Development of PEFC Electrode for Stable Running Under High Temperature and Low Humidity Condition

Introduction It is effective to operate proton exchange membrane fuel cells (PEFC) system at the high temperature (more than 85 oC) to utilize exhaust heat of the PEFC in a wide use. However, when PEFC is operated at a high temperature, it is necessary to prepare membrane-electrode assembly (MEA) corresponding to the low humidification condition of operation because there is the problem that relative humidity of the supply gas decreases, electrolyte in MEA dries and cell performance deteriorates. Ionomer in catalyst layer shows good proton conductivity when it is properly hydrated. In order to prepare the high water-holding catalyst layer showing good cell performance under low humidity condition, it is tested that quantity of water contained in the catalyst layer and behavior of the water detachment by estimating the weight change. Perfluorosulfonic acid-based ionomer and carbonsupported platinum catalyst was mixed, and the prepared catalyst layer includes various additive ratio of ionomer to catalyst layer weight and various ion exchange capacity (IEC) ionomer. Then the catalyst layer was maintained for two hours in the constant temperature and humidity bath which was kept 80 oC and 80%RH in order to adsorb water. After that, I measured a weight change by thermogravimetry analysis (TG) when it was heated in 4oC /min and dried and calculated moisture content from quantity of adsorbed water. In addition, the catalyst layer was applied to cathode electrode of a 25 cm sized cell and tested its characteristic. The cell voltage was measured when it was operated at 0.25A/cm consecutively more than three hours under constant humidity condition.