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

[Display omitted] •A novel Ba0.5Sr0.5Fe0.8Sb0.2O3-δ-Sm0.2Ce0.8O2-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 Ba0.5Sr0.5Fe0.8Sb0.2O3-δ (BSFSb) and fluorite structure Sm0.2Ce0.8O2-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.