Electrochemical properties of the Sm0.5Sr0.5CoO3–La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 (LSGMC5)/LSGMC5 interface modified by an LSGMC5 interlayer synthesized using the citrate method

A La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 (LSGMC5) interlayer synthesized using the citrate method was added between an Sm0.5Sr0.5CoO3 (SSC)–LSGMC5 electrode and an LSGMC5 electrolyte pellet synthesized using a solid-state reaction, and we found that the electrode activity was improved dramatically. The SEM images of the samples demonstrated that the contact between the electrode and the interlayer was much better than the contact between the electrode and electrolyte without the interlayer. The addition of the interlayer resulted in an increased three-phase boundary length and electrode/electrolyte two-phase interfacial area. An SSC–LSGMC5 electrode sintered at 1123 K deposited onto an interlayer sintered at 1673 K exhibited the highest performance among the samples studied. The electrode resistance was about 0.08 Ω cm2 at near equilibrium conditions, and the cathodic overpotential at a current density of 1 A cm−2 was only about 70 mV at 973 K in oxygen. The introduction of the interlayer did not change the oxygen reaction mechanism, and the significant increase in electrode performance was due to the increase in the number of active sites for oxygen reduction.