Construction of Zn-doped RuO2 nanowires for efficient and stable water oxidation in acidic media

Breaking the Activity-Stability Trade-Off of RuO2 via Metallic Ru Bilateral Regulation for Acidic Oxygen Evolution Reaction

Developing highly efficient acidic oxygen evolution reaction (OER) electrocatalysts is crucial for proton exchange membrane water electrolyzer. RuO2 electrocatalysts, which followed a kinetically favorable lattice oxygen mechanism, perform a preferable intrinsic activity, but poor stability for acidic OER. Recent work often sacrifices the intrinsic activity of RuO2 to enhance stability. The balance between the activity and stability of RuO2-based catalysts is still overlooked in current research. Here, we report a controlled method to introduce metallic Ru onto RuO2 catalysts to form the Ru4+─O─Ru0 interfacial structure for decreasing the Ru4+ oxidation state and promoting deprotonation kinetics. Metallic Ru can serve as the electron donor to lower the oxidation state of *Vo-RuO4 2- in Ru/RuO2 for stabilizing the structure of *Vo-RuO4 2--Ru/RuO2 to favour the acidic OER stability. Moreover, the deprotonation kinetics via the interfacial oxygen site between Ru4+ and Ru0 is significantly enhanced on Ru/RuO2 catalysts to improve the acidic OER activity. This work offers a unique perspective to balance the acidic OER activity and stability of RuO2.

Orbital-level band gap engineering of RuO2 for enhanced acidic water oxidation

Developing efficient and stable oxygen evolution reaction electrocatalysts under acidic conditions is crucial for advancing proton-exchange membrane water electrolysers commercialization. Here, we develop a representative strategy through p-orbital atoms (N, P, S, Se) doping in RuO2 to precisely regulate the lattice oxygen-mediated mechanism-oxygen vacancy site mechanism pathway. In situ and ex situ measurements along with theoretical calculations demonstrate that Se doping dynamically adjusts the band gap between the Ru-eg and O-p orbitals during the oxygen evolution reaction process. This modulation accelerates electron diffusion to the external circuit, promotes the lattice oxygen-mediated process, and enhances catalytic activity. Additionally, it facilitates electron feedback and stabilizes oxygen vacancies, thereby promoting the oxygen vacancy site mechanism process and enhancing catalytic stability. The resulting Se-RuOx catalyst achieves efficient proton-exchange membrane water electrolysers performance under industrial conditions with a minimal charge overpotential of 1.67 V to achieve a current density of 1 A cm-2 and maintain long-term cyclability for over 1000 h. This work presents a unique method for guiding the future development of high-performance metal oxide catalysts.

Distribution of Oxygen Vacancies in RuO2 Catalysts and Their Roles in Activity and Stability in Acidic Oxygen Evolution Reaction

By combining density functional theory (DFT) calculations and the cluster expansion (CE) model in an active-learning framework, we comprehensively studied the distribution features of oxygen vacancies (OV's) as well as their contributions to the stability and activity of the RuO2 catalyst in acidic oxygen evolution reaction (OER). The results show that OV's prefer to be located at bridge oxygen sites on the RuO2(110) surface and the next-nearest-neighbor trans positions of surface RuO6 octahedra in pairs due to interactions between two OV's, and high concentrations of OV's exhibit a continuous zigzag distribution in the (110) plane of RuO2. The oxygen vacancy distribution can be explained by the charge repulsion between the low-valent Ru and O, which is referred to as the "heterovalent ion-oxygen exclusion principle". In addition, the DFT results show that the presence of OV's cannot improve the inherent OER activity of specific Ru sites since low-valent Ru sites hinder deprotonation of the second water molecule. Nevertheless, OV's can improve the stability of RuO2 by suppressing the lattice oxygen mechanism (LOM) path. In summary, this work provides deeper insights into the mechanism of the OER of RuO2 with OV's in acidic media and a possible way to improve catalyst performance by using oxygen vacancy engineering.

Synergistic niobium and manganese co-doping into RuO2 nanocrystal enables PEM water splitting under high current

Low-cost ruthenium-based catalysts with high activity have emerged as promising alternatives to iridium-based counterparts for acidic oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE), but the poor stability under high current density remains as a key challenge. Here, we utilize the synergistic complementary strategy of introducing earth-abundant Mn and Nb dopants in ruthenium dioxide (RuO2) for Nb0.1Mn0.1Ru0.8O2 nanoparticle electrocatalyst that exhibits a low overpotential of 209 mV at 10 mA cm-2 and good stability of > 400 h at 0.2 A cm-2 in 0.5 M H2SO4. Significantly, a PEMWE device fabricated with Nb0.1Mn0.1Ru0.8O2 anode can operate continuously at least for 1000 h at 0.5 A cm-2 with 59 μV h-1 decay rate. Operando Raman spectroscopy analysis, differential electrochemical mass spectroscopy measurements, X-ray absorption spectroscopy analysis and theoretical calculations indicate that OER reaction on Nb0.1Mn0.1Ru0.8O2 primarily follows the adsorbate evolution mechanism with much favorable energy barrier accompanied by a locally passivated lattice oxygen mechanism (AEM-LPLOM) and the co-existed Nb and Mn in RuO2 crystal lattice could not only stabilize the lattice oxygen, but also relieve the valence state fluctuation of Ru site to stabilize the catalyst during the reaction.

Engineering high-density microcrystalline boundary with V-doped RuO2 for high-performance oxygen evolution in acid

Designing efficient acidic oxygen evolution catalysts for proton exchange membrane water electrolyzers is challenging due to a trade-off between activity and stability. In this work, we construct high-density microcrystalline grain boundaries (GBs) with V-dopant in RuO2 matrix (GB-V-RuO2). Our theoretical and experimental results indicate this is a highly active and acid-resistant OER catalyst. Specifically, the GB-V-RuO2 requires low overpotentials of 159, 222, and 300 mV to reach 10, 100, and 1500 mA cm-2geo in 0.5 M H2SO4, respectively. Operando EIS, ATR-SEIRAS FTIR and DEMS measurements reveal the importance of GBs in stabilizing lattice oxygen and thus inhibiting the lattice oxygen mediated OER pathway. As a result, the adsorbate evolution mechanism pathway becomes dominant, even at high current densities. Density functional theory analyses confirm that GBs can stabilize V dopant and that the synergy between them modulates the electronic structure of RuO2, thus optimizing the adsorption of OER intermediate species and enhancing electrocatalyst stability. Our work demonstrates a rational strategy for overcoming the traditional activity/stability dilemma, offering good prospects of developing high-performance acidic OER catalysts.

Effect of ionic-bonding d0 cations on structural durability in barium iridates for oxygen evolution electrocatalysis

Iridium has the exclusive chemistry guaranteeing both high catalytic activity and sufficient corrosion resistance in a strong acidic environment under anodic potential. Complex iridates thus attract considerable attention as high-activity electrocatalysts with less iridium utilization for the oxygen evolution reaction (OER) in water electrolyzers using a proton-exchange membrane. Here we demonstrate the effect of chemical doping on the durability of hexagonal-perovskite Bax(M,Ir)yOz-type iridates in strong acid (pH ~ 0). Some aliovalent cations are directly visualized to periodically locate at the octahedral sites bridging the two face-sharing [Ir2O9] dimer or [Ir3O12] trimers in hexagonal-perovskite polytypes. In particular, highly ionic bonding of the d0 Nb5+ and Ta5+ cations with oxygen anions results in notable suppression of lattice oxygen participation during the OER and thus effectively preserves the connectivity between the [Ir3O12] trimers without lattice collapse. Providing an in-depth understanding of the correlation between the electronic structure and bonding nature in crystals, our work suggests that proper control of chemical doping in complex oxides promises a simple but efficient tool to realize OER electrocatalysts with markedly improved durability.

Electron Itinerancy Mediated by Oxygen Vacancies Breaks the Inert Electron Chain to Boost Lithium-Oxygen Batteries Electrocatalysis

The synergistic effect of dopants and oxygen vacancies (Vo) in metal oxides is crucial for enhancing the adsorption and electron transfer processes in lithium-oxygen (Li-O2) batteries; however, the underlying mechanisms remain unclear. Herein, Ru single-atom-modified TiO2 nanorod array (Ru1-TiO2- x) electrocatalysts with abundant Vo were fabricated, serving as an efficient catalyst for Li-O2 batteries. Experimental and theoretical investigations have demonstrated that Vo functions as an "electron pump", facilitating electron itinerant behavior, while Ru1 serves as an "electron buffer" to further activate the [Ru-O-Ti] electronic chain. This synergistic interplay endows Li-O2 batteries with a highly active and stable bidirectional self-regulating capability during the process of circulation, exhibiting an ultra-low charge polarization (0.42V) and exceptional cycling stability (1680 h). Vo and Ru1 synergistically modulate the d-band center at the Ti site to establish an adaptively tunable Ru-Ti dual-active site. This adjustment effectively balances the binding strength with the interface oxygen intermediate (*O), thereby significantly reducing the activation barrier. The Hamiltonian layout further revealed the crucial role of remote orbital coupling in maintaining the structural stability. This study not only provides profound insights into Vo-dependent electron transfer kinetics but also proposes new strategies and theoretical guidance for the activation of inert materials.

Sulfur species induced Fe3+ and Co3+ enrichment in a low-crystalline FeCoNi hydroxide boosts water oxidation

A low-crystalline S-doped FeCoNi hydroxide is developed via a one-step electrodeposition method. The incorporation of S species changes the electronic properties of FeCoNi hydroxide, resulting in the enrichment of active Fe3+ and Co3+ sites, thereby achieving excellent performance for water oxidation in 1 M or realistic 30 wt% KOH solution.

Atomic Ga triggers spatiotemporal coordination of oxygen radicals for efficient water oxidation on crystalline RuO2

Advancements in proton-exchange membrane water electrolyzer depend on developing oxygen evolution reaction electrocatalysts that synergize high activity with stability. Here, we introduce an approach aimed at elevating oxygen evolution reaction performance by enhancing the spatiotemporal coordination of oxygen radicals to promote efficient O-O coupling. A dense, single-atom configuration of oxygen radical donors within interconnected RuO2 nanocrystal framework is demonstrated. The stable oxygen radicals on gallium sites with adaptable Ga-O bonds are thermodynamically favorable to attract those from Ru sites, addressing dynamic adaptation challenges and boosting O-O coupling efficiency. The optimized catalyst achieves a low overpotential of 188 mV at 10 mA cm-2, operates robustly for 800 h at 100 mA cm-2 in acidic conditions, and shows a large current density of 3 A cm-2 at 1.788 V, with stable performance at 0.5 A cm-2 for 200 h, confirming its long-term viability in proton-exchange membrane water electrolyzer applications.

Unlocking Enhanced Catalysis Stability in Acidic Oxygen Evolution: Structural Insights for PEM Applications under High-Current Density

In proton exchange membrane water electrolysis (PEMWE), catalysts for acidic oxygen evolution reaction (OER) that demonstrate high current density and stability are essential. Herein, we synthesized La-doped RuO2 (La-RuO2@TM) nanorod composite catalysts in situ on titanium mesh (TM) using a one-step low-temperature pyrolysis method. La-RuO2@TM displays excellent catalytic performance (1.533 V at 100 mA cm-2) and remarkable stability, showing no significant degradation in performance over 450 hours of operation. Density functional theory (DFT) calculations indicate that the formation of the La-O-Ru local structure modulates the adsorption strength of reaction intermediates, alleviates metal (Ru) leaching, and reduces oxygen loss, significantly enhancing the material's durability in acidic OER. The PEM electrolyzer utilizing La-RuO2@TM operates at 1.815 V with a current density of 1.0 A cm-2, maintaining stable performance for 120 h at 60 °C. This study offers valuable insights for designing efficient and durable acidic OER catalysts.

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

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

Recent Development of Ir- and Ru-Based Electrocatalysts for Acidic Oxygen Evolution Reaction

Proton exchange membrane (PEM) water electrolyzers are one type of the most promising technologies for efficient, nonpolluting and sustainable production of high-purity hydrogen. The anode catalysts account for a very large fraction of cost in PEM water electrolyzer and also determine the lifetime of the electrolyzer. To date, Ir- and Ru-based materials are types of promising catalysts for the acidic oxygen evolution reaction (OER), but they still face challenges of high cost or low stability. Hence, exploring low Ir and stable Ru-based electrocatalysts for acidic OER attracts extensive research interest in recent years. Owing to these great research efforts, significant developments have been achieved in this field. In this review, the developments in the field of Ir- and Ru-based electrocatalysts for acidic OER are comprehensively described. The possible OER mechanisms are first presented, followed by the introduction of the criteria for evaluation of the OER electrocatalysts. The development of Ir- and Ru-based OER electrocatalysts are then elucidated according to the strategies utilized to tune the catalytic performances. Lastly, possible future research in this burgeoning field is discussed.

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.

W-Mediated Electron Accumulation in Ru-O-W Motifs Enables Ultra-Stable Oxygen Evolution Reaction in Acid

The development of efficient and durable oxygen evolution reaction (OER) catalysts is crucial for advancing proton exchange membrane water electrolysis (PEMWE) technology, especially in the pursuit of non-iridium alternatives. Herein, we report a Zn, W co-doped Ru3Zn0.85W0.15Ox (RZW) ternary oxide catalyst that exhibits a low overpotential of 200 mV and remarkable stability for over 4000 hours at 10 mA cm-2 in 0.1 M HClO4. The incorporation of highly electronegative W facilitates the efficient capture of electrons released from the sacrificial Zn species during OER, and subsequently mediated to Ru sites. The observed enhancement in electron density within the stable Ru-O-W motifs substantially improves the anti-overoxidation properties of the Ru active sites. Our findings highlight the importance of strategic metal doping in modulating the electronic structure of OER catalysts during operation, thereby facilitating the development of practical and long-lasting water electrolysis technologies.

Proton Exchange Membrane Water Splitting: Advances in Electrode Structure and Mass-Charge Transport Optimization

Proton exchange membrane water electrolysis (PEMWE) represents a promising technology for renewable hydrogen production. However, the large-scale commercialization of PEMWE faces challenges due to the need for acid oxygen evolution reaction (OER) catalysts with long-term stability and corrosion-resistant membrane electrode assemblies (MEA). This review thoroughly examines the deactivation mechanisms of acidic OER and crucial factors affecting assembly instability in complex reaction environments, including catalyst degradation, dynamic behavior at the MEA triple-phase boundary, and equipment failures. Targeted solutions are proposed, including catalyst improvements, optimized MEA designs, and operational strategies. Finally, the review highlights perspectives on strict activity/stability evaluation standards, in situ/operando characteristics, and practical electrolyzer optimization. These insights emphasize the interrelationship between catalysts, MEAs, activity, and stability, offering new guidance for accelerating the commercialization of PEMWE catalysts and systems.

Establishing the Link Between Oxygen Vacancy and Activity Enhancement in Acidic Water Oxidation of Trigonal Iridium Oxide

Developing durable IrO2-based electrocatalysts with high oxygen evolution reaction (OER) activity under acidic condition is crucial for proton exchange membrane electrolyzers. While oxygen defects are considered potentially important in OER, their direct relationship with catalytic activity has yet to be established. In this study, we introduced abundant oxygen vacancies through Re doping in 2D IrO2 (Re0.03Ir0.97O2), demonstrating their decisive role in enhancing OER performance. The Re0.03Ir0.97O2 catalyst exhibited excellent OER performance with an overpotential of 193 mV at 10 mA cm-2 and sustained activity for over 650 hours, significantly surpassing the undoped catalyst. Moreover, it maintained operation at a cell voltage of 1.70 V (~1200 mA cm-2) for over 140 hours without significant performance degradation. Theoretical calculations coupled with cyclic voltammetry, transient potential scanning and in situ characterizations confirmed the adsorbate evolving mechanism on Re0.03Ir0.97O2, as well as the critical role of Re-induced oxygen vacancies in enhancing OER performance. These findings highlight that oxygen defects directly influence OER activity, providing guidance for the application of oxygen vacancy engineering in electrocatalyst design.

Recent achievements in noble metal-based oxide electrocatalysts for water splitting

The search for sustainable energy sources has accelerated the exploration of water decomposition as a clean H2 production method. Among the methods proposed, H2 production via water electrolysis has garnered considerable attention. However, the process of H2 production from water electrolysis is severely limited by the slow kinetics of the anodic oxygen evolution reaction and large intrinsic overpotentials at the anode; therefore, suitable catalysts need to be found to accelerate the reaction rate. Noble metal-based oxide electrocatalysts retain the advantages of abundant active sites, high electrical conductivity of noble metals, and low cost, which make them promising electrocatalysts; however, they suffer from the challenge of an imbalance between catalytic activity and stability. This review presents recent research progress in noble metals and their oxides as electrocatalysts. In this review, two half-reactions (the hydrogen evolution reaction and the oxygen evolution reaction) of water electrolysis are described. Recently reported methods for the synthesis of noble metal-based oxide electrocatalysts, improvement strategies, and sources of enhanced activity and stability for these types of catalysts are presented. Finally, the challenges and future perspectives in the field are summarised. This review is expected to help improve the understanding of noble metal-based oxide electrocatalysts.

Hydroxylation Strategy Enables Ru-Mn Oxide for Stable Proton Exchange Membrane Water Electrolysis under 1 A cm-2

Ruthenium (Ru)-based catalysts have demonstrated promising utilization potentiality to replace the much expensive iridium (Ir)-based ones for proton exchange membrane water electrolysis (PEMWE) due to their high electrochemical activity and low cost. However, the susceptibility of RuO2-based materials to easily be oxidized to high-valent and soluble Ru species during the oxygen evolution reaction (OER) in acid media hinders the practical application, especially under current density above 500 mA cm-2. Here, a manganese-doped RuO2 catalyst with the hydroxylated metal sites (i.e., H-Mn0.1Ru0.9O2) is synthesized for acidic OER assisted by hydrogen peroxide, where the hydroxylation results in the valence state of the Ru sites below +4. The H-Mn0.1Ru0.9O2 catalyst demonstrates an overpotential of 169 mV at 10 mA cm-2 and promising stability for an OER over 1000 h in an acidic electrolyte. A PEMWE device fabricated with the H-Mn0.1Ru0.9O2 catalyst as the anode shows a current density of 1 A cm-2 at ∼1.65 V, along with a low degradation over continuous tens of hours. Differential electrochemical mass spectrometry (DEMS) results and theoretical calculations confirm that H-Mn0.1Ru0.9O2 performs the OER through the adsorbate evolution mechanism (AEM) pathway, where the synergistic effect of hydroxylation and Mn doping in RuO2 can effectively enhance the stability of Ru sites and lattice oxygen atoms.

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.

Supramolecular Engineering of Vinylene-Linked Covalent Organic Framework - Ruthenium Oxide Hybrids for Highly Active Proton Exchange Membrane Water Electrolysis

The controlled formation of a functional adlayer at the catalyst-water interface is a highly challenging yet potentially powerful strategy to accelerate proton transfer and deprotonation for ultimately improving the performance of proton-exchange membrane water electrolysis (PEMWE). In this study, the synthesis of robust vinylene-linked covalent organic frameworks (COFs) possessing high proton conductivities is reported, which are subsequently hybridized with ruthenium dioxide yielding high-performance anodic catalysts for the acidic oxygen evolution reaction (OER). In situ spectroscopic measurements corroborated by theoretical calculations reveal that the assembled hydrogen bonds formed between COFs and adsorbed oxo-intermediates effectively orient interfacial water molecules, stabilizing the transition states for intermediate formation of OER. This determines a decrease in the energy barriers of proton transfer and deprotonation, resulting in exceptional acidic OER performance. When integrated into a PEMWE device, the system achieves a record current density of 1.0 A cm-2 at only 1.54 V cell voltage, with a long-term stability exceeding 180 h at industrial-level 200 mA cm-2. The approach relying on the self-assembly of an oriented hydrogen-bonded adlayer highlights the disruptive potential of COFs with customizable structures and multifunctional sites for advancing PEMWE technologies.

Phase-Engineered Bi-RuO2 Single-Atom Alloy Oxide Boosting Oxygen Evolution Electrocatalysis in Proton Exchange Membrane Water Electrolyzer

Engineering nanomaterials at single-atomic sites can enable unprecedented catalytic properties for broad applications, yet it remains challenging to do so on RuO2-based electrocatalysts for proton exchange membrane water electrolyzer (PEMWE). Herein, the rational design and construction of Bi-RuO2 single-atom alloy oxide (SAAO) are presented to boost acidic oxygen evolution reaction (OER), via phase engineering a novel hexagonal close packed (hcp) RuBi single-atom alloy. This Bi-RuO2 SAAO electrocatalyst exhibits a low overpotential of 192 mV and superb stability over 650 h at 10 mA cm-2, enabling a practical PEMWE that needs only 1.59 V to reach 1.0 A cm-2 under industrial conditions. Operando differential electrochemical mass spectroscopy analysis, coupled with density functional theory studies, confirmed the adsorbate-evolving mechanism on Bi-RuO2 SAAO and that the incorporation of Bi1 improves the activity by electronic density optimization and the stability by hindering surface Ru demetallation. This work not only introduces a new strategy to fabricate high-performance electrocatalysts at atomic-level, but also demonstrates their potential use in industrial electrolyzers.

Cobalt-Doped Ru@RuO2 Core-Shell Heterostructure for Efficient Acidic Water Oxidation in Low-Ru-Loading Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolysis (PEMWE) is a highly promising hydrogen production technology for enabling a sustainable energy supply. Herein, we synthesize a single-atom Co-doped core-shell heterostructured Ru@RuO2 (Co-Ru@RuO2) catalyst via a combination of ultrafast pulse-heating and calcination methods as an iridium (Ir)-free and durable oxygen evolution reaction (OER) catalyst in acidic conditions. Co-Ru@RuO2 exhibits a low overpotential of 203 mV and excellent stability over a 400 h durability test at 10 mA cm-2. When implemented in industrial PEMWE devices, a current density of 1 A cm-2 is achieved with only 1.58 V under an extremely low catalyst loading of 0.34 mgRu cm-2, which is decreased by 4 to 6 times as compared to other reported Ru-based catalysts. Even at 500 mA cm-2, the PEMWE device could work stably for more than 200 h. Structural characterizations and density functional theory (DFT) calculations reveal that the single-atom Co doping and the core-shell heterostructure of Ru@RuO2 modulate the electronic structure of pristine RuO2, which reduce the energy barriers of OER and improve the stability of surface Ru. This work provides a unique avenue to guide future developments on low-cost PEMWE devices for hydrogen production.

Chloride Residues in RuO2 Catalysts Enhance Its Stability and Efficiency for Acidic Oxygen Evolution Reaction

. Ruthenium dioxide (RuO2) is a benchmark electrocatalyst for proton exchange membrane water electrolyzers (PEMWE), but its stability during the oxygen evolution reaction (OER) is often compromised by lattice oxygen involvement and metal dissolution. Despite that the typical synthesis of RuO2 produces chloride residues, the underlying function of chloride have not well investigated. In this study, we synthesized chlorine-containing RuO2 (RuO2-Cl) and pure RuO2 catalysts with similar morphology and crystallinity. RuO2-Cl demonstrated superior stability, three times greater than that of pure RuO2, and a lower overpotential of 176 mV at 10 mA cm-2. Furthermore, the RuO2-Cl catalysts that were in situ synthesized on a platinum-coated titanium felt could maintain high performance for up to 1200 hours at 100 mA cm-2. Computational and experimental analyses show that chloride stabilizes RuO2 by substituting the bridging oxygen atoms, which subsequently inhibits lattice oxygen evolution and Ru demetallation. Notably, this substitution also lowers the energy barrier of the rate-determining step by strengthening the binding of *OOH intermediates. These findings offer new insights into the previously unknown role of chloride residues and how to improve RuO2 stability.

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.

Boosting Multicolor Emission Enhancement in Two-Dimensional Covalent-Organic Frameworks via the Pressure-Tuned π-π Stacking Mode

Covalent-organic frameworks (COFs) are dynamic covalent porous organic materials constructed from emissive molecular organic building blocks. However, most two-dimensional (2D) COFs are nonemissive or weakly emissive in the solid state owing to the intramolecular rotation and vibration together with strong π-π interactions. Herein, we report a pressure strategy to achieve the bright multicolor emission from yellow to red in the 2D triazine triphenyl imine COF (TTI-COF). Intriguingly, the TTI-COF experiences a 24-fold enhancement under a mild pressure of 2.7 GPa compared with the initial state. Joint experimental and theoretical results reveal that the restricted intramolecular chemical bond vibrations and the reduced π-π interactions originating from the offset stacking mode account for the significant pressure-induced emission enhancement. Furthermore, such piezochromic behavior may be ascribed to the decreased energy gap and enhanced intermolecular interaction. Our investigation offers constructive guidelines for designing 2D COF materials with high photoluminescence performance.

Unravelling the pH-dependent mechanism of ferroelectric polarization on different dynamic pathways of photoelectrochemical water oxidation

Ferroelectric polarization is considered to be an effective strategy to improve the oxygen evolution reaction (OER) of photoelectrocatalysis. The primary challenge is to clarify how the polarization field controls the OER dynamic pathway at a molecular level. Here, electrochemical fingerprint tests were used, together with theoretical calculations, to systematically investigate the free energy change in oxo and hydroxyl intermediates on TiO2-BaTiO3 core-shell nanowires (BTO@TiO2) upon polarization in different pH environments. We demonstrate that the adsorbate evolution mechanism (AEM) dominated in acidic environments, and both positive and negative polarization resulted in a reduction in the oxo-free energy, which inhibited the reaction kinetics. In the oxide path mechanism (OPM) that occurs in alkaline conditions, the ferroelectric polarization exhibits repulsive adsorbate-adsorbate interaction for OH- coverage and free energy shift of the OH- groups. We elucidate that a weakly alkaline electrolyte is the optimal environment for ferroelectric polarization because the positive polarization promotes OH- coverage and facilitates reaction pathway transfer from AEM to OPM; therefore, BTO@TiO2 exhibited a record polarization enhancement to 0.52 mA cm-2 at 1.23 VRHE in pH = 11. This work provides a more accurate insight into the pH-dependent effect of ferroelectric polarization on the OER dynamic pathway than conventional models that are based solely on the regulation of band bending.

Uncovering the role of the Cr dopant in RuO2 in highly efficient acid water oxidation

The design of acidic oxygen evolution reaction (OER) electrocatalysts with high activity and durability is the key to achieving efficient hydrogen production. Herein, we report a Cr-doped RuO2 (Ru0.9Cr0.1O2) catalyst that exhibits good OER activity in acidic electrolytes. The doping of Cr increases the valence state of Ru, which enhances the activity of the catalyst, and a current density of 10 mA cm-2 can be achieved at only 235 mV, which is superior to that of unmodified RuO2 of 299 mV. The Tafel slope of the catalyst was 63.9 mV dec-1, which is much better than that of unmodified RuO2 at 91.1 mV dec-1. In addition, this catalyst was able to maintain stable catalytic performance in 0.5 M H2SO4 for up to 30 hours. Density functional theory (DFT) calculations also showed that Cr doping optimized the adsorption of intermediates at Ru sites and significantly increased the catalytic activity of the Ru sites.

Enhancing the Kinetics of Glucose Electro-Oxidation by Modulating the Binding Energy of Hydroxyl on Cobalt-Based Catalysts

Replacing the sluggish anodic water oxidation reaction with the glucose oxidation reaction (GOR) offers an energy-saving strategy to obtain value-added products during the hydrogen production process. However, rational design of the GOR electrocatalyst with an explicit structure-property relationship remains a challenge. In this study, by using cobalt chalcogenides as model catalysts, we performed an in-depth study of the GOR catalytic mechanism of CoS and CoSe nanosheets. Experimental and theoretical results revealed that the reaction pathway on cobalt chalcogenides strongly depends on their binding energy to hydroxyl (OHBE). For CoS with a weak OHBE, the reaction proceeds through an "electrophilic oxygen" route. While for CoSe, due to the strong OHBE, a surface reconstruction occurs before the GOR and therefore follows the "electrochemical-chemical" route. Inspired by these findings, a customized strategy was proposed to regulate the OHBE of the catalysts, which involved introducing F atoms into CoS to enhance its OHBE, and weakening the OHBE of CoSe by doping with Zn atoms. The optimized F-doped CoS and Zn-doped CoSe catalysts both exhibited significantly improved performance for GOR. This study thus provides a verifiable paradigm for improving the GOR performance via a customized strategy and sheds light on the design of novel catalysts in the future.

Switchable Acidic Oxygen Evolution Mechanisms on Atomic Skin of Ruthenium Metallene Oxides

RuO2 has been considered as a promising, low-cost, and highly efficient catalyst in the acidic oxygen evolution reaction (OER). However, it suffers from poor stability due to the inevitable involvement of the lattice oxygen mechanism (LOM). Here, we construct a unique metallene-based core-skin structure and unveil that the OER pathway of atomic RuO2 skin can be regulated from the LOM to an adsorbate evolution mechanism by altering the core species from metallene oxides to metallenes. This switch is achieved without sacrificing the number of active sites, enabling Pd@RuO2 metallenes to exhibit outstanding acidic OER activity with a low overpotential of 189 mV at 10 mA cm-2, which is 54 mV lower than that of the counterpart PdO@RuO2 metallenes. Additionally, they also exhibit robust stability with negligible activity decay over 100 h at 50 mA cm-2, outperforming most reported RuO2-based catalysts. Multiple spectroscopic analyses and theoretical calculations demonstrate that the Pd-metallene core, acting as an electron donor, increases the migration energy of subsurface oxygen atoms and optimizes the adsorption energy of intermediates on the active Ru sites, enabling a switch in the reaction mechanism. Such a unique metallene-based core-skin structure offers a novel way for tuning the catalytic behaviors of electrocatalysts.

Bifunctional fluorine doped Ru/RuO2 clusters with dynamic electron modification and strong metal-support interaction boost proton exchange membrane water electrolyzer

The sluggish kinetics and inherent instability over the Ru/RuO2 clusters are still enormous challenges in proton exchange membrane (PEM) water electrolyzer. Herein, we innovatively report synergistic modulation of dynamic electron modification and strong metal-support interaction (SMSI) to activate and stabilize bifunctional fluorine doped Ru/RuO2 clusters anchored on carbon nanotube (CNT), thus achieving efficient and stable acidic overall water splitting. Theoretical and experimental studies found that surface metal-fluorine modification layer could dynamically regulate the interfacial electronic environment to stabilize and activate multiple active Ru species; and the SMSI between Ru/RuO2 cluster and CNT maintains stable electronic environment for dynamic electron modification and avoids migrating or shedding of active species in acidic environment. Therefore, the PEM electrolyzer assembled with optimal F5.5-Ru/RuO2@CNT can operate stably for 100 h at a high current density of 100 mA cm-2, which is the first time that bifunctional Ru-based nanocatalysts applied to PEM device at a high current density.

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.

Atomically thin high-entropy oxides via naked metal ion self-assembly for proton exchange membrane electrolysis

Designing efficient Ruthenium-based catalysts as practical anodes is of critical importance in proton exchange membrane water electrolysis. Here, we develop a self-assembly technique to synthesize 1 nm-thick rutile-structured high-entropy oxides (RuIrFeCoCrO2) from naked metal ions assembly and oxidation at air-molten salt interface. The RuIrFeCoCrO2 requires an overpotential of 185 mV at 10 m A cm-2 and maintains the high activity for over 1000 h in an acidic electrolyte via the adsorption evolution mechanism. We discuss the role of each element in the RuIrFeCoCrO2 and find that the Cr, Co, and Ir sites contribute to the catalytic activity, while the Cr atoms weaken the Ru-O bond covalency and improves the catalyst stability. The assembled proton exchange membrane electrolyzer operates stably for more than 600 h at a large current of 1 A cm-2. The naked ion assembly demonstrated in this work may provide an effective pathway for the controlled synthesis of a diversity of high-entropy materials.

Undoped ruthenium oxide as a stable catalyst for the acidic oxygen evolution reaction

Reducing green hydrogen production cost is critical for its widespread application. Proton-exchange-membrane water electrolyzers are among the most promising technologies, and significant research has been focused on developing more active, durable, and cost-effective catalysts to replace expensive iridium in the anode. Ruthenium oxide is a leading alternative while its stability is inadequate. While considerable progress has been made in designing doped Ru oxides and composites to improve stability, the uncertainty in true failure mechanism in acidic oxygen evolution reaction inhibits their further optimization. This study reveals that proton participation capability within Ru oxides is a critical factor contributing to their instability, which can induce catalyst pulverization and the collapse of the electrode structure. By restricting proton participation in the bulk phase and stabilizing the reaction interface, we demonstrate that the stability of Ru-oxide anodes can be notably improved, even under a high current density of 4 A cm‒2 for over 100 h. This work provides some insights into designing Ru oxide-based catalysts and anodes for practical water electrolyzer applications.

Electron-Donating Zr Induces Suppressed Ru Over-Oxidation and Accelerated Deprotonation Process Toward Efficient and Durable Water Electrolysis

The scarcity of cost-effective and durable iridium-free anode electrocatalysts for the oxygen evolution reaction (OER) poses a significant challenge to the widespread application of the proton exchange membrane water electrolyzer (PEMWE). To address the electrochemical oxidation and dissolution issues of Ru-based electrocatalysts, an electron-donating modification strategy is developed to stabilize WRuOx under harsh oxidative conditions. The optimized catalyst with a low Zirconium doping (Zr, 1 wt.%) enhances durability noticeably, with a 77% reduction in degradation rate in the durability test of 10 mA cm-2 in 0.5 m H2SO4. When integrated into a homemade PEMWE device, the Zr-doped catalyst achieves excellent long-term stability, lasting up to 650 h at 100 mA cm⁻2. Additionally, the electronic modulation from the Zr modification leads to superior activity with a low overpotential of 208 mV at 10 mA cm-2. Theoretical calculation results further reveal that electron-donating Zr modification effectively suppresses Ru overoxidation and lattice oxygen participation, maintaining a robust structure during acidic OER. This modification also promotes deprotonation through stronger Brønsted acid sites, significantly improving both long-term stability and activity.

Activity-Stability Relationships in Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a critical process in various sustainable energy technologies. Despite substantial progress in catalyst development, the practical application of OER catalysts remains hindered by the ongoing challenge of balancing high catalytic activity with long-term stability. We explore the inverse trends often observed between activity and stability, drawing on key insights from both experimental and theoretical studies. Special focus is placed on the performance of different electrodes and their interaction with acidic and alkaline media across a range of electrochemical conditions. This Perspective integrates recent advancements to present a thorough framework for understanding the mechanisms underlying the activity-stability relationship, offering strategies for the rational design of next-generation OER catalysts that successfully meet the dual demands of activity and durability.

Tantalum-stabilized ruthenium oxide electrocatalysts for industrial water electrolysis

The iridium oxide (IrO2) catalyst for the oxygen evolution reaction used industrially (in proton exchange membrane water electrolyzers) is scarce and costly. Although ruthenium oxide (RuO2) is a promising alternative, its poor stability has hindered practical application. We used well-defined extended surface models to identify that RuO2 undergoes structure-dependent corrosion that causes Ru dissolution. Tantalum (Ta) doping effectively stabilized RuO2 against such corrosion and enhanced the intrinsic activity of RuO2. In an industrial demonstration, Ta-RuO2 electrocatalyst exhibited stability near that of IrO2 and had a performance decay rate of ~14 microvolts per hour in a 2800-hour test. At current densities of 1 ampere per square centimeter, it had an overpotential 330 millivolts less than that of IrO2.

Boosting the durability of RuO2 via confinement effect for proton exchange membrane water electrolyzer

Ruthenium dioxide has attracted extensive attention as a promising catalyst for oxygen evolution reaction in acid. However, the over-oxidation of RuO2 into soluble H2RuO5 species results in a poor durability, which hinders the practical application of RuO2 in proton exchange membrane water electrolysis. Here, we report a confinement strategy by enriching a high local concentration of in-situ formed H2RuO5 species, which can effectively suppress the RuO2 degradation by shifting the redox equilibrium away from the RuO2 over-oxidation, greatly boosting its durability during acidic oxygen evolution. Therefore, the confined RuO2 catalyst can continuously operate at 10 mA cm-2 for over 400 h with negligible attenuation, and has a 14.8 times higher stability number than the unconfined RuO2 catalyst. An electrolyzer cell using the confined RuO2 catalyst as anode displays a notable durability of 300 h at 500 mA cm-2 and at 60 °C. This work demonstrates a promising design strategy for durable oxygen evolution reaction catalysts in acid via confinement engineering.

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

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

Binary ruthenium dioxide and nickel oxide ultrafine particles loaded on carbon nanotubes for high-stability oxygen evolution reaction at high current densities

RuO2 is an efficient electrocatalyst for the oxygen evolution reaction (OER). However, during the OER process, RuO2 is prone to oxidation into Rux+ (x > 4), leading to its dissolution in the electrolyte and resulting in poor stability of RuO2. Here, we report a bicomponent electrocatalyst, NiO and RuO2 co-loaded on carbon nanotubes (RuO2/NiO/CNT). The results demonstrate that the introduction of NiO suppresses the over-oxidation of RuO2 during the OER process, not only inheriting the excellent catalytic performance of RuO2, but also significantly enhancing the stability of the catalyst for OER at high current densities. In contrast to RuO2/CNT, RuO2/NiO/CNT shows no significant change in activity after 150 h of OER at a current density of 100 mA cm-2. Density functional theory (DFT) calculations indicate that NiO transfers a large number of electrons to RuO2, thereby reducing the oxidation state of Ru. In conclusion, this study provides a detailed analysis of the phenomenon where low-valent metal oxides have the ability to enhance the stability of RuO2 catalysts.

Addressing the Carbonate Issue: Electrocatalysts for Acidic CO2 Reduction Reaction

Electrochemical CO2 reduction reaction (CO2RR) powered by renewable energy provides a promising route to CO2 conversion and utilization. However, the widely used neutral/alkaline electrolyte consumes a large amount of CO2 to produce (bi)carbonate byproducts, leading to significant challenges at the device level, thereby impeding the further deployment of this reaction. Conducting CO2RR in acidic electrolytes offers a promising solution to address the "carbonate issue"; however, it presents inherent difficulties due to the competitive hydrogen evolution reaction, necessitating concerted efforts toward advanced catalyst and electrode designs to achieve high selectivity and activity. This review encompasses recent developments of acidic CO2RR, from mechanism elucidation to catalyst design and device engineering. This review begins by discussing the mechanistic understanding of the reaction pathway, laying the foundation for catalyst design in acidic CO2RR. Subsequently, an in-depth analysis of recent advancements in acidic CO2RR catalysts is provided, highlighting heterogeneous catalysts, surface immobilized molecular catalysts, and catalyst surface enhancement. Furthermore, the progress made in device-level applications is summarized, aiming to develop high-performance acidic CO2RR systems. Finally, the existing challenges and future directions in the design of acidic CO2RR catalysts are outlined, emphasizing the need for improved selectivity, activity, stability, and scalability.

Multitasking-Effect Ca Ions Triggered Symmetry-Breaking of RuO2 Coordination for Acidic Oxygen Evolution Reaction

The development of highly active and stable electrocatalysts for the acid oxygen evolution reaction (OER) is both appealing and challenging. The generation of defects is an emerging strategy for improving the water oxidation efficiency. Herein, we introduced multitasking Ca ions to trigger oxygen vacancies in RuO2, resulting in vacancy-rich RuO2 (RuO2-Ov) nanoparticles with enhanced and sustainable OER activity. The oxygen vacancy in RuO2-Ov breaks the symmetry of the RuO6 octahedron, enhancing the d-band center of Ru and reducing the level of 4d-2p hybridization in Ru-O bonds. This effectively optimizes intermediate adsorption and inhibits Ru dissolution. The RuO2-OV catalyst achieves a current density of 10 mA/cm2 with an overpotential of only 198 mV, stabilizing for over 100 h (degradation rate: 0.2 mV/h). Its mass activity is 17.9 times higher than that of commercial RuO2. Our work highlights that multitasking atomic construction defect engineering effectively balances the seesaw relationship between catalytic activity and stability.

Oxygen Vacancy-Electron Polarons Featured InSnRuO2 Oxides: Orderly and Concerted In-Ov-Ru-O-Sn Substructures for Acidic Water Oxidation

Polymetallic oxides with extraordinary electrons/geometry structure ensembles, trimmed electron bands, and way-out coordination environments, built by an isomorphic substitution strategy, may create unique contributing to concertedly catalyze water oxidation, which is of great significance for proton exchange membrane water electrolysis (PEMWE). Herein, well-defined rutile InSnRuO2 oxides with density-controllable oxygen vacancy (Ov)-free electron polarons are firstly fabricated by in situ isomorphic substitution, using trivalent In species as Ov generators and the adjacent metal ions as electron donors to form orderly and concerted In-Ov-Ru-O-Sn substructures in the tetravalent oxides. For acidic water oxidation, the obtained InSnRuO2 displays an ultralow overpotential of 183 mV (versus RHE) and a mass activity (MA) of 103.02 A mgRu -1, respectively. For a long-term stability test of PEMWE, it can run at a low and unchangeable cell potential (1.56 V) for 200 h at 50 mA cm-2, far exceeding current IrO2||Pt/C assembly in 0.5 m H2SO4. Accelerated degradation testing results of PEMWE with pure water as the electrolyte show no significant increase in voltage even when the voltage is gradually increased from 1 to 5 A cm-2. The remarkably improved performance is associated with the concerted In-Ov-Ru-O-Sn substructures stabilized by the dense Ov-electron polarons, which synergistically activates band structure of oxygen species and adjacent Ru sites and then boosting the oxygen evolution kinetics. More importantly, the self-trapped Ov-electron polaron induces a decrease in the entropy and enthalpy, and efficiently hinder Ru atoms leaching by increasing the lattice atom diffusion energy barrier, achieves long-term stability of the oxide. This work may open a door to design next-generation Ru-based catalysts with polarons to create orderly and asymmetric substructures as active sites for efficient electrocatalysis in PEMWE application.

Atomically engineered interfaces inducing bridging oxygen-mediated deprotonation for enhanced oxygen evolution in acidic conditions

The development of efficient and stable electrocatalysts for water oxidation in acidic media is vital for the commercialization of the proton exchange membrane electrolyzers. In this work, we successfully construct Ru-O-Ir atomic interfaces for acidic oxygen evolution reaction (OER). The catalysts achieve overpotentials as low as 167, 300, and 390 mV at 10, 500, and 1500 mA cm-2 in 0.5 M H2SO4, respectively, with the electrocatalyst showing robust stability for >1000 h of operation at 10 mA cm-2 and negligible degradation after 200,000 cyclic voltammetry cycles. Operando spectroelectrochemical measurements together with theoretical investigations reveal that the OER pathway over the Ru-O-Ir active site is near-optimal, where the bridging oxygen site of Ir-OBRI serves as the proton acceptor to accelerate proton transfer on an adjacent Ru centre, breaking the typical adsorption-dissociation linear scaling relationship on a single Ru site and thus enhancing OER activity. Here, we show that rational design of multiple active sites can break the activity/stability trade-off commonly encountered for OER catalysts, offering good approaches towards high-performance acidic OER catalysts.

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

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

Bi-doped ruthenium oxide nanocrystal for water oxidation in acidic media

There is an urgent need to develop a cost-effective and highly efficient acidic OER catalyst to support the progress of proton exchange membrane water electrolysis technology. Ruthenium-based catalysts, which possess high activity and significantly lower cost compared to iridium-based catalysts, emerge as competitive candidates. However, their suboptimal stability constrains the wide application of RuO2. Herein, we develop ultra-small Bi0.05Ru0.95O2 nanocrystal with diameter of approximately 6.5 ± 0.1 nm for acidic OER. The Bi0.05Ru0.95O2 nanocrystal electrocatalyst exhibits a low overpotential of 203.5 mV at 10 mA cm-2 and 300+ hour stability at a high water-splitting current density of 100 mA cm-2 in 0.5 M H2SO4 with a low decay rate of 0.44 mV h-1. Density functional theory (DFT) calculation results confirmed the adsorbate evolving mechanism (AEM) occurring on Bi0.05Ru0.95O2, which prevents lattice oxygen from participating in the reaction, thus avoiding the collapse of the structure. We proved that the Bi dopants could play a crucial role in not only reducing the energy barrier of the potential-determining step, but also delivering electrons to Ru sites, thereby alleviating the over-oxidation of Ru active sites and enhancing operation durability.

Dual-synergistic effect of medium-entropy metal sulfoselenide nanoparticles toward efficient overall seawater splitting

Developing efficient and durable electrodes for overall water splitting (OWS) in seawater electrolytes is a major challenge. Herein, we synthesized highly active and stable Fe1.2(CoNi)1.8S3Se3 medium-entropy metal sulfoselenide (MESSe) nanoparticles for the electrodes. The Fe1.2(CoNi)1.8S3Se3 MESSe electrode exhibited excellent electrocatalytic performance in alkaline simulated seawater, with a η100 value of 156 mV for the hydrogen evolution reaction and 262 mV for the oxygen evolution reaction. Compared to Fe1.2(CoNi)1.8S6 sulfide and Fe1.2(CoNi)1.8Se6 selenide, the electronic structure of Fe1.2(CoNi)1.8S3Se3 MESSe positively modulates the adsorption/desorption process of *H/*OH intermediate and significantly reduces the free energy of the rate-determining step, thereby accelerating the reaction kinetics of both hydrogen/oxygen evolution reactions. The performance of OWS is significantly enhanced by utilizing the prepared electrode, enabling it to achieve 100 mA cm-2 with only 1.77 V in alkaline simulated seawater. Furthermore, the durability of the electrode is maintained at this high current density in alkaline simulated seawater, alkaline seawater as well as seawater electrolyte. This work will lay the foundation for the development of innovative medium-entropy metal sulfoselenides, promoting their application in a wide range of electrochemical energy systems operating under extreme conditions.

Regulation of Oxide Pathway Mechanism for Sustainable Acidic Water Oxidation

The advancement of acid-stable oxygen evolution reaction (OER) electrocatalysts is crucial for efficient hydrogen production through proton exchange membrane (PEM) water electrolysis. Unfortunately, the activity of electrocatalysts is constrained by a linear scaling relationship in the adsorbed evolution mechanism, while the lattice-oxygen-mediated mechanism undermines stability. Here, we propose a heterogeneous dual-site oxide pathway mechanism (OPM) that avoids these limitations through direct dioxygen radical coupling. A combination of Lewis acid (Cr) and Ru to form solid solution oxides (CrxRu1-xO2) promotes OH adsorption and shortens the dual-site distance, which facilitates the formation of *O radical and promotes the coupling of dioxygen radical, thereby altering the OER mechanism to a Cr-Ru dual-site OPM. The Cr0.6Ru0.4O2 catalyst demonstrates a lower overpotential than that of RuO2 and maintains stable operation for over 350 h in a PEM water electrolyzer at 300 mA cm-2. This mechanism regulation strategy paves the way for an optimal catalytic pathway, essential for large-scale green hydrogen production.

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.

Oxyanion Engineering on RuO2 for Efficient Proton Exchange Membrane Water Electrolysis

In acidic proton exchange membrane water electrolysis (PEMWE), the anode oxygen evolution reaction (OER) catalysts rely heavily on the expensive and scarce iridium-based materials. Ruthenium dioxide (RuO2) with lower price and higher OER activity, has been explored for the similar task, but has been restricted by the poor stability. Herein, we developed an anion modification strategy to improve the OER performance of RuO2 in acidic media. The designed multicomponent catalyst based on sulfate anchored on RuO2/MoO3 displays a low overpotential of 190 mV at 10 mA cm-2 and stably operates for 500 hours with a very low degradation rate of 20 μV h-1 in acidic electrolyte. When assembled in a PEMWE cell, this catalyst as an anode shows an excellent stability at 500 mA cm-2 for 150 h. Experimental and theoretical results revealed that MoO3 could stabilize sulfate anion on RuO2 surface to suppress its leaching during OER. Such MoO3-anchored sulfate not only reduces the formation energy of *OOH intermediate on RuO2, but also impedes both the surface Ru and lattice oxygen loss, thereby achieving the high OER activity and exceptional durability.

The breakthrough of oxide pathway mechanism in stability and scaling relationship for water oxidation

An in-depth understanding of electrocatalytic mechanisms is essential for advancing electrocatalysts for the oxygen evolution reaction (OER). The emerging oxide pathway mechanism (OPM) streamlines direct O-O radical coupling, circumventing the formation of oxygen vacancy defects featured in the lattice oxygen mechanism (LOM) and bypassing additional reaction intermediates (*OOH) inherent to the adsorbate evolution mechanism (AEM). With only *O and *OH as intermediates, OPM-driven electrocatalysts stand out for their ability to disrupt traditional scaling relationships while ensuring stability. This review compiles the latest significant advances in OPM-based electrocatalysis, detailing design principles, synthetic methods, and sophisticated techniques to identify active sites and pathways. We conclude with prospective challenges and opportunities for OPM-driven electrocatalysts, aiming to advance the field into a new era by overcoming traditional constraints.