High-efficiency water dissociation via natural polymer bipolar membranes with alginate/polydopamine-coated halloysite nanotubes and phosphotungstic acid

Abstract

Bipolar membranes (BPMs), composed of anion exchange membrane (AEM) and cation exchange membrane (CEM), hold promise for energy and environmental applications due to their ability to dissociate water into H⁺ and OH⁻ under reverse bias. However, their practical voltage requirements often exceed theoretical potentials, necessitating efficiency optimization. This study introduces an innovative BPM design integrating alginate (SA)-based CEM with chitosan AEM, enhanced by polydopamine-coated halloysite nanotubes (DHNTs) loaded with phosphotungstic acid (HPW). The tubular structure of the DHNTs, modified via dopamine polymerization, improved mechanical stability and proton conductivity, while HPW coating (optimized at 10 wt %) facilitated acid-base interactions, reducing proton hopping distances. Comprehensive characterization (SEM, FTIR, XPS, TGA) confirmed successful HPW coating and structural modification. The optimized BPM exhibited enhanced tensile strength than unmodified BPM with proton conductivity of 36.56 mS/cm and low water dissociation overpotential of 1.188 V at 70 mA/cm². Electrodialysis tests revealed reduced interfacial resistance (IR drop) and increased stability over 48 h, attributed to HPW's catalytic role in accelerating ion transport and minimizing energy loss. The synergy between DHNTs and HPW significantly improved hydrophilicity, mechanical robustness, and energy efficiency, demonstrating the potential of this design for sustainable electrochemical systems. These findings provide critical insights into advanced BPM development for scalable energy and environmental technologies.