Evaporative cooling for polymer electrolyte fuel cells- An operando analysis at technical single cell level

Evaporative cooling has the potential to reduce stack and system volume of polymer electrolyte fuel cells by up to 30% and to cut costs significantly by simplifying the multi-layered structure of bipolar plates and eliminating the need for external humidification. This study provides an experimental proof of concept by analyzing the evaporation behavior, cooling power, internal humidification, electrochemical performance and operational stability of evaporative cooling under technical cell boundary conditions. Isothermal in situ as well as operando studies are carried out in an evapo-ratively cooled fuel cell (15 cm2 active area, 80 degrees C, ambient pressure). Relative humidity boundary conditions imitate the inlet, center and outlet of a technical cell.Main findings show that the evaporation rate is saturation limited at low gas velocities, whereas it is transport limited at higher gas speed. Operando measurements prove that evaporative cooling works at a technical cell level with multiple water supply lines. The entire waste heat is removed and sufficient membrane humidification is achieved when dry inlet gases are used. Furthermore, it is shown that optimal performance is achieved in a counter-flow arrangement. The observed electrochemical performance is comparable to conventional cooling with humidified gases at inlet, center and outlet of the cell.