Flowerlike Ag-Supported Ce-Doped Mn 3 O 4 Nanosheet Heterostructure for a Highly Efficient Oxygen Reduction Reaction: Roles of Metal Oxides in Ag Surface States

Tuning Ag surface states by metal oxides is a feasible method to enhance the oxygen reduction reaction (ORR) performance of Ag-based catalysts. Herein, we develop a heterostructural electrocatalyst of flowerlike Ag-supported nanosheets of metal oxides (Mn 3 O 4 and Ce-doped Mn 3 O 4 ) by a facile two-step solution method for a highly efficient alkaline ORR. Not only does Mn 3 O 4 /Ag exhibit activity comparable to that of commercial Pt/C but also small amounts of Ce 3+ (2–5 mol %) doped into Mn 3 O 4 make the ORR activity and stability outperform those of Pt/C. The roles of the adjustment of Ag surface states induced by the supported Mn 3 O 4 and Ce doping in the enhanced ORR performance were studied. The strong electron transfer from Ag substrates to Mn 3 O 4 makes the d center of Ag shift up, accelerating the kinetics of O–O bond splitting on Ag surfaces (increasing the activity of active sites for O–O bond dissociation). Additionally, 5% Ce 3+ doping further tunes Ag surface electronic structures to improve the ORR performance of Mn 3 O 4 /Ag. Meanwhile, supported Mn 3 O 4 can reduce the adsorption of oxygen-containing species on Ag surfaces by a spillover effect, and the moderately increased oxygen vacancies of Mn 3 O 4 due to 5% Ce doping further increase the active sites on oxide/Ag surfaces and electrochemically active surface areas for the ORR.