Boosting pore formation and mass transfer capacity of catalyst layer by internal boiling drying mode for proton exchange membrane fuel cells

The drying process is the critical step to determine the resulting microstructure and transport properties of catalyst layer (CL) in proton exchange membrane fuel cells (PEMFCs). Drying mode is an essential drying factor affecting the catalyst layer structure, which is poorly understood at present. This study proposes using the gas-liquid equilibrium phase diagram to control the CL drying mode, and investigates the impact of drying mode on CL structure formation and mass transfer capacity. Results indicate that internal boiling drying as a gainful drying mode boosts the CL mass transfer capacity with higher porosity, stronger hydrophobicity, and beneficial cracks. Moreover, the mechanism of internal boiling drying process in the CL is revealed. The disturbing effect created by the vibrant vapor bubbles promotes the formation of the secondary pores under internal boiling drying mode. The high drying rate combined with vapor bubble rupturing at the top cause the rough surface with cracks. The reduced mass transfer impedance and improved performance in single-cell tests suggest that the internal boiling drying mode is a more desirable option for the CL fabrication compared to conventional surface evaporation drying. The findings provide crucial insights for the design and control of CL drying process.