The effect of the piperidinium structure on anion-exchange membranes for applications in alkaline water electrolysis cells

Abstract

To evaluate the effect of the piperidinium structure on the properties of anion-exchange membranes, hydrophilic components containing five different piperidinium head groups were designed and combined with hydrophobic components (hexafluoroisopropylidene biphenylene groups) to obtain a series of target copolymers. The effect of CH₃– and CF₃– substituents was less on the mechanical properties of the copolymer membranes, and more prominent on the hydroxide-ion conductivity and chemical stability in the order of QBP-1 (no substituents) > QBP-2 (with methyl) > QBP-3 (with dimethyl) > QBP-4 (with trifluoromethyl), which was related to the extent of water uptake. QBM-2.7 with ammonium nitrogen at the terminal position of the side chains achieved the highest chemical stability (86% conductivity remaining after a 1000 h stability test in 8 M KOH at 80 °C). A QBM-2.7 membrane was applied to an alkaline water electrolysis cell, which exhibited high current efficiency (76%) and performance (1.62 V at 1.0 A cm⁻²) and was operable for 1000 h with minor changes in the cell performance.