A novel inorganic proton exchange membrane based on self-assembled HPW-meso-silica for direct methanolfuel cells

Abstract

Direct methanol fuel cells (DMFCs) based on high-temperature (100–300 °C) proton exchange membranes (HT-PEMs) offer significant advantages over the current low-temperature DMFCs based on perfluorosulfonic acid (e.g., Nafion™), such as reduction in CO poisoning via faster reaction kinetics, thus increasing the energy efficiency and reducing precious metal loading. This paper reports a novel inorganic proton exchange membrane based on 12-tungstophosphoric acid mesoporous silica (HPW-meso-silica) nanocomposites. The HPW-meso-silica was synthesized via a one-step self-assembly route assisted by a triblock copolymer, Pluronic P123, as the structure-directing surfactant. The threshold of the HPW content in the nanocomposites for the conductivity of mesoporous silica is 5 wt%. The best results were obtained at 25 wt% HPW-meso-silica, delivering a high proton conductivity of 0.091 S cm⁻¹ at 100 °C under 100% relative humidity (RH) and 0.034 S cm⁻¹ at 200 °C under 3% RH and a low activation energy of 14.0 kJ mol⁻¹. The maximum power density of a cell with a 25 wt% HPW-meso-silica membrane is 19 mW cm⁻² at 25 °C and increased to 235 mW cm⁻² at 150 °C in methanol fuel.