Abstract: Electrochemical impedance spectroscopy (EIS) can be utilized to characterize the internal state and electrochemical behaviour of fuel cell. The different polarization processes and states in the fuel cell can be identified and quantified by constructing an appropriate equivalent circuit model for impedance fitting. The effects of current density, operating temperature, pressure, cathode/anode stoichiometry, and cathode/anode relative humidity on the proton exchange membrane fuel cell's electrochemical impedance are systematically studied. Based on the equivalent circuit method, the variation of each frequency band's equivalent resistance and its sensitivity to operating conditions are analysed and discussed. The results demonstrate that fuel cell loss is dominated by activation loss, ohmic loss, and mass transfer loss at low, medium, and high current densities, respectively. Under the fixed current density, the cell temperature, pressure, cathode stoichiometry, and cathode relative humidity significantly influence the impedance spectrum. Ohmic impedance is mostly sensitive to the humidity change of anode and cathode. The anode activation impedance is mainly liable to the anode stoichiometry and anode relative humidity. The cathode activation impedance is mostly sensitive to the cathode stoichiometry, followed by temperature and pressure. Mass transfer impedance is mainly susceptible to cathode excess coefficient, followed by pressure and temperature. The experimental results provide guidance for the working condition optimization and internal state monitoring and diagnosis of fuel cell.

Key words: proton exchange membrane fuel cell, electrochemical impedance spectroscopy, equivalent circuit model, external operating conditions, sensitivity analysis