An insight into the electrocatalytic properties of porous La 0.3 Sr 0.7 Fe 0.7 Cr 0.3 O 3−δ electrodes towards oxygen reduction reaction

The electrocatalytic properties of porous La0.3Sr0.7Fe0.7Cr0.3O3−δ electrodes towards oxygen reduction reaction were investigated as a function of temperature, applied cathodic voltage, and electrode thickness by means of electrochemical impedance spectroscopy technique. The impedance spectra were deconvoluted with the aid of an analysis on the distribution function of relaxation times. The electrode polarization was related to the contribution coming from the elementary steps of surface oxygen exchange process. The electrode reaction was appreciably activated by applying cathodic voltage, attributable to reduction of partial transition metal cations in the electrodes accompanied by creation of oxygen vacancies. The electrocatalytic properties displayed a significant dependence on the electrode thickness, which was explained considering the impact of changing electrode thickness on the kinetics of the reaction steps involved. The lengths of electrocatalytically active region were estimated to be 6–12 μm at temperatures from 700 to 800 °C, while the optimum electrode thickness was ascertained to be around 35 μm at the temperatures. The ~ 35-μm-thick electrode showed a polarization resistance of 0.086 Ω cm2 at 800 °C. The present study demonstrates that oxygen adsorption and disassociation is the key step dictating the kinetics of the overall electrode reaction.