Performance and durability studies of perfluorosulfonic acid ionomers as binders in PEMFC catalyst layers using Electrochemical Impedance Spectroscopy

Abstract

Perfluorosulfonic acids (PFSA) are the most widely used ionomers in Polymer electrolyte membrane fuel cells as both membrane and catalyst layer support. This study presents an electrochemical based analysis of using long-side-chain Nafion® and short-side-chain Aquivion® PFSA ionomers as binders in the catalyst-layers of PEMFC. Membrane electrode assemblies were designed with consistent components, varying only the catalyst ink's ionomer type from 28 wt% Aquivion® to 28 wt% Nafion®. The durability and performance profile of the resulting catalyst-coated-membranes made from using these PFSA ionomers as binders in the catalyst layers was investigated. Semi-empirical modeling shows that the Nafion® ionomer based binders give a catalyst-coated-membrane with a 46.6% higher ohmic resistance compared to using Aquivion® ionomers as binders. The power density analysis also showed that catalyst-coated-membranes made with Aquivion® ionomer based binder gives an output power that is 22.33% higher than catalyst-coated-membranes made with Nafion® ionomers as binders in the catalyst layers. The Aquivion® ionomer binder also shows higher catalyst utilization compared to the Nafion® ionomer binders. The Electrochemical Impedance Spectroscopy– Equivalent Circuit Model analysis showed that the membrane electrode assembly degradation is more pronounced in the Nafion® ionomer based binder compared to its Aquivion® counterpart. It is thus shown that Aquivion® ionomers are better catalyst binders compared to the Nafion® ionomers as they result in catalyst-coated-membranes that are better performing and more durable.