Development of Robust Electrocatalysts Comprising Single-atom Sites with Designed Coordination Environments

Abstract

Single-atom catalysts (SACs), which are composed of singly isolated metal sites and heterogeneous supports, have recently attracted intensive attention as a novel category of electrocatalysts. SACs can not only ultimately reduce the loading amount of noble metals but also exhibit unique reaction activity and selectivity for many reactions. However, the design flexibility of conventional supports of SACs, including nanocarbons and metal oxides, is poor. Therefore, designing coordination environments of metal centers in SACs, which are one of the most significant parameters governing their electrocatalytic properties, has been challenging. This review outlines the synthesis of two kinds of SACs with defined coordination structures and their unique electrocatalytic activities. First, graphenes doped with metals (Fe, Cu, and Ni) and nitrogen atoms, which were prepared by a short-duration heat treatment, function as efficient electrocatalysts for oxygen reduction reactions and CO₂ reduction reactions. Second, metal-doped covalent organic frameworks, which are a class of porous conjugated polymers, exhibit unique electrocatalytic selectivity compared with bulk metals.