Electrochemical behavior of mixed conducting oxide cathode on oxygen excess-type solid electrolyte

Electrochemical oxygen reduction behavior for a half cell composed of a mixed ionic and electronic conducting (MIEC) oxide and an oxygen excess-type solid electrolyte was investigated. A perovskite-type MIEC oxide, (La0.6Sr0.4)(Co1−yFey)O3−δ (LSCF), was employed as a base material for an electrode catalyst of oxygen reduction reaction. As an electrolyte, Al-doped lanthanum silicate [La10(Si5.8Al0.2)O26.9 (ALSO)] was used, which is a new class of oxide ion conductors with apatite-type structure. The evaluated polarization resistance, Rpol, for the reaction largely depended on y, and the minimum resistance was obtained for y = 0.2. The Rpol value was 0.3 Ω cm2 at 1073 K in ambient air [P(O2) = 2.1 × 104 Pa] for y = 0.2. To improve the performance, introduction of silver nano-particles onto the LSCF particles was studied. With the Ag-modification, Rpol at 1073 K could be minimized toward 0.08 Ω cm2. The cathodic overpotential of the electrode evaluated from DC polarization at 1073 K was 18 mV at 0.1 A cm−2.

► (La0.6Sr0.4)(Co0.8Fe0.2)O3 was good cathode for lanthanum silicate electrolytes.
► By Introducing Ag nanoparticles to LSCF, electrode property was largely improved.
► Ag-modified LSCF showed quite small activation energy for polarization resistance.