Development of a PEFC with serpentine hybrid pattern gas channels (5th report, electrochemical impedance spectroscopy analysis of the internal resistances)

The development of a polymer electrolyte fuel cell (PEFC) without external humidification is one of the most important issues to increase total efficiency and reduce cost. We have so far developed hybrid pattern gas flow channels consisting of interdigitated and serpentine gas flow channels for PEFCs without external humidification. The PEFC performance was improved when using the serpentine hybrid flow channels compared with the conventional flow channels. For further study, we have analyzed resistances of the cells with electrochemical impedance spectroscopy in the present study. The proton transfer resistance through the ionomer at the catalyst layer is dominant and its value for the hybrid flow channel is less than half that for the serpentine flow channel. The smaller resistance is possibly ascribed to the interdigitated design that can uniformly distributed reactant gas to each flow channel. The oxygen partial pressure is thereby relatively uniform at the active area. Thus, the interdigitated design can provide uniform current and water distribution. In addition, the hybrid flow channel has a low-pressure serpentine flow channel that helps the catalyst layer to hydrate. Un-reacted gas that contains modest water vapor flows through the channel and supplies water to the catalyst layer.