Mechanistic insights into water transport in polymer electrolyte fuel cells with a variation of cell temperature and relative humidity of inlet gas elucidated by operando synchrotron X-ray radiography

Abstract

Excessive liquid water in the gas diffusion layer (GDL) of polymer electrolyte fuel cells (PEFCs) is known to degrade their performance. PEFCs for automotive applications are required to work over a broad temperature range and over a wide range of relative humidity (RH) levels of the gas in their channels. Time-resolved operando synchrotron X-ray radiography was used to understand the effect of temperature and RH on the condensation and transport of water in PEFCs. The results show that the type of condensation and transport to the channel can be classified into four categories on the basis of the transient behavior of the liquid water distribution. The first category is concurrent liquid and vapor transport, the second is liquid-transport dominated, the third is vapor-only transport, and the fourth is accumulation-only near the ribs. We propose the possibility of oversaturation in the GDL, which is usually not considered in numerical calculations of the water distribution in PEFCs. We also show the possibility that experimental results are inconsistent with continuous water distribution in the in-plane direction, which is predicted under the assumption that the GDL structure is uniform and that capillary pressure transports liquid water in the GDL.