Flowerlike Ag-Supported Ce-Doped Mn₃O₄ Nanosheet Heterostructure for a Highly Efficient Oxygen Reduction Reaction: Roles of Metal Oxides in Ag Surface States

Abstract

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 oxygencontaining 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.

N8− Polynitrogen Stabilized on Nitrogen-Doped Carbon Nanotubes as an Efficient Electrocatalyst for Oxygen Reduction Reaction

“…The ORR polarization curves achieved at different rotating speeds were illustrated in Figure 3a (PN-NCNT) and Figure S1a-d (PN-CNT, NCNT, N 3 − /NCNT, and CNT). As expected, current density increased with the electrode rotating speed increase, which can be attributed to the enhanced diffusion of electrolytes [47,48].…”

Cobalt-doped Mn3O4 nanocrystals embedded in graphene nanosheets as a high-performance bifunctional oxygen electrocatalyst for rechargeable Zn–Air batteries

“…However, the intrinsic ORR and OER activities of Mn 3 O 4 are still unsatisfactory because of its low electrical conductivity and unoptimized electronic structure [16,17]. To solve these issues, considerable efforts, including size modulation [18], the formation of mixed metal oxides [19][20][21], doping with other transition metals [22][23][24][25][26], and hybridization with conductive substrates [17,27,28], have been undertaken to enhance both the OER and ORR activities of pristine Mn 3 O 4 . For instance, Chen and coworkers reported that a mixed-metal oxide, Co x Mn 3-x O 4 , possessed an ORR performance similar to that of the counterpart Pt/C catalyst and proper OER activity, in which the Co/Mn composition and surface valence value were found to affect the extent of oxygen activation [22].…”

Interfacial Engineering of Metal/Metal Oxide Heterojunctions toward Oxygen Reduction and Evolution Reactions

“…Wu et al. further studied metal doping on the ORR activity of Ag/Mn 3 O 4 [45] . They considered Ce, Fe, Co, Ni, and Cu doping of Mn 3 O 4 and found that the doping of Ce into Mn 3 O 4 can elevate the ORR activity of Ag/Mn 3 O 4 higher than Pt/C in 0.1 M KOH (Figure 4d).…”