Water electrolysis using fluorine-free, reinforced sulfo-phenylated polyphenylene membranes

Abstract

Fluorinated proton-exchange membranes (PEMs), such as Nafion™, which is the current state-of-the-art polymer, present environmental challenges, driving the need for more sustainable alternatives for proton-exchange membrane water electrolysis (PEMWE) systems. However, fluorine-free membranes like sulfo-phenylated polyphenylene biphenyl (sPPB-50) often suffer from mechanical instability, excessive swelling, and limited cell durability, which hinder their practical applications. This study explores reinforced fluorine-free sulfo-phenylated polyphenylene membranes (Pemion™) with thicknesses of 15 µm (Pemion-15) and 40 µm (Pemion-40) as a potential solution to these issues. Pemion membranes were compared with both sPPB-50 and Nafion™ 112 (N112), focusing on key properties such as water uptake, dimensional swelling, proton conductivity, and durability in PEMWE applications. The results show that Pemion-reinforced membranes exhibit good performance for PEMWE allowing high current densities at lower voltages. Pemion-40 exhibited a low hydrogen gas crossover compared to sPPB-50 and N112. Under a constant current of 1 A cm−2, Pemion-40 exhibited a voltage loss rate of 1.46 mV h−1 over 100 h of operation. This study highlights the importance of structural reinforcement in enhancing the stability and efficiency of fluorine-free membranes, providing a promising route for sustainable alternatives in PEMWE systems.