The interfaces of Ag-rich and Cu-rich AgCu phases boost oxygen reduction activity

In this study, we demonstrated that the interface between Ag-rich and Cu-rich AgCu phases enhances the oxygen reduction activity of the model alloys. Ag-rich and Cu-rich AgCu alloys (86.8 and 4.5 at. % of Ag, respectively) displayed the homogeneous microstructure representing solid solutions while the AgCu with eutectic composition (59.7 at. % of Ag) showed a typical lamellar structure of Ag-rich and Cu-rich AgCu phases. The eutectic AgCu alloy exhibited better oxygen reaction activity than Ag-rich AgCu alloy despite less phase fraction of Ag-rich AgCu phase. After the activation process, the presence of a CuO layer at the interface of the Ag-rich and Cu-rich AgCu phases was discovered by atom probe tomography analysis. Density functional theory calculations further revealed that the preferential adsorption of OH near the interface between CuO and Ag-rich AgCu lowers the binding strength of OH in the Ag-rich AgCu phase. As a result, the oxygen reduction activity was enhanced by facilitating the most sluggish OH desorption step. These findings provide new insights into the role of phase boundaries in catalytic activity and guidelines for the design of novel electrocatalysts.