Single-atom sites (SASs) are commonly stabilized and influenced by neighboring atoms in the host; disclosing the structure-reactivity relationships of SASs in water electrolysis is one of the grand challenges originating from the tremendous wealth of support materials with complex structures. Through a multidisciplinary view of the design principles, synthesis strategies, characterization techniques, and theoretical analysis of structure-performance correlations, this timely Review is dedicated to summarizing the most recent progress in tailoring bond microenvironments on different supports and discussing the reaction pathways and performance advantages of different SAS structures for water electrolysis. The essence and mechanisms of how SAS structures influence electrocatalysis and the critical requirements for future developments are discussed. Finally, the challenges and perspectives are also provided to stimulate the practical, widespread utilization of SAS catalysts in water-splitting electrolyzers.

Advanced metal-sulfur batteries (MSBs) are regarded as promising next-generation energy storage devices. Recently, engineering polysulfide redox catalysts (PSRCs) to stabilize and catalytically convert polysulfide intermediates is proposed as an effective strategy to address the grand challenge of "shuttle effects" in the cathode. Therefore, modulating the bond interactions and interface microenvironments and disclosing the structure-performance correlations between polysulfide and catalysts are essential to guide the future cathode design in MSBs. Herein, from a multidisciplinary view, the most recent process in the reaction principles, in situ characterizations, bond interaction modulation, and interface microenvironment optimization of polysulfide redox catalysts, is comprehensively summarized. Especially, unique insights are provided into the strategies for tailoring the bond interactions of PSRCs, such as heteroatom doping, vacancy engineering, heterostructure, coordination structure arrangements, and crystal phase modulation. Furthermore, the importance of interface microenvironments and substrate effects in different PSRCs are exposed, and a detailed comparison is given to unveil the critical parameters for their future developments. Finally, the critical design principles on electrode microenvironments for advanced MSBs are also proposed to stimulate the practically widespread utilization of PSRCs-equipped cathodes in MSBs. Overall, this review provides cutting-edge guidance for future developments in high-energy-density and long-life MSBs.

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Single-atom sites (SASs) are commonly stabilized and influenced by neighboring atoms in the host; disclosing the structure-reactivity relationships of SASs in water electrolysis is one of the grand challenges originating from the tremendous wealth of support materials with complex structures. Through a multidisciplinary view of the design principles, synthesis strategies, characterization techniques, and theoretical analysis of structure-performance correlations, this timely Review is dedicated to summarizing the most recent progress in tailoring bond microenvironments on different supports and discussing the reaction pathways and performance advantages of different SAS structures for water electrolysis. The essence and mechanisms of how SAS structures influence electrocatalysis and the critical requirements for future developments are discussed. Finally, the challenges and perspectives are also provided to stimulate the practical, widespread utilization of SAS catalysts in water-splitting electrolyzers.