Spatially Resolved Impedance Spectroscopy on Direct Methanol Fuel Cells Considering Fuel Concentration Oscillations in Gas Channels

Abstract

Impedance spectroscopy is usually carried out by exiting the whole fuel cell or even the whole fuel cell stack. The alternating excitation current or voltage, which is imposed on the cell leads to alternating fuel consumption of the cell. This alternating consumption accumulates in the fuel channels and can lead to significant fuel concentration oscillations in the gas channels of the flow fields. This results in significant chemical excitation of the parts of the fuel cell which are further away from the fuel inlet. Due to the accumulation of this chemical excitation along the gas channel, the measured impedance of these parts of the fuel cell does not characterize the local state of the MEA. This has been reported and experimentally verified in the literature. Since the local state is of interest for the investigation of spatially resolved phenomena, a new measurement technique has been developed.