Control of Particle Size of Pt and Pt Alloy Electrocatalysts Supported on Carbon Black by the Nanocapsule Method

Monodisperse Pt and Pt-M (M = Co, Ru) alloy nanoparticles supported on carbon black (Pt/CB, Pt(2)Ru(3)/CB, Pt(3)Co/CB) were prepared by the nanocapsule method. We have succeeded in controlling the particle size simply by changing the molar ratio of metal precursor(s) to surfactant (M/S) in the preparation, with the other conditions being identical. The particle size was well-controlled between 2.0 and 4.5 nm with a metal loading level of 50 wt % for all catalysts. The compositions of the alloy particles were close to the projected values, with a small standard deviation, i.e., <3.1 atom % for Pt(2)Ru(3) and 1.4 atom % for Pt(3)Co. It was also found that these alloys were in the form of the corresponding solid solutions with the fcc structure.