Electrocatalytic Activities of Atomically Controlled Metal Nanoclusters for Clean Energy Conversion

Abstract

Thiolate stabilized metal nanoclusters containing a few to a few hundreds of atoms exhibit distinctive optical, electrochemical and catalytic properties. In various catalytic applications, metal nanoclusters show unique electrocatalytic activities for clean energy conversion such as hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and CO2 reduction reaction (CO2 RR). The catalytic activities and selectivity of metal nanoclusters can be modified by introducing foreign metal and surface modification. Here we present electronic structures and catalytic activities of atomically controlled Au25(SR)18 (SR = thiolate) and bimetallic nanoclusters. Au25(SC6H13)18–graphene composite led to four electron pathway for ORR revealed by rotating ring-disk electrode experiments. This result indicates that facile oxygen reduction to water occurred at this composite electrode. HER activities of metal nanoclusters were examined by constant potential electrolysis and the binding energies were calculated by density functional theory. HER turnover frequency (TOF) of Au25(SC6H13)18 (8.8 s-1 at -0.6 V vs. RHE) increased by doping of Pt (33.4 s-1). This enhanced HER activity upon Pt-doping is attributed to the facile H-binding on the Pt dopant. TOF of Pt-doped nanoclusters was further increased by surface modification using proton-relaying ligands. Pt-doped nanocluster showed higher HER mass activity than the benchmarking Pt/C nanoparticles. Furthermore, high OER activity of metal nanoclusters was further revealed in alkaline media.