The plasma-assisted formation of Ag@Co3O4 core-shell hybrid nanocrystals for oxygen reduction reaction

•Ag@Co3O4 core-shell hybrid nanocrystal was formed via plasma discharge in water.•The electronic structure of Ag@Co3O4 core-shell hybrid nanocrystal was modified.•Ag@Co3O4 core-shell hybrid nanocrystals showed the best ORR activities.•ORR was enhanced due to the combination of electronic and geometric effects.

In this study, Ag@Co3O4 core-shell hybrid nanocrystals are synthesized using a plasma discharge in water for oxygen reduction reaction in alkaline solutions. A detailed analysis via electron microscopy in combination with EDS elemental mapping conclusively verifies that the reactive oxygen species generated from the plasma-assisted decomposition of water molecules govern the phase structure of the nanocrystals. Under oxidizing conditions, the Co oxide, which is more stable than the Ag oxide, provides the driving force for the segregation and preferential oxidation of Co at the surface. This leads to the formation of the core-shell architecture. The electrochemical measurements for the oxygen reduction reaction reveal that the specific activities of the Ag@Co3O4 core-shell nanocrystals are ca. 5.2 and 2.6 times higher than those of the pure Ag and Ag-Co alloy nanocrystals. The enhanced catalytic performance is attributed to the combination of electronic and geometric effects, which facilitates the OO bond breaking and desorption for the oxygen reduction. The insights gain through this study may serve as a foundation to design better electrochemical oxygen reduction electrocatalysts.

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