Reaction model for cathodes cooperated with oxygen-ion conductors for solid oxide fuel cells using proton-conducting electrolytes

Abstract For solid oxide fuel cells with proton-conducting electrolytes, oxygen is reduced as well as water is formed at the so-called H-TPB where proton, oxygen and electron are available. Proton conductor cooperation to the cathode can thus increase the H-TPB length while oxygen-ion conductor could not. However, previous reports show that oxygen-ion conductor can also significantly increase the cathode performance, suggesting different cathodic mechanism, which is proposed in this work. Oxygen is reduced at O-TPB where oxygen-ion, oxygen and electron meet while H 2 O is formed at the electrode–electrolyte interface. Experimental investigation reveals that the cathodic reactions are primarily limited by the diffusion of O ad − at O-TPB and oxygen-ion transport within the electrode whereas water formation at the interface is not a limiting step. It is further exhibited that Sm 0.5 Sr 0.5 CoO 3− δ electrocatalyst cooperated with SDC (Ce 0.8 Sm 0.2 O 2− δ ), an oxygen-ion conductor, show even higher cathodic performance than that with BCS (BaCe 0.8 Sm 0.2 O 3− δ ), a proton conductor, when BCS is used as the electrolyte.