PEMFC impedance spectroscopy using synthetic wide-band signals

The “state of health” of a fuel cell can be determined by the study of its complex impedance in a frequency domain, usually using impedance spectroscopy (IS) method. In our days, to characterize a PEM using this method, a sine signal sweep is used. The IS is based on the complex measurement of the impedance of a cell along a frequency domain, depending on the electrochemical state of the cell. The main advantage of the IS is the faithfulness between its results and the theoretical ones. These results are analyzed using the electrical Randles model. Our work presents an innovative method to measure the IS. It introduces a system to dramatically reduce the measurement time using as an alternative of the sine signal, a frequency domain synthetic wide-band signal. During the tests, a theoretical wide-band signal is built in the frequency domain. The signal is converted into a temporal one and is used as a stimulus for the fuel cell. The response in terms of cell voltage is captured and the impedance measured. This answer is defined in the same frequency range than the stimulus. The time required for the measurement corresponds to the time of the stimulus and it is in the range of the lower cut-off frequency. The system used as test-bench is composed by an electronic circuit and a PC based software for the signal analysis. This system was built and tested with good results using a PEMFC.