Tailoring the activity via cobalt doping of a two-layer Ruddlesden-Popper phase cathode for intermediate temperature solid oxide fuel cells

Co-doped La3Ni2O7 single phase mix-conductors are successfully fabricated and investigated as cathodes for solid oxide fuel cells. Electrochemical measurement suggests that the polarization resistance of the cell using such cathodes reduce largely when increasing the Co content in La3Ni2O7 cathodes, which is about 1.12 Ω cm2 for La3Ni1.9Co0.1O7 and 0.35 Ω cm2 for La3Ni1.6Co0.4O7 both measured at 650 °C. X-ray photoelectron spectroscopy analysis suggests that the Co-doped La3Ni2O7 samples keep much more oxygen vacancies at high temperatures when compared with those undoped samples, which can benefit both oxygen adsorption and oxygen ion diffusion process in the oxygen reduction reaction. Moreover, both conductivity and magnetic measurements indicate that the covalence of B-O bonds in Co-doped samples can be largely improved because of the more localized 3d electrons in the Co substituted samples, which can further help to accelerate the proton diffusion process. The findings in this research demonstrate that the Co-doped La3Ni2O7 with the two-layer structure can be a promising cathode for proton conducting SOFCs, due to its high activity toward the oxygen reduction reaction.