Coordinating single-atom catalysts on two-dimensional nanomaterials: A paradigm towards bolstered photocatalytic energy conversion

The development of photocatalysts with robust active sites, excellent light-harvesting ability, low electron-hole recombination, and superior activity has been employed over the past decades. Recently, single-atom engineering emerged as a new frontier owing to its exceptional performance in ameliorating photocatalysis. Single-atom photocatalysts endow remarkable electronic structures, maximal atomic utilization efficiency, unsaturated coordination centers, high catalytic activity and selectivity. This review summarizes the advancement of single-atom catalysis (SAC) anchored on two-dimensional (2D) substrates (SA@2D) for photocatalytic energy conversion during the past five years. We will begin with the basic traits of SACs followed by casting an overview of different synthetic approaches and characterization techniques related to SACs. Next, the potential for 2D materials as auspicious substrates of singleatom photocatalysts and the approaches for stabilizing single atoms on the 2D substrates are discussed. In view of the peculiarities of different single-atoms categories (e.g. noble-metal, transition-metal and metal-free SAC), the emerging properties and roles of SAC in photocatalysis are highlighted. Subsequently, the progress of SAs@2D materials for photocatalytic energy conversion in water splitting, CO2 reduction, N-2 reduction and H2O2 production is prospected. Particularly, the interconnection between the coordination chemistry and structure of SACs as well as their energy performance in photocatalysis is elucidated to unravel insightful reaction mechanisms and the structure-performance relationships. Lastly, a summary and perspective are outlined to serve as a guiding scaffold for the development in this energetic realm to enlighten the emergence of the next-generation SACs by taming the functional vitality of SACs. (C) 2022 Elsevier B.V. All rights reserved.