Development of small polymer electrolyte fuel cell stacks

Abstract

The results on the research and development of small polymer electrolyte fuel cell stacks, including the assembly of single cell. 6-cell and 21-cell modules, are described. The important characteristics of the systems are: (i) membrane and electrode assemblies were made with Nafion^® 115 and 117 membranes and particularly low catalyst loading electrodes presenting a geometric area of 20 cm² and a catalyst loading of 0.4 mg Pt/cm²: (ii) bipolar plates were fabricated using a nonporous graphite material in which a series/parallel flow field was machined out: (iii) external distribution of gases to the cells was done using parallel manifolding; (iv) cooling systems were tested employing water/air cooling plates distributed every three cells throughout the stack; (v) the reactant gases were externally humidified using temperature controlled humidification bottles. Testing of the stacks was conducted in a specially designed test station employing nonpressurized H₂/O₂ reactants and measuring the individual and the overall cell voltage vs. current under several conditions for the overall system operation.