Electrochemical investigation of oxygen reduction reaction on La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes deposited by Electrostatic Spray Deposition

The oxygen reduction reaction of La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) cathodes deposited by Electrostatic Spray Deposition (ESD) onto dense Ce0.9Gd0.1O2-delta(CGO) electrolytes was characterized by means of impedance spectroscopy measurements. Three cathodes with distinct morphologies and surface areas were prepared. Impedance measurements were performed at temperatures between 450 and 600 degrees C. at 50 degrees C steps. At each temperature, impedance measurements were performed at five different oxygen partial pressures (p(o2)), between similar to 10(-4) and 1 atm. This approach permitted a systematic evaluation of the influence of microstructure, temperature and p(o2) on the electrochemical behavior of the cathodes. Up to three contributions were identified in the high (HF), medium (MF) and low frequency (LF) ranges. The LF response displays the strongest dependence on oxygen partial pressure with corresponding resistance and capacitance values increasing with decreasing po(2). Contrarily, the resistance associated with the HF response remained practically constant with changing p(o2), while a slight dependence was found for the MF response. The analysis provides support to the assignment of the HF, MF and LF contributions respectively to the ionic transfer at the cathode/electrolyte interface, bulk diffusion of oxygen species and oxygen surface exchange at p(o2) > 10(-2) atm. At lower p(o2),an increasing contribution of oxygen gas-phase diffusion with temperature, evidenced by the LF response, was suggested. (C) 2011 Elsevier B.V. All rights reserved.