Tailoring Lattice Oxygen Binding in Ruthenium Pyrochlores to Enhance Oxygen Evolution Activity

Porous-dual-shell structure and heterojunction Co3O4@NiCo2O4 accelerating polysulfides conversion for all-solid-state lithium sulfur batteries

All-solid-state lithium sulfur batteries (ASSLSBs) hold significant promise in the application of high energy density batteries, yet they suffer from poor ionic conductivity, low Li+ transference number and unsatisfactory lithium polysulfides (LiPSs) conversion. In this paper, porous-dual-shell structure and heterojunction Co3O4@NiCo2O4 is prepared and composited with polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) to address these problems. The superimposed electric field for Co3O4@NiCo2O4 composed of the heterointerfaces -build-in electric field and the surface oxygen-rich vacancies-build-in electric field facilitates the dissociation of Li salts, thus improving the ionic conductivity. It exhibits high ionic conductivity of 1.04 × 10-3 S/cm and Li+ transference number of 0.48 at 60 °C. Besides, the incorporation of Co3O4@NiCo2O4 heterojunction enables fast LiPSs conversion and improves the electrochemical kinetics. The Li//Li cell can work stably for 1100 h at 0.1 mA/cm2. The Li//S cell provides an initial capacity of 1170 mA h/g, a reversible capacity of 620.1mA h/g after 100 cycles and 308.3 mA h/g after 450 cycles at 0.2 C.

CuO/Bi2CuO4 Heterostructured Electrocatalyst for the Efficient Reduction of Nitrate to Ammonia

The electrochemical reduction of nitrate to ammonia (NH3) not only provides an effective approach to balance the perturbed nitrogen cycle for addressing environmental issues but also provides a potential technology for green NH3 synthesis. However, the process is limited by the produced intermediate-nitrite that tends to accumulate on cathode surfaces and multiple competing reactions. Herein, CuO/Bi2CuO4-450 heterostructures are reported as efficient electrocatalysts for the nitrate reduction reaction with extraordinary catalytic activities and selectivities for NH3 production. The optimized catalyst achieves a remarkable Faradaic efficiency (96.49%) and exceptional NH3 yield rate (9.17 mg h-1 mgcat.-1) at -0.5 V versus RHE, surpassing most of the reported Cu-based catalytic systems. The characterization results and theoretical evidence reveal that the interface effect originating from the strong interaction between Bi2CuO4 and CuO tunes the electronic structures of the Cu and Bi active sites for optimized intermediate adsorption and lowers the rate-determining step reaction barriers, resulting in improved catalytic performance. This work offers a strategy to flexibly develop catalysts to promote electrocatalytic techniques for NH3 production by electrochemical nitrate reduction.

Dual-Engineering Tailored Co3O4 Hollow Microspheres Assembled by Nanosheets for Boosting Oxygen Evolution Reaction

The development of efficient, low-cost electrocatalysts for the oxygen evolution reaction (OER) is crucial for advancing sustainable hydrogen production through water splitting. This study presents a dual-engineering strategy to enhance the OER performance of Co3O4 by synthesizing hollow microspheres assembled from nanosheets (HMNs) with abundant oxygen vacancies and highly active crystal facet exposure. Through a modified one-step hydrothermal process, Co3O4 HMNs with exposed (111) and (100) crystal facets were successfully fabricated, demonstrating superior OER activity compared to Co3O4 nanocubes (NCs) with only (100) facet exposure. The optimized Co3O4-5% HMNs exhibited a low overpotential of 330 mV at 10 mA cm-2 and a Tafel slope of 69 mV dec-1. The enhanced performance was attributed to the synergistic effects of crystal facet engineering and defect engineering, which optimized the Co-O bond energy, increased the number of active sites, and improved conductivity. The unique hollow structure further facilitated mass transport and prevented nanosheet stacking, exposing more edge sites for catalytic reactions. This work highlights the potential of geometric and electronic structure modulation in designing high-performance OER catalysts for sustainable energy applications.

Metal-oxygen bonding characteristics dictate activity and stability differences of RuO2 and IrO2 in the acidic oxygen evolution reaction

Ruthenium dioxide (RuO2) and iridium dioxide (IrO2) serve as benchmark electrocatalysts for the acidic oxygen evolution reaction (OER), yet their intrinsic activity-stability relationships remain elusive. Herein, we employ density functional theory (DFT) calculations to systematically investigate the origin of divergent OER catalytic behaviors between RuO2 and IrO2 in acidic media. Mechanistic analyses reveal that RuO2 follows the adsorbate evolution mechanism with superior activity (theoretical overpotential: 0.698 V vs. 0.909 V for IrO2), while IrO2 demonstrates enhanced stability due to a higher dissolution energy change (>2.9 eV vs. -0.306 eV for RuO2). Electronic structure analysis reveals that RuO2 exhibits ionic-dominated metal-oxygen bonds with delocalized electron distribution, facilitating intermediate desorption but promoting detrimental RuO42- dissolution. In contrast, IrO2 features covalent bonding characteristics with more electron filling in Ir-oxygen bonds (2.942 vs. 2.412 for RuO2), thereby stabilizing surface intermediates against dissolution at the expense of higher OER barriers. This work establishes a clear correlation between the bonding nature and electrocatalytic performance metrics, offering fundamental insights for the rational design of acid-stable OER electrocatalysts with optimized activity-stability relationships.

Boosting Urea Electrosynthesis via Asymmetric Oxygen Vacancies in Zn-Doped Fe2O3 Catalysts

Urea electrosynthesis from CO2 and nitrate (NO3 -) provides an attractive pathway for storing renewable electricity and substituting traditional energy-intensive urea synthesis technology. However, the kinetics mismatching between CO2 reduction and NO3 - reduction, as well as the difficulty of C─N coupling, are major challenges in urea electrosynthesis. Herein, we first calculated the free energy of *CO, *OCNO, and *NOH formation over defect-rich Fe2O3 catalysts with different metal dopants, which showed that Zn dopant was a promising candidate. Based on the theoretical study, we developed Zn-doped defect-rich Fe2O3 catalysts (Zn-Fe2O3/OV) containing asymmetric Zn-OV-Fe sites. It exhibited an outstanding urea faradaic efficiency of 62.4% and the remarkable recycling stability. The production rate of urea was as high as 7.48 mg h-1 mgcat -1, which is higher than most of the reported works to date. Detailed control experiments and in situ spectroscopy analyses identified *OCNO as a crucial intermediate for C─N coupling. The Zn-Fe2O3/OV catalyst with asymmetric Zn-OV-Fe sites showed enhanced *CO coverage and promoted *OCNO formation, leading to high efficiency toward urea production.

Recent Progress of Modulating Pristine Metal-Organic Frameworks for Oxygen Reaction Revolution

Highly efficient and stable oxygen evolution reaction (OER) electrocatalysts are essential for electrochemical water splitting. Among non-noble metal-based catalysts, metal-organic frameworks (MOFs) have recently emerged as particularly promising candidates due to their exceptional surface areas, hierarchical porous structures, and tunable morphologies and compositions. The rational regulation of the morphology and electronic structure of pristine MOFs is considered a critical pathway for enhancing active sites and structural stability, thereby significantly boosting the OER catalytic performance. This review systematically presents the recent advancements in modulating pristine MOFs via heterogeneous metal doping, ligand substitution, and hybrid composite construction. With particular emphasis on synthetic methods, modification mechanisms, and the OER properties of MOFs, we analyze the fundamental relationships between structural modifications and electrocatalytic performance. Through the systematic analysis of existing research achievements, this review provides a holistic assessment of current state-of-the-art developments, identifies critical challenges, and proposes future research directions with practical implications for OER electrocatalyst design.

Preparation of Highly Efficient All-pH Bifunctional Water Electrolysis Catalysts Through a Surface Modification Strategy

Electrolytic hydrogen production from water is a very promising technology, and catalysts capable of efficient operation over a wide pH range are essential for energy storage and conversion. Herein, a trace Ru catalytic core restructures nickel foam (NF) under polymeric protection, with temperature gradient control forming HER-active metal monomers at low temperatures and OER-suitable oxides at high temperatures. It is demonstrated that the surface modification strategy can help NF to maintain its own backbone structure during the carbonation process and that the resulting catalysts possess excellent properties. The synthesized catalysts-Ru@NF-KPDA-550 exhibit the lowest OER overpotentials of 183 mV in 0.5 M H2SO4 and 151 mV in 1.0 M KOH, and Ru@NF-KPDA-350 exhibits the lowest HER overpotentials of 11.8 mV in 0.5 M H2SO4 and 13.4 mV in 1.0 M KOH for Ru@NF-KPDA-350 at 10 mA cm-2. The DFT simulations show that the synergistic interaction between Ru and Ni components, which optimizes their d-band centers, enhances the HER and OER pathways, thereby lowering activation barriers and boosting catalytic performance. This work provides a viable strategy for the design of pH-universal electrocatalysts for the overall water splitting.

Leaching-Induced Ti Trapping Stabilizes Amorphous IrOx for Proton Exchange Membrane Water Electrolysis

Transition metal nitrides are promising conductive support materials in oxygen evolution reaction (OER), whereas it is unclear if their electrochemical oxidation during prolonged test would affect the OER catalysts. Herein, we demonstrate that the leaching-induced Ti trapping effect from TiN supports effectively stabilizes the electrochemically oxidized amorphous IrOx catalyst. Structural characterizations reveal that the TiN support experiences severe leaching during OER test, leaving minor amounts of Ti-O species trapping on IrOx clusters, which mitigate the overoxidation of Ir(III) species and elongate the Ir-O bonds. This leads to 70% reduction of lattice oxygen oxidation and the substantially reduced Ir leaching. Additionally, self-thickening of the catalyst layers is found during proton exchange membrane water electrolysis (PEMWE), enabling an ultralow catalyst loading of 87 µgIr cm-2 to obtain a stable operation at 1.0 A cm-2 for 500 h. This work deepens the understanding of TiN-supported catalysts for long-term stable OER electrocatalysis.

Lattice Distortion Broadens the eg Band of Co3O4 to Facilitate p-d Hybridization for Enhanced Electrochemical Nitrate Synthesis

The electrochemical nitrogen oxidation reaction (NOR) presents a sustainable pathway for nitrate synthesis under mild conditions; however, the process is hindered by the inadequate adsorption and activation of N2 on electrocatalysts. In this study, we utilized Co3O4 as a model catalyst and engineered lattice distortions by introducing oxygen vacancies, which expanded the eg band of the active sites to enhance N2 activation. The modified Co3O4 catalyst achieved a Faradaic efficiency of 10.68% and a nitrate yield of 58.80 μg·h-1·mgcat-1. Comprehensive experimental and density functional theory (DFT) analyses demonstrated that these modifications resulted in a shortened Co-N bond length and an elongated N≡N bond, leading to improved p-d hybridization between N2 and Co sites. Moreover, the enhancements in catalytic performance were also attributed to the improved electron transfer properties stemming from the altered band structure of Co3O4. This work provides innovative design principles for catalysts aimed at facilitating complex electrocatalytic reactions with multiple kinetics.

Design and synthesis of Pt/TiO2 catalyst with abundant surface hydroxyl for formaldehyde oxidation

Catalytic oxidation of formaldehyde (HCHO) is a highly effective method for indoor HCHO removal. However, many aspects of the catalytic mechanism remain unclear, making the optimization of catalysts largely empirical. Herein, we report a coupled experimental and computational study of Pt/TiO2 catalysts, with special focus on the functional roles of surface oxygen vacancies and hydroxyl groups in the catalytic oxidation of HCHO. DFT calculations combined with control experiments revealed that the formation of surface oxygen vacancies on TiO2 and their capability in facilitating H2O dissociation are strongly dependent on the exposed facets. Correlating these facet-dependent properties with the determined activity further indicated that the catalytic performance is directly related to the abundance of surface hydroxyl groups, rather than surface oxygen vacancies as commonly assumed. Guided by these insights, we employed a combination of facet-engineering and alkali metal modification strategies to design a potassium-modified Pt/TiO2 catalyst with predominantly exposed {100} facets (denoted as Pt/TiO2{100}-K). The Pt/TiO2{100}-K catalyst showed an impressively high mass-specific reaction rate of 105.7 μmol gPt-1 s-1, along with fairly good stability and moisture tolerance. Further investigations using in situ DRIFTS coupled with on-line GC provided additional insight into the reaction mechanism of HCHO oxidation over the Pt/TiO2{100}-K catalyst.

Leveraging data mining, active learning, and domain adaptation for efficient discovery of advanced oxygen evolution electrocatalysts

Developing advanced catalysts for acidic oxygen evolution reaction (OER) is crucial for sustainable hydrogen production. This study presents a multistage machine learning (ML) approach to streamline the discovery and optimization of complex multimetallic catalysts. Our method integrates data mining, active learning, and domain adaptation throughout the materials discovery process. Unlike traditional trial-and-error methods, this approach systematically narrows the exploration space using domain knowledge with minimized reliance on subjective intuition. Then, the active learning module efficiently refines element composition and synthesis conditions through iterative experimental feedback. The process culminated in the discovery of a promising Ru-Mn-Ca-Pr oxide catalyst. Our workflow also enhances theoretical simulations with domain adaptation strategy, providing deeper mechanistic insights aligned with experimental findings. By leveraging diverse data sources and multiple ML strategies, we demonstrate an efficient pathway for electrocatalyst discovery and optimization. This comprehensive, data-driven approach represents a paradigm shift and potentially benchmark in electrocatalysts research.

Isolated Metal Centers Activate Small Molecule Electrooxidation: Mechanisms and Applications

Electrochemical oxidation of small molecules shows great promise to substitute oxygen evolution reaction (OER) or hydrogen oxidation reaction (HOR) to enhance reaction kinetics and reduce energy consumption, as well as produce high-valued chemicals or serve as fuels. For these oxidation reactions, high-valence metal sites generated at oxidative potentials are typically considered as active sites to trigger the oxidation process of small molecules. Isolated atom site catalysts (IASCs) have been developed as an ideal system to precisely regulate the oxidation state and coordination environment of single-metal centers, and thus optimize their catalytic property. The isolated metal sites in IASCs inherently possess a positive oxidation state, and can be more readily produce homogeneous high-valence active sites under oxidative potentials than their nanoparticle counterparts. Meanwhile, IASCs merely possess the isolated metal centers but lack ensemble metal sites, which can alter the adsorption configurations of small molecules as compared with nanoparticle counterparts, and thus induce various reaction pathways and mechanisms to change product selectivity. More importantly, the construction of isolated metal centers is discovered to limit metal d-electron back donation to CO 2p* orbital and reduce the overly strong adsorption of CO on ensemble metal sites, which resolve the CO poisoning problems in most small molecules electro-oxidation reactions and thus improve catalytic stability. Based on these advantages of IASCs in the fields of electrochemical oxidation of small molecules, this review summarizes recent developments and advancements in IASCs in small molecules electro-oxidation reactions, focusing on anodic HOR in fuel cells and OER in electrolytic cells as well as their alternative reactions, such as formic acid/methanol/ethanol/glycerol/urea/5-hydroxymethylfurfural (HMF) oxidation reactions as key reactions. The catalytic merits of different oxidation reactions and the decoding of structure-activity relationships are specifically discussed to guide the precise design and structural regulation of IASCs from the perspective of a comprehensive reaction mechanism. Finally, future prospects and challenges are put forward, aiming to motivate more application possibilities for diverse functional IASCs.

Tailoring Octahedron-Tetrahedron Synergism in Spinel Catalysts for Acidic Water Electrolysis

The instability issues of oxide-based electrocatalysts during the oxygen evolution reaction (OER) under acidic conditions, caused by the oxidation and dissolution of the catalysts along with the current-capacitance effect, constrain their application in proton exchange membrane water electrolysis (PEMWE). To address these challenges, we tailored the spinel structure of Co3O4 and exploited the synergism between the tetrahedron and octahedron sites by partially substituting Co with Ni and Ru (denoted as NiRuCoOx), respectively. Such a catalyst design creates a Ru-O-Ni electronic coupling effect, facilitating a direct dioxygen radical-coupled OER pathway. Density-functional theory (DFT) calculations and in situ Raman spectroscopy results confirm that Ru is the active site in the diatomic oxygen mechanism while Ni stabilizes lattice oxygen and the Ru-O bonding. The designed NiRuCoOx catalyst exhibits an exceptionally low overpotential of 166 mV to achieve a current density of 10 mA cm-2. Moreover, when serving as the anode in PEMWE, the NiRuCoOx requires 1.72 V to reach a current density of 3A cm-2, meeting the 2026 target set by the U.S. Department of Energy (DOE: 1.8 V@3A cm-2). The PEMWE device can operate stably for more than 1500 h with a significantly reduced performance decay rate of 0.025 mV h-1 compared to commercial RuO2 (2.13 mV h-1). This work provides an efficient method for tailoring the octahedron-tetrahedron sites of spinel Co3O4, which significantly improves the activity and stability of PEMWE.

Efficient electrocatalysis conversion of glycerol to formate in alkaline solution by nickel (oxy)hydroxide supported cobalt nanoneedle arrays

Electrochemical oxidation of glycerol into value-added chemicals represents a sustainable approach for not only valorizing biomass resources but also improving the energy efficiency of electrolysis by replacing the kinetically sluggish oxidation of water at the anode. Here, we present a nickel (oxy)hydroxide supported cobalt nanoneedle arrays catalyst (CoNA-NiOH/NF-2) for effective oxidation of glycerol. The loaded Co(OH)2 forms more oxygen defects, increases the active sites, and enhances the performance of glycerol oxidation. The CoNA-NiOH/NF-2 catalyst significantly reduces energy consumption by achieving a current density of 10 mA cm-2 at a low voltage of 1.22 V vs. RHE, and 100 mA cm-2 at 1.42 V vs. RHE, which is approximately 240 mV lower than oxygen evolution reaction (OER). Additionally, the Faraday efficiency of formate generation reached 98 %. The growth of renewable energy sources will greatly benefit from this strategy, which calls for replacing anodic OER with biomass oxidation.

La-Doping-Induced Lattice Strain and Electronic State Modulation in RuO2 for Electrocatalytic Oxygen Evolution in Acidic Solutions

Pursuing highly active and stable Ru-based catalysts for the oxygen evolution reaction (OER) under acidic conditions is important in advancing proton exchange membrane (PEM) water electrolyzers. Unfortunately, the inadequate stability, especially under a large current density of Ru-based catalysts, still hinders its practical application. Herein, we report a La doping strategy that simultaneously enhances both OER activity and stability of RuO2 in acidic media. The introduction of La into RuO2 induces tensile strain, which effectively weakens the covalency of Ru-O bonds. This structural modification significantly inhibits Ru dissolution, thereby substantially enhancing the stability of RuO2. Meanwhile, La doping modulates the electronic structure of RuO2 and optimizes the adsorption energy of the reaction intermediates, thereby enhancing the electrocatalytic OER activity. Notably, the optimized La0.05-RuO2 electrocatalyst presents an excellent OER performance in 0.5 M H2SO4 electrolyte, which delivers a low overpotential of 190 mV at 10 mA cm-2 and sustains 150 h without obvious decay at 50 mA cm-2. More importantly, a PEM electrolyzer is constructed by using our La0.05-RuO2 as the anode catalyst, which acquires 200 h stability at 1 A cm-2, highlighting its strong potential for practical industrial applications. This work sheds new light on designing high-performance OER catalysts toward PEM electrolyzer applications.

Effectiveness of strain and dopants on breaking the activity-stability trade-off of RuO2 acidic oxygen evolution electrocatalysts

Ruthenium dioxide electrocatalysts for acidic oxygen evolution reaction suffer from mediocre activity and rather instability induced by high ruthenium-oxygen covalency. Here, the tensile strained strontium and tantalum codoped ruthenium dioxide nanocatalysts are synthesized via a molten salt-assisted quenching strategy. The tensile strained spacially elongates the ruthenium-oxygen bond and reduces covalency, thereby inhibiting the lattice oxygen participation and structural decomposition. The synergistic electronic modulations among strontium-tantalum-ruthenium groups both optimize deprotonation on oxygen sites and intermediates absorption on ruthenium sites, lowering the reaction energy barrier. Those result in a well-balanced activity-stability profile, confirmed by comprehensive experimental and theoretical analyses. Our strained electrode demonstrates an overpotential of 166 mV at 10 mA cm-2 in 0.5 M H2SO4 and an order of magnitude higher S-number, indicating comparable stability compared to bare catalyst. It exhibits negligible degradation rates within the long-term operation of single cell and PEM electrolyzer. This study elucidates the effectiveness of tensile strain and strategic doping in enhancing the activity and stability of ruthenium-based catalysts for acidic oxygen evolution reactions.

Electrocatalysis: From Planar Surfaces to Nanostructured Interfaces

The reactions critical for the energy transition center on the chemistry of hydrogen, oxygen, carbon, and the heterogeneous catalyst surfaces that make up electrochemical energy conversion systems. Together, the surface-adsorbate interactions constitute the electrochemical interphase and define reaction kinetics of many clean energy technologies. Practical devices introduce high levels of complexity where surface roughness, structure, composition, and morphology combine with electrolyte, pH, diffusion, and system level limitations to challenge our ability to deconvolute underlying phenomena. To make significant strides in materials design, a structured approach based on well-defined surfaces is necessary to selectively control distinct parameters, while complexity is added sequentially through careful application of nanostructured surfaces. In this review, we cover advances made through this approach for key elements in the field, beginning with the simplest hydrogen oxidation and evolution reactions and concluding with more complex organic molecules. In each case, we offer a unique perspective on the contribution of well-defined systems to our understanding of electrochemical energy conversion technologies and how wider deployment can aid intelligent materials design.

Strontium Doped IrOx Triggers Direct O-O Coupling to Boost Acid Water Oxidation Electrocatalysis

The discovery of efficient and stable electrocatalysts for the oxygen evolution reaction (OER) in acidic conditions is crucial for the commercialization of proton-exchange membrane water electrolyzers. In this work, we propose a Sr(OH)2-assisted method to fabricate a (200) facet highly exposed strontium-doped IrOx catalyst to provide available adjacent iridium sites with lower Ir-O covalency. This design facilitates direct O-O coupling during the acidic water oxidation process, thereby circumventing the high energy barrier associated with the generation of *OOH intermediates. Benefiting from this advantage, the resulting Sr-IrOx catalyst exhibits an impressive overpotential of 207 mV at a current density of 10 mA cm-2 in 0.5 M H2SO4. Furthermore, a PEMWE device utilizing Sr-IrOx as the anodic catalyst demonstrates a cell voltage of 1.72 V at 1 A cm-2 and maintains excellent stability for over 500 hours. Our work not only provides guidance for the design of improved acidic OER catalysts but also encourages the development of iridium-based electrocatalysts with novel mechanisms for other electrocatalytic reactions.

Beyond conventional structures: emerging complex metal oxides for efficient oxygen and hydrogen electrocatalysis

The core of clean energy technologies such as fuel cells, water electrolyzers, and metal-air batteries depends on a series of oxygen and hydrogen-based electrocatalysis reactions, including the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), which necessitate cost-effective electrocatalysts to improve their energy efficiency. In the recent decade, complex metal oxides (beyond simple transition metal oxides, spinel oxides and ABO3 perovskite oxides) have emerged as promising candidate materials with unexpected electrocatalytic activities for oxygen and hydrogen electrocatalysis owing to their special crystal structures and unique physicochemical properties. In this review, the current progress in complex metal oxides for ORR, OER, and HER electrocatalysis is comprehensively presented. Initially, we present a brief description of some fundamental concepts of the ORR, OER, and HER and a detailed description of complex metal oxides, including their physicochemical characteristics, synthesis methods, and structural characterization. Subsequently, we present a thorough overview of various complex metal oxides reported for ORR, OER, and HER electrocatalysis thus far, such as double/triple/quadruple perovskites, perovskite hydroxides, brownmillerites, Ruddlesden-Popper oxides, Aurivillius oxides, lithium/sodium transition metal oxides, pyrochlores, metal phosphates, polyoxometalates and other specially structured oxides, with emphasis on the designed strategies for promoting their performance and structure-property-performance relationships. Moreover, the practical device applications of complex metal oxides in fuel cells, water electrolyzers, and metal-air batteries are discussed. Finally, some concluding remarks summarizing the challenges, perspectives, and research trends of this topic are presented. We hope that this review provides a clear overview of the current status of this emerging field and stimulate future efforts to design more advanced electrocatalysts.

Se vacancies and interface engineering modulated bifunctionality prussian blue analogue derivatives for overall water splitting

It is a challenging task to design and synthesize stable, and high-performance non-precious metals bifunctional catalysts for water-splitting. Herein, the coupling between Se vacancy and interface engineering is highlighted to synthesize a unique CoFeSe hollow nanocubes structure on MXene-modified nickel foam (NF) by in-situ phase transition from bifunctionality prussian blue analogue (PBA) derivatives (VSe-CoFeSe@MXene/NF). DFT theory reveals that the Se vacancy and interface engineering modulate the surface electronic structure and optimize the surface adsorption energy of the intermediates. Experimental data also confirm that the as-prepared CoFeSe@MF catalyst exhibits advanced electrocatalytic properties, 283 mV (OER) and 67 mV (HER) are required to drive the current density of 10 mA cm-2. Notably, it is assembled into a two-electrode system for integral water decomposition, which only requires a low cell potential of 1.57 V at current of 10 mA cm-2, together with excellent durability for 48 h. The strategy is expected to provide a new direction for the design and construction of highly efficient collaborative integrated water decomposition electrocatalysts.

Customized Heteronuclear Dual Single-Atom and Cluster Assemblies via D-Band Orchestration for Oxygen Reduction Reaction

Advanced oxygen reduction reaction (ORR) catalysts, integrating with well-dispersed single atom (SA) and atomic cluster (AC) sites, showcase potential in bolstering catalytic activity. However, the precise structural modulation and in-depth investigation of their catalytic mechanisms pose ongoing challenges. Herein, a proactive cluster lockdown strategy is introduced, relying on the confinement of trinuclear clusters with metal atom exchange in the covalent organic polymers, enabling the targeted synthesis of a series of multicomponent ensembles featuring FeCo (Fe or Co) dual-single-atom (DSA) and atomic cluster (AC) configurations (FeCo-DSA/AC) via thermal pyrolysis. The designed FeCo-DSA/AC surpasses Fe- and Co-derived counterparts by 18 mV and 49 mV in ORR half-wave potential, whilst exhibiting exemplary performance in Zn-air batteries. Comprehensive analysis and theoretical simulation elucidate the enhanced activity stems from adeptly orchestrating dz 2-dxz and O 2p orbital hybridization proximate to the Fermi level, fine-tuning the antibonding states to expedite OH* desorption and OOH* formation, thereby augmenting catalytic activity. This work elucidates the synergistic potentiation of active sites in hybrid electrocatalysts, pioneering innovative targeted design strategies for single-atom-cluster electrocatalysts.

Strategic Design for High-Efficiency Oxygen Evolution Reaction (OER) Catalysts by Triggering Lattice Oxygen Oxidation in Cobalt Spinel Oxides

High-efficiency catalysts with refined electronic structures are highly desirable for promoting the kinetics of the oxygen evolution reaction (OER) and enhancing catalyst durability. This study comprehensively explores strategies involving metal doping and oxygen vacancies for enhancing the acidic OER catalytic activity of Co3O4. Through extensive screening of 3d and 4d transition metals using density functional theory (DFT) simulations, we demonstrate that the incorporation of metal dopants and oxygen vacancies into Co3O4 potentially triggers a transition from the adsorbate evolution mechanism (AEM) to the lattice oxygen oxidation mechanism (LOM) in the oxygen evolution reaction (OER). While the formation of the O-O bond in the intermediate *OOH poses challenges, a significantly reduced overpotential facilitates efficient conversion of O to O2 through the LOM in *OH and lattice oxygen. Additionally, we find that Mn doping can significantly improve the stability of the catalyst. Building upon the rationale above, we employed a dual doping strategy in subsequent experiments to enhance both the activity and stability. Our final design involved the codoping of Mn and Ru in Co3O4, along with an appropriate amount of oxygen vacancies. This catalyst demonstrates a low overpotential (η10 = 230 mV) compared to pure Co3O4 and maintains stable operation for over 120 h, representing a 12-fold increase. By exploring and harnessing the LOM, more efficient, stable, and cost-effective OER catalysts can be designed, providing crucial support for technologies such as water electrolysis in clean energy.

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

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

Enabling Efficient Oxygen Evolution via Anchoring Carbon-Layer-Confined RuOx on a Well-Matched Substrate

Oxygen evolution reaction (OER) is a multistep proton-coupled four-electron process with sluggish kinetics, which seriously limits the hydrogen production efficiency, thus it is of great importance to develop an efficient and stable OER catalyst. In this study, a two-step differential pyrolysis strategy is employed to design a three-dimensional porous microstructured material consisting of RuOx nanoparticles coated by a thin-layer carbon, where the active particles were isolated in separate chambers and the RuOx nanoparticles mainly existed in the form of a heterogeneous interface between RuO2 and partial metallic Ru. The preparation parameters of the catalysts are optimized via combining transient and steady-state polarization properties, and the target catalyst Cat-500-1.5t shows the best OER catalytic performance after ca. 60 h of a chronopotentiometry test in an acidic medium with a much smaller performance change than other samples. The unique design of adopting a carbon layer to form separate reaction chambers largely mitigates the excessive oxidation loss of the active components under strong oxidation potential. The suitability of the catalyst with the loaded substrate and test media is explored, and in an acidic medium, the carbon paper is much better than the titanium fiber, while in an alkaline medium, the titanium fiber is obviously superior to the carbon paper. On both carbon paper and titanium fiber, the performance in an alkaline medium outperforms that in an acidic medium, and the possible reasons for the performance difference are analyzed. Herein, to obtain the actual electrocatalytic performance, the optimal design of the catalyst structure and matching suitable conductive substrate in a specific medium are quite necessary, which provides a feasible strategy for the acquisition of efficient and stable electrocatalysts and the desirable presentation of performance.

Insulator-Transition-Induced Degradation of Pyrochlore Ruthenates in Electrocatalytic Oxygen Evolution and Stabilization through Doping

Ru-based pyrochlores (e.g., Y2Ru2O7-δ) are promised to replace IrO2 in polymer electrolyte membrane (PEM) electrolyzers. It is significant to reveal the cliff attenuation on the oxygen evolution reaction (OER) performance of these pyrochlores. In this work, we monitor the structure changes and electrochemical behavior of Y2Ru2O7-δ over the OER process, and it is found that the reason of decisive OER inactivation is derived from an insulator transition occurred within Y2Ru2O7-δ due to its inner "perfecting" lattice induced by continuous atom rearrangement. Therefore, a stabilization strategy of the Ir-substituted Y2Ru2O7-δ is proposed to alleviate this undesirable behavior. The double-exchange interaction between Ru and Ir in [RuO6] and [IrO6] octahedra leads the charge redistribution with simultaneous spin configuration adjustment. The electronic state in newly formed octahedrons centered with Ru 4d3 (with the state of eg'↑↑a1g ↑ eg 0) and Ir 5d6 (eg'↑↓↑↓a1g ↑↓ eg 0) relieves the uneven electron distributions in [RuO6] orbital. The attenuated Jahn-Teller effect alleviates atom rearrangement, represented as the mitigation of insulator transition, surface reconstruction, and metal dissolution. As results, the Ir-substituted Y2Ru2O7-δ presents the greatly improved OER stability and PEM durability. This study unveils the OER degradation mechanism and stabilization strategy for material design of Ru-based OER catalysts for electrochemical applications.

Structure-Activity Relationships in Oxygen Electrocatalysis

Oxygen electrocatalysis, as the pivotal circle of many green energy technologies, sets off a worldwide research boom in full swing, while its large kinetic obstacles require remarkable catalysts to break through. Here, based on summarizing reaction mechanisms and in situ characterizations, the structure-activity relationships of oxygen electrocatalysts are emphatically overviewed, including the influence of geometric morphology and chemical structures on the electrocatalytic performances. Subsequently, experimental/theoretical research is combined with device applications to comprehensively summarize the cutting-edge oxygen electrocatalysts according to various material categories. Finally, future challenges are forecasted from the perspective of catalyst development and device applications, favoring researchers to promote the industrialization of oxygen electrocatalysis at an early date.

Isolated Octahedral Pt-Induced Electron Transfer to Ultralow-Content Ruthenium-Doped Spinel Co3O4 for Enhanced Acidic Overall Water Splitting

The development of a highly active and stable oxygen evolution reaction (OER) electrocatalyst is desirable for sustainable and efficient hydrogen production via proton exchange membrane water electrolysis (PEMWE) powered by renewable electricity yet challenging. Herein, we report a robust Pt/Ru-codoped spinel cobalt oxide (PtRu-Co3O4) electrocatalyst with an ultralow precious metal loading for acidic overall water splitting. PtRu-Co3O4 exhibits excellent catalytic activity (1.63 V at 100 mA cm-2) and outstanding stability without significant performance degradation for 100 h operation. Experimental analysis and theoretical calculations indicate that Pt doping can induce electron transfer to Ru-doped Co3O4, optimize the absorption energy of oxygen intermediates, and stabilize metal-oxygen bonds, thus enhancing the catalytic performance through an adsorbate-evolving mechanism. As a consequence, the PEM electrolyzer featuring PtRu-Co3O4 catalyst with low precious metal mass loading of 0.23 mg cm-2 can drive a current density of 1.0 A cm-2 at 1.83 V, revealing great promise for the application of noniridium-based catalysts with low contents of precious metal for hydrogen production.

In situ fabrication of a plasmonic Bi@Bi2O2CO3 core-shell heterostructure for photocatalytic CO2 reduction: structural insights into selectivity modulation

The precise design of active sites and light absorbers is essential for developing highly efficient photocatalysts for CO2 reduction. Core-shell heterostructures constructed based on large-sized plasmonic Bi metals are ideal candidates because of the utilization of full-spectrum light and effective charge separation. However, the mechanism of selectivity modulation of large-sized Bi@semiconductor photocatalysts has yet to be explored in depth. Herein, a plasmonic Bi@Bi2O2CO3 core-shell heterostructure was successfully synthesized via a facile solvothermal treatment in deep eutectic solvents, demonstrating highly efficient photocatalytic CO2 reduction. This structure features a sizeable Bi sphere with a thin, epitaxially grown Bi2O2CO3 shell, which allows for the utilization of the entire light spectrum. Additionally, the oxygen vacancies in the Bi2O2CO3 shell can rapidly trap electrons transferred from the Bi core via Bi-O-Bi bonds, thereby forming abundant electron-rich interfaces that serve as the active sites for activating reactant molecules and facilitating the reaction.

Breaking the Bottleneck of Activity and Stability of RuO2-Based Electrocatalysts for Acidic Oxygen Evolution

Electrochemical acidic oxygen evolution reaction (OER) is an important part for water electrolysis utilizing a proton exchange membrane (PEM) apparatus for industrial H2 production. RuO2 has garnered considerable attention as a potential acidic OER electrocatalyst. However, the overoxidation of Ru active sites under high potential conditions is usually harmful for activity and stability, thereby posing a challenge for large-scale commercialization, which needs effective strategies to circumvent the leaching of Ru and further activate Ru sites. Herein, a Mini-Review is presented to summarize the recent developments regarding the activation and stabilization of the Ru active sites and lattice oxygen through the modulation of the d-band center, coordination environment, bridged heteroatoms, and vacancy engineering, as well as structural protection strategies and reaction pathway optimization to promote the acidic OER activity and stability of RuO2-based electrocatalysts. This Mini-Review offers a profound understanding of the design of RuO2-based electrocatalysts with greatly enhanced acidic OER performances.

Enhanced catalytic performance through a single-atom preparation approach: a review on ruthenium-based catalysts

The outstanding catalytic properties of single-atom catalysts (SACs) stem from the maximum atom utilization and unique quantum size effects, leading to ever-increasing research interest in SACs in recent years. Ru-based SACs, which have shown excellent catalytic activity and selectivity, have been brought to the frontier of the research field due to their lower cost compared with other noble catalysts. The synthetic approaches for preparing Ru SACs are rather diverse in the open literature, covering a wide range of applications. In this review paper, we attempt to disclose the synthetic approaches for Ru-based SACs developed in the most recent years, such as defect engineering, coordination design, ion exchange, the dipping method, and electrochemical deposition etc., and discuss their representative applications in both electrochemical and organic reaction fields, with typical application examples given of: Li-CO2 batteries, N2 reduction, water splitting and oxidation of benzyl alcohols. The mechanisms behind their enhanced catalytic performance are discussed and their structure-property relationships are revealed in this review. Finally, future prospects and remaining unsolved issues with Ru SACs are also discussed so that a roadmap for the further development of Ru SACs is established.

Amorphous P-CoOX Promotes the Formation of Hypervalent Ni Species in NiFe LDHs by Amorphous/Crystalline Interfaces for Excellent Catalytic Performance of Oxygen Evolution Reaction

Water electrolysis has become an attractive hydrogen production method. Oxygen evolution reaction (OER) is a bottleneck of water splitting as its four-electron transfer procedure presents sluggish reaction kinetics. Designing composite catalysts with high performance for efficient OER still remains a huge challenge. Here, the P-doped cobalt oxide/NiFe layered double hydroxides (P-CoOX/NiFe LDHs) composite catalysts with amorphous/crystalline interfaces are successfully prepared for OER by hydrothermal-electrodeposition combined method. The results of electrochemical characterizations, operando Raman spectra, and DFT theoretical calculations have demonstrated the electrons in the P-CoOX/NiFe LDHs heterointerfaces are easily transferred from Ni2+ to Co3+ because that the amorphous configuration of P-CoOX can well induce Ni-O-Co orbital coupling. The electron transfer of Ni2+ to the surrounding Fe3+ and Co3+ will lead to the unoccupied eg orbitals of Ni3+ that can promote water dissociation and accelerate *OOH migration to improve OER catalytic performance. The optimized P-CoOX/NiFe LDHs exhibit superior catalytic performance for OER with a very low overpotential of 265 mV at 300 mA cm-2 and excellent long-term stability of 500 h with almost no attenuation at 100 mA cm-2. This work will provide a new method to design high-performance NiFe LDHs-based catalysts for OER.

Accelerated Proton Transfer in Asymmetric Active Units for Sustainable Acidic Oxygen Evolution Reaction

The poor durability of Ru-based catalysts limits the practical application in proton exchange membrane water electrolysis (PEMWE). Here, we report that the asymmetric active units in Ru1-xMxO2 (M = Sb, In, and Sn) binary solid solution oxides are constructed by introducing acid-resistant p-block metal sites, breaking the activity and stability limitations of RuO2 in acidic oxygen evolution reaction (OER). Constructing highly asymmetric Ru-O-Sb units with a strong electron delocalization effect significantly shortens the spatial distance between Ru and Sb sites, improving the bonding strength of the overall structure. The unique two-electron redox couples at Sb sites in asymmetric active units trigger additional chemical steps at different OER stages, facilitating continuous proton transfer. The optimized Ru0.8Sb0.2O2 solid solution requires a superlow overpotential of 160 mV at 10 mA cm-2 and a record-breaking stability of 1100 h in an acidic electrolyte. Notably, the scale-prepared Ru0.8Sb0.2O2 achieves efficient PEMWE performance under industrial conditions. General mechanism analysis shows that the enhanced proton transport in the asymmetric Ru-O-M unit provides a new working pathway for acidic OER, breaking the scaling relationship without sacrificing stability.

Modulating Electronic Structure of Iridium Single-Atom Anchored on 3D Fe-Doped β-Ni(OH)2 Catalyst with Nanopyramid Array Structure for Enhanced Oxygen Evolution Reaction

Developing high-performance electrocatalysts for oxygen evolution reaction (OER) is crucial in the pursuit of clean and sustainable hydrogen energy, yet still challenging. Herein, a spontaneous redox strategy is reported to achieve iridium single-atoms anchored on hierarchical nanosheet-based porous Fe doped β-Ni(OH)2 pyramid array electrodes (SAs Ir/Fe-β-Ni(OH)2), which exhibits high OER performance with a low overpotential of 175 mV at 10 mA cm-2 and a remarkable OER current density in alkaline electrolyte, surpassing Fe-β-Ni(OH)2/NF and IrO2 by 31 and 38 times at 1.43 V versus RHE, respectively. OER catalytic mechanism demonstrates that the conversion of *OH→*O and the active lattice O content can be significantly improved due to the modulation effect of the Ir single atoms on the local electronic structure and the redox behavior of FeNi (oxy) hydroxide true active species. This work provides a promising insight into understanding the OER enhancement mechanism for Ir single-atoms modified FeNi-hydroxide systems.

Advances in Noble Metal Electrocatalysts for Acidic Oxygen Evolution Reaction: Construction of Under-Coordinated Active Sites

Renewable energy-driven proton exchange membrane water electrolyzer (PEMWE) attracts widespread attention as a zero-emission and sustainable technology. Oxygen evolution reaction (OER) catalysts with sluggish OER kinetics and rapid deactivation are major obstacles to the widespread commercialization of PEMWE. To date, although various advanced electrocatalysts have been reported to enhance acidic OER performance, Ru/Ir-based nanomaterials remain the most promising catalysts for PEMWE applications. Therefore, there is an urgent need to develop efficient, stable, and cost-effective Ru/Ir catalysts. Since the structure-performance relationship is one of the most important tools for studying the reaction mechanism and constructing the optimal catalytic system. In this review, the recent research progress from the construction of unsaturated sites to gain a deeper understanding of the reaction and deactivation mechanism of catalysts is summarized. First, a general understanding of OER reaction mechanism, catalyst dissolution mechanism, and active site structure is provided. Then, advances in the design and synthesis of advanced acidic OER catalysts are reviewed in terms of the classification of unsaturated active site design, i.e., alloy, core-shell, single-atom, and framework structures. Finally, challenges and perspectives are presented for the future development of OER catalysts and renewable energy technologies for hydrogen production.

Atomic-Layer IrOx Enabling Ligand Effect Boosts Water Oxidation Electrocatalysis

An in situ formed IrOx (x ≤ 2) layer driven by anodic bias serves as the essential active site of Ir-based materials for oxygen evolution reaction (OER) electrocatalysis. Once being confined to atomic thickness, such an IrOx layer possesses both a favorable ligand effect and maximized active Ir sites with a lower O-coordination number. However, limited by a poor understanding of surface reconstruction dynamics, obtaining atomic layers of IrOx remains experimentally challenging. Herein, we report an idea of material design using intermetallic IrVMn nanoparticles to induce in situ formation of an ultrathin IrOx layer (O-IrVMn/IrOx) to enable the ligand effect for achieving superior OER electrocatalysis. Theoretical calculations predict that a strong electronic interaction originating from an orderly atomic arrangement can effectively hamper the excessive leaching of transition metals, minimizing vacancies for oxygen coordination. Linear X-ray absorption near edge spectra analysis, extended X-ray absorption fine structure fitting outcomes, and X-ray photoelectron spectroscopy collectively confirm that Ir is present in lower oxidation states in O-IrVMn/IrOx due to the presence of unsaturated O-coordination. Consequently, the O-IrVMn/IrOx delivers excellent acidic OER performances with an overpotential of only 279 mV at 10 mA cm-2 and a high mass activity of 2.3 A mg-1 at 1.53 V (vs RHE), exceeding most Ir-based catalysts reported. Moreover, O-IrVMn/IrOx also showed excellent catalytic stability with only 0.05 at. % Ir dissolution under electrochemical oxidation, much lower than that of disordered D-IrVMn/IrOx (0.20 at. %). Density functional theory calculations unravel that the intensified ligand effect optimizes the adsorption energies of multiple intermediates involved in the OER and stabilizes the as-formed catalytic IrOx layer.

High-Entropy Perovskite Oxides as a Family of Electrocatalysts for Efficient and Selective Nitrogen Oxidation

Electrocatalytic nitrogen oxidation reaction (NOR) can convert nitrogen (N2) into nitrate (NO3-) under ambient conditions, providing an attractive approach for synthesis of NO3-, alternative to the current approach involving the harsh Haber-Bosch and Ostwald oxidation processes that necessitate high temperature, high pressure, and substantial carbon emission. Developing efficient NOR catalysts is a prerequisite, which remains a formidable challenge, owing to the weak activation/dissociation of N2. A variety of NOR electrocatalysts have been developed, but their NOR kinetics are still extremely sluggish, resulting in inferior Faradaic Efficiencies. Here, we report a high-entropy Ru-based perovskite oxide (denoted as Ru-HEP) that can function as a high-performance NOR catalyst and exhibit a high NO3- yield rate of 39.0 μmol mg-1 h-1 with a Faradaic Efficiency of 32.8%. Both our experimental results and theoretical calculations suggest that the high-entropy configuration of Ru-HEP perovskite oxide can markedly enhance the oxygen-vacancy concentration, where the Ru sites and their neighboring oxygen vacancies can serve as unsaturated centers and decrease the overall energy barrier for N2 electrooxidation, thereby leading to promoted NOR kinetics. This work presents an alternative avenue for promoting NOR catalysis on perovskite oxides through the high-entropy engineering strategy.

Electrical-Driven Directed-Evolution of Copper Nanowires Catalysts for Efficient Nitrate Reduction to Ammonia

The electrocatalytic conversion of nitrate (NO3 -) to NH3 (NO3RR) at ambient conditions offers a promising alternative to the Haber-Bosch process. The pivotal factors in optimizing the proficient conversion of NO3 - into NH3 include enhancing the adsorption capabilities of the intermediates on the catalyst surface and expediting the hydrogenation steps. Herein, the Cu/Cu2O/Pi NWs catalyst is designed based on the directed-evolution strategy to achieve an efficient reduction of NO3‾. Benefiting from the synergistic effect of the OV-enriched Cu2O phase developed during the directed-evolution process and the pristine Cu phase, the catalyst exhibits improved adsorption performance for diverse NO3RR intermediates. Additionally, the phosphate group anchored on the catalyst's surface during the directed-evolution process facilitates water electrolysis, thereby generating Hads on the catalyst surface and promoting the hydrogenation step of NO3RR. As a result, the Cu/Cu2O/Pi NWs catalyst shows an excellent FE for NH3 (96.6%) and super-high NH3 yield rate of 1.2 mol h-1 gcat. -1 in 1 m KOH and 0.1 m KNO3 solution at -0.5 V versus RHE. Moreover, the catalyst's stability is enhanced by the stabilizing influence of the phosphate group on the Cu2O phase. This work highlights the promise of a directed-evolution approach in designing catalysts for NO3RR.

Defect-rich sonosensitizers based on CeO2 with Schottky heterojunctions for boosting sonodynamic/chemodynamic synergistic therapy

Sonodynamic therapy (SDT) has been recognized as a promising treatment for cancer due to its advantages of superior specificity, non-invasiveness, and deep tissue penetration. However, the antitumor effect of SDT remains restricted by the limited generation of reactive oxygen species (ROS) due to the lack of highly efficient sonosensitizers. In this work, we developed the novel sonosensitizer Pt/CeO2-xSx by constructing oxygen defects through S doping and Pt loading in situ. Large amounts of oxygen defects have been obtained by S doping, endowing Pt/CeO2-xSx with the ability to suppress electron-hole recombination, further promoting ROS production. Moreover, the introduction of Pt nanoparticles can not only produce oxygen in situ for relieving hypoxia but also form a Schottky heterojunction with CeO2-xSx for further inhibiting electron-hole recombination. In addition, Pt/CeO2-xSx could effectively deplete overexpressed glutathione (GSH) via redox reactions, amplifying oxidative stress in the tumor microenvironment (TME). Combined with the excellent POD-mimetic activity, Pt/CeO2-xSx can achieve highly efficient synergistic therapy of SDT and chemodynamic therapy (CDT). All these findings demonstrated that Pt/CeO2-xSx has great potential for cancer therapy, and this work provides a promising direction for designing and constructing efficient sonosensitizers.

Promotion of Acid-Water Oxidation by Lattice Distortion and Orbital Hybridization Induced by Ionic Dopant in Pyrochlore Y2Ru2O7

For acid-water oxidation, pyrochloric ruthenates are thought to be extremely effective electrocatalysts. In this work, through partial B-site replacement with larger M2+ cations, the electronic states of Y2Ru2O7 with strong electron correlations are reasonably managed, by which the inherent performance is tremendously promoted. Based on this, the improved Y2Ru1.9Sr0.1O7 electrocatalyst exhibits an outstanding durability and presents a highly inherent mass activity of 1915.1 A gRu-1 (at 1.53 V vs RHE). The enhanced oxygen-evolving reaction (OER) activity by ionic dopant in YRO pyrochlore can be attributed to two aspects, i.e., the lattice distortion induced inhibition of the grain coarsening, which results in a large surface area for YRO-M and increases the OER active sites, and the weakening of electron correlation via broadening of the Ru 4d bandwidths due to the increase of the average radius of B-site ions, which gives rise to an enhancement of conductivity and a strengthened hybridization between Ru 4d and O 2p orbitals and improves the reaction kinetics. The synergistic effects of lattice distortion and orbital hybridization promote the enhanced OER activity. The results would provide fresh concepts for the design of improved electrocatalysts and underscore the significance of managing the intrinsic performance through the dual modification of microstructure morphology and electronic structure.

Na Substitution Steering RuO6 Unit in Ruthenium Pyrochlores for Enhanced Oxygen Evolution in Acid

Although Ruthenium-based pyrochlore oxides can function as promising catalysts for acidic water oxidation, their limitations in terms of stability and activity still need to be addressed for further application in practical conditions. In this work, the possibility to enhance both oxygen evolution reaction activity and durability of Gd2Ru2O7- δ through partial replacement with Na+ in Gd3+ sites is first offered, leading to the electronic and geometric regulation of active center RuO6. Na+ triggers the emergence of Ru<4+ and the electron rearrangement of active-centered RuO6. Specifically, Ru ions with a negative d-band center after Na+ doping exhibit weaker adsorption energies of *O and result in the conversion of the rate-limiting step from *O/*OOH to *OH/O*, reducing energy barriers for boosting activities. Therefore, the NaxGd2- xRu2O7- δ requires a low overpotential of 260 mV at 10 mA cm-2 in 0.1 m HClO4 electrolyte. Moreover, the higher formation energy of Ru vacancy and less distorted RuO6 enable the as-prepared NaxGd2- xRu2O7- δ to operate steadily at 10 mA cm-2 for 300 h and multi-current chronopotentiometry with current densities from 20 to 100 mA cm-2 for 60 h in acidic proton exchange membrane electrolyzer, respectively.

Probing Surface Transformations of Lanthanum Nickelate Electrocatalysts during Oxygen Evolution Reaction

Monitoring the spontaneous reconstruction of the surface of metal oxides under electrocatalytic reaction conditions is critical to identifying the active sites and establishing structure-activity relationships. Here, we report on a self-terminated surface reconstruction of Ruddlesden-Popper lanthanum nickel oxide (La2NiO4+δ) that occurs spontaneously during reaction with alkaline electrolyte species. Using a combination of high-resolution scanning transmission electron microscopy (HR-STEM), surface-sensitive X-ray photoelectron spectroscopy (XPS), and soft X-ray absorption spectroscopy (sXAS), as well as electrochemical techniques, we identify the structure of the reconstructed surface layer as an amorphous (oxy)hydroxide phase that features abundant under-coordinated nickel sites. No further amorphization of the crystalline oxide lattice (beyond the ∼2 nm thick layer formed) was observed during oxygen evolution reaction (OER) cycling experiments. Notably, the formation of the reconstructed surface layer increases the material's oxygen evolution reaction (OER) activity by a factor of 45 when compared to that of the pristine crystalline surface. In contrast, a related perovskite phase, i.e., LaNiO3, did not show noticeable surface reconstruction, and also no increase in its OER activity was observed. This work provides detailed insight into a surface reconstruction behavior dictated by the crystal structure of the parent oxide and highlights the importance of surface dynamics under reaction conditions.

Regulating Ir-O Covalency to Boost Acidic Oxygen Evolution Reaction

The unsatisfactory oxygen evolution reaction (OER) activity of IrO2 has intensively raised the cost and energy consumption of hydrogen generation from proton exchange membrane water electrolyzers. Here, the acidic OER activity of the rutile IrO2 is significantly enhanced by the incorporation of trivalent metals (e.g., Gd, Nd, and Pr) to increase the Ir-O covalency, while the high-valence (pentavalent or higher) metal incorporation decreases the Ir-O covalency resulting in worse OER activity. Experimental and theoretical analyses indicate that enhanced Ir-O covalency activates lattice oxygen and triggers lattice oxygen-mediated mechanism to enhance OER kinetics, which is verified by the finding of a linear relationship between the natural logarithm of intrinsic activity and Ir-O covalency described by charge transfer energy. By regulating the Ir-O covalency, the obtained Gd-IrO2-δ merely needs 260 mV of overpotential to reach 10 mA cm-2 and shows impressive stability during a 200-h test in 0.5 м H2SO4. This work provides an effective strategy for significantly enhancing the OER activity of the widely used IrO2 electrocatalysts through the rational regulation of Ir-O covalency.

Research Advances of Non-Noble Metal Catalysts for Oxygen Evolution Reaction in Acid

Water splitting is an important way to obtain hydrogen applied in clean energy, which mainly consists of two half-reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, the kinetics of the OER of water splitting, which occurs at the anode, is slow and inefficient, especially in acid. Currently, the main OER catalysts are still based on noble metals, such as Ir and Ru, which are the main active components. Hence, the exploration of new OER catalysts with low cost, high activity, and stability has become a key issue in the research of electrolytic water hydrogen production technology. In this paper, the reaction mechanism of OER in acid was discussed and summarized, and the main methods to improve the activity and stability of non-noble metal OER catalysts were summarized and categorized. Finally, the future prospects of OER catalysts in acid were made to provide a little reference idea for the development of advanced OER catalysts in acid in the future.

Strain-modulated Ru-O Covalency in Ru-Sn Oxide Enabling Efficient and Stable Water Oxidation in Acidic Solution

RuO2 is one of the benchmark electrocatalysts used as the anode material in proton exchange membrane water electrolyser. However, its long-term stability is compromised due to the participation of lattice oxygen and metal dissolution during oxygen evolution reaction (OER). In this work, weakened covalency of Ru-O bond was tailored by introducing tensile strain to RuO6 octahedrons in a binary Ru-Sn oxide matrix, prohibiting the participation of lattice oxygen and the dissolution of Ru, thereby significantly improving the long-term stability. Moreover, the tensile strain also optimized the adsorption energy of intermediates and boosted the OER activity. Remarkably, the RuSnOx electrocatalyst exhibited excellent OER activity in 0.1 M HClO4 and required merely 184 mV overpotential at a current density of 10 mA cm-2 . Moreover, it delivered a current density of 10 mA cm-2 for at least 150 h with negligible potential increase. This work exemplifies an effective strategy for engineering Ru-based catalysts with extraordinary performance toward water splitting.

The Promising Seesaw Relationship Between Activity and Stability of Ru-Based Electrocatalysts for Acid Oxygen Evolution and Proton Exchange Membrane Water Electrolysis

The development of electrocatalysts that are not reliant on iridium for efficient acid-oxygen evolution is a critical step towards the proton exchange membrane water electrolysis (PEMWE) and green hydrogen industry. Ruthenium-based electrocatalysts have garnered widespread attention due to their remarkable catalytic activity and lower commercial price. However, the challenge lies in balancing the seesaw relationship between activity and stability of these electrocatalysts during the acid-oxygen evolution reaction (OER). This review delves into the progress made in Ru-based electrocatalysts with regards to acid OER and PEMWE applications. It highlights the significance of customizing the acidic OER mechanism of Ru-based electrocatalysts through the coordination of adsorption evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM) to attain the ideal activity and stability relationship. The promising tradeoffs between the activity and stability of different Ru-based electrocatalysts, including Ru metals and alloys, Ru single-atomic materials, Ru oxides, and derived complexes, and Ru-based heterojunctions, as well as their applicability to PEMWE systems, are discussed in detail. Furthermore, this paper offers insights on in situ control of Ru active sites, dynamic catalytic mechanism, and commercial application of PEMWE. Based on three-way relationship between cost, activity, and stability, the perspectives and development are provided.

Boosting electrocatalytic performance via electronic structure regulation for acidic oxygen evolution

High-purity hydrogen produced by water electrolysis has become a sustainable energy carrier. Due to the corrosive environments and strong oxidizing working conditions, the main challenge faced by acidic water oxidation is the decrease in the activity and stability of anodic electrocatalysts. To address this issue, efficient strategies have been developed to design electrocatalysts toward acidic OER with excellent intrinsic performance. Electronic structure modification achieved through defect engineering, doping, alloying, atomic arrangement, surface reconstruction, and constructing metal-support interactions provides an effective means to boost OER. Based on introducing OER mechanism commonly present in acidic environments, this review comprehensively summarizes the effective strategies for regulating the electronic structure to boost the activity and stability of catalytic materials. Finally, several promising research directions are discussed to inspire the design and synthesis of high-performance acidic OER electrocatalysts.

Perovskite Oxide as A New Platform for Efficient Electrocatalytic Nitrogen Oxidation

Electrocatalytic nitrogen oxidation reaction (NOR) offers an efficient and sustainable approach for conversion of widespread nitrogen (N2 ) into high-value-added nitrate (NO3 - ) under mild conditions, representing a promising alternative to the traditional approach that involves harsh Haber-Bosch and Ostwald oxidation processes. Unfortunately, due to the weak absorption/activation of N2 and the competitive oxygen evolution reaction, the kinetics of NOR process is extremely sluggish accompanied with low Faradaic efficiencies and NO3 - yield rates. In this work, an oxygen-vacancy-enriched perovskite oxide with nonstoichiometric ratio of strontium and ruthenium (denoted as Sr0.9 RuO3 ) was synthesized and explored as NOR electrocatalyst, which can exhibit a high Faradaic efficiency (38.6 %) with a high NO3 - yield rate (17.9 μmol mg-1  h-1 ). The experimental results show that the amount of oxygen vacancies in Sr0.9 RuO3 is greatly higher than that of SrRuO3 , following the same trend as their NOR performance. Theoretical simulations unravel that the presence of oxygen vacancies in the Sr0.9 RuO3 can render a decreased thermodynamic barrier toward the oxidation of *N2 to *N2 OH at the rate-determining step, leading to its enhanced NOR performance.

Iron substitution enabled lattice oxygen oxidation and cation leaching for promoting surface reconstruction in electrocatalytic oxygen evolution

The low-cost transition metal oxides have drawn widespread interest as alternatives to noble metal-based electrocatalysts for oxygen evolution reaction (OER). Transition metal oxides usually undergo surface reconstruction during electrochemical reaction to form the actual active species. However, in-depth understanding and regulating of the surface reconstruction of active phases for oxides in OER remains an onerous challenge. Herein, we report a simple Fe element substitution strategy to facilitate the surface reconstruction of spinel oxide NiCr2O4 to generate active (oxy)hydroxides. The activated Fe-doped NiCr2O4 (Act-Fe-NCO) exhibits a lower OER overpotential of 259 mV at 10 mA cm-2 than activated NiCr2O4 (Act-NCO, 428 mV), and shows excellent stability for 120 h. The electrochemically activated CV measurement and nanostructure characterizations reveal that Fe substitution could promote the consumption of lattice oxygen during electrochemical activation to induce the leaching of soluble Cr cations, thereby facilitating the reconstruction of remaining Ni cations on the surface into (oxy)hydroxide active species. Moreover, theoretical calculations further demonstrate that the O 2p band center of NiCr2O4 moves towards the Fermi level due to Fe substitution, thus promoting lattice oxygen oxidation and providing greater structural flexibility for surface reconstruction. This work shows a promising way to regulate the surface reconstruction kinetics and OER electrocatalytic activity of transition metal oxides.

Highly Active Pyrochlore-Type Praseodymium Ruthenate Electrocatalyst for Efficient Acid-Water Oxidation

To produce directly combustible hydrogen from water, highly active, acid-resistant, and economical catalysts for oxygen evolution reaction (OER) are needed. An electrocatalyst based on praseodymium ruthenate (Pr2Ru2O7) is presented here that greatly outperforms RuO2 for acid-water oxidation. Specifically, at 10 mA cm-2, this electrocatalyst presents a low overpotential (η) of 213 mV and markedly superior stability. Moreover, Pr2Ru2O7 presents a significant rise in turnover frequency (TOF) and a highly intrinsic mass activity of 1618.8 A gRu-1 (η = 300 mV), exceeding the most commonly reported acid OER catalysts. Density functional theory calculations and electronic structure study demonstrate that the Ru 4d-band center related to the longer Ru-O bond with a large radius of Pr ion in this pyrochlore is lower than that in RuO2, which would optimize the binding between the adsorbed oxygen species and catalytic metal sites and enhance the catalytic intrinsic activity.

Oxygen Defect Engineering Promotes Synergy Between Adsorbate Evolution and Single Lattice Oxygen Mechanisms of OER in Transition Metal-Based (oxy)Hydroxide

The oxygen evolution reaction (OER) activity of transition metal (TM)-based (oxy)hydroxide is dominated by the number and nature of surface active sites, which are generally considered to be TM atoms occupying less than half of surface sites, with most being inactive oxygen atoms. Herein, based on an in situ competing growth strategy of bimetallic ions and OH- ions, a facile one-step method is proposed to modulate oxygen defects in NiFe-layered double hydroxide (NiFe-LDH)/FeOOH heterostructure, which may trigger the single lattice oxygen mechanism (sLOM). Interestingly, by only varying the addition of H2 O2 , one can simultaneously regulate the concentration of oxygen defects, the valence of metal sites, and the ratio of components. The proper oxygen defects promote synergy between the adsorbate evolution mechanism (AEM, metal redox chemistry) and sLOM (oxygen redox chemistry) of OER in NiFe-based (oxy)hydroxide, practically maximizing the use of surface TM and oxygen atoms as active sites. Consequently, the optimal NiFe-LDH/FeOOH heterostructure outperforms the reported non-noble OER catalysts in electrocatalytic activity, with an overpotential of 177 mV to deliver a current density of 20 mA cm-2 and high stability. The novel strategy exemplifies a facile and versatile approach to designing highly active TM-LDH-based OER electrocatalysts for energy and environmental applications.