Pore network simulations of liquid water and oxygen transport in gas diffusion layers with spatially variable wettability

The wettability modification of the gas diffusion layer has a significant effect on water management in proton exchange membrane fuel cells. Therefore, a three-dimensional regular pore network model is developed to numerically investigate the liquid water and oxygen transport in gas diffusion layer with spatially variable wettability. Four types of hydrophilicity configuration are taken into account: uniform configuration, symmetric graded configuration, positive graded configuration and negative graded configuration. Pore-scale analysis shows that adding hydrophilic elements first enhances liquid-gas transport and then decreases. There is an optimum hydrophilic pore fraction (fc) leading to minimum liquid water saturation and maximum limiting current density in each wettability configuration, and the value of fc is related to wettability configuration and gradient but independent of inlet injection points. In addition, the results reveal that oxygen transport not only depends on total liquid water saturation, but also depends on water distribution. Uniform water distribution in the through-plane direction is helpful for oxygen transport, so the gas diffusion layer with positive graded hydrophilicity configuration obtains the highest limiting current density. •Pore network model is used for gas diffusion layer with graded wettability.•Two-phase transport first enhances and then decreases with adding hydrophilic pores.•Oxygen transport is determined by liquid water saturation and distribution.•Wettability distribution affects optimum hydrophilic degree, injection points don't.•Positive wettability configuration with a gradient of 0.1 gives optimal performance.