Analysis of fuel cell impedance characteristics at high current density based on distribution of relaxation times

Vehicle fuel cells tends to operate at high pressure and high power. Performance tests show that increasing temperature and decreasing relative humidity can promote the voltage of fuel cell at high pressure and high load. In order to identify the impedance characteristics and explain the performance loss of fuel cell at high current, this paper designs temperature and humidity sensitivity tests. However, the internal state of the fuel cell is usually unstable at high current, which makes the electrochemical impedance spectroscopy results fluctuate greatly, especially at low frequency. And it cannot be directly analyzed. In this paper, the impedance spectrum is analyzed by the distribution of relaxation times (DRT) method. The diffusion impedance in low frequency range is quantitatively described. By utilizing DRT method, the impedances of fuel cell in different frequency ranges are quantitatively identified, solving the problem that the low-frequency impedance cannot be identified at high current. This technique can be utilized to analyze different polarization losses, and provides a new method for fuel cell fault diagnosis.