Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes: Mechanisms, Challenges, and Prospective Solutions

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.

In Situ Formation of Multi-Principal Element Oxide on a Bulk Nanoporous Intermetallic Alloy for Ultra-Efficient Hydrogen Production at Ampere-Level Current Density

Developing highly efficient and durable electrocatalysts for hydrogen production via water splitting remains a pivotal challenge for sustainable energy. In this work, we present a bulk nanoporous C15 intermetallic alloy synthesized through electrodealloying of a eutectic multiprincipal element precursor. Unlike conventional metallic nanostructures, this catalyst features an ultrathin multiprincipal element oxide (MPEO) layer, which generates abundant active sites and achieves exceptional hydrogen evolution reaction (HER) activity, surpassing most reported catalysts. Crucially, the material demonstrates unprecedented stability at industrial-level current densities (1 A/cm2 at 396 mV), enabled by operando amorphization of the MPEO layer during prolonged operation. This structural evolution stabilizes the catalyst-electrolyte interface while retaining intrinsic activity. Our findings redefine design principles for robust, high-performance electrocatalysts by integrating bulk intermetallic architectures with self-optimizing surface chemistry.

A non-metal doped VTe2 monolayer: theoretical insights into the enhanced mechanism for the hydrogen evolution reaction

Two-dimensional transition metal dichalcogenides (TMDCs), such as vanadium ditelluride (VTe2), have emerged as promising catalysts for the hydrogen evolution reaction (HER) due to their unique layered structures and remarkable electronic properties. However, the catalytic performance of pristine VTe2 remains inferior to that of noble metals. In this study, density functional theory (DFT) calculations were employed to systematically investigate the influence of fourteen different non-metal dopants on the HER activity of VTe2. Our results disclose that N-VTe2, P-VTe2 and As-VTe2 possess exceptional catalytic properties for the HER with the Gibbs free energy of hydrogen adsorption (ΔGH*) values of 0.031, -0.032 and 0.024 eV, respectively. Furthermore, analyses of the geometric and electronic structures reveal that non-metal doping induces localized geometric distortions and charge redistribution, thereby altering the electronic environment of active sites and enhancing catalytic performance. More importantly, a composite descriptor φ, integrating the bond length between doped non-metal atoms and neighboring V atoms (LNM-M) and the pz band center (εpz) of the doped atoms, demonstrates a strong correlation with ΔGH* and may serve as an effective predictor of HER activity. These findings shed light on non-metal doping as an effective strategy for developing efficient, non-noble metal HER catalysts based on TMDCs.

One-Step Electrodeposition of Ternary Metal Sulfide Composite Nanorod Arrays as a Self-Supported Electrocatalyst for the Hydrogen Evolution Reaction

In this study, a self-supported material with a unique ternary metal sulfide nanorod array structure was fabricated in situ on copper foam via a facile one-step electrodeposition approach ((NiCo-Cu)Sx/CF). The electrochemically driven rapid generation of abundant S2- ions from thiourea accelerates their combination with Ni2+ and Co2+, resulting in a catalytically enriched surface on the nanorod array. The high-density nanorod arrays provide maximally accessible active sites, thereby enhancing the hydrogen evolution reaction (HER). The in situ grown self-supported structure effectively eliminates the need for binders (common in conventional catalysts), avoids additional interfacial resistance, and ensures long-term stability during electrocatalytic operation. The synergistic interactions among the metal components (Ni, Co, and Cu) optimize the local electronic environment, creating favorable conditions for catalytic hydrogen evolution. The experimental results demonstrate that the ternary metal sulfide nanocomposite (denoted as (NiCo-Cu)Sx/CF) exhibits superior hydrogen evolution reaction performance compared to its binary counterparts. Remarkably, the catalyst required only 42 and 161 mV overpotential to deliver 10 mA·cm-2 and 100 mA·cm-2 current densities in 1 M KOH, respectively, with 100 h operational stability. This work provides a viable strategy for developing self-supported ternary non-noble metal catalysts for energy conversion applications.

Toward the Ideal Alkaline Hydrogen Evolution Electrocatalyst: a Noble Metal-Free Antiperovskite Optimized with A-Site Tuning

To achieve the ideal non-noble-metal HER electrocatalyst in alkaline media, developing conductive systems with multiple active sites targeting every elementary step in the alkaline HER, is highly desirable but remains a great challenge. Herein, a conductive noble metal-free antiperovskite CdNNi3 is reported with intrinsic metallic characteristics as a highly efficient alkaline HER electrocatalyst, which is designed by the facile A-site tuning strategy with the modulation the electronic structures and interfacial water configurations of antiperovskites. Impressively, the HER performance of CdNNi3 antiperovskite is superior to various state-of-the-art non-noble metal catalysts ever reported, and also outperforms the commercial Raney Ni catalyst when assemble as the cathode in the practical anion exchange membrane water electrolyzer (AEMWE) device. With insights from comprehensive experiments and theoretical calculations, the CdNNi3 can create synergistic dual active sites for catalyzing different elementary steps of the alkaline HER; namely, the Ni site can effectively facilitate the H2O dissociation and OH- desorption, while the unusual Cd-Ni bridge site is active for the optimal H* adsorption and H2 evolution. Such multifunction-site synergy, together with inherent high electrical conductivity, enables the CdNNi3 antiperovskite to fulfill the essential criteria for an ideal non-noble-metal alkaline HER electrocatalyst with excellent performance.

Materials for Electrocatalysis: Future Prospects in Energy Conversion

Electrocatalysts play a pivotal role in various energy conversion processes, such as water splitting, batteries, carbon dioxide reduction, and fuel cell reactions, by significantly reducing the energy barrier and enhancing reaction kinetics. This review highlights the potential of earth-abundant electrocatalysts, with a particular focus on their capabilities in critical electrochemical reactions, including oxygen evolution reaction, carbon dioxide reduction reaction, oxygen reduction reaction and hydrogen evolution reaction. Emphasis is also placed on bifunctional, trifunctional, and tetrafunctional performance, showcasing their adaptability and effectiveness across diverse energy applications. Exploration is done on a range of promising materials, including transition metal chalcogenides, MXenes, metal-organic frameworks, covalent organic frameworks, and layered double hydroxides. By examining their intrinsic properties, structural versatility, and surface engineering strategies, this review sheds light on the factors that govern their catalytic efficiency and stability. The integration of experimental advancements with theoretical insights provides a deeper understanding of mechanisms driving their catalytic activity. Additionally, we address the scalability, cost-effectiveness, and environmental impact of these materials, underlining their potential for large-scale deployment. By synthesizing recent progress and identifying challenges, this work delivers a roadmap for the model and application of multifunctional electrocatalysts, fostering innovations that align with the goals of sustainable energy systems.

Driving Electrochemical Organic Hydrogenations on Metal Catalysts by Tailoring Hydrogen Surface Coverages

Electrochemical hydrogenation, powered by renewable electricity, represents a promising sustainable approach for organic synthesis and the valorization of biomass-derived chemicals. Traditional strategies often rely on alkaline conditions to mitigate the competing hydrogen evolution reaction, posing challenges in sourcing hydrogen atoms for hydrogenation, which can be addressed through localized water dissociation on the electrode surface. In this study, we present a computationally guided design of electrochemical hydrogenation catalysts by optimizing hydrogen coverage density and binding strength on the electrode. Our theoretical investigations identify Cu, Au, and Ag - metals with moderate hydrogen coverage - as promising catalysts for electrochemical hydrogenations in alkaline media. These predictions are experimentally validated using a model organic substrate (acetophenone), achieving yields and faradaic efficiencies of up to 90%. Additionally, Cu, a nonprecious metal, is demonstrated to selectively hydrogenate a wide range of unsaturated compounds, including C═O, C═C, C≡C, and C≡N bonds, at low potentials with moderate to excellent conversion rates and chemoselectivities. This work highlights the potential of tailoring hydrogen coverage on electrode surfaces to rationally design nonprecious metal electrocatalysts for efficient organic hydrogenations. The insights gained here are expected to inform the development of more effective catalysts for organic hydrogenations and other industrially relevant chemical transformations.

Transition metal phosphide/ molybdenum disulfide heterostructures towards advanced electrochemical energy storage: recent progress and challenges

Transition metal phosphide @ molybdenum disulfide (TMP@MoS2) heterostructures, consisting of TMP as the core main catalytic body and MoS2 as the outer shell, can solve the three major problems in the field of renewable energy storage and catalysis, such as lack of resources, cost factors, and low cycling stability. The heterostructures synergistically combine the excellent conductivity and electrochemical performance of transition metal phosphides with the structural robustness and catalytic activity of molybdenum disulfide, which holds great promise for clean energy. This review addresses the advantages of TMP@MoS2 materials and their synthesis methods-e.g., hydrothermal routes and chemical vapor deposition regarding scalability and cost. Their electrochemical energy storage and catalytic functions e.g., hydrogen and oxygen evolution reactions (HER and OER) are also extensively explored. Their potential within battery and supercapacitor technologies is also assessed against leading performance metrics. Challenges toward industry-scale scalability, longevity, and environmental sustainability are also addressed, as are optimization and large-scale deployment strategies.

A Programmable Nanoparticle Conversion Pathway to Monodisperse Polyelemental High Entropy Alloy, Intermetallic, and Multiphase Nanoparticles

Polyelemental nanoparticles (PE NPs), those consisting of four or more elements, exhibit unique properties from synergistic compositional effects. Examples include high entropy alloys, high entropy intermetallics, and multiphase types, including Janus and core-shell architectures. Although colloidal syntheses offer excellent structural control for mono- and bi-elemental compositions, achieving the same control for PE NPs remains challenging. Here, this challenge is addressed with a NP conversion strategy wherein different types of PE NPs - including high entropy alloy, high entropy intermetallic, and multiphase Janus nanoparticles - are achieved through thermal transformation of readily synthesized colloidal core-shell NPs. Through systematic variations in stoichiometry and metal identity to the core-shell precursor NPs, along with atomistic simulations that probe phase stabilities, we deduce that the final mixing states of the various NPs are governed by the balance between the enthalpy and entropy of mixing. Moreover, our annealing method allows us to trap NPs at intermediate states of mixing, creating distinct surface ensembles that were evaluated as catalysts for the hydrogen evolution reaction. This study is the first, to our knowledge, to report colloidally derived precursor NPs enabling the synthesis of all types of PE NPs in a single process. This NP conversion strategy offers a general route to diverse PE NPs.

A Conjugated Porous Organic Polymer as a Metal-Free Bifunctional Electrocatalyst for Enhanced Water Splitting

A conjugated porous organic polymer (SMCOP-4) with imine linkage and triazine functional moiety was rationally designed and synthesized by an imine condensation reaction. The π-conjugated network of SMCOP-4 facilitates electron mobility, enhancing electrochemical activity. Metal-free electrocatalyst SMCOP-4 shows superior performance for HER and OER with a low overpotential of 139 mV and 295 mV, respectively, at 10 mA cm-2 current density and with small Tafel slopes in alkaline electrolytes. Along with the low overpotential values, the electrocatalyst is highly stable at electrochemical conditions. Further, density functional theory calculations were carried out to identify the most active sites in catalyzing the HER and OER on the SMCOP-4 catalyst.

Laser-Induced Co-Doped FePS3 with Massively Phosphorus Sulfur Vacancies Nanosheet for Efficient and Highly Stable Electrocatalytic Oxygen Reaction

Purposely optimizing material structure to reduce the energy change of the rate-determining step (RDS) for promoting oxygen evolution reaction (OER) catalytic performance is a major strategy to enhance the energy efficiency of electrocatalytic water splitting. Density functional theory (DFT) simulations indicate that creating a large number of defects on or inside the 2D FePS3 is very beneficial for its catalytic reaction of OER, especially when there are more defects, the structural diversity of the surface is more conducive to the adsorption and reaction of intermediates. In particular, when Co-doped FePS3 surfaces produce a large number of S and P defects and expose metallic Fe as active sites, its catalytic performance, especially the catalytic stability, is significantly enhanced. A facile and efficient laser-ablation-in-liquid method is then designed to combine Co with 2D layered crystal FePS3. Amazingly, the laser-induced (Fe0.53Co0.46)PS3 sample exhibits excellent OER performance, with an overpotential at 288 mV and a small Tafel slope of 58.3 mV dec-1. Moreover, (Fe0.53Co0.46)PS3 operates stably for 138 h at 10 mA cm-2 and 27 h at 100 mA cm-2, which shows that the stability of (Fe0.53Co0.46)PS3 far exceeds that of most of OER catalysts of Fe─Co system so far, and the comprehensive OER performance is in the first echelon of transition metal catalyst systems. This work proposes an in-depth understanding of the structural mechanism design of massive phosphorus sulfur vacancies by laser-induced manufacturing and will shed new light on promoting the stability of transition metal-based OER catalysts without any precious alternatives.

Manganese-Based Metal-Organic Frameworks and Their Derivatives for Electrochemical Water Splitting: Recent Advances and Future Outlook

Metal-organic frameworks (MOFs) and their derivatives have recently attracted significant interest as promising candidates in water splitting due to their well-defined structural and electronic features, three-dimensional architecture, high surface area, abundance of active sites, remarkable stability, and improved capabilities for mass transport and diffusion. Mn-based MOFs and their derivatives have been extensively studied and demonstrated significant potential in water splitting, inspired largely by the natural photosystem-II. Despite the development of numerous Mn-based electrocatalysts, Mn-MOFs stand out due to their strong synergistic interactions, tunable electronic properties, efficient charge and mass transfer, and straightforward synthesis. However, recent reviews on MOFs have largely overlooked the specific advancements in Mn-MOFs and their derivatives for water-splitting applications. By providing an overview of the uses of Mn-MOFs and their materials, this article seeks to close that gap. It looks at their stability, porosity, and structure as well as how they are used in water splitting. This study offers a deeper knowledge of the properties and uses of Mn-MOFs and their related materials by drawing on groundbreaking research. The link between structure, property, and performance is examined, current advancements in the subject are discussed, difficulties faced are addressed, and potential future developments are taken into account.

Modulation of Hydrogen Desorption Capability of Ruthenium Nanoparticles via Electronic Metal-Support Interactions for Enhanced Hydrogen Production in Alkaline Seawater

The development of efficient and stable electrocatalysts for the hydrogen evolution reaction (HER) is essential for the realization of effective hydrogen production via seawater electrolysis. Herein, the study has developed a simple method that combines electrospinning with subsequent thermal shock technology to effectively disperse ruthenium nanoparticles onto highly conductive titanium carbide nanofibers (Ru@TiC). The electronic metal-support interactions (EMSI) resulted from charge redistribution at the interface between the Ru nanoparticles and the TiC support can optimize hydrogen desorption kinetics of Ru sites and induce the hydrogen spillover phenomenon, thereby improving hydrogen evolution. As a result, the Ru@TiC catalyst exhibits outstanding HER activity, requiring low overpotentials of only 65 mV in alkaline seawater at the current density of 100 mA cm-2. Meanwhile, Ru@TiC demonstrates excellent stability, maintaining consistent operation at 500 mA cm-2 for at least 250 hours. Additionally, an anion exchange membrane electrolyzer incorporating Ru@TiC operated continuously for over 500 hours at 200 mA cm-2 in alkaline seawater. This study highlights the significant potential of robust TiC supports in the fabrication of efficient and enduring electrocatalysts that enhance hydrogen production in complex seawater environments.

Heterostructured Electrocatalysts: from Fundamental Microkinetic Model to Electron Configuration and Interfacial Reactive Microenvironment

Electrocatalysts can efficiently convert earth-abundant simple molecules into high-value-added products. In this context, heterostructures, which are largely determined by the interface, have emerged as a pivotal architecture for enhancing the activity of electrocatalysts. In this review, the atomistic understanding of heterostructured electrocatalysts is considered, focusing on the reaction kinetic rate and electron configuration, gained from both empirical studies and theoretical models. We start from the fundamentals of the microkinetic model, adsorption energy theory, and electric double layer model. The importance of heterostructures to accelerate electrochemical processes via modulating electron configuration and interfacial reactive microenvironment is highlighted, by considering rectification, space charge region, built-in electric field, synergistic interactions, lattice strain, and geometric effect. We conclude this review by summarizing the challenges and perspectives in the field of heterostructured electrocatalysts, such as the determination of transition state energy, their dynamic evolution, refinement of the theoretical approaches, and the use of machine learning.

Probing Under-Utilized Melem as Host Scaffold with Strategic Modulation of Cobalt Oxidation State to Accelerate Alkaline Water Splitting

The potential of cobalt catalysts for sustainable, carbon-neutral hydrogen production through water splitting can be fully achieved by fundamental understanding-driven strategic tuning of metal oxidation states on a uniform scaffold. In pursuit of a stable scaffold that can enhance electrocatalytic activity through metal-N synergism and envisaging that g-C3N4 has inherited its properties from its structurally distinct predecessor, Melem; a comprehensive exploration of s-heptazine (Melem, M) is furnished as host for strategic tuning of cobalt electrocatalysts having variable oxidation states. Co(II)-doped heptazine (CoII@M) catalyzed oxygen evolution reaction (OER) with an overpotential of 302 mV achieving 50 mA cm-2 current density, with minimal charge-transfer resistance (0.41 Ω). Co(0)-doped heptazine nanotube (Co0@M) facilitated the arduous H-O-H bond cleavage for alkaline hydrogen evolution reaction (HER), achieving 50 mA cm-2 current density at 206 mV overpotential, with low charge-transfer resistance of 0.66 Ω, attesting to the scaffold's assistance to electron transfer. The CoII@M||Co0@M assembly shows low cell voltage (1.637 V @ 10 mA cm-2) and promising stability (114 h) for total water splitting. s-heptazine scaffold ensured finer dispersion and stabilization of cobalt active sites in a corrosive environment. The scaffold's substantial stability, attributes to its nitrogen-rich core and extensive H-bonding, unlocks the potential of under-explored melem-based systems for electrocatalytic applications.

Synergistic effects of fluorine doping on CoPS electrocatalysts for highly efficient hydrogen evolution reaction

Exploring earth-abundant electrocatalysts for efficient hydrogen evolution reaction (HER) is important for the development of clean and renewable hydrogen energy. Herein, we demonstrated that fluorine anion doping into CoPS significantly enhanced its hydrogen evolution reaction (HER) activity. Controlled fluorination modulated the surface electronic structure of CoPS active sites, forming an optimized F-CoPS electrocatalyst that exhibited superior performance, achieving an overpotential of only 74 mV at 10 mA cm-2 and 141 mV at 50 mA cm-2, along with remarkable stability over 50 hours. This study provides a novel and feasible approach to enhance the HER performance of ternary pyrite-type transition-metal phosphosulfides.

Enhanced Alkaline Water Electrolysis by the Rational Decoration of RuOx with the In Situ-Grown CoFe Nanolayer

Rational engineering of the surfaces of heterogeneous catalysts (especially the surfaces of supported metals) can endow intriguing catalytic functionalities for electrochemical reactions. However, it often requires complicated steps, and even if it does not, breaking the trade-off between activity and stability is quite challenging. Herein, we present a strategy for reconstructing supported catalysts via in situ growth of metallic nanolayers from the perovskite oxide support. When Ru-coated LaFe0.9Co0.1O3 is thermally reduced, the CoFe nanoalloy spontaneously migrates onto the Ru and greatly increases the physicochemical stability of Ru in alkaline water electrolysis. Benefiting from an 81% reduction in Ru dissolution after decoration, it operates for over 200 h without noticeable degradation. Furthermore, the underlying Ru modifies the electronic structure and surface adsorption properties of the CoFe overlayer toward reaction intermediates, synergistically catalyzing both the oxygen evolution reaction and the hydrogen evolution reaction. Specifically, the mass activity of the oxygen evolution reaction is 64.1 times greater than that of commercial RuO2. Our work highlights a way to protect inherently unstable Ru from dissolution while allowing it to influence surface kinetics from the subsurface sites in heterogeneous catalysts.

Oxygen Reduction Allows Morphology-Tunable Copper Nanoparticle Electrodeposition from Aqueous Nanodroplets

Expanding the tunability of metallic nanoparticles in simple and cost-effective manners is essential for developing heterogeneous catalysts needed for the energy conversion systems of the future. Many current methods of switching between different nanoparticle morphologies and compositions include the use of surfactants, pH adjustments or other coreactants. One relatively unexplored and new route to tuning these nanoparticle properties involves taking advantage of the organic phase surrounding the aqueous droplets used in nanodroplet mediated electrodeposition techniques. These aqueous nanodroplets contain metal precursor salts that electrodeposit nanoparticles when they collide with a sufficiently biased electrode. Organic solvents such as 1,2-dichloroethane, known to have relatively high dioxygen solubilities compared to water, may provide an oxygen rich environment at the droplet interface, promoting heterogeneous oxygen reduction. In this work, the oxygen reduction reaction is used in the electrodeposition of copper to tune the resulting nanoparticle morphologies and compositions. These effects are also compared to those in bulk aqueous electrodeposition. The properties of the nanoparticles and the role of oxygen reduction in their synthesis are probed through electrochemical techniques, electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. When only reducing copper at the electrode, the resulting nanoparticles possess a range of cubic and spherical morphologies and multiple copper oxidation states indicative of zerovalent copper and copper oxide nanoparticles. When reducing both copper and oxygen, the electrodeposited nanoparticles possess a distinctive rod-like morphology with oxidation states and atomic ratios indicative of copper hydroxide. The latter nanoparticle morphology and composition was not attainable when copper was electrodeposited from a bulk aqueous solution at the same applied reducing potential. Our results show that one can take advantage of the fundamental electrochemistry taking place at the aqueous|organic|electrode interface to tune key properties of copper nanoparticles.

Rare-Earth Oxychlorides as Promoters of Ruthenium Toward High-Performance Hydrogen Evolution Electrocatalysts for Alkaline Electrolyzers

Developing efficient electrocatalysts for hydrogen evolution reaction (HER) in alkaline environments is vital for hydrogen production, owing to the extra water dissociation and hydroxyl desorption steps. Here, rare-earth oxychlorides (REOCl) are proposed as innovative promoters for ruthenium as HER electrocatalyst in alkali. The lamellar structure of REOCl with weakly bond [Cl] layers can facilitate the formation of an internal electric field that enhances interphase charge transfer. Taking ruthenium/ neodymium oxychloride (Ru/NdOCl) composites as a case study, sub ≈4 nm Ru nanoparticles are successfully embedded into NdOCl crystals through a rapid self-exothermic process, and the highly-coupled Ru-Cl/O-Nd interfaces are observed as metallic Ru particles with the edge of the NdOCl lamellar layers, where the [Nd2O2] and [Cl] layers act as the negative and positive charge transfer channels, respectively. The enhanced charge transfer between REOCl and Ru makes the highly-coupled Ru/REOCl catalysts show better electrocatalytic activity than both the benchmark Pt and Ru catalysts in alkaline electrolyte. This work will encourage more novel promoters for electrocatalysis and other emerging technologies.

Scrutinization of late first-row transition metals decorated octagonal boron (B8) ring complexes as single-atom catalysts for green hydrogen and oxygen production

Hydrogen as fuel has gained large interest nowadays as a green energy source. Single-atom catalysis has emerged as a promising strategy for producing hydrogen. Herein, we investigated the late first row transition metals (TM = Co, Cu, Zn, Ni and Fe) adsorbed on eight-membered boron ring (TM@B8) as potential single-atom catalysts (SAC) towards hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER), aiming to identify less expensive electrocatalysts with high efficiency. Various properties including interaction energy (E int), energies of frontier molecular orbitals (FMOs), natural bonding orbital (NBO) charges, total density of state (TDOS) spectra and non-covalent interaction (NCI) analyses of considered complexes are explored. These findings demonstrated that both pure TM@B8 and hydrogen-adsorbed TM@B8 complexes have both structural and electronic stability. The Co@B8 complex demonstrated a favorable Gibbs free energy of 0.16 eV toward HER under gaseous conditions. Fe@B8 showed better OER activity having overall η OER of 1.14 eV. These outcomes show the promising potential of TM@B catalysts for both HER and OER processes.

Ordered Pt3Mn Intermetallic Setting the Maximum Threshold Activity of Disordered Variants for Glycerol Electrolysis

Glycerol electrolysis is a promising strategy for generating hydrogen at the cathode and value-added products at the anode. However, the effect of the atomic distribution within catalysts on their catalytic performance remains largely unexplored, primarily because of the inherent complexity of the glycerol oxidation reaction (GOR). Herein, an ordered Pt3Mn (O-Pt3Mn) intermetallic compound and a disordered Pt3Mn (D-Pt3Mn) alloy are used as model catalysts, and their performance in the GOR and hydrogen evolution reaction (HER) is studied. O-Pt3Mn consistently outperforms D-Pt3Mn and commercial Pt/C catalysts. It can generate high-value glycerate at a notable production rate of 17 mM h-1 while achieving an impressively low cell voltage of 0.76 V for glycerol electrolysis, which is ∼0.98 V lower than that required for water electrolysis. Statistical analysis using theoretical calculations reveals that Pt-Pt-Pt hollow sites are crucial for the catalytic GOR and HER. The averaged adsorption energies of key intermediates (simplified as C*, O*, and H*) on diverse catalysts closely correlate with their experimentally observed activity. Our proposed linear models accurately predict these adsorption energies, exhibiting high correlation coefficients ranging from 0.97 to 0.99 and highlighting the significance of the distribution of the topmost and subsurface-corner Mn atoms in determining these adsorption energies. By sampling all possible Mn configurations within the fitted linear models, we confirm that O-Pt3Mn establishes the maximum activity threshold for the GOR and HER compared with any disordered variant. This study presents an innovative framework for exploring the effect of the atomic distribution within catalysts on their catalytic performance and designing high-performance catalysts for complex reactions.

Triacylphosphines as a Novel Class of Phosphorus Sources for the Synthesis of Transition Metal Phosphide Nanoparticles

Transition metal phosphide (TMP) nanoparticles (NPs) are versatile materials for energy conversion/storage applications due to their robustness and many possibilities to tailor NPs' electronic, physical, and chemical properties. One of the hurdles toward their broader implementation is their challenging synthesis exacerbated by the limited choice of phosphorus precursors. On the one hand, the synthesis of TMP NPs can employ various alkyl- or arylphosphines requiring prolonged heating at high temperatures, while on the other hand, highly reactive P(SiMe3)3, white phosphorus, or PH3 pose additional obstacles associated with their hazardous nature, high cost, and limited availability. This work introduces the use of acylphosphines as a new class of phosphorus sources for synthesizing phosphide NPs. They are shown to react with respective metal chlorides at moderate temperatures as low as 250 °C yielding poorly crystalline NPs, which can later be crystallized at 305 °C. After ligand stripping with HPF6, NPs are found to be an effective electrocatalyst for the hydrogen evolution reaction in the acidic medium exhibiting overpotentials as low as 50 mV at a current density of 10 mA cm-2, which is among the lowest overpotentials for these materials and is quite competitive to commercial platinum-based catalysts.

Corrosion-resistant titanium-based electrodes synergistically stabilized with polymer for hydrogen evolution reaction

The economic and reasonable design of highly stable and corrosion-resistant electrodes is fundamental to achieving the industrial-scale hydrogen productions via water electrolysis, but electrodes' premature failures are often caused by corrosion and stress damage. Therefore, these challenges are successfully solved by utilizing conductive and crack-resistant polyaniline "stabilizer" with a mild chemical plating process to construct the catalytic electrode on a titanium substrate (15 %PANI-NiB@Ti) in the present work. The 15 %PANI-NiB@Ti catalytic electrodes have been in continuous operation for 350 h at the current density of 200 mA cm-2 with the high efficiency of 98.4 % in a 323.15 K environment. With the high economy and universality, the catalytic electrodes have good catalytic performance and reliability in the extreme industrial environments, such as high temperature, air, and high current density. Except for the above advantages, the 15 %PANI-NiB@Ti catalytic electrodes also have good cracking resistance, which provides a novel and feasible approach to the industrial application of transition metal catalytic electrodes.

High Mass Transfer Rate in Electrocatalytic Hydrogen Evolution Achieved with Efficient Quasi-Gas Phase System

The adhesion of H2 bubbles on the electrode surface is one of the main factors limiting the performance of H2 evolution of electrolytic water, especially at high current density. To overcome this problem, here a "quasi-gas phase" electrolytic water reaction system based on capillary effect is proposed for the first time to improve the mass transfer efficiency of H2. The typical feature of this reaction system is that the main site of H2 evolution reaction is transferred from the bulk aqueous solution to the gas phase environment above the bulk aqueous solution, thus effectively inhibiting the aggregation of H2 bubbles and reducing the resistance of their diffusion away. Electrochemical test results show that the proposed quasi-gas phase system can significantly reduce the potential required in H2 evolution reaction process at high current density compared with the conventional electrolytic reaction system. Specifically, the overpotential potential is reduced by 0.31 V when the H2 evolution current density of 250 mA cm-2 is achieved.

Ni-Mo nanostructure alloys as effective electrocatalysts for green hydrogen production in an acidic medium

Achieving a net-zero emissions economy requires significant decarbonization of the transportation sector, which depends on the development of highly efficient electrocatalysts. Electrolytic water splitting is a promising approach to this end, with Ni-Mo alloys emerging as strong candidates for hydrogen production catalysts. This study investigates the electrodeposition of Ni and Ni-Mo nanostructured alloys with high molybdenum content onto low-carbon steel cathodes using a novel alkaline green lactate bath. Catalyst morphology, microstructure, and composition were characterized using SEM, XRD, XPS, and EDX. Results showed molybdenum content increased with current density, ranging from 40.14 wt% at 1.12 mA cm-2 to 61.68 wt% at 5.56 mA cm-2, with average particle sizes of 39.4 nm for Ni, 20.7 nm for Ni-2Mo (56% Mo), and 30.8 nm for Ni-4Mo (65% Mo). The alloys comprised tetragonal MoNi4, metallic Ni, metallic Mo, and MoO3 phases. Ni-4Mo exhibited superior HER performance in 0.5 mol L-1 H2SO4, with the lowest Tafel slope (-113 mV dec-1), highest exchange current density (1.250 mA cm-2), and good stability after 250 cycles. It also outperformed Ni-2Mo at -50 mA cm-2, demonstrating its promise as a durable and efficient HER catalyst in acidic media.

Cocktail Effect of 4d/5d Band Twisted High-Entropy Alloys on Carbon Nanotube for Hydrazine Splitting

Herein, multi-walled carbon nanotubes (CNT) embedded with RuPdIrPtAu-high entropy alloys (HEA) via pulsed laser irradiation in liquids are successfully fabricated. The resultant composite synergistically enhances hydrazine oxidation reaction (HzOR)-boosted water electrolysis. Notably, HEA with ≈2-5 nm size, are uniformly distributed across the surface of the CNTs. An optimized HEA/CNT-10 demonstrates exceptional performance in oxygen and hydrogen evolution reactions (OER and HER), depicted by ultralow overpotentials of 30.7 and 330 mV at 10 mA cm-2, respectively. By replacing OER with HzOR, HEA/CNT-10 needs a lower potential of 0.1 V to accomplish 10 mA cm-2, as compared to OER (1.56 V vs. RHE). Moreover, the hydrazine splitting electrolyzer desirable a small voltage of 0.242 V to attain 10 mA cm-2, while maintaining exceptional stability. Experimental and DFT studies validate the cocktail effects and role of multiple metal-sites in HEA/CNT-10, which significantly enhance the efficiency of parallel HER||HzOR processes, highlighting its potential in energy-efficient, hydrogen production. In situ Raman probe indicated the configuration of an acidic environment, monitoring of H3O+, during HER, despite the basic conditions. This is attributed to the dominance of the Heyrovsky step, facilitated by the high catalytic activity of the HEA, coupled with protonation of the CNT surface.

Unconventional Hexagonal Close-Packed High-Entropy Alloy Surfaces Synergistically Accelerate Alkaline Hydrogen Evolution

Accelerating the alkaline hydrogen evolution reaction (HER), which involves the slow cleavage of HO-H bonds and the adsorption/desorption of hydrogen (H*) and hydroxyl (OH*) intermediates, requires developing catalysts with optimal binding strengths for these intermediates. Here, the unconventional hexagonal close-packed (HCP) high-entropy alloy (HEA) atomic layers are prepared composed of five platinum-group metals to enhance the alkaline HER synergistically. The breakthrough is made by layer-by-layer heteroepitaxial deposition of subnanometer RuRhPdPtIr HEA layers on the HCP Ru seeds, despite the thermodynamic stability of Rh, Pd, Pt, and Ir in a face-centered cubic (FCC) structure except for Ru. The synchrotron X-ray absorption spectroscopy (XAS) confirms the atomic mixing and coordination environment of HCP RuRhPdPtIr HEA. Most importantly, they exhibit notable improvements in both electrocatalytic activity and durability for the HER in an alkaline environment, as compared to their FCC RuRhPdPtIr counterparts. Electrochemical measurements, operando XAS analysis, and density functional theory unveil that the binding strengths of H* and OH* intermediates on the active Pt and Ir sites can be weakened and strengthened to a moderate level, respectively, by mixing non-active Ru, Rh, and Pd atoms with Pt and Ir atoms within the HCP HEA with strong synergistic electronic effects.

Highly Active and Durable Nanostructured Nickel-Molybdenum Coatings as Hydrogen Electrocatalysts via Solution Precursor Plasma Spraying

The increasing demand for green hydrogen is driving the development of efficient and durable electrocatalysts for the hydrogen evolution reaction (HER). Nickel-molybdenum (NiMo) alloys are among the best HER electrocatalysts in alkaline electrolytes, and here we report a scalable solution precursor plasma spraying (SPPS) process to produce the highly active Ni4Mo electrocatalysts directly onto metallic substrates. The NiMo coating coated onto inexpensive Ni mesh revealed an excellent HER performance with an overpotential of only 26 mV at -10 mA cm-2 with a Tafel slope of 55 mV dec-1. Excellent operational stability with minimum changes in overpotential were also observed even after extensive 60 hour high-current stability test. In addition, we investigate the influence of different substrates over the catalytic performance and operational stability. We also proposed that a slow, but consistent, dissolution of Mo is the primary degradation mechanism of NiMo-based coatings. This unique SPPS approach enables the scalable production of exceptional NiMo electrocatalysts with remarkable activity and durability, positioning them as ideal cathode materials for practical applications in alkaline water electrolysers.

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.

Ruthenium clusters decorated on lattice expanded hematite Fe2O3 for efficient electrocatalytic alkaline water splitting

Electrocatalytic water splitting in alkaline media plays an important role in hydrogen production technology. Normally, the catalytic activity of commonly used transition metal oxides usually suffers from unsatisfactory electron conductivity and unfavorable binding strength for transition intermediates. To boost the intrinsic catalytic activity, we propose a rational strategy to construct lattice distorted transition metal oxides decorated with noble-metal nanoclusters. This strategy is verified by loading ruthenium clusters onto lithium ion intercalated hematite Fe2O3, which leads to significant distortion of the FeO6 unit cells. A remarkable overpotential of 21 mV with a Tafel slope of 39.8 mV dec-1 is achieved at 10 mA cm-2 for the hydrogen evolution reaction in 1.0 M KOH aqueous electrolyte. The assembled alkaline electrolyzer can catalyse overall water splitting for as long as 165 h at a current density of 250 mA cm-2 with negligible performance degradation, indicating great potential in the field of sustainable hydrogen production.

Uniform anchoring of MoS2 nanosheets on MOFs-derived CoFe2O4 porous nanolayers to construct heterogeneous structural configurations for efficient and stable overall water splitting

Rational interfacial engineering and morphology modulation are recognized as effective strategies to modulate the electronic structure and improving the activity of spinel materials. In this paper, we report a strategy of Fe-induced creation of porous nanolayers of CoFe2O4 with unique morphology derived from MOFs by introducing ferrocene, and then constructed CoFe2O4/MoS2 heterostructures were fabricated by homogeneously anchoring MoS2 nanosheets onto the surface of CoFe2O4. The triple synergistic effect of heterogeneous interfaces, highly active Mo(IV) sites, and unsaturated S effectively accelerates the cycling process between Fe(III)/Fe(II) and Co(III)/Co(II), which in turn enhances the adsorption of reactive intermediates on the active sites, as further corroborates by density functional theory (DFT) calculations. As a result, the CoFe2O4/MoS2 heterostructured catalysts prepared without noble metals exhibit high catalytic performance, necessitating only 270 mV and 229 mV to achieve the current density of 100 mA·cm-2 for OER and HER respectively, which is superior to most of the reported catalysts of interest. In addition, when used in an alkaline electrolyzer, it provides a current density of 10 mA·cm-2 at 1.54 V cell voltage. This work provides a new way for the rational construction of bifunctional water electrolytic catalysts.

Iron Phosphide Nanobundles for Efficient Electrochemical Hydrogen Evolution Reaction in Acidic and Basic Media

Earth-abundant transition metal phosphide (TMP) nanomaterials have gained significant attention as potential replacements for Pt-based electrocatalysts in green energy applications, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. In particular, FeP nanostructures exhibit superior electrical conductivity and high stability. Moreover, their diverse composition and unique crystal structures position FeP nanomaterials as emerging candidates for HER electrocatalysts. However, the synthesis or fabrication method employed for FeP nanostructures can significantly affect their overall electrocatalytic properties. For example, the solution synthesis of pure-phase FeP nanostructures remains challenging due to the formation of multiple binary phases and undesirable agglomeration. In this work, we use a simple approach to synthesizing FeP nanobundles by reacting β-FeOOH (iron oxyhydroxide) with trioctylphosphine (TOP). FeP nanobundles were evaluated as HER electrocatalysts in both acidic and basic conditions, demonstrating good HER activity with overpotential values of 170 and 338 mV at a current density of -10 mA cm-2 in acidic and alkaline solutions, respectively. Additionally, they exhibited low values of Tafel slopes in both acidic and alkaline environments. In acidic media with a pH of 0.45, the nanobundles showed no signs of deterioration for up to 15 h (-50 mA cm-2). In basic media with a pH of 13.69, the nanobundles remain stable for up to 8 h (-50 mA cm-2). These results demonstrate a simple and effective method for producing highly efficient earth-abundant and cost-effective TMP-based electrocatalysts, which could play a vital role in the hydrogen economy of the future.

Electrospun Micro/Nanofiber-Based Electrocatalysts for Hydrogen Evolution Reaction: A Review

Hydrogen is regarded as an ideal energy carrier to cope with the energy crisis and environmental problems due to its high energy density, cleanliness, and renewability. Although there are several primary methods of industrial hydrogen production, hydrogen evolution reaction (HER) is an efficient, eco-friendly, and sustainably green method for the preparation of hydrogen which has attracted considerable attention. However, this technique is characterized by slow reaction kinetics and high energy potential owing to lack of electrocatalysts with cost-effective and high performance which impedes its scale-up. To address this issue, various studies have focused on electrospun micro/nanofiber-based electrocatalysts for HER due to their excellent electron and mass transport, high specific surface area, as well as high porosity and flexibility. To further advance their development, recent progress of highly efficient HER electrospun electrocatalysts is reviewed. Initially, the characteristics of potential high-performance electrocatalysts for HER are elucidated. Subsequently, the advantages of utilizing electrospinning technology for the preparation of electrocatalysts are summarized. Then, the classification of electrospun micro/nanofiber-based electrocatalysts for HER are analyzed, including metal-based electrospun electrocatalyst (noble metals and alloys, transition metals, and alloys), metal-non-metal electrocatalysts (metal sulfide-based electrocatalysts, metal oxide-based electrocatalysts, metal phosphide-based electrocatalysts, metal nitride-based electrocatalysts, and metal carbide-based electrocatalysts), metal-free electrospun micro/nanofiber-based electrocatalysts, and hybrid electrospun micro/nanofiber-based electrocatalysts. Following this, enhancement strategies for electrospun micro/nanofiber-based electrocatalysts are discussed. Finally, current challenges and the future research directions of electrospun micro/nanofiber-based electrocatalysts for HER are concluded.

Nb Doping Induced the Formation of Protective Layer to Improve the Stability of Fe-Ni3S2 for Seawater Electrolysis

The seawater electrolysis to produce hydrogen is a significant topic on alleviating the energy crisis. Here, the Fe, Nb-Ni3S2 catalyst is prepared by metal-doping strategy, and it shows high oxygen evolution reaction (OER) activity in alkaline medium, and only needs 1.491 V to deliver a current density of 100 mA cm-2 in simulated seawater. Using Fe, Nb-Ni3S2 as a bifunctional catalyst, the two-electrode electrolyzer only requires a voltage of 1.751 V (without impedance compensation) to drive the current density of 50 mA cm-2, and can run over 150 h stably in the simulated seawater. Importantly, In situ Raman test demonstrates that the outstanding performance of Fe, Nb-Ni3S2 in simulated seawater is ascribed to the in situ formed sulfate protective layer induced by Nb doping, which can effectively inhibit the corrosion of chloride ion, while the protective layer is absent for Fe-Ni3S2. The stable operation of simulated seawater electrolysis under industrial current density further confirms the stability improvement mechanism of forming protective layer. In short, this study provides a new strategy of using Nb dopants inducing the formation of protective layer to enhance the stability of seawater electrolysis.

Rapid Synthesis of Ruthenium-Copper Nanocomposites as High-Performance Bifunctional Electrocatalysts for Electrochemical Water Splitting

Development of high-performance, low-cost catalysts for electrochemical water splitting is key to sustainable hydrogen production. Herein, ultrafast synthesis of carbon-supported ruthenium-copper (RuCu/C) nanocomposites is reported by magnetic induction heating, where the rapid Joule's heating of RuCl3 and CuCl2 at 200 A for 10 s produces Ru-Cl residues-decorated Ru nanocrystals dispersed on a CuClx scaffold, featuring effective Ru to Cu charge transfer. Among the series, the RuCu/C-3 sample exhibits the best activity in 1 m KOH toward both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with an overpotential of only -23 and +270 mV to reach 10 mA cm-2, respectively. When RuCu/C-3 is used as bifunctional catalysts for electrochemical water splitting, a low cell voltage of 1.53 V is needed to produce 10 mA cm-2, markedly better than that with a mixture of commercial Pt/C+RuO2 (1.59 V). In situ X-ray absorption spectroscopy measurements show that the bifunctional activity is due to reduction of the Ru-Cl residues at low electrode potentials that enriches metallic Ru and oxidation at high electrode potentials that facilitates the formation of amorphous RuOx. These findings highlight the unique potential of MIH in the ultrafast synthesis of high-performance catalysts for electrochemical water splitting.

Alkali Metals Activated High Entropy Double Perovskites for Boosted Hydrogen Evolution Reaction

An efficient and facile water dissociation process plays a crucial role in enhancing the activity of alkaline hydrogen evolution reaction (HER). Considering the intricate influence between interfacial water and intermediates in typical catalytic systems, meticulously engineered catalysts should be developed by modulating electron configurations and optimizing surface chemical bonds. Here, a high-entropy double perovskite (HEDP) electrocatalyst La2(Co1/6Ni1/6Mg1/6Zn1/6Na1/6Li1/6)RuO6, achieving a reduced overpotential of 40.7 mV at 10 mA cm-2 and maintaining exemplary stability over 82 h in a 1 m KOH electrolyte is reported. Advanced spectral characterization and first-principles calculations elucidate the electron transfer from Ru to Co and Ni positions, facilitated by alkali metal-induced super-exchange interaction in high-entropy crystals. This significantly optimizes hydrogen adsorption energy and lowers the water decomposition barrier. Concurrently, the super-exchange interaction enhances orbital hybridization and narrows the bandgap, thus improving catalytic efficiency and adsorption capacity while mitigating hysteresis-driven proton transfer. The high-entropy framework also ensures structural stability and longevity in alkaline environments. The work provides further insights into the formation mechanisms of HEDP and offers guidelines for discovering advanced, efficient hydrogen evolution catalysts through super-exchange interaction.

2D Transition Metal Chalcogenides (TMDs) for Electrocatalytic Hydrogen Evolution Reaction: A Review

Since the MoS2 synthesis, the family of two-dimensional transition metal chalcogenides (TMDs) have been intensively explored theoretically and experimentally. TMDs endowed with adjustable electronic, physical and chemical properties lead to increasing interest in the application of energy storage, molecule detection and catalysis. In the mini review, we present a forward-looking summary of 2D TMDs in hydrogen evolution electrocatalysis, including synthesis methods, hydrogen evolution performance, and optimization strategies. This review will deepen the fundamental understanding of the physical-chemical properties of TMDs with different phases and contribute unveil the universal principle among electronic configuration, atomic arrangement, physical and chemical property for the material design.

Axial ligand-induced high electrocatalytic hydrogen evolution activity of molecular cobaloximes in homo- and heterogeneous medium

Three new molecular cobaloxime complexes with the general formula [ClCo(dpgH)2L] (1-3), where L1 = N-(4-pyridylmethyl)-1,8-naphthalimide, L2 = 4-bromo-N-(4-pyridylmethyl)-1,8-naphthalimide, L3 = 4-piperidin-N-(4-pyridylmethyl)-1,8-naphthalimide, have been synthesized and characterized by UV-Vis, multinuclear NMR, FT-IR and PXRD spectroscopic techniques. The crystal structures of all complexes have also been reported. The electrocatalytic activity of complexes is investigated under two catalysis conditions: (i) homogeneous conditions in acetonitrile using acetic acid (AcOH) as a proton source and (ii) heterogeneous conditions upon immobilization onto the surface of activated carbon cloth (CC). Complex 3 exhibited high electrocatalytic HER activity under both homogeneous and heterogeneous conditions. It catalyses proton reduction to molecular hydrogen in acetonitrile solution at a lower overpotential (640 mV) with a high turnover frequency (TOF) of 524.57 s-1 and demonstrates good stability in acidic conditions. Furthermore, catalytic (working) electrodes are prepared by immobilizing the complexes onto the surface of activated carbon cloth (CC) for electrocatalytic HER under heterogeneous conditions. An impressive HER performance was again obtained with catalytic electrode 3@CC in 1.0 M KOH, achieving a current density of -10 mA cm-2 at an overpotential of 262 mV. Chronoamperometric (CA) studies showed no significant decay of the initial current density for 10 h, indicating the excellent stability of 3@CC. Additionally, UV-Vis and NMR spectral studies of the recovered catalyst after electrocatalysis revealed no structural changes, demonstrating its robustness under reaction conditions.

Ru incorporated into Se vacancy-containing CoSe2 as an efficient electrocatalyst for alkaline hydrogen evolution

In alkaline media, slow water dissociation leads to poor overall hydrogen evolution performance. However, Ru catalysts have a certain water dissociation performance, thus regulating the Ru-H bond through vacancy engineering and accelerating water dissociation. Herein, an excellent Ru-based electrocatalyst for the alkaline HER has been developed by incorporating Ru into Se vacancy-containing CoSe2 (Ru-VSe-CoSe2). The results from X-ray photoelectron spectroscopy, kinetic isotope effect, and cyanide poisoning experiments for four catalysts (namely Ru-VSe-CoSe2, Ru-CoSe2, VSe-CoSe2, and CoSe2) reveal that Ru is the main active site in Ru-VSe-CoSe2 and the presence of Se vacancies greatly facilitates electron transfer from Co to Ru via a bridging Se atom. Thus, electron-rich Ru is formed to optimize the adsorption strength between the active site and H*, and ultimately facilitates the whole alkaline HER process. Consequently, Ru-VSe-CoSe2 exhibits an excellent HER activity with an ultrahigh mass activity of 44.2 A mgRu-1 (20% PtC exhibits only 3 A mgRu-1) and a much lower overpotential (29 mV at 10 mA cm-2) compared to Ru-CoSe2 (75 mV), VSe-CoSe2 (167 mV), CoSe2 (190 mV), and commercial Pt/C (41 mV). In addition, the practical application of Ru-VSe-CoSe2 is illustrated by designing a Zn-H2O alkaline battery with Ru-VSe-CoSe2 as the cathode catalyst, and this battery shows its potential application with a maximum power density of 4.9 mW cm-2 and can work continuously for over 10 h at 10 mA cm-2 without an obvious decay in voltage.

Electrochemical Synthesis of Hollow Nanoparticles via Anodic Transformation of Metastable Core-Shell Precursors

Recent advances in electrosynthesis of nanomaterials expanded structural and compositional variations accessible by the electrochemical method; however, reliably synthesizable morphological variety fall shy of that available by conventional solvothermal synthesis. In this communication, electrochemical preparation of surfactant-free hollow nanoparticles is demonstrated. By anodic conversion of core-shell precursors with metastable cores, hollowed nickel nanoparticles with uniform dimensions were synthesized and characterized. Implementation of TEM grids as the working electrodes, identical location tracking of the morphological evolution of single particles to anodic stimulus has been demonstrated. The synthesized nanoparticles were employed as catalysts for the alkaline hydrogen evolution reaction and exhibited catalytic rates that compare favorably to the Pt/C benchmark. This marks the first pure electrochemical synthesis of hollow nanoparticles and shall contribute to the structural diversification of electrosynthesized nanomaterials.

Improvements in the evaluation of electrocatalytic ammonia oxidation reactions

For a reliable evaluation of the electrocatalytic ammonia oxidation reaction (EAOR), we revised the standard electrode potentials in both aqueous and nonaqueous electrolytes using the solvation energies of ammonia. Moreover, we developed an improved assessment protocol for EAOR systems, particularly for those employing nonaqueous electrolytes and/or nitrogen-containing materials.

Manipulating d-Band Center of Nickel by Single-Iodine-Atom Strategy for Boosted Alkaline Hydrogen Evolution Reaction

Ni-based electrocatalysts have been predicted as highly potential candidates for hydrogen evolution reaction (HER); however, their applicability is hindered by an unfavorable d-band energy level (Ed). Moreover, precise d-band structural engineering of Ni-based materials is deterred by appropriative synthesis methods and experimental characterization. Herein, we meticulously synthesize a special single-iodine-atom structure (I-Ni@C) and characterize the Ed manipulation via resonant inelastic X-ray scattering (RIXS) spectroscopy to fill this gap. The complex catalytic mechanism has been elucidated via synchrotron radiation-based multitechniques (SRMS) including X-ray absorption fine structure (XAFS), in situ synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectroscopy, and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). In particular, RIXS is innovatively applied to reveal the precise regulation of Ni Ed of I-Ni@C. Consequently, the role of such single-iodine-atom strategy is confirmed to not only facilitate the moderate Ed of the Ni site for balancing the adsorption/desorption capacities of key intermediates but also act as a bridge to enhance the electronic interaction between Ni and the carbon shell for forming a localized polarized electric field conducive to H2O dissociation. As a result, I-Ni@C exhibits an enhanced alkaline hydrogen evolution performance with an overpotential of 78 mV at 10 mA/cm2 and superior stability, surpassing the majority of the reported Ni-based catalysts. Overall, this study has managed to successfully tailor the d-band center of materials from the SRMS perspective, which has crucial implications for nanotechnology, chemistry, catalysis, and other fields.

Phase Engineering and Dispersion Stabilization of Cobalt toward Enhanced Hydrogen Evolution

Phase engineering is promising to increase the intrinsic activity of the catalyst toward hydrogen evolution reaction (HER). However, the polymorphism interface is unstable due to the presence of metastable phases. Herein, phase engineering and dispersion stabilization are applied simultaneously to boost the HER activity of cobalt without sacrificing the stability. A fast and facile approach (plasma cathodic electro deposition) is developed to prepare cobalt film with a hetero-phase structure. The polymorphs of cobalt are realized through reduced stacking fault energy due to the doping of Mo, and the high temperature treatment resulted from the plasma discharge. Meanwhile, homogeneously dispersed oxide/carbide nanoparticles are produced from the reaction of plasma-induced oxygen/carbon atoms with electro-deposited metal. The existence of rich polymorphism interface and oxide/carbide help to facilitate H2 production by the tuning of electronic structure and the increase of active sites. Furthermore, oxide/carbide dispersoid effectively prevents the phase transition through a pinning effect on the grain boundary. As-prepared Co-hybrid/CoO_MoC exhibits both high HER activity and robust stability (44 mV at 10 mA cm-2, Tafel slope of 53.2 mV dec-1, no degradation after 100 h test). The work reported here provides an alternate approach to the design of advanced HER catalysts for real application.

Ruthenium-infused nickel sulphide propelling hydrogen generation via synergistic water dissociation and Volmer step promotion

The inclusion of ruthenium (Ru) to decorate nickel sulphide (Ru@NiS/Ni foam) resulted in a highly efficient electrocatalyst for the alkaline HER by enhancing water dissociation at the interface and reducing the energy barrier of the Volmer step. This strategic fusion significantly boosts the catalyst's performance in facilitating hydrogen production.

Influence of deposition conditions on performance of Ni3S2 as the bifunctional electrocatalyst in alkaline solutions by galvanostatic deposition

The electrodeposition method is a popular synthesis method due to its low cost, simplicity, and short synthesis time. In addition, this synthesis route results in the preparation of a self-supporting electrocatalyst, which eliminates the use of binders and ultimately facilitates the durability as well as the activity of the catalyst. In this work, a series of Ni3S2/Ni mesh electrodes are prepared by galvanostatic deposition at different deposition current densities and times. The morphology, microstructure, and elemental composition distribution of these obtained electrodes are characterized, and the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance of the series of Ni3S2/Ni meshes are tested. The results show that the Ni3S2/Ni mesh electrodes electrodeposited at 30 mA cm-2 for 1200 s have superior electrochemical performance for HER and OER. The overpotentials of Ni3S2/Ni mesh 30 mA cm-2-1200 s are 236 and 244 mV for HER and OER, respectively, at a current density of 10 mA cm-2. In addition, the Tafel slopes for HER and OER are 113 mV dec-1 and 176 mV dec-1, respectively. This research provides some valuable insights into the use of the electrodeposition method for the fabrication of electrocatalysts.

Improving Molecular-Dynamics Simulations for Solid-Liquid Interfaces with Machine-Learning Interatomic Potentials

Emerging developments in artificial intelligence have opened infinite possibilities for material simulation. Depending on the powerful fitting of machine learning algorithms to first-principles data, machine learning interatomic potentials (MLIPs) can effectively balance the accuracy and efficiency problems in molecular dynamics (MD) simulations, serving as powerful tools in various complex physicochemical systems. Consequently, this brings unprecedented enthusiasm for researchers to apply such novel technology in multiple fields to revisit the major scientific problems that have remained controversial owing to the limitations of previous computational methods. Herein, we introduce the evolution of MLIPs, provide valuable application examples for solid-liquid interfaces, and present current challenges. Driven by solving multitudinous difficulties in terms of the accuracy, efficiency, and versatility of MLIPs, this booming technique, combined with molecular simulation methods, will provide an underlying and valuable understanding of interdisciplinary scientific challenges, including materials, physics, and chemistry.

Partially oxidized inter-doped RuNi alloy aerogel for the hydrogen evolution reaction in both alkaline and acidic media

A facile reduction and doping process is employed with the supercritical ethanol drying method to form RuNi alloy aerogels. The optimized heterostructure comprising RuNi metal, RuO2, and NiO phases is synthesized through partial oxidation. When applied to the surface of Ni foam, the multiphase aerogels form a morphology of highly porous 0D colloidal aerogel networks on the surface. RuNi alloy-Ni foam oxidized at 350 °C (RuNi-350@NF) has an overpotential of 89 and 61 mV in 1 M KOH and 0.5 M H2SO4 media at 50 mA cm-2, as well as satisfactory long-term stability. Additionally, the Tafel slopes in alkaline and acidic media are found to be 34 and 30.9 mV dec-1, respectively. Furthermore, it exhibits long-term stability (35 h) in alkaline and acidic media at high current densities of 50 mA cm-2, respectively. This study presents a novel strategy for developing exceptionally efficient and free-standing 3D porous aerogel electrocatalysts with potential applications in hydrogen production.

Modulating Surface Cation Concentration via Tuning the Molecular Structures of Ethylene Glycol-Functionalized PEDOT for Improved Alkaline Hydrogen Evolution Reaction

The sluggish catalytic kinetics of nonprecious metal-based electrocatalysts often hinder them from achieving efficient hydrogen evolution reactions (HERs). Poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives have been promising materials for various electrochemical applications. Nevertheless, previous studies have demonstrated that PEDOT coatings can be detrimental to HER performance. In this study, we investigated the alkaline HER efficiency of nickel foam coated with three types of ethylene glycol (EG)-functionalized EDOT. Specifically, EDOT derivatives bearing hydroxyl (-OH) and methoxy (-OCH3) end groups on the EG side chain and molecules containing two EDOT units are interconnected via EG moieties. EG groups are selected due to their strong interaction with alkali metal cations. Intriguingly, improved HER performance is observed on all electrodes coated with EG-functionalized EDOTs. Electrochemical impedance spectroscopy, electrochemical quartz crystal microbalance with dissipation, and XPS analysis are employed to explore the origin of enhanced HER efficiency. The results suggest the EG moieties can induce locally concentrated ions near the electrode surface and facilitate water dissociation through noncovalent interactions. The influence of EG chain length is systematically investigated by synthesizing molecules with di-EG, tetra-EG, and hexa-EG functionalities. This study highlights the importance of molecular design in modifying electrode surface properties to promote alkaline HER.

Recent Advancements in Ascribing Several Platinum Free Electrocatalysts Pertinent to Hydrogen Evolution from Water Reduction

The advancement of a sustainable and scalable catalyst for hydrogen production is crucial for the future of the hydrogen economy. Electrochemical water splitting stands out as a promising pathway for sustainable hydrogen production. However, the development of Pt-free electrocatalysts that match the energy efficiency of Pt while remaining economical poses a significant challenge. This review addresses this challenge by highlighting latest breakthroughs in Pt-free catalysts for the hydrogen evolution reaction (HER). Specifically, we delve into the catalytic performance of various transition metal phosphides, metal carbides, metal sulphides, and metal nitrides toward HER. Our discussion emphasizes strategies for enhancing catalytic performance and explores the relationship between structural composition and the performance of different electrocatalysts. Through this comprehensive review, we aim to provide insights into the ongoing efforts to overcome barriers to scalable hydrogen production and pave the way for a sustainable hydrogen economy.

Tuning the Local Environment of Pt Species at CNT@MO2-x (M = Sn and Ce) Heterointerfaces for Boosted Alkaline Hydrogen Evolution

As the most promising hydrogen evolution reaction (HER) electrocatalysts, platinum (Pt)-based catalysts still struggle with sluggish kinetics and expensive costs in alkaline media. Herein, we accelerate the alkaline hydrogen evolution kinetics by optimizing the local environment of Pt species and metal oxide heterointerfaces. The well-dispersed PtRu bimetallic clusters with adjacent MO2-x (M = Sn and Ce) on carbon nanotubes (PtRu/CNT@MO2-x) are demonstrated to be a potential electrocatalyst for alkaline HER, exhibiting an overpotential of only 75 mV at 100 mA cm-2 in 1 M KOH. The excellent mass activity of 12.3 mA μg-1Pt+Ru and specific activity of 32.0 mA cm-2ECSA at an overpotential of 70 mV are 56 and 64 times higher than those of commercial Pt/C. Experimental and theoretical investigations reveal that the heterointerfaces between Pt clusters and MO2-x can simultaneously promote H2O adsorption and activation, while the modification with Ru further optimizes H adsorption and H2O dissociation energy barriers. Then, the matching kinetics between the accelerated elementary steps achieved superb hydrogen generation in alkaline media. This work provides new insight into catalytic local environment design to simultaneously optimize the elementary steps for obtaining ideal alkaline HER performance.