Electrochemical impedance spectroscopy analysis of Pr_0.8 Sr _0.2 Co_0.5 Fe_0.5 O_3-δ as cathode material for intermediate temperature solid oxide fuel cells

The electrochemical properties of Pr_0.8 Sr_0.2 Co _0.5 Fe_0.5 O_3-δ used as cathode material for solid oxide fuel cells were investigated. Powder samples were prepared using the combustion synthesis technique. Pr_0.8 Sr_0.2 Co _0.5 Fe_0.5 O_3-δ crystallized in the orthorhombic space group Pnma (no. 62) with a=5.447 (4) Å, b=5.425 (1) Å, and c=7.680 (3) Å. The final reliable factors of the Rietveld refinement were Rwp =3.75%, R_p =2.95%, and R_exp =3.15%. Electrochemical impedance spectroscopy (EIS) measurements were used to characterize the overpotential of the Pr_0.8 Sr_0.2 Co _0.5 Fe_0.5 O_3-δ electrodes on the Ce _0.8 Sm_0.2 O_2-δ electrolyte as a function of temperature and applied dc voltages. The EIS data showed the presence of two relaxation processes at different frequencies. The resistance associated with the high frequency process was almost independent from the applied bias, whereas the resistance associated with the low frequency semicircle sharply decreased with increasing temperature and applied dc voltage. These findings suggested that the temperature-voltage-activated process could be attributed to the oxygen reduction reaction at the electrode surface, whereas the high frequency process was associated with the electrochemical charge-transfer reactions across the electrode-electrolyte interface. This demonstrated that the cathode performance can be improved by optimizing its microstructure, especially by extending the electrochemically active three-phase boundary length.