCO2RR), particularly toward the formation of multicarbon (C2+) products. However, the reasons for this selectivity and the effect of catalyst precursors have not yet been clarified. Hence, we employed a redox strategy to induce strain on the surface of Cu nanocrystals. Oxidative transformation was employed to convert Cu nanocrystals to CuxO nanocrystals; these were subsequently electrochemically reduced to form Cu catalysts, while maintaining their compressive strain. Using a flow cell configuration, a current density of 1 A/cm2 and Faradaic efficiency exceeding 80% were realized for the C2+ products. The selectivity ratio of C2+/C1 was also remarkable at 9.9, surpassing that observed for the Cu catalyst under tensile strain by approximately 7.6 times. In-situ Raman and infrared spectroscopy revealed a decrease in the coverage of K+ ion-hydrated water (K·H2O) on the compressively strained Cu catalysts, consistent with molecular dynamics simulations and density functional theory calculations. Finite element method simulations confirmed that reducing the coverage of coordinated K·H2O water increased the probability of intermediate reactants interacting with the surface, thereby promoting efficient C-C coupling and enhancing the yield of C2+ products. These findings provide valuable insights into targeted design strategies for Cu catalysts used in the eCO2RR.

Terbium- and samarium-doped Li2ZrO3 perovskite materials as efficient and stable electrocatalysts for alkaline hydrogen evolution reactions

The preparation of highly active, rare earth, non-platinum-based catalysts for hydrogen evolution reactions (HER) in alkaline solutions would be useful in realizing green hydrogen production technology. Perovskite oxides are generally regarded as low-active HER catalysts, owing to their unsuitable hydrogen adsorption and water dissociation. In this article, we report on the synthesis of Li2ZrO3 perovskites substituted with samarium and terbium cations at A-sites for the HER. LSmZrO3 (LSmZO) and LTbZrO3 (LTbZO) perovskite oxides are more affordable materials, starting materials in abundance, environmentally friendly due to reduced usage of precious metal and moreover have potential for several sustainable synthesis methods compared to commercial Pt/C. The surface and elemental composition of the prepared materials have been confirmed by X-ray photoelectron spectroscopy (XPS). The morphology and composition analyses of the LSmZO and LTbZO catalysts showed spherical and regular particles, respectively. The electrochemical measurements were used to study the catalytic performance of the prepared catalyst for hydrogen evolution reactions in an alkaline solution. LTbZO generated 2.52 mmol/g/h hydrogen, whereas LSmZO produced 3.34 mmol/g/h hydrogen using chronoamperometry. This was supported by the fact that the HER electrocatalysts exhibited a Tafel slope of less than 120 mV/dec in a 1.0 M alkaline solution. A current density of 10 mA/cm2 is achieved at a potential of less than 505 mV. The hydrogen production rate of LTbZO was only 58.55%, whereas LSmZO had a higher Faradaic efficiency of 97.65%. The EIS results demonstrated that HER was highly beneficial to both electrocatalysts due to the relatively small charge transfer resistance and higher capacitance values.

Approaching Splendid Catalysts for Li-CO2 Battery from the Theory to Practical Designing: A Review

Lithium carbon dioxide (Li-CO2) batteries, noted for their high discharge voltage of approximately 2.8 V and substantial theoretical specific energy of 1876 Wh kg-1, represent a promising avenue for new energy sources and CO2 emission reduction. However, the practical application of these batteries faces significant hurdles, particularly at high current densities and over extended cycle lives, due to their complex reaction mechanisms and slow kinetics. This paper delves into the recent advancements in cathode catalysts for Li-CO2 batteries, with a specific focus on the designing philosophy from composition, geometry, and homogeneity of the catalysts to the proper test conditions and real-world application. It surveys the possible catalytic mechanisms, giving readers a brief introduction of how the energy is stored and released as well as the critical exploration of the relationship between material properties and performances. Specifically, optimization and standardization of test conditions for Li-CO2 battery research is highlighted to enhance data comparability, which is also critical to facilitate the practical application of Li-CO2 batteries. This review aims to bring up inspiration from previous work to advance the design of more effective and sustainable cathode catalysts, tailored to meet the practical demands of Li-CO2 batteries.

Unraveling Stoichiometry Effect in Nickel-Tungsten Alloys for Efficient Hydrogen Oxidation Catalysis in Alkaline Electrolytes

Anion-exchange membrane fuel cells provide the possibility to use platinum group metal-free catalysts, but the anodic hydrogen oxidation reaction (HOR) suffers from sluggish kinetics and its source is still debated. Here, over nickel-tungsten (Ni-W) alloy catalysts, we show that the Ni : W ratio greatly governs the HOR performance in alkaline electrolyte. Experimental and theoretical studies unravel that alloying with W can tune the unpaired electrons in Ni, tailoring the potential of zero charge and the catalytic surface to favor hydroxyl adsorption (OHad). The OHad species coordinately interact with potassium (K+) ions, which break the K+ solvation sheath to leave free water molecules, yielding an improved connectivity of hydrogen-bond networks. Consequently, the optimal Ni17W3 alloy exhibits alkaline HOR activity superior to the state-of-the-art platinum on carbon (Pt/C) catalyst and operates steadily with negligible decay after 10,000 cycles. Our findings offer new understandings of alloyed HOR catalysts and will guide rational design of next-generation catalysts for fuel cells.

Flexible tungsten disulfide superstructure engineering for efficient alkaline hydrogen evolution in anion exchange membrane water electrolysers

Anion exchange membrane (AEM) water electrolysis employing non-precious metal electrocatalysts is a promising strategy for achieving sustainable hydrogen production. However, it still suffers from many challenges, including sluggish alkaline hydrogen evolution reaction (HER) kinetics, insufficient activity and limited lifetime of non-precious metal electrocatalysts for ampere-level-current-density alkaline HER. Here, we report an efficient alkaline HER strategy at industrial-level current density wherein a flexible WS2 superstructure is designed to serve as the cathode catalyst for AEM water electrolysis. The superstructure features bond-free van der Waals interaction among the low Young's modulus nanosheets to ensure excellent mechanical flexibility, as well as a stepped edge defect structure of nanosheets to realize high catalytic activity and a favorable reaction interface micro-environment. The unique flexible WS2 superstructure can effectively withstand the impact of high-density gas-liquid exchanges and facilitate mass transfer, endowing excellent long-term durability under industrial-scale current density. An AEM electrolyser containing this catalyst at the cathode exhibits a cell voltage of 1.70 V to deliver a constant catalytic current density of 1 A cm-2 over 1000 h with a negligible decay rate of 9.67 μV h-1.