Electrochemical parameter estimation in operating proton exchange membrane fuel cells

A novel methodology for the diagnosis of an operating proton exchange membrane fuel cell (PEMFC) is proposed in this manuscript. The cell impedance can be represented as the sum of two terms: the membrane resistance and a second-order transfer function. An experimental procedure and a method to estimate the parameters of this impedance model from the experimental data, by applying parameter identification techniques, are proposed. The experimental procedure consists in reading the dynamic response of the cell voltage and current after the occurrence of small changes in the load value. This experimental procedure, intended for application on operating cells, does not significantly interfere with the cell operation. It has been designed supposing that the frequency range of the relevant cell phenomena is 1 Hz to 5 kHz. The required experimental equipment is inexpensive and easily portable. Analytical relationships have been derived in order to calculate the following cell electrochemical parameters from the model parameters: the diffusion resistance, the charge transfer resistance, the diffusion-related time constant, the membrane resistance and the double layer capacitance.