Perovskite-Type Solid Solution Nano-Electrocatalysts Enable Simultaneously Enhanced Activity and Stability for Oxygen Evolution

Complex Iridate Solid Solutions for Catalyzing Oxygen Evolution Reaction: Comparison of Elemental Leaching and Stability Numbers

As predicted by the Hume-Rothery rules, forming solid solutions of rutile IrO2 with other metal oxides that have different crystal structures is thermodynamically challenging. Consequently, achieving high solubility of foreign elements in Ir-based solid-solution oxides has been significantly limited. We demonstrate that hexagonal-perovskite BaIrO3 can serve as a flexible matrix oxide capable of incorporating a wide spectrum of (post)transition-metal cations with different electronic structures, ranging from d0 to d10 configurations. Among 12 cation solutes, Ta5+, Nb5+, and Zr4+ are found to be stable without substantial leaching during the oxygen evolution reaction (OER) under acidic condition. Acceptor-type trivalent cations, including Sc3+, In3+, and Fe3+, are identified to leach out gradually from the particle surface while enhancing the OER catalytic activity. Both X-ray absorption spectroscopy and ab initio molecular dynamics simulations consistently show that the robust face-sharing [IrO6] octahedral framework of the solid solutions remains unperturbed unless electrochemical leaching rapidly occurs. As a result, notably high S-numbers, on the order of 106, are achievable at pH = 1. Although our work focuses on single-element incorporation, it is suggested that the solid-solution methodology is an effective strategy for developing stable, long-lasting OER catalysts with further reduced Ir usage for acidic water oxidation.

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

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

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.

Alloying Strategy Regulating Size and Electronic Structure of Mo0.25Nb0.75Se2 to Achieve High-Performance Lithium-Sulfur Batteries

The utilization of catalysts in lithium--sulfur batteries has proven to be an efficacious avenue for enhancing the kinetics of polysulfide conversion. Specially, the size and electronic structure of catalysts play a pivotal role in harnessing the active sites and intrinsic catalysis activity. Outstanding MoSe2 and NbSe2 are were selected from 16 universal transition metal selenides based on the proposed binary descriptor. Then, an alloying strategy is was devised to prepare Mo0.25Nb0.75Se2 flakelets for further improvement of the intrinsic catalysis. The integration of density functional theory calculations and electrochemical analysis demonstrates that alloying Mo with Nb can regulate the surface energy and indexes of band match and lattice mismatch, thereby enabling Mo0.25Nb0.75Se2 to possess a small size, suitable adsorption energy and low reaction energy barrier. This optimization enhances the catalysis of sulfur reduction/evolution reaction and the reversible deposition/stripping of lithium. Consequently, an assembled Ah-level pouch cell is realized with dramatic cycle stability. With the electrolyte/sulfur ratio of 2.36 μL mg S-1, the cell can deliver a high energy density of up to 505.4 Wh kgtotal -1. This work pioneers a universal strategy for sculpting the geometric configurations and electronic structures of catalysts, to achieve enhanced catalytic activity and precise interpretation of structure-activity relationships.

Recent Progress in Balancing the Activity, Durability, and Low Ir Content for Ir-Based Oxygen Evolution Reaction Electrocatalysts in Acidic Media

Proton exchange membrane (PEM) electrolysis faces challenges associated with high overpotential and acidic environments, which pose significant hurdles in developing highly active and durable electrocatalysts for the oxygen evolution reaction (OER). Ir-based nanomaterials are considered promising OER catalysts for PEM due to their favorable intrinsic activity and stability under acidic conditions. However, their high cost and limited availability pose significant limitations. Consequently, numerous studies have emerged aimed at reducing iridium content while maintaining high activity and durability. Furthermore, the research on the OER mechanism of Ir-based catalysts has garnered widespread attention due to differing views among researchers. The recent progress in balancing activity, durability, and low iridium content in Ir-based catalysts is summarized in this review, with a particular focus on the effects of catalyst morphology, heteroatom doping, substrate introduction, and novel structure development on catalyst performance from four perspectives. Additionally, the recent mechanistic studies on Ir-based OER catalysts is discussed, and both theoretical and experimental approaches is summarized to elucidate the Ir-based OER mechanism. Finally, the perspectives on the challenges and future developments of Ir-based OER catalysts is presented.

Controlled Structural Activation of Iridium Single Atom Catalyst for High-Performance Proton Exchange Membrane Water Electrolysis

Iridium single atom catalysts are promising oxygen evolution reaction (OER) electrocatalysts for proton exchange membrane water electrolysis (PEMWE), as they can reduce the reliance on costly Ir in the OER catalysts. However, their practical application is hindered by their limited stability during PEMWE operation. Herein, we report on the activation of Ir-doped CoMn2O4 in acidic electrolyte that leads to enhanced activity and stability in acidic OER for long-term PEMWE operation. In-depth material characterization combined with electrochemical analysis and theoretical calculations reveal that activating Ir-doped CoMn2O4 induces controlled restructuring of Ir single atoms to IrOx nanoclusters, resulting in an optimized Ir configuration with outstanding mass activity of 3562 A gIr-1 at 1.53 V (vs RHE) and enhanced OER stability. The PEMWE using activated Ir-doped CoMn2O4 exhibited a stable operation for >1000 h at 250 mA cm-2 with a low degradation rate of 0.013 mV h-1, demonstrating its practical applicability. Furthermore, it remained stable for more than 400 h at a high current density of 1000 mA cm-2, demonstrating long-term durability under practical operation conditions.

Ensuring Stability of Anode Catalysts in PEMWE: From Material Design to Practical Application

Proton Exchange Membrane Water Electrolysis (PEMWE) has emerged as a clean and effective approach for the conversion and storage of renewable electricity, particularly due to its compatibility with fluctuating photovoltaic and wind power. However, the high cost and limited performance of iridium oxide catalysts (i. e. IrO2) used as anode catalyst in industrial PEM electrolyzers remain significant obstacles to widespread application. Although numerous low-cost and efficient alternative catalysts have been developed in laboratory research, comprehensive stability studies critical for industrial use are often overlooked. This leads to the failure of performance transfer from catalysts tested in liquid half-cell systems to those employed in PEM electrolyzers. This concept presents a thorough overview for the stability issues of anode catalysts in PEMWE, and discuss their degradation mechanisms in both liquid half-cell systems and PEM electrolyzers. We summarize the comprehensive protocols for assessment and characterization, analyze the effective strategies for stability optimization, and explore the opportunities for designing viable anode catalysts for PEM electrolyzers.

Dynamic Self-Healing of the Reconstructed Phase in Perovskite Oxides for Efficient and Stable Electrocatalytic OER

Neither electrocatalytic activity nor structural stability is inconsequential in water electrolysis. Unfortunately, they have to be compromised in practice, especially in the anodic redox chemistry of lattice oxygen. Herein, the discovery of a La1- xCexFeO3 perovskite is presented which shows both good stability and high catalytic activity. Using advanced operando characterizations, it is identified that the self-healing evolution of the La1- xCexFeO3 perovskite plays a key role during water oxidation in the lattice oxygen-mediated mechanism (LOM) pathway. Unlike irreversible reconstruction, the formation of reconstructed active-phase α-FeOOH is reversed by re-crystallization of surface La1- xCexFeO3 upon return to noncatalytic conditions. The self-healing transformation of the α-FeOOH termination layer on the stable La1- xCexFeO3 core imparts remarkable long-term stability as well as excellent electrocatalytic performance. As a result, a composition La0.9Ce0.1FeO3@FeOOH is designed that exhibits ultralow overpotentials of 257 and 312 mV to achieve 10 and 100 mA cm-2, respectively. The findings provide insight into self-healing behavior toward engineering perovskite oxides for efficient and stable oxygen electrocatalysis.

Integrating Interactive Ir Atoms into Titanium Oxide Lattice for Proton Exchange Membrane Electrolysis

Iridium (Ir)-based oxide is the state-of-the-art electrocatalyst for acidic water oxidation, yet it is restricted to a few Ir-O octahedral packing modes with limited structural flexibility. Herein, the geometric structure diversification of Ir is achieved by integrating spatially correlated Ir atoms into the surface lattice of TiO2 and its booting effect on oxygen evolution reaction (OER) is investigated. Notably, the resultant i-Ir/TiO2 catalyst exhibits much higher electrocatalytic activity, with an overpotential of 240 mV at 10 mA cm-2 and excellent stability of 315 h at 100 mA cm-2 in acidic electrolyte. Both experimental and theoretical findings reveal that flexible Ir─O─Ir coordination with varied geometric structure plays a crucial role in enhancing OER activity, which optimize the intermediate adsorption by adjusting the d-band center of active Ir sites. Operando characterizations demonstrate that the interactive Ir─O─Ir units can suppress over-oxidation of Ir, effectively widening the stable region of Ir species during the catalytic process. The proton exchange membrane (PEM) electrolyzer, equipped with i-Ir/TiO2 as an anode, gives a low driving voltage of 1.63 V at 2 A cm-2 and maintains stable performance for over 440 h. This work presents a general strategy to eliminate the inherent geometric limitations of IrOx species, thereby inspiring further development of advanced catalyst designs.

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.

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.

High-Valence Cu Induced by Photoelectric Reconstruction for Dynamically Stable Oxygen Evolution Sites

Oxygen vacancies are generally considered to play a crucial role in the oxygen evolution reaction (OER). However, the generation of active sites created by oxygen vacancies is inevitably restricted by their condensation and elimination reactions. To overcome this limitation, here, we demonstrate a novel photoelectric reconstruction strategy to incorporate atomically dispersed Cu into ultrathin (about 2-3 molecular) amorphous oxyhydroxide (a-CuM, M = Co, Ni, Fe, or Zn), facilitating deprotonation of the reconstructed oxyhydroxide to generate high-valence Cu. The in situ XAFS results and first-principles calculations reveal that Cu atoms are stabilized at high valence during the OER process due to Jahn-Teller distortion, resulting in para-type double oxygen vacancies as dynamically stable catalytic sites. The optimal a-CuCo catalyst exhibits a record-high mass activity of 3404.7 A g-1 at an overpotential of 300 mV, superior to the benchmarking hydroxide and oxide catalysts. The developed photoelectric reconstruction strategy opens up a new pathway to construct in situ stable oxygen vacancies by high-valence Cu single sites, which extends the design rules for creating dynamically stable active sites.

Built-In Electric Field Boosted Overall Water Electrolysis at Large Current Density for the Heterogeneous Ir/CoMoO4 Nanosheet Arrays

Advanced bifunctional electrocatalysts are essential for propelling overall water splitting (OWS) progress. Herein, relying on the obvious difference in the work function of Ir (5.44 eV) and CoMoO4 (4.03 eV) and the constructed built-in electric field (BEF), an Ir/CoMoO4/NF heterogeneous catalyst, with ultrafine Ir nanoclusters (1.8 ± 0.2 nm) embedded in CoMoO4 nanosheet arrays on the surface of nickel foam skeleton, is reported. Impressively, the Ir/CoMoO4/NF shows remarkable electrocatalytic bifunctionality toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), especially at large current densities, requiring only 13 and 166 mV to deliver 10 and 1000 mA cm-2 for HER and 196 and 318 mV for OER. Furthermore, the Ir/CoMoO4/NF||Ir/CoMoO4/NF electrolyzer demands only 1.43 and 1.81 V to drive 10 and 1000 mA cm-2 for OWS. Systematical theoretical calculations and tests show that the formed BEF not only optimizes interfacial charge distribution and the Fermi level of both Ir and CoMoO4, but also reduces the Gibbs free energy (ΔGH*, from 0.25 to 0.03 eV) and activation energy (from 13.6 to 8.9 kJ mol-1) of HER, the energy barrier (from 3.47 to 1.56 eV) and activation energy (from 21.1 to 13.9 kJ mol-1) of OER, thereby contributing to the glorious electrocatalytic bifunctionality.

KIr4O8 Nanowires with Rich Hydroxyl Promote Oxygen Evolution Reaction in Proton Exchange Membrane Water Electrolyzer

The sluggish kinetics for anodic oxygen evolution reaction (OER) and insufficient catalytic performance over the corresponding Ir-based catalysts are still enormous challenges in proton exchange membrane water electrolyzer (PEMWE). Herein, it is reported that KIr4O8 nanowires anode catalyst with more exposed active sites and rich hydroxyl achieves a current density of 1.0 A cm-2 at 1.68 V and possesses excellent catalytic stability with 1230 h in PEMWE. Combining in situ Raman spectroscopy and differential electrochemical mass spectroscopy results, the modified adsorbate evolution mechanism is proposed, wherein the rich hydroxyl in the inherent structure of KIr4O8 nanowires directly participates in the catalytic process for favoring the OER. Density functional theory calculation results further suggest that the enhanced proximity between Ir (d) and O (p) band center in KIr4O8 can strengthen the covalence of Ir-O, facilitate the electron transfer between adsorbents and active sites, and decrease the energy barrier of rate-determining step from OH* to O* during the OER.

Ru Single Atoms Integrated into Cobalt Oxide Spinel Structure with Interstitial Carbon for Enhanced Electrocatalytic Water Oxidation

Oxygen evolution reaction (OER) plays a critical role in energy conversion technologies. Significant progress has been made in alkaline conditions. In contrast, it remains a challenge to develop stable OER electrocatalysts in acidic conditions. Herein, a new strategy is reported to stabilize single atoms integrated into cobalt oxide spinel structure with interstitial carbon (Ru0.27Co2.73O4), where the optimized Ru0.27Co2.73O4 exhibits a low overpotential of 265, 326, and 367 mV to reach a current density of 10, 50, and 100 mA cm2, respectively. More importantly, Ru0.27Co2.73O4 has long-term stability of up to 100 h, representing one of the most stable OER electrocatalysts. X-ray adsorption spectroscopy (XAS) characterization and density functional theory (DFT) calculations jointly demonstrate that the significant catalytic performance of Ru0.27Co2.73O4 is due to the synergistic effect between the Ru and Co sites and the bridging O ligands, as well as the significant reduction of the OER energy barrier. This work provides a new perspective for designing and constructing efficient non-noble metal-based electrocatalysts for water splitting.

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

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

Locking the lattice oxygen in RuO2 to stabilize highly active Ru sites in acidic water oxidation

Ruthenium dioxide is presently the most active catalyst for the oxygen evolution reaction (OER) in acidic media but suffers from severe Ru dissolution resulting from the high covalency of Ru-O bonds triggering lattice oxygen oxidation. Here, we report an interstitial silicon-doping strategy to stabilize the highly active Ru sites of RuO2 while suppressing lattice oxygen oxidation. The representative Si-RuO2-0.1 catalyst exhibits high activity and stability in acid with a negligible degradation rate of ~52 μV h-1 in an 800 h test and an overpotential of 226 mV at 10 mA cm-2. Differential electrochemical mass spectrometry (DEMS) results demonstrate that the lattice oxygen oxidation pathway of the Si-RuO2-0.1 was suppressed by ∼95% compared to that of commercial RuO2, which is highly responsible for the extraordinary stability. This work supplied a unique mentality to guide future developments on Ru-based oxide catalysts' stability in an acidic environment.

Sr-Stabilized IrMnO2 Solid Solution Nano-Electrocatalysts with Superior Activity and Excellent Durability for Oxygen Evolution Reaction in Acid Media

The development of cost-effective catalysts for oxygen evolution reaction (OER) in acidic media is of paramount importance. This work reports that Sr-doped solid solution structural ultrafine IrMnO2 nanoparticles (NPs) (≈1.56 nm) on the carbon nanotubes (Sr-IrMnO2 /CNTs) are efficient catalysts for the acidic OER. Even with the Ir use dosage 3.5 times lower than that of the commercial IrO2 , the Sr-IrMnO2 /CNTs only need an overpotential of 236.0 mV to drive 10.0 mA cm-2 and show outstanding stability for >400.0 h. Its Ir mass activity is 39.6 times higher than that of the IrO2 at 1.53 V. The solid solution and Sr-doping structure of Sr-IrMnO2 are the main origin of the high catalytic activity and excellent stability of the Sr-IrMnO2 /CNTs. The density function theory calculations indicate that the solid solution structure can promote strong electronic coupling between Ir and Mn, lowering the energy barrier of the OER rate-determining step. The Sr-doping can enhance the stability of Ir against the chemical corrosion and demetallation. Water electrolyzers and proton exchange membrane water electrolyzers assembled with the Sr-IrMnO2 /CNTs show superb performance and excellent durability in the acid media.

Co-Co Dinuclear Active Sites Dispersed on Zirconium-doped Heterostructured Co9 S8 /Co3 O4 for High-current-density and Durable Acidic Oxygen Evolution

Developing cost-effective and sustainable acidic water oxidation catalysts requires significant advances in material design and in-depth mechanism understanding for proton exchange membrane water electrolysis. Herein, we developed a single atom regulatory strategy to construct Co-Co dinuclear active sites (DASs) catalysts that atomically dispersed zirconium doped Co9 S8 /Co3 O4 heterostructure. The X-ray absorption fine structure elucidated the incorporation of Zr greatly facilitated the generation of Co-Co DASs layer with stretching of cobalt oxygen bond and S-Co-O heterogeneous grain boundaries interfaces, engineering attractive activity of significantly reduced overpotential of 75 mV at 10 mA cm-2 , a breakthrough of 500 mA cm-2 high current density, and water splitting stability of 500 hours in acid, making it one of the best-performing acid-stable OER non-noble metal materials. The optimized catalyst with interatomic Co-Co distance (ca. 2.80 Å) followed oxo-oxo coupling mechanism that involved obvious oxygen bridges on dinuclear Co sites (1,090 cm-1 ), confirmed by in situ SR-FTIR, XAFS and theoretical simulations. Furthermore, a major breakthrough of 120,000 mA g-1 high mass current density using the first reported noble metal-free cobalt anode catalyst of Co-Co DASs/ZCC in PEM-WE at 2.14 V was recorded.

Strategies for improving the stability of perovskite for photocatalysis: A review of recent progress

Photocatalysis is currently a hot research field, which provides promising processes to produce green energy sources and other useful products, thus eventually benefiting carbon emission reduction and leading to a low-carbon future. The development and application of stable and efficient photocatalytic materials is one of the main technical bottlenecks in the field of photocatalysis. Perovskite has excellent performance in the fields of photocatalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), carbon dioxide reduction reaction (CO2RR), organic synthesis and pollutant degradation due to its unique structure, flexibility and resulting excellent photoelectric and catalytic properties. The stability problems caused by perovskite's susceptibility to environmental influences hinder its further application in the field of photocatalysis. Therefore, this paper innovatively summarizes and analyzes the existing methods and strategies to improve the stability of perovskite in the field of photocatalysis. Specifically, (i) component engineering, (ii) morphological control, (iii) hybridization and encapsulation are thought to improve the stability of perovskites while improving photocatalytic efficiency. Finally, the challenges and prospects of perovskite photocatalysts are discussed, which provides constructive thinking for the potential application of perovskite photocatalysts.

Electrocatalytic Water Oxidation Activity-Stability Maps for Perovskite Oxides Containing 3d, 4d and 5d Transition Metals

Improving catalytic activity without loss of catalytic stability is one of the core goals in search of low-iridium-content oxygen evolution electrocatalysts under acidic conditions. Here, we synthesize a family of 66 SrBO3 perovskite oxides (B=Ti, Ru, Ir) with different Ti : Ru : Ir atomic ratios and construct catalytic activity-stability maps over composition variation. The maps classify the multicomponent perovskites into chemical groups with distinct catalytic activity and stability for acidic oxygen evolution reaction, and highlights a chemical region where high catalytic activity and stability are achieved simultaneously at a relatively low iridium level. By quantifying the extent of hybridization of mixed transition metal 3d-4d-5d and oxygen 2p orbitals for multicomponent perovskites, we demonstrate this complex interplay between 3d-4d-5d metals and oxygen atoms in governing the trends in both activity and stability as well as in determining the catalytic mechanism involving lattice oxygen or not.

Densely populated tiny RuO2 crystallites supported by hierarchically porous carbon for full acidic water splitting

The exploitation of highly active bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic media has been a subject receiving immense interest. However, the existing catalysts usually suffer from low catalytic efficiency and poor corrosion resistance under acidic conditions. Herein, we report a facile molten salt method to fabricate ruthenium dioxide nanoparticles supported by hierarchically porous carbon (RuO2/PC) as a bifunctional electrocatalyst for full water splitting under strong acidic conditions. The formation of a densely populated nanocrystalline RuO2/carbon heterostructure helps expose catalytic sites, accelerates the mass transfer rate, and further enhances the acid resistance of RuO2 nanoparticles. The as-synthesized RuO2/PC consequently exhibits superior catalytic performance for the OER with an overpotential of 181 mV upon 10 mA cm-2 compared to that of the commercial RuO2 (343 mV) and a comparable performance to Pt/C for the HER (47.5 mV upon 10 mA cm-2) in 0.5 M H2SO4. The RuO2/PC shows promising stability with little degradation over ∼24 h. Impressively, the water electrolyzer based on RuO2/PC shows an overpotential of 326 mV at 10 mA cm-2, much lower than that of the electrolyzer based on the combination of Pt/C and RuO2 (400 mV), indicating its great potential towards practical application.

Unraveling the Most Relevant Features for the Design of Iridium Mixed Oxides with High Activity and Durability for the Oxygen Evolution Reaction in Acidic Media

Proton exchange membrane water electrolysis (PEMWE) is the technology of choice for the large-scale production of green hydrogen from renewable energy. Current PEMWEs utilize large amounts of critical raw materials such as iridium and platinum in the anode and cathode electrodes, respectively. In addition to its high cost, the use of Ir-based catalysts may represent a critical bottleneck for the large-scale production of PEM electrolyzers since iridium is a very expensive, scarce, and ill-distributed element. Replacing iridium from PEM anodes is a challenging matter since Ir-oxides are the only materials with sufficient stability under the highly oxidant environment of the anode reaction. One of the current strategies aiming to reduce Ir content is the design of advanced Ir-mixed oxides, in which the introduction of cations in different crystallographic sites can help to engineer the Ir active sites with certain characteristics, that is, environment, coordination, distances, oxidation state, etc. This strategy comes with its own problems, since most mixed oxides lack stability during the OER in acidic electrolyte, suffering severe structural reconstruction, which may lead to surfaces with catalytic activity and durability different from that of the original mixed oxide. Only after understanding such a reconstruction process would it be possible to design durable and stable Ir-based catalysts for the OER. In this Perspective, we highlight the most successful strategies to design Ir mixed oxides for the OER in acidic electrolyte and discuss the most promising lines of evolution in the field.

Lattice-Strain Engineering for Heterogenous Electrocatalytic Oxygen Evolution Reaction

The energy efficiency of metal-air batteries and water-splitting techniques is severely constrained by multiple electronic transfers in the heterogenous oxygen evolution reaction (OER), and the high overpotential induced by the sluggish kinetics has become an uppermost scientific challenge. Numerous attempts are devoted to enabling high activity, selectivity, and stability via tailoring the surface physicochemical properties of nanocatalysts. Lattice-strain engineering as a cutting-edge method for tuning the electronic and geometric configuration of metal sites plays a pivotal role in regulating the interaction of catalytic surfaces with adsorbate molecules. By defining the d-band center as a descriptor of the structure-activity relationship, the individual contribution of strain effects within state-of-the-art electrocatalysts can be systematically elucidated in the OER optimization mechanism. In this review, the fundamentals of the OER and the advancements of strain-catalysts are showcased and the innovative trigger strategies are enumerated, with particular emphasis on the feedback mechanism between the precise regulation of lattice-strain and optimal activity. Subsequently, the modulation of electrocatalysts with various attributes is categorized and the impediments encountered in the practicalization of strained effect are discussed, ending with an outlook on future research directions for this burgeoning field.

Ruthenium-Manganese Solid Solution Oxide with Enhanced Performance for Acidic and Alkaline Oxygen Evolution Reaction

Proton exchange membrane water electrolysers and alkaline exchange membrane water electrolysers for hydrogen production suffer from sluggish kinetics and the limited durability of the electrocatalyst toward oxygen evolution reaction (OER). Herein, a rutile Ru0.75 Mn0.25 O2-δ solid solution oxide featured with a hierarchical porous structure has been developed as an efficient OER electrocatalyst in both acidic and alkaline electrolyte. Specifically, compared with commercial RuO2 , the catalyst displays a superior reaction kinetics with small Tafel slope of 54.6 mV dec-1 in 0.5 M H2 SO4 , thus allowing a low overpotential of 237 and 327 mV to achieve the current density of 10 and 100 mA cm-2 , respectively, which is attributed to the enhanced electrochemically active surface area from the porous structure and the increased intrinsic activity owing to the regulated Ru>4+ proportion with Mn incorporation. Additionally, the sacrificial dissolution of Mn relieves the leaching of active Ru species, leading to the extended OER durability. Besides, the Ru0.75 Mn0.25 O2-δ catalyst also shows a highly improved OER performance in alkaline electrolyte, rendering it a versatile catalyst for water splitting.

Custom-Made Piezoelectric Solid Solution Material for Cancer Therapy

Piezoelectric material-mediated sonodynamic therapy (SDT) has received considerable research interest in cancer therapy. However, the simple applications of conventional piezoelectric materials do not realize the full potential of piezoelectric materials in medicine. Therefore, the energy band structure of a piezoelectric material is modulated in this study to meet the actual requirement for cancer treatment. Herein, an elaborate PEGylated piezoelectric solid solution 0.7BiFeO3 -0.3BaTiO3 nanoparticles (P-BF-BT NPs) is synthesized, and the resultant particles achieve excellent piezoelectric properties and their band structure is tuned via band engineering. The tuned band structure of P-BF-BT NPs is energetically favorable for the synchronous production of superoxide radicals (•O2 - ) and oxygen (O2 ) self-supply via water splitting by the piezoelectric effect. Besides, the P-BF-BT NPs can initiate the Fenton reaction to generate hydroxyl radical (•OH), and thus, chemodynamic therapy (CDT) can be augmented by ultrasound. Detailed in vitro and in vivo research has verified the promising effects of multimodal imaging-guided P-BF-BT NP-mediated synergistic SDT/CDT by the piezo-Fenton process in hypoxic tumor elimination, accompanied by high therapeutic biosafety. The current demonstrates a novel strategy for designing and synthesizing "custom-made" piezoelectric materials for cancer therapy in the future.

Colossal Ionic Conductivity in Interphase Strain-Engineered Nanocomposite Films

Owing to their wide application in oxide-based electrochemical and energy devices, ion conductors have attracted considerable attention. However, the ionic conductivity of the developed systems is still too low to satisfy the low-temperature application. In this study, by developing the emergent interphase strain engineering method, we achieve a colossal ionic conductivity in SrZrO₃-xMgO nanocomposite films, which is over one order of magnitude higher than that of the currently widely used yttria-stabilized zirconia below 673 K. Atomic-scale electron microscopy studies ascribe this superior ionic conductivity to the periodically well-aligned SrZrO₃ and MgO nanopillars that feature coherent interfaces. Wherein, a tensile strain as large as +1.7% is introduced into SrZrO₃, expanding the c-lattice and distorting the oxygen octahedra to decrease the oxygen migration energy. Combining with theoretical assessments, we clarify the strain-dependent oxygen migration path and energy and unravel the mechanisms for strain-tuned ionic conductivity. This study provides a new scope for the property improvement of wide-range ion conductors by strain engineering.

Colossal Dielectric Perovskites of Calcium Copper Titanate (CaCu3 Ti4 O12 ) with Low-Iridium Dopants Enables Ultrahigh Mass Activity for the Acidic Oxygen Evolution Reaction

Oxygen evolution reaction (OER) under acidic conditions becomes of significant importance for the practical use of a proton exchange membrane (PEM) water electrolyzer. In particular, maximizing the mass activity of iridium (Ir) is one of the maiden issues. Herein, the authors discover that the Ir-doped calcium copper titanate (CaCu₃Ti₄O₁₂, CCTO) perovskite exhibits ultrahigh mass activity up to 1000 A g_Ir ^-1 for the acidic OER, which is 66 times higher than that of the benchmark catalyst, IrO₂ . By substituting Ti with Ir in CCTO, metal-oxygen (M-O) covalency can be significantly increased leading to the reduced energy barrier for charge transfer. Further, highly polarizable CCTO perovskite referred to as "colossal dielectric", possesses low defect formation energy for oxygen vacancy inducing a high number of oxygen vacancies in Ir-doped CCTO (Ir-CCTO). Electron transfer occurs from the oxygen vacancies and Ti to the substituted Ir consequentially resulting in the electron-rich Ir and -deficient Ti sites. Thus, favorable adsorptions of oxygen intermediates can take place at Ti sites while the Ir ensures efficient charge supplies during OER, taking a top position of the volcano plot. Simultaneously, the introduced Ir dopants form nanoclusters at the surface of Ir-CCTO, which can boost catalytic activity for the acidic OER.

Activity-Stability Balance: The Role of Electron Supply Effect of Support in Acidic Oxygen Evolution

Developing efficient and durable electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane (PEM) electrolyzers represents a significant challenge. Herein, the cobalt-ruthenium oxide nano-heterostructures are successfully synthesized on carbon cloth (CoO_x /RuO_x -CC) for acidic OER through a simple and fast solution combustion strategy. The rapid oxidation process endows CoO_x /RuO_x -CC with abundant interfacial sites and defect structures, which enhances the number of active sites and the charge transfer at the electrolyte-catalyst interface, promoting the OER kinetics. Moreover, the electron supply effect of the CoO_x support allows electrons to transfer from Co to Ru sites during the OER process, which is beneficial to alleviate the ion leaching and over-oxidation of Ru sites, improving the catalyst activity and stability. As a self-supported electrocatalyst, CoO_x /RuO_x -CC displays an ultralow overpotential of 180 mV at 10 mA cm^-2 for OER. Notably, the PEM electrolyzer using CoO_x /RuO_x -CC as the anode can be operated at 100 mA cm^-2 stably for 100 h. Mechanistic analysis shows that the strong catalyst-support interaction is beneficial to redistribute the electronic structure of RuO bond to weaken its covalency, thereby optimizing the binding energy of OER intermediates and lowering the reaction energy barrier.

V-Integration Modulates t2g -Electrons of a Single Crystal Ir1- x (Ir0.8 V0.2 O2 )x -BHC for Boosted and Durable OER in Acidic Electrolyte

Realizing efficacious π-donation from the O 2p orbital to electron-deficient metal (t_2g ) d-orbitals along with separately tuned adsorption of *O and *OOH, is an imperious pre-requisite for an electrocatalyst design to demonstrate boosted oxygen evolution reaction (OER) performance. To regulate the π-donation and the adsorption ability for *O and *OOH, herein, a facile strategy to modulate the electron transfer from electron-rich t_2g -orbitals to electron-deficient t_2g -orbitals, via strong π-donation from the π-symmetry lone pairs of the bridging O^2- , and the d-band center of a biomimetic honeycomb (BHC)-like nanoarchitecture (Ir_{1- x} (Ir_0.8 V_0.2 O₂ )_x -BHC) is introduced. The suitable integration of V heteroatoms in the single crystal system of IrO₂ decreases the electron density on the neighboring Ir sites, and causes an upshift in the d-band center of Ir_{1- x} (Ir_0.8 V_0.2 O₂ )_x -BHC, weakening the adsorption of *O while strengthening that of *OOH, lowers the energy barrier for OER. Therefore, BHC design demonstrates excellent OER performance (shows a small overpotential of 238 mV at 10 mA cm^-2 and a Tafel slope of 39.87 mV dec^-1 ) with remarkable stability (130 h) in corrosive acidic electrolyte. This work opens a new corridor to design robust biomimetic nanoarchitectures of modulated π-symmetry (t_2g ) d-orbitals and the band structure, to achieve excellent activity and durability in acidic environment.

Long-Term Stability Challenges and Opportunities in Acidic Oxygen Evolution Electrocatalysis

Polymer electrolyte membrane water electrolysis (PEMWE) has been regarded as a promising technology for renewable hydrogen production. However, acidic oxygen evolution reaction (OER) catalysts with long-term stability impose a grand challenge in its large-scale industrialization. In this review, critical factors that may lead to catalyst's instability in couple with potential solutions are comprehensively discussed, including mechanical peeling, substrate corrosion, active-site over-oxidation/dissolution, reconstruction, oxide crystal structure collapse through the lattice oxygen-participated reaction pathway, etc. Last but not least, personal prospects are provided in terms of rigorous stability evaluation criteria, in situ/operando characterizations, economic feasibility and practical electrolyzer consideration, highlighting the ternary relationship of structure evolution, industrial-relevant activity and stability to serve as a roadmap towards the ultimate application of PEMWE.

A Highly Active, Long-Lived Oxygen Evolution Electrocatalyst Derived from Open-Framework Iridates

The acidic oxygen evolution reaction underpins several important electrical-to-chemical energy conversions, and this energy-intensive process relies industrially on iridium-based electrocatalysts. Here, phase-selective synthesis of metastable strontium iridates with open-framework structure and their unexpected transformation into a highly active, ultrastable oxygen evolution nano-electrocatalyst are presented. This transformation involves two major steps: Sr²⁺ /H⁺ ion exchange in acid and in situ structural rearrangement under electrocatalysis conditions. Unlike its dense perovskite-structured polymorphs, the open-framework iridates have the ability to undergo rapid proton exchange in acid without framework amorphization. The resulting protonated iridates further reconstruct into ultrasmall, surface-hydroxylated, (200) crystal plane-oriented rutile nanocatalyst, instead of the common amorphous IrO_x H_y phase, during acidic oxygen evolution. Such microstructural characteristics are found to benefit both the oxidation of hydroxyls and the formation of OO bonds in electrocatalytic cycle. As a result, the open-framework iridate derived nanocatalyst gives a comparable catalytic activity to the most active iridium-based oxygen evolution electrocatalysts in acid, and retains its catalytic activity for more than 1000 h.

Modulating the electronic structure of CoS2 by Sn doping boosting urea oxidation for efficient alkaline hydrogen production

Urea electrocatalytic oxidation afforded by renewable energies is highly promising to replace the sluggish oxygen evolution reaction in water splitting for hydrogen production while realizing the treatment of urea-rich waste water. Therefore, the development of efficient and cost-effective catalysts for water splitting assisted by urea is highly desirable. Herein, Sn-doped CoS₂ electrocatalysts were reported with the engineered electronic structure and the formation of Co-Sn dual active sites for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER), respectively. Consequently, the number of active sites and the intrinsic activity were enhanced simultaneously and the resultant electrodes exhibited outstanding electrocatalytic activity with a very low potential of 1.301 V at 10 mA·cm^-2 for UOR and an overpotential of 132 mV at 10 mA·cm^-2 for HER. Therefore, a two-electrode device was assembled by employing Sn(2)-CoS₂/CC and Sn(5)-CoS₂/CC and the constructed cell required only 1.45 V to approach a current density of 10 mA·cm^-2 along with good durability for at least 95 h assisted by urea. More importantly, the assembled electrolyzer can be powered by commercial dry battery to generate numerous gas bubbles on the surface of the electrodes, demonstrating the high potential of the as-fabricated electrodes for applications in hydrogen production and pollutant treatment at a low-voltage electrical energy input.

Iron-Doped Monoclinic Strontium Iridate as a Highly Efficient Oxygen Evolution Electrocatalyst in Acidic Media

Ir-based perovskite oxides are efficient electrocatalysts for anodic oxygen evolution. This work presents a systematic study of the doping effects of Fe on the OER activity of monoclinic SrIrO₃ to reduce the consumption of Ir. The monoclinic structure of SrIrO₃ was retained when the Fe/Ir ratio was less than 0.1/0.9. Upon further increases in the Fe/Ir ratio, the structure of SrIrO₃ changed from a 6H to 3C phase. The SrFe_0.1Ir_0.9O₃ had the highest activity among the investigated catalysts with the lowest overpotential of 238 mV at 10 mA cm^-2 in 0.1 M HClO₄ solution, which could be attributed to the oxygen vacancies induced by the Fe dopant and the IrOx formed upon the dissolution of Sr and Fe. The formation of oxygen vacancies and uncoordinated sites at the molecular level may be responsible for the improved performance. This work explored the effect of Fe dopants in boosting the OER activity of SrIrO₃, thus providing a detailed reference to tune perovskite-based electrocatalyst by Fe for other applications.

Highly active and stable OER electrocatalysts derived from Sr2MIrO6 for proton exchange membrane water electrolyzers

Proton exchange membrane water electrolysis is a promising technology to produce green hydrogen from renewables, as it can efficiently achieve high current densities. Lowering iridium amount in oxygen evolution reaction electrocatalysts is critical for achieving cost-effective production of green hydrogen. In this work, we develop catalysts from Ir double perovskites. Sr2CaIrO6 achieves 10 mA cm-2 at only 1.48 V. The surface of the perovskite reconstructs when immersed in an acidic electrolyte and during the first catalytic cycles, resulting in a stable surface conformed by short-range order edge-sharing IrO6 octahedra arranged in an open structure responsible for the high performance. A proton exchange membrane water electrolysis cell is developed with Sr2CaIrO6 as anode and low Ir loading (0.4 mgIr cm-2). The cell achieves 2.40 V at 6 A cm-2 (overload) and no loss in performance at a constant 2 A cm-2 (nominal load). Thus, reducing Ir use without compromising efficiency and lifetime.

Emerging Heterogeneous Supports for Efficient Electrocatalysis

Electrocatalysis plays a fundamental role in many fields, such as metallurgy, medicine, chemical industry, and energy conversion. Anchoring active electrocatalysts with controllable loading and uniform dispersion onto suitable supports has become an attractive topic. This is because the supports can not only have the potential to improve catalytic activity and stability through the interaction between support and catalytic center, but also can reduce precious metal consumption by improving atomic utilization. Herein, recent theoretical and experimental progresses concerning the development of supports to anchor electrocatalytic materials are first reviewed. Next, their controllable syntheses, characterization techniques, metal-support electronic interactions, and structure-performance relationships are presented. Some representative carbon supports and non-carbonaceous supports, as well as recently reported star supports such as 2D supports, single atom catalysts, and self-supported catalysts are also summarized. In addition, the significant role of support in stabilizing and regulating catalytic active sites is particularly emphasized. Finally, challenges, opportunities, key problems, and further promising solutions for supported catalysts are proposed.

Multistage Electron Distribution Engineering of Iridium Oxide by Codoping W and Sn for Enhanced Acidic Water Oxidation Electrocatalysis

Developing efficient and robust anodic electrocatalysts to implement the proton-exchange membrane (PEM) electrolyzer is critical for hydrogen generation. Nevertheless, the only known applicable anode catalyst IrO_x in PEM electrolyzers still requires high overpotential due to the weak binding energy between oxygen intermediates and active sites, limiting its wide applications. Herein, a ternary Ir_0.7 W_0.2 Sn_0.1 O_x nanocatalyst synthesized through a sol-gel strategy, exhibits a low overpotential of 236 mV (10 mA cm^-2 _geo ) for thoxygen evolution reaction (OER), accompanied with robust durability over 220 h at 1 A cm^-2 _geo in 0.5 m H₂ SO₄ . Moreover, the optimized Ir_0.7 W_0.2 Sn_0.1 O_x delivers a prominent mass activity of 722.7 A g^-1 _Ir at 1.53 V (vs RHE), which is around 34 times higher compared with that of IrO_x . The mircrostructural analyses reveal that codoping of W and Sn stabilizes Ir with a valence state lower than 4+ through multistage charge redistribution, avoiding the overoxidation of Ir above 1.6 V versus RHE and enhancing the acidic OER performance. Additionally, density functional theory calculations reveal that codoping of W and Sn moves the d band center of Ir to the Fermi level, thus enhancing the binding energies of oxygen intermediates with Ir sites and decreasing the energy barrier toward acidic OER.

Strategies for Electrochemically Sustainable H2 Production in Acid

Acidified water electrolysis with fast kinetics is widely regarded as a promising option for producing H2 . The main challenge of this technique is the difficulty in realizing sustainable H2 production (SHP) because of the poor stability of most electrode catalysts, especially on the anode side, under strongly acidic and highly polarized electrochemical environments, which leads to surface corrosion and performance degradation. Research efforts focused on tuning the atomic/nano structures of catalysts have been made to address this stability issue, with only limited effectiveness because of inevitable catalyst degradation. A systems approach considering reaction types and system configurations/operations may provide innovative viewpoints and strategies for SHP, although these aspects have been overlooked thus far. This review provides an overview of acidified water electrolysis for systematic investigations of these aspects to achieve SHP. First, the fundamental principles of SHP are discussed. Then, recent advances on design of stable electrode materials are examined, and several new strategies for SHP are proposed, including fabrication of symmetrical heterogeneous electrolysis system and fluid homogeneous electrolysis system, as well as decoupling/hybrid-governed sustainability. Finally, remaining challenges and corresponding opportunities are outlined to stimulate endeavors toward the development of advanced acidified water electrolysis techniques for SHP.

Ultrahigh-Current-Density and Long-Term-Durability Electrocatalysts for Water Splitting

Hydrogen economy is imagined where excess electric energy from renewable sources stored directly by electrochemical water splitting into hydrogen is later used as clean hydrogen fuel. Electrocatalysts with the superhigh current density (1000 mA cm^-2 -level) and long-term durability (over 1000 h), especially at low overpotentials (<300 mV), seem extremely critical for green hydrogen from experiment to industrialization. Along the way, numerous innovative ideas are proposed to design high efficiency electrocatalysts in line with industrial requirements, which also stimulates the understanding of the mass/charge transfer and mechanical stability during the electrochemical process. It is of great necessity to summarize and sort out the accumulating knowledge in time for the development of laboratory to commercial use in this promising field. This review begins with examining the theoretical principles of achieving high-efficiency electrocatalysts with high current densities and excellent durability. Special attention is paid to acquaint efficient strategies to design perfect electrocatalysts including atomic structure regulation for electrical conductivity and reaction energy barrier, array configuration constructing for mass transfer process, and multiscale coupling for high mechanical strength. Finally, the importance and the personal perspective on future opportunities and challenges, is highlighted.

Highly active and stable surface structure for oxygen evolution reaction originating from balanced dissolution and strong connectivity in BaIrO3 solid solutions

Catalysts for the oxygen evolution reaction (OER) are receiving great interest since OER remains the bottleneck of water electrolyzers for hydrogen production. Especially, OER in acidic solutions is crucial since it produces high current densities and avoids precipitation of carbonates. However, even the acid stable iridates undergo severe dissolution during the OER. BaIrO₃ has the strongest IrO₆ connectivity and stable surface structure, yet it suffers from lattice collapse after OER cycling, making it difficult to improve the OER durability. In the present study, we have successfully developed an OER catalyst with both high intrinsic activity and stability under acidic conditions by preventing the lattice collapse after repeated OER cycling. Specifically, we find that the substitution of Ir-site with Mn for BaIrO₃ in combination with OER cycling leads to a remarkable activity enhancement by a factor of 28 and an overall improvement in stability. This dual enhancement of OER performance was accomplished by the novel strategy of slightly increasing the Ir-dissolution and balancing the elemental dissolution in BaIr_1−xMn_xO₃ to reconstruct a rigid surface with BaIrO₃-type structure. More importantly, the mass activity for BaIr_0.8Mn_0.2O₃ reached ∼73 times of that for IrO₂, making it a sustainable and promising OER catalyst for energy conversion technologies.

We have prevented lattice collapse and developed an OER catalyst with both high activity and stability by slightly increasing Ir-dissolution and balancing the elemental dissolution in BaIr_1−xMn_xO₃ for reconstructing the rigid catalytic surface.

Regulating the Interfacial Electron Density of La0.8Sr0.2Mn0.5Co0.5O3/RuOx for Efficient and Low-Cost Bifunctional Oxygen Electrocatalysts and Rechargeable Zn-Air Batteries

La_0.8Sr_0.2Mn_0.5Co_0.5O₃ (LSMC) perovskite anchored with RuO_x (LSMC-Ru) is fabricated as a new bifunctional electrocatalyst, with low dosage (2.43 wt %) and high utilization of noble metal Ru. The LSMC-Ru exhibits outstanding bifunctional activity with a low potential gap of 0.72 V between the oxygen evolution reaction (OER) potential at 10 mA cm^-2 and the oxygen reduction reaction (ORR) half-wave potential. The strong electronic interaction between RuO_x and LSMC is confirmed by both experiments and theoretical calculations. Consequently, the electron-rich Mn centers promote ORR, while the electron-deficient Ru centers facilitate OER. A Zn-air battery using the LSMC-Ru air electrode delivers a peak power density of 159 mW cm^-2 and a low charge-discharge potential gap of 0.58 V at 2 mA cm^-2. The high round-trip energy efficiency of 60.6% is retained after 300 cycles. This strategy of anchoring a low dosage noble metal catalyst to perovskite can be extended to other systems of noble metal-non-noble metal composite electrocatalysts to achieve both competitive performance and low cost.

Tunable surface electric field of electrode materials via constructing Schottky heterojunctions for selective conversion of trash ions to treasures

Surface electric field of catalyst is widely recognized as one of the key points to boost catalytic activity. However, there is still a lack of convenient ways to tune the surface electric field to selectively boost the catalytically conversions of different types of reactants in specific catalytic reaction. Here, we introduce a concept-new method to tune the surface electric field of electrode materials by adjusting the number and density of heterojunctions inside. Both theoretical and experimental results prove that the well-designed surface electric field of an electrocatalyst plays a key role in facilitating pre-adsorption and/or activation of reactants for selective conversion of trash ions to useful products in hydrogen evolution reaction, oxygen evolution reaction and NO x - reduction reaction.

Structural Variations of Metal Oxide-Based Electrocatalysts for Oxygen Evolution Reaction

Electrocatalytic oxygen evolution reaction (OER), an important electrode reaction in electrocatalytic and photoelectrochemical cells for a carbon-free energy cycle, has attracted considerable attention in the last few years. Metal oxides have been considered as good candidates for electrocatalytic OER because they can be easily synthesized and are relatively stable during the OER process. However, inevitable structural variations still occur to them due to the complex reaction steps and harsh working conditions of OER, thus impending the further insight into the catalytic mechanism and rational design of highly efficient electrocatalysts. The aim of this review is to disclose the current research progress toward the structural variations of metal oxide-based OER electrocatalysts. The origin of structural variations of metal oxides is discussed. Based on some typical oxides performing OER activity, the external and internal factors that influence the structural stability are summarized and then some general approaches to regulate the structural variation process are provided. Some operando methods are also concluded to monitor the structural variation processes and to identify the final active structure. Additionally, the unresolved problems and challenges are presented in an attempt to get further insight into the mechanism of structural variations and establish a rational structure-catalysis relationship.