Gradient ionomer designed cathode catalyst layer for proton exchange membrane fuel cells with enhanced performance

Abstract

The catalyst layer (CL) plays a critical role in the electrochemical reactions that occur in proton exchange membrane fuel cells (PEMFCs). In this study, we employ ionomers with varying equivalent weight (EW) values to create a gradient cathode catalyst layer (CCL) to enhance mass transport and improve water management capability within PEMFC. The best performance is achieved for the membrane electrode assembly (MEA) with gradient CL when the ratio of short side chain (SSC) ionomer near the proton membrane to long side chain (LSC) ionomer near the gas diffusion layer is 3:1. The cell voltage reaches 0.689 V@2.0 A cm−2 (78 °C, 150 kPa, stoic. H2/Air = 2.2/3.2) representing improvements of 55 mV and 14 mV over the MEA with homogeneous CLs containing only LSC ionomer or only SSC ionomer. The porosity measurement indicates that the gradient CL increased the porosity of the MEA. Electrochemical characterization provides evidence that this gradient ionomer design enhances catalyst utilization and reduces mass transfer losses. Furthermore, the durability assessment of the MEAs reveals less performance degradation in the gradient CCL. Therefore, utilizing ionomers with different EW values to construct a gradient CCL is an effective strategy to achieve high power output and long life of PEMFCs.