Assisted cold start of a PEMFC with a thermochemical preheater: A numerical study

The cold start of polymer electrolyte fuel cells (PEMFC) remains a challenge for their automotive applications, due to blockage of the electrode pores with frozen or liquid water yielding a lower efficiency or even a failure of the start-up. One solution is the preheating of the PEMFC with a thermochemical preheater, e.g. a metal hydride reactor, which releases heat upon hydrogen absorption. To the authors’ knowledge, this is the first work presenting a 2D transient physical model for the coupled system of PEMFC and thermochemical preheater. The aims are investigating different cold start strategies and proposing a strategy to achieve rapid start-ups. Internal heating, i.e. only relying on the waste heat of the fuel cell, yields high heating rates, which mainly stems from the Ohmic resistance and the overpotential of the oxygen reduction reaction. According to the simulations, lower cell voltages yield higher heating rates and are thus beneficial for cold starts, e.g. a start-up from -16 °C with 0.5 V fails, while the same start with 0.1 V succeeds. However, there is a critical temperature, for which the start-up will fail due to freezing and/or flooding of the cathode catalyst layer. External heating, i.e. preheating the cell at OCV with the metal hydride reactor, enables cold starts from lower temperatures, but the heating rate is one order of magnitude lower compared to the internal heating. The assisted cold start strategy combines an external heating phase and an internal heating phase to minimize the cold start time, e.g. a start-up from -20 °C can be achieved with the present model within 23 s.