Single-Atom Cr-N4 Sites with High Oxophilicity Interfaced with Pt Atomic Clusters for Practical Alkaline Hydrogen Evolution Catalysis

In situ doping Pt single atoms into 3D flower-like 1T-MoS2 via Pt-S bond for efficient hydrogen evolution reaction

Combining single atoms via phase transition engineering (from 2H to 1T) remains a challenge in MoS2-based catalysts. Herein, we report that Pt single atoms (PtSA) were doped into a 3D flower-like 1T-MoS2 catalyst (PtSA@MoS2) using a Pt-S bonding strategy. Doping with PtSA induced a phase transition in MoS2 from the 2H phase to the 1T phase. PtSA@MoS2 exhibited outstanding hydrogen evolution reaction (HER) performance, featuring an overpotential of 25 mV at 10 mA cm-2, a Tafel slope of 43.6 mV dec-1, and excellent long-term stability. The Pt-S first-shell scattering of PtSA@MoS2 in extended X-ray absorption fine structure (EXAFS) directly indicated that the PtSA was anchored near S atoms, forming Pt-S bonds. Furthermore, S atoms proximal to Pt functioned as catalytically active sites for HER, with Pt acting as an electron transfer mediator, facilitating the electron transfer from Mo to Pt and then to S. The p-band center of S showed a positive shift, indicating that PtSA@MoS2 interacted weakly with hydrogen, thereby accelerating the desorption of H atoms to generate H2. Additionally, PtSA@MoS2 exhibited a ΔGH* of only -0.13 eV, which also favored H2 production.

Inhibiting Dissolution of Platinum with Atomic Rare Earth Bridged by Nitrogen to Boost Alkaline Hydrogen Evolution

The unfavorable water dissociation and continuous dissolution of Pt single-atom catalysts significantly impede their practical application in alkaline anion exchange membrane water electrolyzers (AEMWEs). Herein, by integrating the electron-buffer functionality of rare earth single atoms (RE = Pr, Ce, Gd, Sm) dispersed on N-doped carbon substrates (N─C) with Pt single atoms, a novel catalyst Pt/RE-N-C is reported. The constructed Pt─N─Ce bridge causes electron enrichment on Pt sites and deficiency on RE sites, which favors adsorption of Hads and OHads, respectively, and significantly promotes water dissociation. Meanwhile, the increased covalency of Pt─N bond inhibits detachment and thermal vibration of Pt atoms. As a representative, Pt/Ce─N─C requires an overpotential of only 22 mV to reach a current density of 10 mA cm-2. The excellent mass activity of 7.16 A mgPt -1 at an overpotential of 50 mV is 37.7 times higher than that of commercial Pt/C (0.19 A mgPt -1). More importantly, the AEMWE with Pt/Ce─N─C (with a loading of only 32 µgPt cm-2) as the cathode catalyst exhibits an ultralow potential (1.79 V) and high stability at an industrial current density of 1.0 A cm-2. This work demonstrates the advantages and potential of using RE single atoms for high-efficient energy conversion.

Engineering the regulation strategy of active sites to explore the intrinsic mechanism over single‑atom catalysts in electrocatalysis

The development of efficient and sustainable energy sources is a crucial strategy for addressing energy and environmental crises, with a particular focus on high-performance catalysts. Single-atom catalysts (SACs) have attracted significant attention because of their exceptionally high atom utilization efficiency and outstanding selectivity, offering broad application prospects in energy development and chemical production. This review systematically summarizes the latest research progress on SACs in five key electrochemical reactions: hydrogen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, and oxygen evolution reaction. Initially, a brief overview of the current understanding of electrocatalytic active sites in SACs is provided. Subsequently, the electrocatalytic mechanisms of these reactions are discussed. Emphasis is placed on various modification strategies for SAC surface-active sites, including coordination environment regulation, electronic structure modulation, support structure regulation, the introduction of structural defects, and multifunctional site design, all aimed at enhancing electrocatalytic performance. This review comprehensively examines SAC deactivation and poisoning mechanisms, highlighting the importance of stability enhancement for practical applications. It also explores the integration of density functional theory calculations and machine learning to elucidate the fundamental principles of catalyst design and performance optimization. Furthermore, various synthesis strategies for industrial-scale production are summarized, providing insights into commercialization. Finally, perspectives on future research directions for SACs are highlighted, including synthesis strategies, deeper insights into active sites, the application of artificial intelligence tools, and standardized testing and performance requirements.

Erbium-doped cobalt oxide with an electron supply effect boosting electrocatalytic oxygen evolution

Cobalt oxide for oxygen evolution reaction (OER) often suffers from over-oxidation and structural instability under alkaline conditions. We develop erbium (Er)-doped CoO microspheres with the assistance of L-aspartic acid, which show superior OER activity and stability by leveraging the electron supply effect of Er to optimize electron structure and prevent over-oxidation.

Structural evolution of metal single-atoms and clusters in catalysis: Which are the active sites under operative conditions?

The structural evolution of metal single-atoms and clusters has been recognized as the new frontier in catalytic reactions under operative conditions, playing a crucial role in key aspects of catalytic behavior, including activity, selectivity, stability, and atomic efficiency as well as precise tunability in heterogeneous catalysis. Accurately identifying the structural evolution of metal single-atoms and clusters during real reactions is essential for addressing fundamental issues such as active sites, metal-support interactions, deactivation mechanisms, and thereby guiding the design and fabrication of high-performance single-atom and cluster catalysts. However, how to evaluate the dynamic structural evolution of metal species during catalytic reactions is still lacking, hindering their industrial applications. In this review, we discuss the behaviors of dynamic structural evolution between metal single-atoms and clusters, explore the driving force and major factors, highlight the challenges and inherent limitations encountered, and present relevant future research trends. Overall, this review provides valuable insights that can inspire researchers to develop novel and efficient strategies for accurately identifying the structural transformations of metal single-atoms and clusters.

Vacancy and Dopant Co-Constructed Active Microregion in Ru-MoO3- x/Mo2AlB2 for Enhanced Acidic Hydrogen Evolution

Accurate identification of catalytic active regions is crucial for the rational design and construction of hydrogen evolution catalysts as well as the targeted regulation of their catalytic performance. Herein, the low crystalline-crystalline hybrid MoO3- x/Mo2AlB2 with unsaturated coordination and rich defects is taken as the precursor. Through the Joule heating reaction, the Ru-doped MoO3- x/Mo2AlB2 catalyst is successfully constructed. Building on the traditional view that individual atoms or vacancies act as active sites, this article innovatively proposes the theory that vacancies and doped atoms synergistically construct active microregions, and multiple electron-rich O atoms within the active microregions jointly serve as hydrogen evolution active sites. Based on X-ray absorption fine structure analysis and first-principles calculations, there is a strong electron transfer among Ru atoms, Mo atoms, and O atoms, leading to extensive O atoms with optimized electronic structure in the active microregions. These O atoms exhibit an H* adsorption free energy close to zero, thereby enhancing the catalytic activity for hydrogen evolution. This work provides a brand-new strategy for the design and preparation of electrocatalytic materials and the systematic regulation of the local electronic structure of catalysts.

Reductive Supramolecular In Situ Construction of Nano-Platinum Effectively Couples Cathodic Hydrogen Evolution and Anodic Alcohol Oxidation

The deployment of high-performance catalysts and the acceleration of anodic reaction kinetics are key measures to achieve maximum energy efficiency in overall water electrolysis hydrogen production systems. Here, an innovative strategy is developed by directly constructing a supramolecular framework embedded with boron clusters and cucurbituril as reducing agent. This approach enabled the in situ conversion of Pt⁴⁺ into highly dispersed, small-sized nano-platinum, which are subsequently distributed on a boron-carbon-nitrogen (BCN) matrix. The resulting Pt/BNHCSs catalyst demonstrates the ability to facilitate electrocatalytic water splitting for hydrogen production across multiple scenarios while simultaneously accelerating the anodic methanol oxidation kinetics, significantly outperforming commercial Pt/C catalyst in various aspects. The cathodic hydrogen evolution-anodic methanol oxidation coupling system constructed using the Pt/BNHCSs greatly reduces the overall energy consumption of the electrolysis system. In situ attenuated total reflection Fourier transform infrared and online differential electrochemical mass spectrometry reveals that the catalyst interface enhances H₂O adsorption and promotes the CH₃OH→CO conversion process, and density functional theory calculations indicated that the BCN support facilitated the evolution of H₂O to H₂ and CH₃OH to CO, elucidating the mechanism by which Pt/BNHCSs simultaneously promoted hydrogen production and methanol oxidation.

Surface Reconstruction of An Integrated CoO-Co2Mo3O8 Electrode Enabling Efficient Ampere-Level Hydrogen Evolution in Alkaline Water or Seawater

To accelerate the water dissociation in the Volmer step and alleviate the destruction of bubbles to the physical structure of catalysts during the alkaline hydrogen evolution, an integrated electrode of cobalt oxide and cobalt-molybdenum oxide grown on Ni foam, named CoO-Co2Mo3O8, is designed. This integrated electrode enhances the catalyst-substrate interaction confirmed by a micro-indentation tester, and thus hinders the destruction of the physical structure of catalysts caused by bubbles. Electrochemical testing shows the occurrence of a surface reconstruction of the integrated electrode, and CoO is transformed into Co(OH)2, denoted as Co(OH)2-Co2Mo3O8. Theoretical calculations determine that Co(OH)2-Co2Mo3O8 has significantly low activation barrier for water dissociation and presents easy hydroxide desorption, which accelerate the catalytic reaction. Electrochemical experiments show that Co(OH)2-Co2Mo3O8 exhibits outstanding activity, reaching current density values of -100 and -1000 mA cm-2 with overpotentials only 57.8 and 195.8 mV, respectively. Furthermore, it demonstrates excellent stability at -500 and -1000 mA cm-2 for 200 h. Combined with the previously reported anode, the two-electrode system also provides the stable operation from 100 to 1000 mA cm-2 for 600 h in alkaline solution, and over 200 h at 500 and 1000 mA cm-2 in alkaline seawater.

Regulating Interfacial H2O Activity and H2 Bubbles by Core/Shell Nanoarrays for 800 h Stable Alkaline Seawater Electrolysis

The catalytic activity and stability under high current densities for hydrogen evolution reactions (HER) are impeded by firm adherence and coverage of H2 bubbles to the catalytic sites. Herein, we systematically synthesize core/shell nanoarrays to engineer bubble transport channels, which further remarkably regulate interfacial H2O activity, and swift H2 bubble generation and release. The self-supported catalyst holds uniform ultra-low Ru active sites of 0.38 wt% and promotes the rapid formation of plentiful small H2 bubbles, which are rapidly released by the upright channels, mitigating the blockage of active sites and avoiding surface damage from bubble movements. As a result, these core/shell nanoarrays achieve ultralow overpotentials of 18 and 24 mV to reach 10 mA cm-2 for HER in 1 M KOH freshwater and seawater, respectively. Additionally, the assembled electrolyzer demonstrates stable durability over 800 hours with a high current density of 2 A cm-2 in 1 M KOH seawater. The techno-economic analysis (TEA) indicates that the unit cost of the hydrogen production system is nearly half of the DOE's (Department of Energy) 2026 target. Our work addresses the stability challenges of HER and highlights its potential as a sustainable and economically feasible solution for large-scale hydrogen production of seawater.

Hydrogen Binding Energy Is Insufficient for Describing Hydrogen Evolution on Single-Atom Catalysts

The design principles for metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) in the hydrogen evolution reaction (HER) have been extensively studied. Yet, consensus remains elusive, hindering advancements in hydrogen energy technologies. Although the hydrogen binding energy (ΔGH*) has long been used as a key HER descriptor during the past two decades, originating from the activity volcano of metallic surfaces, its applicability to HER SACs has been met with significant controversy. Herein, we investigate the effects of HO*/O* poisoning and H* coverage on SACs with varied metal centers and coordination environments using pH-dependent surface Pourbaix diagrams at the reversible hydrogen electrode (RHE) scale and microkinetic modeling. Our findings reveal that HO* poisoning, realistic H* adsorption strengths at active metal sites, and the potential HER activity at the coordinating N-sites are crucial factors that should be considered for accurate descriptor development. Experimental validation using a series of M-phthalocyanine/CNT catalysts (M = Co, Ni, Cu) confirms the theoretical predictions, with excellent agreement in exchange current densities and the role of N-sites in Ni/Cu-phthalocyanine/CNT catalysts. This work provides answers to a long-lasting debate on HER descriptors by establishing ΔGH* and ΔGHO* as a combined HER descriptor for SACs, offering new guidelines for catalyst design.

Pt/α-MoC Catalyst Boosting pH-Universal Hydrogen Evolution Reaction at High Current Densities

Constructing subnanometric electrocatalysts is an efficient method to synergistically accelerate H2O dissociation and H+ reduction for pH-universal hydrogen evolution reaction (HER) for industrial water electrolysis to produce green hydrogen. Here, we construct a subnanometric Pt/α-MoC catalyst, where the α-MoC component can dissociate water effectively, with the rapid proton release kinetics of Pt species on Pt/α-MoC to obtain a good HER performance at high current densities in all-pH electrolytes. Quasi-in situ X-ray photoelectron spectroscopy analyses and density functional theory calculations confirm the highly efficient water dissociation capability of α-MoC and the thermodynamically favorable desorption process of hydrolytically dissociated protons on Pt sites at the high current density. Consequently, Pt/α-MoC requires only a low overpotential of 125 mV to achieve a current density of 1000 mA cm-2. Moreover, a Pt/α-MoC-based proton exchange membrane water electrolysis device exhibits a low cell voltage (1.65 V) and promising stability over 300 h with no performance degradation at an industrial-level current density of 1 A cm-2. Notably, even at a current of 100 A, the cell voltage remains low at 2.15 V, demonstrating Pt/α-MoC's promising potential as a scalable alternative for industrial hydrogen production. These findings elucidate the synergistic mechanism of α-MoC and atomically dispersed Pt in promoting efficient HER, offering valuable guidance for the design of electrocatalysts in high current density hydrogen.

Manipulating Interfacial Water Via Metallic Pt1Co6 Sites on Self-Adaptive Metal Phosphides to Enhance Water Electrolysis

Metallizing active sites to control the structural and kinetic dissociation of water at the catalyst-electrolyte interface, along with elucidating its mechanism under operating conditions, is a pivotal innovation for the hydrogen evolution reaction (HER). Here, a design of singly dispersed Pt-Co sites in a fully metallic state on nanoporous Co2P, tailored for HER, is introduced. An anion-exchange-membrane water electrolyzer equipped with this catalyst can achieve the industrial current densities of 1.0 and 2.0 A cm-2 at 1.71 and 1.85 V, respectively. It is revealed that the singly dispersed Pt-Co sites undergo self-adaptive distortion under operating conditions, which form a Pt1Co6 configuration with a strongly negative charge that optimizes reactant binding and reorganizes the interfacial water structure, resulting in an improved concentration of potassium (K+) ions in the closest ion plane. The K+ ions interact cooperatively with H2O (K·H2O), which strengthens the Pt-H binding interaction and facilitates the polarization of the H─OH bond, leading to improved HER activity. This study not only propels the advancement of cathodic catalysts for water electrolysis but also delineates a metallization strategy and an interface design principle, thereby enhancing electrocatalytic reaction rates.

Partially Interstitial Silicon-Implanted Ruthenium as an Efficient Electrocatalyst for Alkaline Hydrogen Evolution

To enhance the alkaline hydrogen evolution reaction (HER), it is crucial, yet challenging, to fundamentally understand and rationally modulate potential catalytic sites. In this study, we confirm that despite calculating a low water dissociation energy barrier and an appropriate H adsorption free energy (ΔG*H) at Ru-top sites, metallic Ru exhibits a relatively inferior activity for the alkaline HER. This is primarily because the Ru-top sites, which are potential H adsorption sites, are recessive catalytic sites, compared with the adjacent Ru-hollow sites that have a strong ΔG*H. To promote the transformation of Ru-top sites from recessive to dominant catalytic sites, interstitial Si atoms are implanted into the hollow sites. However, complete interstitial implantation leads to a high water dissociation energy barrier at the RuSi intermetallic surface. Thus, we present a partial interstitial incorporation strategy to form a Ru-RuSi heterostructure that not only converts the Ru-top sites from recessive to dominant catalytic sites but also preserves the low water dissociation energy barrier at the Ru surface. Moreover, the spontaneously formed built-in electric fields bidirectionally optimize the adsorption ability of the Ru sites, thereby greatly reducing the thermodynamic energy barrier and enhancing the alkaline HER.

In-situ construction of vertically Fe doped CoMoP nanosheet honeycomb as bifunctional electrocatalysts for efficient overall water splitting

The bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) are crucial pivot in water electrolysis territory. In this study, vertically Fe incorporated CoMoP (Fe-CoMoP) nanosheet honeycomb product with super-hydrophilic and aerophobic features was projected and generated through the straightforward hydrothermal technique and phosphatized process. The Fe-CoMoP catalyst exhibits more distinguished intrinsic activity, accessible active sites, effective charge transfer and weak adhesion of gas bubbles. The overpotentials of dual-function Fe-CoMoP are 87.1 mV for HER and 244.4 mV for OER to drive the current density of 10 mA cm-2. At room temperature, the overall water splitting reaction of Fe-CoMoP as cathode and anode is carried out at 1.54 V to reach 10 mA cm-2 with good stability. Simultaneously, the Fe-CoMoP couple electrolyzer also presents remarkable water splitting activity and durability in simulated industry circumstances of 6 M KOH, 60 °C at 500 mA cm-2, which are close to practical conditions.

Modulating Built-In Electric Field Strength in Ru/RuO2 Interfaces through Ni Doping to Enhance Hydrogen Conversion at Ampere-level Current

Improving the alkaline hydrogen evolution reaction (HER) efficiency is essential for developing advanced anion exchange membrane water electrolyzers (AEMWEs) that operate at industrial ampere-level currents. Herein, we employ density functional theory (DFT) calculations to identify Ni-RuO2 as the leading candidate among various 3d transition metal-doped M-RuO2 (where metal M includes Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn). The incorporation of Ni atoms facilitates the partial reduction of RuO2, resulting in the formation of a Ni-Ru/RuO2 interface having a significant built-in electric field (BIEF) during electrochemical reactions. The resulted BIEF enhances electron transfer across the interface, which is critical in lowering energy barriers and accelerating the hydrogen evolution reaction (HER) kinetics. As a result, the Ni-RuO2 catalyst exhibits an overpotential of 134 mV at 1 A cm-2 and a low Tafel slope of 20.85 mV dec-1, with just 0.03 mg cm-2 of Ru loading. The highly effective BIEF, therefore, plays a pivotal role in the catalyst's remarkable performance, allowing the Ni-RuO2-based AEMWE to require only 1.71 V to maintain stable operation at 1 A cm-2 over a 1000-hour period.

Fabricating Lattice-Confined Pt Single Atoms With High Electron-Deficient State for Alkali Hydrogen Evolution Under Industrial-Current Density

The confining effect is essential to regulate the activity and stability of single-atom catalysts (SACs), but the universal fabrication of confined SACs is still a great challenge. Here, various lattice-confined Pt SACs supported by different carriers are constructed by a universal co-reduction approach. Notably, Pt single atoms confined in the lattice of Ni(OH)2 (Pt1/Ni(OH)2) with a high electron-deficient state exhibit excellent activity for basic hydrogen evolution reaction (HER). Specifically, Pt1/Ni(OH)2 just requires 15 mV to get 10 mA cm-2 and the mass activity of Pt1/Ni(OH)2 is 15 times of commercial Pt/C. Moreover, Pt1/Ni(OH)2 assembled in an alkaline water electrolyzer shows 1030 h durability under the industrial current density of 800 mA cm-2. In situ spectroscopy techniques reveal Pt─H and "free" OH radical can be directly observed for Pt1/Ni(OH)2, confirming the lattice-confined Pt single atoms play a key role during HER. Further density functional theory uncovers the Pt 3d orbital strongly hybridizes with O 2p and Ni 3d orbitals in Ni(OH)2, which quickly optimizes the electronic state of the Pt site, thus largely reducing the energy barrier of the rate-determining step to 0.16 eV for HER. Finally, this synthesis method is extended to construct other 9 lattice-confined SACs.

Dominant Role of Coexisting Ruthenium Nanoclusters Over Single Atoms to Enhance Alkaline Hydrogen Evolution Reaction

Developing efficient and cost-effective electrocatalysts to replace expensive carbon-supported platinum nanoparticles for the alkaline hydrogen evolution reaction remains an important challenge. Recently, an innovative catalyst, composed of ruthenium single atoms (Ru1) integrated with small Ru nanoclusters (RuNC), has attracted considerable attention from the scientific community. However, because of its complexity, this catalyst remains a topic of some debate. Here, a method is reported of precisely controlling the ratios of Ru1 to RuNC on a nitrogenated carbon (NC)-based porous organic framework to produce Ru/NC catalysts, by using different amounts (0, 5, 10 wt.%) of reducing agent. The Ru/NC-10 catalyst, formed with 10 wt.% reducing agent, delivered the best performance under alkaline conditions, indicating that RuNC played a significant role in actual alkaline hydrogen evolution reaction (HER). An anion exchange membrane water electrolyzer (AEMWE) system using the Ru/NC-10 catalyst required a significantly lower operating voltage (1.72 V) than the commercial Pt/C catalyst (1.95 V) to achieve 500 mA cm-2. Moreover, the system can be operated at 100 mA cm-2 without notable performance decay for over 180 h. Theoretical calculations supported these experimental findings that Ru1 contributed to the water dissociation process, while RuNC is more actively associated with the hydrogen recombination process.

Controllable Detachment of Organic Ligands on Ultrathin Amorphous Nanosheets Tailors the Electron-Aggregation for Accelerated pH-Universal Hydrogen Reaction

Tailoring the local environment of catalyst surface has emerged as an effective strategy to enhance the reaction kinetics involving multiple intermediates. For hydrogen evolution reactions (HER), the driving factors for hydrogen aggregation and migration which are poorly understood in depth affects the reaction kinetics especially over a wide pH range. Inspired by the selectivity of the catalyst surface microenvironment for intermediates, an interfacial electrocatalyst composed of Ru ultrafine nanocatalysts anchored onto monolayer amorphous (a-WCoNiO) nanosheets with electron-rich microenvironment induced by an organic oleylamine ligand is designed to realize high-performance pH-universal HER. This Ru/a-WCoNiO possesses impressively low overpotentials of -13, -14, and -14 mV at 10 mA cm-2 in 0.5 m H2SO4, 1 m KOH and 1 m PBS, respectively, ranking among the best HER catalysts reported to date. Benefiting from the electron-rich microenvironment, the Ru/a-WCoNiO exhibits record-high turnover frequency (TOF) and mass activity (MA), which is more than 47.9 times higher than that of commercial 20% Pt/C. Importantly, other precious metals are loaded on a-WCoNiO and enhancing their mass current density for pH-universal HER. It is believed that this developed approach of organic modifiers tailored local microenvironment has practical significance and advantages for designing other high-performance catalysts.

Alleviating O-Intermediates Adsorption Strength over PdRhCu Ternary Metallene via Ligand Effect for Enhanced Oxygen Reduction in Practical PEMFCs

Expediting the torpid kinetics of the acidic oxygen reduction reaction (ORR) is a crucial yet formidable challenge toward advancing proton exchange membrane fuel cells (PEMFCs) for commercialization. The cutting-edge Pd-based nanomaterials for acidic ORR are hindered by their low intrinsic activities and significant CO poisoning, stemming from the challenge of simultaneously optimizing surface adsorption toward various adsorbates. Herein, we introduce an ultrathin PdRhCu ternary metallene (PdRhCu metallene) for boosting acidic ORR in PEMFC. Mechanistic studies have identified that the incorporation of Cu into the PdRh configuration could downshift the d-band center on Pd to promote weakened the adsorption of key intermediates, ensuring efficient electron transfer between the PdRhCu ternary metal sites and the adsorbates, thereby lowering the energy barriers of the rate-determining step in ORR. As a proof-of-concept, the optimized PdRhCu metallene demonstrates impressive ORR performance with a high half-wave potential (0.93 VRHE), negligible activity decay after 10 000 cycles, and superior anti-CO-poisoning capacity compared to counterparts and commercial Pt/C catalysts. Intriguingly, the PdRhCu metallene-assembled PEMFC achieves an impressive maximum power density of 820 mW cm-2 with high electrocatalytic stability under the H2/air conditions, paving avenues for further advancements in metallene electrocatalyst engineering toward the practical implementation of PEMFCs.

Accelerated Selective Electrooxidation of Ethylene Glycol and Inhibition of C-C Dissociation Facilitated by Surficial Oxidation on Hollowed PtAg Nanostructures via In Situ Dynamic Evolution

Electro-upgrading of low-cost alcohols such as ethylene glycol is a promising and sustainable approach for the production of value-added chemicals while substituting energy-consuming OER in water splitting. However, the sluggish kinetics and possibility of C-C dissociation make the design of selective and efficient electrocatalysts challenging. Herein, we demonstrate the synthesis of a hollowed bimetallic PtAg nanostructure through an in situ dynamic evolution method that could efficiently drive the selective electrochemical ethylene glycol oxidation reaction (EGOR). The resulting mild surficial oxidation has intrinsically improved EGOR activity, exhibiting a remarkable performance toward glycolate (selectivity up to 99.2% and faradic efficiency ∼97%) at high current density with low overpotential (355 mA·cm-2 at 1.0 V, 16.3 A·mgPt -1), exceeding prior outcomes. Through comprehensive operando characterization and theoretical calculations, this study systematically reveals that the in situ formation of Pt-O(H)ad is pivotal for modulating the electronic structure of surface and facilitating the selective electrooxidation and adsorption of -CH2OH. The competitive C-C dissociation pathway toward HCOO- is concurrently inhibited in comparison to Pt. An industrial-level current coupled with hydrogen production at low cell voltages was also achieved. These findings offer more in-depth mechanistic understanding of the EGOR's reaction pathway mediated by surface environment in Pt-based electrocatalysts.

Mechanism of Hydrogen Generation Catalyzed by a Single Atom and Its Spin Regulation

Single-atom catalysts exhibit the excellent catalytic activity and selectivity, making them widely applicable in the fields of advanced materials, environmental science, and chemical synthesis. However, understanding the mechanism of single-atom catalytic reactions, such as the hydrogen generation reaction, is still challenging, which notably hampers the optimization and precise control of the reaction. Here, we immobilize a single-metal atom model catalyst into a single-molecule electrical detection platform for in situ monitoring of the catalytic hydrogen generation process at the single-event level. In combination with theoretical and experimental studies, the catalytic mechanisms of the hydrogen generation reaction, especially the selection of the catalytic center through charge, spin, and orbital quantum control, are elucidated. In addition, a hydrogen generation process via quantum spin-induced catalysis is observed, in which the turnover frequency increases by about 65 times at a magnetic field of 50 mT. This study provides valuable insights into the intrinsic mechanism of single-metal atom catalysis and opens up unique avenues for their precise control, thus offering a useful strategy for efficiently developing clean energy.

The Spin-Selective Channels in Fully-Exposed PtFe Clusters Enable Fast Cathodic Kinetics of Li-O2 Battery

In Li-O2 batteries (LOBs), the electron transfer between triplet O2 and singlet Li2O2 possesses a spin-dependent character but is still neglected, while the spin-conserved electron transfer without losing phase information should guarantee fast kinetics and reduced energy barriers. Here, we provide a paradigm of spin-selective catalysis for LOB that the ferromagnetic quantum spin exchange interactions between Pt and Fe atoms in fully-exposed PtFe clusters filter directional e-spins for spin-conserved electron transfer at Fe-Fe sites. The kinetics of O2/Li2O2 redox reaction is markedly accelerated as predicted by theoretical calculations, showing dramatically decreased relaxation time of the rate determining step for more than one order of magnitude, compared with the Fe clusters without spin-selective behavior. In consequence, the assembled LOB provides ultrahigh energy conversion efficiency of 89.6 % at 100 mA g-1 under a discharge-charge overpotential of only 0.32 V. This work provides new insights into the spin-dependent mechanisms of O2/Li2O2 redox reaction, and the strategy of constructing spin catalysts at atomic level.

Tailored Metal-Organic Framework-Based Nanozymes for Enhanced Enzyme-Like Catalysis

The global crisis of bacterial infections is exacerbated by the escalating threat of microbial antibiotic resistance. Nanozymes promise to provide ingenious solutions. Here, we reported a homogeneous catalytic structure of Pt nanoclusters with finely tuned metal-organic framework (ZIF-8) channel structures for the treatment of infected wounds. Catalytic site normalization showed that the active site of the Pt aggregates structure with fine-tuned pore modifications structure had a catalytic capacity of 14.903×105 min-1, which was 18.7 times higher than that of the Pt particles in monodisperse state in ZIF-8 (0.793×105 min-1). In situ tests revealed that the change from homocleavage to heterocleavage of hydrogen peroxide at the interface of the nanozyme was one of the key reasons for the improvement of nanozyme activity. Density-functional theory and kinetic simulations of the reaction interface jointly determine the role of the catalytic center and the substrate channel together. Metabolomics analysis showed that the developed nanozyme, working in conjunction with reactive oxygen species, could effectively block energy metabolic pathways within bacteria, leading to spontaneous apoptosis and bacterial rupture. This pioneering study elucidates new ideas for the regulation of artificial enzyme activity and provides new perspectives for the development of efficient antibiotic substitutes.

Loading Pt Nanoparticles on Ultrathin Amorphous Nanobelts for Enhanced Hydrogen Production

Due to unique metal-support interactions, loaded structures have been widely used in the structural design of hydrogen-extraction reaction (HER) electrocatalysts. However, the development of catalysts that are both active and stable remains a great challenge. Herein, we successfully anchored Pt nanoparticles on ultrathin nanobelts to construct a crystalline/amorphous Pt NPs/CNWOx NBs heterostructure, which possesses the dual advantages of fast electron transfer in crystalline materials and effective exposure of active sites in amorphous materials. The obtained catalyst exhibits great HER catalytic performance in both 0.5 M H2SO4 and 1 M KOH. Compared with CNWOx nanobelts, Pt-loaded Pt NPs/CNWOx NBs exhibits lower overpotentials and faster HER kinetics. For acidic and alkaline HER, the catalyst required only low overpotentials of 35 mV and 60 mV to achieve a current density of 10 mA cm-2, respectively, which is even better than that of commercial Pt/C. And Pt NPs/CNWOx NBs shows almost no degradation after long time stability tests. It is found that the composite structure of crystalline/amorphous, the heterogeneous interface and the introduction of Pt synergize with each other to achieve increased number of active sites and enhanced intrinsic activity, resulting in excellent electrocatalytic HER activity and stability.

Identifying the Bifunctional Mechanism in Alkaline Water Electrolysis by Lewis Pairs at the Single-Atom Scale

The bifunctional mechanism, involving multiactive compositions to simultaneously dissociate water molecules and optimize intermediate adsorption, has been widely used in the design of catalysts to boost water electrolysis for sustainable hydrogen energy production but remains debatable due to difficulties in accurately identifying the reaction process. Here, we proposed the concept of well-defined Lewis pairs in single-atom catalysts, with a unique acid-base nature, to comprehensively understand the exact role of multiactive compositions in an alkaline hydrogen evolution reaction. By facilely adjusting active moieties, the induced synergistic effect between Lewis pairs (M-P/S/Cr pairs, M = Ru, Ir, Pt) can significantly facilitate the cleavage of the H-OH bond and accelerate the removal of intermediates, thereby switching the rate-determining step from the Volmer step to the Heyrovsky step. Moreover, the representative Ru-P Lewis pairs deliver an impressive 266 h durability at a high industrial current density of 2 A cm-2 without activity decay in anion-exchange membrane water electrolysis, and the concept can be extended to modify commercial noble-metal-based catalysts for performance enhancement. This work not only sheds light on the important effect of the bifunctional mechanism in alkaline water electrolysis at the single-atom scale but also offers a universal descriptor for the rational design of advanced catalysts.

Unveiling the role of silicon in boosting electrochemical carbon dioxide reduction via carbon nanotubes@bismuth silicates

Electrochemical CO2 reduction reaction (CO2RR) is one of the most attractive measures to achieve the carbon neutral goal by converting CO2 into high-value chemicals such as formate. Si in Bi silicates is promising to enhance CO2 adsorption and activation due to its strong oxygenophilicity. Whereas, its role in boosting CO2RR via the cheap Bi-based catalysts is still not clear. Herein, we design CNT@Bi silicates catalyst, demonstrating the highest FEHCOOH of 96.3 % at -0.9 V vs. reversible hydrogen electrode with good stability. Through X-ray photoelectron spectroscopy (XPS), in-situ Attenuated Total Reflectance-Fourier Transform Infrared (In-situ ATR-SEIRAS) experiments, and Density Functional Theory (DFT) calculations, the role of Si in Bi silicates was unveiled: tuning the electronic structure of Bi, weakening the Bi-O bond, and strengthening electron transfer from Bi to CO2, thereby promoting the generation of CO2*- and *OCHO intermediates. Additionally, carbon nanotubes (CNTs) promote not only the conductivity but also the generation of abundant oxygen vacancies in CNT@Bi silicates evidenced by the electron transfer from CNT to Bi silicates from XPS results. Further, the CNT@Bi silicates endows it with the highest electrochemical activation area. These findings suggest the effectiveness of Si in Bi silicates and structure tuning to design highly selective CO2RR catalyst for HCOOH production.

CeO2-δ as Electron Donor in Co0.07Ce0.93O2-δ Solid Solution Boosts Alkaline Water Splitting

Optimizing the electronic structure with increasing intrinsic stability is a usual method to enhance the catalysts' performance. Herein, a series of cerium dioxide (CeO2-δ) based solid solution materials is synthesized via substituting Ce atoms with transition metal (Co, Cu, Ni, etc.), in which Co0.07Ce0.93O2-δ shows optimized band structure because of electron transition in the reaction, namely Co3+ (3d64s0) + Ce3+ (4f15d 06s0) → Co2+ (3d74s0) + Ce4+ (4f05d06s0), with more stable electronic configuration. The in situ Raman spectra show a stable F2g peak at ≈452 cm-1 of Co0.07Ce0.93O2-δ, while the F2g peak in CeO2-δ almost disappeared during HER progress, demonstrating the charge distribution of *H adsorbed on Co0.07Ce0.93O2-δ is more stable than *H adsorbed on CeO2-δ. Density functional theory calculations reveal that Co0.07Ce0.93O2-δ solid solution increases protonation capacity and favors for formation of *H in alkaline media. General guidelines are formulated for optimizing adsorption capacity and the volcano plot demonstrates the excellent catalytic performance of Co0.07Ce0.93O2-δ solid solution. The alkaline anion exchange membrane water electrolysis based on Co0.07Ce0.93O2-δ/NiFe LDH realizes a current density of 1000 mA cm-2 at ≈1.86 V in alkaline seawater at 80 °C and exhibits long-term stability for 450 h.

Alkaline Hydrogen Evolution Reaction Electrocatalysts for Anion Exchange Membrane Water Electrolyzers: Progress and Perspective

For the aim of achieving the carbon-free energy scenario, green hydrogen (H2) with non-CO2 emission and high energy density is regarded as a potential alternative to traditional fossil fuels. Over the last decades, significant breakthroughs have been realized on the alkaline hydrogen evolution reaction (HER), which is a fundamental advancement and efficient process to generate high-purity H2 in the laboratory. Based on this, the development of the practical industry-oriented anion exchange membrane water electrolyzer (AEMWE) is on the rise, showing competitiveness with the incumbent megawatt-scale H2 production technologies. Still, great challenges lie in exploring the electrocatalysts with remarkable activity and stability for alkaline HER, as well as bridging the gap of performance difference between the three-electrode cell and AEMWE devices. In this perspective, we systematically discuss the in-depth mechanisms for activating alkaline HER electrocatalysts, including electronic modification, defect construction, morphology control, synergistic function, field effect, etc. In addition, the current status of AEMWE is reviewed, and the underlying bottlenecks that impede the application of HER electrocatalysts in AEMWE are summarized. Finally, we share our thoughts regarding the future development directions of electrocatalysts toward both alkaline HER and AEMWE, in the hope of advancing the commercialization of water electrolysis technology for green H2 production.

Graphene-supported MN4 single-atom catalysts for multifunctional electrocatalysis enabled by axial Fe tetramer coordination

Multifunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are crucial for development of the key electrochemical energy storage and conversion devices, for which single-atom catalyst (SAC) has present great promises. Very recently, some experimental works showed that structurally well-defined ultra-small transition-metal clusters (such as Fe and Co tetramers, denoted as Fe4 and Co4, respectively), can efficiently modulate the catalytic behavior of SACs by axial coordination. Herein, taking the graphene-supported MN4 SACs as representatives, we theoretically explored the feasibility of realizing multifunctional SACs for ORR, OER and HER by this novel axial coordination engineering. Through extensive first-principles calculations, from 23 candidates, IrN4 decorated with Fe4 (IrN4/Fe4) is identified as the promising trifunctional catalyst with the theoretical overpotential of 0.43, 0.51 and 0.30 V for OER, ORR and HER, respectively. RhN4/Fe4 and CoN4/Fe4 are recognized as potential OER and ORR bifunctional catalysts. In addition, NiN4/Fe4 exhibits the best ORR activity with an overpotential of 0.30 V, far superior to the pristine NiN4 SAC (0.88 V). Electronic structure analyses reveal that the significantly enhanced ORR/OER activity can be ascribed to the orbital and charge redistribution of Ni/Ir active center, resulting from its electronic interaction with Fe4 cluster. This work could stimulate and guide the rational design of graphene-based multifunctional SACs realized by axial coordination of small TM clusters, and provide insights into the modulation mechanism.

Understanding Pt Active Sites on Nitrogen-Doped Carbon Nanocages for Industrial Hydrogen Evolution with Ultralow Pt Usage

Engineering microstructures of Pt and understanding the related catalytic mechanism are critical to optimizing the performance for hydrogen evolution reaction (HER). Herein, Pt dispersion and coordination are precisely regulated on hierarchical nitrogen-doped carbon nanocages (hNCNCs) by a thermal-driven Pt migration, from edge-hosted Pt-N2Cl2 single sites in the initial Pt1/hNCNC-70 °C catalyst to Pt clusters/nanoparticles and back to in-plane Pt-NxC4-x single sites. Thereinto, Pt-N2Cl2 presents the optimal HER activity (6 mV@10 mA cm-2) while Pt-NxC4-x shows poor HER activity (321 mV@10 mA cm-2) due to their different Pt coordination. Operando characterizations demonstrate that the low-coordinated Pt-N2 intermediates derived from Pt-N2Cl2 under the working condition are the real active sites for HER, which enable the multi-H adsorption mechanism with an ideal H* adsorption energy of nearly 0 eV, thereby the high activity, as revealed by theoretical calculations. In contrast, the high-coordinated Pt-NxC4-x sites only allow the single-H adsorption with a positive adsorption energy and thereby the low HER activity. Accordingly, with an ultralow Pt loading of only 25 μgPt cm-2, the proton exchange membrane water electrolyzer assembled using Pt1/hNCNC-70 °C as the cathodic catalyst achieves an industrial-level current density of 1.0 A cm-2 at a low cell voltage of 1.66 V and high durability, showing great potential applications.

Engineering both intrinsic characteristic and local microenvironment of platinum sites toward highly efficient oxygen reduction reaction

The optimization of the adsorption of oxygen-containing intermediates on platinum (Pt) sites of Pt-based electrocatalysts is crucial for the oxygen reduction reaction process. Currently, a large amount of researches mainly focus on modifying the bulk structure of the electrocatalysts, however, the vital role of solvent effect on the phase interfaces is often overlooked. Here, we successfully developed an electrocatalyst in which the ordered PtCo alloy anchors on the cobalt (Co) single-atoms/clusters decorated support (Co1,nNC) and its surface is further optimized using hydrophobic ionic liquid (IL). Experimental studies and theoretical calculations indicate that compressive stress on Pt lattice contributed by intrinsic structure and the local hydrophobicity caused by IL on the surface can suppress the stabilization of *OH on Pt. This synergistic effect affords outstanding catalytic performance, exhibiting a half-wave potential (E1/2) of 0.916 V vs. RHE and a mass activity (MA) of 1350.3 mA mgPt-1 in 0.1 mol/L perchloric acid (0.1 M HClO4) electrolyte, much better than the commercial Pt/C (0.849 V vs. RHE and 145.5 mA mgPt-1 for E1/2 and MA, respectively). Moreover, the E1/2 of IL-PtCo/Co1,nNC only lost 5 mV after 10,000 cyclic voltammetry (CV) cycles due to a strong and synergistic contact of the intermetallic PtCo alloy with the Co1,nNC support and IL. This research provides an effective method for designing efficient electrocatalysts by combining intrinsic structure and surface modification.

Independent Control Over the H/OH Adsorption: Breaking the Trade-Off Between H/OH-Adsorption and H2O-Dissociation of Platinum-Group Metal Electrocatalyst for Hydrogen Evolution Reaction

Platinum-group metals catalysts (such as Rh, Pd, Ir, Pt) have been the most efficient hydrogen evolution reaction (HER) electrocatalysts due to their moderate H adsorption strength, while the high H2O-dissociation barrier in alkaline media restrains the catalytic performance of PGM catalysts. However, the optimization of the H2O-dissociation barrier and *H/*OH binding energy toward their individual optima is limited due to the constraints of their scaling relationship on a single active site. Here, a coordinatively unsaturated "M─Ox─W" (M = Rh, Pd, Ir, Pt) active area is constructed, where H and OH species are anchored on Pt-group metal sites and inactive W sites for individual regulation. By combining experiments and density functional theory calculations, the introduction of extra OH-adsorption sites (coordinatively unsaturated WO3-x) avoids the competitive adsorption of H and OH on the single site, while the enhanced OH-adsorption capacity on the coordinatively unsaturated WO3-x effectively facilitates the adsorption/dissociation of interfacial H2O. As a result, the representative Rh-WO3-x catalyst exhibits outstanding catalytic activity and durability for HER. The findings of this work not only provide valuable insights for the design of efficient PGM catalysts for HER but also shed light on the development of electrocatalysts for other catalytic reactions.

Developing Catalysts for Membrane Electrode Assemblies in High Performance Polymer Electrolyte Membrane Water Electrolyzers

Extensive research is underway to achieve carbon neutrality through the production of green hydrogen via water electrolysis, powered by renewable energy. Polymer membrane water electrolyzers, such as proton exchange membrane water electrolyzer (PEMWE) and anion exchange membrane water electrolyzer (AEMWE), are at the forefront of this research. Developing highly active and durable electrode catalysts is crucial for commercializing these electrolyzers. However, most research is conducted in half-cell setups, which may not fully represent the catalysts' effectiveness in membrane-electrode-assembly (MEA) devices. This review explores the catalysts developed for high-performance PEMWE and AEMWE MEA systems. Only the catalysts reporting on the MEA performance were discussed in this review. In PEMWE, strategies aim to minimize Ir use for the oxygen evolution reaction (OER) by maximizing activity, employing metal oxide-based supports, integrating secondary elements into IrOx lattices, or exploring non-Ir materials. For AEMWE, the emphasis is on enhancing the performance of NiFe-based and Co-based catalysts by improving electrical conductivity and mass transport. Pt-based and Ni-based catalysts for the hydrogen evolution reaction (HER) in AEMWE are also examined. Additionally, this review discusses the unique considerations for catalysts operating in pure water within AEMWE systems.

Twin-distortion modulated ultra-low coordination PtRuNi-Ox catalyst for enhanced hydrogen production from chemical wastewater

The development of efficient and robust catalysts for hydrogen evolution reaction is crucial for advancing the hydrogen economy. In this study, we demonstrate that ultra-low coordinated hollow PtRuNi-Ox nanocages exhibit superior catalytic activity and stability across varied conditions, notably surpassing commercial Pt/C catalysts. Notably, the PtRuNi-Ox catalysts achieve current densities of 10 mA cm-2 at only 19.6 ± 0.1, 20.9 ± 0.1, and 21.0 ± 0.1 mV in alkaline freshwater, chemical wastewater, and seawater, respectively, while maintaining satisfied stability with minimal activity loss after 40,000 cycles. In situ experiments and theoretical calculations reveal that the ultra-low coordination of Pt, Ru, and Ni atoms creates numerous dangling bonds, which lower the water dissociation barrier and optimizing hydrogen adsorption. This research marks a notable advancement in the precise engineering of atomically dispersed multi-metallic centers in catalysts for energy-related applications.

Fundamental Insights into the Direct Electron Transfer Mechanism on Ag Atomic Cluster

The nonradical oxidation pathway for pollutant degradation in Fenton-like catalysis is favorable for water treatment due to the high reaction rate and superior environmental robustness. However, precise regulation of such reactions is still restricted by our poor knowledge of underlying mechanisms, especially the correlation between metal site conformation of metal atom clusters and pollutant degradation behaviors. Herein, we investigated the electron transfer and pollutant oxidation mechanisms of atomic-level exposed Ag atom clusters (AgAC) loaded on specifically crafted nitrogen-doped porous carbon (NPC). The AgAC triggered a direct electron transfer (DET) between the terminal oxygen (Oα) of surface-activated peroxodisulfate and the electron-donating substituents-containing contaminants (EDTO-DET), rendering it 11-38 times higher degradation rate than the reported carbon-supported metal catalysts system with various single-atom active centers. Heterocyclic substituents and electron-donating groups were more conducive to degradation via the EDTO-DET system, while contaminants with high electron-absorbing capacity preferred the radical pathway. Notably, the system achieved 79.5% chemical oxygen demand (COD) removal for the treatment of actual pharmaceutical wastewater containing 1053 mg/L COD within 30 min. Our study provides valuable new insights into the Fenton-like reactions of metal atom cluster catalysts and lays an important basis for revolutionizing advanced oxidation water purification technologies.

Satellite Pd Single-Atom Embraced AuPd Alloy Nanoclusters for Enhanced Hydrogen Evolution

The fabrication of hybrid active sites that synergistically contain nanoclusters and single atoms (SAs) is vital for electrocatalysts to achieve excellent activity and durability. Herein, we develop a ligand-assisted pyrolysis strategy using nanoclusters (Au4Pd2(SC2H4Ph)8) with alloy cores and protected ligands to build AuPd cluster sites embraced by satellite Pd SAs. In the thermal drive control process, different thermodynamic properties of the alloy atoms and the confinement effects of organic ligands allow for the mild spillover of the single-component metal Pd, resulting in the formation of AuPd alloy nanoclusters tightly encompassed by isolated Pd atoms. Experiments and theoretical calculations indicated that the satellite Pd atoms can optimize the electronic structure of the AuPd nanoclusters and Au sites in the alloy to facilitate the adsorption and dissociation of H2O, thus enhancing the hydrogen evolution reaction (HER) activity. The optimal AuPdNCs/PdSAs-600 exhibits outstanding electrocatalytic activity toward HER, with overpotentials of 21 and 38 mV at 10 mA cm-2 in acidic and alkaline media, respectively. Moreover, the mass activity and turnover frequency of AuPdNCs/PdSAs-600 are one order of magnitude higher than those of commercial Pd/C and Pt/C catalysts. This facile strategy for constructing hybrid catalytic centers using ligand-protected nanoclusters provides efficient insights for the further design of nanocluster-based electrocatalysts synergized by SAs.

WS2 Moiré Superlattices Supporting Au Nanoclusters and Isolated Ru to Boost Hydrogen Production

Maximizing the catalytic activity of single-atom and nanocluster catalysts through the modulation of the interaction between these components and the corresponding supports is crucial but challenging. Herein, guided by theoretical calculations, a nanoporous bilayer WS2 Moiré superlattices (MSLs) supported Au nanoclusters (NCs) adjacent to Ru single atoms (SAs) (Ru1/Aun-2LWS2) is developed for alkaline hydrogen evolution reaction (HER) for the first time. Theoretical analysis suggests that the induced robust electronic metal-support interaction effect in Ru1/Aun-2LWS2 is prone to promote the charge redistribution among Ru SAs, Au NCs, and WS2 MSLs support, which is beneficial to reduce the energy barrier for water adsorption and thus promoting the subsequent H2 formation. As feedback, the well-designed Ru1/Aun-2LWS2 electrocatalyst exhibits outstanding HER performance with high activity (η10 = 19 mV), low Tafel slope (35 mV dec-1), and excellent long-term stability. Further, in situ, experimental studies reveal that the reconstruction of Ru SAs/NCs with S vacancies in Ru1/Aun-2LWS2 structure acts as the main catalytically active center, while high-valence Au NCs are responsible for activating and stabilizing Ru sites to prevent the dissolution and deactivation of active sites. This work offers guidelines for the rational design of high-performance atomic-scale electrocatalysts.

Hexa-atom Pt Catalyst Fabricated by a Ligand Engineering Strategy for Efficient Hydrogen Oxidation Reaction

Atomically precise supported nanocluster catalysts (APSNCs), which feature exact atomic composition, well-defined structures, and unique catalytic properties, offer an exceptional platform for understanding the structure-performance relationship at the atomic level. However, fabricating APSNCs with precisely controlled and uniform metal atom numbers, as well as maintaining a stable structure, remains a significant challenge due to uncontrollable dispersion and easy aggregation during synthetic and catalytic processes. Herein, we developed an effective ligand engineering strategy to construct a Pt6 nanocluster catalyst stabilized on oxidized carbon nanotubes (Pt6/OCNT). The structural analysis revealed that Pt6 nanoclusters in Pt6/OCNT were fully exposed and exhibited a planar structure. Furthermore, the obtained Pt6/OCNT exhibited outstanding acidic HOR performances with a high mass activity of 18.37 A ⋅ mgpt -1 along with excellent stability during a 24 h constant operation and good CO tolerance, surpassing those of the commercial Pt/C. Density functional theory (DFT) calculations demonstrated that the unique geometric and electronic structures of Pt6 nanoclusters on OCNT altered the hydrogen adsorption energies on catalytic sites and thus lowered the HOR theoretical overpotential. This work presents a new prospect for designing and synthesizing advanced APSNCs for efficient energy electrocatalysis.

Semi-Ionic F Modified N-Doped Porous Carbon Implanted with Ruthenium Nanoclusters toward Highly Efficient pH-Universal Hydrogen Generation

Developing high electroactivity ruthenium (Ru)-based electrocatalysts for pH-universal hydrogen evolution reaction (HER) is challenging due to the strong bonding strengths of key Ru─H/Ru─OH intermediates and sluggish water dissociation rates on active Ru sites. Herein, a semi-ionic F-modified N-doped porous carbon implanted with ruthenium nanoclusters (Ru/FNPC) is introduced by a hydrogel sealing-pyrolying-etching strategy toward highly efficient pH-universal hydrogen generation. Benefiting from the synergistic effects between Ru nanoclusters (Ru NCs) and hierarchically F, N-codoped porous carbon support, such synthesized catalyst displays exceptional HER reactivity and durability at all pH levels. The optimal 8Ru/FNPC affords ultralow overpotentials of 17.8, 71.2, and 53.8 mV at the current density of 10 mA cm-2 in alkaline, neutral, and acidic media, respectively. Density functional theory (DFT) calculations elucidate that the F-doped substrate to support Ru NCs weakens the adsorption energies of H and OH on Ru sites and reduces the energy barriers of elementary steps for HER, thus enhancing the intrinsic activity of Ru sites and accelerating the HER kinetics. This work provides new perspectives for the design of advanced electrocatalysts by porous carbon substrate implanted with ultrafine metal NCs for energy conversion applications.

Recent Advances on Two-Dimensional Nanomaterials Supported Single-Atom for Hydrogen Evolution Electrocatalysts

Water electrolysis has been recognized as a promising technology that can convert renewable energy into hydrogen for storage and utilization. The superior activity and low cost of catalysis are key factors in promoting the industrialization of water electrolysis. Single-atom catalysts (SACs) have attracted attention due to their ultra-high atomic utilization, clear structure, and highest hydrogen evolution reaction (HER) performance. In addition, the performance and stability of single-atom (SA) substrates are crucial, and various two-dimensional (2D) nanomaterial supports have become promising foundations for SA due to their unique exposed surfaces, diverse elemental compositions, and flexible electronic structures, to drive single atoms to reach performance limits. The SA supported by 2D nanomaterials exhibits various electronic interactions and synergistic effects, all of which need to be comprehensively summarized. This article aims to organize and discuss the progress of 2D nanomaterial single-atom supports in enhancing HER, including common and widely used synthesis methods, advanced characterization techniques, different types of 2D supports, and the correlation between structural hydrogen evolution performance. Finally, the latest understanding of 2D nanomaterial supports was proposed.

Dimensionality-Tailored Ferromagnetism in Quasi-Two-Dimensional MnSe2 for the Magnetoelectrochemical Hydrogen Evolution Reaction in Alkaline Media

The application of an external magnetic field to the cathode shows great promise in facilitating the hydrogen evolution reaction (HER) via water electrolysis. However, the criteria for designing such cathodes are still under investigation. Among various aspects, understanding the effect of different magnetic states of the cathode material is crucial, especially for the HER in alkaline conditions, which possesses different reaction steps compared to that in acidic conditions. Herein, we present MnSe2 as a cathode material for the magneto-electrocatalytic HER in alkaline media, utilizing its dimension-dependent magnetic phase transition. By tailoring its dimensionality, we have achieved room-temperature ferromagnetism in its quasi-two-dimensional (2D) form, whereas its bulk counterpart exhibits paramagnetism. Upon being subjected to a low external magnetic field of 0.4 T at -182 mV (vs RHE) overpotential, quasi-2D MnSe2 exhibited a 120% improvement in current density compared to itself at zero magnetic field, while negligible changes were observed in the bulk material. This performance enhancement under a magnetic field could originate from the higher spin polarization of the ferromagnetic catalyst. This work signifies a conceptual advancement of the catalyst's spin state in magnetically enhanced electrocatalytic reaction kinetics.

Oxophilic gallium single atoms bridged ruthenium clusters for practical anion-exchange membrane electrolyzer

The development of highly efficient and durable alkaline hydrogen evolution reaction (HER) catalysts is crucial for achieving high-performance practical anion exchange membrane water electrolyzer (AEMWE) at ampere-level current density. Herein, we report a design concept by employing Ga single atoms as an electronic bridge to stabilize the Ru clusters for boosting alkaline HER performance in practical AEMWE. Experimental and theoretical results collectively reveal that the bridged Ga sites trigger strong metal-support interaction for the homogeneous distribution of Ru clusters with high density, as well as optimize the Ru-H bond strength due to the electron transfer between Ru and Ga for enhanced intrinsic HER activity. Moreover, the oxophilic Ga sites near the Ru clusters tend to adsorb the hydroxyl species and accelerate the water dissociation for sufficient proton supplement in an alkaline medium. The Ru-GaSA/N-C catalyst exhibits a low overpotential of 4 ± 1 mV (10 mA cm-2) and high mass activity of 9.3 ± 0.5 A mg-1Ru at -0.05 V vs RHE. In particular, the Ru-GaSA/N-C-based AEMWE in 1 M KOH delivers a voltage of only 1.74 V to reach an industrial current density of 1 A cm-2, and can steadily operate at 1 A cm-2 for more than 170 h.

Visual Eosin Y-Based Photosensitization Sensing Systems for Ultrasensitive Detection of Diclofenac with Single-Atom Co─N2O2 Site-Immobilized g-C3N4 Nanosheets

It is highly desired to develop a visual sensing system for ultrasensitive detection of colorless diclofenac (DCF), yet with a significant challenge. Herein, a novel dye-based photosensitization sensing system has been successfully developed for detecting DCF for the first time, in which the used dye eosin Y (DeY) can strongly absorb visible light and then be decolorized obviously by transferring photogenerated electrons to g-C3N4 nanosheets (CN), while the built single-atomic Co─N2O2 sites on CN by boron-oxygen connection can competitively adsorb DCF to impede the photosensitization decoloration of DeY. This system exhibits a broad detection range from 8 ng L-1 to 2 mg L-1 with 535 nm light, an exceptionally low detection limit (3.5 ng L-1), and remarkable selectivity. Through the time-resolved, in situ technologies, and theoretical calculations, the decolorization of DeY is attributed to the disruption of DeY's conjugated structure caused by the triplet excited state electron transfer from DeY to CN, meanwhile, the adsorbed oxygen facilitates the charge transfer process. The preferential adsorption of DCF mainly depends on the strong interactions between the as-constructed single-atom Co and Cl in DCF. This study opens an innovative light-driven sensing system by combining dye and single-atom metal/nanomaterial for visually intuitive detection of environmental pollutants.

Stabilizing Few-Atom Platinum Clusters by Zinc Single-Atom-Glue for Efficient Anti-Markovnikov Alkene Hydrosilylation

Few-atom metal clusters (FAMCs) exhibit superior performance in catalyzing complex molecular transformations due to their special spatial environments and electronic states, compared to single-atom catalysts (SACs). However, achieving the efficient and accurate synthesis of FAMCs while avoiding the formation of other species, such as nanoparticles and SACs, still remains challenges. Herein, we report a two-step strategy for synthesis of few-atom platinum (Pt) clusters by predeposition of zinc single-atom-glue (Zn1) on MgO nanosheets (Ptn-Zn1/MgO), where FAMCs can be obtained over a wide range of Pt contents (0.09 to 1.45 wt %). Zn atoms can act as Lewis acidic sites to allow electron transfer between Zn and Pt through bridging O atoms, which play a crucial role in the formation and stabilization of few-atom Pt clusters. Ptn-Zn1/MgO exhibited a high selectivity of 93 % for anti-Markovnikov alkene hydrosilylation. Moreover, an excellent activity with a turnover frequency of up to 1.6×104 h-1 can be achieved, exceeding most of the reported Pt SACs. Further theoretical studies revealed that the Pt atoms in Ptn-Zn1/MgO possess moderate steric hindrance, which enables high selectivity and activity for hydrosilylation. This work presents some guidelines for utilizing atomic-scale species to increase the synthesis efficiency and precision of FAMCs.

Advances of Synergistic Electrocatalysis Between Single Atoms and Nanoparticles/Clusters

Combining single atoms with clusters or nanoparticles is an emerging tactic to design efficient electrocatalysts. Both synergy effect and high atomic utilization of active sites in the composite catalysts result in enhanced electrocatalytic performance, simultaneously provide a radical analysis of the interrelationship between structure and activity. In this review, the recent advances of single-atomic site catalysts coupled with clusters or nanoparticles are emphasized. Firstly, the synthetic strategies, characterization, dynamics and types of single atoms coupled with clusters/nanoparticles are introduced, and then the key factors controlling the structure of the composite catalysts are discussed. Next, several clean energy catalytic reactions performed over the synergistic composite catalysts are illustrated. Eventually, the encountering challenges and recommendations for the future advancement of synergistic structure in energy-transformation electrocatalysis are outlined.

Atomic Ru-Pt dual sites boost the mass activity and cycle life of alkaline hydrogen evolution

The development of highly efficient and ultrastable electrocatalysts for hydrogen generation from water/real seawater faces huge challenges. Herein, porous carbon-supported amorphous RuPt nanoclusters (Ru5.67Pt/PC) achieve mass activities of 42.28/10.93 A mgPt-1 and ultralong cycling stability in alkaline water/seawater because of the unique cluster structure and atomic Ru-Pt dual sites.

Synthesis of Fe2O3 Nanorod and NiFe2O4 Nanoparticle Composites on Expired Cotton Fiber Cloth for Enhanced Hydrogen Evolution Reaction

The design of cheap, noble-metal-free, and efficient electrocatalysts for an enhanced hydrogen evolution reaction (HER) to produce hydrogen gas as an energy source from water splitting is an ideal approach. Herein, we report the synthesis of Fe2O3 nanorods-NiFe2O4 nanoparticles on cotton fiber cloth (Fe2O3-NiFe2O4/CF) at a low temperature as an efficient electrocatalyst for HERs. Among the as-prepared samples, the optimal Fe2O3-NiFe2O4/CF-3 electrocatalyst exhibits good HER performance with an overpotential of 127 mV at a current density of 10 mA cm-2, small Tafel slope of 44.9 mV dec-1, and good stability in 1 M KOH alkaline solution. The synergistic effect between Fe2O3 nanorods and NiFe2O4 nanoparticles of the heterojunction composite at the heterointerface is mainly responsible for improved HER performance. The CF is an effective substrate for the growth of the Fe2O3-NiFe2O4 nanocomposite and provides conductive channels for the active materials' HER process.

d-band center engineering of single Cu atom and atomic Ni clusters for enhancing electrochemical CO2 reduction to CO

The rational design of catalysts with atomic dispersion and a deep understanding of the catalytic mechanism is crucial for achieving high performance in CO2 reduction reaction (CO2RR). Herein, we present an atomically dispersed electrocatalyst with single Cu atom and atomic Ni clusters supported on N-doped mesoporous hollow carbon sphere (CuSANiAC/NMHCS) for highly efficient CO2RR. CuSANiAC/NMHCS demonstrates a remarkable CO Faradaic efficiency (FECO) exceeding 90% across a potential range of -0.6 to -1.2 V vs. reversible hydrogen electrode (RHE) and achieves its peak FECO of 98% at -0.9 V vs. RHE. Theoretical studies reveal that the electron redistribution and modulated electronic structure-notably the positive shift in d-band center of Ni 3d orbital-resulting from the combination of single Cu atom and atomic Ni clusters markedly enhance the CO2 adsorption, facilitate the formation of *COOH intermediate, and thus promote the CO production activity. This study offers fresh perspectives on fabricating atomically dispersed catalysts with superior CO2RR performance.

Single-Atom Titanium on Mesoporous Nitrogen, Oxygen-Doped Carbon for Efficient Photo-thermal Catalytic CO2 Cycloaddition by a Radical Mechanism

Developing efficient and earth-abundant catalysts for CO2 fixation to high value-added chemicals is meaningful but challenging. Styrene carbonate has great market value, but the cycloaddition of CO2 to styrene oxide is difficult due to the high steric hindrance and weak electron-withdrawing ability of the phenyl group. To utilize clean energy (such as optical energy) directly and effectively for CO2 value-added process, we introduce earth-abundant Ti single-atom into the mesoporous nitrogen, oxygen-doped carbon nanosheets (Ti-CNO) by a two-step method. The Ti-CNO exhibits excellent photothermal catalytic activities and stability for cycloaddition of CO2 and styrene oxide to styrene carbonate. Under light irradiation and ambient pressure, an optimal Ti-CNO produces styrene carbonate with a yield of 98.3 %, much higher than CN (27.1 %). In addition, it shows remarkable stability during 10 consecutive cycles. Its enhanced catalytic performance stems from the enhanced photothermal effect and improved Lewis acidic/basic sites exposed by the abundant mesopores. The experiments and theoretical simulations demonstrate the styrene oxide⋅+ and CO2⋅- radicals generated at the Lewis acidic (Tiδ+) and basic sites of Ti-CNO under light irradiation, respectively. This work furnishes a strategy for synthesizing advanced single-atom catalysts for photo-thermal synergistic CO2 fixation to high value products via a cycloaddition pathway.

Achieving Negatively Charged Pt Single Atoms on Amorphous Ni(OH)2 Nanosheets with Promoted Hydrogen Absorption in Hydrogen Evolution

Single-atom (SA) catalysts with nearly 100% atom utilization have been widely employed in electrolysis for decades, due to the outperforming catalytic activity and selectivity. However, most of the reported SA catalysts are fixed through the strong bonding between the dispersed single metallic atoms with nonmetallic atoms of the substrates, which greatly limits the controllable regulation of electrocatalytic activity of SA catalysts. In this work, Pt-Ni bonded Pt SA catalyst with adjustable electronic states was successfully constructed through a controllable electrochemical reduction on the coordination unsaturated amorphous Ni(OH)2 nanosheet arrays. Based on the X-ray absorption fine structure analysis and first-principles calculations, Pt SA was bonded with Ni sites of amorphous Ni(OH)2, rather than conventional O sites, resulting in negatively charged Ptδ-. In situ Raman spectroscopy revealed that the changed configuration and electronic states greatly enhanced absorbability for activated hydrogen atoms, which were the essential intermediate for alkaline hydrogen evolution reaction. The hydrogen spillover process was revealed from amorphous Ni(OH)2 that effectively cleave the H-O-H bond of H2O and produce H atom to the Pt SA sites, leading to a low overpotential of 48 mV in alkaline electrolyte at -1000 mA cm-2 mg-1Pt, evidently better than commercial Pt/C catalysts. This work provided new strategy for the controllable modulation of the local structure of SA catalysts and the systematic regulation of the electronic states.