The influence of current constriction on the impedance of polarizable electrodes - Application to fuel cell electrodes

The restriction of the de current to small electrolyte surface areas (e.g., three-phase boundaries) leads to a considerable current constriction close to these current carrying surface regions. The influence of the corresponding inhomogeneous potential distributions on the ac impedance is discussed using finite element calculations. It is demonstrated that current constriction resistances, although determined by the electrolyte properties, can contribute to the low-frequency part of the impedance spectra, which is usually attributed to the electrode polarization. An equivalent circuit is suggested to analyze, deconvolute, and interpret the resulting spectra. As a special example, gas electrodes for fuel cells are considered.