Design of Ru-Ni diatomic sites for efficient alkaline hydrogen oxidation

Engineering Local Coordination and Electronic Structures of Dual-Atom Catalysts

Heterogeneous dual-atom catalysts (DACs), defined by atomically precise and isolated metal pairs on solid supports, have garnered significant interest in advancing catalytic processes and technologies aimed at achieving sustainable energy and chemical production. DACs present board opportunities for atomic-level structural and property engineering to enhance catalytic performance, which can effectively address the limitations of single-atom catalysts, including restricted active sites, spatial constraints, and the typically positive charge nature of supported single metal species. Despite the rapid progress in this field, the intricate relationship between local atomic environments and the catalytic behavior of dual-metal active sites remains insufficiently understood. This review highlights recent progress and major challenges in this field. We begin by discussing the local modulation of coordination and electronic structures in DACs and its impact on catalytic performance. Through specific case studies, we demonstrate the importance of optimizing the entire catalytic ensemble to achieve efficient, selective, and stable performance in both model and industrially relevant reactions. Additionally, we also outline future research directions, emphasizing the challenges and opportunities in synthesis, characterization, and practical applications, aiming to fully unlock the potential of these advanced catalysts.

Atomically Dispersed Co-Ru Dimer Catalyst Boosts Conversion of Polysulfides toward High-Performance Lithium-Sulfur Batteries

The sluggish sulfur redox reaction in lithium-sulfur (Li-S) batteries triggers the development of highly active electrocatalysts for accelerating the polysulfides conversion kinetics. Rational design of catalysts with satisfactory active sites and high atom utilization toward multistep sulfur-based conversion is much desired but remains challenging. Here, it is shown that the well-designed Co-Ru dimer sites confined on carbon matrix could effectively manipulate the sulfur-involved conversion reactions and thus improve Li-S batteries performance. The orbital coupling of Co-Ru dimer induces the orbital regulation for the atomic pair, resulting the favored lithium polysulfides adsorption strength and lowed conversion energy barrier, as confirmed by systematic electrochemical characterizations and theoretical calculation. Besides, the intrinsic catalytic activity of Ru from Co-Ru moiety also accelerates the Li2S dissociation reaction. Taken together, the as-constructed Co-Ru dimer sites render the Li-S battery with excellent performance, delivering energy density of 468 Wh kg-1 of total assembled pouch cell. This study offers a rational design of catalysts for boosting the catalytic performance in Li-S batteries.

Atomic Symbiotic-Catalyst for Low-Temperature Zinc-Air Battery

Atomic-level designed electrocatalysts, including single-/dual-atom catalysts, have attracted extensive interests due to their maximized atom utilization efficiency and increased activity. Herein, a new electrocatalyst system termed as "atomic symbiotic-catalyst", that marries the advantages of typical single-/dual-atom catalysts while addressing their respective weaknesses, was proposed. In atomic symbiotic-catalyst, single-atom MNx and local carbon defects formed under a specific thermodynamic condition, act synergistically to achieve high electrocatalytic activity and battery efficiency. This symbiotic-catalyst shows greater structural precision and preparation accessibility than those of dual-atom catalysts owing to its reduced complexity in chemical space. Meanwhile, it outperforms the intrinsic activities of conventional single-atom catalysts due to multi-active-sites synergistic effect. As a proof-of-concept study, an atomic symbiotic-catalyst comprising single-atom MnN4 moieties and abundant sp3-hybridized carbon defects was constructed for low-temperature zinc-air battery, which exhibited a high peak power density of 76 mW cm-2 with long-term stability at -40 °C, representing a top-level performance of such batteries.

Highly Distorted High-Entropy Alloy Aerogels for High-Efficiency Hydrogen Oxidation Reaction

The development of efficient electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is essential for anion exchange membrane fuel cells and advancing the hydrogen economy. Herein, we demonstrated PtRuRhPdIr high-entropy alloy aerogels (HEAAs) with highly distorted structure as efficient HOR electrocatalysts and realized effective control of PtRu-based metallic aerogels (MAs) with elemental components ranging from two to seven. Specially, PtRuRhPdIr HEAAs on carbon (PtRuRhPdIr HEAAs/C) exhibit excellent HOR activity, with Pt group metal (PGM)-normalized mass activity (5.75 A mgPGM-1) at 50 mV and exchange current density normalized by electrochemical surface area (0.69 mA cm-2), approximately 16.9 and 4.1 times that of the commercial Pt/C (0.34 A mgPGM-1, 0.17 mA cm-2), respectively. The mechanism study shows that the highly distorted PtRuRhPdIr HEAAs provide abundant unsaturated sites for HOR, and the synergistic effect of multiple-active sites balances the adsorption of H* and *OH, boosting the HOR performance.

Breaking symmetry for better catalysis: insights into single-atom catalyst design

Breaking structural symmetry has emerged as a powerful strategy for fine-tuning the electronic structure of catalytic sites, thereby significantly enhancing the electrocatalytic performance of single-atom catalysts (SACs). The inherent symmetric electron density in conventional SACs, such as M-N4 configurations, often leads to suboptimal adsorption and activation of reaction intermediates, limiting their catalytic efficiency. By disrupting this symmetry of SACs, the electronic distribution around the active center can be modulated, thereby improving both the selectivity and adsorption strength for key intermediates. These changes directly impact the reaction pathways, lowering energy barriers, and enhancing catalytic activity. However, achieving precise modulation through SAC symmetry breaking for better catalysis remains challenging. This review focuses on the atomic-level symmetry-breaking strategies of catalysts, including charge breaking, coordination breaking, and geometric breaking, as well as their electrocatalytic applications in electronic structure tuning and active site modulation. Through modifications to the M-N4 framework, three primary configurations are achieved: unsaturated coordination M-Nx(x=1,2,3), non-metallic doping MX-Nx(x=1,2,3), and bimetallic doping M1M2-N4. Advanced characterization techniques combined with density functional theory (DFT) elucidate the impact of these strategies on oxidation, reduction, and bifunctional catalytic reactions. This review highlights the significance of symmetry-breaking structures in catalysis and underscores the need for further research to achieve precise control at the atomic-level.

Electrosynthesis of Urea on High-Density Ga─Y Dual-Atom Catalyst via Cross-Tuning

Electrochemically converting carbon dioxide (CO2) and nitrate (NO3 -) into urea via the C─N coupling route offers a sustainable alternative to the traditional industrial urea production technology, but it is still limited by poor yield rate, low Faradaic efficiency, and insufficient coupling kinetics. Herein, a high-density Ga─Y dual-atom catalyst is developed with loading up to 14.1 wt.% of Ga and Y supported on N, P-co-doped carbon substrate (Ga/Y-CNP) for urea electrosynthesis. The catalyst facilitates efficient C─N coupling through co-reduction of CO2 and NO3 -, resulting in a high urea yield rate of 41.9 mmol h-1 g-1 and a Faradaic efficiency of 22.1% at -1.4 V versus the reversible hydrogen electrode. In situ spectroscopy and theoretical calculations reveal that the superior performance is attributed to the cross-tuning between adjacent pair Ga─Y sites, which can mutually optimize their electronic states for facilitating CO2 reduction to *CO at Ga sites and promoting NO3 - conversion to hydroxylamine (*NH2OH) at Y sites, followed by spontaneous coupling of *CO and *NH2OH intermediates at Ga─Y sites to form C─N bonds. This work offers a pioneering strategy to manipulate C─N coupling pathways by cross-tuning active sites to produce high-value-added chemicals.

In Situ Grown RuNi Alloy on ZrNiNx as a Bifunctional Electrocatalyst Boosts Industrial Water Splitting

Alkaline water electrolysis represents a pivotal technology for green hydrogen production yet faces critical challenges including limited current density and high energy input. Herein, a heterostructured bimetallic nitrides supported RuNi alloy (RuNi/ZrNiNx) is developed through in situ epitaxial growth under ammonolysis, achieving exceptional bifunctional activity and durability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 m KOH electrolyte. The RuNi/ZrNiNx exhibits a HER current density of -2 A cm-2 at an overpotential of 392.8 mV, maintaining initial overpotential after 1000 h continuous electrolysis at -500 mA cm-2. For OER, it delivers a current density of 2 A cm-2 at 1.822 V versus RHE, and sustains stable operation for 705 h at 500 mA cm-2. Experimental and theoretical studies unveil that the charge redistribution-induced high-valence Zr centers effectively polarize H─O bonds and promote water dissociation, and the electron-deficient interface Ru sites optimize hydrogen desorption kinetics. Dynamic OH spillovers from Zr sites to the adjacent tri-coordinated Ni hollow sites in NiNx promote rapid *OH intermediate desorption and active site regeneration. Notably, the tri-coordinated Ni hollow sites in NiNx proximal to Zr atoms exhibit tailored adsorption strength for oxo-intermediates, enabling a more energetically favorable pathway for O2 production.

Cluster-Scale Multisite Interface Reinforces Ruthenium-Based Anode Catalysts for Alkaline Anion Exchange Membrane Fuel Cells

Ruthenium (Ru) is a more cost-effective alternative to platinum anode catalysts for alkaline anion-exchange membrane fuel cells (AEMFCs), but suffers from severe competitive adsorption of hydrogen (Had) and hydroxyl (OHad). To address this concern, a strongly coupled multisite electrocatalyst with highly active cluster-scale ruthenium-tungsten oxide (Ru-WOx) interface, which could eliminate the competitive adsorption phenomenon and achieve high coverage of OHad and Had at Ru and WOx domains, respectively, is designed. The experimental and theoretical results demonstrate that WOx domain functions as a proton sponge to perpetually accommodate the activated hydrogen species that spillover from the adjacent Ru domain, and the resulting WO-Had species are readily coupled with Ru-OHad at the heterointerface to finish the hydrogen oxidation reaction with faster kinetics via the thermodynamically favorable Tafel-Volmer mechanism. The AEMFC delivers a high peak power density of 1.36 W cm-2 with a low anode catalyst loading of 0.05 mgRu cm-2 and outstanding durability (negligible voltage decay over 80-h operation at 500 mA cm-2). This work offers completely new insights into understanding the alkaline HOR mechanism and designing advanced anode catalysts for AEMFCs.

Isolated Metal Centers Activate Small Molecule Electrooxidation: Mechanisms and Applications

Electrochemical oxidation of small molecules shows great promise to substitute oxygen evolution reaction (OER) or hydrogen oxidation reaction (HOR) to enhance reaction kinetics and reduce energy consumption, as well as produce high-valued chemicals or serve as fuels. For these oxidation reactions, high-valence metal sites generated at oxidative potentials are typically considered as active sites to trigger the oxidation process of small molecules. Isolated atom site catalysts (IASCs) have been developed as an ideal system to precisely regulate the oxidation state and coordination environment of single-metal centers, and thus optimize their catalytic property. The isolated metal sites in IASCs inherently possess a positive oxidation state, and can be more readily produce homogeneous high-valence active sites under oxidative potentials than their nanoparticle counterparts. Meanwhile, IASCs merely possess the isolated metal centers but lack ensemble metal sites, which can alter the adsorption configurations of small molecules as compared with nanoparticle counterparts, and thus induce various reaction pathways and mechanisms to change product selectivity. More importantly, the construction of isolated metal centers is discovered to limit metal d-electron back donation to CO 2p* orbital and reduce the overly strong adsorption of CO on ensemble metal sites, which resolve the CO poisoning problems in most small molecules electro-oxidation reactions and thus improve catalytic stability. Based on these advantages of IASCs in the fields of electrochemical oxidation of small molecules, this review summarizes recent developments and advancements in IASCs in small molecules electro-oxidation reactions, focusing on anodic HOR in fuel cells and OER in electrolytic cells as well as their alternative reactions, such as formic acid/methanol/ethanol/glycerol/urea/5-hydroxymethylfurfural (HMF) oxidation reactions as key reactions. The catalytic merits of different oxidation reactions and the decoding of structure-activity relationships are specifically discussed to guide the precise design and structural regulation of IASCs from the perspective of a comprehensive reaction mechanism. Finally, future prospects and challenges are put forward, aiming to motivate more application possibilities for diverse functional IASCs.

Optimized Adsorption of Had and OHad over Amorphous SrRuPtOxHy Nanobelts towards Efficient Alkaline Fuel Cell Catalysis

PtRu-based catalysts toward hydrogen oxidation reaction (HOR) suffer from low efficiency, CO poisoning and over-oxidation at high potentials. In this work, an amorphization strategy is adopted for preparation of amorphous SrRuPtOxHy nanobelts (a-SrRuPtOxHy NBs). The a-SrRuPtOxHy NBs has optimized adsorption of intermediates (H and OH), increased number of active sites, highly weakened CO poisoning and enhanced anti-oxidation ability owing to the special amorphous structure. Consequently, a-SrRuPtOxHy NBs displays superior HOR performance with a mass activity of 7.5 A/mgPt+Ru, 25 and 5 times of that of SrRuPt(OH)x NBs and commercial PtRu/C, respectively, and long-lasting stability. Besides, a peak power density of 750 mW/cm2 and a specific power of 14.8 W/mgPt+Ru have been achieved for a-SrRuPtOxHy NBs at a low loading of 0.05 mgPt+Ru/cm2, surpassing many reported HOR catalysts. Mechanism investigation indicates that Pt and Ru are present in oxide/hydroxide forms and H in a-SrRuPtOxHy NBs participates in HOR. Ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations show that there are three catalytic mechanisms participating in a-SrRuPtOxHy NBs, which all exhibit low catalytic barrier and highly improved HOR efficiency. This work provides a new strategy for designing high-performance catalysts towards fuel cells.

An Efficient H2S-Tolerant Hydrogen Oxidation Electrocatalyst Enabled by a Lewis Acid Modifier for Fuel Cells

Industrial hydrogen fuel typically comprises about 5 ppm of hydrogen sulfide (H2S), incurring irreversible poisoning of platinum on carbon (Pt/C) catalyst in fuel cells. For realistic use, H2S should be removed to below 4 ppb; this process, however, is challenging and costly. We describe an exceptional H2S-tolerant yet high-performing hydrogen oxidation reaction (HOR) catalyst prepared by chemical grafting of chromic oxide (Cr2O3) onto a molybdenum-nickel (MoNi4) alloy. Cr2O3 as a Lewis acid enhances the specific adsorption of hydroxyl ions, which in turn prevents from S2- diffusing to the catalyst surface via electrostatic repulsion. Meanwhile, the adsorbed hydroxyl species boost HOR kinetics through improving the hydrogen-bond networks in electrical double layers. The composite catalyst achieved HOR performance comparable to that of commercial Pt/C in an alkaline electrolyte. Moreover, a fuel cell using this catalyst as anode can survive 5 ppm of H2S without deactivation, compared with rapid degradation observed over the Pt/C counterpart.

High-Density Accessible Iron Single-Atom Catalyst for Durable and Temperature-Adaptive Laminated Zinc-Air Batteries

Designing single-atom catalysts (SACs) with high density of accessible sites by improving metal loading and sites utilization is a promising strategy to boost the catalytic activity, but remains challenging. Herein, a high site density (SD) iron SAC (D-Fe-N/C) with 11.8 wt.% Fe-loading is reported. The in situ scanning electrochemical microscopy technique attests that the accessible active SD and site utilization of D-Fe-N/C reach as high as 1.01 × 1021 site g-1 and 79.8%, respectively. Therefore, D-Fe-N/C demonstrates superior oxygen reduction reaction (ORR) activity in terms of a half-wave potential of 0.918 V and turnover frequency of 0.41 e site-1 s-1. The excellent ORR property of D-Fe-N/C is also demonstrated in the liquid zinc-air batteries (ZABs), which exhibit a high peak power density of 306.1 mW cm-2 and an ultra-long cycling stability over 1200 h. Moreover, solid-state laminated ZABs prepared by presetting an air flow layer show a high specific capacity of 818.8 mA h g-1, an excellent cycling stability of 520 h, and a wide temperature-adaptive from -40 to 60 °C. This work not only offers possibilities by improving metal-loading and catalytic site utilization for exploring efficient SACs, but also provides strategies for device structure design toward advanced ZABs.

Cost-Effective RuNi Solid Solutions Prepared by Electrodeposition for Efficient Alkaline Hydrogen Evolution

The development of efficient hydrogen evolution reaction (HER) catalysts is crucial for water electrolysis. Currently, Ru-based catalysts are considered top contenders, but issues with stability, activity, and cost remain. In this work, RuNi alloys possessing a solid solution structure within the Ru lattice are prepared via straightforward electrodeposition on various substrates and assessed as HER catalysts in alkaline media. A RuNi solid solution containing 9.8 at. % Ni deposited on Ti substrate, wherein the Ni content greatly surpasses the solubility limit of Ni in Ru at room temperature, exhibits a considerably low overpotential of 28 mV at a current density of 10 mA cm- 2, along with good long-term stability (less than 100 mV increase in overpotential after 600 h). The enhancement in HER performance results from the increased electron density around Ru atoms due to Ni coordination, which facilitates the desorption of H* from the catalyst surface to produce H2. Concurrently, incorporating Ni reduces the Ru usage, rendering the RuNi alloy a viable cost-effective HER catalyst for practical applications.

Facilitating alkaline hydrogen evolution kinetics via interfacial modulation of hydrogen-bond networks by porous amine cages

The electrode-electrolyte interface is pivotal in the electrochemical kinetics. However, modulating the electrochemical interface at the atomic or molecular level is challenging due to the lack of efficient interfacial regulators. Here, we employ a porous amine cage as an interfacial modifier to Pt cluster in a confining configuration, largely enhancing alkaline HER kinetics by facilitating charge transfer. In situ electrochemical surface-enhanced Raman spectra, in combination with the ab initio molecular dynamics simulation, elucidates that the interaction between water and the -NH- moiety of cage frame softens the H-bonds net of interfacial water, making it more flexible for charge transfer. Moreover, our investigation pinpointed that the -NH- moiety acted as a pump for charge transfer by Grotthuss mechanism, lowering the kinetic barrier for hydrogen adsorption. Our findings highlight the strategy of establishing a soft-confining interfacial modifier by porous cage, offering opportunities to optimize electrochemical interfaces and promote reaction kinetics in a targeted way.

Pd1Ni2 Trimer Sites Drive Efficient and Durable Hydrogen Oxidation in Alkaline Media

Anion-exchange membrane fuel cell (AEMFC) is a cost-effective hydrogen-to-electricity conversion technology under a zero-emission scenario. However, the sluggish kinetics of the anodic hydrogen oxidation reaction (HOR) impedes the commercial implementation of AEMFCs. Here, we develop a Pd single-atom-embedded Ni3N catalyst (Pd1/Ni3N) with unconventional Pd1Ni2 trimer sites to drive efficient and durable HOR in alkaline media. Integrating theoretical and experimental analyses, we demonstrate that dual Pd1Ni2 sites achieve a "*H on Pd1Ni2-HV + *OH on Pd1Ni2-HN" adsorption mode, effectively weakening the overstrong *H and *OH adsorptions on pristine Ni3N. Owing to the unique coordination mode and atomically dispersed catalytic sites, the resulting Pd1/Ni3N catalyst delivers a high intrinsic and mass activity together with excellent antioxidation capability and CO tolerance. Specifically, the HOR mass activity of Pd1/Ni3N reaches 7.54 A mgPd-1 at the overpotential of 50 mV. The AEMFC employing Pd1/Ni3N as the anode catalyst displays a high power density of 31.7 W mgPd-1 with an ultralow anode precious metal loading of only 0.023 mgPd cm-2. This study provides guidance for the design of high-performance alkaline HOR catalytic sites at the atomic level.

An Interstitial Boron Inserted Metastable Hexagonal Rh Nanocrystal for Efficient Hydrogen Oxidation Electrocatalysis

Constructing metastable phase structure plays an important role in changing the physicochemical properties and improving the catalytic performance of nanocrystals. Unfortunately, the synthesis of metastable phase metallic nanocrystals is highly challenging, mainly due to the thermodynamically unstable ground-state. Here, we report a synthesis of unconventional metastable hexagonal rhodium nanocrystal (Bint-Rhhcp/C) via interstitial boron insertion. The insertion of boron atoms into the interstitial sites of cubic Rh lattice not only induces the atomic arrangements from face-centered cubic (fcc) to hexagonal close-packed (hcp), but also stabilizes the metastable hexagonal Rh structure. Benefiting from the phase transition and interstitial boron doping, the Bint-Rhhcp/C catalyst exhibits remarkable catalytic performance toward hydrogen oxidation reaction (HOR) under alkaline media, with a mass activity of 1.413 mA μgPGM -1. Experimental measurements including in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations indicate that the strengthened adsorption of hydroxyl species on the electrode surface of Bint-Rhhcp/C is responsible for the reconstruction of interfacial water structure and increased water proportions in the gap region in the electric double layers. As a result, the increased water connectivity and hydrogen bond network facilitate high-efficiency hydrogen transfer across the interface, thereby boost the alkaline HOR performance.

Hollow Pt-Encrusted RuCu Nanocages Optimizing OH Adsorption for Efficient Hydrogen Oxidation Electrocatalysis

As one of the best candidates for hydrogen oxidation reaction (HOR), ruthenium (Ru) has attracted significant attention for anion exchange membrane fuel cells (AEMFCs), although it suffers from sluggish kinetics under alkaline conditions due to its strong hydroxide affinity. In this work, we develop ternary hollow nanocages with Pt epitaxy on RuCu (Pt-RuCu NCs) as efficient HOR catalysts for application in AEMFCs. Experimental characterizations and theoretical calculations confirm that the synergy in optimized Pt8.7-RuCu NCs significantly modifies the electronic structure and coordination environment of Ru, thereby balancing the binding strengths of H* and OH* species, which leads to a markedly enhanced HOR performance. Specifically, the optimized Pt8.7-RuCu NCs/C achieves a mass activity of 5.91 A mgPt+Ru -1, which is ~3.3, ~2.2, and ~15.0 times higher than that of RuCu NCs/C (1.38 A mgRu -1), PtRu/C (1.83 A mgPt+Ru -1) and Pt/C (0.37 A mgPt -1), respectively. Impressively, the specific peak power density of fuel cells reaches 15.9 W mgPt+Ru -1, significantly higher than those of most reported PtRu-based fuel cells.

Solvation Effect-Determined Mechanisms of Cation Exchange Reactions for Efficient Multicomponent Nanocatalysts

Cation exchange (CE) reaction is a classical synthesis method for creating complex structures. A lock of study on intrinsic mechanism limits its understanding and practical application. Using X-ray absorption spectroscopy, we observed that the evolution from Ru-Cl to Ru-O/OH occurs during the CE between K2RuCl6 and CoSn(OH)6 in aqueous solution, while CE between K2PtCl6 and CoSn(OH)6 is inhibited due to the failure of structural evolution from Pt-Cl to Pt-O/OH. Theoretical simulations imply that the interaction between Ru-O and CoSn(OH)6 with Co vacancy (CoVCoSn(OH)6) endows the electron transfer, as a result of strengthened adsorption on CoVCoSn(OH)6. Moreover, this mechanism is validated for CE between K2RuCl6 and ASn(OH)6 (A=Mg, Ca, Mn, Co, Cu, Zn), and CE between K2PdCl6/Na3RhCl6/K2IrCl6 and CoSn(OH)6. Impressively, the Pt-free CoRuSn(OH)x produced via CE displays a mass activity and a power density of 15.0 A mgRu -1 and 11.6 W mgRu -1, respectively, for anion exchange membrane fuel cell (AEMFC) exceeding the values of commercial PtRu/C (11.8 A mgRu+Pt -1 and 9.0 W mgRu+Pt -1). This work, for the first time, reveals the intrinsic mechanism of CE as structural evolution of target ion breaking through the traditional classic etch-adsorption mechanism and will promote fundamental research and practical application in various fields.

Defect Engineering of Metal-Based Atomically Thin Materials for Catalyzing Small-Molecule Conversion Reactions

Recently, metal-based atomically thin materials (M-ATMs) have experienced rapid development due to their large specific surface areas, abundant electrochemically accessible sites, attractive surface chemistry, and strong in-plane chemical bonds. These characteristics make them highly desirable for energy-related conversion reactions. However, the insufficient active sites and slow reaction kinetics leading to unsatisfactory electrocatalytic performance limited their commercial application. To address these issues, defect engineering of M-ATMs has emerged to increase the active sites, modify the electronic structure, and enhance the catalytic reactivity and stability. This review provides a comprehensive summary of defect engineering strategies for M-ATM nanostructures, including vacancy creation, heteroatom doping, amorphous phase/grain boundary generation, and heterointerface construction. Introducing recent advancements in the application of M-ATMs in electrochemical small molecule conversion reactions (e.g., hydrogen, oxygen, carbon dioxide, nitrogen, and sulfur), which can contribute to a circular economy by recycling molecules like H2, O2, CO2, N2, and S. Furthermore, a crucial link between the reconstruction of atomic-level structure and catalytic activity via analyzing the dynamic evolution of M-ATMs during the reaction process is established. The review also outlines the challenges and prospects associated with M-ATM-based catalysts to inspire further research efforts in developing high-performance M-ATMs.

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

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

Strategies for Achieving Carbon Neutrality: Dual-Atom Catalysts in Focus

Carbon neutrality is a fundamental strategy for achieving the sustainable development of human society. Catalyzing CO2 reduction into various high-value-added fuels serves as an effective pathway to achieve this strategic objective. Atom-dispersed catalysts have received extensive attention due to their maximum atomic utilization, high catalytic selectivity, and exceptional catalytic performance. Dual-atom catalysts (DACs), as an extension of single-atom catalysts (SACs), not only retain the advantages of SACs, but also produce many new properties. This review initiates its exploration by elucidating the mechanism of CO2 reduction reaction (CO2RR) from CO2 adsorption and CO2 activation. Then, a comprehensive summary of recently developed preparation methods of DACs is presented. Importantly, the mechanisms underlying the promoted catalytic performance of DACs in comparison to SACs are subjected to a comprehensive analysis from adjustable adsorption capacity, tunable electronic structure, strong synergistic effect, and enhanced spacing effect, elucidating their respective superiorities in CO2RR. Subsequently, the application of DACs in CO2RR is discussed in detail. Conclusively, the prospective trajectories and inherent challenges of CO2RR are expounded upon concerning the continued advancement of DACs. This thorough review not only enhances the comprehension of DACs within CO2RR but also accentuates the prospective developments in the design of sophisticated catalytic materials.

Tailoring a Transition Metal Dual-Atom Catalyst via a Screening Descriptor in Li-S Batteries

The adsorption-conversion paradigm of polysulfides during the sulfur reduction reaction (SRR) is appealing to tackle the shuttle effect in Li-S batteries, especially based upon atomically dispersed electrocatalysts. However, mechanistic insights into such catalytic systems remain ambiguous, limiting the understanding of sulfur electrochemistry and retarding the rational design of available catalysts. Herein, we systematically explore the polysulfide adsorption-conversion essence via a geminal-atom model system to understand the catalyst roles toward an expedited SRR. A descriptor involving an electronic structure index (IES) and electron affinity index (IEA) is proposed, considering the geometric and electronic dictation within a Fe/M (M: 3d-block transition metal) atomic ensemble. With the aid of theoretical computation, we managed to identify the SRR thermodynamic/kinetic trends of Fe/M moieties. Guided by these findings, we in target design a Fe/V-NC dual-atom catalyst, which harvests a minimum IES and maximum IEA, accordingly demonstrating enhanced polysulfide adsorption-conversion and improved full-cell performances. Such a consistency between a computational descriptor and experimental evidence highlights the importance of an atomic catalyst screen and selection for Li-S batteries.

Expediting the Volmer Step of Alkaline Hydrogen Oxidation with High-Efficiency and CO-Tolerance by Ru-O-Eu Bridge

The quest for economical and highly efficient nanomaterials for the alkaline hydrogen oxidation reaction (HOR) is imperative in advancing the technology of anion exchange membrane fuel cells (AEMFCs). Efforts using Pt-based electrocatalysts for alkaline HOR are greatly plagued by their finitely intrinsic activities and significant CO poisoning, stemming from the difficulty of simultaneously optimizing surface adsorption toward different hydrogen-related adsorbates. Herein, Ru clusters coupled with Eu2O3 immobilized within N-doped carbon nanofibers (Ru/Eu2O3@N-CNFs) are developed toward drastically boosted electrocatalysis for HOR via a d-p-f gradient orbital coupling strategy. Theoretical calculations and in situ operando spectroscopy discover that the induction of Eu2O3 optimizes the Ru site electronic structure via constructing the gradient orbital coupling of Ru(3d)-O(2p)-Eu(4f), leading to optimal H intermediates, improved adsorption ability of OH and reduced energy barrier of water formation, and promoted CO oxidation, endowing the Ru/Eu2O3 as the promising catalyst alternative for fast alkaline hydrogen electrooxidation. As a result, the Ru/Eu2O3@N-CNFs reach an impressive kinetic current densities (jk) value of 156.3 mA cm-2 at 50 mV (38.4 times higher than Pt/C), and decent stability over 35000 s continuous operation. This comprehensive investigation featuring d-p-f gradient orbital coupling provides valuable insights for the strategic development of high-performance Ru-based materials for HOR and beyond.

The Role of Phosphorus on Alkaline Hydrogen Oxidation Electrocatalysis for Ruthenium Phosphides

Transition metal/p-block compounds are regarded as the most essential materials for electrochemical energy converting systems involving various electrocatalysis. Understanding the role of p-block element on the interaction of key intermediates and interfacial water molecule orientation at the polarized catalyst-electrolyte interface during the electrocatalysis is important for rational designing advanced p-block modified metal electrocatalysts. Herein, taking a sequence of ruthenium phosphides (including Ru2P, RuP and RuP2) as model catalysts, we establish a volcanic-relation between P-proportion and alkaline hydrogen oxidation reaction (HOR) activity. The dominant role of P for regulating hydroxyl binding energy is validated by active sites poisoning experiments, pH-dependent infection-point behavior, in situ surface enhanced infrared absorption spectroscopy, and density functional theory calculations, in which P could tailor the d-band structure of Ru, optimize the hydroxyl adsorption sites across the Ru-P moieties, thereby leading to improved proportion of strongly hydrogen-bonded water and facilitated proton-coupled electron transfer process, which are responsible for the enhanced alkaline HOR performance.

Facet-Controlled Synthesis of Unconventional-Phase Metal Alloys for Highly Efficient Hydrogen Oxidation

Facet control and phase engineering of metal nanomaterials are both important strategies to regulate their physicochemical properties and improve their applications. However, it is still a challenge to tune the exposed facets of metal nanomaterials with unconventional crystal phases, hindering the exploration of the facet effects on their properties and functions. In this work, by using Pd nanoparticles with unconventional hexagonal close-packed (hcp, 2H type) phase, referred to as 2H-Pd, as seeds, a selective epitaxial growth method is developed to tune the predominant growth directions of secondary materials on 2H-Pd, forming Pd@NiRh nanoplates (NPLs) and nanorods (NRs) with 2H phase, referred to as 2H-Pd@2H-NiRh NPLs and NRs, respectively. The 2H-Pd@2H-NiRh NRs expose more (100)h and (101)h facets on the 2H-NiRh shells compared to the 2H-Pd@2H-NiRh NPLs. Impressively, when used as electrocatalysts toward hydrogen oxidation reaction (HOR), the 2H-Pd@2H-NiRh NRs show superior activity compared to the NiRh alloy with conventional face-centered cubic (fcc) phase (fcc-NiRh) and the 2H-Pd@2H-NiRh NPLs, revealing the crucial role of facet control in enhancing the catalytic performance of unconventional-phase metal nanomaterials. Density functional theory (DFT) calculations further unravel that the excellent HOR activity of 2H-Pd@2H-NiRh NRs can be attributed to the more exposed (100)h and (101)h facets on the 2H-NiRh shells, which possess high electron transfer efficiency, optimized H* binding energy, enhanced OH* binding energy, and a low energy barrier for the rate-determining step during the HOR process.

p-d Orbital Hybridization Induced by Asymmetrical FeSn Dual Atom Sites Promotes the Oxygen Reduction Reaction

With more flexible active sites and intermetal interaction, dual-atom catalysts (DACs) have emerged as a new frontier in various electrocatalytic reactions. Constructing a typical p-d orbital hybridization between p-block and d-block metal atoms may bring new avenues for manipulating the electronic properties and thus boosting the electrocatalytic activities. Herein, we report a distinctive heteronuclear dual-metal atom catalyst with asymmetrical FeSn dual atom sites embedded on a two-dimensional C2N nanosheet (FeSn-C2N), which displays excellent oxygen reduction reaction (ORR) performance with a half-wave potential of 0.914 V in an alkaline electrolyte. Theoretical calculations further unveil the powerful p-d orbital hybridization between p-block stannum and d-block ferrum in FeSn dual atom sites, which triggers electron delocalization and lowers the energy barrier of *OH protonation, consequently enhancing the ORR activity. In addition, the FeSn-C2N-based Zn-air battery provides a high maximum power density (265.5 mW cm-2) and a high specific capacity (754.6 mA h g-1). Consequently, this work validates the immense potential of p-d orbital hybridization along dual-metal atom catalysts and provides new perception into the logical design of heteronuclear DACs.

Sub-2 nm Microstrained High-Entropy-Alloy Nanoparticles Boost Hydrogen Electrocatalysis

High-entropy alloys (HEAs) confine multifarious elements into the same lattice, leading to intense lattice distortion effect. The lattice distortion tends to induce local microstrain at atomic level and thus affect surface adsorptions toward different adsorbates in various electrocatalytic reactions, yet remains unexplored. Herein, this work reports a class of sub-2 nm IrRuRhMoW HEA nanoparticles (NPs) with distinct local microstrain induced by lattice distortion for boosting alkaline hydrogen oxidation (HOR) and evolution reactions (HER). This work demonstrates that the distortion-rich HEA catalysts with optimized electronic structure can downshift the d-band center and generate uncoordinated oxygen sites to enhance the surface oxophilicity. As a result, the IrRuRhMoW HEA NPs show a remarkable HOR kinetic current density of 8.09 mA µg-1 PGM at 50 mV versus RHE, 8.89, 22.47 times higher than those of IrRuRh NPs without internal strain and commercial Pt/C, respectively, which is the best value among all the reported non-Pt based catalysts. IrRuRhMoW HEA NPs also display great HER performances with a turnover frequency (TOF) value of 5.93 H2 s-1 at 70 mV versus RHE, 4.6-fold higher than that of Pt/C catalyst, exceeding most noble metal-based catalysts. Experimental characterizations and theoretical studies collectively confirm that weakened hydrogen (Had) and enhanced hydroxyl (OHad) adsorption are achieved by simultaneously modulating the hydrogen adsorption binding energy and surface oxophilicity originated from intensified ligand effect and microstrain effect over IrRuRhMoW HEA NPs, which guarantees the remarkable performances toward HOR/HER.

A catalyst family of high-entropy alloy atomic layers with square atomic arrangements comprising iron- and platinum-group metals

We report a catalyst family of high-entropy alloy (HEA) atomic layers having three elements from iron-group metals (IGMs) and two elements from platinum-group metals (PGMs). Ten distinct quinary compositions of IGM-PGM-HEA with precisely controlled square atomic arrangements are used to explore their impact on hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). The PtRuFeCoNi atomic layers perform enhanced catalytic activity and durability toward HER and HOR when benchmarked against the other IGM-PGM-HEA and commercial Pt/C catalysts. Operando synchrotron x-ray absorption spectroscopy and density functional theory simulations confirm the cocktail effect arising from the multielement composition. This effect optimizes hydrogen-adsorption free energy and contributes to the remarkable catalytic activity observed in PtRuFeCoNi. In situ electron microscopy captures the phase transformation of metastable PtRuFeCoNi during the annealing process. They transform from random atomic mixing (25°C), to ordered L10 (300°C) and L12 (400°C) intermetallic, and finally phase-separated states (500°C).

Synergistic Effects of Dual-Doping with Ni and Ru in Monolayer VS2 Nanosheet: Unleashing Enhanced Performance for Acidic HER through Defects and Strain

Amidst the escalating quest for clean energy, the hydrogen evolution reaction (HER) in acidic conditions has taken center stage, catalyzing the search for advanced electrocatalysts. The efficacy of these materials is predominantly dictated by the active site density on their surfaces. The propensity is leveraged for monolayer architectures to introduce defects, enhancing surface area, and increasing active sites. Doping enhances defects and fine-tunes catalyst activity. In this vein, defect-enriched monolayer nanosheets doped with nickel and a trace amount of ruthenium in VS2 (SL-Ni-Ru-VS2) are engineered and characterized. Evaluation in 0.5 m H2SO4 solution unveils that the catalyst achieves overpotentials as low as 20 and 41 mV at current densities of -10 and -100 mA cm⁻2. Impressively, the catalyst maintains a mass activity of 13.08 A mg⁻¹Ru, even with minimal Ru incorporation, indicating exceptional catalytic efficiency. This monolayer catalyst sustains its high activity at lower overpotentials, demonstrating its practical applicability. The comprehensive analysis, which combines experimental data and computational simulations, indicates that the co-doping of Ni and Ru enhances the electrocatalytic properties of VS2. This research offers a strategic framework for crafting cutting-edge electrocatalysts specifically designed for enhanced performance in the HER.

Platinum-Ruthenium Dual-Atomic Sites Dispersed in Nanoporous Ni0.85Se Enabling Ampere-Level Current Density Hydrogen Production

Alkaline anion-exchange-membrane water electrolyzers (AEMWEs) using earth-abundant catalysts is a promising approach for the generation of green H2. However, the AEMWEs with alkaline electrolytes suffer from poor performance at high current density compared to proton exchange membrane electrolyzers. Here, atomically dispersed Pt-Ru dual sites co-embedded in nanoporous nickel selenides (np/Pt1Ru1-Ni0.85Se) are developed by a rapid melt-quenching approach to achieve highly-efficient alkaline hydrogen evolution reaction. The np/Pt1Ru1-Ni0.85Se catalyst shows ampere-level current density with a low overpotential (46 mV at 10 mA cm-2 and 225 mV at 1000 mA cm-2), low Tafel slope (32.4 mV dec-1), and excellent long-term durability, significantly outperforming the benchmark Pt/C catalyst and other advanced large-current catalysts. The remarkable HER performance of nanoporous Pt1Ru1-Ni0.85Se is attributed to the strong intracrystal electronic metal-support interaction (IEMSI) between Pt-Se-Ru sites and Ni0.85Se support which can greatly enlarge the charge redistribution density, reduce the energy barrier of water dissociation, and optimize the potential determining step. Furthermore, the assembled alkaline AEMWE with an ultralow Pt and Ru loading realizes an industrial-level current density of 1 A cm-2 at 1.84 volts with high durability.

Balancing the Binding of Intermediates Enhances Alkaline Hydrogen Oxidation on D-Band Center Modulated Pd Sites

Exploring efficient alkaline hydrogen oxidation reaction (HOR) electrocatalysts is of great concern for constructing anion exchange membrane fuel cells (AEMFCs). Herein, d-band center modulated PdCo alloys with ultralow Pd content anchored onto the defective carbon support (abbreviated as PdCo/NC hereafter) are proposed as highly efficient HOR catalyst. The as-prepared catalyst exhibits exceptional HOR performance compared to the Pt/C catalyst, achieving thermodynamically spontaneous and kinetically preferential reactions. Specifically, the resultant PdCo/NC demonstrates a marked enhancement in alkaline HOR performance, with the highest mass and specific activities of 1919.6 mA mgPd-1 and 1.9 mA cm-2, 51.1 and 4.2 times higher than those of benchmark of Pt/C, along with an excellent stability in a chronoamperometry test. In the analysis of in situ Raman spectra, it was discovered that tetrahedrally coordinated H-bonded water molecules were formed during the HOR process. This indicates that the promotion of interfacial water molecule formation and enhancement of HOR activities in PdCo/NC are facilitated by defect engineering and the turning of d-band center in PdCo alloy. The essential knowledge obtained in this study could open up a new direction for modifying the electronic structure of cost-effective HOR catalysts through electronic structure engineering.

Atomically dispersed Iridium on Mo2C as an efficient and stable alkaline hydrogen oxidation reaction catalyst

Hydroxide exchange membrane fuel cells (HEMFCs) have the advantages of using cost-effective materials, but hindered by the sluggish anodic hydrogen oxidation reaction (HOR) kinetics. Here, we report an atomically dispersed Ir on Mo2C nanoparticles supported on carbon (IrSA-Mo2C/C) as highly active and stable HOR catalysts. The specific exchange current density of IrSA-Mo2C/C is 4.1 mA cm-2ECSA, which is 10 times that of Ir/C. Negligible decay is observed after 30,000-cycle accelerated stability test. Theoretical calculations suggest the high HOR activity is attributed to the unique Mo2C substrate, which makes the Ir sites with optimized H binding and also provides enhanced OH binding sites. By using a low loading (0.05 mgIr cm-2) of IrSA-Mo2C/C as anode, the fabricated HEMFC can deliver a high peak power density of 1.64 W cm-2. This work illustrates that atomically dispersed precious metal on carbides may be a promising strategy for high performance HEMFCs.

High-Stability RuNi/C Electrocatalyst for Efficient Hydrogen Oxidation Reaction in Alkaline Condition

The Ru-based catalyst for hydrogen oxidation reaction (HOR) with remarkable activity and reliability at high potential range remains a formidable challenge. Herein, the RuNi/C nanoparticles are customized, in which NiRu alloy is tightly wrapped with a carbon layer, delivering 2.2-fold and 8.3-fold enhancement in kinetic current density than that of commercial Pt/C and Ru/C, respectively. Notably, the current density maintains 2.93 mA cm-2 disk at 0.6 V vs RHE, which effectively improves the stability of Ru-based catalysts at high voltage. The NiRu alloy triggers electron redistribution between two metal elements and regulates the surface adsorption performance, coupled with a tightly wrapped outer carbon layer which is in situ formed with alloy as a good conductor of electronic and protection from the electrolyte. This work not only provides a novel electrocatalyst for efficient HOR with its potential for industrial application but also opens up a new avenue for designing highly active catalytic systems.

Research progress of dual-atom site catalysts for photocatalysis

Dual-atom site catalysts (DASCs) have sparked considerable interest in heterogeneous photocatalysis as they possess the advantages of excellent photoelectronic activity, photostability, and high carrier separation efficiency and mobility. The DASCs involved in these important photocatalytic processes, especially in the photocatalytic hydrogen evolution reaction (HER), CO2 reduction reaction (CO2RR), N2/nitrate reduction, etc., have been extensively investigated in the past few years. In this review, we highlight the recent progress in DASCs that provides fundamental insights into the photocatalytic conversion of small molecules. The controllable preparation and characterization methods of various DASCs are discussed. Subsequently, the reaction mechanisms of the formation of several important molecules (hydrogen, hydrocarbons and ammonia) on DASCs are introduced in detail, in order to probe the relationship between DASCs's structure and photocatalytic activity. Finally, some challenges and outlooks of DASCs in the photocatalytic conversion of small molecules are summarized and prospected. We hope that this review can provide guidance for in-depth understanding and aid in the design of efficient DASCs for photocatalysis.

Revealing the role of a bridging oxygen in a carbon shell coated Ni interface for enhanced alkaline hydrogen oxidation reaction

Encapsulating metal nanoparticles inside carbon layers is a promising approach to simultaneously improving the activity and stability of electrocatalysts. The role of carbon layer shells, however, is not fully understood. Herein, we report a study of boron doped carbon layers coated on nickel nanoparticles (Ni@BC), which were used as a model catalyst to understand the role of a bridging oxygen in a carbon shell coated Ni interface for the improvement of the hydrogen oxidation reaction (HOR) activity using an alkaline electrolyte. Combining experimental results and density functional theory (DFT) calculations, we find that the electronic structure of Ni can be precisely tailored by Ni-O-C and Ni-O-B coordinated environments, leading to a volcano type correlation between the binding ability of the OH* adsorbate and HOR activity. The obtained Ni@BC with a optimized d-band center displays a remarkable HOR performance with a mass activity of 34.91 mA mgNi-1, as well as superior stability and CO tolerance. The findings reported in this work not only highlight the role of the OH* binding strength in alkaline HOR but also provide guidelines for the rational design of advanced carbon layers used to coat metal electrocatalysts.

CO-Tolerant Hydrogen Oxidation Electrocatalysts for Low-Temperature Hydrogen Fuel Cells

The severe performance degradation of low-temperature hydrogen fuel cells upon exposure to trace amounts of carbon monoxide (CO) impurities in reformate hydrogen fuels is one of the challenges that hinders their commercialization. Despite significant efforts that have been made, the CO-tolerance performance of electrocatalysts for the hydrogen oxidation reaction (HOR) is still unsatisfactory. This Perspective discusses the path forward for the rational design of CO-tolerant HOR electrocatalysts. The fundamentals of the CO-tolerant mechanisms on commercialized platinum group metal (PGM) electrocatalysts via either promoting CO electrooxidation or weakening CO adsorption are provided, and comprehensive discussions based on these strategies are presented with typical examples. Given the recent progress, some emerging strategies, including blocking CO diffusion with a barrier layer and developing non-PGM HOR catalysts, are also discussed. We conclude with a discussion of the strengths and limitations of these strategies along with the perspectives of the major challenges and opportunities for future research on CO-tolerant HOR electrocatalysts.

Current Status and Perspectives of Dual-Atom Catalysts Towards Sustainable Energy Utilization

The exploration of sustainable energy utilization requires the implementation of advanced electrochemical devices for efficient energy conversion and storage, which are enabled by the usage of cost-effective, high-performance electrocatalysts. Currently, heterogeneous atomically dispersed catalysts are considered as potential candidates for a wide range of applications. Compared to conventional catalysts, atomically dispersed metal atoms in carbon-based catalysts have more unsaturated coordination sites, quantum size effect, and strong metal-support interactions, resulting in exceptional catalytic activity. Of these, dual-atomic catalysts (DACs) have attracted extensive attention due to the additional synergistic effect between two adjacent metal atoms. DACs have the advantages of full active site exposure, high selectivity, theoretical 100% atom utilization, and the ability to break the scaling relationship of adsorption free energy on active sites. In this review, we summarize recent research advancement of DACs, which includes (1) the comprehensive understanding of the synergy between atomic pairs; (2) the synthesis of DACs; (3) characterization methods, especially aberration-corrected scanning transmission electron microscopy and synchrotron spectroscopy; and (4) electrochemical energy-related applications. The last part focuses on great potential for the electrochemical catalysis of energy-related small molecules, such as oxygen reduction reaction, CO2 reduction reaction, hydrogen evolution reaction, and N2 reduction reaction. The future research challenges and opportunities are also raised in prospective section.

An All-Climate Nonaqueous Hydrogen Gas-Proton Battery

Rechargeable hydrogen gas batteries, driven by hydrogen evolution and oxidation reactions (HER/HOR), are emerging grid-scale energy storage technologies owing to their low cost and superb cycle life. However, compared with aqueous electrolytes, the HER/HOR activities in nonaqueous electrolytes have rarely been studied. Here, for the first time, we develop a nonaqueous proton electrolyte (NAPE) for a high-performance hydrogen gas-proton battery for all-climate energy storage applications. The advanced nonaqueous hydrogen gas-proton battery (NAHPB) assembled with a representative V2(PO4)3 cathode and H2 anode in a NAPE exhibits a high discharge capacity of 165 mAh g-1 at 1 C at room temperature. It also efficiently operates under all-climate conditions (from -30 to +70 °C) with an excellent electrochemical performance. Our findings offer a new direction for designing nonaqueous proton batteries in a wide temperature range.

Implanting oxophilic metal in PtRu nanowires for hydrogen oxidation catalysis

Bimetallic PtRu are promising electrocatalysts for hydrogen oxidation reaction in anion exchange membrane fuel cell, where the activity and stability are still unsatisfying. Here, PtRu nanowires were implanted with a series of oxophilic metal atoms (named as i-M-PR), significantly enhancing alkaline hydrogen oxidation reaction (HOR) activity and stability. With the dual doping of In and Zn atoms, the i-ZnIn-PR/C shows mass activity of 10.2 A mgPt+Ru-1 at 50 mV, largely surpassing that of commercial Pt/C (0.27 A mgPt-1) and PtRu/C (1.24 A mgPt+Ru-1). More importantly, the peak power density and specific power density are as high as 1.84 W cm-2 and 18.4 W mgPt+Ru-1 with a low loading (0.1 mg cm-2) anion exchange membrane fuel cell. Advanced experimental characterizations and theoretical calculations collectively suggest that dual doping with In and Zn atoms optimizes the binding strengths of intermediates and promotes CO oxidation, enhancing the HOR performances. This work deepens the understanding of developing novel alloy catalysts, which will attract immediate interest in materials, chemistry, energy and beyond.

A Highly-Efficient Boron Interstitially Inserted Ru Anode Catalyst for Anion Exchange Membrane Fuel Cells

Developing high-performance electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is crucial for the commercialization of anion exchange membrane fuel cells (AEMFCs). Here, boron interstitially inserted ruthenium (B-Ru/C) is synthesized and used as an anode catalyst for AEMFC, achieving a peak power density of 1.37 W cm-2 , close to the state-of-the-art commercial PtRu catalyst. Unexpectedly, instead of the monotonous decline of HOR kinetics with pH as generally believed, an inflection point behavior in the pH-dependent HOR kinetics on B-Ru/C is observed, showing an anomalous behavior that the HOR activity under alkaline electrolyte surpasses acidic electrolyte. Experimental results and density functional theory calculations reveal that the upshifted d-band center of Ru after the intervention of interstitial boron can lead to enhanced adsorption ability of OH and H2 O, which together with the reduced energy barrier of water formation, contributes to the outstanding alkaline HOR performance with a mass activity of 1.716 mA µgPGM -1 , which is 13.4-fold and 5.2-fold higher than that of Ru/C and commercial Pt/C, respectively.

Well-defined Ni3N nanoparticles armored in hollow carbon nanotube shell for high-efficiency bifunctional hydrogen electrocatalysis

Alkaline H2-O2 fuel cells and water electrolysis are crucial for hydrogen energy recycling. However, the sluggish kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) in an alkaline medium pose significant obstacles. Thus, it is imperative but challenging to develop highly efficient and stable non-precious metal electrocatalysts for alkaline HOR and HER. Here, we present the intriguing synthesis of well-defined Ni3N nanoparticles armored within an N-doped hollow carbon nanotube shell (Ni3N@NC) via the conversion of a hydrogen-bonded organic framework (HOF) to metal-organic framework (MOF), followed by high-temperature pyrolysis. As-developed Ni3N@NC demonstrates exceptional bifunctionality in alkaline HOR/HER electrocatalysis, with a high HOR limiting current density of 2.67 mA cm-2 comparable to the benchmark 20 wt% Pt/C, while achieving a lead in overpotential of 145 mV and stronger CO-tolerance. Additionally, it achieves a low overpotential of 21 mV to attain a HER current density of 10 mA cm-2 with long-term stability up to 340 h, both exceeding those of Pt/C. Structural analyses and electrochemical studies reveal that the remarkable bifunctional hydrogen electrocatalytic performance of Ni3N@NC can be ascribed to the synergistic coupling among the well-dispersed small-sized Ni3N nanoparticles, chain-mail structure, and optimized electronic structure enabled by strong metal-support interaction. Furthermore, theoretical calculations indicate that the high-efficiency HOR/HER observed in Ni3N@NC is attributed to the strong OH- affinity, moderate H adsorption, and enhanced water formation/dissociation ability of the Ni3N active sites. This work underscores the significance of rational structural design in enhancing performance and inspires further development of advanced nanostructures for efficient hydrogen electrocatalysis.

Optimizing Hydrogen and Hydroxyl Adsorption over Ru/WO2.9 Metal/Metalloid Heterostructure Electrocatalysts for Highly Efficient and Stable Hydrogen Oxidation Reactions in Alkaline Media

The development of high-performance, stable and platinum-free electrocatalysts for the hydrogen oxidation reaction (HOR) in alkaline media is crucial for the commercial application of anion exchange membrane fuel cells (AEMFCs). Ruthenium, as an emerging HOR electrocatalyst with a price advantage over platinum, still needs to solve the problems of low intrinsic activity and easy oxidation. Herein, Ru nanoparticles are anchored on the oxygen-vacancy-rich metalloid WO2.9 by interfacial engineering to create abundant and efficient Ru and WO2.9 interfacial active sites for accelerated HOR in alkaline media. Ru/WO2.9 /C displays excellent catalytic activity with mass activity (8.29 A mgNM -1 ) and specific activity (1.32 mA cmNM -2 ), which are 2.5/3.3 and 21.8/8.3 times that of PtRu/C and Pt/C, respectively. Moreover, Ru/WO2.9 /C exhibits excellent CO tolerance and operational stability. Experimental and theoretical studies reveal that the improved charge transfer from Ru to WO2.9 in the metal/metalloid heterostructure significantly tune the electronic structure of Ru sites and optimize the hydrogen binding energy (HBE) of Ru. While, WO2.9 provides abundant hydroxyl adsorption sites. Therefore, the equilibrium adsorption of hydrogen and hydroxyl at the interface of Ru/WO2.9 will be realized, and the oxidation of metal Ru would be avoided, thereby achieving excellent HOR activity and durability.

Nanotip-Induced Electric Field for Hydrogen Catalysis

Local electric field induced by the lightning-rod effect attracts great attention for regulating the local microenvironment and electronic properties of active sites. Nevertheless, local electric-field-assisted applications are mainly limited to metals with strong surface plasmonic resonance properties (e.g., Au, Ag, and Cu). Herein, we fabricate RuCu snow-like nanosheets (SNSs) with high-curvature nanotips for enhancing the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER). Theoretical simulations show that RuCu SNSs can induce a strong local electric field around the sharp nanotips, which favors the accumulation of OH- for HOR and H+ for HER. Cu incorporation can modulate the binding strength of OH* and H*, leading to significantly enhanced HOR and HER performance. Impressively, the mass activity of RuCu SNSs for alkaline HOR is 31.3 times higher than that of RuCu nanocrystals without sharp tips. Besides, the required overpotential for reaching 10 mA cm-2 during HER over RuCu SNSs is 14.0 mV.

Sub-3 nm Pt@Ru toward Outstanding Hydrogen Oxidation Reaction Performance in Alkaline Media

Anion-exchange membrane fuel cells (AEMFCs) are promising alternative hydrogen conversion devices. However, the sluggish kinetics of the hydrogen oxidation reaction in alkaline media hinders further development of AEMFCs. As a synthesis method commonly used to prepare disordered PtRu alloys, the impregnation process is ingeniously designed herein to synthesize sub-3 nm Pt@Ru core-shell nanoparticles by sequentially reducing Pt and Ru at different annealing temperatures. This method avoids complex procedures and synthesis conditions for organic synthesis systems, and the atomic structure evolution of the synthesized core-shell nanoparticles can be tracked. The synthesized Pt@Ru electrocatalyst shows an ultrasmall average size of ∼2.5 nm and thereby a large electrochemical surface area (ECSA) of 166.66 m2 gPt+Ru-1. Exchange current densities (j0) normalized to the mass (Pt + Ru) and ECSA of this electrocatalyst are 8.0 and 5.8 times as high as those of commercial Pt/C, respectively. To the best of our knowledge, the achieved mass-normalized j0 measured by rotating disk electrodes is the highest reported so far. The membrane electrode assembly test of the Pt@Ru electrocatalyst shows a peak power density of 1.78 W cm-2 (0.152 mgPt+Ru cmanode-2), which is higher than that of commercial PtRu/C (1.62 W cm-2, 0.211 mgPt+Ru cmanode-2). The improvement of the intrinsic activity can be attributed to the electron transfer from the Ru shell to the Pt core, and the ultrafine particles further enhance the mass activity. This work reveals the feasibility of using simple impregnation to synthesize fine core-shell nanocatalysts and the importance of investigating the atomic structure of PtRu nanoparticles and other disordered alloys.

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.

Rechargeable Hydrogen-Chlorine Battery Operates in a Wide Temperature Range

Hydrogen-chlorine (H2-Cl2) fuel cells have distinct merits due to fast electrochemical kinetics but are afflicted by high cost, low efficiency, and poor reversibility. The development of a rechargeable H2-Cl2 battery is highly desirable yet challenging. Here, we report a rechargeable H2-Cl2 battery operating statically in a wide temperature ranging from -70 to 40 °C, which is enabled by a reversible Cl2/Cl- redox cathode and an electrocatalytic H2 anode. A hierarchically porous carbon cathode is designed to achieve effective Cl2 gas confinement and activate the discharge plateau of Cl2/Cl- redox at room temperature, with a discharge plateau at ∼1.15 V and steady cycling for over 500 cycles without capacity decay. Furthermore, the battery operation at an ultralow temperature is successfully achieved in a phosphoric acid-based antifreezing electrolyte, with a reversible discharge capacity of 282 mAh g-1 provided by the highly porous carbon at -70 °C and an average Coulombic efficiency of 91% for more than 300 cycles at -40 °C. This work offers a new strategy to enhance the reversibility of aqueous chlorine batteries for energy storage applications in a wide temperature range.

Directional electronic tuning of Ni nanoparticles by interfacial oxygen bridging of support for catalyzing alkaline hydrogen oxidation

Metallic nickel (Ni) is a promising candidate to substitute Pt-based catalysts for hydrogen oxidation reaction (HOR), but huge challenges still exist in precise modulation of the electronic structure to boost the electrocatalytic performances. Herein, we present the use of single-layer Ti3C2Tx MXene to deliberately tailor the electronic structure of Ni nanoparticles via interfacial oxygen bridges, which affords Ni/Ti3C2Tx electrocatalyst with exceptional performances for HOR in an alkaline medium. Remarkably, it shows a high kinetic current of 16.39 mA cmdisk-2 at the overpotential of 50 mV for HOR [78 and 2.7 times higher than that of metallic Ni and Pt/C (20%), respectively], also with good durability and CO antipoisoning ability (1,000 ppm) that are not available for conventional Pt/C (20%) catalyst. The ultrahigh conductivity of single-layer Ti3C2Tx provides fast transmission of electrons for Ni nanoparticles, of which the uniform and small sizes endow them with high-density active sites. Further, the terminated -O/-OH functional groups on Ti3C2Tx directionally capture electrons from Ni nanoparticles via interfacial Ni-O bridges, leading to obvious electronic polarization. This could enhance the Nids-O2p interaction and weaken Nids-H1s interaction of Ni sites in Ni/Ti3C2Txenabling a suitable H-/OH-binding energy and thus enhancing the HOR activity.

Pb-Modified Ultrathin RuCu Nanoflowers for Active, Stable, and CO-resistant Alkaline Electrocatalytic Hydrogen Oxidation

CO poisoning of Pt group metal (PGM) catalysts is a chronic problem for hydrogen oxidation reaction (HOR), the anodic reaction of hydroxide exchange membrane fuel cell (HEMFC) for converting H2 to electric energy in sustainable manner. We demonstrate here an ultrathin Ru-based nanoflower modified with Pb (PbRuCu NF) as an active, stable, and CO-resistant catalyst for alkaline HOR. Mechanism studies show that the presence of Pb can weaken the adsorption of *H, strengthen *OH adsorption to facilitate CO oxidation, as a result of significantly enhanced HOR activity and improved CO tolerance. Furthermore, in situ electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) suggests that Pb acts as oxygen-rich site to regulate the behavior of the linear CO adsorption. The optimized Pb1.04 -Ru92 Cu8 /C displays a mass activity and specific activity of 1.10 A mgRu -1 and 5.55 mA cm-2 , which are ≈10 and ≈31 times higher than those of commercial Pt/C. This work provides a facile strategy for the design of Ru-based catalyst with high activity and strong CO-resistance for alkaline HOR, which may promote the fundamental researches on the rational design of functional catalysts.

Atomically Dispersed Cobalt/Copper Dual-Metal Catalysts for Synergistically Boosting Hydrogen Generation from Formic Acid

The development of practical materials for (de)hydrogenation reactions is a prerequisite for the launch of a sustainable hydrogen economy. Herein, we present the design and construction of an atomically dispersed dual-metal site Co/Cu-N-C catalyst allowing significantly improved dehydrogenation of formic acid, which is available from carbon dioxide and green hydrogen. The active catalyst centers consist of specific CoCuN6 moieties with double-N-bridged adjacent metal-N4 clusters decorated on a nitrogen-doped carbon support. At optimal conditions the dehydrogenation performance of the nanostructured material (mass activity 77.7 L ⋅ gmetal -1  ⋅ h-1 ) is up to 40 times higher compared to commercial 5 % Pd/C. In situ spectroscopic and kinetic isotope effect experiments indicate that Co/Cu-N-C promoted formic acid dehydrogenation follows the so-called formate pathway with the C-H dissociation of HCOO* as the rate-determining step. Theoretical calculations reveal that Cu in the CoCuN6 moiety synergistically contributes to the adsorption of intermediate HCOO* and raises the d-band center of Co to favor HCOO* activation and thereby lower the reaction energy barrier.

Stabilizing Low-Valence Single Atoms by Constructing Metalloid Tungsten Carbide Supports for Efficient Hydrogen Oxidation and Evolution

Designing novel single-atom catalysts (SACs) supports to modulate the electronic structure is crucial to optimize the catalytic activity, but rather challenging. Herein, a general strategy is proposed to utilize the metalloid properties of supports to trap and stabilize single-atoms with low-valence states. A series of single-atoms supported on the surface of tungsten carbide (M-WCx , M=Ru, Ir, Pd) are rationally developed through a facile pyrolysis method. Benefiting from the metalloid properties of WCx , the single-atoms exhibit weak coordination with surface W and C atoms, resulting in the formation of low-valence active centers similar to metals. The unique metal-metal interaction effectively stabilizes the low-valence single atoms on the WCx surface and improves the electronic orbital energy level distribution of the active sites. As expected, the representative Ru-WCx exhibits superior mass activities of 7.84 and 62.52 A mgRu -1 for the hydrogen oxidation and evolution reactions (HOR/HER), respectively. In-depth mechanistic analysis demonstrates that an ideal dual-sites cooperative mechanism achieves a suitable adsorption balance of Had and OHad , resulting in an energetically favorable Volmer step. This work offers new guidance for the precise construction of highly active SACs.