Use of Poly(styrene-co-acrylic Acid) in a Composite Ion-Solvating Membrane for Water Electrolysis

Ion-solvating membranes (ISMs) have recently emerged as a promising class of materials for alkaline water electrolysis. Their non microporous polymer architecture and the absence of alkaline labile functional groups pave the way for a new generation of hybrid electrolyzers that combine the key features and advantages of conventional alkaline water electrolyzers (AWE) with those of proton exchange membrane water electrolyzers (PEMWE). Herein, a styrene-acrylic acid copolymer was synthesized and deposited onto a commercial microporous polypropylene support, yielding a composite ISM that couples an ion exchange capacity (IEC) of 2.72 mmol g–1 with good mechanical properties (tensile strength of 65 MPa). The electrochemical performance of the membranes was evaluated by through-plane conductivity measurements (24 mS cm–1, with KOH 4 M at 70 °C) and operation in an electrolyzer cell (reaching a cell voltage of 1.89 V at a current density of 1 A cm–2, with KOH 4 M at 70 °C). Polymer stability was assessed by monitoring structural changes via 1H NMR spectroscopy after an aging treatment in KOH 4 M at 70 °C for 720 h. Additionally, long-term electrolysis was investigated through a discontinuous cell test over 150 h. No detectable signs of degradation were observed in either test.