Preparations of an inorganic-framework proton exchange nanochannel membrane

Abstract

In this work, a proton exchange membrane composed of straight and aligned proton conducting nanochannels is developed. Preparation of the membrane involves the surface sol-gel method assisted with a through-hole anodic aluminum oxide (AAO) template to form the framework of the PEM nanochannels. A monomolecular layer (SO3H(CH2)3Si(OCH3)3) is subsequently added onto the inner surfaces of the nanochannels to shape a proton-conducting pathway. Straight nanochannels exhibit long range order morphology, contributing to a substantial improvement in the proton mobility and subsequently proton conductivity. In addition, the nanochannel size can be altered by changing the surface sol-gel condition, allowing control of the active species/charge carrier selectivity via pore size exclusion. The proton conductivity of the nanochannel membrane is reported as high as 11.3 mS cm−1 at 70 °C with a low activation energy of 0.21 eV (20.4 kJ mol−1). First-principle calculations reveal that the activation energy for proton transfer is impressively low (0.06 eV and 0.07 eV) with the assistance of water molecules.