Pt Utilization Analysis at Low RH Condition

Pt utilization, i.e. the ratio of the electrochemically active Pt surface area of a MEA to the Pt surface area of the catalyst, was analyzed at 20-100%RH, 40-80°C. Pt utilization significantly decreased with decreasing RH for Pt/C catalysts in which Pt particles are supported not only on the carbon surface but also inside the carbon, while kept high even at low RH in the samples with Pt particles supported only on the carbon surface. We presume that this is because the Pt particles inside are not covered with ionomers and protons cannot access any longer at low RH.