Promoted electrocatalytic activity and ionic transport simultaneously in dual functional Ba_0.5Sr_0.5Fe_0.8Sb_0.2O_3-δ-Sm_0.2Ce_0.8O_2-δ heterostructure

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_0.5Sr_0.5Fe_0.8Sb_0.2O_3-δ (BSFSb) and fluorite structure Sm_0.2Ce_0.8O_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.