Application of Electrochemical Impedance Spectroscopy for Fuel Cell Characterization: PEFC and Oxygen Reduction Reaction in Alkaline Solution

The most common method used to characterise the electrochemical performance of fuel cells is the recording of current/voltage U(i) curves. Separation of electrochemical and ohmic contributions to the U(i) characteristics requires additional experimental techniques like electrochemical impedance spectroscopy (EIS). The application of EIS is an approach to determine parameters which have proved to be indispensable for the characterisation and development of all types of fuel cell electrodes and electrolyte electrode assemblies [1]. In addition to ElS semi-empirical approaches based on simplified mathematical models can be used to fit experimental U(i) curves [2]. By varying the operating conditions of the fuel cell and by the simulation of the measured EIS with an appropriate equivalent circuit, it is possible to split the cell impedance into electrode impedances and electrolyte resistance. Integration in the current density domain of the individual impedance elements enables the calculation of the individual overpotentials in the fuel cell (PEFC) and the assignment of Voltage loss to the different processes. In case of using a three electrode cell configuration with a reference electrode, one can directly determine the corresponding overvoltage. For the evaluation of the measured impedance spectra the porous electrode model of Gohr [3] was used. This porous electrode model includes different impedance contributions like impedance of the interface porous layer/pore, interface porous layer/electrolyte, interface porous layer/bulk, impedance of he porous layer and impedance of the pores filled by electrolyte.