Proton-Selective Ion Transport in ZSM-5 Zeolite Membrane

The ionic ZSM-5 zeolite membranes were investigated for proton-selective ion separation in electrolyte solutions relevant to redox flow batteries. The zeolite membrane achieved exceptional selectivity for proton over V 4+ (VO 2+ ), Cr 2+, and Fe 2+ via size-exclusion at the zeolitic channel openings, and remarkably low area specific resistance resulted from its hydrophilic surface, copious extraframework protons, and micron-scale thickness. The ZSM-5 membrane, as a new type of ion separator, demonstrated substantially reduced self-discharge rates and enhanced efficiencies for the all-vanadium and iron–chromium flow batteries as compared to the benchmark Nafion membrane. Findings of this research show that ionic microporous zeolite membranes can potentially overcome the challenge of trade-off between ion selectivity and conductivity associated with conventional polymeric ion separators.