Localized Impedance Measurements along a Single Channel of a Solid Polymer Fuel Cell

A method is presented, for the first time, for measuring the localized electrochemical impedance spectroscopy response over a frequency range of 0.1 Hz to 10 kHz as a function of position in a solid polymer fuel cell. The highly idealized fuel cell on which the measurements were performed is composed of a single linear flow channel. Measurements have been made at both 0.8 and 0.6 V. A distribution of impedance characteristics is seen along the channel with evidence of mass transport effects that are not evident from localized dc measurements. The membrane conductivity does not vary with position at both potentials, as is expected from the fact that reactant gases are fully humidified. A time constant characteristic of convective transport within the flow channel dominates the low frequency response at low potentials. This response is caused by consumption of reactant upstream of the point at which the measurement is made.