Performance of Sulfonated Phenylated Polyphenylene Membrane As a Polymer Electrolyte Membrane for Water Electrolysis

Abstract

Traditionally perfluorosulfonic acid (PFSA) membranes such as Nafion are used as membranes for polymer electrolyte membrane water electrolysis (PEMWE) due to their excellent chemical stability, good mechanical strength and high ionic conductivity [1], and low hydrogen permeation. The issue of hydrogen crossover, especially at low current densities or high operating pressures is still of concern since it represents product loss and reduced efficiency. Sulfonated phenylated polyphenylene (sPPP) membranes have been found to be promising electrolyte membranes for electrochemical applications. These sPPPs display significantly less gas crossover compared to Nafion. In addition, they also have high proton conductivity, and are resilient to free radical attack [2]. These properties make them particularly attractive for use in water electrolysis. Tantalum carbide supported iridium based catalysts (IrOx/TaC) have been shown to be potential candidates for use as oxygen evolution reaction (OER) catalysts for water electrolysis [3]. In this study, the use of IrOx/TaC catalyst used in conjunction with sulfonated phenylated polyphenylene membranes as alternative materials for PEMWE to achieve improved performance (utilization and reduced gas crossover) and reduce material costs was investigated. The IrOx/TaC was synthesized in-house using a surfactant mediated method. At low loading, the IrOx/TaC has shown performance comparable to state-of-the-art catalysts. Electrolyser membrane electrode assemblies (MEA)s were fabricated using sPPP membranes, IrOx/TaC (anode) and carbon supported platinum (Pt/C) catalyst (cathode). The electrochemical performance of the MEAs was tested in a single cell electrolyser equipped with an in-situ reference electrode. Current-voltage (I-V) curves were obtained potentiostatically at 80 °C. The I-V performance curves obtained were compared with Nafion based MEAs fabricated using the same IrOx/TaC catalyst. The conductivity of the MEAs was also determined. Scanning electron microscopy (SEM) was used to analyze the morphology and elemental distribution of the electrode surfaces and the cross-section of the MEAs.