New insights into understanding the effect of water content on proton exchange membrane fuel cell output power

Abstract

Water content plays a crucial role in achieving high output power for proton exchange membrane fuel cells (PEMFCs) because it governs the conduction of H⁺ ions, as established in existing literature. However, the distribution of ionomer within the catalyst layer significantly impacts PEMFC performance, and this distribution is closely related to water content. Consequently, water content may influence PEMFC performance by altering ionomer distribution. Experimental results indicate that water content has a substantial effect on the charge transfer resistance (Rct); when the relative humidity (RH) increases from 30 % to 80 %, Rct decreases by 26.5 % at a current density of 100 mA·cm⁻². The change in the structure of the catalyst layer induced by water content is the primary reason for the observed reduction in Rct. As the pores in the catalyst layer become increasingly filled with water, more sulfonic acid groups (SO3⁻) are hydrated, forming a network that facilitates H⁺ conduction. This enhances the accessibility of H⁺ ions within the catalyst layer, thereby decreasing Rct. However, excessive water content can lead to water flooding of the catalyst, which reduces the coverage of the ionomer on the platinum (Pt) surface. When H⁺ ions cannot reach the areas of the catalyst that are not covered by the ionomer, those regions of Pt cannot form effective active sites, ultimately reducing the catalyst’s utilization rate. This study provides a new perspective on the impact of water content on PEMFC performance.