Enhanced Acidic Water Oxidation by Dynamic Migration of Oxygen Species at the Ir/Nb2 O5-x Catalyst/Support Interfaces

Hierarchical porous anti-spinel Fe3O4 nanoparticles anode for ultra-high capacitance storage and ultra-long life with nearly-zero strain via in-situ electrochemical redox

Iron oxides are widely used for electrochemical energy storage, however, low conductivity and poor reversibility still limit their potential. In this paper, we proposed a simple hydrothermal pore-making and subsequent in-situ electrochemical redox method to synthesize hierarchical porous Fe3O4 nanoparticle anodes. Benefiting from the self-supporting electrode design and abundant surface area and pore pathways, the ion transport efficiency and conductivity of the anode are enhanced, and the generation of inert phases induced by excess charge buildup is also greatly mitigated. Ex-situ X-ray diffraction shows that the crystal structure remains stable with nearly zero strain generation throughout the charging and discharging process. Due to this structural advantage, the P-Fe3O4@CC electrode exhibits a specific capacitance of 1918.3 F g-1 in KOH (at 2 A g-1), with 97.3 % capacity retention after 10,000 cycles. Notably, the assembled symmetric supercapacitors P-Fe3O4@CC//P-Fe3O4@CC and asymmetric supercapacitors P-Fe3O4@CC//CoNi-LDH@CC exhibit maximum energy densities of 158.0 Wh kg-1 (at 2.0 kW kg-1) and 108.9 Wh kg-1 (at 1.5 kW kg-1), respectively. This study confirms the effectiveness of the synergistic effect of hierarchical porous structure and anti-spinel crystal structure to enhance charge storage and structural stabilization for Fe3O4 anodes.

Enhancing Heterointerface Coupling for Durable Industrial-Level Proton Exchange Membrane Water Electrolysis

The industrial-level application of proton exchange membrane water electrolysis (PEMWE) lies in the capacity of operating at high current density in order for higher power density and lower operational cost. However, it poses a significant challenge to the overall performance of catalysts. Heterointerface engineering has emerged as an ideal strategy for addressing the anodic intrinsic activity limitations. Nevertheless, due to the fragile interface structure with weak interactions between different components, it is difficult to maintain the high activity and long-term stability of heterostructured catalysts. Herein, we report a ternary heterostructured catalyst, RuIrOx-CeO2, featuring a strong-coupled interface between RuIrOx phase and CeO2 phase. This strong-coupled interface exhibits both electronic and oxygen interaction, which effectively inhibits the active phase separation. When applied in PEMWE (0.8 mgIr cm-2 for the anode and 0.4 mgPt cm-2 for the cathode), the resultant catalyst expresses impressive activity, achieving a current density of 3.0 A cm-2 at a cell voltage of 1.75 V in PEMWE and demonstrates a stable 2000-h operation at 5.0 A cm-2 with an imperceptible voltage degradation of <1 µV h-1.

Single-Atom Ru-Triggered Lattice Oxygen Redox Mechanism for Enhanced Acidic Water Oxidation

Activating the oxygen anionic redox presents a promising avenue for developing highly active oxygen evolution reaction (OER) electrocatalysts for proton-exchange membrane water electrolyzers (PEMWE). Here, we engineered a lattice-confined Ru single atom dispersed on a lamellar manganese oxide (MnO2) cation site. The strong Ru-O bond induced an upward shift in the O 2p band, enhancing metal-oxygen covalency and reshaping the OER mechanism toward lattice oxygen oxidation pathway with increased activity. In situ spectral characterization combined with density functional theory (DFT) calculations revealed that electron transfer from Mn to Ru alleviates the Jahn-Teller effect within the MnO6 octahedral structure, stabilizing the lattice. The layered Ru/MnO2 architecture also promotes the rapid replenishment of oxygen vacancies, preventing structural collapse. As a result, the optimized Ru/MnO2 electrocatalyst achieves an OER overpotential of only 179 mV at 10 mA cm-2 in 0.5 M H2SO4, along with exceptional durability over 1000 h at 100 mA cm-2. Moreover, the Ru/MnO2-based PEM device requires only 1.71 V to reach 1 A cm-2 and shows a durability of 500 h at 500 mA cm-2.

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.

Highly Efficient and Durable Anode Catalyst Layer Constructed with Deformable Hollow IrOx Nanospheres in Low-Iridium PEM Water Electrolyzer

Reducing iridium packing density (gIr cm-3 electrode) represents a critical pathway to lower geometric Ir loading in proton exchange membrane water electrolyzers (PEMWEs), yet conventional approaches often cause performance issues of anode catalyst layer due to decreased structural stability and limited electron/mass transport efficiency. Here, we present deformable hollow IrOx nanospheres (dh-IrOx) as a structural-engineered catalyst architecture that achieves an ultralow Ir packing density (20% of conventional IrO2 nanoparticle-based electrodes) while maintaining high catalytic activity and durability at reduced Ir loadings. Scalable synthesis of dh-IrOx via a hard-template method-featuring precise SiO2 nanosphere templating and conformal Ir(OH)3 coating-enables batch production of tens of grams. Through cavity dimension and shell thickness optimization, dh-IrOx demonstrates excellent mechanical resilience to necessary electrode fabrication stresses, including high-shear agitation, ultrasonic processing and hot-pressing. In the anode catalyst layer, the quasi-ordered close packing of dh-IrOx nanospheres simultaneously maximizes electrochemically active surface area, suppresses particle migration and agglomeration, and establishes percolated electron highways and rapid mass transport channels. The architected anode delivers high PEMWE performance (e.g., 1 A cm-2 @1.60 V and 2 A cm-2 @1.75 V@80 °C), while demonstrating excellent operational durability with <1.5% voltage loss over 3000 h.

Ir/Mn Co-Mixing and Oxide-Support Interaction Modulation Through Plasma Promoted Asymmetric Oxygen Coupling for Stable Acidic Oxygen Evolution

Developing efficient and stable catalysts that facilitate the oxygen-evolution reaction (OER) through an oxide-path mechanism (OPM) is of considerable interest. However, it remains a significant challenge due to the stringent structural requirements of these catalysts. This work reports that using a strategy that integrates the Ir/Mn co-mixing and the strong oxide-support interaction (SOSI) modulation, efficient and stable Ir-based catalysts that follow the OPM for the acidic OER can be developed. The strategy mainly relies on optimizing the distance of oxygeneous intermediate adsorption sites by the Ir/Mn co-mixing and modulating the SOSI of the catalysts through plasma defect engineering to trigger the OPM pathway with a lower energy barrier. The density-functional-theory (DFT) calculations reveal a strong electronic coupling between Ir and Mn via the Ir─O─Mn bond and a ready coupling of oxygeneous adsorbed on the Ir site with those on the Mn site, leading to an asymmetric oxygen coupling for the OER. The developed catalyst merely requires an overpotential of 240 mV to drive 10 mA cm-2 with the Ir mass-activity > 75 times higher than that of the IrO2. When used in the proton-exchange-membrane water-electrolyzers, it shows high performance and excellent stability at an industrial-level current density of 1.0 A cm-2.

Constructing Stable Bifunctional Electrocatalyst of Co─Co2Nb5O14 with Reversible Interface Reconstitution Ability for Sustainable Zn-Air Batteries

Transition metal and metal oxide heterojunctions have been widely studied as bifunctional oxygen reduction/evolution reaction (ORR/OER) electrocatalysts for Zn-air batteries, but the dynamic changes of transition metal oxides and the interface during catalysis are still unclear. Here, bifunctional electrocatalyst of Co─Co2Nb5O14 is reported, containing lattice interlocked Co nanodots and Co2Nb5O14 nanorods, which construct a strong metal-support interaction (SMSI) interface. Unlike the recognition that transition metals mainly serve as ORR active sites and metal oxides as OER active sites, it is found that both ORR/OER sites originate from Co2Nb5O14, while Co acts as an electronic regulatory unit. The SMSI interface promotes dynamic electron transfer between Co/Co2Nb5O14, and the reversible active sites of Nb4+/Nb5+ realize bidirectional adsorption/migration of intermediates, thereby achieving dynamic reversible interface reconstitution. The electrocatalyst shows a high ORR half-wave potential of 0.84 V, a low OER overpotential of 296.3 mV, and great cycling stability over 30000 s. The ZAB shows a high capacity of 850.6 mA h·gZn-1 and can stably run 2050 cycles at 10 mA·cm⁻2. Moreover, the constructed solid-state ZAB also shows leading cycling stability in comparison with the previous studies.

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.

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

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

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

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

IrO2/MnO2 metal oxide-support interaction enables robust acidic water oxidation

The sluggish kinetics, poor stability, and high iridium loading in acidic oxygen evolution reaction (OER) present significant challenges for proton exchange membrane water electrolyzers (PEMWE). While supported catalysts can enhance the utilization and activity of Ir atoms, they often fail to mitigate the detrimental effects of over-oxidation and dissolution of Ir. Here, we leverage the redox properties of the Mn3+/Mn4+ couple as electronic modulators to develop a low-iridium, durable electrocatalyst for acidic OER. Specifically, IrO2 nanoparticles are anchored onto MnO2 nanowires (denoted as IrO2/MnO2), through a molten salt-assisted synthesis method. This optimized IrO2/MnO2 electrocatalyst features a substantially reduced iridium content and enhanced electronic structure due to strong metal-support interactions. Remarkably, the IrO2/MnO2 catalyst demonstrates 7-fold increase in intrinsic activity and superior durability compared to commercial IrO2. Both theoretical and experimental results indicate that dynamic electron transfer between Ir and Mn facilitates the rapid formation of highly oxidized iridium sites while simultaneously preventing excessive oxidation, thereby enhancing both the kinetics and stability for OER. A PEMWE utilizing IrO2/MnO2 as the anode catalyst achieves 2000 mA cm-2 @ 1.89 V without requiring supporting acidic electrolyte. Importantly, the PEMWE exhibits negligible degradation under harsh industrial operating conditions (1000 mA cm-2) with an Ir loading as low as 0.5 mg cm-2, while maintaining a low energy consumption of 45.58 kWh kg-1 H2, corresponding to the green hydrogen production cost of $0.9 kg-1 H2, significantly lower than the 2026 US-DOE target, underscoring its potential for practical application.

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.

Local Oxygen Vacancy-Mediated Oxygen Exchange for Active and Durable Acidic Water Oxidation

Developing an active and durable acidic oxygen evolution reaction (OER) catalyst is vital for implementing a proton exchange membrane water electrolyzer (PEMWE) in sustainable hydrogen production. However, it remains dauntingly challenging to balance high activity and long-term stability under harsh acidic and oxidizing conditions. Herein, through developing the universal rare-earth participated pyrolysis-leaching approach, we customized the active and long lifespan pseudo-amorphous IrOx with locally ordered rutile IrO2 and unique defect sites (IrOx-3Nd). IrOx-3Nd achieved a low overpotential of 206 mV and long-term durability of 2200 h with a slow degradation rate of 0.009 mV  h-1 at 10 mA cm-2, and, more importantly, high efficiency in PEMWE (1.68 V at 1 A cm-2 for 1000 h) for practical hydrogen production. Utilizing in situ characterizations and theoretical calculations, we found that lattice oxygen vacancies (Ov) and contracted Ir-O in locally ordered rutile IrO2 induced the Ov-modulated lattice oxygen exchange process, wherein thermodynamically spontaneous occupation of surface hydroxyl groups on Ov and effective promotion of O─O coupling and lattice oxygen recovery accounted for enhanced activity and durability. This work underscores the importance of tailor-made local configuration in boosting activity and durability of OER catalyst and different insights into the promotion mechanism.

An Up-Scalable Solid-State Approach to Synthesize Iridium Nanoparticles on ATO for Water Splitting

Proton exchange membrane water electrolysis (PEMWE) technology commercialization strongly relies on developing efficient and cost-effective anode catalysts. One key challenge is the high cost associated with IrO2, which can be mitigated by reducing iridium (Ir) loading. A promising approach to achieving this is using a conductive support material to anchor Ir/IrO2. In this study, we explored depositing metallic Ir on antimony-doped tin oxide (ATO) using a solid-state method. This approach is straightforward and time-efficient. Among four samples with 50 wt % Ir loading, one prepared with NaOH in 100% ethanol (Ir/ATO-NE) exhibited the highest specific oxygen evolution reaction (OER) performance. The Ir/ATO-NE catalyst achieved 340 A gIr-1 at 1.6 V (versus RHE), surpassing a commercial IrO2 catalyst, which showed 282 A gIr-1. Additionally, Ir/ATO-NE demonstrated the lowest Tafel slope, indicating enhanced oxygen evolution kinetics and long-term durability comparable to commercial catalysts. Electron microscopy revealed uniform Ir nanoparticle (NP) sizes and a complete layer of Ir NPs on the support, in contrast to other samples. This study introduces a synthesis protocol for Ir catalysts that is efficient, simple, and effective for oxygen evolution in acidic media.

Bias-Induced Ga-O-Ir Interface Breaks the Limits of Adsorption-Energy Scaling Relationships for High-Performing Proton Exchange Membrane Electrolyzers

Rationally manipulating the in situ formed catalytically active surface of catalysts remains a significant challenge for achieving highly efficient water electrolysis. Herein, we present a bias-induced activation strategy to modulate in situ Ga leaching and trigger the dynamic surface restructuring of lamellar Ir@Ga2O3 for the electrochemical oxygen evolution reaction. The in situ reconstructed Ga-O-Ir interface sustains high water oxidation rates at oxygen evolution reaction (OER) overpotentials. We found that OER at the Ga-O-Ir interface follows a bi-nuclear adsorbate evolution mechanism with unsaturated IrOx as the active sites, while GaOx atoms play an indirect role in promoting water dissociation to form OH* and transferring OH* to Ir sites. This breaks the scaling relationship of the adsorption energies between OH* and OOH*, significantly lowering the energy barrier of the rate-limiting step and greatly increasing reactivity. The Ir@Ga2O3 catalyst achieves lower overpotentials, a current density of 2 A cm-2 at 1.76 V, and stable operation up to 1 A cm-2 in scalable proton exchange membrane water electrolyzer (PEMWE) at 1.63 V, maintaining stable operation at 1 A cm-2 over 1000 hours with a degradation rate of 11.5 μV h-1. This work prompted us to jointly address substrate-catalyst interactions and catalyst reconstruction, an underexplored path, to improve activity and stability in Ir PEMWE anodes.

Advances in Oxygen Evolution Reaction Electrocatalysts via Direct Oxygen-Oxygen Radical Coupling Pathway

Oxygen evolution reaction (OER) is a cornerstone of various electrochemical energy conversion and storage systems, including water splitting, CO2/N2 reduction, reversible fuel cells, and rechargeable metal-air batteries. OER typically proceeds through three primary mechanisms: adsorbate evolution mechanism (AEM), lattice oxygen oxidation mechanism (LOM), and oxide path mechanism (OPM). Unlike AEM and LOM, the OPM proceeds via direct oxygen-oxygen radical coupling that can bypass linear scaling relationships of reaction intermediates in AEM and avoid catalyst structural collapse in LOM, thereby enabling enhanced catalytic activity and stability. Despite its unique advantage, electrocatalysts that can drive OER via OPM remain nascent and are increasingly recognized as critical. This review discusses recent advances in OPM-based OER electrocatalysts. It starts by analyzing three reaction mechanisms that guide the design of electrocatalysts. Then, several types of novel materials, including atomic ensembles, metal oxides, perovskite oxides, and molecular complexes, are highlighted. Afterward, operando characterization techniques used to monitor the dynamic evolution of active sites and reaction intermediates are examined. The review concludes by discussing several research directions to advance OPM-based OER electrocatalysts toward practical applications.

Durable Acidic Oxygen Evolution Via Self-Construction of Iridium Oxide/Iridium-Tantalum Oxide Bi-Layer Nanostructure with Dynamic Replenishment of Active Sites

Proton exchange membrane (PEM) water electrolysis presents considerable advantages in green hydrogen production. Nevertheless, oxygen evolution reaction (OER) catalysts in PEM water electrolysis currently encounter several pressing challenges, including high noble metal loading, low mass activity, and inadequate durability, which impede their practical application and commercialization. Here we report a self-constructed layered catalyst for acidic OER by directly using an Ir-Ta-based metallic glass as the matrix, featuring a nanoporous IrO2 surface formed in situ on the amorphous IrTaOx nanostructure during OER. This distinctive architecture significantly enhances the accessibility and utilization of Ir, achieving a high mass activity of 1.06 A mgIr-1 at a 300 mV overpotential, 13.6 and 31.2 times greater than commercial Ir/C and IrO2, respectively. The catalyst also exhibits superb stability under industrial-relevant current densities in acid, indicating its potential for practical uses. Our analyses reveal that the coordinated nature of the surface-active Ir species is effectively modulated through electronic interaction between Ir and Ta, preventing them from rapidly evolving into high valence states and suppressing the lattice oxygen participation. Furthermore, the underlying IrTaOx dynamically replenishes the depletion of surface-active sites through inward crystallization and selective dissolution, thereby ensuring the catalyst's long-term durability.

Highly conductive composite anode catalysts featuring a fused Ir nano-network towards proton exchange membrane electrocatalysis

A boride-assisted method has been presented to synthesize a fused Ir nano-network supported on TiO2 as highly conductive composite catalysts (Ir NN@TiO2) for the reaction of oxygen evolution in acid. The Ir NN@TiO2 can be utilized to construct an anode catalyst layer of a proton exchange membrane water electrolyzer (PEMWE) with a low iridium content of 0.3 mgIr cm-2. The low-iridium-loading PEMWE exhibits excellent performance, i.e., 2.9 A cm-2@1.9 V with Nafion 115 membrane, and operates stably at a current density of 1.0 A cm-2 for over 1000 h.

Spillover of active oxygen intermediates of binary RuO2/Nb2O5 nanowires for highly active and robust acidic oxygen evolution

Over-oxidation of surface ruthenium active sites of RuOx-based electrocatalysts leads to the formation of soluble high-valent Ru species and subsequent structural collapse of electrocatalysts, which results in their low stability for the acidic oxygen evolution reaction (OER). Herein, a binary RuO2/Nb2O5 electrocatalyst with abundant and intimate interfaces has been rationally designed and synthesized to enhance its OER activity in acidic electrolyte, delivering a low overpotential of 179 mV at 10 mA cm-2, a small Tafel slope of 73 mV dec-1, and a stabilized catalytic durability over a period of 750 h. Extensive experiments have demonstrated that the spillover of active oxygen intermediates from RuO2 to Nb2O5 and the subsequent participation of lattice oxygen of Nb2O5 instead of RuO2 for the acidic OER suppressed the over-oxidation of surface ruthenium species and thereby improved the catalytic stability of the binary electrocatalysts.

Strong Heteroatomic Bond-Induced Confined Restructuring on Ir-Mn Intermetallics Enable Robust PEM Water Electrolyzers

Low-iridium acid-stabilized electrocatalysts for efficient oxygen evolution reaction (OER) are crucial for the market deployment of proton exchange membrane (PEM) water electrolysis. Manipulating the in situ reconstruction of Ir-based catalysts with favorable kinetics is highly desirable but remains elusive. Herein, we propose an atomic ordering strategy to modulate the dynamic surface restructuring of catalysts to break the activity/stability trade-off. Under working conditions, the strong heteroatom-bonded structure triggers rational surface-confined reconstruction to form self-stabilizing amorphous (oxy)hydroxides on the model Ir-Mn intermetallic (IMC). Combined in situ/ex situ characterizations and theoretical analysis demonstrate that the induced strong covalent Ir-O-Mn units in the catalytic layer weaken the formation barrier of OOH* and promote the preferential dynamic replenishment/conversion pathway of H2O molecules to suppress the uncontrollable participation of lattice oxygen (about 2.6 times lower than that of pure Ir). Thus, a PEM cell with Ir-Mn IMC as anode "pre-electrocatalyst" (0.24 mgIr cm-2) delivers an impressive performance (3.0 A cm-2@1.851 V@80 °C) and runs stably at 2.0 A cm-2 for more than 2,000 h with the cost of USD 0.98 per kg H2, further validating its promising application. This work highlights surface-confined evolution triggered by strong heteroatom bonds, providing insights into the design of catalysts involving surface reconstruction.

Lattice-Doped Ir Cooperating with Surface-Anchored IrOx for Acidic Oxygen Evolution Reaction with Ultralow Ir Loading

Reducing iridium (Ir) loading while maintaining efficiency and stability is crucial for the acidic oxygen evolution reaction (OER). In this study, we develop a synthetic method of sequential electrochemical deposition and high-temperature thermal shock to produce an IrOx/Ir-WO3 electrocatalyst with ∼1.75 nm IrOx nanoparticles anchoring on Ir-doped WO3 nanosheets. The IrOx/Ir-WO3 electrocatalyst with a low Ir loading of 0.035 mg cm-2 demonstrates a low overpotential of 239 mV to achieve a current density of 10 mA cm-2 and a mass activity of 6.6 × 104 A gIr-1 @1.75 V vs RHE in 0.5 M H2SO4. IrOx/Ir-WO3 on carbon paper as the anode and Pt/C as the cathode work stably for 40 h at 30 mA cm-2 in a proton exchange membrane water electrolyzer. It is found that the cooperation of lattice-doped Ir and surface-anchored IrOx enhances the activity and stability of IrOx/Ir-WO3 for acidic OER. Specifically, the doped Ir reduces the electron density of the anchored IrOx, thus optimizing the adsorption energy of oxygen-containing intermediates and the kinetic barrier of H2O dissociation, leading to an enhanced activity of IrOx/Ir-WO3. Also, the Ir-WO3 support provides electrons to retard the overoxidation and dissolution of Ir atoms from the anchored IrOx during acidic OER.

Efficient Nitrate to Ammonia Conversion on Bifunctional IrCu4 Alloy Nanoparticles

Electrochemical nitrate reduction (NO3RR) to ammonia presents a promising alternative strategy to the traditional Haber-Bosch process. However, the competitive hydrogen evolution reaction (HER) reduces the Faradaic efficiency toward ammonia, while the oxygen evolution reaction (OER) increases the energy consumption. This study designs IrCu4 alloy nanoparticles as a bifunctional catalyst to achieve efficient NO3RR and OER while suppressing the unwanted HER. This is achieved by operating the NO3RR at positive potentials using the IrCu4 catalyst, which allows a Faradaic efficiency of 93.6% for NO3RR. When applied to OER catalysis, the IrCu4 alloy also shows excellent results, with a relatively low overpotential of 260 mV at 10 mA cm-2. Stable ammonia production can be achieved for 50 h in a 16 cm2 flow electrolyzer in simulated working conditions. Our research provides a pathway for optimizing NO3RR through bifunctional catalysts in a tandem approach.

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.

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.

Advanced Ir-Based Alloy Electrocatalysts for Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzer (PEMWE) coupled with renewable energy to produce hydrogen is an important part of clean energy acquisition in the future. However, the slow kinetics of the oxygen evolution reaction (OER) hinder the large-scale application of PEM water electrolysis technology. To deal with the problems existing in the PEM electrolyzer and improve the electrolysis efficiency, substantial efforts are invested in the development of cost-effective and stable electrocatalysts. Within this scenario, the different OER reaction mechanisms are first discussed here. Based on the in-depth understanding of the reaction mechanism, the research progress of low-iridium noble metal alloys is reviewed from the aspects of special effects, design strategies, reaction mechanisms, and synthesis methods. Finally, the challenges and prospects of the future development of high-efficiency and low-precious metal OER electrocatalysts are presented.

Transforming Adsorbate Surface Dynamics in Aqueous Electrocatalysis: Pathways to Unconstrained Performance

Developing highly efficient catalysts to accelerate sluggish electrode reactions is critical for the deployment of sustainable aqueous electrochemical technologies, yet remains a great challenge. Rationally integrating functional components to tailor surface adsorption behaviors and adsorbate dynamics would divert reaction pathways and alleviate energy barriers, eliminating conventional thermodynamic constraints and ultimately optimizing energy flow within electrochemical systems. This approach has, therefore, garnered significant interest, presenting substantial potential for developing highly efficient catalysts that simultaneously enhance activity, selectivity, and stability. The immense promise and rapid evolution of this design strategy, however, do not overshadow the substantial challenges and ambiguities that persist, impeding the realization of significant breakthroughs in electrocatalyst development. This review explores the latest insights into the principles guiding the design of catalytic surfaces that enable favorable adsorbate dynamics within the contexts of hydrogen and oxygen electrochemistry. Innovative approaches for tailoring adsorbate-surface interactions are discussed, delving into underlying principles that govern these dynamics. Additionally, perspectives on the prevailing challenges are presented and future research directions are proposed. By evaluating the core principles and identifying critical research gaps, this review seeks to inspire rational electrocatalyst design, the discovery of novel reaction mechanisms and concepts, and ultimately, advance the large-scale implementation of electroconversion technologies.

Enhanced Acidic Oxygen Evolution Reaction Performance by Anchoring Iridium Oxide Nanoparticles on Co3O4

The sluggish kinetics of the anodic process, known as the oxygen evolution reaction (OER), has posed a significant challenge for the practical application of proton exchange membrane water electrolyzers in industrial settings. This study introduces a high-performance OER catalyst by anchoring iridium oxide nanoparticles (IrO2) onto a cobalt oxide (Co3O4) substrate via a two-step combustion method. The resulting IrO2@Co3O4 catalyst demonstrates a significant enhancement in both catalytic activity and stability in acidic environments. Notably, the overpotential required to attain a current density of 10 mA cm-2, a commonly used benchmark for comparison, is merely 301 mV. Furthermore, stability is maintained over a duration of 80 h, as confirmed by the minimal rise in overpotential. Energy spectrum characterizations and experimental results reveal that the generation of OER-active Ir3+ species on the IrO2@Co3O4 surface is induced by the strong interaction between IrO2 and Co3O4. Theoretical calculations further indicate that IrO2 sites loaded onto Co3O4 have a lower energy barrier for *OOH deprotonation to form desorbed O2. Moreover, this interaction also stabilizes the iridium active sites by maintaining their chemical state, leading to superior long-term stability. These insights could significantly impact the strategies for designing and synthesizing more efficient OER electrocatalysts for broader industrial application.

Ir-O-Mn embedded in porous nanosheets enhances charge transfer in low-iridium PEM electrolyzers

Using metal oxides to disperse iridium (Ir) in the anode layer proves effective for lowering Ir loading in proton exchange membrane water electrolyzers (PEMWE). However, the reported low-Ir-based catalysts still suffer from unsatisfying electrolytic efficiency and durability under practical industrial working conditions, mainly due to insufficient catalytic activity and mass transport in the catalyst layer. Herein we report a class of porous heterogeneous nanosheet catalyst with abundant Ir-O-Mn bonds, achieving a notable mass activity of 4 A mgIr-1 for oxygen evolution reaction at an overpotential of 300 mV, which is 150.6 times higher than that of commercial IrO2. Ir-O-Mn bonds are unraveled to serve as efficient charge-transfer channels between in-situ electrochemically-formed IrOx clusters and MnOx matrix, fostering the generation and stabilization of highly active Ir3+ species. Notably, Ir/MnOx-based PEMWE demonstrates comparable performance under 10-fold lower Ir loading (0.2 mgIr cm-2), taking a low cell voltage of 1.63 V to deliver 1 A cm-2 for over 300 h, which positions it among the elite of low Ir-based PEMWEs.

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.

Identifying and tuning coordinated water molecules for efficient electrocatalytic water oxidation

Coordination complexes are promising candidates for powerful electrocatalytic oxygen evolution reaction but challenges remain in favoring the kinetics behaviors through local coordination regulation. Herein, by refining the synergy of carboxylate anions and multiconjugated benzimidazole ligands, we tailor a series of well-defined and stable coordination complexes with three-dimensional supramolecular/coordinated structures. The coordinated water as potential open coordination sites can directly become intermediates, while the metal center easily achieves re-coordination with water molecules in the pores to resist lattice oxygen dissolution. In situ experiments and theory simulations indicate that nickel centers with neighboring coordinated water molecules follow an intramolecular oxygen coupling mechanism with a low thermodynamic energy barrier. With more coordinated water introduced, an optimized intramolecular oxygen coupling process may appear for favoring the reaction kinetics. As such, a low overpotential of 248 mV at 10 mA cm-2 and long-term stability of 200 h are achieved. This study underscores the potential of crafting coordinated water molecules for efficient electrocatalysis applications.

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.

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

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

A Complex Oxide Containing Inherent Peroxide Ions for Catalyzing Oxygen Evolution Reactions in Acid

Proton exchange membrane water electrolyzers powered by sustainable energy represent a cutting-edge technology for renewable hydrogen generation, while slow anodic oxygen evolution reaction (OER) kinetics still remains a formidable obstacle that necessitates basic comprehension for facilitating electrocatalysts' design. Here, we report a low-iridium complex oxide La1.2Sr2.7IrO7.33 with a unique hexagonal structure consisting of isolated Ir(V)O6 octahedra and true peroxide O22- groups as a highly active and stable OER electrocatalyst under acidic conditions. Remarkably, La1.2Sr2.7IrO7.33, containing 59 wt % less iridium relative to the benchmark IrO2, shows about an order of magnitude higher mass activity, 6-folds higher intrinsic activity than the latter, and also surpasses the state-of-the-art Ir-based oxides ever reported. Combined electrochemical, spectroscopic, and density functional theory investigations reveal that La1.2Sr2.7IrO7.33 follows the peroxide-ion participation mechanism under the OER condition, where the inherent peroxide ions with accessible nonbonded oxygen states are responsible for the high OER activity. This discovery offers an innovative strategy for designing advanced catalysts for various catalytic applications.

PEDOT:PSS Nanoparticle Membranes for Organic Solvent Nanofiltration

Recycling of valuable solutes and recovery of organic solvents via organic solvent nanofiltration (OSN) are important for sustainable development. However, the trade-off between solvent permeability and solute rejection hampers the application of OSN membranes. To address this issue, the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) nanoparticle membrane with hierarchical pores is constructed for OSN via vacuum filtration. The small pores (the free volume of the polymer chain) charge for the solute rejection (high rejection efficiency for low molecule weight solute) and allow solvent passing while the large pores (the void between two PEDOT:PSS nanoparticles) promote the solvent transport. Owing to the lack of connectivity among the large pores, the fabricated PEDOT:PSS nanoparticle membrane enhanced solvent permeance while maintaining a high solute rejection efficiency. The optimized PEDOT:PSS membrane affords a MeOH permeance of 7.2 L m-2 h-1 bar-1 with over 90% rejection of organic dyes, food additives, and photocatalysts. Moreover, the rigidity of PEDOT endows the membrane with distinctive stability under high-pressure conditions. The membrane is used to recycle the valuable catalysts in a methanol solution for 150 h, maintaining good separation performance. Considering its high separation performance and stability, the proposed PEDOT:PSS membrane has great potential for industrial applications.

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

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

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.

Extremely Active and Robust Ir-Mn Dual-Atom Electrocatalyst for Oxygen Evolution Reaction by Oxygen-Oxygen Radical Coupling Mechanism

A novel Ir-Mn dual-atom electrocatalyst is synthesized by a facile ion-exchange method by incorporating Ir in SrMnO3, which yields an extremely high activity and stability for the oxygen evolution reaction (OER). The ion exchange process occurs in a self-limitation way, which favors the formation of Ir-Mn dual-atom in the IrMnO9 unit. The incorporation of Ir modulates the electronic structure of both Ir and Mn, thereby resulting in a shorter distance of the Ir-Mn dual-atom (2.41 Å) than the Mn-Mn dual-atom (2.49 Å). The modulated Ir-Mn dual-atom enables the same spin direction O (↑) of the adsorbed *O intermediates, thus facilitating the direct coupling of the two adsorbed *O intermediates to release O2 via the oxygen-oxygen radical coupling mechanism. Electrochemical tests reveal that the Ir-SrMnO3 exhibits a superior OER's activity with a low overpotential of 207 mV at 10 mA cm-2 and achieves a mass specific activity of 1100 A gIr -1 at 1.5 V. The proton-exchange-membrane water electrolyzer with the Ir-SrMnO3 catalyst exhibits a low electrolysis voltage of 1.63 V at 1.0 A cm-2 and a stable 2000-h operation with a decay of only 15 μV h-1 at 0.5 A cm-2.

Construction of the Co3O4/Nb2O5 Composite Catalyst with a Prickly Spherelike Architecture for CO2 Cycloaddition with Styrene Oxide

A high-performance Nb2O5-based catalyst for the cycloaddition of CO2 with SO is designed by properly unifying the concepts of compositional regulation and architectural engineering. The Co3O4/Nb2O5 composite catalyst shows an intriguing prickly spherelike morphology. It exhibits a high styrene carbonate (SC) yield of 94.3% within 4 h (0.0824 mol g-1 h-1) under mild reaction conditions (0.4 MPa of CO2 and a reaction temperature of 90 °C) assisted by tetrabutylammonium bromide (TBAB). The coupling of Co3O4, which chemically interacts with Nb2O5, can effectively modulate the electronic structures of Nb2O5, constructing abundant acid/base sites for effectively activating the reactants and boosting the intrinsic activity. The high activity, cost-effectiveness, and good recyclability make the tailor-made Co3O4/Nb2O5 prickly spheres more appealing for commercial applications. This work offers new insights into designing and constructing well-integrated metal oxide composites for the cycloaddition of CO2 with an epoxide.

Optimal Electrocatalyst Design Strategies for Acidic Oxygen Evolution

Hydrogen, a clean resource with high energy density, is one of the most promising alternatives to fossil. Proton exchange membrane water electrolyzers are beneficial for hydrogen production because of their high current density, facile operation, and high gas purity. However, the large-scale application of electrochemical water splitting to acidic electrolytes is severely limited by the sluggish kinetics of the anodic reaction and the inadequate development of corrosion- and highly oxidation-resistant anode catalysts. Therefore, anode catalysts with excellent performance and long-term durability must be developed for anodic oxygen evolution reactions (OER) in acidic media. This review comprehensively outlines three commonly employed strategies, namely, defect, phase, and structure engineering, to address the challenges within the acidic OER, while also identifying their existing limitations. Accordingly, the correlation between material design strategies and catalytic performance is discussed in terms of their contribution to high activity and long-term stability. In addition, various nanostructures that can effectively enhance the catalyst performance at the mesoscale are summarized from the perspective of engineering technology, thus providing suitable strategies for catalyst design that satisfy industrial requirements. Finally, the challenges and future outlook in the area of acidic OER are presented.

Enriched Oxygen Coverage Localized within Ir Atomic Grids for Enhanced Oxygen Evolution Electrocatalysis

Inefficient active site utilization of oxygen evolution reaction (OER) catalysts have limited the energy efficiency of proton exchange membrane (PEM) water electrolysis. Here, an atomic grid structure is demonstrated composed of high-density Ir sites (≈10 atoms per nm2) on reactive MnO2-x support which mediates oxygen coverage-enhanced OER process. Experimental characterizations verify the low-valent Mn species with decreased oxygen coordination in MnO2-x exert a pivotal impact in the enriched oxygen coverage on the surface during OER process, and the distributed Ir atomic grids, where highly electrophilic Ir─O(II-δ)- bonds proceed rapidly, render intense nucleophilic attack of oxygen radicals. Thereby, this metal-support cooperation achieves ultra-low overpotentials of 166 mV at 10 mA cm-2 and 283 mV at 500 mA cm-2, together with a striking mass activity which is 380 times higher than commercial IrO2 at 1.53 V. Moreover, its high OER performance also markedly surpasses the commercial Ir black catalyst in PEM electrolyzers with long-term stability.

Designing neighboring-site activation of single atom via tunnel ions for boosting acidic oxygen evolution

Realizing an efficient turnover frequency in the acidic oxygen evolution reaction by modifying the reaction configuration is crucial in designing high-performance single-atom catalysts. Here, we report a "single atom-double site" concept, which involves an activatable inert manganese atom redox chemistry in a single-atom Ru-Mn dual-site platform with tunnel Ni ions as the trigger. In contrast to conventional single-atom catalysts, the proposed configuration allows direct intramolecular oxygen coupling driven by the Ni ions intercalation effect, bypassing the secondary deprotonation step instead of the kinetically sluggish adsorbate evolution mechanism. The strong bonding of Ni ions activates the inert manganese terminal groups and inhibits the cross-site disproportionation process inherent in the Mn scaffolding, which is crucial to ensure the dual-site platform. As a result, the single-atom Ru-Ni-Mn octahedral molecular sieves catalyst delivers a low overpotential, adequate mass activity and good stability.

Supported IrO2 Nanocatalyst with Multilayered Structure for Proton Exchange Membrane Water Electrolysis

The design of a low-iridium-loading anode catalyst layer with high activity and durability is a key challenge for a proton exchange membrane water electrolyzer (PEMWE). Here, the synthesis of a novel supported IrO2 nanocatalyst with a tri-layered structure, dubbed IrO2@TaOx@TaB that is composed of ultrasmall IrO2 nanoparticles anchored on amorphous TaOx overlayer of TaB nanorods is reported. The composite electrocatalyst shows great activity and stability toward the oxygen evolution reaction (OER) in acid, thanks to its dual-interface structural feature. The electronic interaction in IrO2/TaOx interface can regulate the coverage of surface hydroxyl groups, the Ir3+/ Ir4+ ratio, and the redox peak potential of IrO2 for enhancing OER activity, while the dense TaOx overlayer can prevent further oxidation of TaB substrate and stabilize the IrO2 catalytic layers for improving structural stability during OER. The IrO2@TaOx@TaB can be used to fabricate an anode catalyst layer of PEMWE with an iridium-loading as low as 0.26 mg cm-2. The low-iridium-loading PEMWE delivers high current densities at low cell voltages (e.g., 3.9 A cm-2@2.0 V), and gives excellent activity retention for more than 1500 h at 2.0 A cm-2 current density.

Half-metallization Atom-Fingerprints Achieved at Ultrafast Oxygen-Evaporated Pyrochlores for Acidic Water Oxidation

The stability and catalytic activity of acidic oxygen evolution reaction (OER) are strongly determined by the coordination states and spatial symmetry among metal sites at catalysts. Herein, an ultrafast oxygen evaporation technology to rapidly soften the intrinsic covalent bonds using ultrahigh electrical pulses is suggested, in which prospective charged excited states at this extreme avalanche condition can generate a strong electron-phonon coupling to rapidly evaporate some coordinated oxygen (O) atoms, finally leading to a controllable half-metallization feature. Simultaneously, the relative metal (M) site arrays can be orderly locked to delineate some intriguing atom-fingerprints at pyrochlore catalysts, where the coexistence of metallic bonds (M─M) and covalent bonds (M─O) at this symmetry-breaking configuration can partially restrain crystal field effect to generate a particular high-spin occupied state. This half-metallization catalyst can effectively optimize the spin-related reaction kinetics in acidic OER, giving rise to 10.3 times (at 188 mV overpotential) reactive activity than pristine pyrochlores. This work provides a new understanding of half-metallization atom-fingerprints at catalyst surfaces to accelerate acidic water oxidation.

Boron-Induced Interstitial Effects Drive Water Oxidation on Ordered Ir-B Compounds

Interstitial filling of light atoms strongly affects the electronic structure and adsorption properties of the parent catalyst due to ligand and ensemble effects. Different from the conventional doping and surface modification, constructing ordered intermetallic structures is more promising to overcome the dissolution and reconstruction of active sites through strong interactions generated by atomic periodic arrangement, achieving joint improvement in catalytic activity and stability. However, for tightly arranged metal lattices, such as iridium (Ir), obtaining ordered filling atoms and further unveiling their interstitial effects are still limited by highly activated processes. Herein, we report a high-temperature molten salt assisted strategy to form the intermetallic Ir-B compounds (IrB1.1) with ordered filling by light boron (B) atoms. The B residing in the interstitial lattice of Ir constitutes favorable adsorption surfaces through a donor-acceptor architecture, which has an optimal free energy uphill in rate-determining step (RDS) of oxygen evolution reaction (OER), resulting in enhanced activity. Meanwhile, the strong coupling of Ir-B structural units suppresses the demetallation and reconstruction behavior of Ir, ensuring catalytic stability. Such B-induced interstitial effects endow IrB1.1 with higher OER performance than commercial IrO2, which is further validated in proton exchange membrane water electrolyzers (PEMWEs).

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.

Atomically Dispersed Iridium on Polyimide Support for Acidic Oxygen Evolution

Designing a high-performing iridium (Ir) single-atom catalyst is desired for acidic water electrolysis, which shows enormous potential given its high catalytic activity toward acidic oxygen evolution reaction (OER) with minimum usage of precious Ir metal. However, it still remains a substantial challenge to stabilize the Ir single atoms during the OER operation without sacrificing the activity. Here, we report a high-performing OER catalyst by immobilizing Ir single atoms on a polyimide support, which exhibits a high mass activity on a carbon paper electrode while simultaneously achieving outstanding stability with negligible decay for 360 h. The resulting electrode (denoted as Ir1-PI@CP) reaches a 49.7-fold improvement in mass activity compared to the counterpart electrode prepared without polyimide support. Both our experimental and theoretical results suggest that, owing to the strong metal-support interactions, the polyimide support can enhance the Ir 5d states of Ir single atoms in Ir1-PI@CP, which can tailor the adsorption energies of intermediates and decrease the thermodynamic barrier at the rate-determining step of the OER, but also facilitate the proton-electron-transfer process and improve the reaction kinetics. This work offers an alternative avenue for developing single-atom catalysts with superior activity and durability toward various catalytic systems and beyond.

Toward Realistic Models of the Electrocatalytic Oxygen Evolution Reaction

The electrocatalytic oxygen evolution reaction (OER) supplies the protons and electrons needed to transform renewable electricity into chemicals and fuels. However, the OER is kinetically sluggish; it operates at significant rates only when the applied potential far exceeds the reversible voltage. The origin of this overpotential is hidden in a complex mechanism involving multiple electron transfers and chemical bond making/breaking steps. Our desire to improve catalytic performance has then made mechanistic studies of the OER an area of major scientific inquiry, though the complexity of the reaction has made understanding difficult. While historically, mechanistic studies have relied solely on experiment and phenomenological models, over the past twenty years ab initio simulation has been playing an increasingly important role in developing our understanding of the electrocatalytic OER and its reaction mechanisms. In this Review we cover advances in our mechanistic understanding of the OER, organized by increasing complexity in the way through which the OER is modeled. We begin with phenomenological models built using experimental data before reviewing early efforts to incorporate ab initio methods into mechanistic studies. We go on to cover how the assumptions in these early ab initio simulations─no electric field, electrolyte, or explicit kinetics─have been relaxed. Through comparison with experimental literature, we explore the veracity of these different assumptions. We summarize by discussing the most critical open challenges in developing models to understand the mechanisms of the OER.

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

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

Thermal Shock Synthesis for Loading Sub-2 nm Ru Nanoclusters on Titanium Nitride as a Remarkable Electrocatalyst toward Hydrogen Evolution Reaction

Heterogeneous catalysts embracing metal entities on suitable supports are profound in catalyzing various chemical reactions, and substantial synthetic endeavors in metal-support interaction modulation are made to enhance catalytic performance. Here, it is reported the loading of sub-2 nm Ru nanocrystals (NCs) on titanium nitride support (HTS-Ru-NCs/TiN) via a special Ru-Ti interaction using the high-temperature shock (HTS) method. Direct dechlorination of the adsorbed RuCl3, ultrafast nucleation process, and short coalescence duration at ultrahigh temperatures contribute to the immobilization of Ru NCs on TiN support via producing the Ru-Ti interfacial perimeter. HTS-Ru-NCs/TiN shows remarkable activity toward hydrogen evolution reaction (HER) in alkaline solution, yielding ultralow overpotentials of 16.3 and 86.6 mV to achieve 10 and 100 mA cm-2, respectively. The alkaline and anion exchange membrane water electrolyzers assembled using HTS-Ru-NCs/TiN yield 1.0 A cm-2 at 1.65 and 1.67 V, respectively, which validate its applicability in the hydrogen production industry. Theoretical simulations reveal the favorable formation of Ru─O and Ti─H bonds at the interfacial perimeters between Ru NCs and TiN, which accelerates the prerequisite water dissociation kinetics for enhanced HER activity. This exemplified work motivates the design of specific interfacial perimeters via the HTS strategy to improve the performance of diverse catalysis.

Manipulating electron redistribution between iridium and Co6Mo6C bridging with a carbon layer leads to a significantly enhanced overall water splitting performance at industrial-level current density

Nowadays, alkaline water electrocatalysis is regarded as an economical and highly effective approach for large-scale hydrogen production. Highly active electrocatalysts functioning under large current density are urgently required for practical industrial applications. In this work, we present a meticulously designed methodology to anchor Ir nanoparticles on Co6Mo6C nanofibers (Co6Mo6C-Ir NFs) bridging with nitrogen-doped carbon as efficient bifunctional electrocatalysts with both excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity and stability in alkaline media. With a low Ir content of 5.9 wt%, Co6Mo6C-Ir NFs require the overpotentials of only 348 and 316 mV at 1 A cm-2 for the HER and OER, respectively, and both maintain stability for at least 500 h at ampere-level current density. Consequently, an alkaline electrolyzer based on Co6Mo6C-Ir NFs only needs a voltage of 1.5 V to drive 10 mA cm-2 and possesses excellent durability for 500 h at 1 A cm-2. Density functional theory calculations reveal that the introduction of Ir nanoparticles is pivotal for the enhanced electrocatalytic activity of Co6Mo6C-Ir NFs. The induced interfacial electron redistribution between Ir and Co6Mo6C bridging with nitrogen-doped carbon dramatically modulates the electron structure and activates inert atoms to generate more highly active sites for electrocatalysis. Moreover, the optimized electronic structure is more conducive to the balance of the adsorption and desorption energies of reaction intermediates, thus significantly promoting the HER, OER and overall water splitting performance.