Effect of particle size on the electrocatalytic activity of platinum dispersions in carbon matrix electrodes for phosphoric acid fuel cells

The loss in electrocatalytic activity of Pt particles in carbon matrix elec trodes has been experimentally and theoretically investigated as a function of Pt particle size. The measurement of the cathodic potentiostatic curren t transient showed that a decrease in oxygen reduction current due to carbo xyl group formation, relative to the oxygen reduction current in the absenc e of carboxyl group, increased with a decreasing Pt particle size. This rel ative value is a measure of the loss in specific activity. A model describi ng the electrocatalytic activity loss has been proposed by introducing a ne w parameter, characterising the effective dead active area produced by the carboxyl group formation, relative to the total active area free of the car boxyl group. The agreement of the experimentally determined relative curren t decrease with the calculated relative value of the effective dead active area confirms the model.