Pore-scale numerical investigation of water–gas flow and heat transport in gas diffusion layers with varying fiber/additive content and hydrophobicity

Additives such as binders and hydrophobic agents are commonly introduced into the fibrous Gas Diffusion Layer (GDL) of proton exchange membrane fuel cells to enhance mechanical strength and facilitate water management. However, the effect of additive/fiber content and surface wettability on water removal, oxygen diffusion, and heat conduction remains insufficiently understood. In this work, we develop a stochastic GDL reconstruction framework with systematically varied fiber and additive content. The reconstructed structures are analyzed through pore–throat network extraction, interface-resolved two-phase flow simulations, as well as oxygen diffusion and heat conduction simulations under dry and partially saturated conditions. The variation in surface wettability caused by the coating of hydrophobic additives is simulated by the contact angle. The results reveal that increased fiber content significantly restricts pore space, thereby weakening oxygen diffusivity and increasing breakthrough pressure, while having a limited impact on stabilized water saturation and thermal conductivity. Additives, particularly at high loadings, reduce pore connectivity and gas transport, though enhanced hydrophobicity partially mitigates these effects. Oxygen diffusivity is found to be particularly sensitive to changes in effective pore space caused by additive inclusion and water occupation. These findings present a comprehensive quantitative perspective on how additive design modulates GDL transport properties and provide a simulation-based framework for optimizing fuel cell GDL microstructure.