Flowerlike Ag-Supported Ce-Doped Mn3O4 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 (Mn3O4 and Ce-doped Mn3O4 ) by a facile two-step solution method for a highly efficient alkaline ORR Not only does Mn3O4 /Ag exhibit activity comparable to that of commercial Pt/C but also small amounts of Ce3+ (2-5 mol %) doped into Mn3O4 make the ORR activity and stability outperform those of Pt/C. The roles of the adjustment of Ag surface states induced by the supported Mn3O4 and Ce doping in the enhanced ORR performance were studied. The strong electron transfer from Ag substrates to Mn3O4 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% Ce3+ doping further tunes Ag surface electronic structures to improve the ORR performance of Mn3O4 /Ag. Meanwhile, supported Mn3O4 can reduce the adsorption of oxygen-containing species on Ag surfaces by a spillover effect, and the moderately increased oxygen vacancies of Mn3O4 due to 5% Ce doping further increase the active sites on oxide/Ag surfaces and electrochemically active surface areas for the ORR.