Determination of effective water vapor diffusion coefficient in pemfc gas diffusion layers

The primary removal of product water in proton exchange membrane (PEM) fuel cells is through the cathode gas diffusion layer (GDL) which necessitates the understanding of vapor and liquid transport of water through porous media. In this investigation, the effect of microporous layer (MPL) coatings, GDL thickness, and polytetrafluorethylene (PTFE) loading on the effective water vapor diffusion coefficient is studied. MRC Grafil, SGL Sigracet, and Toray TGP-H GDL samples are tested experimentally with and without MPL coatings and varying PTFE loadings. A dynamic diffusion test cell is developed to produce a water vapor concentration gradient across the GDL and induce diffusion mass transfer. Tests are conducted at ambient temperature and flow rates of 500, 625, and 750 sccm. MPL coatings and increasing levels of PTFE content introduce significant resistance to diffusion while thickness has negligible effects.

► An experimental apparatus for measuring effective water vapor diffusivity in a PEMFC gas diffusion layer is developed.
► Effective water vapor diffusivity in a PEMFC gas diffusion layer is measured for MRC Grafil, SGL Sigracet and Toray TGP-H samples at 25 °C.
► Effect of MPL and PTFE content on the effective water vapor diffusivity is measured.
► MPL coatings and increasing level of PTFE coating introduce significant resistance to diffusion, whereas the thickness has negligible effect for the samples investigated.