Process modeling of the ohmic loss in proton exchange membrane fuel cells

The impedance characteristics of the ohmic loss in proton exchange membrane fuel cells are studied analytically, presenting a process model. The governing equations describing the ohmic loss and the water transport in the membrane and the cathode gas diffusion layer are analytically solved and the impedance is determined. Then, an equivalent circuit is presented as a function of the fuel cell properties and operating conditions. Various characteristics and specifications of the determined equivalent circuit are studied. The results obtained from the equivalent circuit are in agreement with the measured fuel cell impedances reported in the literature. It is shown that the membrane ohmic loss is the dominant part of the high frequency resistance, and the membrane and cathode gas diffusion layer water transport impacts the low frequency arc and the inductive loop in the Nyquist plot, respectively. Also, the membrane diffusion coefficient can be extracted from the time constant of the low frequency semi-circle in the Nyquist plot.