Optimization of reactants relative humidity for high performance of polymer electrolyte membrane fuel cells with co-flow and counter-flow configurations

A three-dimensional multiphase polymer electrolyte membrane (PEM) fuel cell model is employed to investigate the membrane and liquid water transport property as well as cell performance with the co-flow and counter-flow configurations under different reactant relative humidity (RH) conditions. Numerical results indicate that a lower anode RH with a cathode RH of 100% or a lower cathode RH with an anode RH of 100% leads to a decrement in cell performance at high operational voltages and an increment in cell performance at low operational voltages. With moderate or high anode and cathode RH, the liquid water saturation in porous electrodes is the limiting factor in cell performance improvement; but with low anode and cathode RH, the membrane water content becomes the limiting factor. Moreover, the counter-flow configuration shows differences in the membrane and liquid water distributions in comparison with the co-flow configuration. This study also found that the counter-flow configuration with the anode and cathode RH of 50% greatly increases the current density by 21.21% compared with the co-flow configuration under the anode and cathode RH of 100% at the operational voltage of 0.4 V, therefore, the counter-flow configuration with moderate anode and cathode RH is recommended for the optimal operation of a parallel flow field PEM fuel cell.