Platinum single-atom catalyst coupled with transition metal/metal oxide heterostructure for accelerating alkaline hydrogen evolution reaction

Sustainable and cost-efficient hydrogen production using platinum clusters at minimal loading

Proton exchange membrane water electrolysis stands as a promising technology for sustainable hydrogen production, although its viability hinges on minimizing platinum (Pt) usage without sacrificing catalytic efficiency. Central to this challenge is enhancing the intrinsic activity of Pt while ensuring the stability of the catalyst. We herein present a Mo2TiC2 MXene-supported Pt nanocluster catalyst (Mo2TiC2-PtNC) that requires a minimal Pt content (36 μg cm-2) to function, yet remains highly active and stable. Operando spectroscopy and theoretical simulation provide evidence for anomalous charge transfer from the MXene substrate to PtNC, thus generating highly efficient electron-rich Pt sites for robust hydrogen evolution. When incorporated into a proton exchange membrane electrolyzer, the catalyst affords more than 8700 h at 200 mA cm-2 under ambient temperature with a decay rate of just 2.2 μV h-1. All the performance metrics of the present Mo2TiC2-PtNC catalysts are on par with or even surpass those of current hydrogen evolution electrocatalysts under identical operation conditions, thereby challenging the monopoly of high-loading Pt/C-20% in the current electrolyzer design.

Rapid synthesis of metastable materials for electrocatalysis

Metastable materials are considered promising electrocatalysts for clean energy conversions by virtue of their structural flexibility and tunable electronic properties. However, the exploration and synthesis of metastable electrocatalysts via traditional equilibrium methods face challenges because of the requirements of high energy and precise structural control. In this regard, the rapid synthesis method (RSM), with high energy efficiency and ultra-fast heating/cooling rates, enables the production of metastable materials under non-equilibrium conditions. However, the relationship between RSM and the properties of metastable electrocatalysts remains largely unexplored. In this review, we systematically examine the unique benefits of various RSM techniques and the mechanisms governing the formation of metastable materials. Based on these insights, we establish a framework, linking RSM with the electrocatalytic performance of metastable materials. Finally, we outline the future directions of this emerging field and highlight the importance of high-throughput approaches for the autonomous screening and synthesis of optimal electrocatalysts. This review aims to provide an in-depth understanding of metastable electrocatalysts, opening up new avenues for both fundamental research and practical applications in electrocatalysis.

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.

A salen-based dinuclear cobalt(ii) polymer with direct and indirect synergy for electrocatalytic hydrogen evolution

Optimizing the spatial arrangement and geometric configuration of dinuclear metal sites within catalysts to leverage the dinuclear metal synergistic catalysis (DMSC) effect is a promising strategy for enhancing catalytic performance. In this work, we report a salen-based dinuclear cobalt covalent organic polymer (Co2-COP) that exhibits both direct and indirect DMSC synergistic effects, significantly improving catalytic efficiency for the electrocatalytic alkaline hydrogen evolution reaction (HER). Notably, one of the Co atoms in this structural unit features an OH- anion. The OH- anion facilitates both H2O adsorption through p-p orbital overlapping interaction and the subsequent OH* intermediate removal by pre-attracting cations. As a result, Co2-COP exhibits superior HER activity that surpasses its single-atom counterpart by a factor of 36. Control experiments and theoretical calculations revealed that the enhanced catalytic efficiency of Co2-COP is attributed to both the direct DMSC effect between two CoII ions, and the indirect DMSC involving the OH- anion and alkali cations. This synergistic interaction significantly facilitates water activation and accelerates the removal of the OH* intermediate, all of which are intricately linked to the unique dinuclear structure of the material.

An Electrochemically-Driven Reconstruction Strategy to Realize Highly Crystalline Covalent Organic Frameworks for Enhanced Hydrogen Evolution Reaction

Developing diverse methods to approach highly crystalline covalent organic frameworks (COFs) for improvement of their electrocatalytic hydrogen evolution reaction (HER) activity is important but very challenging. Herein, for the first time, an electrochemically-driven reconstruction strategy is demonstrated to convert semi-polymerized low-crystalline COFs into highly crystalline, structurally ordered COFs with enhanced HER activity. In situ and ex situ characterizations reveal that cyclic voltammetry (CV) cycles can promote crystallinity, thereby leading to improved conductivity, increased active site density, and superior stability. As a result, the highly crystalline COF achieves low overpotentials of 103.6 and 219.4 mV at 10 and 50 mA cm-2, respectively, with excellent stability (1200 h at 50 mA cm-2). More importantly, this strategy is generalizable and effective for various imine-linked COFs with different bonding types, significantly improving their crystallinity and HER activity. This work not only establishes a novel method for constructing highly crystalline COFs but also demonstrates the versatility of electrochemically driven structural modulation in enhancing the catalytic performance of COFs.

Pulsed laser synthesis of free-standing Pt single atoms in an ice block for enhancing photocatalytic hydrogen evolution of g-C3N4

This study reports an innovative synthesis method of a Pt/g-C3N4 single atom catalyst for enhancing photocatalytic hydrogen evolution. The method involves the synthesis of free-standing Pt single atoms within an H2PtCl6 ice block using a pulsed laser reduction process, followed by transferring them onto few-layer g-C3N4 through electrostatic adsorption at low temperature. This approach eliminates the need for high-energy lasers and porous support materials during laser solid-phase synthesis. The photocatalytic activities of Pt/g-C3N4 synthesized under various laser conditions are evaluated to optimize the synthesis parameters. The optimal Pt/g-C3N4 catalyst demonstrates a significantly higher photocatalytic hydrogen evolution capability (320 μmol h-1), 129 times that of pure g-C3N4 (2.2 μmol h-1). This work expands the laser-solid phase synthesis method, offering a promising route for the production of single atom catalysts with simple operation, clear synthetic pathways, low cost, and environmental friendliness.

A Nanostructured Ru-Mn-Nb Alloy with Oxygen-Enriched Boundaries for Ampere-Level Hydrogen Evolution

Development of active and cost-effective electrocatalysts to substitute platinum-based catalysts in alkaline hydrogen evolution reactions (HERs) remains a challenge. The synergistic effect between different elements in alloy catalysts can regulate electronic structure and thereby provide an abundance of catalytic sites for reactions. Thus, alloy catalysts are suitable candidates for future energy applications. Conventional methods for enhancing the performance of alloy catalysts have mainly focused on element composition and thus have often neglected to examine catalyst design. In this paper, a ruthenium-manganese-niobium alloy catalyst (Ru62Mn12Nb21O5) is reported with a supra-nanocrystalline dual-phase structure that is fabricated through combinatorial magnetron co-sputtering at ambient temperatures. The induced crystal-crystal heterostructure of Ru62Mn12Nb21O5 reduced system energy, thereby achieving balance between stability and catalytic activity. Ru62Mn12Nb21O5 exhibited excellent HER performance, as demonstrated by low HER overpotential (18 mV at 10 mA cm-2) and robust stability (300 h at 1.2 A cm-2). Moreover, oxygen-rich interfaces in Ru62Mn12Nb21O5 enhanced charge transfer and the kinetics of water dissociation as well as optimized hydrogen adsorption/desorption processes, thus boosting HER performance. The crystal-crystal heterostructure and oxygen-rich interfaces in Ru62Mn12Nb21O5 are induced by its dual-phase nanocrystalline structure, which represents a new structural design for enhancing the performance of catalysts for sustainable energy development.

Platinum-Nickel Oxide Cluster-Cluster Heterostructure Enabling Fast Hydrogen Evolution for Anion Exchange Membrane Water Electrolyzers

Carbon black has been extensively employed as the support for noble metal catalysts for electrocatalysis applications. However, the nearly catalytic inertness and weak interaction with metal species of carbon black are two major obstacles that hinder the further improvement of the catalytic performance. Herein, we report a surface functionalization strategy by decorating transition metal oxide clusters on the commercial carbon black to offer specific catalytic activity and enhanced interaction with metal species. In the case of NiOx cluster-decorated carbon black, a strongly coupled cluster-cluster heterostructure consisting of Pt clusters and NiOx clusters (Pt-NiOx/C) is formed and delivers greatly enhanced alkaline hydrogen evolution kinetics. The NiOx clusters can not only accelerate the hydrogen evolution process as the co-catalyst, but also optimize the adsorption of H intermediates on Pt and stabilize the Pt clusters. Notably, the anion exchange membrane water electrolyzer with Pt-NiOx/C as the cathode catalyst (with a loading of only 50 μgPt cm-2) delivers the most competitive electrochemical performance reported to date, requiring only 1.90 V to reach a current density of 2 A cm-2. The results demonstrate the significance of surface functionalization of carbonaceous supports toward the development of advanced electrocatalysts.

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.

Surface Reconstruction of An Integrated CoO-Co2Mo3O8 Electrode Enabling Efficient Ampere-Level Hydrogen Evolution in Alkaline Water or Seawater

To accelerate the water dissociation in the Volmer step and alleviate the destruction of bubbles to the physical structure of catalysts during the alkaline hydrogen evolution, an integrated electrode of cobalt oxide and cobalt-molybdenum oxide grown on Ni foam, named CoO-Co2Mo3O8, is designed. This integrated electrode enhances the catalyst-substrate interaction confirmed by a micro-indentation tester, and thus hinders the destruction of the physical structure of catalysts caused by bubbles. Electrochemical testing shows the occurrence of a surface reconstruction of the integrated electrode, and CoO is transformed into Co(OH)2, denoted as Co(OH)2-Co2Mo3O8. Theoretical calculations determine that Co(OH)2-Co2Mo3O8 has significantly low activation barrier for water dissociation and presents easy hydroxide desorption, which accelerate the catalytic reaction. Electrochemical experiments show that Co(OH)2-Co2Mo3O8 exhibits outstanding activity, reaching current density values of -100 and -1000 mA cm-2 with overpotentials only 57.8 and 195.8 mV, respectively. Furthermore, it demonstrates excellent stability at -500 and -1000 mA cm-2 for 200 h. Combined with the previously reported anode, the two-electrode system also provides the stable operation from 100 to 1000 mA cm-2 for 600 h in alkaline solution, and over 200 h at 500 and 1000 mA cm-2 in alkaline seawater.

Corrosion-resistant single-atom catalysts for direct seawater electrolysis

Direct seawater electrolysis (DSE) for hydrogen production is an appealing method for renewable energy storage. However, DSE faces challenges such as slow reaction kinetics, impurities, the competing chlorine evolution reaction at the anode, and membrane fouling, making it more complex than freshwater electrolysis. Therefore, developing catalysts with excellent stability under corrosion and fulfilling activity is vital to the advancement of DSE. Single-atom catalysts (SACs) with excellent tunability, high selectivity and high active sites demonstrate considerable potential for use in the electrolysis of seawater. In this review, we present the anodic and cathodic reaction mechanisms that occur during seawater cracking. Subsequently, to meet the challenges of DSE, rational strategies for modulating SACs are explored, including axial ligand engineering, carrier effects and protective layer coverage. Then, the application of in-situ characterization techniques and theoretical calculations to SACs is discussed with the aim of elucidating the intrinsic factors responsible for their efficient electrocatalysis. Finally, the process of scaling up monoatomic catalysts for the electrolysis of seawater is described, and some prospective insights are provided.

Atomically Dispersed Mn-Ir Sites on 2D Amorphous Carbon Materials Synergistically Boost Electrochemical Overall Water Splitting

Enhancing the activity and durability of noble-metal-based catalysts for overall water splitting is crucial for advancing sustainable energy conversion. In this study, a novel catalyst, PBN-Ir/Mn, is reported, developed through a self-healing process of the polyhexabenzocoronene network (PBN) that incorporates both Mn and Ir atoms. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and X-ray absorption spectroscopy (XAS) characterizations confirm a unique atomic-scale Ir-Ir-Mn triangular structure on the porous PBN substrate. The synergy between Mn and Ir atoms leads to superior water electrolysis performance, with ultra-low overpotentials of 11 mV for the hydrogen evolution reaction (HER) and 220 mV for the oxygen evolution reaction (OER) at 10 mA cm-2. PBN-Ir/Mn also achieves outstanding mass activities, reaching 425.92 A mg-1 for HER and 152.28 A mg-1 OER. Moreover, PBN-Ir/Mn demonstrates exceptional durability in overall water splitting, maintaining stable performance over 100 h in a full-cell setup, surpassing commercial benchmarks. Density functional theory (DFT) calculations reveal that Mn doping modifies the d-band center of Ir, reducing the activation energy barriers and significantly enhancing both activity and stability. The high performance and stability of PBN-Ir/Mn, combined with its scalability for gram-scale synthesis, highlight its potential for industrial applications and multifunctional catalysis.

Electrochemically grown porous platinum for electrocatalysis and optical applications

Localized electrochemically grown porous platinum layers on 2D and 3D microstructured materials enable a wide range of applications from electrocatalysis to optoelectronics. These layers exhibit a thickness gradient and surface corner overloading due to electric charge accumulation at the sharp corners. On one hand, these effects can be applied to create ultra-large surface area catalysts or electrocatalysts. On the other hand, they can be mitigated by guiding the electric field at the nanoscale. Here, we show that porous platinum grown on rough conductive silicon synergistically catalyses the electroreduction of CO2 in a humid gaseous atmosphere, overcoming the disadvantage of CO2´s low water solubility. In addition, using template-directed growth of porous platinum, we tuned the optical response of an infrared (IR) metamaterial fabricated by micropatterning on Si/NiCr/Ti substrates and constructed a broad absorber on potential IR-functional microcomponents.

Boosting Alkaline Hydrogen Evolution by Creating Atomic-Scale Pair Cocatalytic Sites in Single-Phase Single-Atom-Ruthenium-Incorporated Cobalt Oxide

Compared with acidic environments, promoting the water dissociation process is crucial for speeding up hydrogen evolution reaction (HER) kinetics in alkaline electrolyte. Although the construction of heterostructured electrocatalysts by hybridizing noble metals with metal (hydr)oxides has been reported as a feasible approach to achieve high performance, the high cost, complicated fabrication process, and unsatisfactory mass activity limit their large-scale applications. Herein, we report a single-phase HER electrocatalyst composed of single-atom ruthenium (Ru) incorporated into a cobalt oxide spine structure (denoted as Ru SA/Co3O4), which possesses exceptional HER performance in alkaline media via unusual atomic-scale Ru-Co pair sites. In particular, Ru SA/Co3O4 exhibits a very low overpotential of 44 mV at 10 mA cm-2 and an outstanding mass activity of 4700 mA mg-1 at 50 mV overpotential, superior to those of commercial Pt/C, Ru nanoparticles supported on Co3O4 (denoted as Ru NP/Co3O4) and other reported Ru-based electrocatalysts. With insights from theoretical calculations, the synergistic interactions between Ru and Co pair active sites in Ru SA/Co3O4 are revealed to catalyze diverse fundamental steps of the alkaline HER; i.e., the Ru sites can effectively accelerate water adsorption/dissociation and OH- desorption, whereas the Co sites are favorable for H* adsorption and H2 evolution.

Atomic-scale self-rearrangement of hetero-metastable phases into high-density single-atom catalysts for the oxygen evolution reaction

Maximizing metal-substrate interactions by self-reconstruction of coadjutant metastable phases can be a delicate strategy to obtain robust and efficient high-density single-atom catalysts. Here, we prepare high-density iridium atoms embedded ultrathin CoCeOOH nanosheets (CoCe-O-IrSA) by the electrochemistry-initiated synchronous evolution between metastable iridium intermediates and symmetry-breaking CoCe(OH)2 substrates. The CoCe-O-IrSA delivers an overpotential of 187 mV at 100 mA cm-2 and a steady lifespan of 1000 h at 500 mA cm-2 for oxygen evolution reaction. Furthermore, the CoCe-O-IrSA is applied as a robust anode in an anion-exchange-membrane water electrolysis cell for seawater splitting at 500 mA cm-2 for 150 h. Operando experimental and theoretical calculation results demonstrate that the reconstructed thermodynamically stable iridium single atoms act as highly active sites by regulating charge redistribution with strongly p-d-f orbital couplings, enabling electron transfer facilitated, the adsorption energies of intermediates optimized, and the surface reactivity of Co/Ce sites activated, leading to high oxygen evolution performance. These results open up an approach for engineering metastable phases to realize stable single-atom systems under ambient conditions toward efficient energy-conversion applications.

Pt/α-MoC Catalyst Boosting pH-Universal Hydrogen Evolution Reaction at High Current Densities

Constructing subnanometric electrocatalysts is an efficient method to synergistically accelerate H2O dissociation and H+ reduction for pH-universal hydrogen evolution reaction (HER) for industrial water electrolysis to produce green hydrogen. Here, we construct a subnanometric Pt/α-MoC catalyst, where the α-MoC component can dissociate water effectively, with the rapid proton release kinetics of Pt species on Pt/α-MoC to obtain a good HER performance at high current densities in all-pH electrolytes. Quasi-in situ X-ray photoelectron spectroscopy analyses and density functional theory calculations confirm the highly efficient water dissociation capability of α-MoC and the thermodynamically favorable desorption process of hydrolytically dissociated protons on Pt sites at the high current density. Consequently, Pt/α-MoC requires only a low overpotential of 125 mV to achieve a current density of 1000 mA cm-2. Moreover, a Pt/α-MoC-based proton exchange membrane water electrolysis device exhibits a low cell voltage (1.65 V) and promising stability over 300 h with no performance degradation at an industrial-level current density of 1 A cm-2. Notably, even at a current of 100 A, the cell voltage remains low at 2.15 V, demonstrating Pt/α-MoC's promising potential as a scalable alternative for industrial hydrogen production. These findings elucidate the synergistic mechanism of α-MoC and atomically dispersed Pt in promoting efficient HER, offering valuable guidance for the design of electrocatalysts in high current density hydrogen.

Unlocking Peak Efficiency in Anion-Exchange Membrane Electrolysis with Iridium-Infused Ni/Ni2P Heterojunction Electrocatalysts

Developing cost-effective, highly efficient, and durable bifunctional electrocatalysts for water electrolysis remains a significant challenge. Nickel-based materials have shown promise as catalysts, but their efficiency in alkaline electrolytes is still lacking. Fascinatingly, Mott-Schottky catalysts can fine-tune electron density at interfaces, boosting intermediate adsorption and facilitating desorption to reduce the energy barrier. In this study, iridium-implanted Mott-Schottky Ni/Ni2P nanosheets (IrSA-Ni/Ni2P) is introduced, which are delivered from the metal-organic framework and employ them as the bifunctional catalysts for water electrolysis devices. This catalyst requires a small 54 mV overpotential for hydrogen evolution reaction (HER) and 192 mV for oxygen evolution reaction (OER) to reach 10 mA·cm-2 in a 1.0 m KOH electrolyte. Density functional theory (DFT) calculations reveal that the incorporation of Ir atoms with enriched interfaces between Ni and Ni2P can promote the active sites and be favorable for the HER and OER. This discovery highlights the most likely reactive sites and offers a valuable blueprint for designing highly efficient and stable catalysts tailored for industrial-scale electrolysis. The IrSA-Ni/Ni2P electrode exhibits exceptional current density and outstanding stability in a single-cell anion-exchange membrane electrolyzer.

Fabricating Lattice-Confined Pt Single Atoms With High Electron-Deficient State for Alkali Hydrogen Evolution Under Industrial-Current Density

The confining effect is essential to regulate the activity and stability of single-atom catalysts (SACs), but the universal fabrication of confined SACs is still a great challenge. Here, various lattice-confined Pt SACs supported by different carriers are constructed by a universal co-reduction approach. Notably, Pt single atoms confined in the lattice of Ni(OH)2 (Pt1/Ni(OH)2) with a high electron-deficient state exhibit excellent activity for basic hydrogen evolution reaction (HER). Specifically, Pt1/Ni(OH)2 just requires 15 mV to get 10 mA cm-2 and the mass activity of Pt1/Ni(OH)2 is 15 times of commercial Pt/C. Moreover, Pt1/Ni(OH)2 assembled in an alkaline water electrolyzer shows 1030 h durability under the industrial current density of 800 mA cm-2. In situ spectroscopy techniques reveal Pt─H and "free" OH radical can be directly observed for Pt1/Ni(OH)2, confirming the lattice-confined Pt single atoms play a key role during HER. Further density functional theory uncovers the Pt 3d orbital strongly hybridizes with O 2p and Ni 3d orbitals in Ni(OH)2, which quickly optimizes the electronic state of the Pt site, thus largely reducing the energy barrier of the rate-determining step to 0.16 eV for HER. Finally, this synthesis method is extended to construct other 9 lattice-confined SACs.

Lattice atom-bridged chemical bond interface facilitates charge transfer for boosted photoelectric response

The construction of chemical bonds at heterojunction interfaces currently presents a promising avenue for enhancing photogenerated carrier interfacial transfer. However, the deliberate modulation of these interfacial chemical bonds remains a significant challenge. In this study, we successfully established a p-n junction composed of atomic-level Pt-doped CeO2 and 2D metalloporphyrins metal-organic framework nanosheets (Pt-CeO2/CuTCPP(Fe)), which enables the realization of photoelectric enhancement by regulating the interfacial Fe-O bond and optimizing the built-in electric field. Atomic-level Pt doping in CeO2 leads to an increased density of oxygen vacancies and lattice mutation, which induces a transition in interfacial Fe-O bonds from adsorbed oxygen (Fe-OA) to lattice oxygen (Fe-OL). This transition changes the interfacial charge flow pathway from Fe-OA-Ce to Fe-OL, effectively reducing the carrier transport distance along the atomic-level charge transport highway. This results in a 2.5-fold enhancement in photoelectric performance compared with the CeO2/CuTCPP(Fe). Furthermore, leveraging the peroxidase-like activity of the p-n junction, we employed this functional heterojunction interface to develop a photoelectrochemical immunoassay for the sensitive detection of prostate-specific antigens.

Confined Flash Pt1/WCx inside Carbon Nanotubes for Efficient and Durable Electrocatalysis

Exploiting cost-effective hydrogen evolution reaction (HER) catalysts is crucial for sustainable hydrogen production. However, currently reported nanocatalysts usually cannot simultaneously sustain high catalytic activity and long-term durability. Here, we report the efficient synthesis and activity tailoring of a chainmail catalyst, isolated platinum atom anchored tungsten carbide nanocrystals encapsulated inside carbon nanotubes (Pt1/WCx@CNTs), by confined flash Joule heating technique. The instantaneous carbothermal reduction reaction enables the millisecond formation of Pt1/WCx nanostructures from CNT-encapsulated polyoxometalates, where nanotubes serve as both heating conductors and robust chainmails. The Pt1/WCx@CNTs exhibit prominent catalytic performance toward acid HER with a low overpotential of 45.2 mV at 10 mA cm-2 and long-term durability over 500 h of continuous running. Mechanism studies reveal the strong metal-support interaction on Pt1/WCx optimizes the charge redistribution at the Pt1-W2C interface and the hydrogen adsorption/desorption behavior. This study offers a potential avenue for ultrafast and activity-controllable synthesis of highly stable single-atom catalysts.

Enhanced Glycerol Electrooxidation Capability of NiO by Suppressing the Accumulation of Ni4+ Sites

Glycerol electrooxidation (GOR), as a typical nucleophilic biomass oxidation reaction, provides a promising anodic alternative for coupling green hydrogen generation at the cathode. However, the challenges of identifying active sites and elucidating reaction mechanisms greatly limit the design of high-performance catalysts. Herein, we use NiO and Ni/NiO as model catalysts to investigate glycerol oxidation. Electrochemical measurements and operando spectroscopic studies uncovered that Ni2+/Ni3+ species are the true active sites of NiO for GOR at lower potentials. However, the Ni2+/Ni3+ species formed on the NiO surface were easily converted to Ni4+ species (NiO2) at higher potentials, which not only contributed to the overoxidation of glycerol electrolysis products but also worked as the main active sites of the competitive oxygen evolution reaction (OER), resulting in the rapid decay of Faradic efficiencies (FEs) at high potentials. Interestingly, for Ni/NiO, only Ni3+ species were formed on the surface. Experimental and density functional theory (DFT) investigations indicated that due to the relatively lower average valence state of Ni in Ni/NiO and strong electronic interaction on the Ni/NiO interface, the surface reconstruction of Ni/NiO was effectively manipulated. Only Ni/NiO → NiOOH (Ni3+) transformation was observed, and the formation of Ni4+ species was greatly suppressed. As a result, Ni/NiO delivered superior GOR activity, and the FE did not drop apparently at high potentials. This work offers mechanistic insight into how to identify and maintain the true active sites of catalytic materials for value-added nucleophile electrooxidation reactions.

A Ni2P/NiMoOx nanocone electrocatalyst for efficient hydrogen evolution: tip-enhanced local electric field effect

The sluggish kinetics of the hydrogen evolution reaction (HER) result in a high overpotential in alkaline solutions. A high-curvature metal oxide heterostructure can effectively boost the electrocatalytic HER by leveraging the tip-enhanced local electric field effect. Herein, Ni2P/NiMoOx nanocones were synthesised on a nickel foam (NF) substrate by etching a metal-organic framework template. The Ni2P/NiMoOx nanocones on the NF substrate served as an advanced electrocatalyst for the HER. Analysis using the finite element method indicated that the high-curvature tips of the Ni2P/NiMoOx nanocones enhanced the local electric field, resulting in a higher concentration of hydrated K+ ions (K(H2O)6+), which facilitated water dissociation and accelerated the reaction kinetics. The tip-enhanced local electric field effect accelerates the mass transfer rate, and the heterostructure promotes charge transfer to activate the active center, thereby synergically enhancing the electrocatalytic reaction. The Ni2P/NiMoOx nanocone electrocatalyst exhibited low overpotentials of 49, 137 and 274 mV at 10, 100 and 500 mA cm-2, respectively, under alkaline conditions for the HER. In addition, the electrocatalyst demonstrated excellent stability over 200 h at 300 mA cm-2. This study provides a promising approach for developing efficient electrocatalysts that facilitate the HER in alkaline solutions.

Mitigating A-Site Segregation in Pyrochlore Oxides: Enhancing Oxygen Evolution Reaction Performance through Surface Engineering

Significant progress has been achieved in enhancing the oxygen evolution reaction (OER) performance of pyrochloric oxides through geometric and electronic structure regulation. However, the issue of A-site cation segregation in these materials remains underexplored. In this study, Bi2Ru2O7, a promising OER electrocatalyst, is synthesized via a sol-gel method, and its surface is modified using l-ascorbic acid to address Bi3+ segregation. This treatment selectively removes the Bi2O3 passivation layer, inducing an amorphous RuOx layer that forms a heterostructure with crystalline Bi2Ru2O7. This engineered structure significantly enhances catalytic performance, reducing the overpotential to 259 mV at 10 mA cm-2 and maintaining stability after continuous operation for >30 h. Comprehensive characterization, electrochemical testing, and density functional theory calculations reveal that the improvements stem from an increased number of oxygen vacancies and enhanced electron transfer. This work underscores the importance of surface engineering to mitigate A-site segregation, providing a new strategy for optimizing Ru-based pyrochlores in energy conversion technologies.

Ohmic Contact Heterostructures Immobilized Pt Single Atoms for Boosting Alkaline Hydrogen Evolution Reaction

Pt single-atoms catalysts have been widely confirmed as ideal electrocatalysts for high-efficiency hydrogen evolution reaction (HER), but their activity and durability at high current density remain great challenges, especially in alkaline media. Herein, a unique Ohmic contact heterostructure is fabricated by integrating Ni and NiO to immobilize Pt single-atoms (Ni-NiO-Pt) via Pt-O4 coordination for boosting the alkaline HER. Owing to transient high temperature and pressure in the laser ablation process, Ohmic contact heterojunctions are constructed at the interfaces between metal Ni core and nanoporous semiconducting NiO shell with adequate oxygen vacancies. The large work function difference triggers the electron transfer from Ni to Pt-decorated NiO, which dramatically eliminates the electron conduction impedance and regulates the charge redistribution. Density functional theory calculation unveils that the multiple regulations of energy barrier and charge redistribution on Ohmic contact endow Ni-NiO-Pt with outstanding electrical conductivity and favorable hydrogen binding energy. Consequently, Ni-NiO-Pt displays superior alkaline HER performances with an overpotential of 23.54 mV at 10 mA cm-2 and protruding durability for 75 h at 500 mA cm-2, drastically outperforming commercial Pt/C and most reported HER electrocatalysts. The immobilization of Pt single-atoms on Ohmic contact opens up an avenue toward the rational design of high-efficiency electrocatalysts.

Accelerating Tandem Electroreduction of Nitrate to Ammonia via Multi-Site Synergy in Mesoporous Carbon-Supported High-Entropy Intermetallics

The electrochemical nitrate reduction reaction (NO3 -RR) for ammonia (NH3) synthesis represents a significant technological advancement, yet it involves a cascade of elementary reactions alongside various intermediates. Thus, the development of multi-site catalysts for enhancing NO3 -RR and understanding the associated reaction mechanisms for NH3 synthesis is vital. Herein, a versatile approach is presented to construct platinum based high-entropy intermetallic (HEI) library for NH3 synthesis. The HEI nanoparticles (NPs) are uniformly supported on a 2D nitrogen doped mesoporous carbon (N-mC) framework, featured with adjustable compositions (up to eight elements) and a high degree of atomic order (over 90%). Guided by the density functional theory (DFT) calculations and atomic structural analysis, a quinary Pt0.8Fe0.2Co0.2Ni0.2Cu0.2 HEI NPs based N-mC catalyst is designed, which demonstrates a large ammonia Faradaic efffciency (>97%) and a remarkable recyclability (>20 cycles) under both acidic and basic conditions. The combined in situ experimental analysis and further DFT calculation suggests that the well-defined multi-sites nature of the HEI NPs cooperate for a tandem reduction mechanism, in which the Pt-X (X represents the other four transition elements) bridging sites offer optimal adsorption for key nitrogen-oxygen species while the Pt sites facilitate the generation and adsorption of *H species.

Electronic Structure Engineering of RuNi Alloys Decrypts Hydrogen and Hydroxyl Active Site Separation and Enhancement for Efficient Alkaline Hydrogen Evolution

Rational design of the active sites of hydrolysis dissociation intermediates to weaken their active site competition and toxicity is a key challenge to achieve efficient and stable hydrogen evolution reaction (HER) in ruthenium-containing alloys. Density Functional Theory (DFT) simulations reveal that the transfer of the d-band electrons from Ru to Ni in RuNi alloys results in a Gibbs free energy of -0.12 eV for the Ru0.250Ni Fcc-site H*. In addition, the high spin state of the electrons outside the Ru nucleus strengthens the adsorption of OH* on the Ru─Ni bond, which weakens the active-site competition and toxicity successfully. This theoretical prediction is confirmed by electrodeposition of prepared aRuxNi, and the RuNi alloys obtained by Ru atom doping have excellent HER properties. aRu0.250Ni has overpotentials of 38 and 162.4 mV at -10 and -100 mA cm-2, respectively, and can be stably operated at -100 mA cm-2 Dual-electrode system aRu0.250Ni//bRu0Ni demonstrates an ultra-low battery voltage (1.86 V @500 mA cm-2) and excellent stability (24 h@300 mA cm-2). This holistic work resolves the mechanism of active site separation and strengthening in RuNi alloys, and provides a new design idea for the preparation of highly efficient alkaline HER electrodes.

Transforming Adsorbate Surface Dynamics in Aqueous Electrocatalysis: Pathways to Unconstrained Performance

Developing highly efficient catalysts to accelerate sluggish electrode reactions is critical for the deployment of sustainable aqueous electrochemical technologies, yet remains a great challenge. Rationally integrating functional components to tailor surface adsorption behaviors and adsorbate dynamics would divert reaction pathways and alleviate energy barriers, eliminating conventional thermodynamic constraints and ultimately optimizing energy flow within electrochemical systems. This approach has, therefore, garnered significant interest, presenting substantial potential for developing highly efficient catalysts that simultaneously enhance activity, selectivity, and stability. The immense promise and rapid evolution of this design strategy, however, do not overshadow the substantial challenges and ambiguities that persist, impeding the realization of significant breakthroughs in electrocatalyst development. This review explores the latest insights into the principles guiding the design of catalytic surfaces that enable favorable adsorbate dynamics within the contexts of hydrogen and oxygen electrochemistry. Innovative approaches for tailoring adsorbate-surface interactions are discussed, delving into underlying principles that govern these dynamics. Additionally, perspectives on the prevailing challenges are presented and future research directions are proposed. By evaluating the core principles and identifying critical research gaps, this review seeks to inspire rational electrocatalyst design, the discovery of novel reaction mechanisms and concepts, and ultimately, advance the large-scale implementation of electroconversion technologies.

Photocatalytic Semiconductor-Metal Hybrid Nanoparticles: Single-Atom Catalyst Regime Surpasses Metal Tips

Semiconductor-metal hybrid nanoparticles (HNPs) are promising materials for photocatalytic applications, such as water splitting for green hydrogen generation. While most studies have focused on Cd containing HNPs, the realization of actual applications will require environmentally compatible systems. Using heavy-metal free ZnSe-Au HNPs as a model, we investigate the dependence of their functionality and efficiency on the cocatalyst metal domain characteristics ranging from the single-atom catalyst (SAC) regime to metal-tipped systems. The SAC regime was achieved via the deposition of individual atomic cocatalysts on the semiconductor nanocrystals in solution. Utilizing a combination of electron microscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy, we established the presence of single Au atoms on the ZnSe nanorod surface. Upon increased Au concentration, this transitions to metal tip growth. Photocatalytic hydrogen generation measurements reveal a strong dependence on the cocatalyst loading with a sharp response maximum in the SAC regime. Ultrafast dynamics studies show similar electron decay kinetics for the pristine ZnSe nanorods and the ZnSe-Au HNPs in either SAC or tipped systems. This indicates that electron transfer is not the rate-limiting step for the photocatalytic process. Combined with the structural-chemical characterization, we conclude that the enhanced photocatalytic activity is due to the higher reactivity of the single-atom sites. This holistic view establishes the significance of SAC-HNPs, setting the stage for designing efficient and sustainable heavy-metal-free photocatalyst nanoparticles for numerous applications.

Soft nanoforest of metal single atoms for free diffusion catalysis

Metal single atoms are of increasing importance in catalytic reactions. However, the mass diffusion is yet substantially limited by the confined surface of the support in comparison to homogeneous catalysis. Here, we demonstrate that cylindrical micellar brushes with highly solvated poly(2-vinylpyridine) coronas can immobilize 33 types of metal single atoms with 8.3 to 40.9 weight % contents on conventional electrodes under ambient conditions. This is favored by the forest-like hierarchically open soft structure of the micellar brushes and the dynamic coordination between the metals and the pyridine groups. It was found that the nanoforests of individual noble metal single atoms can be well solvated in an aqueous electrolyte to comprehensively expose the atomic active sites and the nanoforest of Pt single atoms on nickel foam reveals high electrochemical performance for hydrogen evolution. The micellar brush support also enables the simultaneous anchoring of multiple single atoms on the cathode of an anion-exchange membrane electrolyzer for long-term stable water electrolysis.

Arrayed metal phosphide heterostructure by Fe doping for robust overall water splitting

Transition metal phosphides (TMPs) show promise in water electrolysis due to their electronic structures, which activate hydrogen/oxygen reaction intermediates. However, TMPs face limitations in catalytic efficiency due to insufficient active sites, poor conductivity, and multiple intermediate steps in water electrolysis. Here, we synthesize a highly efficient bifunctional self-supported electrocatalyst, which consists of an N-doped carbon shell anchored on Fe-doped CoP/Co2P arrays on nickel foam (NC@Fe-CoxP/NF) using hydrothermal and phosphorization techniques. Experimental and theoretical results indicate that the modified morphology, with increased active site density and a tunable electronic structure induced by Fe doping in the CoP/Co2P heterostructure, leads to superior water electrolysis performance. The resulting NC@Fe0.1-CoP/Co2P/NF catalyst exhibits overpotentials of 122 mV for the hydrogen evolution reaction (HER) and 270 mV for the oxygen evolution reaction (OER) at 100 mA cm-2. Furthermore, using NC@Fe0.1-CoP/Co2P/NF as both the cathode and anode in an alkaline electrolyzer enables the cell system to achieve 100 mA cm-2 at a voltage of 1.70 V, while maintaining long-term catalytic durability. This work may pave the way for designing self-supported, highly efficient electrocatalysts for practical water electrolysis applications.

Interface Electron Transfer Direction-Tuned Urea Electrooxidation Over Multi-Interface Nickel Sulfide Heterojunctions

Hydrogen can be produced by electrolyzing urea aqueous solution under smaller overpotentials, owing to the lower thermodynamic potential of urea oxidation reaction (UOR) at anode than oxygen evolution reaction (OER). The efficient and selective electrocatalysts for UOR are crucial to achieve this. Herein, two NiS-based NiS/Ni3S2 and NiS/NiS2 heterojunctions with Ni cores embedding in nitrogen-doped carbon nanotubes (NiS/Ni3S2- and NiS/NiS2-Ni@NCNT) are demonstrated as efficient UOR electrocatalysts. The electrocatalytic UOR performance over heterojunctions is efficiently tuned by altering the electron transfer direction on their interfaces. NiS/Ni3S2-Ni@NCNT with interface electrons transferring from Ni3S2 to NiS, delivers a 10 mA cm-2 UOR current density in 1.0 m KOH with 0.5 m urea at 1.37 V, superior to NiS/NiS2-Ni@NCNT with the electron transfer direction from NiS to NiS2. Experimental and theoretical calculation results reveal that NiS/Ni3S2 Mott-Schottky heterojunctions facilitate the rapid in situ formation of NiOOH active species by removing electrons of Ni3S2, and also accelerate the adsorption and conversion of urea molecules and key intermediates of *CON2 at its interfaces. This work demonstrates an interface electron transfer direction tuning strategy on heterojunctions for harvesting high-performance UOR electrocatalysts.

Isolated Rhodium Atoms Activate Porous TiO2 for Enhanced Electrocatalytic Conversion of Nitrate to Ammonia

The direct electrochemical reduction of nitrate to ammonia is an efficient and environmentally friendly technology, however, developing electrocatalysts with high activity and selectivity remains a great challenge. Single-atom catalysts demonstrate unique properties and exceptional performance across a range of catalytic reactions, especially those that encompass multi-step processes. Herein, a straightforward and cost-effective approach is introduced for synthesizing single-atom dispersed Rh on porous TiO2 spheres (Rh1-TiO2), which functions as an efficient electrocatalyst for the electroreduction of NO3 - to NH3. The synthesized Rh1-TiO2 catalyst achieve a maximum NH3 Faradaic efficiency (FE) of 94.7% and an NH3 yield rate of 29.98 mg h-1 mgcat -1 at -0.5 V versus RHE in a 0.1 M KOH+0.1 M KNO3 electrolyte, significantly outperforming not only undoped TiO2 but also Ru, Pd, and Ir single-atom doped titania catalysts. Density functional theory calculations reveal that the incorporation of Rh single atom significantly enhances charge transfer between adsorbed NO3 - and the active site. The Rh atoms not only serve as the highly active site for electrochemical nitrate reduction reaction (NO3RR), but also activates the adjacent Ti sites through optimizating the electronic structure, thereby reducing the energy barrier of the rate-limiting step. Consequently, this results in a substantial enhancement in electrochemical NO3RR performance. Furthermore, this synthetic method has the potential to be extended to other single-atom catalysts and scaled up for commercial applications.

Constructing Dense CoRu-CoMoO4 Heterointerfaces with Electron Redistribution for Synergistically Boosted Alkaline Electrocatalytic Water Splitting

Constructing metal alloys/metal oxides heterostructured electrocatalysts with abundant and strongly coupling interfaces is vital yet challenging for practical electrocatalytic water splitting. Herein, CoRu nanoalloys uniformly anchored on CoMoO4 nanosheet heterostructured electrocatalyst (CoRu-CoMoO4/NF) are synthesized via a self-templated strategy by simply annealing of Ru-etched CoMoO4/NF precursor in a reduction atmosphere. The dense and robustly coupled interface not only provides abundant active sites for water splitting but also strengthens the charge transfer efficiency. Furthermore, the theoretical calculations unveil that the strong electronic interaction at CoRu-CoMoO4 interface can induce an interfacial electron redistribution and reduce the energetic barriers for the hydrogen and oxygen intermediates, thereby accelerating the  hydrogen evolution reaction (HER) and  oxygen evolution reaction (OER) kinetics. The resultant catalyst only requires the overpotentials of 49 mV for HER and 209 mV for OER at 10 mA cm-2. Moreover, the constructed CoRu-CoMoO4||CoRu-CoMoO4 two-electrode cell achieves a cell voltage of 1.54 V at 10 mA cm-2, outperforming the benchmark Pt/C||IrO2. This work explores an avenue for the rational design of heterostructured electrocatalysts with abundant interfaces for practical water-splitting electrocatalysis.

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.

Electronic Structure Modulating of W18O49 Nanospheres by Niobium Doping for Efficient Hydrogen Evolution Reaction

Hydrogen, known for its high energy density and environmental benefits, serves as a prime substitute for fossil fuels. Nonetheless, the hydrogen evolution reaction (HER), essential in electrolysis, encounters challenges with slow kinetics and significant overpotential, which elevate costs and reduce efficiency. Thus, developing efficient electrocatalysts to reduce HER overpotential is vital to enhance hydrogen production efficiency and minimize energy consumption. Adjusting the electronic structure of transition metal oxides via elemental doping is a potent strategy to improve the effectiveness of electrocatalysts for hydrogen evolution. In this work, we synthesized a set of niobium-doped tungsten oxides (Nbx-W18O49) under anoxic conditions using a straightforward "one-pot" solvothermal approach. After doping Nb, the oxygen vacancy content inside W18O49 was increased, which induced a synergistic effect with the active sites of tungsten. In acidic environments, the hydrogen evolution activity of the Nb0.6-W18O49 electrocatalyst is second only by 20 wt % Pt/C. It attains a current density of -10 mA cm-2 at an overpotential of 102 mV. By comparison with W18O49, Nb0.4-W18O49 and Nb0.5-W18O49, Nb0.6-W18O49 demonstrates a reduced charge transfer resistance, which significantly enhances its conductivity and the speed of electron movement across interfaces. Coupled with this feature are notably faster HER kinetics. Additionally, it exhibits excellent stability, meaning it maintains its performance and structural integrity over prolonged periods and under various operational conditions. This article provides a new perspective for discovering inexpensive and efficient hydrogen evolution electrocatalyst materials.

Biphasic 1T/2H-MoS2 Nanosheets In Situ Vertically Anchored on Reduced Graphene Oxide via Covalent Coupling of the Mo-O-C Bond for Enhanced Electrocatalytic Hydrogen Evolution

Transition-metal dichalcogenides (TMDs) have recently emerged as promising electrocatalysts for the hydrogen evolution reaction owing to their tunable electronic properties. However, TMDs still encounter inherent limitations, including insufficient active sites, poor conductivity, and instability; thus, their performance breakthrough mainly depends on structural optimization in hybridization with a conductive matrix and phase modulation. Herein, a 1T/2H-MoS2/rGO hybrid was rationally fabricated, which is characterized by biphasic 1T/2H-MoS2 nanosheets in situ vertically anchored on reduced graphene oxide (rGO) with strong C-O-Mo covalent coupling. The rGO substrate improves the conductivity and ensures high-dispersed 1T/2H-MoS2 nanosheets to expose plentiful highly active edges. More importantly, the strong heterointerface electrical interaction by the C-O-Mo covalent bond can enhance the charge-transfer efficiency and reinforce structural stability. Furthermore, the integration with the appropriate 2H phase is in favor of stabilization of the metastable 1T phase; thus, the ratio of 1T and 2H was precisely regulated to balance activity and stability. With these advantages, the 1T/2H-MoS2/rGO catalyst presents a satisfactory activity and stability, as confirmed by the relatively low overpotential (268 and 140 mV at 10 mA cm-2) and the small Tafel slope (102 and 86 mV dec-1) in alkaline and acidic media, respectively. The theory calculations disclose that the electronic structure redistribution has been optimized via the strong coupled C-O-Mo heterointerface and phase interface, significantly reducing the adsorption free energy of hydrogen and improving intrinsic activity.

Anchoring Pt Single-Atom Sites on Vacancies of MgO(Al) Nanosheets as Bifunctional Catalysts to Accelerate Hydrogenation-Cyclization Cascade Reactions

The direct hydrogenation of 2-nitroacylbenzene to 2,1-benzisoxazole presents a significant challenge in the pharmaceutical and fine chemicals industries. In this study, a defect engineering strategy is employed to create bifunctional single-atom catalysts (SACs) by anchoring Pt single atoms onto metal vacancies within MgO(Al) nanosheets. The resultant Pt1/MgO(Al) SAC displays an exceptional catalytic activity and selectivity in the hydrogenation-cyclization of 2-nitroacylbenzene, achieving a 97.5 % yield at complete conversion and a record-breaking turnover frequency of 458.8 h-1 under the mild conditions. The synergistic catalysis between the fully exposed single-atom Pt sites within a unique Pt-O-Mg/Al moiety and the abundant basic sites of the MgO(Al) support is responsible for this outstanding catalytic performance. The current work, therefore, paves the way for developing bifunctional or multifunctional SACs that can enhance efficient organocatalytic conversions.

Pt Single Atom-Doped Triphasic VP-Ni3P-MoP Heterostructure: Unveiling a Breakthrough Electrocatalyst for Efficient Water Splitting

Enhancement of an alkaline water splitting reaction in Pt-based single-atom catalysts (SACs) relies on effective metal-support interactions. A Pt single atom (PtSA)-immobilized three-phased PtSA@VP-Ni3P-MoP heterostructure on nickel foam is presented, demonstrating high catalytic performance. The existence of PtSA on triphasic metal phosphides gives an outstanding performance toward overall water splitting. The PtSA@VP-Ni3P-MoP performs a low overpotential of 28 and 261 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at a current density of 10 and 25 mA cm-2, respectively. The PtSA@VP-Ni3P-MoP (+,-) alkaline electrolyzer achieves a minimum cell voltage of 1.48 V at a current density of 10 mA cm-2 for overall water splitting. Additionally, the electrocatalyst exhibits a substantial Faradaic yield of ≈98.12% for H2 and 98.47% for O2 at a current density of 50 mA cm-2. Consequently, this study establishes a connection for understanding the active role of single metal atoms in substrate configuration for catalytic performance. It also facilitates the successful synthesis of SACs, with a substantial loading on transition metal phosphides and maximal atomic utilization, providing more active sites and, thereby enhancing electrocatalytic activity.

Electronic Structure Regulated Carbon-Based Single-Atom Catalysts for Highly Efficient and Stable Electrocatalysis

Single-atom-catalysts (SACs) with atomically dispersed sites on carbon substrates have attained great advancements in electrocatalysis regarding maximum atomic utilization, unique chemical properties, and high catalytic performance. Precisely regulating the electronic structure of single-atom sites offers a rational strategy to optimize reaction processes associated with the activation of reactive intermediates with enhanced electrocatalytic activities of SACs. Although several approaches are proposed in terms of charge transfer, band structure, orbital occupancy, and the spin state, the principles for how electronic structure controls the intrinsic electrocatalytic activity of SACs have not been sufficiently investigated. Herein, strategies for regulating the electronic structure of carbon-based SACs are first summarized, including nonmetal heteroatom doping, coordination number regulating, defect engineering, strain designing, and dual-metal-sites scheming. Second, the impacts of electronic structure on the activation behaviors of reactive intermediates and the electrocatalytic activities of water splitting, oxygen reduction reaction, and CO2/N2 electroreduction reactions are thoroughly discussed. The electronic structure-performance relationships are meticulously understood by combining key characterization techniques with density functional theory (DFT) calculations. Finally, a conclusion of this paper and insights into the challenges and future prospects in this field are proposed. This review highlights the understanding of electronic structure-correlated electrocatalytic activity for SACs and guides their progress in electrochemical applications.

Twin-distortion modulated ultra-low coordination PtRuNi-Ox catalyst for enhanced hydrogen production from chemical wastewater

The development of efficient and robust catalysts for hydrogen evolution reaction is crucial for advancing the hydrogen economy. In this study, we demonstrate that ultra-low coordinated hollow PtRuNi-Ox nanocages exhibit superior catalytic activity and stability across varied conditions, notably surpassing commercial Pt/C catalysts. Notably, the PtRuNi-Ox catalysts achieve current densities of 10 mA cm-2 at only 19.6 ± 0.1, 20.9 ± 0.1, and 21.0 ± 0.1 mV in alkaline freshwater, chemical wastewater, and seawater, respectively, while maintaining satisfied stability with minimal activity loss after 40,000 cycles. In situ experiments and theoretical calculations reveal that the ultra-low coordination of Pt, Ru, and Ni atoms creates numerous dangling bonds, which lower the water dissociation barrier and optimizing hydrogen adsorption. This research marks a notable advancement in the precise engineering of atomically dispersed multi-metallic centers in catalysts for energy-related applications.

Efficient Electrocatalytic Hydrodechlorination and Detoxification of Chlorophenols by Palladium-Palladium Oxide Heterostructure

Electrocatalytic hydrodechlorination is a promising approach for simultaneous pollutant purification and valorization. However, the lack of electrocatalysts with high catalytic activity and selectivity limits its application. Here, we propose a palladium-palladium oxide (Pd-PdO) heterostructure for efficient electrocatalytic hydrodechlorination of recalcitrant chlorophenols and selective formation of phenol with superior Pd-mass activity (1.35 min-1 mgPd-1), which is 4.4 times of commercial Pd/C and about 10-100 times of reported Pd-based catalysts. The Pd-PdO heterostructure is stable in real water matrices and achieves selective phenol recovery (>99%) from the chlorophenol mixture and efficient detoxification along chlorophenol removal. Experimental results and computational modeling reveal that the adsorption/desorption behaviors of zerovalent Pd and PdO sites in the Pd-PdO heterostructure are optimized and a synergy is realized to promote atomic hydrogen (H*) generation, transfer, and utilization: H* is efficiently generated at zerovalent Pd sites, transferred to PdO sites, and eventually consumed in the dechlorination reaction at PdO sites. This work provides a promising strategy to realize the synergy of Pd with different valence states in the metal-metal oxide heterostructure for simultaneous decontamination, detoxification, and resource recovery from halogenated organic pollutants.

Single Atom Catalysts Based on Earth-Abundant Metals for Energy-Related Applications

Anthropogenic activities related to population growth, economic development, technological advances, and changes in lifestyle and climate patterns result in a continuous increase in energy consumption. At the same time, the rare metal elements frequently deployed as catalysts in energy related processes are not only costly in view of their low natural abundance, but their availability is often further limited due to geopolitical reasons. Thus, electrochemical energy storage and conversion with earth-abundant metals, mainly in the form of single-atom catalysts (SACs), are highly relevant and timely technologies. In this review the application of earth-abundant SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or products with high energy content is discussed. The oxygen reduction reaction is also appraised, which is primarily harnessed in fuel cell technologies and metal-air batteries. The coordination, active sites, and mechanistic aspects of transition metal SACs are analyzed for two-electron and four-electron reaction pathways. Further, the electrochemical water splitting with SACs toward green hydrogen fuel is discussed in terms of not only hydrogen evolution reaction but also oxygen evolution reaction. Similarly, the production of ammonia as a clean fuel via electrocatalytic nitrogen reduction reaction is portrayed, highlighting the potential of earth-abundant single metal species.

Tantalum-induced reconstruction of nickel sulfide for enhanced bifunctional water splitting: Separate activation of the lattice oxygen oxidation and hydrogen spillover

Designing highly active and stable bifunctional catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under alkaline conditions is crucial for sustainable overall water splitting. Herein, we present a targeted reconstruction of Ni3S2 by introducing tantalum, achieving remarkable overall water splitting performance through the separate activation of the lattice oxygen mechanism and hydrogen spillover. Electrochemical Mass Spectrometry and in-situ Raman spectroscopy reveal that tantalum induces Ni3S2 to reconstruct into nickel hydroxide during OER, thereby enhancing catalytic activity via the activation of the lattice oxygen mechanism. In the corresponding HER, tantalum promotes the reconstruction of Ni3S2 into oxysulfide, facilitates hydrogen spillover, and acts as an anchor to shorten the spillover distance, improving the HER catalytic performance, as verified by the kinetic isotope effect and theoretical calculations. Therefore, the catalyst-based anion exchange membrane water electrolyzer system achieves a current density of 1 A cm-2 at just 1.97 V, maintaining continuous operation for 500 h. This study offers new insights into the design of bifunctional catalysts, advancing the development of efficient and robust overall water splitting catalysts.

Oriented Crystal Polarization Tuning Bulk Charge and Single-Site Chemical State for Exceptional Hydrogen Photo-Production

Rapid bulk charge recombination and mediocre surface catalytic sites harshly restrict the photocatalytic activities. Herein, the aforementioned concerns are well addressed by coupling macroscopic spontaneous polarization and atomic-site engineering of CdS single-crystal nanorods for superb H2 photo-production. The oriented growth of CdS nanorods along the polar axis, vectorially superimposing substantial polar units with orderly arrangement, renders a strong polarization electric field (20.1 times enhancement), which boosts bulk charge separation with an efficiency up to 72.4% (80.4-fold). Remarkably, polarization electric field alters the chemical state of Pt single sites by orderly reducing the binding energy of Pt atom with stepwise polarization enhancement of CdS substrate, which increases the onsite electron density of Pt from 10.232 to 10.261e- and *H key intermediates, providing preponderant Volmer-Tafel/Volmer-Heyrovsky reaction pathways with significantly decreased energy barriers for H2 production. Thus, highly polarized CdS nanorods with atomically dispersed Pt sites perform an outstanding H2 space-time yield of 118.5 mmol g-1 h-1 and apparent quantum efficiency of 57.7% at λ = 420 nm, and a record-high H2 turnover frequency of 57798.4 h-1, being one of the best catalysts for photocatalytic H2 evolution. This work highlights the function of polarization in manipulating charge separation and catalytic reaction.

WS2 Moiré Superlattices Supporting Au Nanoclusters and Isolated Ru to Boost Hydrogen Production

Maximizing the catalytic activity of single-atom and nanocluster catalysts through the modulation of the interaction between these components and the corresponding supports is crucial but challenging. Herein, guided by theoretical calculations, a nanoporous bilayer WS2 Moiré superlattices (MSLs) supported Au nanoclusters (NCs) adjacent to Ru single atoms (SAs) (Ru1/Aun-2LWS2) is developed for alkaline hydrogen evolution reaction (HER) for the first time. Theoretical analysis suggests that the induced robust electronic metal-support interaction effect in Ru1/Aun-2LWS2 is prone to promote the charge redistribution among Ru SAs, Au NCs, and WS2 MSLs support, which is beneficial to reduce the energy barrier for water adsorption and thus promoting the subsequent H2 formation. As feedback, the well-designed Ru1/Aun-2LWS2 electrocatalyst exhibits outstanding HER performance with high activity (η10 = 19 mV), low Tafel slope (35 mV dec-1), and excellent long-term stability. Further, in situ, experimental studies reveal that the reconstruction of Ru SAs/NCs with S vacancies in Ru1/Aun-2LWS2 structure acts as the main catalytically active center, while high-valence Au NCs are responsible for activating and stabilizing Ru sites to prevent the dissolution and deactivation of active sites. This work offers guidelines for the rational design of high-performance atomic-scale electrocatalysts.

Silver Nanowire Aerogel Support Promotes Stable Hydrogen Evolution Reaction at High Current Density

The stability of electrocatalysts during the hydrogen evolution reaction (HER) is vital for efficient production of hydrogen energy. Herein, we demonstrate that silver nanowire aerogel-based support (AABS) could facilitate the construction of HER catalysts with extraordinary long-term stability. A full nanostructure catalyst of nickel phosphide based formed on AABS (Ni2P-Ni5P4@AABS) was prepared to achieve an overpotential of 687 mV (without iR compensation) for HER at the current density of 1 A cm-2 in 0.5 M H2SO4. Excitingly, the stable HER performance was kept for 42 days during the long-term stability (i-t) test at high current density (0.5-1 A cm-2). The excellent HER performance of the Ni2P-Ni5P4@AABS catalyst is attributed to rapid electron transport pathways, numerous more accessible active sites, and support induced enhanced catalytic activity. The support effect was highlighted by a proposed phenomenological two-channel model for electron transport, which provides fresh insights into the design strategy for energy storage and delivery.

Covalent Organic Frameworks for Electrocatalysis: Design, Applications, and Perspectives

Covalent organic frameworks (COFs) are an innovative class of crystalline porous polymers composed of light elements such as C, N, O, etc., linked by covalent bonds. The distinctive properties of COFs, including designable building blocks, large specific surface area, tunable pore size, abundant active sites, and remarkable stability, have led their widespread applications in electrocatalysis. In recent years, COF-based electrocatalysts have made remarkable progress in various electrocatalytic fields, including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, nitrogen reduction reaction, nitrate reduction reaction, and carbon dioxide reduction reaction. This review begins with an introduction to the design and synthesis strategies employed for COF-based electrocatalysts. These strategies include heteroatom doping, metalation of COF and building monomers, encapsulation of active sites within COF pores, and the development of COF-based derived materials. Subsequently, a systematic overview of the recent advancements in the application of COF-based catalysts in electrocatalysis is presented. Finally, the review discusses the main challenges and outlines possible avenues for the future development of COF-based electrocatalysts.

Structural evolution and catalytic mechanisms of perovskite oxides in electrocatalysis

Electrocatalysis plays a pivotal role in driving the progress of modern technologies and industrial processes such as energy conversion and emission reduction. Perovskite oxides, an important family of electrocatalysts, have garnered substantial attention in diverse catalytic reactions because of their highly tunable composition and structure, as well as their considerable activity and stability. This review delves into the mechanisms of electrocatalytic reactions that use perovskite oxides as electrocatalysts, while also providing a comprehensive summary of the potential key factors that influence catalytic activity across various reactions. Furthermore, this review offers an overview of advanced characterizations used for studying catalytic mechanisms and proposes approaches to designing highly efficient perovskite oxide electrocatalysts.

Platinum/Platinum Sulfide on Sulfur-Doped Carbon Nanosheets with Multiple Interfaces toward High Hydrogen Evolution Activity

Platinum (Pt)-based materials are among the most competitive electrocatalysts for the hydrogen evolution reaction (HER) due to suitable hydrogen adsorption energy. Due to the rarity of Pt, it is desirable to develop cost-effective Pt-based electrocatalysts with low Pt loading. Herein, Pt/PtS electrocatalysts on S-doped carbon nanofilms (PPS/C) have been successfully fabricated through a precursor reduction route with a complex of Pt and 1-dodecanethiol (1-DDT) as the precursor. The PPS/C achieved at 400 °C (PPS/C-400) exhibits excellent HER performances with an ultralow overpotential of 41.3 mV, a low Tafel slope of 43.1 mV dec-1 at a current density of 10 mA cm-2, and a long-term stability of 10 h, superior to many recently reported Pt-based HER electrocatalysts. More importantly, PPS/C-400 shows a high mass-specific activity of 0.362 A mgPt-1 at 30 mV, which is 1.88 times of that of commercial 20% Pt/C (0.193 A mgPt-1). The introduction of sulfur leads to the formation of PtS, which not only reduces the content of Pt but also realizes the interface regulation of Pt/PtS, as well as the doping of carbon. Both regulations make the resulting catalyst have abundant active centers and rapid electron transfer/transport, which is conducive to balancing the adsorption and resolution of intermediate products, and finally achieving great mass-specific activity and stability. The research work may provide ideas for designing effective Pt-based multi-interface electrocatalysts.

Design and synthesis of magnesium-modified copper oxide nanosheets as efficient electrocatalysts for CO2 reduction

Electroreduction of carbon dioxide (CO2) to multiple carbon products plays a significant role in carbon neutrality and the production of valuable chemicals. Herein, we developed a magnesium-modified copper oxide nanosheet catalyst (Mg-CuO) using a post-impregnation method. Comprehensive elemental analysis demonstrated the effective incorporation of magnesium into CuO nanosheets, resulting in a noticeable alteration of the electron density of Cu atoms. Consequently, the Mg-CuO nanosheets exhibited an increased efficiency for CO2 electroreduction in comparison with the unmodified CuO nanosheets. The optimized Mg-CuO catalyst exhibited faradaic efficiencies of 46.33% for ethylene production and 62.64% for C2+ production at -1.3 V vs. reversible hydrogen electrode (RHE). DFT proved that the introduction of Mg species could increase the charge density of Cu and decrease the adsorption energy of *CO, which promoted C-C coupling and enhanced the selectivity of C2+ products. This study presents an effective way to adjust the electronic structure of common copper-based electrocatalysts and the corresponding interaction with *CO, resulting in an improved faradaic efficiency of C2+ products.