Correlation between proton conductivity, hydrophilicity, and thermal stability of chitosan/montmorillonite composite membrane modified GPTMS and their performance in direct methanol fuel cell

Abstract

Chitosan based inorganic hybrid membrane is a promising organic–inorganic hybrids for the development of high performance proton exchange membrane (PEM). The immobilization of modified montmorillonite (MMT) using GPTMS within chitosan matrix would possess superior physicochemical characteristics due to more hydrogen bonding formation introduced by GPTMS. Therefore, higher number hydrogen bond formation can be expected in Ch/MMT-GPTMS membrane rather than in pure Ch membrane. A fully hydrated membrane at elevated temperatures is desirable for efficient proton conduction in the membranes. It remains a critical challenge to maintain proper hydration of the membranes for the operation of the direct methanol fuel cell (DMFC). The microstructure obtained by SEM for composites showed that filler was successfully incorporated and relatively well dispersed in the chitosan polymer matrix. The role of surface modification of MMT filler by GPTMS have increase the functional group that can form hydrogen bonding which suitable for interaction with water. High water uptake is favourable for high performance PEM to facilitate great numbers of protons hopping and diffusion through the membrane. In addition, greater hydrogen bonding formation would lead to the tighter packing of composite membrane, resulting in higher bonding strength and higher thermal resistance. The Ch/MMT-GPTMS composite membrane with 5 wt% filler loading exhibited the best proton conductivity are 4.66 mScm-1, with water contact angle value of 64.73°. A maximum power density of 0.24 mWcm-2 was obtained with a 2M methanol feed. The relationship of water contact angle, water upake, membrane swelling, thermal stability, and proton conductivity shown suitable trend, it means that all quality of them are related to the hydrophilicity properties.