Dopants fixation of Ruthenium for boosting acidic oxygen evolution stability and activity

Role of Interfacial Water in Improving the Activity and Stability of Lattice-Oxygen-Mediated Acidic Oxygen Evolution on RuO2

Although RuO2-based electrocatalysts have been widely studied for acidic oxygen evolution reaction (OER), triggering the conventional adsorbate evolution mechanism to suppress kinetically favorable lattice oxygen mechanism (LOM) pathway at the expense of activity is the state-of-the-art strategy. To date, approaches to simultaneously achieve remarkable activity and stability of RuO2-based electrocatalysts through the kinetically favorable LOM pathway toward acidic OER are still elusive. Herein, we report that RuS0.45Ox catalyst with the synergetic regulation of asymmetric S-Ru-O microstructure and Ru-SO4 local environments can simultaneously boost the lattice-oxygen-mediated OER activity and stability under acidic electrolyte. Experimental results, including operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy, operando X-ray photoelectron spectroscopy, and theoretical studies, indicate the dynamic evolution of interfacial water structure from hydrogen-bond water to free-H2O on the surface of RuS0.45Ox. The generated continuous free-H2O-enriched local environment is in favor of accelerating the sluggish kinetics of interfacial water dissociation and facilitating the replenishment of lattice oxygen vacancies generated during the lattice-oxygen-mediated OER process, thereby significantly enhancing the stability. Consequently, the obtained RuS0.45Ox displays remarkable acidic OER performance with 160 mV to reach 10 mA cm-2, and robust stability with negligible activity decay over 500 h at 100 mA cm-2.

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.

Regulating Ru-Ru Distance in RuO2 Catalyst by Lattice Hydroxyl for Efficient Water Oxidation

Highly active and durable electrocatalysts for the oxygen evolution reaction (OER) are crucial for proton exchange membrane water electrolysis (PEMWE). While doped RuO2 catalysts demonstrate good activity and stability, the presence of dopants limits the number of exposed active sites and complicates Ru recovery. Here, we present a monometallic RuO2 (d-RuO2) with lattice hydroxyl in the periodic structure as a high-performance OER electrocatalyst. The obtained d-RuO2 catalyst exhibits a low overpotential of 150 mV and long-term operational stability of 500 h at 10 mA cm-2, outperforming many Ru/Ir-based oxides ever reported. A PEMWE device using d-RuO2 sustains operation for 348 h at 200 mA cm-2. In-situ characterization reveals that the incorporation of lattice hydroxyl increases the Ru-Ru distance, which facilitates the turnover of the Ru oxidation state and promotes the formation of stable edge-sharing [RuO6] octahedra during the OER, thereby accelerating the formation of O-O bonds and suppressing the overoxidation of Ru sites. Additionally, the small particle size of the catalyst decreases the three-phase contact line and promotes bubble release. This study will provide insights into the design and optimization of catalysts for various electrochemical reactions.

Electron donation from carbon support enhances the activity and stability of ultrasmall ruthenium dioxide nanoparticles in acidic oxygen evolution reaction

Developing non-iridium (Ir)-based electrocatalysts with good stability and activity for acid oxygen evolution reaction (OER) is of great importance for electrocatalytic water splitting. Ruthenium dioxide (RuO2), which has lower price and higher OER activity, has been recognized as an attractive alternative to Ir-based electrocatalyst for acidic OER. However, the stability of most Ru-based electrocatalysts faces a great challenge in acidic condition. Here, a highly stable and active RuO2-based catalyst, tiny RuO2 nanoparticles inlaid onto carbon support (RuO2/C), is successfully prepared for acidic OER. Such a structure can efficiently inhibit the over-growth of RuO2 nanoparticles and prevent the agglomeration of RuO2 nanoparticles. Moreover, it is found that carbon support donate electron to RuO2 nanoparticles, which enhances the OER activity and stability of RuO2 during acidic OER. The RuO2/C exhibits an impressive OER performance with a low overpotential (197 mV at 10 mA cm-2) and low degradation rate (0.035 mV h-1) over a 450-h stability test in 0.5 M H2SO4, which are much better than the commercial Ir/C, RuO2 and the reported Ru-based electrocatalysts. This work provides an efficient strategy to simultaneously improve both stability and activity of Ru-based catalysts for acidic water oxidation.

Simple and Scalable Introduction of Single-Atom Mn on RuO2 Electrocatalysts for Oxygen Evolution Reaction with Long-Term Activity and Stability

Electrochemical oxygen evolution reaction (OER) is the bottleneck for realizing renewable powered green hydrogen production through water splitting due to the challenges of electrode stability under harsh oxidative environments and electrolytes with extreme acidity and basicity. Here, we introduce a single-atom manganese-incorporated ruthenium oxide electrocatalyst via a facile impregnation approach for catalyzing the OER across a wide pH range, while solving the stability issues of RuO2. The modified catalyst maintains stability for over 1000 h, delivering a current density of 10 mA cm-2 at a 213 mV overpotential in acid (pH 0), 570 mV in potassium bicarbonate (pH 8.8), and 293 mV in alkaline media (pH 14), demonstrating exceptional durability under various conditions. When used as an anode for realistic water-splitting systems, Mn-modified RuO2 performs at 1000 mA cm-2 with a voltage of 1.69 V (Nafion 212 membrane) for proton-exchange membrane water electrolysis, and 1.84 V (UTP 220 diaphragm) for alkaline water electrolysis, exhibiting low degradation and verifying its substantial potential for practical 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.

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.

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.

Amorphous RuO2 Nanozymes with an Excellent Catalytic Efficiency Superior to Natural Peroxidases

Developing efficient peroxidase-like nanozymes to surpass natural enzymes remains a significant challenge. Herein, an amorphous RuO2 nanozyme with peroxidase-like activity is synthesized for activating H2O2 with a specific activity of 1492.52 U mg-1, outperforming the crystalline RuO2 nanozymes by a factor of 22 and far superior to natural peroxidases. Amorphous RuO2 nanozymes with long-range disordered atomic arrangements can effectively elongate the O─O bonds in H2O2. Abundant oxygen vacancies in amorphous RuO2 nanozymes lead to an upshift of the d-band center, enhancing the exceptional adsorption strength of H2O2, which improve the electron transfer efficiency and ensure superior peroxidase-like activity. Accordingly, a nanozyme-linked immunosorbent assay is developed for the precise and sensitive detection of prostate-specific antigens with a detection limit as low as 0.52 pg mL-1. This study introduces a simple approach for developing high-performance peroxidase-like nanozymes to improve the analytical performances of prostate-specific antigens in clinical diagnostics.

Interstitial-Substitutional-Mixed Solid Solution of RuO2 Nurturing a New Pathway Beyond the Activity-Stability Linear Constraint in Acidic Water Oxidation

The acidic oxygen evolution reaction (OER) electrocatalysts for proton exchange membrane electrolyzer (PEMWE) often face a trade-off between activity and stability due to inherent linear relationship and overoxidation of metal atoms in highly oxidative environments, while following the conventional adsorbate evolution mechanism (AEM). Herein, a favorable AEM-derived proton acceptor-electron donor mechanism (PAEDM) is proposed in RuO2 by constructing interstitial-substitutional mixed solid solution structure (denoted as C,Ta-RuO2), which can effectively break the activity-stability trade-off of RuO2 in acidic OER. In situ spectroscopy experiments and theoretical calculations reveal that the interstitial C as the proton acceptor reduces the deprotonation energy barrier, enhancing catalytic activity, while the substitutional Ta as the electron donor donates electrons to the Ru sites via bridging oxygen, weakening the Ru─O bond covalency and preventing over-oxidation of surface Ru, thereby ensuring long-term stability. Under the guidance of this mechanism, the optimized C,Ta-RuO2 simultaneously achieves far low overpotential (η10 = 171 mV) and ultra-long stability (over 1300 h) for the acidic OER. More remarkably, a homemade PEMWE using C,Ta-RuO2 as the anode also shows high water splitting performance (1.63 V@1 A cm-2). This work supplies a novel strategy to guide future developments on efficient OER electrocatalysts toward water oxidation.

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.

Co-Motif-Engineered RuO2 Nanosheets for Robust and Efficient Acidic Oxygen Evolution

The development of efficient and reliable acidic oxygen evolution reaction (OER) electrocatalysts represents a crucial step in the process of water electrolysis. RuO2, a benchmark OER catalyst, suffers from limited large-scale applicability due to its tendency toward the less stable lattice oxygen mechanism (LOM). This work reports the synthesis of Co-doped RuO2 nanosheets with a unique porous morphology composed of interconnected grains via a facile molten salt method. Co doping modulates the grain size, effectively increasing the specific surface area and introducing oxygen vacancies. These oxygen vacancies, coupled with the Co dopants, form Co-O(V) motifs that tune the electronic configuration of Ru. This structural engineering promotes a shift in the OER mechanism from the detrimental LOM pathway to the more efficient adsorbate evolution mechanism (AEM), significantly enhancing the stability of the RuO2 matrix in acidic environments. The optimized Co0.108-RuO2 catalyst exhibits a low overpotential of 214 mV at 10 mA cm-2 and remarkable stability over commercial RuO2 and undoped counterparts, owing to the synergistic effect of the increased surface area, Co-O(V) motifs, and favored AEM pathway. This strategy of utilizing Co doping to engineer morphology, electronic structure, and reaction mechanism offers a promising avenue for developing high-performance OER electrocatalysts.

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.

Synergistic Composition and Surface Engineering of Ruthenium-Cobalt Hydroxide Nanowires for Efficient Oxygen Evolution Catalysis

Developing efficient electrocatalysts that improve the rate-determining step (RDS) kinetics is crucial to addressing the kinetically sluggish oxygen evolution reaction (OER). This study introduces ruthenium (Ru)-cobalt(II) hydroxide (Co(OH)₂) electrocatalysts for high-performance OER by combining compositional and thermodynamic surface engineering. Density functional theory (DFT) is employed to identify the ideal composition, with experimental validation conducted through electrodeposition, enabling facile control over a wide range of compositions for nanowire catalyst synthesis. Pourbaix diagram analysis helps establish precise synthesis conditions for developing surface nanostructures. The optimized Ru-Co(OH)₂ catalyst demonstrates exceptional performance, achieving overpotentials of 189 mV at 10 mA cm⁻2 and 292 mV at 50 mA cm⁻2, significantly outperforming other compositions. The exceptional electrocatalytic performance can be attributed to two key factors: strengthened OH adsorption energy due to optimal composition, which lowers the energy barrier of the rate-determining step in the OER, and increased specific surface area resulting from surface nanostructure formation.

Unraveling Compressive Strain and Oxygen Vacancy Effect of Iridium Oxide for Proton-Exchange Membrane Water Electrolyzers

Iridium-based electrocatalysts are commonly regarded as the sole stable operating acidic oxygen evolution reaction (OER) catalysts in proton-exchange membrane water electrolysis (PEMWE), but the linear scaling relationship (LSR) of multiple reaction intermediates binding inhibits the enhancement of its activity. Herein, the compressive strain and oxygen vacancy effect exists in iridium dioxide (IrO2)-based catalyst by a doping engineering strategy for efficient acidic OER activity. In situ synchrotron characterizations elucidate that compressive strain can enhance Ir─O covalency and reduce the Ir─Ir bond distance, and oxygen vacancy (Ov) as an electronic regulator causes rapid adsorption of water molecules on the Ir and adjacent Ov (Ir─Ov) pair site to be coupled directly into *O─O* intermediates. Importantly, hence, volcano-shape curves are established between the compressive strain/oxygen vacancy and OER current using OER as the probe reaction. Theoretical calculation reveals Ni dopant can modulate Ir 5d- and O 2p-band centers for increasing overlap of Ir 5d and O 2p orbits to trigger a continuous metal site-oxygen vacancy synergistic mechanism (MS-OVSM) pathway, successfully breaking the LSR of intermediates binding during OER. Therefore, the resultant proton-exchange membrane water electrolysis (PEMWE) device fabricated using T-0.24Ni/IrO2 delivers a current density of 500 mA cm-2 and operates stably for 500 h.

Polyol-Intermediated Facile Synthesis of B5-Site-Rich Ru-Based Nanocatalysts for COx-Free Hydrogen Production via Ammonia Decomposition

Herein, a B5-site-rich Ru/MgAl2O4 nanocatalyst for the production of COx-free hydrogen from ammonia (NH3) is synthesized using the polyol method. The polyol method enables size-sensitive Ru-nanoparticle growth and controlled B5-site formation on the catalyst by tuning the carbon-chain length of the polyol solvent used, obviating the use of a separate stabilizer and enhancing electron donation from Ru (with a high surface electron density) and π-back bonding. The Ru/MgAl2O4 (BG) catalyst synthesized using butylene glycol (a long-carbon-chain solvent) contains 2.5 nm Ru particles uniformly dispersed on its surface and abundant B5 sites at (0 0 2)/(0 1 1). Moreover, the Ru/MgAl2O4 (BG) catalyst exhibits lower activation energy (48.9 kJ mol-1) and higher H2 formation rate (565-1,236 mmol gcat -1 h-1 at 350-450 °C and a weight hourly space velocity of 30,000 mL gcat -1 h-1) during the NH3 decomposition reaction than catalysts with a similar Ru particle size and high metal dispersion synthesized by the impregnation and deposition-precipitation methods. This high performance is possibly because the abundant electron-donating B5 sites on the catalyst surface accelerate the recombination-desorption of N2, which is the rate-determining step of the NH3 decomposition reaction at low temperatures. Thus, this study facilitates clean hydrogen production.

Anode Alchemy on Multiscale: Engineering from Intrinsic Activity to Impedance Optimization for Efficient Water Electrolysis

The past decade has seen significant progress in proton exchange membrane water electrolyzers (PEMWE), but the growing demand for cost-effective electrolytic hydrogen pushes for higher efficiency at lower costs. As a complex system, the performance of PEMWE is governed by a combination of multiscale factors. This review summarizes the latest progress from quantum to macroscopic scales. At the quantum level, electron spin configurations can be optimized to enhance catalytic activity. At the nano and meso scales, advancements in atomic structure optimization, crystal phase engineering, and heterostructure design improve catalytic performance and mass transport. At the macro scale, innovative techniques in gas bubble management and internal resistance reduction drive further efficiency gains under ampere-level operating conditions. These modifications at the quantum level cascade through meso- and macro-scales, affecting charge transfer, reaction kinetics, and gas evolution management. Unlike conventional approaches that focus solely on one scale-either at the catalyst level (e.g., atomic, or crystal modifications) or at the device level (e.g., porous transport layers design)-combining multiscale optimizations unlocks greater performance improvements. Finally, a perspective on future opportunities for multiscale engineering in PEMWE anode design toward commercial viability is offered.

Feasibility of Active and Durable Lattice Oxygen-Mediated Oxygen Evolution Electrocatalysts in Proton Exchange Membrane Water Electrolyzers Through d0 Metal Ion Incorporation

The primary hurdle faced in the practical application of proton exchange membrane water electrolyzer (PEMWE) involves improving the intrinsic kinetic activity of oxygen evolution reaction (OER) electrocatalysts while concurrently enhancing their durability. Although electrocatalysts based on lattice oxygen-mediated mechanism (LOM) have the potential to significantly enhance the activity in OER without being restricted by scaling relationships, they are neglected in acidic electrolytes due to limited durability. In this study, an innovative approach is presented to simultaneously promote the activation of lattice oxygen and improve the durability of LOM-based OER electrocatalysts by incorporating d0 metal ions into the RuO2 electrocatalyst. Leveraging the unique electronic properties of the d0 metal ion, the O 2p band center and Ru-O covalency of the electrocatalyst are successfully engineered, resulting in the change in OER mechanism. Furthermore, in a single cell of PEMWE, the LOM-based electrocatalyst demonstrates outstanding performance, achieving 3.0 A cm-2 at 1.81 V and maintaining durability for 100 h at 200 mA cm-2, surpassing commercial RuO2. This innovative strategy challenges the traditional viewpoint that suppressing lattice oxygen activation in OER is essential for enhancing PEMWE durability, offering new perspectives for the development of OER electrocatalysts in acidic electrolytes.

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.

Inhibiting Overoxidation of Dynamically Evolved RuO2 to Achieve a Win-Win in Activity-Stability for Acidic Water Electrolysis

Proton exchange membrane (PEM) water electrolysis offers an efficient route to large-scale green hydrogen production, in which the RuO2 catalyst exhibits superior activity but limited stability. Unveiling the atomic-scale structural evolution during operando reaction conditions is critical but remains a grand challenge for enhancing the durability of the RuO2 catalyst in the acidic oxygen evolution reaction (a-OER). This study proposes an adaptive machine learning workflow to elucidate the potential-dependent state-to-state global evolution of the RuO2(110) surface within a complex composition and configuration space, revealing the correlation between structural patterns and stability. We identify the active state with distorted RuO5 units that self-evolve at low potential, which exhibits minor Ru dissolution and an activity self-promotion phenomenon. However, this state exhibits a low potential resistance capacity (PRC) and evolves into inert RuO4 units at elevated potential. To enhance PRC and mitigate the overevolution of the active state, we explore the metal doping engineering and uncover an inverse volcano-type doping rule: the doped metal-oxygen bond strength should significantly differ from the Ru-O bond. This rule provides a theoretical framework for designing stable RuO2-based catalysts and clarifies current discrepancies regarding the roles of different metals in stabilizing RuO2. Applying this rule, we predict and confirm experimentally that Na can effectively stabilize RuO2 in its active state. The synthesized Na-RuO2 operates in a-OER for over 1800 h without any degradation and enables long-term durability in PEM electrolysis. This work enhances our understanding of the operando structural evolution of RuO2 and aids in designing durable catalysts for a-OER.

Synergistic Modulation of Multisite Electronic States via Erbium Doping and NiCoP Hybridization for Enhanced Anion Exchange Membrane Water Splitting

Water dissociation in anion exchange membrane water electrolysis (AEMWE) faces significant energy barriers, posing a challenge for reducing cell voltage. Herein, we engineered CoP nanosheets by doping Er and hybridizing with NiCoP to optimize local electronic states and accelerate H2O dissociation during the hydrogen evolution reaction. The resulting Er0.1-CoP/NiCoP catalyst achieves a low overpotential of 154 mV at -500 mA cm-2 in 1.0 M KOH. An AEM electrolyzer comprising an Er0.1-CoP/NiCoP@NF cathode demonstrates a low cell voltage of 1.672 V and stability exceeding 1000 h at 500 mA cm-2 (50 °C). Characterization, density functional theory (DFT) calculations, and ab initio molecular dynamics (AIMD) simulations reveal that Er doping and NiCoP hybridization synergistically modulate charge distribution across multisites, shifting the p-band centers away from the Fermi level. These adjustments optimize the free energy of H* adsorption (ΔGH*) and improve OH*/H2O* adsorption, thereby facilitating H2O dissociation and H2 evolution.

Constructing weak Ru-Mo metallic bonds to suppress Ru overoxidation for durable acidic water oxidation

Although reducing the Ru-O covalency suppresses the loss of lattice oxygen, it also weakens the electron transfer of the Ru-Obri-Mo configuration, leading to Ru overoxidation. Herein, doping Mo into RuO2 weakens the Ru-O covalency and forms weak Ru-Mo metallic bonds to compensate for the electron density of Ru, where the Mo0.125Ru0.875O2 catalyst exhibits stable PEM performance at 300 mA cm-2 for 500 h.

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.

Nanoporous high-entropy alloys and metallic glasses: advanced electrocatalytic materials for electrochemical water splitting

Electrochemical water splitting is a promising approach to convert renewable energy into hydrogen energy and is beneficial for alleviating environmental pollution and energy crises, and is considered a clean method to achieve dual-carbon goals. Electrocatalysts can effectively reduce the reaction energy barrier and improve reaction efficiency. However, designing electrocatalysts with high activity and stability still faces significant challenges, which are closely related to the structure and electronic configuration of catalysts. Nanoporous high-entropy alloys (np-HEAs) and metallic glasses (np-MGs), characterized by long-range chemical disorder intertwined with local chemical order combined with three-dimensional, interconnected nanoporous structure, exhibit distinctive electrocatalytic properties and application potential for electrochemical water splitting. To promote the widespread application of np-HEAs and np-MGs, it is of great significance to rationally design and apply them in the field of electrolytic water splitting. In this review, the basic principles of hydrogen evolution reaction and oxygen evolution reaction as well as the fabrication techniques of np-HEAs and np-MGs are introduced. The recent progress in the efficient application of np-HEAs and np-MGs in electrochemical water splitting, and the current challenges and prospects are summarized. This review will provide theoretical guidance for the development of np-HEAs and np-MGs in electrochemical water splitting applications.

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.

Mn0.75Ru0.25O2 with Low Ru Concentration for Active and Durable Acidic Oxygen Evolution

Ruthenium has emerged as a promising alternative to iridium in water-splitting anodes. However, it becomes overoxidized and dissolves at industry-relevant working conditions. To enhance the activity and stability of electrocatalysts for oxygen evolution reaction, an isostructural rutile MnRu oxide with low Ru concentration (Mn0.75Ru0.25O2) is synthesized and an asymmetric Mn-O-Ru dual-site active center is developed. It exhibits 154 mV overpotential at 10 mA cm-2 and can operate stably at 200 mA cm-2 for 670 h with a degradation rate of 29 uV/h-1. A proton exchange membrane water electrolyzer achieves stable operation at 1 A cm-2 for 700 h with a degradation rate of 53 uV h-1. Structural analysis and isotopic labeling correlate the asymmetric nature of the Mn-O-Ru dual-site active center, which facilitates the oxygen evolution reaction along the radical coupling pathway, with the stabilization of the cations and the lattice oxygen in isostructural rutile Mn0.75Ru0.25O2.

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

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

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.

Modulating Electronic Correlations in Ruthenium Oxides for Highly Efficient Oxygen Evolution Reaction

Elucidating the electronic factors dominating the adsorption properties of transition-metal oxides is essential to construct highly efficient oxygen-evolving catalysts for hydrogen production by water splitting but remains a great challenge. Electron correlation from on-site Coulomb repulsion (U) among d-electrons is generally believed to significantly affect the electronic structure of these materials; however, it has long been neglected in studying their adsorption properties. Here, by choosing ruthenium oxide as a model system, we demonstrate the role of electron correlation on the electrocatalytic activity toward oxygen evolution reaction (OER). Our density functional theory plus U calculations on rutile RuO2 reveal that the electron correlation can tune the adsorption energies for oxygenated intermediate and optimize them after the metallic oxide being a Mott insulator upon increasing U. By regulating the RuO6 octahedral network, we constructed and synthesized a series of strongly correlated ruthenium oxides, where the Mott insulating ones indeed exhibit a superior OER performance to the metallic RuO2. Our work builds a bridge between the electrochemistry and Mott physics for transition-metal oxides, opening a new avenue for designing advanced catalysts.

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.

Breaking the Stability-Activity Trade-off of Oxygen Electrocatalyst by Gallium Bilateral-Regulation for High-Performance Zinc-Air Batteries

The rational design of metal oxide catalysts with enhanced oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance is crucial for the practical application of aqueous rechargeable zinc-air batteries (a-r-ZABs). Precisely regulating the electronic environment of metal-oxygen (M-O) active species is critical yet challenging for improving their activity and stability toward OER and ORR. Herein, we propose an atomic-level bilateral regulation strategy by introducing atomically dispersed Ga for continuously tuning the electronic environment of Ru-O and Mn-O in the Ga/MnRuO2 catalyst. The Ga/MnRuO2 catalyst breaks the stability-activity restriction, showing remarkable bifunctional performance with a low potential gap (ΔE) of 0.605 V and super durability with negligible performance degradation (300,000 ORR cycles or 30,000 OER cycles). The theoretical calculations revealed that the strong coupling electron interactions between Ga and Ru-O/Mn-O tuned the valence state distribution of the metal center, effectively modulating the adsorption behavior of *O/*OH, thus optimizing the reaction pathways and reducing the reaction barriers. The a-r-ZABs based on Ga/MnRuO2 catalysts exhibited excellent performance with a wide working temperature range of -20-60 °C and a long lifetime of 2308 hours (i.e., 13,848 cycles) under a current density of 5 mA cm-2 at -20 °C.

Dual Doping in Precious Metal Oxides: Accelerating Acidic Oxygen Evolution Reaction

Developing a highly active and stable catalyst for acidic oxygen evolution reactions (OERs), the key half-reaction for proton exchange membrane water electrolysis, has been one of the most cutting-edge topics in electrocatalysis. A dual-doping strategy optimizes the catalyst electronic environment, modifies the coordination environment, generates vacancies, and introduces strain effects through the synergistic effect of two elements to achieve high catalytic performance. In this review, we summarize the progress of dual doping in RuO2 or IrO2 for acidic OERs. The three main mechanisms of OERs are dicussed firstly, followed by a detailed examination of the development history of dual-doping catalysts, from experimentally driven dual-doping systems to machine learning (ML) and theoretical screening of dual-doping systems. Lastly, we provide a summary of the remaining challenges and future prospects, offering valuable insights into dual doping for acidic OERs.

Electrochemical Removal of Se(IV) from Wastewater Using RuO2-Based Catalysts

The removal of selenite (SeO32-) from water is challenging due to the risk of secondary pollutants. To address this, we developed RuO2-based nanocatalysts on the titanium plate (RuO2/TP) for direct electrochemical reduction of Se(IV) to elemental selenium [Se(0)]. Optimizing Sn doping in RuO2 nanoparticles to induce charge redistribution enabled the Ru0.9Sn0.1Ox/TP catalyst to achieve ∼90% Se(IV) removal across concentrations of 0.1, 1, and 10 mM at -2 mA cm-2 over 8 h, outperforming undoped RuO2/TP. Furthermore, Ru0.9Sn0.1Ox/TP also maintained ∼90% removal efficiency in 1 mM of Se(IV) solutions containing competitive anions (0.5 M Cl-, 0.1 M SO42-, 0.01 M NO3-, and their mixtures), demonstrating suitability for complex wastewater treatment. Importantly, the catalysts were recyclable, with no observable contamination introduced into the solution. Density functional theory (DFT) calculations suggest that Sn doping effectively reduces the energy barrier for the reduction of Se(IV) to Se(0).

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.

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.

Defects trigger redox reactivities between metal and lattice oxygen in high-entropy layered double hydroxide for boosting oxygen evolution in alkaline

The oxygen evolution reaction (OER) at the anode undergoes a sluggish multi-step process, thereby impeding overall water splitting. As the classical adsorbate evolution mechanism (AEM) involves multiple oxygen-containing intermediates, such as *OH, *O and *OOH, breaking the linear relationship of the adsorption energies between *OH and *OOH is the key to efficient oxygen evolution. Herein, we report a high-entropy FeCoNiAlZn layered double hydroxide decorated with defects (E-FeCoNiAlZn LDH) for boosting oxygen evolution in alkaline. The product exhibits high OER activity with a low overpotential of 220 at 10 mA cm-2 and outstanding stability with negligible decline after 100 h operation. The defects in E-FeCoNiAlZn LDH not only enhance the adsorption of *OH by metal sites but also foster the release of oxygen from lattice, which triggers the coupled oxygen evolution mechanism (COM). This mechanism has only *OH and *OO intermediates, perfectly avoiding the obstacles of linear relationship between *OH and *OOH. Theoretical calculations demonstrate that the introduction of defects enhances the adsorption of *OH due to the presence of unsaturated bonds. Additionally, it is evidence that the O 2p band is elevated, leading to a weakening of the metal-O bond and a reduction of the energy barrier for OO coupling.

Oxidative reconstructed Ru-based nanoclusters forming heterostructures with lanthanide oxides for acidic water oxidation

Achieving rapid anodic oxygen evolution reaction (OER) kinetics and improving the stability of the corresponding ruthenium (Ru)-based catalysts is a current priority for the realisation of industrial water splitting. However, the activity and stability of O2 evolution in electrocatalysis are largely inhibited by the insufficient adsorption of the reactant H2O and too strong adsorption of the intermediate OOH*, as well as by the dissolution of the active site due to excessive oxidation. To solve this challenge, herein, we developed a regulatory strategy combining lanthanide oxides and metal oxidative reconfiguration. The introduction of Eu2O3 effectively promotes the adsorption of H2O, optimizes the adsorption energy of OOH*, and reduces the reaction energy barrier of acidic OER process. And the metal oxidation remodeling process exposed more active sites and prevented the peroxidation process. The optimized Ru/Eu2O3@CNT catalyst showed the highest catalytic activity and stability in acidic OER. Its mass activity was 1219.1 A gRu-1 and the TOF value reached 4.4 s-1 at 1.48 V. Additionally, Ru/Eu2O3@CNT after oxidative reconstruction demonstrates the industrially needed current density of 1.0 A cm-2 at 1.71 V in PEM electrolyser, achieving stability in excess of 200 h.

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.

Atomic-level Ru-Ir mixing in rutile-type (RuIr)O2 for efficient and durable oxygen evolution catalysis

The success of proton exchange membrane water electrolysis (PEMWE) depends on active and robust electrocatalysts to facilitate oxygen evolution reaction (OER). Heteroatom-doped-RuOx has emerged as a promising electrocatalysts because heteroatoms suppress lattice oxygen participation in the OER, thereby preventing the destabilization of surface Ru and catalyst degradation. However, identifying suitable heteroatoms and achieving their atomic-scale coupling with Ru atoms are nontrivial tasks. Herein, to steer the reaction pathway away from the involvement of lattice oxygen, we integrate OER-active Ir atoms into the RuO2 matrix, which maximizes the synergy between stable Ru and active Ir centers, by leveraging the changeable growth behavior of Ru/Ir atoms on lattice parameter-modulated templates. In PEMWE, the resulting (RuIr)O2/C electrocatalysts demonstrate notable current density of 4.96 A cm-2 and mass activity of 19.84 A mgRu+Ir-1 at 2.0 V. In situ spectroscopic analysis and computational calculations highlight the importance of the synergistic coexistence of Ru/Ir-dual-OER-active sites for mitigating Ru dissolution via the optimization of the binding energy with oxygen intermediates and stabilization of Ru sites.

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.

Designing Ru-B-Cr Moieties to Activate the Ru Site for Acidic Water Electrolysis under Industrial-Level Current Density

Developing highly efficient non-iridium-based active sites for acidic water splitting is still a huge challenge. Herein, unique Ru-B-Cr moieties have been constructed in RuO2 nanofibers (NFs) to activate Ru sites for water electrolysis, which overcomes the bottleneck of RuO2-based catalysts usually possessing low activity for the hydrogen evolution reaction (HER) and poor stability for the oxygen evolution reaction (OER). The fabricated Cr, B-doped RuO2 NFs exhibit low overpotentials of 205 and 379 mV for acidic HER and OER at 1 A cm-2 with outstanding stability lasting 1000 and 188 h, respectively. The assembled acidic electrolyzer also possesses great hydrogen production efficiency and durability at a high current density. Experimental and theoretical explorations reveal that the formation of Ru-B-Cr moieties effectively optimizes the atomic configurations and modulates the adsorption/desorption free energy of reaction intermediates to achieve exceptional HER and OER performance.

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.

Doping Ti into RuO2 to Accelerate Bridged-Oxygen-Assisted Deprotonation for Acidic Oxygen Evolution Reaction

The development of efficient and durable electrocatalysts for the acidic oxygen evolution reaction (OER) is essential for advancing renewable hydrogen energy technology. However, the slow deprotonation kinetics of oxo-intermediates, involving the four proton-coupled electron steps, hinder the acidic OER progress. Herein, a RuTiOx solid solution electrocatalyst is investigated, which features bridged oxygen (Obri) sites that act as proton acceptors, accelerating the deprotonation of oxo-intermediates. Electrochemical tests, infrared spectroscopy, and density functional theory results reveal that the moderate proton adsorption energy on Obri sites facilitates fast deprotonation kinetics through the adsorbate evolution mechanism. This process effectively prevents the over-oxidation and deactivation of Ru sites caused by the lattice oxygen mechanism. Consequently, RuTiOx shows a low overpotential of 198 mV at 10 mA cm-2 geo and performance exceeding 1400 h at 50 mA cm-2 geo with negligible deactivation. These insights into the OER mechanism and the structure-function relationship are crucial for the advancement of catalytic systems.

Enriched Electrophilic Oxygen Species on Ru Optimize Acidic Water Oxidation

Ruthenium oxide (RuO2) is considered one of the most promising catalysts for replacing iridium oxide (IrO2) in the acidic oxygen evolution reaction (OER). Nevertheless, the performance of RuO2 remains unacceptable due to the dissolution of Ru and the lack of *OH in acidic environments. This paper reports a grain boundary (GB)-rich porous RuO2 electrocatalyst for the efficient and stable acidic OER. The involvement of GB regulates the valence state of Ru and weakens the interaction between Ru and O, effectively facilitating *OH adsorption and *OOH formation. Notably, achieved a record-high catalytic activity (145 mV at 10 mA cm-2) with a low Tafel slope (40.9 mV dec-1) and a remarkable mass activity of 332 mA mg-1 Ru at 1.5 V versus reversible hydrogen electrode is achieved. Additionally, the porous RuO2 exhibits superb stability with an ultra-low degradation rate of 26 µV h-1 over a 50-day durability test. This study opens a viable pathway for the development of efficient and robust Ru-based acidic OER electrocatalysts.

Dynamic-Cycling Zinc Sites Promote Ruthenium Oxide for Sub-Ampere Electrochemical Water Oxidation

Although iridium-based electrocatalysts are commonly regarded as the sole stable operating acidic oxygen evolution reaction (OER) catalysts in proton-exchange membrane water electrolysis (PEMWE) devices, their exorbitant cost and scarcity severely restrict their widespread application. Herein, we introduce a promising alternative to iridium: zinc-doped ruthenium dioxide (TE-Zn/RuO2), which exhibits remarkable and enduring activity for acidic OER. In situ characterizations elucidate that the dynamic cycling of zinc dopants serves as both electron acceptors and donors, facilitating the activation of Ru sites at low overpotentials while thwarting peroxidation at high overpotentials, thus concurrently achieving heightened activity and robust stability. Additionally, the incorporation of zinc induces weakened Ru-O covalency, thereby stabling *OOH intermediates and instigating a sustained adsorbate evolution mechanism, dramatically stabilizing the RuO2 lattice. Importantly, the TE-Zn/RuO2 catalyst as an anode exhibits good stability over 300 h at a water-splitting current of 500 mA cm-2 in the PEMWE device, underscoring its considerable promise for practical applications.

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

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