Surface modification of mordenite in Nafion composite membrane for direct ethanol fuel cell and its characterizations: Effect of types of silane coupling agent

Abstract

Mordenite (MOR) has been used to solve the alcohol crossover in direct ethanol fuel cells. However, the lack of compatibility has been a problem. This paper shows the compatibility improvement of MOR in a Nafion composite membrane for use in a fuel cell using four types of silane coupling agents: gamma-glycidoxypropyltrimethoxysilane (GMPTS), (3-mercaptopropyl)trimethoxysilane (MPTS), (3-mercaptopropyl)triethoxysilane (MPTES) and (3-mercaptopropyl)methyl-dimethoxysilane (MPDMS). The coupling agents were used to treat the MOR surface before mixing with Nafion. Each type of silane was treated carefully and differently, depending on its structure. Their characterizations were also described. The results showed that better compatibility and a noticeable reduction in ethanol permeability were achieved when using all silane-treated MOR in the composite. It was found that the Nafion/MOR-MPTES membrane had the highest proton conductivity at all temperature ranges from 30 to 70°C. This was due to the fact that the sulfhydryl (SH) functional group in MPTES provided the sulfonic group in its structure after the oxidation in the surface treatment process. These sulfonic groups at the MOR surface facilitated proton transport and improved the selectivity of the membrane.