Effect of Cross Flow on Performance of a PEM Fuel Cell

A serpentine flow channel is one of the most common and practical channel layouts for a PEM fuel cell since it ensures the removal of water produced in a cell. While the reactant flows along the flow channel, it can also leak or cross to neighboring channels via the porous gas diffusion layer due to a high pressure gradient. Such a cross flow leads to effective water removal in a gas diffusion layer thus enlarging the active area for reaction although this cross flow has largely been ignored in previous studies. In this study, neutron radiography is applied to investigate the liquid water accumulation and its effect on the performance of a PEM fuel cell. Liquid water tends to accumulate in the gas diffusion layer adjacent to the flow channel area while the liquid water formed in the gas diffusion layer next to the channel land area seems to be effectively removed by the cross leakage flow between the adjacent flow channels. The amount of liquid water accumulation in the cell is dependant on the cell operating temperature, the pressure drop in the flow channel and the current density. It is shown that the cell performance is strongly affected by the presence and accumulation of liquid water, especially at high current densities and resulting in performance hysteresis for load variations. The rate of liquid water production is also mathematically modeled to analyze the effect of the cell operating temperature and pressure drop on the liquid water formation in a cell.