Investigating the electrochemical performance of Nd_1-xSr_xCo_0.8Fe_0.2O_3−δ (0 ≤ x ≤ 0.85) as cathodes for intermediate temperature solid oxide fuel cells

Perovskite-type structure oxides with the nominal chemical composition Nd_1-xSr_xCo_0.8Fe_0.2O_3−δ (0 ≤ x ≤ 0.85) (NSCF) were synthesized by solid-state method to investigate the effect of Sr-doping on the crystal structure and electrochemical performance in the intermediate temperature range of 600 °C–750 °C. The electrical conductivity of the sintered NSCF pellets was found to be in the range of 300–1000 S cm⁻¹. All the NSCF compositions showed a transition from semiconducting to metallic behavior with an increase in temperature. NSCF showed reactivity with the La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. The electrochemical performance was tested by preparing the symmetrical cells with the configuration 70 wt% NSCF +30 wt% LSGM using LSGM electrolyte in the temperature range of 650–800 °C. AC-impedance results showed a decrease in polarization resistance (Rp) of the cathode with increase in Sr-doping due to increase in electrical conductivity. Among the samples studied, composite electrode of Nd_0.3Sr_0.7Co_0.8Fe_0.2O_3−δ – LSGM showed the lowest area specific resistance (ASR) of 0.1 Ω cm² at 750 °C in air. It was chosen to investigate the effect of pO₂ on the electrochemical performance of the cathode to determine the rate determining step (RDS) in oxygen reduction reaction (ORR). Dissociation of molecular oxygen into oxygen atoms seems to be the RDS in the ORR.