Selective Deposition of Metals onto Molecularly Tethered Gold Nanoparticles: The Influence of Silver Deposition on Oxygen Electroreduction

摘要

Multimetallic nanoparticles (NPs) are being explored for their promising electrocatalytic properties that arise from synergistic interactions between multiple metals on the nanoscale. Despite the promising properties of these materials, it is still not fully understood how various attributes of a multimetallic NP electrocatalyst (i.e., composition, structure, and interface to an electrode) contribute to its electrocatalytic activity due to the lack of fabrication methods that allow subnanometer control over these variables. We developed an approach to construct bimetallic nanoparticle-functionalized electrodes in situ through the selective deposition of a second metal onto the surface of gold or silver nanoparticles previously bound to a boron-doped diamond electrode through a molecular interface. We used this approach to investigate the role of bimetallic composition and structure of silver gold nanoparticle (Ag-AuNP) electrocatalysts on the oxygen reduction reaction (ORR) in alkaline media. This method allowed for a series of Ag-AuNP electrocatalysts with varying elemental composition, core size, and/or metallic arrangement to be rapidly generated while preserving the molecular NP/electrode interface and the original NP core morphology. We found that the addition of Ag to the surface of 2 nm AuNPs resulted in a significantly enhanced 4-electron ORR electrocatalytic activity in alkaline media compared to that of other Ag-AuNPs studied, demonstrating the influence of metallic arrangement and NP core size on electrocatalytic activity. These results suggest that the 2 nm AuNP core allows Ag to deposit onto its surface in uniquely catalytically active structures and that the observed ORR activity is not simply a result of electronic interactions between the two elements or the presence of bimetallic sites. The approach described in this work can be used to fabricate other multimetallic nanoparticle-functionalized electrodes, which can facilitate the rapid investigation of the electrocatalytic properties of a variety of compositions while preserving important aspects of the electrocatalyst structure, particularly the nanoparticle core morphology and nanoparticle/electrode interface.