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Catalyst precise synthesis at the atomic level is of great importance for establishing structure–activity relationships and developing advanced catalysts with high efficiency. Atomic layer deposition (ALD) relies on sequential self-limiting molecular surface reactions on substrates. Such unique features not only ensures to achieve uniform deposition on powder surfaces with high surface areas, but also offers a powerful capability of control of the deposited materials with near atomic precision. This perspective will discuss new opportunities in atomically-precise synthesis of heterogeneous catalysts using ALD. As examples, I will describe the recent key developments in ALD synthesis of supported metal single atoms, homonuclear and heteronuclear dimers, bimetallic nanoparticles as well as atomically-dispersed metal (hydro)oxide species on metal nanoparticles to form 3-dimentional metal–oxide interfaces. Such atom-by-atom construction of supported catalysts from the bottom up is hardly achieved by other synthetic methods, thus would greatly deepen atomic-level understanding of structure–activity relationships. Given the rapid development of technologies in ALD coating on powders at a large scale, atom-by-atom synthesis of heterogeneous catalysts using ALD sheds dawn light on precise catalysis for industrial applications in the near future. Graphic Abstract

The excessive dependence on fossil fuels contributes to the majority of CO2 emissions, influencing on the climate change. One promising alternative to fossil fuels is green hydrogen, which can be produced through water electrolysis from renewable electricity. However, the variety and complexity of hydrogen evolution electrocatalysts currently studied increases the difficulty in the integration of catalytic theory, catalyst design and preparation, and characterization methods. Herein, this review first highlights design principles for hydrogen evolution reaction (HER) electrocatalysts, presenting the thermodynamics, kinetics, and related electronic and structural descriptors for HER. Second, the reasonable design, preparation, mechanistic understanding, and performance enhancement of electrocatalysts are deeply discussed based on intrinsic and extrinsic effects. Third, recent advancements in the electrocatalytic water splitting technology are further discussed briefly. Finally, the challenges and perspectives of the development of highly efficient hydrogen evolution electrocatalysts for water splitting are proposed. This review presents varieties of representative hydrogen evolution reaction (HER) electrocatalysts benefited from intrinsic and extrinsic design strategies and gives insight into classical/novel descriptors and reaction mechanism to provide the audience with a broad and basic understanding. Moreover, the progress on water‐splitting technology is also discussed. Some invigorating perspectives on the challenges and future directions at the HER field are provided.

HighlightsFundamental principles underlying the design of oxide catalysts, including the influence of crystal structure, and electronic structure on their performance are summarized and analyzed.Challenges associated with developing oxide catalysts and the potential strategies are discussed.The electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are fundamental processes in a range of energy conversion devices such as fuel cells and metal–air batteries. ORR and OER both have significant activation barriers, which severely limit the overall performance of energy conversion devices that utilize ORR/OER. Meanwhile, ORR is another very important electrochemical reaction involving oxygen that has been widely investigated. ORR occurs in aqueous solutions via two pathways: the direct 4-electron reduction or 2-electron reduction pathways from O2 to water (H2O) or from O2 to hydrogen peroxide (H2O2). Noble metal electrocatalysts are often used to catalyze OER and ORR, despite the fact that noble metal electrocatalysts have certain intrinsic limitations, such as low storage. Thus, it is urgent to develop more active and stable low-cost electrocatalysts, especially for severe environments (e.g., acidic media). Theoretically, an ideal oxygen electrocatalyst should provide adequate binding to oxygen species. Transition metals not belonging to the platinum group metal-based oxides are a low-cost substance that could give a d orbital for oxygen species binding. As a result, transition metal oxides are regarded as a substitute for typical precious metal oxygen electrocatalysts. However, the development of oxide catalysts for oxygen reduction and oxygen evolution reactions still faces significant challenges, e.g., catalytic activity, stability, cost, and reaction mechanism. We discuss the fundamental principles underlying the design of oxide catalysts, including the influence of crystal structure, and electronic structure on their performance. We also discuss the challenges associated with developing oxide catalysts and the potential strategies to overcome these challenges.

HighlightsThe review explores single atom catalysts (SACs) for photocatalytic H2O2 production, highlighting their unique structure, properties, and advantages over traditional catalysts. It emphasizes the importance of metal atom types, host material selection, and coordination environment in SACs design.The article explains how SACs enhance photocatalytic H2O2 production by improving light absorption, charge generation, migration, and lowering energy barriers for reactant adsorption and activation.The review acknowledges challenges and future research directions in SACs for H2O2 photosynthesis.This comprehensive review provides a deep exploration of the unique roles of single atom catalysts (SACs) in photocatalytic hydrogen peroxide (H2O2) production. SACs offer multiple benefits over traditional catalysts such as improved efficiency, selectivity, and flexibility due to their distinct electronic structure and unique properties. The review discusses the critical elements in the design of SACs, including the choice of metal atom, host material, and coordination environment, and how these elements impact the catalytic activity. The role of single atoms in photocatalytic H2O2 production is also analysed, focusing on enhancing light absorption and charge generation, improving the migration and separation of charge carriers, and lowering the energy barrier of adsorption and activation of reactants. Despite these advantages, several challenges, including H2O2 decomposition, stability of SACs, unclear mechanism, and low selectivity, need to be overcome. Looking towards the future, the review suggests promising research directions such as direct utilization of H2O2, high-throughput synthesis and screening, the creation of dual active sites, and employing density functional theory for investigating the mechanisms of SACs in H2O2 photosynthesis. This review provides valuable insights into the potential of single atom catalysts for advancing the field of photocatalytic H2O2 production.

HighlightsCritical strategies for converting wastes to catalysts are summarized.Applications of waste-derived catalysts in hydrogen evolution reaction, oxygen evolution reaction, and overall water electrolysis are comprehensively reviewed.Perspectives in the development of waste-derived catalysts are analyzed.The sustainable production of green hydrogen via water electrolysis necessitates cost-effective electrocatalysts. By following the circular economy principle, the utilization of waste-derived catalysts significantly promotes the sustainable development of green hydrogen energy. Currently, diverse waste-derived catalysts have exhibited excellent catalytic performance toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water electrolysis (OWE). Herein, we systematically examine recent achievements in waste-derived electrocatalysts for water electrolysis. The general principles of water electrolysis and design principles of efficient electrocatalysts are discussed, followed by the illustration of current strategies for transforming wastes into electrocatalysts. Then, applications of waste-derived catalysts (i.e., carbon-based catalysts, transitional metal-based catalysts, and carbon-based heterostructure catalysts) in HER, OER, and OWE are reviewed successively. An emphasis is put on correlating the catalysts’ structure–performance relationship. Also, challenges and research directions in this booming field are finally highlighted. This review would provide useful insights into the design, synthesis, and applications of waste-derived electrocatalysts, and thus accelerate the development of the circular economy-driven green hydrogen energy scheme.

This quantum chemical study presents the ligand effect and a structure–property relationship in the cationic ring-opening polymerization (CROP) of ε-caprolactone using zirconocene catalysts. We first examined the effects of catalyst structure on the initiation and chain propagation steps of the CROP process. A total of 54 catalyst structures were investigated to understand the influence of the ligand structure on the stability of the catalyst–monomer complex and polymerization activity. The properties of the catalysts were analyzed in terms of ancillary ligands, ligand substituents, and bridging units. Calculations showed that the polymerization follows a proposed cationic mechanism, with ring opening occurring via alkyl-bond cleavage. A correlation between complex stability and activation energy was also observed, with ligand substituents dominating in both steps. While the ancillary ligands directly affect the HOMO energy level, the bridges are mainly responsible for the catalyst geometries, resulting in reduced complex stability and higher activation energy for the propagation step. This study contributes to a better understanding of the structural characteristics of zirconocene catalysts, which offers guidance for improving CROP activities in lactone polymerization.

Developing efficient electrocatalysts for water electrolysis is critical for sustainable hydrogen energy development. For enhancing the catalytic performance of metal catalysts, dual doping has attracted enormous interest for its high effectiveness and facile realization. Dual doping is effective for tuning the electronic properties, enhancing the electrical conductivity, populating active sites, and improving the stability of metal catalysts. In this review, recent developments in cation–cation, cation–anion, and anion–anion dual‐doped catalysts for water splitting are comprehensively summarized and discussed. An emphasis is put on illustrating how dual doping regulates the external and internal properties and boosts the catalytic performance of catalysts. Additionally, perspectives are pointed out to guide future research on engineering high‐performance heteroatom‐doped electrocatalysts.

Electrochemical water splitting has attracted considerable attention for the production of hydrogen fuel by using renewable energy resources. However, the sluggish reaction kinetics make it essential to explore precious‐metal‐free electrocatalysts with superior activity and long‐term stability. Tremendous efforts have been made in exploring electrocatalysts to reduce the energy barriers and improve catalytic efficiency. This review summarizes different categories of precious‐metal‐free electrocatalysts developed in the past 5 years for alkaline water splitting. The design strategies for optimizing the electronic and geometric structures of electrocatalysts with enhanced catalytic performance are discussed, including composition modulation, defect engineering, and structural engineering. Particularly, the advancement of operando/in situ characterization techniques toward the understanding of structural evolution, reaction intermediates, and active sites during the water splitting process are summarized. Finally, current challenges and future perspectives toward achieving efficient catalyst systems for industrial applications are proposed. This review will provide insights and strategies to the design of precious‐metal‐free electrocatalysts and inspire future research in alkaline water splitting. This review summarizes recent advances in precious‐metal‐free electrocatalysts for efficient alkaline water splitting, and the design strategies for enhanced performance including component modulation, defect engineering, and structural engineering, along with insights into operando/in situ characterization for a comprehensive understanding of the structural evolution and functionalities of electrocatalysts during the water splitting reactions.

Electrochemical oxidation of small molecules (e.g., water, urea, methanol, hydrazine, and glycerol) has gained growing scientific interest in the fields of electrochemical energy conversion/storage and environmental remediation. Designing cost‐effective catalysts for the electrooxidation of small molecules (ESM) is thus crucial for improving reaction efficiency. Recently, earth‐abundant amorphous transition metal (TM)‐based nanomaterials have aroused souring interest owing to their earth‐abundance, flexible structures, and excellent electrochemical activities. Hundreds of amorphous TM‐based nanomaterials have been designed and used as promising ESM catalysts. Herein, recent advances in the design of amorphous TM‐based ESM catalysts are comprehensively reviewed. The features (e.g., large specific surface area, flexible electronic structure, and facile structure reconstruction) of amorphous TM‐based ESM catalysts are first analyzed. Afterward, the design of various TM‐based catalysts with advanced strategies (e.g., nanostructure design, component regulation, heteroatom doping, and heterostructure construction) is fully scrutinized, and the catalysts’ structure‐performance correlation is emphasized. Future perspectives in the development of cost‐effective amorphous TM‐based catalysts are then outlined. This review is expected to provide practical strategies for the design of next‐generation amorphous electrocatalysts. This review comprehensively summarizes recent advances in the development of earth‐abundant amorphous catalysts for the electrooxidation of small molecules. Features of amorphous electrocatalysts are discussed, and key amorphous catalyst design strategies are illustrated.

Inspired by the single-atom catalysts (SACs) concept, we rationally design a series of Pt single atom catalysts embedded in different transition metal nanoclusters through first-principles calculations. In these so-called “crown-jewel” (CJ) structures, Pt atoms (jewels) occupy the vertex sites of the metal nanocluster (crown) surface. We investigated the thermal stability and oxygen reduction reaction (ORR) catalytic activity of these catalysts. The results reveal that CJ-structured PtCu nanoclusters are stable and possess a comparable or even better ORR activity compared to Pt catalyst, making it a promising candidate for low-cost ORR catalysts. The effect of cluster size on the adsorption strength of ORR intermediates and catalytic property has also been studied. Furthermore, the overall ORR catalytic activity trend of these SACs is explained based on analysis of their electronic properties. A descriptor Ψ was established to provide further insight into the correlation between the electronic structure and catalytic activity, which provides a design strategy for new ORR catalysts. More importantly, we reveal that this electronic descriptor can be extended to predict other CJ-structured nanoclusters.