1D transient model for frost heave in PEFCs - III. Heat transfer, microporous layer, and cycling effects

A computational model based on a frost heave mechanism has been developed to simulate the potential physical damage in polymer electrolyte fuel cells during shutdown to a frozen state. In previous studies by the authors, an analytical model was developed and it was determined that potentially damaging ice lens formation between the catalyst layer and membrane, or between the catalyst layer and the diffusion media under the channel, but not under the landings, can occur under the right conditions. In this study, the role of the microporous layer, multiple cycle accumulated damage, and the direction and rate of heat flux are explored. It was determined that unfrozen water motion occurs toward colder locations during freezing, which can lead to unfavorable ice formation under certain circumstances. The role of the microporous layer on freeze damage mitigation is also important, as it could act to trap liquid water in the catalyst layer. Strategies to mitigate freeze/ thaw damage via water removal are proposed, which include controlling the heat transfer direction and rate during shutdown, and the use of engineering materials which facilitate the purging process. (c) 2007 The Electrochemical Society.