Investigation of proton conductivity of inorganic–organic hybrid membranes based on boronic acid and tetrazole

Abstract

In this study, proton conducting membranes based on 4-vinyl benzene boronic acid (VBBA) and 5-(methacrylamido) tetrazole (MTet) were synthesized, and their thermal, electrochemical and proton conducting properties were explored. 5-(methacrylamido) tetrazole (MTet) was copolymerized with 4-vinyl benzene boronic acid (VBBA) via conventional free radical copolymerization. The obtained copolymers, P(VBBA-co-MTet), were then doped with phosphoric acid (PA) to produce inorganic–organic hybrid proton conducting membranes. Structural analyses were carried out by Fourier Transform Infrared Spectroscopy (FTIR) and 1H-NMR (Nuclear Magnetic Resonance). The composition of the copolymers was determined by elemental analysis. Thermogravimetric Analysis (TGA) confirmed that the samples were thermally stable up to approximately 170 °C. The surface morphology was characterized by Scanning Electron Microscopy (SEM). Cyclic voltammetry (CV) results demonstrated that the oxidative stability of the samples is 3 V. In the absence of humidity, P(VBBA-co-MTet)-2H3PO4 (S3-2H3PO4) has a maximum proton conductivity of 0.021 Scm−1 at 150 °C. This value was higher than those of previously reported acid doped P(VBBA-co-VIm) and P(VBBA-co-VTri) membranes. Formation of highly conductive, flexible and insoluble free standing films indicates that the matrix has a potential to be used in proton exchange membrane fuel cells (PEMFC).