Evaporation of water from gas diffusion layers (GDL) is an important process for water management in polymer electrolyte fuel cells. At temperatures around 80 °C and locally under-saturated conditions, evaporation can have a significant impact on the GDL saturation.

 However, little is known about the evaporation rates of water in gas diffusion layers. First ex-situ results at room temperature and for low saturations have been reported in [1]. But for a better understanding of the evaporation rates under real operating temperatures, generic data is required at different temperatures and saturation levels.

 Using a special setup, which is applicable also for X-ray imaging of water saturation, water surface and GDL structure, evaporation rates are determined for well-controlled gas speeds (over the surface of the GDL),, temperatures of up to 80 °C and relevant liquid saturations. Figure 1 shows data (including reproducibility) for Toray TGPH 060 material as function of temperature up to 80 °C, at a capillary pressure of 10 mbar and gas velocity of 6 m/s.

[1] I. V. Zenyuk, A. Lamibrac, J. Eller, D. Y. Parkinson, F. Marone, F. N. Büchi, and A. Z. Weber, J. Phys. Chem. C, 2016, 120 (50), pp 28701–28711

Figure 1: Evaporation rates from Toray TGPH 060 gas diffusion layer material a) as function of temperature at a gas velocity of 6.0 m/s; b) as function of gas velocity on the GDL surface at 60 °C; both for a dry gas stream and capillary pressure of 10 mbar; data shown based on preliminary set-up.