Comparative evaluation of heating techniques for room temperature startup of a PEMFC

We study the use of different external heating techniques for startup of a PEM fuel cell initially at room temperature. If a hot liquid is used to heat the fuel cell, the startup time depends on the Reynolds number of the hot liquid flow and also on the convective heat transfer coefficient at the liquid channel/bipolar plate interface. Therefore, apart from the energy required to heat the liquid, additional power is required for the external hot liquid pump. Fuel cell can also be directly heated by using electric heaters. Thin flexible heaters were found to be most suitable for the purpose as they allow the use of thin bipolar plates and reduce the thermal contact resistance at the heater/bipolar plate interface. The thermal mass of the bipolar plates was found to be an important factor affecting the startup time. Hence using materials with lower heat capacities reduces startup time. Embedding a heating element in the GDL reduces the startup time as the thermal mass of the GDLs and MEA is much smaller than the bipolar plate. GDLs with low through-plane thermal conductivities and high in-plane thermal conductivities are able to further reduce the startup time when used in conjunction with a heating element in the GDL.