Morphological transformation of perfluorinated sulfonic acid ionomer via ionic complex formation at a high entropy state

Abstract

Proton exchange membranes (PEMs) act as conductors in PEM fuel cells (PEMFCs) to transport protons from the anode to the cathode in the membrane electrode assembly (MEA). Because protons are transported via the hydrophilic channels of the PEMs, the morphological control of these channels has been considered a key issue that influences their electrochemical performance. In this study, we propose a simple route that provides fast proton transport pathways via the morphological transformation of hydrophilic channels in a commercially available perfluorinated sulfonic acid (PFSA) ionomer, Nafion®. It is based on the formation of ionic complexes when metallic salts are added during the membrane fabrication process, instead of using PFSA ionomers with tuned chemical structures. The effectiveness of this strategy is theoretically verified by performing molecular simulations for the ionic cluster formation mechanism. The formation of the ionic complexes in a high entropy state is found to be advantageous in decreasing the distance between ionic clusters, improving proton transport efficiency resulting in higher proton conductivity and single cell performance without any additional chemical and processing step causing the production cost increase.