Freezing characteristics of supercooled water in the membrane electrode assembly of polymer electrolyte fuel cells

This study investigated the freezing characteristics of supercooled water in the membrane electrode assembly (MEA) to clarify low-temperature startup issues of polymer electrolyte fuel cells (PEFCs). Gas diffusion layers (GDLs) with different polytetrafluoroethylene (PTFE) contents, microporous layers (MPL), and polymer electrolyte membranes (PEM) with catalyst layers (CL) were employed. To reproduce practical PEFC conditions, a device capable of applying assembly pressure was developed, and temperature changes during freezing of supercooled water inside the MEA were measured. The effects of assembly pressure and PTFE content in the GDL on freezing behavior were examined. To identify the MEA region most susceptible to freezing initiation, the freezing probabilities of the entire MEA and GDL + MPL were evaluated, and that of PEM + CL was statistically deduced. The results show that freezing probability increases with assembly pressure, whereas higher PTFE content leads to greater supercooling at freezing onset. Comparison among the MEA components revealed that PEM + CL freezes more readily than GDL + MPL, demonstrating that the catalyst-layer region has the highest ice-nucleating activity within the MEA.