High-Performance Nafion Membrane Modified Using a 1,2,4-Triazole Derivative

Abstract

Proton exchange membrane fuel cells (PEMFCs) are promising power generating devices due to their high energy densities and clean energy emission. Perfluorosulfonic acid (PFSA) based proton exchange membranes, such as Nafion membranes, which have high hydrolytic and oxidative stabilities and excellent proton conductivities are the most commonly used membranes in PEMFCs [1]. Recently, PFSA research has been focused on improving chemical and mechanical stabilities and degradations in the membranes and ionomers. PFSA membranes need to be thinner, lower cost and higher glass transition temperature (T g) materials and have higher conductivities at high temperature under low humidity conditions [2]. We studied Nafion composite membranes using various base additives [3–10]. Base additives were well incorporated into the nanostructure of the sulfonic acid phase in the Nafion polymers. Some base additives showed strong interactions among the hydrophilic terminal sulfonic acid functional groups on the nanoscale, which can be exploited to change the morphology in a nanostructure. From these results, we developed a new method for controlling the conduction path. Modifying the polymer structure of a Nafion membrane by adding a 1,2,4-triazole derivative and then removing it led to higher performance. The ion cluster size of the modified Nafion membrane was larger than that of the original Nafion membrane. The ion exchange capacity (IEC) was the same as that of the Nafion ionomer, but the conductivity was higher due to the modified membrane structure, which has a higher proton mobility. The cell performance of the modified Nafion membrane was better than that of Nafion 212, and in particular, the performance under low relative humidity (RH) conditions was improved. Our simple method using a 1,2,4-triazole derivative as an additive can be applied to the modification of other perfluorosulfonic acid (PFSA) and hydrocarbon polymer electrolytes and will contribute to the improvement of cell performances under high and low RH conditions. Acknowledgements This work was partially supported by the MEXT program for development of environmental technology using nanotechnology.