Activity Trends of Binary Silver Alloy Nanocatalysts for Oxygen Reduction Reaction in Alkaline Media

The electrocatalytic activity of Pt-based alloys exhibits a strong dependence on their electronic structures, but a relationship between electronic structure and oxygen reduction reaction (ORR) activity in Ag-based alloys is still not clear. Here, a vapor deposition based approach is reported for the preparation of Ag₇₅ M₂₅ (M = Cu, Co, Fe, and In) and Ag_x Cu_100-x (x = 0, 25, 45, 50, 55, 75, 90, and 100) nanocatalysts and their electronic structures are determined by valence band spectra. The relationship of the d-band center and ORR activity exhibits volcano-shape behaviors, where the maximum catalytic activity is obtained for Ag₇₅ Cu₂₅ alloys. The ORR enhancement of Ag₇₅ Cu₂₅ alloys originates from the 0.12 eV upshift in d-band center relative to pure Ag, which is different from the downshift in the d-band center in Pt-based alloys. The activity trend for these Ag₇₅ M₂₅ alloys is in the order of Ag₇₅ Cu₂₅ > Ag₇₅ Fe₂₅ > Ag₇₅ Co₂₅ . These results provide an insight to understand the activity and stability enhancement of Ag₇₅ Cu₂₅ and Ag₅₀ Cu₅₀ catalysts by alloying.