Coolant induced variable temperature flow field for improved performance of proton exchange membrane fuel cells

The objective of the coolant induced variable temperature flow field concept is to maintain high membrane water content along the entire flow field without external humidification and without occurrence of liquid water inside the cell at higher currents. This is achieved by imposing a temperature gradient in the cathode downstream direction in such manner that the product water is just sufficient to maintain close to 100% relative humidity along the entire flow field. The concept must be feasible for stack applications and flexible to enable efficient operation under significantly different operating conditions. The concept is investigated via interactive combination of computational fluid dynamics modeling and experimental validation for two membranes, namely Nafion^® 212 and Nafion^® 115. Additional calculations are also carried out for a five-cell stack with Nafion^® 212 membranes. The results of the computational fluid dynamics model are compared with the experimental data. Calculated and measured current density and relative humidity distributions along the cell give insight in the membrane water content and membrane water flux. With the coolant induced variable temperature flow field concept it is possible to achieve close to 100% relative humidity along the entire flow field without the requirement for external humidification, and to minimize the occurrence of liquid water inside the cell, resulting in improved performance of the cell in comparison with commonly used isothermal operation.