Analyses of Self‐Humidification and Suppression of Gas Crossover in Pt‐Dispersed Polymer Electrolyte Membranes for Fuel Cells

Abstract

New polymer electrolyte membranes for polymer‐electrolyte‐membrane (PEM) fuel cells (PEFCs) have been developed. Platinum nanocrystals ( d = 1–2 nm) were highly dispersed in a Nafion 112 film (Pt‐PEM, thickness 50 μm) 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 amount of water vapor produced by the recombination and the faradaic reaction was analyzed together with those of consumed H 2 and O 2 by monitoring humidity in the exhausting gases from PEFCs operated with dry H 2 and O 2 at 80°C. The H 2 used for the self‐humidification increased with increasing output current density, but the total H 2 consumption decreased to ca. 2/3 of that in normal membranes. All H 2 O produced inside the Pt‐PEM was found to be exhausted from the anode, resulting in the efficient humidification of the membrane on the anode side, which is dried by electro‐osmotic drag. Thus, the resistance of the Pt‐PEM was lowered to 0.04 Ω 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 cathode catalyst layer, and eliminated any disturbance of O 2 diffusion by H 2 O 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 from the viewpoints of the simplification of control systems, cold starts, or response to abrupt load changes.