Phosphomolybdic acid and mixed phosphotungstic/phosphomolybdic acid chitosan membranes as polymer electrolyte for H2/O2fuel cells

Abstract

Flat, free-standing phosphomolybdic acid and mixed phosphotungstic/phosphomolybdic acid chitosan membranes were prepared by in-situ ionotropic gelation process at room temperature on porous alumina support firstly impregnated by heteropolyacid. Scanning electron microscopy revealed the formation of compact and homogenous polymeric membranes, whose thickness resulted to be dependent on reticulation time, and almost independent on the employed heteropolyacid nature and concentration. X-ray diffraction and Fourier transform infrared spectroscopy evidenced the formation of crystalline membranes without appreciable concentration of unprotonated NH2groups and heteropolyacid ions with preserved Keggin structure. The polymeric films were tested as proton conductor in low temperature H2–O2fuel cell. Chitosan/phosphomolybdic acid membranes allowed to get peak power of 60 mW cm−2, while better results were obtained with mixed membranes, reticulated in phosphomolybdic acid and functionalized in phosphotungstic acid, allowing to measure a peak power of 350 mW cm−2with a proton conductivity of ∼7 mS cm−1.