Transition-Metal-Doped RuIr Bifunctional Nanocrystals for Overall Water Splitting in Acidic Environments

Acidic Oxygen Evolution Reaction: Fundamental Understanding and Electrocatalysts Design

Water electrolysis driven by "green electricity" is an ideal technology to realize energy conversion and store renewable energy into hydrogen. With the development of proton exchange membrane (PEM), water electrolysis in acidic media suitable for many situations with an outstanding advantage of high gas purity has attracted significant attention. Compared with hydrogen evolution reaction (HER) in water electrolysis, oxygen evolution reaction (OER) is a kinetic sluggish process that needs a higher overpotential. Especially in acidic media, OER process poses higher requirements for the electrocatalysts, such as high efficiency, high stability and low costs. This review focuses on the acidic OER electrocatalysis, reaction mechanisms, and critical parameters used to evaluate performance. Especially the modification strategies applied in the design and construction of new-type electrocatalysts are also summarized. The characteristics of traditional noble metal-based electrocatalysts and the noble metal-free electrocatalysts developed in recent decades are compared and discussed. Finally, the current challenges for the most promising acidic OER electrocatalysts are presented, together with a perspective for future water electrolysis.

Atomic Strain Wave-Featured LaRuIr Nanocrystals: Achieving Simultaneous Enhancement of Catalytic Activity and Stability toward Acidic Water Splitting

Rare earth microalloying nanocrystals have gotten widespread attention due to their unprecedented performances with customization-defected nanostructures, divided energy bands, and ensembled surface chemistry, regarded as a class of ideal electrocatalysts for oxygen evolution reaction (OER). Herein, a lanthanide microalloying strategy is proposed to fabricate strain wave-featured LaRuIr nanocrystals with oxide skin through a rapid crystal nucleation, using thermally assisted sodium borohydride reduction in aqueous solution at 60 °C. The atomic strain waves with alternating compressive and tensile strains, resulting from La-stabilized edge dislocations in form of Cottrell atmospheres. In 0.5 m H2SO4, the LaRuIr displays an overpotential of 184 mV at 10 mA cm-2, running at a steadily cell voltage for 60 h at 50 mA cm-2, eightfold enhancement of IrO2||Pt/C assemble in PEMWE. The coupled compressive and tensile profiles boost the OER kinetics via faster AEM and LOM pathways. Moreover, the tensile facilitates surface structure stabilization through dynamic refilling of lattice oxygen vacancies by the adsorbed oxyanions on La, Ru, and Ir sites, eventually achieving a long-term stability. This work contributes to developing advanced catalysts with unique strain to realize simultaneous improvement of activity and durability by breaking the so-called seesaw relationship between them during OER for water splitting.

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.

Ultra-Thin RuIr Alloy as Durable Electrocatalyst for Seawater Hydrogen Evolution Reaction

The development of efficient, high-performance catalysts for hydrogen evolution reaction (HER) remains a significant challenge, especially in seawater media. Here, RuIr alloy catalysts are prepared by the polyol reduction method. Compared with single-metal catalysts, the RuIr alloy catalysts exhibited higher activity and stability in seawater electrolysis due to their greater number of reactive sites and solubility resistance. The RuIr alloy has an overpotential of 75 mV@10 mA cm-2, which is similar to that of Pt/C (73 mV), and can operate stably for 100 hours in alkaline seawater. Density functional theory (DFT) calculations indicate that hydrogen atoms adsorbed at the top sites of Ru and Ir atoms are more favorable for HER and are most likely to be the reactive sites. This work provides a reference for developing highly efficient and stable catalysts for seawater electrolysis.

Recent Advances in Iridium-based Electrocatalysts for Acidic Electrolyte Oxidation

Ongoing research to develop advanced electrocatalysts for the oxygen evolution reaction (OER) is needed to address demand for efficient energy conversion and carbon-free energy sources. In the OER process, acidic electrolytes have higher proton concentration and faster response than alkaline ones, but their harsh strongly acidic environment requires catalysts with greater corrosion and oxidation resistance. At present, iridium oxide (IrO2) with its strong stability and excellent catalytic performance is the catalyst of choice for the anode side of commercial PEM electrolysis cells. However, the scarcity and high cost of iridium (Ir) and the unsatisfactory activity of IrO2 hinder industrial scale application and the sustainable development of acidic OER catalytic technology. This highlights the importance of further research on acidic Ir-based OER catalysts. In this review, recent advances in Ir-based acidic OER electrocatalysts are summarized, including fundamental understanding of the acidic OER mechanism, recent insights into the stability of acidic OER catalysts, highly efficient Ir-based electrocatalysts, and common strategies for optimizing Ir-based catalysts. The future challenges and prospects of developing highly effective Ir-based catalysts are also discussed.

Designing 3d Transition Metal Cation-Doped MRuOx As Durable Acidic Oxygen Evolution Electrocatalysts for PEM Water Electrolyzers

The continuous dissolution and oxidation of active sites in Ru-based electrocatalysts have greatly hindered their practical application in proton exchange membrane water electrolyzers (PEMWE). In this work, we first used density functional theory (DFT) to calculate the dissolution energy of Ru in the 3d transition metal-doped MRuOx (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) to evaluate their stability for acidic oxygen evolution reaction (OER) and screen out ZnRuOx as the best candidate. To confirm the theoretical predictions, we experimentally synthesized these MRuOx materials and found that ZnRuOx indeed displays robust acidic OER stability with a negligible decay of η10 after 15 000 CV cycles. Of importance, using ZnRuOx as the anode, the PEMWE can run stably for 120 h at 200 mA cm-2. We also further uncover the stability mechanism of ZnRuOx, i.e., Zn atoms doped in the outside of ZnRuOx nanocrystal would form a "Zn-rich" shell, which effectively shortened average Ru-O bond lengths in ZnRuOx to strengthen the Ru-O interaction and therefore boosted intrinsic stability of ZnRuOx in acidic OER. In short, this work not only provides a new study paradigm of using DFT calculations to guide the experimental synthesis but also offers a proof-of-concept with 3d metal dopants as RuO2 stabilizer as a universal principle to develop high-durability Ru-based catalysts for PEMWE.

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.

Strain Effects in Ru-Au Bimetallic Aerogels Boost Electrocatalytic Hydrogen Evolution

To improve the sluggish kinetics of the hydrogen evolution reaction (HER), a key component in water-splitting applications, there is an urgent desire to develop efficient, cost-effective, and stable electrocatalysts. Strain engineering is proving an efficient strategy for increasing the catalytic activity of electrocatalysts. This work presents the development of Ru-Au bimetallic aerogels by a simple one-step in situ reduction-gelation approach, which exhibits strain effects and electron transfer to create a remarkable HER activity and stability in an alkaline environment. The surface strain induced by the bimetallic segregated structure shifts the d-band center downward, enhancing catalysis by balancing the processes of water dissociation, OH* adsorption, and H* adsorption. Specifically, the optimized catalyst shows low overpotentials of only 24.1 mV at a current density of 10 mA cm-2 in alkaline electrolytes, surpassing commercial Pt/C. This study can contribute to the understanding of strain engineering in bimetallic electrocatalysts for HER at the atomic scale.

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

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

Bicontinuous RuO2 nanoreactors for acidic water oxidation

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

Thermal-Driven Orderly Assembly of Ir-atomic Chains on α-MnO2 with Enhanced Performance for Acidic Oxygen Evolution

The development of acid-stable oxygen evolution reaction electrocatalysts is essential for high-performance acidic water electrolysis. Herein, we report the results of one-dimensional (1D) nanorods (NRs) IrCeMnO@Ir containing ~20 wt . % Iridium (Ir) as an efficient anode electrocatalyst, synthesized via a one-step cation exchange strategy. Owing to the presence of 1D channels of the nanorod architecture and the unique electronic structure, the IrCeMnO@Ir exhibited 69 folds more mass activity than that of commercial IrO2 as well as over 400 h stability with only a 20 mV increase in overpotential. DFT calculations and control experiments demonstrated that CeO2 serves as an electron buffer to accelerate the kinetics of the rate-determined step for the significantly enhanced activity and suppress the over-oxidation of Ir species as well as their dissolution for impressively promoted stability under practical conditions. Our work opens up a feasible strategy to boost OER activity and stability simultaneously.

Nanoscale Design for High Entropy Alloy Electrocatalysts

Due to their distinctive physical and chemical characteristics, high entropy alloys (HEAs), a class of alloys comprising multiple elements, have garnered a lot of attention. It is demonstrated recently that HEA electrocatalysts increase the activity and stability of several processes. In this paper, the most recent developments in HEA electrocatalysts research are reviewed, and the performance of HEAs in catalyzing key reactions in water electrolysis and fuel cells is summarized. In addition, the design strategies for HEA electrocatalysts optimization is introduced, which include component selection, size optimization, morphology control, structural engineering, crystal phase regulation, and theoretical prediction, which can guide component selection and structural design of HEA electrocatalysts.

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

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.

Designing Efficient Non-Precious Metal Electrocatalysts for High-Performance Hydrogen Production: A Comprehensive Evaluation Strategy

Developing abundant Earth-element and high-efficient electrocatalysts for hydrogen production is crucial in effectively reducing the cost of green hydrogen production. Herein, a strategy by comprehensively considering the computational chemical indicators for H* adsorption/desorption and dehydrogenation kinetics to evaluate the hydrogen evolution performance of electrocatalysts is proposed. Guided by the proposed strategy, a series of catalysts are constructed through a dual transition metal doping strategy. Density Functional Theory (DFT) calculations and experimental chemistry demonstrate that cobalt-vanadium co-doped Ni3N is an exceptionally ideal catalyst for hydrogen production from electrolyzed alkaline water. Specifically, Co,V-Ni3N requires only 10 and 41 mV in alkaline electrolytes and alkaline seawater, respectively, to achieve a hydrogen evolution current density of 10 mA cm-2. Moreover, it can operate steadily at a large industrial current density of 500 mA cm-2 for extended periods. Importantly, this evaluation strategy is extended to single-metal-doped Ni3N and found that it still exhibits significant universality. This study not only presents an efficient non-precious metal-based electrocatalyst for water/seawater electrolysis but also provides a significant strategy for the design of high-performance catalysts of electrolyzed water.

Rare-Earth-Modified NiS2 Improves OH Coverage for an Industrial Alkaline Water Electrolyzer

The low coverage rate of anode OH adsorption under high current density conditions has become an important factor restricting the development of an industrial alkaline water electrolyzer (AWE). Here, we present our rare earth modification promotion strategy on using the rare earth oxygen-friendly interface to increase the OH coverage of the NiS2 surface for efficient AWE anode catalysis. Density functional theory calculations predict that rare earths can enhance the coverage of surface OH, and the synthesis reaction mechanism is discussed in the synthesis process spectrum. Experimentally, by preparing a series of rare-earth-modified NiS2, the relationship between OH coverage, active site density, and catalytic activity was established by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, time-resolved absorption spectra, and so on. The unique oxygenophilic properties of rare earths enhance OH coverage, thereby increasing the density of active sites for efficient catalysis. Furthermore, Eu2O3/NiS2 was assembled into the AWE equipment and operated stably for over 240 h at a current density of 300 mA cm-2 under industrial conditions of 80 °C and 30% KOH. Rare-earth-modified NiS2 exhibits better catalytic activity than traditional non-noble metal anode catalysts Ni(OH)2 and NiS2, providing a new approach for rare earth promotion to solve the problem of low OH coverage in the AWE anode.

A review of modulation strategies for improving the catalytic performance of transition metal sulfide self-supported electrodes for the hydrogen evolution reaction

Electrocatalytic water splitting is considered to be one of the most promising technologies for large-scale sustained production of H2. Developing non-noble metal-based electrocatalytic materials with low cost, high activity and long life is the key to electrolysis of water. Transition metal sulfides (TMSs) with good electrical conductivity and a tunable electronic structure are potential candidates that are expected to replace noble metal electrocatalysts. In addition, self-supported electrodes have fast electron transfer and mass transport, resulting in enhanced kinetics and stability. In this paper, TMS self-supported electrocatalysts are taken as examples and their recent progress as hydrogen evolution reaction (HER) electrocatalysts is reviewed. The HER mechanism is first introduced. Then, based on optimizing the active sites, electrical conductivity, electronic structure and adsorption/dissociation energies of water and intermediates of the electrocatalysts, the article focuses on summarizing five modulation strategies to improve the activity and stability of TMS self-supported electrode electrocatalysts in recent years. Finally, the challenges and opportunities for the future development of TMS self-supported electrodes in the field of electrocatalytic water splitting are presented.

Strain-modulated Ru-O Covalency in Ru-Sn Oxide Enabling Efficient and Stable Water Oxidation in Acidic Solution

RuO2 is one of the benchmark electrocatalysts used as the anode material in proton exchange membrane water electrolyser. However, its long-term stability is compromised due to the participation of lattice oxygen and metal dissolution during oxygen evolution reaction (OER). In this work, weakened covalency of Ru-O bond was tailored by introducing tensile strain to RuO6 octahedrons in a binary Ru-Sn oxide matrix, prohibiting the participation of lattice oxygen and the dissolution of Ru, thereby significantly improving the long-term stability. Moreover, the tensile strain also optimized the adsorption energy of intermediates and boosted the OER activity. Remarkably, the RuSnOx electrocatalyst exhibited excellent OER activity in 0.1 M HClO4 and required merely 184 mV overpotential at a current density of 10 mA cm-2 . Moreover, it delivered a current density of 10 mA cm-2 for at least 150 h with negligible potential increase. This work exemplifies an effective strategy for engineering Ru-based catalysts with extraordinary performance toward water splitting.

The Promising Seesaw Relationship Between Activity and Stability of Ru-Based Electrocatalysts for Acid Oxygen Evolution and Proton Exchange Membrane Water Electrolysis

The development of electrocatalysts that are not reliant on iridium for efficient acid-oxygen evolution is a critical step towards the proton exchange membrane water electrolysis (PEMWE) and green hydrogen industry. Ruthenium-based electrocatalysts have garnered widespread attention due to their remarkable catalytic activity and lower commercial price. However, the challenge lies in balancing the seesaw relationship between activity and stability of these electrocatalysts during the acid-oxygen evolution reaction (OER). This review delves into the progress made in Ru-based electrocatalysts with regards to acid OER and PEMWE applications. It highlights the significance of customizing the acidic OER mechanism of Ru-based electrocatalysts through the coordination of adsorption evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM) to attain the ideal activity and stability relationship. The promising tradeoffs between the activity and stability of different Ru-based electrocatalysts, including Ru metals and alloys, Ru single-atomic materials, Ru oxides, and derived complexes, and Ru-based heterojunctions, as well as their applicability to PEMWE systems, are discussed in detail. Furthermore, this paper offers insights on in situ control of Ru active sites, dynamic catalytic mechanism, and commercial application of PEMWE. Based on three-way relationship between cost, activity, and stability, the perspectives and development are provided.

Boosting electrocatalytic performance via electronic structure regulation for acidic oxygen evolution

High-purity hydrogen produced by water electrolysis has become a sustainable energy carrier. Due to the corrosive environments and strong oxidizing working conditions, the main challenge faced by acidic water oxidation is the decrease in the activity and stability of anodic electrocatalysts. To address this issue, efficient strategies have been developed to design electrocatalysts toward acidic OER with excellent intrinsic performance. Electronic structure modification achieved through defect engineering, doping, alloying, atomic arrangement, surface reconstruction, and constructing metal-support interactions provides an effective means to boost OER. Based on introducing OER mechanism commonly present in acidic environments, this review comprehensively summarizes the effective strategies for regulating the electronic structure to boost the activity and stability of catalytic materials. Finally, several promising research directions are discussed to inspire the design and synthesis of high-performance acidic OER electrocatalysts.

MoS2 Nanoflowers Grown on Plasma-Induced W-Anchored Graphene for Efficient and Stable H2 Production Through Seawater Electrolysis

Herein, it is found that 3D transition metal dichalcogenide (TMD)-MoS2 nanoflowers-grown on 2D tungsten oxide-anchored graphene nanosheets (MoS2 @W-G) functions as a superior catalyst for the hydrogen evolution reaction (HER) under both acidic and alkaline conditions. The optimized weight ratio of MoS2 @W-G (MoS2 :W-G/1.5:1) in 0.5 M H2 SO4 achieves a low overpotential of 78 mV at 10 mA cm-2 , a small Tafel slope of 48 mV dec-1 , and a high exchange current density (0.321 mA cm⁻2 ). Furthermore, the same MoS2 @W-G composite exhibits stable HER performance when using real seawater, with Faradaic efficiencies of 96 and 94% in acidic and alkaline media, respectively. Density functional theory calculations based on the hybrid MoS2 @W-G structure model confirm that suitable hybridization of 3D MoS2 and 2D W-G nanosheets can lower the hydrogen adsorption: Gibbs free energy (∆GH* ) from 1.89 eV for MoS2 to -0.13 eV for the MoS2 @W-G composite. The excellent HER activity of the 3D/2D hybridized MoS2 @W-G composite arises from abundance of active heterostructure interfaces, optimizing the electrical configuration, thereby accelerating the adsorption and dissociation of H2 O. These findings suggest a new approach for the rational development of alternative 3D/2D TMD/graphene electrocatalysts for HER applications using seawater.

Constructing Nanoporous Ir/Ta2 O5 Interfaces on Metallic Glass for Durable Acidic Water Oxidation

Although proton exchange membrane water electrolyzers (PEMWE) are considered as a promising technique for green hydrogen production, it remains crucial to develop intrinsically effective oxygen evolution reaction (OER) electrocatalysts with high activity and durability. Here, a flexible self-supporting electrode with nanoporous Ir/Ta2O5 electroactive surface is reported for acidic OER via dealloying IrTaCoB metallic glass ribbons. The catalyst exhibits excellent electrocatalytic OER performance with an overpotential of 218 mV for a current density of 10 mA cm-2 and a small Tafel slope of 46.1 mV dec-1 in acidic media, superior to most electrocatalysts. More impressively, the assembled PEMWE with nanoporous Ir/Ta2 O5 as an anode shows exceptional performance of electrocatalytic hydrogen production and can operate steadily for 260 h at 100 mA cm-2 . In situ spectroscopy characterizations and density functional theory calculations reveal that the modest adsorption of OOH* intermediates to active Ir sites lower the OER energy barrier, while the electron donation behavior of Ta2 O5 to stabilize the high-valence states of Ir during the OER process extended catalyst's durability.

Regulating the electronic structure of metal-organic frameworks via ion-exchanged Ir dispersion for robust overall water splitting

A facile ion exchange strategy to fabricate CoIrx-BDC with atomically dispersed Ir is developed towards overall water splitting. The optimized CoIr3-BDC requires only 12 and 81 mV to deliver 10 and 100 mA cm-2 alkaline HER, respectively, and only 245 mV to reach 100 mA cm-2 alkaline OER.

Metal Alloys-Structured Electrocatalysts: Metal-Metal Interactions, Coordination Microenvironments, and Structural Property-Reactivity Relationships

Metal alloys-structured electrocatalysts (MAECs) have made essential contributions to accelerating the practical applications of electrocatalytic devices in renewable energy systems. However, due to the complex atomic structures, varied electronic states, and abundant supports, precisely decoding the metal-metal interactions and structure-activity relationships of MAECs still confronts great challenges, which is critical to direct the future engineering and optimization of MAECs. Here, this timely review comprehensively summarizes the latest advances in creating the MAECs, including the metal-metal interactions, coordination microenvironments, and structure-activity relationships. First, the fundamental classification, design, characterization, and structural reconstruction of MAECs are outlined. Then, the electrocatalytic merits and modulation strategies of recent breakthroughs for noble and non-noble metal-structured MAECs are thoroughly discussed, such as solid solution alloys, intermetallic alloys, and single-atom alloys. Particularly, unique insights into the bond interactions, theoretical understanding, and operando techniques for mechanism disclosure are given. Thereafter, the current states of diverse MAECs with a unique focus on structural property-reactivity relationships, reaction pathways, and performance comparisons are discussed. Finally, the future challenges and perspectives for MAECs are systematically discussed. It is believed that this comprehensive review can offer a substantial impact on stimulating the widespread utilization of metal alloys-structured materials in electrocatalysis.

The mechanism of nanozyme activity of ZnO-Co3O4-v: Oxygen vacancy dynamic change and bilayer electron transfer pathway for wound healing and virtual reality revealing

Since the catalyst's surface was the major active location, the inner structure's contribution to catalytic activity was typically overlooked. Here, ZnO-Co3O4-v nanozymes with several surfaces and bulk oxygen vacancies were created. The O atoms of H2O2 moved inward to preferentially fill the oxygen vacancies in the interior and form new "lattice oxygen" by the X-ray photoelectron spectroscopy depth analysis and X-ray absorption fine structure. The internal Co2+ continually transferred electrons to the surface for a continuous catalytic reaction, which generated a significant amount of reactive oxygen species. Inner and outer double-layer electron cycles accompanied this process. A three-dimensional model of ZnO-Co3O4-v was constructed using virtual reality interactive modelling technology to illustrate nanozyme catalysis. Moreover, the bactericidal rate of ZnO-Co3O4-v for Methionine-resistant Staphylococcus aureus and Multiple drug resistant Escherichia coli was as high as 99%. ZnO-Co3O4-v was biocompatible and might be utilized to heal wounds following Methionine-resistant Staphylococcus aureus infection. This work offered a new idea for nanozymes to replace of conventional antibacterial medications.

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.

Loading IrOx Clusters on MnO2 Boosts Acidic Water Oxidation via Metal-Support Interaction

Noble metal-based electrocatalysts are crucial for efficient acidic water oxidation to develop green hydrogen energy. However, traditional noble metal catalysts loaded on inactive substrates show limited intrinsic catalytic activity, and their large sizes have compromised the atom efficiency of these noble metals. Herein, IrOx nanoclusters with sizes below 2 nm, displaying high atom-utilization efficiency of Ir species, were supported on a redox-active MnO2 nanosubstrate (IrOx/MnO2) with different phases (α-MnO2, δ-MnO2, and ε-MnO2) to explore the optimal combination. Electrochemical measurements showed that IrOx/ε-MnO2 had excellent OER performance with a low overpotential of 225 mV at 10 mA cm-2 in 0.5 M H2SO4, superior to its counterpart, IrOx/α-MnO2 (242 mV) and IrOx/δ-MnO2 (286 mV). Moreover, it also delivered robust stability with no obvious change in operating potential at 10 mA cm-2 during 50 h of continuous operation. Combining the XPS results and Bader charge analysis, we demonstrated that the strong metal-support interactions of IrOx/ε-MnO2 could effectively regulate the electronic structures of the active Ir atoms and stabilize IrOx nanoclusters on supports to suppress their detachment, resulting in significantly enhanced catalytic activity and stability for acidic OER. DFT calculations further supported that the enhanced catalytic OER performance of IrOx/ε-MnO2 could be ascribed to the appropriate strength of interactions between the active Ir sites and the reaction intermediates of the potential-determining step (*O and *OOH) regulated by the redox-active substrates.

Misoriented high-entropy iridium ruthenium oxide for acidic water splitting

Designing an efficient catalyst for acidic oxygen evolution reaction (OER) is of critical importance in manipulating proton exchange membrane water electrolyzer (PEMWE) for hydrogen production. Here, we report a fast, nonequilibrium strategy to synthesize quinary high-entropy ruthenium iridium-based oxide (M-RuIrFeCoNiO2) with abundant grain boundaries (GB), which exhibits a low overpotential of 189 millivolts at 10 milliamperes per square centimeter for OER in 0.5 M H2SO4. Microstructural analyses, density functional calculations, and isotope-labeled differential electrochemical mass spectroscopy measurements collectively reveal that the integration of foreign metal elements and GB is responsible for the enhancement of activity and stability of RuO2 toward OER. A PEMWE using M-RuIrFeCoNiO2 catalyst can steadily operate at a large current density of 1 ampere per square centimeter for over 500 hours. This work demonstrates a pathway to design high-performance OER electrocatalysts by integrating the advantages of various components and GB, which breaks the limits of thermodynamic solubility for different metal elements.

Single-Atom Pt Embedded in Defective Layered Double Hydroxide for Efficient and Durable Hydrogen Evolution

Electrocatalysis in neutral conditions is appealing for hydrogen production by utilizing abundant wastewater or seawater resources. Single-atom catalysts (SACs) immobilized on supports are considered one of the most promising strategies for electrocatalysis research. While they have principally exhibited breakthrough activity and selectivity for the hydrogen evolution reaction (HER) electrocatalysis in alkaline or acidic conditions, few SACs were reported for HER in neutral media. Herein, we report a facile strategy to tailor the water dissociation active sites on the NiFe LDH by inducing Mo species and an ultralow single atomic Pt loading. The defected NiFeMo LDH (V-NiFeMo LDH) shows HER activity with an overpotential of 89 mV at 10 mA cm-2 in 1 M phosphate buffer solutions. The induced Mo species and the transformed NiO/Ni phases after etching significantly increase the electron conductivity and the catalytic active sites. A further enhancement can be achieved by modulating the ultralow single atom Pt anchored on the V-NiFeMo LDH by potentiostatic polarization. A potential as low as 37 mV is obtained at 10 mA cm-2 with a pronounced long-term durability over 110 h, surpassing its crystalline LDH materials and most of the HER catalysts in neutral medium. Experimental and density functional theory calculation results have demonstrated that the synergistic effects of Mo/SAs Pt and phase transformation into NiFe LDH reduce the kinetic energy barrier of the water dissociation process and promote the H* conversion for accelerating the neutral HER.

Stable and oxidative charged Ru enhance the acidic oxygen evolution reaction activity in two-dimensional ruthenium-iridium oxide

The oxygen evolution reactions in acid play an important role in multiple energy storage devices. The practical promising Ru-Ir based catalysts need both the stable high oxidation state of the Ru centers and the high stability of these Ru species. Here, we report stable and oxidative charged Ru in two-dimensional ruthenium-iridium oxide enhances the activity. The Ru0.5Ir0.5O2 catalyst shows high activity in acid with a low overpotential of 151 mV at 10 mA cm-2, a high turnover frequency of 6.84 s-1 at 1.44 V versus reversible hydrogen electrode and good stability (618.3 h operation). Ru0.5Ir0.5O2 catalysts can form more Ru active sites with high oxidation states at lower applied voltages after Ir incorporation, which is confirmed by the pulse voltage induced current method. Also, The X-ray absorption spectroscopy data shows that the Ru-O-Ir local structure in two-dimensional Ru0.5Ir0.5O2 solid solution improved the stability of these Ru centers.

Recent advances in proton exchange membrane water electrolysis

Proton exchange membrane water electrolyzers (PEMWEs) are an attractive technology for renewable energy conversion and storage. By using green electricity generated from renewable sources like wind or solar, high-purity hydrogen gas can be produced in PEMWE systems, which can be used in fuel cells and other industrial sectors. To date, significant advances have been achieved in improving the efficiency of PEMWEs through the design of stack components; however, challenges remain for their large-scale and long-term application due to high cost and durability issues in acidic conditions. In this review, we examine the latest developments in engineering PEMWE systems and assess the gap that still needs to be filled for their practical applications. We provide a comprehensive summary of the reaction mechanisms, the correlation among structure-composition-performance, manufacturing methods, system design strategies, and operation protocols of advanced PEMWEs. We also highlight the discrepancies between the critical parameters required for practical PEMWEs and those reported in the literature. Finally, we propose the potential solution to bridge the gap and enable the appreciable applications of PEMWEs. This review may provide valuable insights for research communities and industry practitioners working in these fields and facilitate the development of more cost-effective and durable PEMWE systems for a sustainable energy future.

Breaking the Activity and Stability Bottlenecks of Electrocatalysts for Oxygen Evolution Reactions in Acids

Oxygen evolution reaction (OER) is a cornerstone reaction for a variety of electrochemical energy conversion and storage systems such as water splitting, CO2 /N2 reduction, reversible fuel cells, and metal-air batteries. However, OER catalysis in acids suffers from extra sluggish kinetics due to the additional step of water dissociation along with its multiple electron transfer processes. Furthermore, OER catalysts often suffer from poor stability in harsh acidic electrolytes due to the severe dissolution/corrosion processes. The development of active and stable OER catalysts in acids is highly demanded. Here,  the recent advances in OER electrocatalysis in acids are reviewed and the key strategies are summarized to overcome the bottlenecks of activity and stability for both noble-metal-based and noble metal-free catalysts, including i) morphology engineering, ii) composition engineering, and iii) defect engineering. Recent achievements in operando characterization and theoretical calculations are summarized which provide an unprecedented understanding of the OER mechanisms regarding active site identification, surface reconstruction, and degradation/dissolution pathways. Finally, views are offered on the current challenges and opportunities to break the activity-stability relationships for acidic OER in mechanism understanding, catalyst design, as well as standardized stability and activity evaluation for industrial applications such as proton exchange membrane water electrolyzers and beyond.

Controlling basal plane sulfur vacancy in water splitting MoSx/NiF electrocatalysts through electric-field-assisted pulsed laser ablation

Eco-friendly, efficient, and durable electrocatalysts from earth-abundant materials are crucial for water splitting through hydrogen and oxygen generation. However, available methods to fabricate electrocatalysts are either hazardous and time-consuming or require expensive equipment, hindering the large-scale, eco-friendly production of artificial fuels. Here, we present a rapid, single-step method for producing MoS_x/NiF electrocatalysts with controlled sulfur-vacancies via electric-field-assisted pulsed laser ablation (EF-PLA) in liquid and in-situ deposition on nickel foam, enabling efficient water splitting. Electric-field parameters efficiently control S-vacancy active sites in electrocatalysts. Higher electric fields yield a MoS_x/NiF electrocatalyst with a larger density of S-vacancy sites, suited for HER due to lower Gibbs free energy for H∗ adsorption, while lower electric fields produce an electrocatalyst with lower S-vacancy sites, better suited for OER, as shown by both experimental and theoretical results. The present work opens a horizon in designing high-efficiency catalysts, for a wide range of chemical reactions.

NiCoP-nanocubes-decorated CoSe2 nanowire arrays as high-performance electrocatalysts toward oxygen evolution reaction

Designing effective, robust, and low-cost catalysts for oxygen evolution reaction (OER) is an urgent requirement yet challenging task in water electrolysis. In this study, a NiCoP-nanocubes-decorated CoSe₂ nanowires arrays three-dimensional/two-dimensional (3D/2D) electrocatalyst (NiCoP-CoSe₂-2) was developed for catalyzing OER via a combined selenylation, co-precipitation, and phosphorization method. The as-obtained NiCoP-CoSe₂-2 3D/2D electrocatalyst exhibits a low overpotential of 202 mV at 10 mA cm^-2 with a small Tafel slope of 55.6 mV dec^-1, which is superior to most of reported CoSe₂ and NiCoP-based heterogeneous electrocatalysts. Experimental analyses and density functional theory (DFT) calculations proof that the interfacial coupling and synergy between CoSe₂ nanowires and NiCoP nanocubes are not only beneficial to strengthen the charge transfer ability and accelerate reaction kinetics, but also facilitate the optimization of interfacial electronic structure, thereby enhancing the OER property of NiCoP-CoSe₂-2. This study offers insights for the investigation and construction of transition metal phosphide/selenide heterogeneous electrocatalyst toward OER in alkaline media and broadens the prospect of industrial applications in energy storage and conversion fields.

Electrocatalysts for the Oxygen Evolution Reaction in Acidic Media

The well-established proton exchange membrane (PEM)-based water electrolysis, which operates under acidic conditions, possesses many advantages compared to alkaline water electrolysis, such as compact design, higher voltage efficiency, and higher gas purity. However, PEM-based water electrolysis is hampered by the low efficiency, instability, and high cost of anodic electrocatalysts for the oxygen evolution reaction (OER). In this review, the recently reported acidic OER electrocatalysts are comprehensively summarized, classified, and discussed. The related fundamental studies on OER mechanisms and the relationship between activity and stability are particularly highlighted in order to provide an atomistic-level understanding for OER catalysis. A stability test protocol is suggested to evaluate the intrinsic activity degradation. Some current challenges and unresolved questions, such as the usage of carbon-based materials and the differences between the electrocatalyst performances in acidic electrolytes and PEM-based electrolyzers are also discussed. Finally, suggestions for the most promising electrocatalysts and a perspective for future research are outlined. This review presents a fresh impetus and guideline to the rational design and synthesis of high-performance acidic OER electrocatalysts for PEM-based water electrolysis.

Facile fabrication of hierarchical ultrathin Rh-based nanosheets for efficient hydrogen evolution

Rational design of efficient and stable electrocatalysts for the hydrogen evolution reaction (HER) has attracted wide attention. Noble metal-based electrocatalysts with ultrathin structures and highly exposed active surfaces are essential to boost the HER performance, while the simple synthetic strategies remain challenging. Herein, we reported a facile urea-mediated method to synthesize hierarchical ultrathin Rh nanosheets (Rh NSs) without using toxic reducing agents and structure directing agents in the reaction. The hierarchical ultrathin nanosheet structure and grain boundary atoms endow Rh NSs with excellent HER activities, which only requires a lower overpotential of 39 mV in 0.5 M H2SO4 compared to the 80 mV of Rh nanoparticles (Rh NPs). Extending the synthesis method to alloys, hierarchical ultrathin RhNi nanosheets (RhNi NSs) can be also obtained. Benefiting from the optimization of electronic structure and abundant active surfaces, RhNi NSs only require an overpotential of 27 mV. This work provides a simple and promising method to construct ultrathin nanosheet electrocatalysts for highly active electrocatalytic performance.

Nano Si-Doped Ruthenium Oxide Particles from Caged Precursors for High-Performance Acidic Oxygen Evolution

RuO₂ is well known as the benchmark acidic oxygen evolution reaction (OER) catalyst, but its practical application has been impeded by its limited durability. Herein, it is presented that the stability of ruthenium oxide can be significantly improved by pretrapping RuCl₃ precursors within a cage compound possessing 72 aromatic rings, which leads to well carbon-coated RuO_x particles (Si-RuO_x @C) after calcination. The catalyst survives in 0.5 M H₂ SO₄ for an unprecedented period of 100 hours at 10 mA cm^-2 with minimal overpotential change during OER. In contrast, RuO_x prepared from similar non-tied compounds doesn't exhibit such catalytic activity, highlighting the importance of the preorganization of Ru precursors within the cage prior to calcination. In addition, the overpotential at 10 mA cm^-2 in acid solution is only 220 mV, much less than that of commercial RuO₂ . X-ray absorption fine structure (FT-EXAFS) reveals the Si doping through unusual Ru-Si bond, and density functional theory (DFT) calculation reveals the importance of the Ru-Si bond in enhancing both the activity and stability of the catalyst.

Self-Reconstructed Spinel Surface Structure Enabling the Long-Term Stable Hydrogen Evolution Reaction/Oxygen Evolution Reaction Efficiency of FeCoNiRu High-Entropy Alloyed Electrocatalyst

High catalytic efficiency and long-term stability are two main components for the performance assessment of an electrocatalyst. Previous attention has been paid more to efficiency other than stability. The present work is focused on the study of the stability processed on the FeCoNiRu high-entropy alloy (HEA) in correlation with its catalytic efficiency. This catalyst has demonstrated not only performing the simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with high efficiency but also sustaining long-term stability upon HER and OER. The study reveals that the outstanding stability is attributed to the spinel oxide surface layer developed during evolution reactions. The spinel structure preserves the active sites that are inherited from the HEA's intrinsic structure. This work will provide an insightful direction/pathway for the design and manufacturing activities of other metallic electrocatalysts and a benchmark for the assessment of their efficiency-stability relationship.

Ternary alloy (FeCoNi) nanoparticles supported on hollow porous carbon with defects for enhanced oxygen evolution reaction

Low-cost non-noble metal nanoparticles are promising electrocatalysts that can catalyze oxygen evolution reaction (OER). Various factors such as poor activity and stability hinder the practical applications of these materials. The electroactivity and durability of the electrocatalysts can be improved by optimizing the morphology and composition of the materials. Herein, we report the successful synthesis of hollow porous carbon (HPC) catalysts loaded with ternary alloy (FeCoNi) nanoparticles (HPC-FeCoNi) for efficient OER. HPC is firstly synthesized by a facile carbon deposition method using the hierarchical porous zeolite ZSM-5 as the hard template. Numerous defects are generated on the carbon shell during the removal of zeolite template. Subsequently, FeCoNi alloy nanoparticles are supported on HPC by a sequence of impregnation and H₂ reduction processes. The synergistic effect between carbon defects and FeCoNi alloy nanoparticles endows the catalyst with an excellent OER performance (low overpotential of 219 mV; Tafel slope of 60.1 mV dec^-1) in a solution of KOH (1 M). A stable potential is maintained during the continuous operation over 72 h. The designed HPC-FeCoNi presents a platform for the development of electrocatalysts that can be potentially applied for industrial OER.

Understanding the Copper-Iridium Nanocrystals as Highly Effective Bifunctional pH-universal Electrocatalysts for Water Splitting

It is pivotal to develop an economical, effective, and stable catalyst to promote the oxygen/hydrogen evolution reaction (OER/HER) throughout pH electrolytes, as the demand for hydrogen energy will increase greatly with the future development. Herein, a series of Ir-Cu nanoparticle composite carbon (Ir_xCu_y/C) catalysts are successfully synthesized using ethylene glycol reduction. In addition, the structure, morphology and composition of the electrocatalysts were systematically characterized, and the OER/HER performance of the catalysts was also tested under different pH conditions. According to experimental findings, amorphous Ir₃Cu/C has superior competent performance to catalyze oxygen (O₂) production in alkaline and acidic environments. The comparatively low overpotentials required are 222 mV and 304 mV, respectively, while generating a current density of 10 mA cm^-2. The reduced amount of precious metal and the further improvement in activity and durability make Ir₃Cu/C an excellent noble metal-based electrocatalyst. Meanwhile, IrCu/C has significant electrocatalytic performance for the HER in acidic media.

Oxygen Evolution/Reduction Reaction Catalysts: From In Situ Monitoring and Reaction Mechanisms to Rational Design

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are core steps of various energy conversion and storage systems. However, their sluggish reaction kinetics, i.e., the demanding multielectron transfer processes, still render OER/ORR catalysts less efficient for practical applications. Moreover, the complexity of the catalyst-electrolyte interface makes a comprehensive understanding of the intrinsic OER/ORR mechanisms challenging. Fortunately, recent advances of in situ/operando characterization techniques have facilitated the kinetic monitoring of catalysts under reaction conditions. Here we provide selected highlights of recent in situ/operando mechanistic studies of OER/ORR catalysts with the main emphasis placed on heterogeneous systems (primarily discussing first-row transition metals which operate under basic conditions), followed by a brief outlook on molecular catalysts. Key sections in this review are focused on determination of the true active species, identification of the active sites, and monitoring of the reactive intermediates. For in-depth insights into the above factors, a short overview of the metrics for accurate characterizations of OER/ORR catalysts is provided. A combination of the obtained time-resolved reaction information and reliable activity data will then guide the rational design of new catalysts. Strategies such as optimizing the restructuring process as well as overcoming the adsorption-energy scaling relations will be discussed. Finally, pending current challenges and prospects toward the understanding and development of efficient heterogeneous catalysts and selected homogeneous catalysts are presented.

Semicrystalline IrOx with Abundant Boundaries for Overall Water Splitting

Inorganic compounds with different crystalline and amorphous states may show distinct properties in catalytic applications. In this work, we control the crystallization level by fine thermal treatment and synthesize a semicrystalline IrO_x material with the formation of abundant boundaries. Theoretical calculation reveals that the interfacial iridium with a high degree of unsaturation is highly active for the hydrogen evolution reaction compared to individual counterparts based on the optimal binding energy with hydrogen (H*). At the heat treatment temperature of 500 °C, the obtained IrO_x-500 catalyst has dramatically promoted hydrogen evolution kinetics, endowing the iridium catalyst with a bifunctional activity for acidic overall water splitting with a total voltage of only 1.554 V at a current density of 10 mA cm^-2. In light of the remarkable boundary-enhanced catalysis effects, the semicrystalline material should be further developed for other applications.

Single atomic Ru in TiO2 boost efficient electrocatalytic water oxidation to hydrogen peroxide

Electrocatalytic two-electron water oxidation affords a promising approach for distributed production of H₂O₂ using electricity. However, it suffers from the trade-off between the selectivity and high production rate of H₂O₂ due to the lack of suitable electrocatalysts. In this study, single atoms of Ru were controllably introduced into titanium dioxide to produce H₂O₂ through an electrocatalytic two-electron water oxidation reaction. The adsorption energy values of OH intermediates could be tuned by introducing Ru single atoms, offering superior H₂O₂ production under high current density. Notably, a Faradaic efficiency of 62.8% with an H₂O₂ production rate of 24.2 μmol min^-1 cm^-2 (>400 ppm within 10 min) was achieved at a current density of 120 mA cm^-2. Consequently, herein, the possibility of high-yield H₂O₂ production under high current density was demonstrated and the importance of regulating intermediate adsorption during electrocatalysis was evidenced.

Construction of nickel sulfide phase-heterostructure for alkaline hydrogen evolution reaction

Constructing transitionmetalsulfides (TMSs) heterostructure is an effective strategy to optimize the catalytic performance for hydrogen evolution reaction (HER) in alkaline medium. Herein, the rhombohedral nickel sulfide/hexagonal nickel sulfide (r-NiS/h-NiS) catalysts with the NiS phase-heterostructure were successfully fabricated by a simple one pot method. The r-NiS/h-NiS (1.25) (1.25 means the theoretical mole ratio of S and Ni added to reaction) displayed the excellent HER performance with low overpotential (101 ± 1 mV@10 mA cm^-2) and small Tafel slope (62.10 ± 0.1 mV dec^-1), which were superior to the pure phase r-NiS and h-NiS. In this work, the improved HER catalytic performances were attributed to the dense coupling interfaces between the r-NiS and h-NiS. This work shows the feasibility of construction NiS phase-heterostructure and provides a novel strategy for the application of NiS for water splitting.

Coaxial Nanofiber IrOx@SbSnOx as an Efficient Electrocatalyst for Proton Exchange Membrane Dehumidifier

Development of efficient catalysts for oxygen evolution reaction (OER) remains challenging in PEM dehumidifier or vapor electrolyzer. This study developed novel coaxial IrO_x@SbSnO_x nanofiber (NF) catalysts by electrospinning using a dual-channel needle. This method ensures the fibrous structure and the uniform loading of Ir oxide on the support of antimony tin oxide (ATO). IrO₂@SbSnO_x nanoparticles were synthesized for comparison. Characterizations showed that the active area and charge transfer resistance of NF was 1.47 times and 17.72% of that of commercial ones, respectively. The overpotential of NF at 10 mA·cm^-2 was 359 mV, much smaller than that of commercial IrO₂ (418 mV). In addition, the reaction overpotential of NF increased by only 38 mV after 1000 cyclic voltammetry cycles, indicating good electrochemical stability. To explore the enhancement mechanism, first-principles calculations were conducted for theoretically simulating the hetero-structures. Based on d-band theory, the structure formed between ATO and IrO₂ can effectively weaken the adsorption of oxygen intermediates on the catalyst surface, which reduces the OER energy barrier from 1.705 to 1.632 eV, causing an over 15% decrease of overpotential after loading on ATO. As a practical attempt, we applied the new catalysts in real PEM assembly for air dehumidification and found that the performance was improved by about 2 times compared with that using commercial catalysts. This study provides a research direction for the design of one-dimensional NF catalysts and their using in PEM applications.

A RuCoBO Nanocomposite for Highly Efficient and Stable Electrocatalytic Seawater Splitting

Efficient and stable electrocatalysts are critically needed for the development of practical overall seawater splitting. The nanocomposite of RuCoBO has been rationally engineered to be an electrocatalyst that fits these criteria. The study has shown that a calcinated RuCoBO-based nanocomposite (Ru₂Co₁BO-350) exhibits an extremely high catalytic activity for H₂ and O₂ production in alkaline seawater (overpotentials of 14 mV for H₂ evolution and 219 mV for O₂ evolution) as well as a record low cell voltage (1.466 V@10 mA cm^-2) and long-term stability (230 h @50 mA cm^-2 and @100 mA cm^-2) for seawater splitting. The results show that surface reconstruction of Ru₂Co₁BO-350 occurs during hydrogen evolution reaction and oxygen evolution reaction, which leads to the high activity and stability of the catalyst. The reconstructed surface is highly resistant to Cl^- corrosion. The investigation suggests that a new strategy exists for the design of high-performance Ru-based electrocatalysts that resist anodic corrosion during seawater splitting.