A fundamental viewpoint on the hydrogen spillover phenomenon of electrocatalytic hydrogen evolution

A systematic investigation on the advantage of confinement effect by nitrogen doped carbon nanotubes for hydrogen evolution reaction

Robust hydrogen evolution reaction (HER) electrocatalyst is of significance important for the realization of water splitting technology. In this work, we report the nitrogen doped carbon nanotubes confined CoRu alloy nanoparticles (CoRu@NCNT) as superior HER electrocatalyst. The d band center of Ru atom is downshifted resulting in loosening the hydrogen binding strength; therefore, a robust HER activity is achieved for CoRu@NCNT with mass activity enhanced by 6-time than commercial Pt/C and CoRu/NCNT in both acidic and alkaline mediums. Moreover, compared to CoRu/NCNT electrocatalyst, CoRu@NCNT exhibits a better HER performance attributed to the prevention of avoidable surface oxidation of Ru. Moreover, a more moderate Gibbs free energy for hydrogen is achieved for CoRu@NCNT. Similarly, the stability of CoRu@NCNT outperforms CoRu/NCNT stemming from the NCNT confinement effect suppressing the movement and coalescence of CoRu nanoparticles.

Pd1-O-Ti dual sites for efficient electrochemical active hydrogen generation and bromate reduction

Atomic hydrogen (H*) plays a crucial role in electrochemical reduction technology towards various environmental and energy applications, but suffers from low utilization efficiency arisen from the undesirable H-H dimerization and the competitive adsorption between water molecule with reactants on the traditional adjacent catalytic sites. Herein, we anchored Pd single atoms on the naturally formed titanium oxide of titanium foam to construct Pd1-O-Ti dual-site electrocatalyst with spatially isolated water dissociation and H* utilization site, which synchronously inhibits the H-H dimerization and the competitive adsorption of water molecule and targeted reactants. Experiments and theoretical calculations revealed that the Ti-O sites could synergistically dissociate water to H*, which overflowed to nearby Pd single-atom sites for designed reduction reactions and utilization benefiting from the hydrogen spillover ability of titanium oxide substrate. These Pd1-O-Ti dual sites delivered almost 100 % bromate reduction efficiency with a rate constant of 1.57 h-1, far superior to those of Pdn-O-Ti with adjacent Pd sites (0.52 h-1), Pd1-N-C with single sites (0.04 h-1) and commercial Pd/C (0.18 h-1), respectively. This study sheds light on the importance of integrating synergistic active sites for complicated electrochemical reactions, and provide new insights in improving H* utilization for environmental remediation.

Tailored electronic interaction between metal-support trigger reverse hydrogen spillover for efficient hydrogen evolution

The triggering of fast hydrogen spillover through regulating the charge rearrangement of the metal-support serves as a crucial mechanism for decoupling the activity of HER catalysts from the adsorption properties, which not only contributes to enhancing the performance of the catalysts but also facilitates the production of green hydrogen. Herein, we tailor the electronic interaction between two-dimensional (2D) nitrogen-doped MoC (N-MoC) nanosheets and anultra-low content of Pt nanoclusters (1 wt%) to trigger reverse hydrogen spillover and modulate the electronic structure of Pt, thus achieving efficient and stable HER. Compared to Pt/C (0.229 A mgPt-1), Pt/N-MoC demonstrates a mass activity of 12.945 A mgPt-1, representing an enhancement of nearly 57.5 times. Notably, the excellent electrocatalytic performance was verified in the proton exchange membrane water electrolyzer configuration. Combining experimental and theoretical analysis, anultra-low load of Pt nanocluster (1 wt%) integrated with N-MoC nanosheets can induce a charge transfer from N-MoC to Pt, thus modulating the d-band center of Pt to improve the hydrogen adsorption properties and achieving fast hydrogen desorption (ΔG = 0.019 eV); furthermore, a small difference in work function between Pt nanoclusters and the N-MoC were achieved to dilute charge accumulation between the metal-support interface, thus reducing the energy barrier of hydrogen spillover.

Crystal facet-induced reconstruction of MoN-supported Co pre-catalysts for optimized active sites and enhanced alkaline hydrogen evolution

The self-reconstruction of electrocatalysts during the cathodic hydrogen evolution reaction (HER) has garnered significant interest due to its impact on microstructure and electrocatalytic efficiency. Understanding the mechanisms driving this transformation is crucial for the development of high-performance HER pre-catalysts. In this study, an efficient Co(OH)2 (001)/MoN (002) heterostructured catalyst is fabricated through the self-reconstruction of the Co/MoN pre-catalyst and the mechanism of facet-induced reconstruction is investigated in detail. This Co/MoN pre-catalyst exhibits an impressive 58 % reduction in overpotential at a constant current density of 100 mA cm-2 over 5 h. It ultimately achieves a low overpotential of 339 mV at 1 A cm-2, outperforming commercial Pt/C under similar current conditions, while maintaining high current activity with 99.4 % retention after 110 h of continuous electrolysis. Operando characterizations and theoretical simulations reveal that metallic Co dissolves rapidly under bias as H+ ions infiltrate the interstitial spaces, and the dissolved Co2+ ions preferentially deposit as Co(OH)2 nanosheets. This deposition aligns with the (001) facet of Co(OH)2 and the prominent (002) plane of the MoN matrix through lattice matching, exhibiting a very low interfacial formation energy. Density-functional theory analysis reveals that the alignment of the crystal facets between Co(OH)2(001) and MoN (002) enhances electron transfer and modulates the interface to boost the water dissociation and hydrogen adsorption activity and kinetics. Our results underscore the importance of precise control over the reconstruction process for cathodic HER and facilitate the development of advanced transition metal-based electrocatalysts for industrial alkaline hydrogen production.

Built-in Electric Field in Ru/CoP Bifunctional Electrocatalyst Enhances Hydrazine-Assisted Water Splitting

Electrocatalytic hydrazine-assisted water splitting, incorporating the hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), offers a promising avenue for hydrogen production. Herein, a Ru/CoP heterostructure is introduced, which enhances bifunctional catalytic activity through interfacial interaction induced by the built-in electric field between Ru nanoparticles and CoP nanosheets. This interaction optimizes the adsorption of intermediates and facilitates improved HER performances by weakening the strong adsorption of active hydrogen species (*H) on Ru and enhancing *H coverage on CoP through hydrogen spillover. Additionally, this electron interaction promotes the adsorption of N2H4 and its subsequent dehydrogenation, vital for HzOR activity. The heterostructure's significant reduction in required potentials for both reactions underscores its efficiency and potential economic benefits over traditional systems. Furthermore, the study validates the feasibility of using this approach for practical applications in sustainable hydrogen production, emphasizing its lower operational costs and enhanced catalytic stability and activity. This work not only showcases the practical applications of Ru/CoP but also underscores the broader applicability of heterostructure strategy in designing efficient bifunctional electrocatalysts.

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

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

Advances in Nickel-Based Catalysts for Alkaline Water Electrolysis: Comprehensive Review of Current Research Direction for HER and OER Applications

Nickel-based catalysts are among the most promising materials for electrocatalytic water splitting, particularly for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. Their abundance, cost-effectiveness, and tunable electrochemical properties make them attractive alternatives to precious metal catalysts. This review provides a comprehensive analysis of the advancements in nickel-based catalysts, including pure nickel, alloys, oxides, hydroxides, and spinels, emphasizing their synthesis methods, structural properties, and electrocatalytic performance. Recent nanostructuring, doping, and hybridization innovations with conductive supports have significantly enhanced catalytic activity, stability, and efficiency. Despite notable progress, challenges remain in improving long-term durability, minimizing surface degradation, and scaling up production for industrial applications. Addressing these limitations through advanced catalyst design, in situ characterization, and integration with renewable energy sources will be crucial for widely adopting nickel-based catalysts in sustainable hydrogen production. This review highlights the key developments and future directions in the field, underscoring the role of nickel-based materials in enabling the hydrogen economy and global decarbonization efforts.

Synergistic Effect of Boron and Oxygen Coordination on Ruthenium Clusters for Industrial Water Splitting in Alkaline Medium

The alteration in the coordination environment of metal atoms can manipulate their electronic structure and regulate the electrocatalytic hydrogen evolution activity. In this work, synchrotron radiation tests prove that the boron (B) and oxygen (O) elements co-coordinate with ruthenium clusters (RuC) on the surface of B-O modified reduced graphene oxide. The electrochemical tests demonstrate that this unique structure electrocatalyst presents an overpotential of 12 mV in 1 M KOH condition and for over 120 h at the current of -1 A cm-2, indicating potential practical applications. The quasi in-situ X-ray photoelectron spectroscopy and in-situ infrared spectroscopy confirmed that the B-O diatomic coordination can modulate the synergy between the substrate and the RuC catalytic site, enhancing the intrinsic catalytic activity and ion migration efficiency. The first principles calculation further proves that B-O diatomic coordination will reduce the desorption barrier of H* and construct a complete hydrogen migration path. This study discloses the significance of the synergistic effect of two anions to enhance the catalytic activity of the catalyst by altering the coordination environment of ruthenium clusters.

High-entropy layered double hydroxides tailor Pt electron state for promoting acidic hydrogen evolution reaction

Despite the advancement of the Pt-catalyzed hydrogen evolution reaction (HER) through oxophilic metal-hydroxide surface hybridization, its stability in acidic solutions remains unsatisfactory. This is primarily due to excessive aggregation of active hydrogen, which hinders subsequent hydrogen desorption, coupled with the poor operational stability of metal hydroxides. In this study, we have designed Pt nanoparticles-modified NiFeCoCuCr high-entropy layered double hydroxides (Pt/HE-LDH) that exhibit exceptional catalytic activity toward HER in acidic electrolytes. Our findings reveal that the built-in electric field (BIEF) between Pt and HE-LDH facilitates the charge redistribution at Pt/HE-LDH interface, driven by the difference in work function. Additionally, effective hydrogen spillover from Pt nanoparticles to HE-LDH bidirectionally optimizes the Gibbs free energy for hydrogen adsorption. Furthermore, the interactions among the multi-metal sites, along with high entropy-induced phase stability, contribute to superior stability in acidic electrolytes. This work not only presents a straightforward strategy for enhancing hydrogen spillover from Pt but also improves the durability of metal hydroxides under acidic HER conditions.

2D Metastable-Phase Hafnium Oxide Triggers Hydrogen Spillover for Boosting Hydrogen Production

Hydrogen (H) manipulation plays a significantly important role in many important applications, in which the occurrence of hydrogen spillover generally shows substrate-dependent behavior. It therefore remains an open question about how to trigger the hydrogen spillover on the substrates that are generally hydrogen spillover forbidden. Here a new metastable-phase 2D edge-sharing oxide: six-hexagonal phase-hafnium oxide (Hex-HfO2, space group: P63mc (186)) with the coordination number of six is demonstrated, which serves as an ideal platform for activating efficient hydrogen spillover after loading Ru nanoclusters (Ru/Hex-HfO2). For a stark comparison, the hydrogen spillover is strongly forbidden when using stable monoclinic phase HfO2 (M-HfO2, space group: P21/c (14), coordination number: seven) as the substrate. When applied in an acidic hydrogen evolution reaction (HER), Ru/Hex-HfO2 exhibits a low overpotential of 8 mV at 10 mA cm-2 and a high Ru utilization activity of 14.37 A mgRu -1 at 30 mV. Detailed mechanism reveals the positive H adsorption free energy on Hex-HfO2, indicating that H is more likely to spillover on Hex-HfO2. Furthermore, the strong interaction between Ru and Hex-HfO2 optimizes the desorption of hydrogen intermediate, thus facilitating the surface H spillover. The discovery provides new guidance for developing metastable-phase oxide substrates for advanced catalysis.

Promoting Efficient Ruthenium Sites With Lewis Acid Oxide for the Accelerated Hydrogen and Chlor-Alkali Co-Production

Ruthenium (Ru) -based catalysts have been considered a promising candidate for efficient sustainable hydrogen and chlor-alkali co-production. Theoretical calculations have disclosed that the hollow sites on the Ru surface have strong adsorption energies of H and Cl species, which inevitably leads to poor activity for cathodic hydrogen evolution reaction (HER) and anodic chlorine evolution reaction (CER), respectively. Furthermore, it have confirmed that anchoring Lewis acid oxide nanoparticles such as MgO on the Ru surface can induce the formation of the onion-like charge distribution of Ru atoms around MgO nanoparticles, thereby exposing the Ru-bridge sites at the interface as excellent H and Cl adsorption sites to accelerate both HER and CER. Under the guidance of theoretical calculations, a novel dispersed MgO nanoparticles on Ru (MgOx-Ru) electrocatalyst is successfully prepared. In strongly alkaline and saline media, MgOx-Ru recorded excellent HER and CER electrocatalytic activity with a very low overpotential of 19 mV and 74 mV at the current density of 10 mA cm-2, respectively. More stirringly, the electrochemical test with MgOx-Ru as both anodic and cathodic electrodes under simulated chlor-alkali electrolysis conditions demonstrated superior electrocatalytic performance to the industrial catalysts of commercial 20 wt% Pt/C and dimensionally stable anode (DSA).

Photonic Sintering as an Electrode Structuring Process to Improve Electrocatalytic Activity and Durability in Anion Exchange Membrane Water Electrolysis

Hydrogen production via water electrolysis is essential for achieving carbon-free energy. However, enhancing the performance of these systems, particularly at the electrode level, remains challenging. Photonic sintering (PS) is proposed as a highly effective post-treatment method for electrodes, highlighting the importance of electrode design and optimization. PS significantly enhances the catalytic activity and durability of spinel-type copper-cobalt oxide-based anodes for the oxygen evolution reaction and Pt@C-based cathodes for the hydrogen evolution reaction, which are attributed to structural and chemical modifications, including active site control, optimized surface chemical bonding, improved catalyst-substrate adhesion, and generation of a reduced surface. PS-treated electrodes maintain well-preserved electrochemical active sites and pore structures, which are crucial for activation polarization and mass transport kinetics. Consequently, an anion exchange membrane water electrolysis cell with PS-treated electrodes achieved 89.57% cell efficiency, 3.91 W cm-2 area-specific power at 1.8 V, and a low degradation rate of 0.049 mV h-1 (at 0.5 A cm-2) and 0.136 mV h-1 (at 1.0 A cm-2) over 500 h. This research overcomes the traditional trade-off between activity and durability, indicating that PS can be widely applied across various energy fields, including electrochemical storage and conversion.

Electrocatalytic Hydrogenation Boosted by Surface Hydroxyls-Modulated Hydrogen Migration over Nonreducible Oxides

The migration of atomic hydrogen species over heterogeneous catalysts is deemed essential for hydrogenation reactions, a process closely related to the catalyst's functionalities. While surface hydroxyls-assisted hydrogen spillover is well documented on reducible oxide supports, its effect on widely-used nonreducible supports, especially in electrocatalytic reactions with water as the hydrogen source, remains a subject of debate. Herein, a nonreducible oxide-anchored copper single-atom catalyst (Cu1/SiO2) is designed and uncover that the surface hydroxyls on SiO2 can serve as efficient transport channels for hydrogen spillover, thereby enhancing the activated hydrogen coverage on the catalyst and favoring the hydrogenation reaction. Using electrocatalytic dechlorination as a model reaction, the Cu1/SiO2 catalyst delivers hydrodechlorination activity 42 times greater than that of commercial Pd/C. An integrated experimental and theoretical investigation elucidates that surface hydroxyls facilitate the spillover of hydrogen intermediates formed at the Cu sites, boosting the coverage of active hydrogen on the surface of the Cu1/SiO2. This work demonstrates the feasibility of surface hydroxyls acting as transport channels for hydrogen-species to boost hydrogen spillover on nonreducible oxide supports and paves the way for designing advanced selective hydrogenation electrocatalysts.

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.

Single-Atom Enables Reverse Hydrogen Spillover for High-Performance Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) offer a promising avenue for sustainable energy conversion, however, their commercial potential is hindered by sluggish proton-involved oxygen reduction reaction (P-ORR) kinetics and inadequate durability of cathode materials. Here, a novel single-atom Ru anchor on BaCe0.125Fe0.875O3-δ (BCF) perovskite, synthesized by a facile and scalable solid-state approach, as a potential cathode for PCFCs is reported. Theoretical and experimental analyses demonstrate that the single-atom Ru on BCF, characterized by a unique 4-coordinate Ru-O-Fe configuration, not only induces reverse hydrogen spillover but also acts as an active site for P-ORR. The application of the optimized 2Ru-BCF (2 wt.% Ru) cathode in a single cell delivers an exceptional peak power density of 1.78 W cm-2 at 700 °C, along with excellent operational stability over 200 h. These findings provide new insights into single-atom engineering, advancing the commercial viability of PCFCs.

Intensifying Interfacial Reverse Hydrogen Spillover for Boosted Electrocatalytic Nitrate Reduction to Ammonia

Rational regulation of active hydrogen (*H) behavior is crucial for advancing electrocatalytic nitrate reduction reaction (NO3RR) to ammonia (NH3), yet in-depth understanding of the *H generation, transfer, and utilization remains ambiguous, and explorations for *H dynamic optimization are urgently needed. Herein we engineer a Ni3N nanosheet array intimately decorated with Cu nanoclusters (NF/Ni3N-Cu) for remarkably boosted NO3RR. From comprehensive experimental and theoretical investigations, the Ni3N moieties favors water dissociation to generate *H, and then *H can rapidly transfer to the Cu via unique reverse hydrogen spillover mediating interfacial Ni-N-Cu bridge bond, thus increasing *H coverage on the Cu site for subsequent deoxygenation/hydrogenation. More impressively, such intriguing reverse hydrogen spillover effect can be further strengthened via elegant engineering of the Ni3N/Cu heterointerface with more intimate contact. Consequently, the NF/Ni3N-Cu with Cu nanoclusters intimate anchoring presents record NH3 yield rate of 1.19 mmol h-1 cm-2 and Faradaic efficiency of 98.7 % at -0.3 V vs. RHE, being on par with the state-of-the-art ones. Additionally, with NF/Ni3N-Cu as the cathode, a high-performing Zn-NO3 - battery can be assembled. This contribution illuminates a novel pathway to optimize *H behavior via distinct reverse hydrogen spillover for promoted NO3RR and other hydrogenation reactions.

Atomically dispersed cerium on copper tailors interfacial water structure for efficient CO-to-acetate electroreduction

Electrosynthesis of acetate from carbon monoxide (CO) powered by renewable electricity offers one promising avenue to obtain valuable carbon-based products but undergoes unsatisfied selectivity because of the competing hydrogen evolution reaction. We report here a cerium single atoms (Ce-SAs) modified crystalline-amorphous dual-phase copper (Cu) catalyst, in which Ce SAs reduce the electron density of the dual-phase Cu, lowering the proportion of interfacial K+ ion hydrated water (K·H2O) and thereby decreasing the H* coverage on the catalyst surface. Meanwhile, the electron transfer from dual-phase Cu to Ce SAs yields Cu+ species, which boost the formation of active atop-adsorbed *CO (COatop), improving COatop-COatop coupling kinetics. These together lead to the preferential pathway of ketene intermediate (*CH2-C=O) formation, which then reacts with OH- enriched by pulsed electrolysis to generate acetate. Using this catalyst, we achieve a high Faradaic efficiency of 71.3 ± 2.1% toward acetate and a time-averaged acetate current density of 110.6 ± 2.0 mA cm-2 under a pulsed electrolysis mode. Furthermore, a flow-cell reactor assembled by this catalyst can produce acetate steadily for at least 138 hours with selectivity greater than 60%.

Remote Carbon Monoxide Spillover Improves Tandem Urea Electrosynthesis

Electrocatalytic urea synthesis from carbon dioxide (CO2) and nitrate (NO3 -) offers a promising alternative to traditional industrial methods. However, current catalysts face limitations in the supplies of CO* and Nrelated* intermediates, and their coupling, resulting in unsatisfactory urea production efficiency and energy consumption. To overcome these challenges, we carried out tandem electrosynthesis approach using ruthenium dioxide-supported palladium-gold alloys (Pd2Au1/RuO2). This catalyst system effectively catalyzes CO2-to-CO* conversion on Pd2Au1 and NO3 --to-NH2* conversion on RuO2. Crucially, the minimized work function difference between two components promotes remote CO* spillover from Pd2Au1 to RuO2, improving effective coupling of CO* and NH2* for urea production. Our catalyst demonstrated exceptional performance, achieving a record-high Faradaic efficiency for urea (FEurea) of 75.6±0.5 % and a urea production rate (rurea) of 73.5±0.8 mmol gcat -1 h-1. Notably, this was accomplished with an ultralow energy consumption of 18.9 kWh kgurea -1. We also successfully demonstrate the long-term stability of our catalyst in a flow cell, achieving over 160 h of uninterrupted urea and formate production with consistent profitability. This achievement represents a significant step towards the large-scale practical application of sustainable urea electrosynthesis.

Capturing Copper Single Atom in Proton Donor Stimulated O-End Nitrate Reduction

Ammonia (NH3) is vital in global production and energy cycles. Electrocatalytic nitrate reduction (e-NO3RR) offers a promising route for nitrogen (N) conversion and NH3 synthesis, yet it faces challenges like competing reactions and low catalyst activity. This study proposes a synergistic mechanism incorporating a proton donor to mediate O-end e-NO3RR, addressing these limitations. A novel method combining ultraviolet radiation reduction, confined synthesis, and microwave treatment was developed to create a model catalyst embedding Cu single atoms on La-based nanoparticles (p-CNCusLan-m). DFT analysis emphasizes the critical role of La-based clusters as proton donors in e-NO3RR, while in situ characterization reveals an O-end adsorption reduction mechanism. The catalyst achieves a remarkable Faraday efficiency (FENH3) of 97.7%, producing 10.6 mol gmetal -1 h-1 of NH3, surpassing most prior studies. In a flow cell, it demonstrated exceptional stability, with only a 9% decrease in current density after 111 hours and a NH3 production rate of 1.57 mgNH3/h/cm-2. The proton donor mechanism's effectiveness highlights its potential for advancing electrocatalyst design. Beyond NH3 production, the O-end mechanism opens avenues for exploring molecular-oriented coupling reactions in e-NO3RR, paving the way for innovative electrochemical synthesis applications.

Undercoordinated Two-Dimensional Pt Nanoring Stabilized by a Ring-on-Sheet Nanoheterostructure for Highly Efficient Alkaline Hydrogen Evolution Reaction

Platinum (Pt) is a state-of-the-art electrocatalyst for green hydrogen production in alkaline electrolytes. The delicate design and fabrication of two-dimensional (2D) Pt nanocatalysts can significantly enhance atomic utilization efficiency, while further improving intrinsic catalytic performance by modulating the density of surface active sites. However, the high surface energy and morphology complexity of 2D nanostructures often result in poor structural stability under the working conditions. Here, we report the synthesis of a 2D ring-on-sheet nanoheterostructure featuring abundant low-coordination Pt sites in which a defect-rich Pt nanoring is stabilized by an ultrathin 2D rhodium (Rh) support. The Rh@Pt nanoring exhibits remarkably enhanced activity and stability in an electrocatalytic hydrogen evolution reaction in alkaline media compared to defect-free Rh@Pt core-shell nanoplates and commercial Pt/C. This work provides new insights for the design and synthesis of 2D nanoheterostructures with abundant surface active sites for efficient and durable electrocatalysis.

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

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

Effects of oxygen vacancies on hydrogenation efficiency by spillover in catalysts

Hydrogen spillover is crucial for hydrogenation reactions on supported catalysts. The properties of supports have been reported to be very important for affecting hydrogen spillover and the subsequent hydrogenation process. The introduction of oxygen vacancies offers a promising strategy to enhance efficiency of catalysts. Recent advanced characterization and theoretical modeling techniques have provided us with increasing new insights for understanding hydrogen spillover effects. However, a comprehensive understanding of oxygen vacancy effects on hydrogen spillover and hydrogenation efficiency of catalysts is still lacking. This review focuses on the recent advances in support effects especially oxygen vacancy effects on improving the efficiency of catalysts from three process aspects including hydrogen dissociation, active hydrogen spillover, and hydrogenation by spillover. The challenges in studying the effects on hydrogenations by spillover on the supported catalysts are highlighted at the end of the review. It aims to provide valuable strategies for the development of high-performance catalytic hydrogenation materials.

Targeted Conversion of Biomass into Primary Diamines via Carbon Shell-Confined Cobalt Nanoparticles

Primary diamines are valuable yet challenging to synthesize due to issues such as product and intermediate condensation and catalyst poisoning. To address these problems, effective synthesis systems must be explored. Here, 2,5-bis(aminomethyl)furan (BAMF), a biomass-derived primary diamine, is chosen as the model for constructing such a system. A series of carbon-shell confined Co nanoparticles (Co@CNT-x) are fabricated to synthesize BAMF. The Co@CNT-700 catalyst, with ca. 4 layers of carbon shells, achieves an outstanding 96% isolated yield of BAMF through the reductive amination of 2,5-diformylfuran dioxime. In this system, an excess NH3 atmosphere is necessary to prevent condensation reactions by competitive reactions, while the carbon shells protect the catalyst from NH3 and amine poisoning. Control experiments indicate that 2,5-diformylfuran dioxime primarily follows a H2-assisted dehydration pathway to form key imine intermediates, while side products such as amides and nitriles can also eventually be converted into BAMF by Co@CNT-700, leading to its excellent selectivity. Notably, by employing a sequential three-step strategy, ca. 87% BAMF can be achieved by directly using biomass as the raw material. To evaluate the tolerance of this system, 9 other important aromatic, cycloalkyl, and linear alkyl primary diamines, such as 1,4-cyclohexanediamine, are obtained in high yields of 87-99%.

Modulating the Coverage of Adsorbed Hydrogen via Hydrogen Spillover Enables Selective Electrocatalytic Hydrogenation of Phenol to Cyclohexanone

Selective electrocatalytic hydrogenation (ECH) of phenol is a sustainable route to produce cyclohexanone, an industrially important feedstock for polymer synthesis. However, attaining high selectivity and faradaic efficiency (FE) for cyclohexanone remain challenging, owning to over-hydrogenation of phenol to cyclohexanol and competition of hydrogen evolution reaction (HER). Herein, by employing hydrogen spillover effect, we modulate adsorbed hydrogen species (Hads) coverage on Pt surface via migration to TiO2 in an anatase TiO2-supported Pt catalyst. In ECH of phenol, a high selectivity (94 %) and good FE (63 %) for cyclohexanone are obtained, showing more advantageous performance compared with previous reports. Cyclic voltammetry (CV) tests and electrochemical Raman spectroscopy reveal that Hads migrated from Pt to TiO2. We propose that TiO2-induced hydrogen spillover contributes to low Hads coverage over Pt, which effectively hinders over-hydrogenation of cyclohexanone and HER. We establish a scaling relationship between the intensity of hydrogen spillover and cyclohexanone selectivity by varying the types of anatase TiO2, and show the universality of the strategy over other reducible metal oxides as the support (rutile TiO2, CeO2 and WO3). This work showcases an effective strategy for tuning hydrogenation selectivity in electro-catalysis, by taking advantage of thermo-catalytically well-documented hydrogen spillover effect.

High-Entropy Oxychalcogenide for Hydrogen Spillover Enhanced Hydrogen Evolution Reaction in Proton and Anion Exchange Membrane Water Electrolyzers

The hydrogen spillover phenomenon provides an expeditious reaction pathway via hydrogen transfer from a strong H adsorption site to a weak H adsorption site, enabling a cost-efficient hydrogen evolution reaction (HER) analogous to platinum with moderate H adsorption energy. Here, a high-entropy oxychalcogenide (HEOC) comprising Co, Ni, Mo, W, O, Se, and Te is prepared by a two-step electrochemical deposition for hydrogen spillover-enhanced HER in acidic and alkaline water electrolysis. The anodic-cathodic reversal current enables the co-deposition of cations and aliovalent anions, facilitating a glass structure with multiple active sites for hydrogen spillover. The HEOC exhibits low overpotentials of 52 and 57 mV to obtain a current density of 10 mA cm-2 in acidic and alkaline media, respectively, and long-term stability for 500 h. The electrochemical and analytical approaches elucidate the hydrogen transfer toward Mo/W-O sites in both acid and alkaline HERs. Meanwhile, the other sites act as hydrogen adsorption or water dissociation-derived hydroxide adsorption sites, showing accommodable behavior in acidic and alkaline media. The HEOC exhibits a practically high current of 1 A cm-2 at cell voltages of 1.78 and 1.89 V and long-term stability for 100 h in proton and anion exchange membrane water electrolyzers, respectively.

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.

Band Engineering of Mn-P Alloy Enables HER-suppressed Aqueous Manganese Ion Batteries

Aqueous manganese ion batteries hold potential for stationary storage applications owing to their merits in cost, energy density, and environmental sustainability. However, the formidable challenge is the instability of metallic manganese (Mn) anodes in aqueous electrolytes due to severe hydrogen evolution reaction (HER), which is more serious than the commonly studied Zn metal anodes. Moreover, the mechanism of HER side reactions has remained unclear. Herein, we design a series of Mn-P alloying anodes by precisely regulating their energy band structures to mitigate the HER issue. It is found that the serious HER primarily originates from the spontaneous Mn-H2O reaction driven by the excessively high HOMO energy level of Mn, rather than electrocatalytic water splitting. Owing to a reduced HOMO energy level and enhanced electron escape work function, the MnP anode achieves an evidently enhanced cycle durability (over 1000 hours at a high current density of 5 mA cm-2). The MnP||AgVO full cell with an N/P ratio of 4 exhibits better rate capability and extended cycle life (7000 cycles) with minimal capacity degradation than the cell using metallic Mn anode (less than 100 cycles). This study provides a practical approach for developing highly durable aqueous Mn ion batteries.

Separating nanobubble nucleation for transfer-resistance-free electrocatalysis

Electrocatalytic gas-evolving reactions often result in bubble-covered surfaces, impeding the mass transfer to active sites. Such an issue will be worsened in practical high-current-density conditions and can cause sudden cell failure. Herein, we develop an on-chip microcell-based total-internal-reflection-fluorescence-microscopy to enable operando imaging of bubbles at sub-50 nm and dynamic probing of their nucleation during hydrogen evolution reaction. Using platinum-interfacial metal layer-graphene as model systems, we demonstrate that the strong binding energy between interfacial metal layer and graphene-evidenced by a reduced metal-support distance and enhanced charge transfer-facilitates hydrogen spillover from platinum to the graphene support due to lower energy barriers compared to the platinum-graphene system. This results in the spatial separation of bubble nucleation from the platinum surface, notably enhancing catalytic activity, as demonstrated in both microcell and polymer electrolyte membrane cell experiments. Our findings offer insights into bubble nucleation control and the design of electrocatalytic interfaces with minimized transfer resistance.

Multi-Dimensional High-Entropy Materials for Energy Conversion Reactions: Current State and Future Trends

The high-entropy materials (HEMs), composed of five or more elements, have attracted significant attention in electrocatalysis due to their unique physicochemical properties arising from the existence of multi-elements compositions. Beyond chemical composition, microstructure significantly influences the catalytic performance and even the catalytic mechanism towards energy conversion reactions. Given the rapid proliferation of research on HEMs and the critical roles of microstructure in their catalytic performance, a timely and comprehensive review of recent advancements is imperative. This review meticulously examines the synthesis methods and physicochemical characteristics of HEMs with distinct one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) morphologies. By highlighting representative examples from the past five years, we elucidate the unique properties of HEMs with 1D, 2D, and 3D microstructures, detailing their intricate influence on electrocatalytic performance, aiming to spur further advancements in this promising research area.

Electronic Metal-Support Interaction Induces Hydrogen Spillover and Platinum Utilization in Hydrogen Evolution Reaction

The substantial promotion of hydrogen evolution reaction (HER) catalytic performance relies on the breakup of the Sabatier principle, which can be achieved by the alternation of the support and electronic metal support interaction (EMSI) is noticed. Due to the utilization of tungsten disulfides as support for platinum (Pt@WS2), surprisingly, Pt@WS2 demands only 31 mV overpotential to attain 10 mA cm-2 in acidic HER test, corresponding to a 2.5-fold higher mass activity than benchmarked Pt/C. The pH dependent electrochemical measurements associated with H2-TPD and in situ Raman spectroscopy indicate a hydrogen spillover involved HER mechanism is confirmed. The WS2 support triggers a higher hydrogen binding strength for Pt leading to the increment in hydrogen concentration at Pt sites proved by upshifted d band center as well as lower Gibbs free energy of hydrogen, favourable for hydrogen spillover. Besides, the WS2 shows a comparably lower effect on Gibbs free energy for different Pt layers (-0.50 eV layer-1) than carbon black (-0.88 eV layer-1) contributing to a better Pt utilization. Also, the theoretical calculation suggests the hydrogen spillover occurs on the 3rd Pt layer in Pt@WS2; moreover, the energy barrier is lowered with increment in hydrogen coverage on Pt. Therefore, the boosted HER activity attributes to the EMSI effect caused hydrogen spillover and enhancement in Pt utilization efficiency.

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

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

UNLEASH: Ultralow Nanocluster Loading of Pt via Electro-Acoustic Seasoning of Heterocatalysts

The shift toward sustainable energy has fueled the development of advanced electrocatalysts to enable green fuel production and chemical synthesis. To date, no material outperforms Pt-group catalysts for key electrocatalytic reactions, necessitating advanced catalysts that minimize use of these rare and expensive constituents (i.e., Pt) to reduce cost without sacrificing activity. Whilst a myriad of routes involving co-synthesis of Pt with other elements have been reported, the Pt is often buried within the bulk of the composite, rendering a large proportion of it inaccessible to the interfacial electrocatalytic reaction. Surface decoration of Pt on arbitrary substrates is therefore desirable to maximize catalytic activity; nevertheless, Pt electrodeposition suffers from clustering and ripening effects that result in large (⌀ 0.1 - 1 μ m $\diameter \ \!0.1-1\ \umu{\rm m}$ ) aggregates that hinder electrocatalytic activity. Herein, an unconventional synthesis method is reported that utilizes high-frequency (10 MHz) acoustic waves to electrochemically 'season' a gold working electrode with an ultralow loading of Pt nanoclusters. The UNLEASH platform is shown to facilitate high-density dispersion of nanometer-order clusters at the bimetallic interface to enable superior atomic utilization of Pt. This is exemplified by its utility for methanol oxidation reaction (MOR), wherein a mass activity of 5.28 Amg Pt - 1 ${\rm mg}_{\rm Pt}^{-1}$ is obtained, outperforming all other Au/Pt bimetallic electrocatalysts reported to date.

Hydrogen Spillover-Bridged Interfacial Water Activation of WCx and Hydrogen Recombination of Ru as Dual Active Sites for Accelerating Electrocatalytic Hydrogen Evolution

Tungsten carbide (WCx) is a promising alternative to platinum catalysts for hydrogen evolution reaction (HER). However, strong tungsten-hydrogen bond hinders hydrogen desorption while favoring H+ reduction, thus limiting HER kinetics. Inspired by the phenomenon of hydrogen spillover in heterogeneous catalysis, a ruthenium (Ru) doped-driven activated hydrogen migration from WCx surface to Ru is reported. This approach achieved high activity with an ultralow overpotential of 9.0 mV at 10 mA·cm-2 and superior stability at an industrial-grade current density of 1.0 A·cm-2 @ 1.65 V. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and operando electrochemical impedance spectra revealed that this exceptional hydrogen production-which surpasses that of previously reported Pt/C catalysts-is attributable to the outstanding ability of WCx to induce water dissociation and hydrogen spillover from WCx to Ru surface. During the HER process, the rigid interfacial water network negatively affected the HER efficiency under alkaline conditions. The WCx sites disrupted this rigid structure, facilitating the contact between activated hydrogen (H*) and WCx sites. Subsequently, H* migrates to Ru surface, where hydrogen recombination occurs to produce H2. This work paves a new avenue for the construction of coupled catalysts at the atomic scale to facilitate HER 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.

Operando Stable Palladium Hydride Nanoclusters Anchored on Tungsten Carbides Mediate Reverse Hydrogen Spillover for Hydrogen Evolution

Proton exchange membrane (PEM) electrolysis holds great promise for green hydrogen production, but suffering from high loading of platinum-group metals (PGM) for large-scale deployment. Anchoring PGM-based materials on supports can not only improve the atomic utilization of active sites but also enhance the intrinsic activity. However, in practical PEM electrolysis, it is still challenging to mediate hydrogen adsorption/desorption pathways with high coverage of hydrogen intermediates over catalyst surface. Here, operando generated stable palladium (Pd) hydride nanoclusters anchored on tungsten carbide (WCx) supports were constructed for hydrogen evolution in PEM electrolysis. Under PEM operando conditions, hydrogen intercalation induces formation of Pd hydrides (PdHx) featuring weakened hydrogen binding energy (HBE), thus triggering reverse hydrogen spillover from WCx (strong HBE) supports to PdHx sites, which have been evidenced by operando characterizations, electrochemical results and theoretical studies. This PdHx-WCx material can be directly utilized as cathode electrocatalysts in PEM electrolysis with ultralow Pd loading of 0.022 mg cm-2, delivering the current density of 1 A cm-2 at the cell voltage of ~1.66 V and continuously running for 200 hours without obvious degradation. This innovative strategy via tuning the operando characteristics to mediate reverse hydrogen spillover provide new insights for designing high-performance supported PGM-based electrocatalysts.

Pt-decorated spinel MnCo2O4 nanosheets enable ampere-level hydrazine assisted water electrolysis

Coupling hydrazine oxidation reaction (HzOR) with hydrogen evolution reaction (HER) has been widely concerned for high efficiency of green hydrogen preparation with low energy consumption. However, the lacking of bifunctional electrodes with ampere-level performance severely limits its industrialization. Herein, we put forward an efficient active site anchored strategy for MnCo2O4 nanosheet arrays on nickel foam (NF) by introducing Pt species (denoted as Pt-MnCo2O4/NF), which is standing for excellent bifunctional electrodes. The Pt-MnCo2O4/NF delivers ultralow potentials of -195 mV and 350 mV at 1000 mA cm-2 as well as robust stability for HzOR and HER, respectively. The study of in-situ Raman and reaction kinetics reveal that the formation of key adsorbed *NH2 and *N2H4 intermediates and the rapidly oxidization of intermediates with a fast interfacial charge transfer on Pt-MnCo2O4/NF. Remarkably, the Pt-MnCo2O4/NF assembled two-electrode hydrazine assisted water electrolyzer realizes current density of 100 mA cm-2 and 1000 mA cm-2 at 0.16 V and 0.62 V with over 80 h stability. This work provides a promising way to design efficient electrodes for energy-saving H2 generation under ampere-level current density.

Ni Cluster-Decorated Single-Atom Catalysts Achieve Near-Unity CO2-to-CO Conversion with an Ultrawide Potential Window of ≈1.7 V

Developing efficient electrocatalysts for CO2 reduction to CO within a broad potential range is meaningful for cascade application integration. In this work, hydrogen spillover is created and utilized to cultivate a proton-rich environment via the simple thermolysis of a Ni-doped Zn coordination polymer (Zn CPs (Ni)) to create asymmetric Ni single atoms co-located with adjacent Ni nanoclusters on nitrogen-doped carbon, termed as NiNC&SA/N-C, which expedites the hydrogenation of adsorbed CO2. Therefore, the sample demonstrates near-unity CO2-to-CO conversion efficiency under pH-universal conditions in ultra-wide potential windows: -0.39 to -2.05 V versus RHE with the current densities ranging from 0.1 to 1.0 A cm-2 in alkaline conditions, -0.83 to -2.40 V versus RHE from 0.1 to 0.9 A cm-2 in neutral environments, and -0.98 to -2.25 V versus RHE across 0.1 to 0.8 A cm-2 in acid conditions. Corresponding in situ measurements and density functional theory (DFT) calculations suggest that the enhanced H2O dissociation and more efficient hydrogen spillover on NiNC&SA/N-C (compared to NiSA/N-C) accelerate the protonation of adsorbed CO2 to form *COOH intermediates. This work emphasizes the significant role of proton spillover in CO2RR, opening novel avenues for designing high-performance catalysts applicable to various electrocatalytic processes.

Phase Engineering-Mediated D-Band Center of Ru Sites Promote the Hydrogen Evolution Reaction Under Universal pH Condition

The rational design of pH-universal electrocatalyst with high-efficiency, low-cost and large current output suitable for industrial hydrogen evolution reaction (HER) is crucial for hydrogen production via water splitting. Herein, phase engineering of ruthenium (Ru) electrocatalyst comprised of metastable unconventional face-centered cubic (fcc) and conventional hexagonal close-packed (hcp) crystalline phase supported on nitrogen-doped carbon matrix (fcc/hcp-Ru/NC) is successfully synthesized through a facile pyrolysis approach. Fascinatingly, the fcc/hcp-Ru/NC displayed excellent electrocatalytic HER performance under a universal pH range. To deliver a current density of 10 mA cm-2, the fcc/hcp-Ru/NC required overpotentials of 16.8, 23.8 and 22.3 mV in 1 M KOH, 0.5 M H2SO4 and 1 M phosphate buffered solution (PBS), respectively. Even to drive an industrial-level current density of 500 and 1000 mA cm-2, the corresponding overpotentials are 189.8 and 284 mV in alkaline, 202 and 287 mV in acidic media, respectively. Experimental and theoretical calculation result unveiled that the charge migration from fcc-Ru to hcp-Ru induced by work function discrepancy within fcc/hcp-Ru/NC regulate the d-band center of Ru sites, which facilitated the water adsorption and dissociation, thus boosting the electrocatalytic HER performance. The present work paves the way for construction of novel and efficient electrocatalysts for energy conversion and storage.

Synergistic Coordination Effect and Metal-Support Interaction Engineering of Single-Atom Mn-N2 Sites for Boosting Sensitive and Selective Dopamine Biosensing in Human Serum

Coordination environment of metal atoms is core for designing high-performance single-atom catalysts (SACs), while metal-support interaction also has an important effect on structure-function relationship. Nevertheless, the interaction effect of metal-support is mostly ignored. Through synergistic regulation of coordination environment and metal-support interaction, Mn SAC with atom-dispersed Mn-N2 sites on dopamine (DA) support is synthesized for sensitive and selective DA oxidation based on theoretical calculations and experimental explorations. MnN2 presents the more optimal catalytic site for DA oxidation than other coordination conditions, enhancing sensitivity including a wide range, a low limit of detection, and particularly a very low catalytic potential. The construction of Mn-N2 active sites on DA carbon promotes the coupling between Mn metal atoms and DA support, decreasing work function, facilitating electron exchange, shortening response time, and boosting selectivity. Both the catalytic mechanism of Mn SAC toward DA and the relation construction of catalyst's structure and catalytic function are established.

Pd hydride metallene aerogels with lattice hydrogen participation for efficient hydrogen evolution reaction

Hydrogen adsorption and desorption in single-phase catalysts often occur at a single catalytic site based on the traditional hydrogen evolution reaction (HER) pathway, which makes it difficult to break the limitation entailed by the Sabatier principle. Herein, β-Pd hydride metallene (β-PdHene) aerogels are synthesized as advanced HER catalysts. A lattice hydrogen-involved mechanism is reported to separate adsorption and desorption sites, which is thermodynamically favorable compared to the traditional reaction pathway. In situ differential electrochemical mass spectrometry and theoretical calculations reveal that lattice hydrogen as additional active sites directly participate in the HER process. Consequently, β-PdHene aerogels exhibit a low overpotential of only 20 mV at 10 mA cm-2 and remarkable HER stability, which are even comparable to commercial Pt/C. Our work opens an avenue to rationally develop highly active HER catalysts, bypassing the design limitations of catalysts under traditional mechanisms.

S-S Bond Strategy at Sulfide Heterointerface: Reversing Charge Transfer and Constructing Hydrogen Spillover for Boosted Hydrogen Evolution

Developing efficient electrocatalyst in sulfides for hydrogen evolution reaction (HER) still poses challenges due to the lack of understanding the role of sulfide heterointerface. Here, we report a sulfide heterostructure RuSx/NbS2, which is composed of 3R-type NbS2 loaded by amorphous RuSx nanoparticles with S-S bonds formed at the interface. As HER electrocatalyst, the RuSx/NbS2 shows remarkable low overpotential of 38 mV to drive a current density of 10 mA cm-2 in acid, and also low Tafel slope of 51.05 mV dec-1. The intrinsic activity of RuSx/NbS2 is much higher than that of Ru/NbS2 reference as well as the commercial Pt/C. Both experiments and theoretical calculations unveil a reversed charge transfer at the interface from NbS2 to RuSx that driven by the formation of S-S bonds, resulting in electron-rich Ru configuration for strong hydrogen adsorption. Meanwhile, electronic redistribution induced by the sulfide heterostructure facilitates hydrogen spillover (HSo) effect in this system, leading to accelerated hydrogen desorption at the basal plane of NbS2. This study provides an effective S-S bond strategy in sulfide heterostructure to synergistically modulate the charge transfer and adsorption thermodynamics, which is very valuable for the development of efficient electrocatalysts in practical applications.

Constructing Built-in-Electric Field for Boosting Electrocatalytic Water Splitting

Electrocatalytic water splitting shows great potential for producing clean and green hydrogen, but it is hindered by slow reaction kinetics. Advanced electrocatalysts are needed to lower the energy barriers. The establishment of built-in electric fields (BIEF) in heterointerfaces has been found to be beneficial for speeding up electron transfer, increasing electrical conductivity, adjusting the local reaction environment, and optimizing the chemisorption energy with intermediates. Engineering and modifying the BIEF in heterojunctions offer significant opportunities to enhance the electronic properties of catalysts, thus improving the reaction kinetics. This comprehensive review focuses on the latest advances in BIEF engineering in heterojunction catalysts for efficient water electrolysis. It highlights the fundamentals, engineering, modification, characterization, and application of BIEF in electrocatalytic water splitting. The review also discusses the challenges and future prospects of BIEF engineering. Overall, this review provides a thorough examination of BIEF engineering for the next generation of water electrolysis devices.

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.

Hydrogen spillover for boosted catalytic activity towards hydrazine oxidation

A nanoflower-like MoO2-Rh electrocatalyst exhibits a 3.5-fold higher mass activity in the hydrazine oxidation reaction compared with metallic Rh, attributed to the hydrogen spillover, acting as a hydrogen pump to deplete hydrogen from the Rh active site.

Tungsten oxide-based electrocatalysts for energy conversion

The advancement of cutting-edge energy conversion technologies offers significant potential for addressing environmental challenges, enhancing energy security, improving economic competitiveness, and promoting resource conservation. This progress necessitates the development of advanced electrocatalysts. WOx demonstrates high intrinsic catalytic activity, excellent conductivity, an abundance of active sites, and remarkable stability, positioning it as a promising candidate for electrocatalytic reactions. Recently, there has been swift advancement in the development of WOx-based catalysts for various energy-conversion reactions. This review provides a thorough summary of recent developments in WOx-based catalysts for electrocatalytic reactions, emphasizing their multifunctional roles as active species, electron-transfer carriers, hydrogen spillover carriers, and microenvironment regulators. Moreover, it highlights the applications of WOx-based catalysts across different electrocatalytic reactions, with particular focus on the structure-activity relationship. Finally, the review discusses the challenges and future directions of these technologies, as well as key research areas necessary for achieving large-scale applications.

2D MXene/MBene Superlattice with Narrow Bandgap as Superior Electrocatalyst for High-Performance Lithium-Oxygen Battery

Lithium-oxygen (Li-O2) battery with large theoretical energy density (≈3500 Wh kg-1) is one of the most promising energy storage and conversion systems. However, the slow kinetics of oxygen electrode reactions inhibit the practical application of Li-O2 battery. Thus, designing efficient electrocatalysts is crucial to improve battery performance. Here, Ti3C2 MXene/Mo4/3B2-x MBene superlattice is fabricated its electrocatalytic activity toward oxygen redox reactions in Li-O2 battery is studied. It is found that the built-in electric field formed by a large work function difference between Ti3C2 and Mo4/3B2-x will power the charge transfer at the interface from titanium (Ti) site in Ti3C2 to molybdenum (Mo) site in Mo4/3B2-x. This charge transfer increases the electron density in 4d orbital of Mo site and decreases the d-band center of Mo site, thus optimizing the adsorption of intermediate product LiO2 at Mo site and accelerating the kinetics of oxygen electrode reactions. Meanwhile, the formed film-like discharge products (Li2O2) improve the contact with electrode and facilitate the decomposition of Li2O2. Based on the above advantages, the Ti3C2 MXene/Mo4/3B2-x MBene superlattice-based Li-O2 battery exhibits large discharge specific capacity (17 167 mAh g-1), low overpotential (1.16 V), and superior cycling performance (475 cycles).

In situ ammonium formation mediates efficient hydrogen production from natural seawater splitting

Seawater electrolysis using renewable electricity offers an attractive route to sustainable hydrogen production, but the sluggish electrode kinetics and poor durability are two major challenges. We report a molybdenum nitride (Mo2N) catalyst for the hydrogen evolution reaction with activity comparable to commercial platinum on carbon (Pt/C) catalyst in natural seawater. The catalyst operates more than 1000 hours of continuous testing at 100 mA cm-2 without degradation, whereas massive precipitate (mainly magnesium hydroxide) forms on the Pt/C counterpart after 36 hours of operation at 10 mA cm-2. Our investigation reveals that ammonium groups generate in situ at the catalyst surface, which not only improve the connectivity of hydrogen-bond networks but also suppress the local pH increase, enabling the enhanced performances. Moreover, a zero-gap membrane flow electrolyser assembled by this catalyst exhibits a current density of 1 A cm-2 at 1.87 V and 60 oC in simulated seawater and runs steadily over 900 hours.

Rationally Designed Mo/Ru-Based Multi-Site Heterogeneous Electrocatalyst for Accelerated Alkaline Hydrogen Evolution Reaction

The rational design of multi-site electrocatalysts with three different functions for facile H2O dissociation, H-H coupling, and rapid H2 release is desirable but difficult to achieve. This strategy can accelerate the sluggish kinetics of the hydrogen evolution reaction (HER) under alkaline conditions. To resolve this issue, a Mo/Ru-based catalyst with three different active sites (Ru/Mo2C/MoO2) is rationally designed and its performance in alkaline HER is evaluated. The experimental results and density functional theory calculations revealed that, at the heterogeneous Mo2C/MoO2 interface, the higher valence state of Mo (MoO2) and the lower valence state of Mo (Mo2C) exhibited strong OH- and H-binding energies, respectively, which accelerated H2O dissociation. Moreover, the interfacial Ru possessed an appropriate hydrogen binding energy for H-H coupling and subsequent H2 evolution. Thus, this catalyst significantly accelerated the Volmer step and the Tafel step and, consequently, HER kinetics. This catalyst also demonstrated low overpotentials of 19 and 160 mV at current densities of 10 and 1000 mA cm-2, respectively, in alkaline media and long-term stability superior to that of most state-of-the-art alkaline HER electrocatalysts. This work provides a rational design principle for advanced multi-site catalytic systems, which can realize multi-electron electrocatalytic reactions.

Improved Nitrate-to-Ammonia Electrocatalysis through Hydrogen Poisoning Effects

Electrochemical conversion from nitrate to ammonia is a key step in sustainable ammonia production. However, it suffers from low productive efficiency or high energy consumption due to a lack of desired electrocatalysts. Here we report nickel cobalt phosphide (NiCoP) catalysts for nitrate-to-ammonia electrocatalysis that display a record-high catalytic current density of -702±7 mA cm-2, ammonia production rate of 5415±26 mmol gcat -1 h-1 and Faraday efficiency of 99.7±0.2 % at -0.3 V vs. RHE, affording the estimated energy consumption as low as 22.7 kWh kgammonia -1. Theoretical and experimental results reveal that these catalysts benefit from hydrogen poisoning effects, which leave behind catalytically inert adsorbed hydrogen species (HI*) at Co-hollow sites and thereupon enable ideally reactive HII* at secondary Co-P sites. The dimerization between HI* and HII* for H2 evolution is blocked due to the catalytic inertia of HI* thereby the HII* drives nitrate hydrogenation timely. With these catalysts, the continuous ammonia production is further shown in an electrolyser with a real energy consumption of 18.9 kWh kgammonia -1.

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.