Enhanced Performance of Ionomer Binder with Shorter Side-Chains, Higher Dispersibility, and Lower Equivalent Weight

Abstract

Interaction between the ionomer binder and catalyst nanoparticles in catalyst ink is well known to play an important role in the performance of proton exchange membrane fuel cells (PEMFCs) because it determines the final micro-morphology of the catalyst layer. Herein, we investigated the 3M series of perfluorinated sulfonic acid (PFSA) ionomer binders, which have higher polymeric main-chain mobilities, increased solubilities, shorter side-chains, and lower equivalent weights than the Nafion 1100 series of ionomers. The molecular mobility was determined by 19F nuclear magnetic resonance (NMR), and the differences in the structure of the catalyst layer surfaces were identified using field-emission scanning electron microscopy (FE-SEM) and Hg intrusion porosimetry (MIP). The 3M binder with high dispersibility exhibits more developed and connected secondary pore catalyst layer structures and fewer clustered agglomerates; thus, it shows higher performance in a single cell, particularly under conditions of low relative humidity (RH). A comparative study of the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results of the 3M and Nafion series of ionomer binders is also included. These insights help us elucidate the reason for the difference in performance by different ionomers and provide the foundation for improving the fuel cell performance of Nafiontype ionomers.ª 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim