Preparation and Characterization of Hybrid Hydrotalcite-Sulfonated Polyetheretherketone (SPEEK) Cation-Exchange Membranes

Abstract

Direct methanol fuel cells (DMFCs) can be operated using liquid methanol directly as a fuel. However, DMFCs face two major technical hurdles, namely, slow anodic methanol oxidation kinetics and methanol crossover across the polymer electrolyte membrane. Commercial membranes, such as Nafion, are expensive and more than 40% of the methanol is often lost through crossover during fuel-cell operation. Therefore, our study’s long-term goal is to develop a new, cost-effective membrane with superior methanol barrier properties, and reasonable proton conductivity. As part of this effort, we have prepared composite membranes by incorporating hydrotalcite (HT) particles into sulfonated poly(ether ether ketone) (SPEEK). Their properties are strongly dependent on the degree of sulfonation of the polymer matrix, and on the weight fraction of HT particles present in the hybrid membrane. Some of these HT-SPEEK hybrid membranes exhibit good properties, with the addition of the HT filler increasing the proton conductivity, while simultaneously decreasing the methanol permeability. The log(C/P) performance index of some of these membranes (where C/P is the ratio of the proton conductivity of the membrane divided by its methanol permeability) is comparable to that of the commercially available Nafion membranes.