Bifunctional catalysts for alkaline oxygen reduction reaction via promotion of ligand and ensemble effects at Ag/MnO x nanodomains

Daniel A. Slanac, Anthony Lie, Joel A. Paulson, Keith J. Stevenson, Keith P. Johnston

Research output: Contribution to journalArticlepeer-review

71 Citations (Scopus)

Abstract

Achieving synergy between inexpensive metals and metal oxides is a key challenge for the development of highly active, economical catalysts. We report the synthesis and characterization of a highly active oxygen reduction reaction (ORR) catalyst composed of Ag particles (3 nm) in intimate contact with thin (∼1 nm) MnO x domains on Vulcan carbon (VC) as shown via electron microscopy. A new electroless co-deposition scheme, whereby MnO 4 - ions are reduced by carbon, formed nanosized MnO x reduction centers for Ag nanoparticle deposition. A bifunctional mechanism for ORR is proposed, in which the HO 2 - intermediate is formed electrochemically and is regenerated via disproportionation into OH - and O 2. A 3× mass activity enhancement is observed for Ag-MnO x/VC (125 mA/mgAg+MnO x) over the linear combination of pure component activities using rotating disk voltammetry. The Ag-MnO x/VC mass activity is comparable to commercial Pd/VC (111 mA/mg Pd) and Pt/VC (136 mA/mg Pt). Furthermore, the number of electrons transferred for ORR reaches 3.5 for Ag-MnO x, higher than for MnO x (2.8) and close to the full four-electron ORR. The synergy can be rationalized by ensemble effects, where Ag and MnO x domains facilitate the formation and disproportionation of HO 2 -, respectively, and ligand effects from the unique electronic interaction at the Ag-MnO x interface.

Original languageEnglish
Pages (from-to)11032-11039
Number of pages8
JournalJournal of Physical Chemistry C
Volume116
Issue number20
DOIs
Publication statusPublished - 24 May 2012
Externally publishedYes

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