Covalently crosslinking of sulfonated poly (4,4′-diphenylether-5,5′-bibenzimidazole) with triazine frameworks for using as the diaphragm in amphoteric water electrolytic cells

Abstract

It is an attractive way to produce hydrogen for energy storage via water electrolysis by using unstable energy sources changing with time and geographical location. However, water electrolysis still suffers some problems from such as low operating current density. We herein propose a novel bipolar membrane crosslinked with bipyridine covalent triazine frameworks (bipCTF) based on sulfonated poly (4,4′-diphenylether-5,5′-bibenzimidazole) (SOPBI). The prepared bipCTF-SOPBI membranes exhibit the highest ionic conductivity of 143 mS cm−1 to protons, and of 48.0 mS cm−1 to hydroxide ions at 80 °C after doping with H2SO4/NaOH, respectively. Using the proposed membrane as the diaphragm for the acid-alkaline amphoteric water electrolysis, a current density of 1.29 A cm−2 is achieved at a voltage of 2.5 V at 80 °C. The electrolytic cell system could work stably at a current density of 100 mA cm−2 at 20 °C for 90 h.