Experimental Investigation of Sub-Zero (0 degree C) Operation of Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) have been touted as potential energy conversion devices of the future. By combining hydrogen and oxygen in an electrochemical reaction, electrical power is produced. These systems can operate more efficiently than internal combustion engines and are being implemented in a wide variety of applications. These systems, although progressing much over the past few decades, face many technical challenges before reaching commercial viability. One such area of focus is their operation in sub-zero (0 °C) environments where the byproduct water is prone to freezing. This report discusses both the theory and experimental investigation of freezing conditions on PEMFCs. Visualization of ice formation inside a PEMFC was captured using 3D neutron tomography which pinpointed specific locations and quantities of ice in the membrane electrode assembly (MEA). Such detailed views are useful to both academic and industrial cell designers. Tests were also conducted on PEMFC cold-start from temperatures as low as -8 °C. A cell that could be switched to run under either interdigitated or parallel flow-field configurations was analyzed for cold-start capability. The interdigitated design, which removes greater amounts of water from the cell due to convective transport under land areas, was shown to successfully start unassisted from a lower temperature than the diffusion limited parallel design. These results may provide a means to reduce the amount of energy required to heat and start a PEMFC from freezing temperatures. Finally, the design consequences of a transitional flow-field cell are investigated by analyzing the power curves for both interdigitated and parallel flow-field configurations. A hybrid design strategy was realized by shifting between the two flow types to maximize system output power.