AC-IMPEDANCE STUDY OF THE OXYGEN REDUCTION-MECHANISM ON LA1-XSRXMNO3 IN SOLID OXIDE FUEL-CELLS

The kinetics of the oxygen reduction reaction at the La0.85Sr0.15MnO3/ ZrO2-Y2O3 electrode has been studied by ac impedance spectroscopy. The results show that there are three time constants present in the syste m, each one corresponding to a rate limiting step of the total reactio n mechanism. The time constant at high frequencies has been attributed to the charge transfer of oxide ions from the interface electrode/ele ctrolyte to oxide ion vacancies in the electrolyte. The two other time constants, at medium frequencies and low frequencies, have been attri buted to O-2(2-) dissociation and diffusion steps, respectively.