Effect of operating pressure on the system efficiency of a methane-fuelled solid polymer fuel cell power source

The energy conversion efficiency of a fuel cell is directly related to its operating voltage. In general increasing the fuel and oxidant pressure increases the cell potential. However, additional energy is required to compress the gases in order to raise the pressure, negating the efficiency gains achieved in the cells. System designers seek to balance complexity, cost and system efficiency. The overall system efficiency is highly dependent on the interaction and interconnection of the components. For a system which includes a solid polymer fuel cell (SPFC) stack, a methane fuel processor and a compressor/expander an analysis has been carried out to assess the functional relationship between the operating pressure and efficiency. For a system configuration which includes a high-temperature fuel processor and a 40-kWe stack, an 8% improvement in efficiency was predicted for the higher operating pressure (25% for 1.5 bar(a) and 33% for 4 bar(a).