Pore trapping mechanisms in two-phase flows through fuel cells porous media
Conference contribution, 2019
The peak performances in fuel cells are strongly limited by flooding of the electrodes. Flooding occurs as a consequence of the intense electrochemical reaction in the cell, when, at high current density, a high amount of water is produced and trapped in the gas diffusion layers (GDLs). The trapped water blocks the pores of the fibrous GDLs and impedes the uniform diffusion of fuel gas along the cell area. Therefore, a fast removal of water from the porous layer is demanded. How to enhance such a mechanism in order to improve the water management remains still an open question. In the present study we address this problem with an innovative bottom-up approach: by means of Lattice-Boltzmann simulations, we investigate the effects of the microstructure at the pore-scale on the two-phase flows dynamics, in order to optimise the GDLs design and obtain an efficient water management at the macroscale. Results show that, during imbibition, the wetting phase can be trapped at the pore throat, impeding liquid removal. The trapping mechanism is primarily governed by the thermodynamic energy barriers induced by the pore expansions, in a complementary way to Haines jump during drainage. This undesired phenomenon is exacerbated in hydrophobic media during imbibition. These findings suggest a possible new route for innovative design of gas diffusion layers in fuel cells applications.