Prospects of non-noble metal single atoms embedded in two-dimensional (2D) carbon and non-carbon-based structures in electrocatalytic applications

[Display omitted] •Isolated single atoms exhibit high effectiveness in electrocatalytic applications.•Advantages of non-noble metal single atoms anchored to 2D supports are reviewed.•Strategies for preparing single-atom catalysts are described.•Sources of the high catalytic selectivity of single-atom catalysts are presented.•Future outlooks for non-noble metal single-atom catalysts are highlighted. The idea of single-atom catalysts (SACs) has gained attention in electrocatalysis owing to its high efficiencies in energy conversion reactions. Supported single-atoms (SAs) exhibit major advantages, such as high atom utilization, strong interfacial interaction, and well-defined active centers, compared with nanoparticles. From a practical point of view, SACs comprising non-noble metals seem to be an attractive alternative to expensive noble-metal catalytic systems. As the intrinsic activity and the electronic structure of SACs are governed by the support material and coordination environment of the metal species. Two-dimensional (2D) materials could be a promising candidates for supporting SAs owing to their high chemical stabilities and layered structures. This review provides an overview of recent developments in 2D materials-supported non-noble metal SACs for electrochemical energy conversion applications. The relevance of performing the comprehensive characterization of the 2D supported catalysts to elucidate their catalytic activities under different reaction conditions were highlighted. In light of recent findings in the field, we discussed the existing challenges and future opportunities regarding the correlation between the 2D structures and activities of SACs toward electrochemical energy conversion reactions.