Nano-size effect of Au catalyst for electrochemical reduction of oxygen in alkaline electrolyte

Oxygen reduction reaction (ORR) in alkaline electrolyte (0.5 mol/L KOH) was studied on a series of carbon supported Au nanoparticles (NPs) with average sizes ranging from 3 to 14 nm, using the rotating disk electrode methods. Downsizing the Au NPs from 14 to 3 nm resulted in continued enhancement in both the intrinsic and mass-specific activity of Au for ORR but produced no influence on the reaction mechanism or number of transferred electrons per O-2-reduction. Careful analyses of the particle shapes of Au NPs with varied sizes by using high-resolution transmission electron microscopy enabled us to estimate the fraction of surface Au atoms at different positions or coordination (energy) state. Correlating the fraction of high energy surface atoms with the Au activity for ORR disclosed the importance of high energy surface atoms in enhancing the intrinsic activity of Au. Fundamental correlation between the Au intrinsic activity for ORR and the experimentally determined surface electronic structure of Au NPs was also established. (C) 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.