Oxygen electroreduction on small (<10 nm) and {100}-oriented Pt nanoparticles

Abstract

Oxygen reduction reaction (ORR) was studied on {100}-oriented Pt nanoparticles with sizes 3 to 7 nm in sulphuric acid solution. The distribution and size of nanoparticles was analysed by transmission electron microscopy and metal loading was determined by inductively coupled plasma optical emission spectroscopy. The synthesised nanoparticles have about 40% of Pt(100) facet and 10% Pt(111) as determined from Ge and Bi adsorption, respectively. The four Pt/C catalysts with metal loading from 25 to 38 wt% were tested for ORR activity in 0.5 M H2SO4 solution using the rotating disk electrode method. It was found that the ORR proceeds mainly via a 4-electron pathway with the rate-limiting step being the transfer of the first electron to O2 molecule. The mass activities for ORR increase with decreasing the particle size, but specific activity and mass-specific activity have a maximum at 4.6 nm particle size. This means the most optimal {100}-oriented Pt size for ORR is around 4.6 nm in sulphuric acid solution.