Hot air convection drying characteristics and microstructures of Pt/C catalyst layers in proton exchange membrane fuel cells

Large-scale fabrication of membrane electrode assemblies for proton exchange membrane fuel cells normally uses hot air convection drying of the catalyst layer (CL). The temperature, velocity, and relative humidity of the hot air affect the CL microstructure and, consequently, the power generation rate. This study experimentally investigated the impact of the hot air temperatures (30 °C, 50 °C, 70 °C and 90 °C), velocities (0.5, 1.0, 1.5 and 2 m/s) and relative humidities (5%, 10%, 20% and 30%) on the CL drying characteristics and microstructures. The mass loss was recorded by an electronic balance as the slurry coating dried with the CL microstructure then evaluated using a scanning electron microscope and nitrogen absorption-desorption measurements. The drying was almost completed for all cases within 90 s. A correlation was then developed for the CL hot air convection drying moisture ratio which was best fit by the two-term exponential model. The correlation accurately predicted the data for low relative humidities with average differences within 10%. The hot air temperature, velocity and relative humidity can significantly affect the CL pore size. High temperatures and velocities formed thicker CLs, while high relative humidities led to thinner CLs. These results indicate that the CL microstructure can be regulated by controlling the drying conditions.