High-temperature proton exchange membranes from microporous polyacrylamide caged phosphoric acid

Abstract

To enhance the H₃PO₄ loading and therefore proton conductivity, freeze-dried microporous polyacrylamide (PAM) was doped with a highly concentrated H₃PO₄ aqueous solution, leading to high percentages of cages of H₃PO₄ in the PAM membranes for potential use in high-temperature proton exchange membranes (PEMs). A H₃PO₄ fraction of 92.0 wt% and a proton conductivity as high as 0.132 S cm⁻¹ at 183 °C were obtained. The H₃PO₄ loading by microporous PAM membranes obeys a Fickian diffusion process. Protons migrate along the channels from the H₃PO₄ bonded PAM framework or PO⋯H–O hydrogen bonds of H₃PO₄ molecules according to the Grotthuss mechanism. This new concept, in combination with high conductivity, good H₃PO₄ retention and simple-synthesis, opens a new approach to high-temperature PEMs.