ANALYSES OF SELF-HUMIDIFICATION AND SUPPRESSION OF GAS CROSSOVER IN PT-DISPERSED POLYMER ELECTROLYTE MEMBRANES FOR FUEL-CELLS

New polymer electrolyte membranes for polymer-electrolyte-membrane (PE M) fuel cells (PEFCs) have been developed. Platinum nanocrystals (d = 1-2 nm) were highly dispersed in a Nafion 112 film (Pt-PEM, thickness 50 mu m) to catalyze the recombination of the crossover H-2 with O-2, and the water generated was found to humidify the Pt-PEM directly. In order to clarify the self-humidifying properties in the Pt-PEM, the am ount of water vapor produced by the recombination and the faradaic rea ction was analyzed together with those of consumed H-2 and O-2 by moni toring humidity in the exhausting gases from PEFCs operated with dry H -2 and O-2 at 80 degrees C. The H-2 used for the self-humidification i ncreased with increasing output current density, but the total H-2 con sumption decreased to ca. 2/3 of that in normal membranes. All H2O pro duced inside the Pt-PEM was found to be exhausted from the anode, resu lting in the efficient humidification of the membrane on the anode sid e, which is dried by electro-osmotic drag. Thus, the resistance of the Pt-PEM was lowered to 0.04 Omega cm(2). It is also found that the Pt- PEM improved the cathode potential distinctively which was ascribed to elimination of the chemical reaction of crossover gases in the cathod e catalyst layer, and eliminated any disturbance of O-2 diffusion by H 2O vapor produced by the reaction. The operation of PEFCs with minimal or no humidification by using Pt-PEMs is essential in applications to power sources for electric vehicles or various electronic devices fro m the viewpoints of the simplification of control systems, cold starts : or response to abrupt load changes.