Interface engineering breaks both stability and activity limits of RuO2 for sustainable water oxidation

Oxidized Overlayers of Ruthenium and Iridium as Electrocatalysts for Anodic Reactions

Renewable energy technologies often rely on rutile tetravalent oxides, such as ruthenium(IV) oxide and iridium(IV) oxide, to catalyze anodic reactions that are paired with fuel formation. Herein, we report the synthesis of angstrom-scale and nanoscale oxidized overlayers of ruthenium (o-RuOx) and iridium (o-IrOx) from simple aqueous precursors grown on earth-abundant supports and state-of-the-art oxide electrocatalysts. The resulting overlayers exhibit distinct redox features and chemical states as indicated by cyclic voltammetry, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. The electrocatalysts exhibit increased activity towards anodic reactions. In particular, annealed o-RuOx grown on TiO2 (a-TiO2/o-RuOx) results in an electrocatalyst with an overpotential of 213, 206, and 14 mV at 10 mA cm-2 for the oxygen evolution reaction (OER) in acid, the OER in base, and the chlorine evolution reaction, respectively. The activity of a-TiO2/o-RuOx corresponds to a 47.7×, 117.4×, and 1.3× increase in ruthenium mass activity compared to RuO2 towards the OER in acid, the OER in base, and the chlorine evolution reaction, respectively. These findings highlight the unique chemistry of oxidized overlayers and their potential to meet operational demands for renewable energy technologies.

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.

Heterogeneous Interfaces of Ni3Se4 Nanoclusters Decorated on a Ni3N Surface Enhance Efficient and Durable Hydrogen Evolution Reactions in Alkaline Electrolyte

Transition metal selenides (TMSes) have been identified as cost-efficient alternatives to platinum (Pt) for the alkaline hydrogen evolution reaction (HER) owing to their distinct electronic properties and excellent conductivity. However, they encounter challenges such as sluggish water dissociation and severe oxidative degradation, requiring further optimizations. In this study, we developed a dual-site heterogeneous catalyst, Ni3Se4-Ni3N, by decorating Ni3Se4 nanoclusters on a Ni3N substrate. This catalyst design promoted significant interfacial electronic interactions, modulated electronic structures, and enhanced the adsorption of the intermediates. Various spectroscopic analyses and theoretical calculations revealed that the nitride surfaces improved water adsorption and dissociation, enriching the surface with adsorbed hydrogen (H*) atoms, while the Se sites facilitated hydrogen coupling and subsequent release of H2. Following a hydrogen spillover mechanism, the surface-adsorbed hydrogen atoms were transferred to nearby electron-dense selenide sites for H2 formation and release. Consequently, the optimized catalyst demonstrated improved HER activity, requiring only an ∼60 mV overpotential at 10 mA cm-2 current density and maintained stability under higher potential conditions.

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.

Engineering High-Density Grain Boundaries in Ru0.8Ir0.2Ox Solid-Solution Nanosheets for Efficient and Durable OER Electrocatalysis

The oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE) has long stood as a formidable challenge for green hydrogen sustainable production, hindered by sluggish kinetics, high overpotentials, and poor durability. Here, these barriers are transcended through a novel material design: strategic engineering of high-density grain boundaries within solid-solution Ru0.8Ir0.2Ox ultrathin nanosheets. These carefully tailored grain boundaries and synergistic Ir─Ru interactions, reduce the coordination of Ru atoms and optimize the distribution of charge, thereby enhancing both the catalytic activity and stability of the nanosheets, as verified by merely requiring an overpotential of 189 mV to achieve 10 mA cm-2 in acidic electrolyte. In situ electrochemical techniques, complemented by theoretical calculations, reveal that the OER follows an adsorption evolution mechanism, demonstrating the pivotal role of grain boundary engineering and electronic modulation in accelerating reaction kinetics. Most notably, the Ru0.8Ir0.2Ox exhibits outstanding industrial-scale performance in PEMWE, reaching 4.0 A cm-2 at 2 V and maintaining stability for >1000 h at 500 mA cm-2. This efficiency reduces hydrogen production costs to $0.88 kg-1. This work marks a transformative step forward in designing efficient, durable OER catalysts, offering a promising pathway toward hydrogen production technologies and advancing the global transition to sustainable energy.

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.

Modulating the covalency of Ru-O bonds by dynamic reconstruction for efficient acidic oxygen evolution

Developing ruthenium-based oxide catalysts capable of suppressing lattice oxygen participation in the catalytic reaction process is crucial for maintaining stable oxygen evolution reaction (OER) under acidic conditions. Herein, we delicately construct a RuO2 nanoparticle-anchored LiCoO2 nanosheet electrocatalyst (RuO2/LiCoO2), achieving dynamic optimization of RuO2 during the reaction process and improving catalytic stability. Benefiting from the unique electrochemical delithiation characteristics of the LiCoO2 support, the covalency of the Ru-O bond is effectively regulated during the OER process. The weakened Ru-O covalent bond inhibits the participation of lattice oxygen in the catalytic reaction and ensures the continuous operation of the Ru active sites. Moreover, the extended Ru-O bond in the optimized RuO2/LiCoO2 catalyst reduces the formation energy barrier of the *OOH intermediates, accelerating the progress of the OER. As a result, the RuO2/LiCoO2 catalyst requires only an overpotential of 150 ± 2 mV at 10 mA cm-2 in 0.5 M H2SO4 and operates stably for 2000 h at 1 A cm-2 in a proton exchange membrane water electrolysis. This work opens new avenues for designing efficient ruthenium-based catalysts.

Hafnium incorporation modulating the electronic structure of NiFe layered double hydroxides for effective oxygen evolution

Transition metal Hf doping in NiFe LDHs alters the chemical environment of Ni and Fe, enhancing the electronic synergy among the three metals. In an alkaline environment, the prepared NiFeHf LDH electrodes display a low OER overpotential of 177 mV at 10 mA cm-2, demonstrating superior OER activity.

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.

Corrosion-resistant single-atom catalysts for direct seawater electrolysis

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

Optimizing Stability and Efficiency in Low-Content Noble Metal-Doped Aerogel Catalysts for Oxygen Evolution Reaction

This study presents the development of an efficient Oxygen Evolution Reaction (OER) electrocatalyst by doping low-content Ruthenium (Ru) into FexCo5-x (oxy)hydroxide aerogel matrix. The aerogel, synthesized using a sol-gel process and supercritical drying, ensures uniform dispersion of Ru within the porous structure, significantly regulating the catalytic performance and stability of the OER electrocatalyst. The incorporation of Ru not only enriches the active sites but also generates synergistic effects with existing active sites, further improving the overall catalytic efficiency. The optimized catalyst with low Ru content delivers outstanding performance metrics, e.g., 1%Ru-Fe4Co1 catalyst demonstrates outstanding OER performance, with an onset overpotential (ηonset) of 177.4 mV, η10 of 214.3 mV, η100 of 335.9 mV, a Tafel slope of 41 mV dec⁻¹, and remarkable Mass Activity of 569.1 A/gmetal at 1.63 V (vs. RHE). It also exhibits good stability under operational conditions, maintaining performance at temperatures up to 60 °C and enduring high current densities up to 250 mA cm- 2. Density Functional Theory (DFT) simulation elucidates the optimal doping level and uniform distribution enhance the reaction kinetics, leading to superior catalytic performance. This research provides new insights into the design of cost-effective, high-performance OER electrocatalysts by modulating low-content noble metals in aerogels.

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.

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.

Interface Engineering of RuO2/Ni-Co3O4 Heterostructures for enhanced acidic oxygen evolution reaction

RuO2 has been recognized as a standard electrocatalyst for acidic oxygen evolution reaction (OER). Nonetheless, its high cost and limited durability are still ongoing challenges. Herein, a RuO2/Ni-Co3O4 heterostructure confining a heterointerface (between RuO2 and Ni-doped Co3O4) is constructed to realize enhanced OER performance. Specifically, RuO2/Ni-Co3O4 containing a low Ru content (2.7 ± 0.3 wt%) achieves an overpotential of 186 mV at a current density of 10 mA cm-2 with a long-run stability (≥1300 h). Also, it exhibits a mass activity of 1202.29 mA mgRu-1 at an overpotential of 250 mV, exceeding commercial RuO2. The results disclose an optimum electron transfer at the heterointerface, wherein Ni doping improves the adsorption energy of oxygen-containing intermediates, thereby facilitating OER. This study presents an effective approach for designing highly active and stable OER electrocatalysts.

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.

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.

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.

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

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

Phosphorus-doped nickel-iron hydroxides/MXene for efficient electrochemical water oxidation

Herein, NiFeP/Ti2C@NF was synthesized from a hydrothermal process and chemical conversion, and exhibited a low overpotential of 177 mV at j = 50 mA cm-2, a low Tafel slope of 56 mV dec-1, and a very competitive stable activity in alkaline electrolyte, proposing a strategy for efficient OER and overall water splitting.

Stabilization of High-Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis

Heterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH-/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high-valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH- ions coupling at an open circuit condition. With excluding the Co2+ sites, the as-derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

Accelerated galvanic interaction for the fabrication of core-shell nanowires to boost the hydrogen evolution reaction

As an essential reaction of water splitting in alkaline solution, the hydrogen evolution reaction (HER) is seriously limited by its ponderous dynamics and the dissolution of Ru. Herein, we propose a strategy for the electrochemical deposition of Ru nanoparticles on the surface of Ag nanowires (Ag NWs) to generate a core-shell Ru@Ag/AgCl catalyst through an accelerated galvanostatic interaction conducted in RuCl3 solution. The active sites of Ru were precisely controlled by tailoring the number of cycles in cyclic voltammetry (CV). Interestingly, the as-designed Ru@Ag/AgCl-200 electrode maintained its original morphology after 200 CV cycles, demonstrating the high stability of the designed electrocatalyst. The electrochemical performance of the Ru@Ag/AgCl-200 catalyst justifies its excellent HER performance, including a low overpotential of 40.2 mV at a current density of 10 mA cm-2, small Tafel slope of 53.24 mV dec-1, and great stability, compared to other control catalysts. Furthermore, the Ru@Ag/AgCl-200 catalyst delivered a low output potential of 1.53 V and sustained long-term stability of 50 h at a current density of 10 mA cm-2 for water splitting. This work provides a framework for accelerated galvanostatic interaction for the controlled synthesis of Ru-based catalysts, which can be used for boosting the HER in alkaline solutions.

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.

Surface Cladding Engineering via Oxygen Sulfur Distribution for Stable Electrocatalytic Oxygen Production

Inevitable leaching and corrosion under anodic oxidative environment greatly restrict the lifespan of most catalysts with excellent primitive activity for oxygen production. Here, based on Fick' s Law, we present a surface cladding strategy to mitigate Ni dissolution and stabilize lattice oxygen triggering by directional flow of interfacial electrons and strong electronic interactions via constructing elaborately cladding-type NiO/NiS heterostructure with controlled surface thickness. Multiple in situ characterization technologies indicated that this strategy can effectively prevent the irreversible Ni ions leaching and inhibit lattice oxygen from participating in anodic reaction. Combined with density functional theory calculations, we reveal that the stable interfacial O-Ni-S arrangement can facilitate the accumulation of electrons on surficial NiO side and weaken its Ni-O covalency. This would suppress the overoxidation of Ni and simultaneously fixing the lattice oxygen, thus enabling catalysts with boosted corrosion resistance without sacrificing its activity. Consequently, this cladding-type NiO/NiS heterostructure exhibits excellent performance with a low overpotential of 256 mV after 500 h. Based on Fick's law, this work demonstrates the positive effect of surface modification through precisely adjusting of the oxygen-sulfur exchange process, which has paved an innovative and effective way to solve the instability problem of anodic oxidation.

Atomically Dispersed Vanadium-Induced Ru-V Dual Active Sites Enable Exceptional Performance for Acidic Water Oxidation

Regulating the catalytic reaction pathway to essentially break the activity/stability trade-off that limits RuO2 and thus achieves exceptional stability and activity for the acidic oxygen evolution reaction (OER) is important yet challenging. Herein, we propose a novel strategy of incorporating atomically dispersed V species, including O-bridged V dimers and V single atoms, into RuO2 lattices to trigger direct O-O radical coupling to release O2 without the generation of *OOH intermediates. Vn-RuO2 showed high activity with a low overpotential of 227 mV at 10 mA cm-2 and outstanding stability during a 1050 h test in acidic electrolyte. Operando spectroscopic studies and theoretical calculations revealed that compared with the V single atom-doping case, the introduction of the V dimer into RuO2 further decreases the Ru-V atomic distance and weakens the adsorption strength of the *O intermediate to the active V site, which supports the more energetically favorable oxygen radical coupling mechanism (OCM). Furthermore, the highly asymmetric Ru-O-V local structure stabilizes the surface Ru active center by lowering the valence state and increasing the resistance against overoxidation, which result in outstanding stability. This study provides insight into ways of increasing the intrinsic catalytic activity and stability of RuO2 by atomically dispersed species modification.

Experimental Realization of Fluoroborophene

Borophene, an anisotropic metallic Dirac material exhibits superlative physical and chemical properties. While the lack of bandgap restricts its electronic chip applications, insufficient charge carrier density and electrochemical/catalytically active sites, restricts its energy storage and catalysis applications. Fluorination of borophene can induce bandgap and yield local electron injection within its crystallographic lattice. Herein, a facile synthesis of fluoroborophene with tunable fluorine content through potassium fluoride-assisted solvothermal-sonochemical combinatorial approach is reported. Fluoroborophene monolayers with lateral dimension 50 nm-5 µm are synthesized having controlled fluorine content (12-35%). Fluoroborophene exhibits inter-twinned crystallographic structure, with fluorination-tunable visible-range bandgap ≈1.5-2.5 eV, and density functional theory calculations also corroborate it. Fluoroborophene is explored for electrocatalytic oxygen evolution reaction in an alkaline medium and bestow a good stability. Tunable bandgap, electrophilicity and molecular anchoring capability of fluoroborophene will open opportunities for novel electronic/optoelectronic/spintronic chips, energy storage devices, and in numerous catalytic applications.

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.

Significantly Enhanced Acidic Oxygen Evolution Reaction Performance of RuO2 Nanoparticles by Introducing Oxygen Vacancy with Polytetrafluoroethylene

The supported RuO2 catalysts are known for their synergistic and interfacial effects, which significantly enhance both catalytic activity and stability. However, polymer-supported RuO2 catalysts have received limited attention due to challenges associated with poor conductivity. In this study, we successfully synthesized the RuO2-polytetrafluoroethylene (PTFE) catalyst via a facile annealing process. The optimized nucleation and growth strategies enable the formation of RuO2 particles (~13.4 nm) encapsulating PTFE, establishing a conductive network that effectively addresses the conductivity issue. Additionally, PTFE induces the generation of oxygen vacancies and the formation of stable RuO2/PTFE interfaces, which further enhance the acidic OER activity and the stability of RuO2. As a result, the RuO2-PTFE catalyst exhibits a low overpotential of 219 mV at 10 mA cm⁻2 in the three-electrode system, and the voltage of the RuO2-PTFE||commercial Pt/C system can keep 1.50 V for 800 h at 10 mA cm-2. This work underscores the versatility of PTFE as a substrate for fine-tuning the catalyst morphology, the crystal defect, and the stable interface outerwear. This work not only broadens the application scope of PTFE in catalyst synthesis but also provides a novel approach to the design of high-performance metallic oxide catalysts with tailored oxygen vacancy concentration and stable polymer outerwear.

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.

High Coverage Sub-Nano Iridium Cluster on Core-Shell Cobalt-Cerium Bimetallic Oxide for Highly Efficient Full-pH Water Splitting

The construction of sub-nanometer cluster catalysts (<1 nm) with almost complete exposure of active atoms serves as a promising avenue for the simultaneous enhancement of atom utilization efficiency and specific activity. Herein, a core-shell cobalt-cerium bimetallic oxide protected by high coverage sub-nanometer Ir clusters (denoted as Ir cluster@CoO/CeO2) is constructed by a confined in situ exsolution strategy. The distinctive core-shell structure endows Ir cluster@CoO/CeO2 with enhanced intrinsic activity and high conductivity, facilitating efficient charge transfer and full-pH water splitting. The Ir cluster@CoO/CeO2 achieves low overpotentials of 49/215, 52/390, and 54/243 mV at 10 mA cm-2 for hydrogen evolution reaction/oxygen evolution reaction (HER/OER) in 0.5 m H2SO4, 1.0 m PBS, and 1.0 m KOH, respectively. The small decline in performance after 300 h of operation renders it one of the most effective catalysts for full-pH water splitting. DFT calculations indicate that oriented electron transfer (along the path from Ce to Co and then to Ir) creates an electron-rich environment for surface Ir clusters. The reconstructed interface electronic environment provides optimized intermediates adsorption/desorption energy at the Ir site (for HER) and at the Ir-Co site (for OER), thus simultaneously speeding up the HER/OER kinetics.

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.

Tracking Water Dissociation on RuO2(110) Using Atomic Force Microscopy and First-Principles Simulations

The interaction between interfacial water and transition metal oxides is a primary enabling step for the oxygen evolution reaction (OER). RuO2 is a prototypical OER electrocatalyst whose ability to activate interfacial water molecules is essential to its OER activity. We image the dissociation of surface water into OH* and O* on RuO2(110), where * denotes adsorbed species, using atomic force microscopy. Starting from the surface-bound water molecules, which form a one-dimensional network along the rows of Ru surface sites, increasing the oxidative potential strips hydrogen away and transforms the water molecules into OH* and O*. This oxidative step changes the pattern of the adsorbates from one- to two-dimensional. First-principles calculations with interfacial polarization, capacitive charging, and adsorbate interactions attribute this evolution to the cooperative dehydrogenation of adsorbed water and OH* on RuO2. We use these results to map the surface phase diagram of RuO2(110) and provide a quantitative interpretation of its cyclic voltammetry. Our result provides the visualization of the water dissociation on a conductive oxide surface, a critical step in the OER, and demonstrates that the water activation is a collective phenomenon at RuO2(110) electrodes.

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.

Regulating Ru-O Bond and Oxygen Vacancies of RuO2 by Ta Doping for Electrocatalytic Oxygen Evolution in Acid Media

Proton exchange membrane water electrolysis (PEMWE) is considered an ideal green hydrogen production technology with promising application prospects. However, the development of efficient and stable acid electroanalytic oxygen electrocatalysts is still a challenging bottleneck. This progress is achieved by adopting a strategic approach with the introduction of the high valence metal Ta to regulate the electronic configuration of RuO2 by manipulating its local microenvironment to optimize the stability and activity of the electrocatalysts. The Ta-RuO2 catalysts are notable for their excellent electrocatalytic activity, as evidenced by an overpotential of only 202 mV at 10 mA cm-2, which significantly exceeds that of homemade RuO2 and commercial RuO2. Furthermore, the Ta-RuO2 catalyst exhibits exceptional stability with negligible potential reduction observed after 50 h of electrolysis. Theoretical calculations show that the asymmetric configuration of Ru-O-Ta breaks the thermodynamic activity limitations usually associated with adsorption evolution, weakening the energy barrier for the formation of the OOH* formation. The strategic approach presented in this study provides an important reference for the development of a stable active center for acid water splitting.

Stability of electrocatalytic OER: from principle to application

Hydrogen energy, derived from the electrolysis of water using renewable energy sources such as solar, wind, and hydroelectric power, is considered a promising form of energy to address the energy crisis. However, the anodic oxygen evolution reaction (OER) poses limitations due to sluggish kinetics. Apart from high catalytic activity, the long-term stability of electrocatalytic OER has garnered significant attention. To date, several research studies have been conducted to explore stable electrocatalysts for the OER. A comprehensive review is urgently warranted to provide a concise overview of the recent advancements in the electrocatalytic OER stability, encompassing both electrocatalyst and device developments. This review aims to succinctly summarize the primary factors influencing OER stability, including morphological/phase change and electrocatalyst dissolution, as well as mechanical detachment, alongside chemical, mechanical, and operational degradation observed in devices. Furthermore, an overview of contemporary approaches to enhance stability is provided, encompassing electrocatalyst design (structural regulation, protective layer coating, and stable substrate anchoring) and device optimization (bipolar plates, gas diffusion layers, and membranes). Hopefully, more attention will be paid to ensuring the stable operation of electrocatalytic OER and the future large-scale water electrolysis applications. This review presents design principles aimed at addressing challenges related to the stability of electrocatalytic OER.

Sequential oxygen evolution and decoupled water splitting via electrochemical redox reaction of nickel hydroxides

Alkaline water electrolysis is a promising low-cost strategy for clean and sustainable hydrogen production but is largely limited by the sluggish anodic oxygen evolution reaction and the challenges in maintaining adequate separation between H2 and O2. Here, we reveal an anodic-cathodic sequential oxygen evolution process via electrochemical oxidation and subsequent reduction of Ni hydroxides, enabling much lower overpotentials than conventional anodic oxygen evolution. By using (isotope-labeled) differential electrochemical mass spectrometry and in situ Raman spectroscopy combined with density functional theory calculations, we evidence that the sequential oxygen evolution originates from the electrochemical oxidation of Ni hydroxides to NiOO- active species while undergoing a different, reductive step of NiOO- for the final release of O2 due to weakened Ni-O covalency. Based on this sequential process, we propose and demonstrate a hybrid water electrolysis and energy storage device, which enables time-decoupled hydrogen and oxygen evolution and electrochemical energy storage in the Ni hydroxides.

Interface-Strengthened Ru-Based Electrocatalyst for High-Efficiency Proton Exchange Membrane Water Electrolysis at Industrial-Level Current Density

Developing an OER electrocatalyst that balances high performance with low cost is crucial for widely adopting PEM water electrolyzers. Ru-based catalysts are gaining attention for their cost-effectiveness and high activity, positioning them as promising alternatives to Ir-based catalysts. However, Ru-based catalysts can be prone to oxidation at high potentials, compromising their durability. In this study, we utilize a simple synthesis method to synthesize a SnO2, Nb2O5, and RuO2 composite catalyst (SnO2/Nb2O5@RuO2) with multiple interfaces and abundant oxygen vacancies. The large surface area and numerous active sites of the SnO2/Nb2O5@RuO2 catalyst lead to outstanding acidic oxygen evolution reaction (OER) performance, achieving current densities of 10, 50, and 200 mA cm-2 at ultralow overpotentials of 287, 359, and 534 mV, respectively, significantly surpassing commercial IrO2. Moreover, incorporating Nb2O5 into the SnO2/Nb2O5@RuO2 alters the electronic structure at the interfaces and generates a high density of oxygen vacancies, markedly enhancing durability. Consequently, the membrane electrode composed of SnO2/Nb2O5@RuO2 and commercial Pt/C demonstrated stable operation in the PEM cell for 25 days at an industrial current density of 1 A cm-2. This research presents a convenient approach for developing a highly efficient and durable Ru-based electrocatalyst, underscoring its potential for proton exchange membrane water electrolysis.

A strongly coupled oxide-support heterostructure for efficient acidic water oxidation

The synthesized RuO2/MnCo2O4.5 nano-heterostructure possesses dense interfaces and abundant defect structures, synergistically balancing oxygen evolution reaction (OER) activity and stability. RuO2/MnCo2O4.5 exhibits a low overpotential of 190 mV at 10 mA cm-2. The proton exchange membrane (PEM) electrolyzer assembled can operate at 200 mA cm-2 stably for 50 h.

Selective Synthesis of Organonitrogen Compounds via Electrochemical C-N Coupling on Atomically Dispersed Catalysts

The C-N coupling reaction demonstrates broad application in the fabrication of a wide range of high value-added organonitrogen molecules including fertilizers (e.g., urea), chemical feedstocks (e.g., amines, amides), and biomolecules (e.g., amino acids). The electrocatalytic C-N coupling pathways from waste resources like CO2, NO3-, or NO2- under mild conditions offer sustainable alternatives to the energy-intensive thermochemical processes. However, the complex multistep reaction routes and competing side reactions lead to significant challenges regarding low yield and poor selectivity toward large-scale practical production of target molecules. Among diverse catalyst systems that have been developed for electrochemical C-N coupling reactions, the atomically dispersed catalysts with well-defined active sites provide an ideal model platform for fundamental mechanism elucidation. More importantly, the intersite synergy between the active sites permits the enhanced reaction efficiency and selectivity toward target products. In this Review, we systematically assess the dominant reaction pathways of electrocatalytic C-N coupling reactions toward various products including urea, amines, amides, amino acids, and oximes. To guide the rational design of atomically dispersed catalysts, we identify four key stages in the overall reaction process and critically discuss the corresponding catalyst design principles, namely, retaining NOx/COx reactants on the catalyst surface, regulating the evolution pathway of N-/C- intermediates, promoting C-N coupling, and facilitating final hydrogenation steps. In addition, the advanced and effective theoretical simulation and characterization technologies are discussed. Finally, a series of remaining challenges and valuable future prospects are presented to advance rational catalyst design toward selective electrocatalytic synthesis of organonitrogen molecules.

Selective Activation of Lattice Oxygen Site Through Coordination Engineering to Boost the Activity and Stability of Oxygen Evolution Reaction

Although Ru-based materials are among the outstanding catalysts for the oxygen evolution reaction (OER), the instability issue still haunts them and impedes the widespread application. The instability of Ru-based OER catalysts is generally ascribed to the formation of soluble species through the over-oxidation of Ru and structural decomposition caused by involvement of lattice oxygen. Herein, an effective strategy of selectively activating the lattice oxygen around Ru site is proposed to improve the OER activity and stability. Our synthesized spinel-type electrocatalyst of Ru and Zn co-doped Co3O4 showed an ultralow overpotential of 172 mV at 10 mA cm-2 and a long-term stability reaching to 100 hours at 10 mA cm-2 for alkaline OER. The experimental results and theoretical simulations demonstrated that the lattice oxygen site jointly connected with the octahedral Ru and tetrahedral Zn atoms became more active than other oxygen sites near Ru atom, which further lowered the reaction energy barriers and avoided generating excessive oxygen vacancies to enhance the structural stability of Ru sites. The findings hope to provide a new perspective to improve the catalytic activity of Ru-incorporated OER catalysts and the stability of lattice-oxygen-mediated mechanism.

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

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

Tailoring atomically local electric field of NiFe layered double hydroxides with Ag dopants to boost oxygen evolution kinetics

The demand for clean energy sources has driven focus towards advanced electrochemical systems. However, the sluggish kinetics of the oxygen evolution reaction (OER) constrain the energy conversion efficiency of relevant devices. Herein, a one-step method is reported to grow oxygen vacancies (Vo) rich NiFeAg layered double hydroxides nanoclusters on carbon cloth (Vo-NiFeAg-LDH/CC) for serving as the self-supporting electrode to catalyze OER. The OER performance of Vo-NiFeAg-LDH/CC has been remarkably enhanced through Ag and Vo co-modification compared with pristine NiFe-LDH, achieving a low Tafel slope of 49.7 mV dec-1 in 1 m KOH solution. Additionally, the current density of Vo-NiFeAg-LDH/CC is 3.23 times higher than that of the state-of-art IrO2 at 2 V under an alkaline flow electrolyzer setup. Theoretical calculations and experimental results collectively demonstrate that Ag dopant and Vo strengthen the O* adsorption with active sites, further promoting the deprotonation step from OH* to O* and accelerating the catalytic reaction. In a word, this work clarifies the structural correlation and synergistic mechanism of Ag dopant and Vo, providing valuable insights for the rational design of catalyst for renewable energy applications.

γ-MnO2 as an Electron Reservoir for RuO2 Oxygen Evolution Catalyst in Acidic Media

Developing highly active and durable catalysts in acid conditions remains an urgent issue due to the sluggish kinetics of oxygen evolution reaction (OER). Although RuO2 has been a state-of-the-art commercial catalyst for OER, it encounters poor stability and high cost. In this study, the electronic reservoir regulation strategy is proposed to promote the performance of acidic water oxidation via constructing a RuO2/MnO2 heterostructure supported on carbon cloth (CC) (abbreviated as RuO2/MnO2/CC). Theoretical and experimental results reveal that MnO2 acts as an electron reservoir for RuO2. It facilitates electron transfer from RuO2, enhancing its activity prior to OER, and donates electrons to RuO2, improving its stability after OER. Consequently, RuO2/MnO2/CC exhibits better performance compared to commercial RuO2, with an ultrasmall overpotential of 189 mV at 10 mA cm-2 and no signs of deactivation even after 800 h of electrolysis in 0.5 m H2SO4 at 10 mA cm-2. When applied as the anode in a proton exchange membrane water electrolyzer, the cost-efficient RuO2/MnO2/CC catalyst only requires a cell voltage of 1.661 V to achieve the water-splitting current of 1 A cm-2, and the noble metal cost is as low as US$ 0.00962 cm-2, indicating potential for practical applications.

Synergistic Effect Enables the Dual-Metal Doped Cobalt Telluride Particles as Potential Electrocatalysts for Oxygen Evolution in Alkaline Electrolyte

Cobalt (Co)-based materials have been widely investigated as hopeful noble-metal-free alternatives for the oxygen evolution reaction (OER) in alkaline electrolytes, which is crucial for generating hydrogen by water electrolysis. Herein, cobalt-based telluride particles with good electronic conductivity as anodic electrocatalysts were prepared under vacuum by the solid-state strategy, which display remarkable activities toward the OER. Nickel (Ni) and iron (Fe) codoped cobalt telluride (NiFe-CoTe) exhibits an overpotential of 321 mV to achieve a current density of 10 mA cm-2 and a Tafel slope of 51.8 mV dec-1, outperforming the performances of CoTe, CoTe2, and IrO2. According to the DFT calculation, the adsorbed hydroxyl-assisted adsorbate evolution mechanism was proposed for the OER process of NiFe-CoTe, which reveals the synergetic effect toward OER induced by codoping of the Ni and Fe atoms. This work proposes a rational strategy to prepare cobalt-based tellurides as efficient OER catalysts in alkaline electrolytes, providing a new strategy to prepare and regulate metal-based tellurides for catalysis and beyond.

Surface-Modified Ruthenium Nanorods for an Ampere-Level Bifunctional Hydrogen Evolution Reaction/Oxygen Evolution Reaction Electrocatalyst

The practical applications of bifunctional ruthenium-based electrocatalysts with two active sites of Ru nanoparticles covered with RuO2 skins are limited. One reason is the presence of multiple equally distributed facets, some of which are inactive. In contrast, ruthenium nanorods with a high aspect ratio have multiple unequally distributed facets containing the dominance of active faces for efficient electrocatalysis. However, the synthesis of ruthenium nanorods has not been achieved due to difficulties in controlling the growth. Additionally, it is known that the adsorption capacity of intermediates can be impacted by the surface of the catalyst. Inspired by these backgrounds, the surface-modified (SM) ruthenium nanorods having a dominant active facet of hcp (100) through chemisorbed oxygen and OH groups (SMRu-NRs@NF) are rationally synthesized through the surfactant coordination method. SMRu-NRs@NF exhibits excellent hydrogen evolution in acid and alkaline solutions with an ultralow overpotential of 215 and 185 mV reaching 1000 mA cm-2, respectively. Moreover, it has also shown brilliant oxygen evolution electrocatalysis in alkaline solution with a low potential of 1.58 V to reach 1000 mA cm-2. It also exhibits high durability over 143 h for the evolution of oxygen and hydrogen at 1000 mA cm-2. Density functional theory studies confirmed that surface modification of a ruthenium nanorod with chemisorbed oxygen and OH groups can optimize the reaction energy barriers of hydrogen and oxygen intermediates. The surface-modified ruthenium nanorod strategy paves a path to develop the practical water splitting electrocatalyst.

2D Ruthenium-Chromium Oxide with Rich Grain Boundaries Boosts Acidic Oxygen Evolution Reaction Kinetics

Ruthenium oxide is currently considered as the promising alternative to Ir-based catalysts employed for proton exchange membrane water electrolyzers but still faces the bottlenecks of limited durability and slow kinetics. Herein, a 2D amorphous/crystalline heterophase ac-Cr0.53Ru0.47O2-δ substitutional solid solution with pervasive grain boundaries (GBs) is developed to accelerate the kinetics of acidic oxygen evolution reaction (OER) and extend the long-term stability simultaneously. The ac-Cr0.53Ru0.47O2-δ shows a super stability with a slow degradation rate and a remarkable mass activity of 455 A gRu -1 at 1.6 V vs RHE, which is ≈3.6- and 5.9-fold higher than those of synthesized RuO2 and commercial RuO2, respectively. The strong interaction of Cr-O-Ru local units in synergy with the specific 2D structural characteristics of ac-Cr0.53Ru0.47O2-δ dominates its enhanced stability. Meanwhile, high-density GBs and the shortened Ru-O bonds tailored by amorphous/crystalline structure and Cr-O-Ru interaction regulate the adsorption and desorption rates of oxygen intermediates, thus accelerating the overall acidic OER kinetics.

Electrochemically Induced Ru/CoOOH Synergistic Catalyst as Bifunctional Electrode Materials for Alkaline Overall Water Splitting

Efficient and affordable price bifunctional electrocatalysts based on transition metal oxides for oxygen and hydrogen evolution reactions have a balanced efficiency, but it remains a significant challenge to control their activity and durability. Herein, a trace Ru (0.74 wt.%) decorated ultrathin CoOOH nanosheets (≈4 nm) supported on the surface of nickel foam (Ru/CoOOH@NF) is rationally designed via an electrochemically induced strategy to effectively drive the electrolysis of alkaline overall water splitting. The as-synthesized Ru/CoOOH@NF electrocatalysts integrate the advantages of a large number of different HER (Ru nanoclusters) and OER (CoOOH nanosheets) active sites as well as strong in-suit structure stability, thereby exhibiting exceptional catalytic activity. In particular, the ultra-low overpotential of the HER (36 mV) and the OER (264 mV) are implemented to achieve 10 mA cm-2. Experimental and theoretical calculations also reveal that Ru/CoOOH@NF possesses high intrinsic conductivity, which facilitates electron release from H2O and H-OH bond breakage and accelerates electron/mass transfer by regulating the charge distribution. This work provides a new avenue for the rational design of low-cost and high-activity bifunctional electrocatalysts for large-scale water-splitting technology and expects to help contribute to the creation of various hybrid electrocatalysts.

Tailoring hypervalent Nickel induced by oxygen vacancy toward enhanced oxygen evolution reaction performance in self-supporting NiFe-(oxy)hydroxides electrodes

NiFe-(oxy)hydroxides are the most active transition metal oxide electrocatalysts for oxygen evolution reaction (OER) under the alkaline media. Herein, we controllably manipulated oxygen vacancy (VO)-tunable NiFe-(oxy) hydroxides that their OER performances possessed a volcano-type relationship with VO concentration, positively-correlated with Ni3+/Ni2+ ratio. Theoretical simulations further unearthed the enhanced activation and dissociation of H2O by the inserting of VO. As a result, the optimal sample featuring the Ni3+/Ni2+ ratio of 30.3 % and VO of 23.8 % exhibited the overpotential of 243 mV at the current density of 100 mA cm-2, simultaneously lasting 120 h durability without any attenuation, exceding the most reported NiFe-(oxy)hydroxides. This work offers an innovative view to understand the OER performance using hypervalent Ni ratio induced by VO defects.

Oxygen Radical Coupling on Short-Range Ordered Ru Atom Arrays Enables Exceptional Activity and Stability for Acidic Water Oxidation

The discovery of efficient and stable electrocatalysts for oxygen evolution reaction (OER) in acid is vital for the commercialization of the proton-exchange membrane water electrolyzer. In this work, we demonstrate that short-range Ru atom arrays with near-ideal Ru-Ru interatomic distances and a unique Ru-O hybridization state can trigger direct O*-O* radical coupling to form an intermediate O*-O*-Ru configuration during acidic OER without generating OOH* species. Further, the Ru atom arrays suppress the participation of lattice oxygen in the OER and the dissolution of active Ru. Benefiting from these advantages, the as-designed Ru array-Co3O4 electrocatalyst breaks the activity/stability trade-off that plagues RuO2-based electrocatalysts, delivering an excellent OER overpotential of only 160 mV at 10 mA cm-2 in 0.5 M H2SO4 and outstanding durability during 1500 h operation, representing one of the best acid-stable OER electrocatalysts reported to date. 18O-labeled operando spectroscopic measurements together with theoretical investigations revealed that the short-range Ru atom arrays switched on an oxide path mechanism (OPM) during the OER. Our work not only guides the design of improved acidic OER catalysts but also encourages the pursuit of short-range metal atom array-based electrocatalysts for other electrocatalytic reactions.

Bicontinuous RuO2 nanoreactors for acidic water oxidation

Improving activity and stability of Ruthenium (Ru)-based catalysts in acidic environments is eager to replace more expensive Iridium (Ir)-based materials as practical anode catalyst for proton-exchange membrane water electrolyzers (PEMWEs). Here, a bicontinuous nanoreactor composed of multiscale defective RuO2 nanomonomers (MD-RuO2-BN) is conceived and confirmed by three-dimensional tomograph reconstruction technology. The unique bicontinuous nanoreactor structure provides abundant active sites and rapid mass transfer capability through a cavity confinement effect. Besides, existing vacancies and grain boundaries endow MD-RuO2-BN with generous low-coordination Ru atoms and weakened Ru-O interaction, inhibiting the oxidation of lattice oxygen and dissolution of high-valence Ru. Consequently, in acidic media, the electron- and micro-structure synchronously optimized MD-RuO2-BN achieves hyper water oxidation activity (196 mV @ 10 mA cm-2) and an ultralow degradation rate of 1.2 mV h-1. A homemade PEMWE using MD-RuO2-BN as anode also conveys high water splitting performance (1.64 V @ 1 A cm-2). Theoretical calculations and in-situ Raman spectra further unveil the electronic structure of MD-RuO2-BN and the mechanism of water oxidation processes, rationalizing the enhanced performance by the synergistic effect of multiscale defects and protected active Ru sites.