Effects of cathode gas diffusion layer porosity and contact angle distributions along through-plane direction on the performance of polymer electrolyte membrane fuel cell

In the present work, a numerical model for polymer electrolyte membrane fuel cell (PEMFC) has been employed to investigate the effects of porosity and contact angle distributions of the porous layer on the performance of PEMFC. The three-dimensional, two-phase, and non-isothermal flow solver considers heat transfer, electrochemical reaction, and liquid water saturation. Various cases with different cathode gas diffusion layer (GDL) porosities are performed. The results showed that a better performance is achieved when the GDL porosity is increased because of the reduced mass transport resistance of oxygen. The effects of the porosity distributions on the PEMFC performance were examined by comparing the predictions from the cases with non-uniform porosity and uniform porosity in the cathode GDL. It was shown that the current density of the cases with non-uniform porosity is higher than that of the uniform porosity case when the operation voltage is low. This is due to the fact that non-uniform porosity distributions in the cathode GDL enhance the reactant transport. When the operation voltage is high, the current densities of the cases with non-uniform porosity and uniform porosity are almost the same. Moreover, the influence of contact angle distributions in cathode GDL was explored. Various cases with gradient-decreasing, gradient-increasing, and uniform constant contact angles from GDL/channel interface to GDL/catalyst layer interface were studied. It was found that the case with gradient-increasing contact angle has a better performance due to the larger capillary pressure difference to remove more water. The poor performance of the case with gradient-decreasing contact angle is related to the phenomenon of flooding in the catalyst layer.