Effect of Sputtered Film of Platinum on Low Platinum Loading Electrodes on Electrode Kinetics of Oxygen Reduction in Proton Exchange Membrane Fuel Cells

-Localization of Pt electrocatalyst by sputter deposition of a thin film (5OOA) on the front surface of a fuel cell electrode containing a supported electrocatalyst (20% Pt/C, 0.4mgcm-* loading) has been known to exhibit higher fuel cell performance as compared to that on the electrode without the sputtered flm. This study compares the electrode kinetic parameters, electrochemically active surface areas, activation energies and reaction orders for the oxygen reduction reaction (ORR) in the sputtered and unsputtered electrodes in proton exchange membrane fuel cells as functions of temperature and pressure. Comparison of the cell performance at 5 atm and 95°C indicates an almost 4 fold improvement in ORR activity at 0.9 V vs. rhe and a similar 3.6 fold improvement in the exchange current densities. The increment in the electrochemically active surface area was about two fold, thereby indicating that factors beyond a surface area increment were responsible for the observed activity enhancement in the ORR. Evaluation of ORR electrode kinetics as a function of temperature indicated a lower activation energy for ORR on the sputtered electrode, as compared to that on the unsputtered electrode. The reaction orders for ORR were, however, the same for both electrodes and were similar to previously obtained values at the Pt microelectrode/Nafion interface, thereby indicating no change in the rate determining step for ORR. This paper also presents the morphological characterization of the electrode/membrane interface using the SEM/EDAX technique, which clearly signifies the two types of Pt-unsupported and supported.