Alkaline chlorine resilient bipolar membrane for saline water electrolysis

Abstract

Bipolar membranes (BPMs) provide differential pH environments for water electrolysis, enabling the use of acid-compatible HER catalysts and base-compatible OER catalysts. In this study, a chemically and oxidatively stable bipolar membrane (BPM) was prepared by laminating a cation exchange layer (CEL) and an anion exchange layer (AEL), both synthesized through superacid-catalyzed reactions of isatin and N-methyl piperidone with terphenyl, followed by sulfonation and quaternization, respectively. To enhance water dissociation performance, a membrane (T-BPM) with an interfacial layer of TiO₂ nanoparticles was prepared. This T-BPM demonstrated lower activation energy and improved conductivity compared to the pristine BPM, making it a promising candidate for alkaline water splitting. It has excellent alkaline stability observed over 15 days in 5 M KOH with merely 3.0% weight change. Water electrolysis studies using the reported Ru-impregnated amine-functionalized multi-walled carbon nanotubes (Ru@AM-MWCNT) catalyst in water and KOH containing solutions showed excellent performance, achieving a current density of 801 mA cm⁻² at 2.2 V in 0.5 M KOH at 80 °C. This current density surpassed existing literature benchmarks and demonstrated superior alkaline stability compared to neat BPMs. The improvement is attributed to weak hydrogen bonding between TiO₂ and the polymer backbone, which reduces degradation, along with enhanced ion conduction for water splitting. These results highlight the potential of TiO₂ as an interfacial layer in conjunction with ether-free polymers in BPMs for water electrolysis applications.