A model based investigation of evaporative cooling for polymer electrolyte fuel cells – Stack level analysis
Michael Striednig, Magali Cochet, Pierre Boillat, Thomas J. Schmidt, Félix N. Büchi
Abstract
Conventional cooling systems of polymer electrolyte fuel cells are responsible for a significant share of stack and system volume, mass and cost. Evaporative cooling shows the potential to overcome these hurdles by simplifying the design of bipolar plates and eliminating the need for an external humidifier. Thus, evaporative cooling can significantly contribute towards reaching the DOE fuel cell system power density target of 850 W/L. This paper investigates the potentials and limits of evaporative cooling at stack level. For this, a zero-dimensional model has been developed, incorporating mass and energy balances as well as electrochemistry and evaporation. Main findings show that evaporative cooling is feasible over a wide range of operating conditions. The cooling performance is a function of temperature, gas pressures and stoichiometric ratios, where the temperature shows the largest leverage. A feasible operating window is proposed, which is slightly shifted towards higher temperatures (80–95 °C), lower pressures (100–200 kPa) and higher cathode stoichiometric ratios (>1.5) compared to conventional fuel cells. A slight decrease in electrochemical performance (ca. 3% at 1.5 A/cm2) is easily compensated by the volume and weight saving potential of up to 30% and thus substantially reduced cost.