Promoted electrocatalytic activity and ionic transport simultaneously in dual functional Ba0.5Sr0.5Fe0.8Sb0.2O3-δ-Sm0.2Ce0.8O2-δ heterostructure

• A novel Ba 0.5 Sr 0.5 Fe 0.8 Sb 0.2 O 3-δ -Sm 0.2 Ce 0.8 O 2-δ (BSFSb-SDC) heterostructure is developed for dual electrode and electrolyte functionality. • The BSFSb-SDC heterostructure shows faster charge and mass transfer, and enhanced ion transport through interface of BSFSb and SDC. • The high ionic conductivity at the interface of BSFSb and SDC is assisted with built-in-electric field (BIEF) produced by the differnce in electron density of states in individual structures. • BSFSb-SDC shows excellent electrode and electrolyte functionality, and it exhibts power density of > 1000 mWcm −2 at 550 °C. Structural doping is often used to prepare materials with high oxygen-ion conductivity and electrocatalytic function, but its wider application in solid oxide fuel cells (SOFCs) is still a major challenge. Here, a novel approach to developing materials with fast ionic conduction and high electrocatalytic activity is reported. A semiconductor-ionic heterostructure of perovskite Ba 0.5 Sr 0.5 Fe 0.8 Sb 0.2 O 3-δ (BSFSb) and fluorite structure Sm 0.2 Ce 0.8 O 2-δ (SDC) is developed. The BSFSb-SDC heterostructure exhibits a high ionic conductivity >0.1 S cm −1 (vs 0.01 S cm −1 of SDC) and achieves a remarkable fuel cell performance (>1000 mWcm −2 ) at 550 °C. It was found that the BSFSb-SDC has both electrolyte and electrode (cathode) functions with enhanced ionic transport and electrocatalytic activity simultaneously. When using BSFSb-SDC as an electrolyte, the interface energy-band reconstruction and charge transfer at particle level forming a built-in electric field (BIEF) and it make electronic confinement. The BIEF originates from the potential gradient due to differences in the electron density of BSFSb and SDC particles/grains facilitates ionic conduction at the interface of the BSFSb and SDC particles. This work provides a new insight in designing functional materials with high ionic conductivity and electrocatalytic function, which can be used both for energy conversion and storage device.