Evaluation of covalently and ionically cross-linked PBI-excess blends for application in SO2 electrolysis

Abstract

Proton exchange membranes (PEM) containing various combinations of PPOBr (pol(2,6-dimethylbromide-1,4-phenylene oxide, covalently cross-linked) or PWN (poly(tetrafluorostyrene-4-phosphonic acid), ionically cross-linked) were evaluated for their suitability in an SO2 electrolyser environment. Since H2SO4 is produced during the oxidation of SO2 in the presence of water, the membranes used in the electrolyser must be both chemically and electrochemically stable. Acid stability tests showed that the blend membranes are stable in 80 wt % acidic media at 80 °C for 120 h. The electrochemical characterisation included polarisation curves, voltage stepping and long term operation. Using polarisation curves two blend combinations were selected for the voltage stepping. Both types of blend membranes showed high stability up to 110 cycles while the F6PBI/PPOBr blend membrane had comparable (to N115®) long term operating voltage, while the F6PBI/PWN blend membrane showed improved voltage, attaining 0.781 V compared to the 0.812 V obtained when using N115 at 0.1 A cm−2