Preparation and electrochemical stability of Co-doped La_1.5Sr_0.5Ni_1−xCo_xO_4+δ cathode materials

A series of Co-doped La_1.5Sr_0.5Ni_1−xCo_xO_4+δ cathode materials ( x =0, 0.2, 0.4 and 0.6) were synthesized by sol-gel method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), coefficient of thermal expansion (CTE) measurement and scanning electron microscope (SEM). The results suggest that all La_1.5Sr_0.5Ni_1−xCo_xO_4+δ samples have a single pure phase with the perovskite-like structure and the doping with the Co element can increase the CTE value. Using La_1.5Sr_0.5Ni_1−xCo_xO_4+δ as the cathode materials in the solid oxide fuel cell (SOFC), their electrical conductivity and electrochemical impedance spectroscopy were measured. The results indicate that the conductivity increases with the increase of Co doping amount and the La_1.5Sr_0.5N_i0.6Co_0.4O_4+δ sample with x = 0.4 displays the highest conductivity of 51.21 S/cm at 800 ℃; however, a higher content of Co (x > 0.4) leads to a decrease of the conductivity. In addition, La_1.5Sr_0.5N_0.6Co_0.4O_4+δ exhibits the lowest polarization resistance of 4.180 Ω·cm² in electrochemical impedance spectrum at 700 ℃, displaying its excellent electrochemical properties as the cathode materials.