Highly Proton Conductive Zn(II)-Based Metal-Organic Framework/Nafion® Composite Membrane for Fuel Cell Application

Abstract

Employing the concept of coordination networks, the conductivity of Nafion® was amplified by fabricating a composite based on Nafion® and an inexpensive and highly proton-conductive three-dimensional metal-organic framework (MOF), namely, {[(Me2NH2)3(SO4)]2[Zn2(ox)3]}n (1, Me = methyl, ox = oxalate). The proton conductivity increased by more than 18% for the MOF 1/Nafion® composite membrane, e in comparison to pristine cast Nafion® membrane. Such improvement in conductivity can be attributed to the interionic proton hopping through the extended hydrogen bonding networks, higher concentration of proton carriers, 3D hydrogen pathways (including nanopores on the surface of the MOF 1 crystals) and higher degree of crystallinity. Along with slightly higher thermal stability, increased ion exchange capacity (IEC) and optimum water uptake were observed, with the addition of 1 wt.% of MOF 1 to Nafion® appearing to be maximally efficient. This study offers a cost-effective and facile fabrication technique for a variety of proton exchange membranes with characteristic proton-conducting properties for fuel cell applications.