Single-nanoparticle electrochemical collision for study of the size-dependent activity of Au nanoparticles during hydrogen evolution reaction

Identifying the intrinsic electrocatalytic activity of an individual nanoparticle is essential to reveal the structure-activity relations of catalysts. However, it is challenging as the performance of catalysts is typically evaluated with ensembles, providing an elusive averaged response of complex catalyst-modified electrodes. Herein, a single-nanoparticle electrochemical collision (SNEC)-based method was employed to characterize the electrocatalysis of citrate-capped Au NPs with six different particle sizes, and investigate the size-dependent electrocatalytic activity of Au NPs toward hydrogen evolution reaction (HER) at the single-particle level. Results showed that the geometric activity of Au NPs showed a decreasing trend as the size increased from 5 nm to 40 nm, consisting with the linear sweep voltammetry (LSV) data that the onset potentials and potentials to reaching at HER currents of 50 μA cm⁻² shifted negatively as the size of Au NPs increased. Also noteworthy is that the measured geometric activity of single Au NP toward HER was 5~6 orders of magnitude higher than the ensemble data derived from the LSV tests. The extraordinary enhancement of catalytic activity is believed to originate from the high accessible surface area of monodispersed Au NPs. Hence, the proposed SNEC-based method could investigate the intrinsic electrocatalytic activity of NPs in solution at the single-particle level, and achieve true size-activity correlation, which may provide effective guidance for the rational design of advanced electrocatalysts.