Study on the enhancement of the interfacial properties between membrane and electrode for direct methanol fuel cell

Abstract

Direct methanol fuel cells (DMFC) are expected to achieve a high power density due to a high volumetric energy density of methanol as a fuel. However, the performance of DMFC is restricted by the following problems. The major pressing problems associated with the DMFC are the slow anode reaction such as the oxidation of methanol, fuel crossover through the membrane from anode to cathode, and short life time due to interfacial instability between the Pt catalyst layer and the polymer electrolyte membrane. Some binary or tertiary Pt alloy catalysts and alternative membranes have been investigated as a solution of slow anode reaction, and methanol crossover. Still, the problem of life time in DMFC has not been significantly improved. The short life time of DMFC may be mainly caused by the increased interfacial resistance due to the delamination formed at the interface between polymer electrolyte membrane and Pt catalyst layers. This problem of short life time is necessary to be solved for the commercialization of DMFC. Therefore, it is quite important to control the interface between membrane and electrode for the long-term operation of DMFC. In this study, the ideas for the improvement of interfacial properties between membrane and electrode were proposed and its effects were carefully discussed. In order to enhance the interfacial properties of membrane electrode assembly (MEA), new processing of MEA was attempted. Heat treatment of MEA at 130℃ could produce higher proton conductivity of Nafion binder due to the ionic cluster formation and less dissolution in 2M methanol solution due to the increase of crystallinity of Nafion binder. Thus, it was found that the heat treatment of MEA could improve the stability at the interface of the membrane/electrode and catalyst/binder, leading to the higher performance and long-term stability of the MEA. In this study, the decay rate of annealed MEA is about 4.8 $\mu Whr^{-1}$, therefore, 3,000 hrs operation of DMFC is exp...