Zwitterionic silica copolymer based crosslinked organic–inorganic hybrid polymer electrolyte membranes for fuel cell applications

Abstract

Zwitterionic (ZI) copolymers (consisting of sulfonic acid and amine groups) with plenty of –Si(OCH)₃groups similar to stems, branches and fruits of vines from a bionic aspect, were synthesized as a cross-linking agent. Organic–inorganic hybrid zwitterionic membranes (ZIMs), with high flexibility, charge density and conductivity, was prepared using poly(vinyl alcohol) (PVA). Developed ZIMs with dual acidic and basic functional groups, exhibited high stabilities, water retention ability and cation selectivity. The ZIMs (especially Si–70%) were designed to possess all the required properties (water uptake: 40.6%; ion-exchange capacity: 1.52 equiv. g⁻¹; electro-osmotic flux: (2.34 × 10⁻⁵ cm s⁻¹A⁻¹); and conductivity: 9.67 × 10⁻² S cm⁻¹. ZIMs were designed to possess all of the required properties of a proton-conductive membrane, namely, reasonable swelling, good mechanical, dimensional, and oxidative strength, flexibility, and low methanol permeability along with good proton conductivity due to zwitterionic functionality. Moreover, Si–70% and a Nafion117 membrane exhibited comparable DMFC performance. Also, investigation on a multi-ionic organic–inorganic hybrid ZIM as polymer electrolyte membranes (PEMs) will give rise to a new developing field in materials and membrane science.