Self‐Humidifying Polymer Electrolyte Membranes for Fuel Cells

Abstract

Polymer electrolyte fuel cells have attracted enormous interest as a primary power source for electric vehicles. Water management in the electrolyte is one of the complicated problems to be overcome. A new self‐humidifying electrolyte membrane is proposed to solve this problem. Self‐humidification allows the use of very thin membranes, simultaneously allowing high performance of the cell. Use of the new, thin membranes makes the system very simple and ready for cold starts and also amenable to abrupt load changes. The electrolyte is comprised of 50 μm thick Nafion membrane containing 0.07 mg/cm 2 of platinum catalyst particles ( d = 1 to 2 nm) and a few weight percent of a hygroscopic material such as silica or titania ( d = ca. 5 to 7 nm) . The platinum particles catalyze the oxidation of crossover hydrogen with oxygen to generate water, which in turn is adsorbed by the oxide particles. The cell shows exceptionally stable and high performance even under ambient pressure conditions when operated with hydrogen saturated with water at 20°C and dry oxygen. The internal resistance was measured to be 0.06 Ω cm 2 , and the output of the cell was 0.63 W/cm 2 i.e. , 0.9 A/cm 2 at 0.7 V with an energy efficiency of 60%. The output was 1 W/cm 2 in the voltage region of 0.6 to 0.4 V yielding current densities of 1.6 to 2.5 A/cm 2 . Hydrogen depleted for self‐humidification was estimated to be less than a few percent under these operating conditions.