Tetrazole functionalization: A new strategy toward stable ion-solvating polymer electrolytes for alkaline water electrolysis

A new class of ion-solvating membranes based on a tetrazole functionalized vinyl copolymer is introduced. The membranes are prepared from poly(styrene-co-acrylonitrile), by converting the acrylonitrile groups to tetrazole pendants in a one-step click-type [3+2] cycloaddition reaction, and the tetrazole content is controlled by adjusting the acrylonitrile content of the starting material. Due to the weak acidity of the tetrazole pendants, nearly complete ionization to the corresponding tetrazolides occurs when the membranes are equilibrated in aqueous KOH. Model system studies and DFT simulations show that this suppresses the electrophilicity of the functional group, which results in a material with remarkable stability with no signs of degradation after nearly 4000 h in 25 wt.% KOH at 80 °C. The electrolyte-imbibed membranes support ion conductivity up to 90 mS cm-1 in 15 wt% KOH at 80 °C, which allows for stable electrolysis operation for 600 h with performance characteristics comparable to that of the conventional Zirfon separator.