Electrochemical investigation of oxygen reduction reaction on La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) cathodes deposited by Electrostatic Spray Deposition

摘要

The oxygen reduction reaction of La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ)(LSCF) cathodes deposited by Electrostatic Spray Deposition (ESD) onto dense Ce_(0.9)Gd_(V)O_(2-δ) (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 ℃, at 50 ℃ steps. At each temperature, impedance measurements were performed at five different oxygen partial pressures (po_2), between ～10~(-4) and 1 atm. This approach permitted a systematic evaluation of the influence of microstructure, temperature and po_2 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 po_2, 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 po_2 > 10~(-2) atm. At lower po_2, an increasing contribution of oxygen gas-phase diffusion with temperature, evidenced by the IF response, was suggested.