Proton Exchange Membrane Water Electrolysis Incorporating Sulfo-Phenylated Polyphenylene Catalyst Coated Membranes

Abstract

Herein, fully hydrocarbon-based ionomer catalyst coated membranes (CCM)s based on sulfo-phenylated polyphenylene biphenyl (sPPB-H+) are evaluated in a proton exchange membrane water electrolyzer cell at 70 °C. In conjunction with catalyst layers incorporating Nafion® D520 ionomer, sPPB-H+ membranes require a lower applied potential than reference Nafion® NR112 recast membranes of equal thickness, e.g., 1.66 V vs 1.75 V at 1 A cm−2. Initially, sPPB-H+ membranes yield substantially lower gas crossover compared to the CCMs containing NR112 membrane, however, increasing gas crossover and a higher rates of voltage evolution is measured during a stability test at 1 A cm−2. A reinforced and commercialized membrane of similar chemistry (Pemion®) is also evaluated, demonstrating smaller changes to the initial gas crossover owing to higher mechanical stability. Employment of sPPB-H+ as the catalyst layer binder is also investigated, where the highest efficiency for all-sPPB-H+ CCMs is achieved when the anode and cathode ionomer content are 20 wt%, which from electrochemical impedance spectroscopy is predominately attributed to changes in the proton conductivity within the catalyst layer. Despite this advancement, high ionomer swelling and catalyst delamination led to shorter electrolyzer lifetimes for the all hydrocarbon and non fluorinated membrane electrode assembly, informing future ionomer development.