Use of Poly(styrene- <i>co</i> -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.