Electrochemical-leaching route for the size-controllable synthesis of copper-based oxygen reduction reaction catalysts: From nanoparticles to atomic clusters and single atoms

Size-controllable synthesis of non-noble metal particles ranging from nanometer to subnanometer and atomic level is of great significance for demonstrating the size effects of metallic catalysts towards oxygen reduction reaction (ORR) catalysis. Herein, we propose an electrochemical leaching strategy for the top-down synthesis of Cu nanoparticles (NPs), atomic clusters (ACs) and single atoms (SAs) on sulfur-doped reduced graphene oxide (SrGO). Within this strategy, Cu NPs (about 8 nm) were electrodeposited and subsequently controllably downsized to ACs (about 2 nm) and SAs (<1 nm) via a stripping voltammetry method by adjusting the termination potential. The effective control in the size of active Cu species allowed us to conveniently investigate the size effect of Cu on ORR in multiscale. Single-atom Cu exhibited good ORR performance with a half-wave potential of 0.86 V and an electron transfer number of 3.98, as well as a long-term stability, much superior to other larger Cu particles. Our findings open a new avenue for top-down synthesis of metal particles with desirable sizes, which will effectively benefit the future design of size-controlled ORR electrocatalysts.