Shaping triple-conducting semiconductor BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3-δ into an electrolyte for low-temperature solid oxide fuel cells

Interest in low-temperature operation of solid oxide fuel cells is growing. Recent advances in perovskite phases have resulted in an efficient H ⁺ /O ^2- /e ^- triple-conducting electrode BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3-δ for low-temperature fuel cells. Here, we further develop BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3-δ for electrolyte applications by taking advantage of its high ionic conduction while suppressing its electronic conduction through constructing a BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3-δ -ZnO p-n heterostructure. With this approach, it has been demonstrated that BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3-δ can be applied in a fuel cell with good electrolyte functionality, achieving attractive ionic conductivity and cell performance. Further investigation confirms the hybrid H ⁺ /O ^2- conducting capability of BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3-δ -ZnO. An energy band alignment mechanism based on a p-n heterojunction is proposed to explain the suppression of electronic conductivity and promotion of ionic conductivity in the heterostructure. Our findings demonstrate that BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3-δ is not only a good electrode but also a highly promising electrolyte. The approach reveals insight for developing advanced low-temperature solid oxide fuel cell electrolytes.