Hisatoshi Fukumoto

Development of a PEM fuel cell under low humidified conditions

The life performance must be improved in order to commercialize polymer electrolyte (membrane) fuel cells (PEMFCs). A decline of the cell voltage has been found to result from deterioration of the materials and a localization of the reaction in the cell. We investigated the localization phenomenon, measuring the current density in the cell. The distribution of current density was measured by divided and isolated electrodes for a long period of operation. At the beginning of generation of electricity, a high-current region is observed in the lower gas channel which is relatively humid. However, the high-current region gradually moves to the upper dry channel in proportion to the voltage drop, which is noticeable under conditions of low-humidity operation. This reaction seems to be reversible, since the PEMFC can mostly recover the initial performance, once it is restarted. Improving the MEA and gas separators for low humidified conditions on the basis of this internal analysis, we operated a 20-cell PEMFC stack of 0.4 kWe for 5000 h, and the stack showed −1.5 mV/1000 h of average voltage degradation.

Induction of In-plane Current at Start-and-Stop Operations on a PEFC

In-plane induction currents in electrodes and bipolar plates by reactant fed into a PEFC were evaluated using a 20-segmented cell. When hydrogen was fed into anode in the condition of anode (negative electrode) and cathode (positive electrode) exposed air, in-plane currents were detected in both electrodes in spite of the open-circuit condition. In-plane currents of anode and cathode in each segment had each other opposite direction and nearly equal quantity. Simultaneously, carbon dioxide and oxygen were also detected in the cathode exhaust.

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.