Non-isothermal cold start of polymer electrolyte fuel cells

A multiphase, three-dimensional model has been developed to describe non-isothermal cold start of a polymer electrolyte fuel cell (PEFC) and to delineate intricate interactions between ice formation and heat generation during cold start. The effect of rising cell temperature is numerically explored by comparing a non-isothermal cold start with an isothermal one. It is found that more water is transported into the membrane and less ice formation occurs in the cathode catalyst layer (CL) in the presence of rising cell temperature. In addition, the more hydrated membrane and the rising cell temperature greatly lower the membrane resistance, thus giving rise to higher cell voltage. A lumped thermal analysis significantly over-estimates the overall thermal requirement of self-startup as a cell requires only a portion of its active area to reach the freezing point and be ice-free and operable. It is also found that pre-startup conditions have significant influence on cold start. Procedures to minimize residual water inside the cell prior to cold start, such as gas purge, are critically important. Finally, non-isothermal cold start becomes much easier from higher ambient temperatures.