Facilitating room-temperature oxygen ion migration via Co–O bond activation in cobaltite films

Oxygen ion migration in strongly correlated oxides can cause dramatic changes in the crystal structure, chemical and magnetoelectric properties, which holds promising for a wide variety of applications in catalysis, energy conversion, and electronics. However, the high strength and stability of metal-oxygen (M-O) bonds cause a large thermodynamic barrier for oxygen migration. Here, we designed Co-O bond activation in cobaltite (SrCoO_x) films by Au-nanodot-decoration. Charge transfer from Au to SrCoO_x effectively weakens the Co-O bond, meanwhile Co-O-Au synergistic bonding remarkably decreases the migration barrier of oxygen ions. Fast oxygen evolution occurs at the perimeter of the Au/SrCoO_x interface, and the chemical potential gradient of O^2- drives inner ion diffusion to the surface. Consequently, bias-free topotactic phase reduction from perovskite SrCoO_3-δ to brownmillerite SrCoO_2.5 has been achieved at room temperature. Our finding explores a new dimension to accelerate oxygen ion kinetics in transition-metal oxides from the aspect of interfacial bond activation, which is significant for developing oxide/noble-metal interfaces for high-efficiency ion migration and redox catalysis at low temperature.