Analysis of platinum particle size and oxygen reduction in phosphoric acid

The influence of particle size on the reduction of oxygen on supported platinum (Pt) electrocatalysts (Pt on carbon black) in phosphoric acid was investigated. The results confirm earlier evidence that indicates the mass activity (A g-1 Pt) and specific activity (?A cm-2 Pt) of Pt at 900 mV (vs rhe) change with particle size in a manner which corresponds to the change in the relative fraction of Pt surface atoms on the (111) and (100) faces of the Pt particle, assuming a cubo-octahedral geometry. It is further concluded from the measurements in this study, and from some published data, that the interparticle separation distance betweeen Pt particles on the carbon support is not the factor controlling the activity of Pt for oxygen reduction.