Platinum-based single-atom catalysts (SACs) are among the most promising candidates for the practical applications of electrochemical hydrogen evolution reaction (HER), but their catalytic efficiency remains to be further enhanced. Herein, a welldesigned nanoarray-structured nitrogen-doped graphite foil (NNGF) substrate is introduced to support Pt SACs in Pt−N 4 construction (Pt 1 /NNGF) for HER. Within NNGF, the constructed nanoarray-structured surficial layer for supporting Pt SACs could enhance the exposure of active sites to the electrolyte and improve the reaction and diffusion kinetics; meanwhile, the retained graphite structures in bulk NNGF provide not only the required electrical conductivity but also the mechanical stability and flexibility. Because of such double-layer structures of NNGF, stable Pt−N 4 construction, and binder-free advantages, the Pt 1 / NNGF electrode exhibits a low overpotential of 0.023 V at 10 mA cm −2 and a small Tafel slope of 29.1 mV dec −1 as well as an excellent long-term durability.

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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.

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