Efficient CO Oxidation Using Dendrimer-Encapsulated Pt Nanoparticles Activated with <2% Cu Surface Atoms

Abstract

In this paper, we show that the onset potential for CO oxidation electrocatalyzed by ∼2 nm dendrimer-encapsulated Pt nanoparticles (Pt DENs) is shifted negative by ∼300 mV in the presence of a small percentage (<2%) of Cu surface atoms. Theory and experiments suggest that the catalytic enhancement arises from a cocatalytic Langmuir-Hinshelwood mechanism in which the small number of Cu atoms selectively adsorb OH, thereby facilitating reaction with CO adsorbed to the dominant Pt surface. Theory suggests that these Cu atoms are present primarily on the (100) facets of the Pt DENs.

Dendrimer-encapsulated nanoparticle-core micelles as a modular strategy for particle-in-a-box-in-a-box nanostructures

“…Dendrimers are hyperbranched molecules and are archetypical soft nanoparticles in the 1-10 nanometer range with the potential to encapsulate molecules, 5 or nanoparticles. [6][7][8] Amis and Crooks and collaborators extensively studied the encapsulation of bare nanoparticles with polyamidoamino (PAMAM) dendrimers, [8][9][10] and via various NMR techniques we unambiguously proved that ( palladium) nanoparticles are formed and reside inside these dendrimers, thus forming so-called dendrimer-encapsulated nanoparticles (DENs). 11,12 Micelles provide a method to self-assemble multiple, e.g., polymeric, molecular building blocks into welldefined structures typically in the 10-100 nanometer range.…”

Nanostructuring determines poisoning: tailoring CO adsorption on PtCu bimetallic nanoparticles

“…According to literature, many PtCu samples feature more negative onset potential for CO oxidation than pure Pt, seen e.g. in Cu@Pt core@shell NPs produced by electrochemical reduction of Cu followed by a partial galvanic replacement with Pt, 21 NPs with a Cu-core to Pt-shell gradient structure, 53 Pt NPs with a small content of dissolved Cu, 54 even PtCu alloy NPs prepared using a reducing agent in basic media followed by a partial galvanic replacement with Pt. 25 This is indeed observed in the CO stripping plots in Fig.…”

“…32,33 If any, as aforementioned, such surface Cu atoms could be beneficial for a somewhat stronger OH adsorption, which could tune the CO oxidation performance towards CO 2 . 54 Focusing on the CO adsorption on surface Pt atoms, a comparison is made between reference Pt 201 NP, pristine Cu 79 @Pt 122 , and other Cu@Pt models where a Pt surface atom is fully surrounded by Cu atoms-having both surface and subsurface Cu neighbors-or superficially surrounded-having View Article Online only surface Cu neighbors-. In the latter case, models were relaxed and analyzed, in which the surface Cu atoms were removed, mimicking the aforementioned Cu selective oxidation used to prepare the PtCu S1-S3 samples.…”

Correlating Surface Structures and Electrochemical Activity Using Shape-Controlled Single-Pt Nanoparticles

“…In contrast to bulk materials, however, where single-crystal electrodes with well-defined surface structures are available, ,,− ensembles of catalytic NPs are always, at least to some extent, polydisperse. ,,− That is, although there have been several improvements in NP synthetic methods that have served to narrow the degree of heterogeneity of NP ensembles, they are not perfect. − For understanding the fundamentals of catalytic reactions, this means that usually only an average structure can be correlated to an average function; the atomic-level details are, to some extent, subjugated by the heterogeneity of the ensemble. Indeed, a small subpopulation of NP structures can sometimes dominate catalytic activity. , To avoid the intrinsic heterogeneity discussed above, and hence to better understand the relationship between surface structure and catalytic activity for NPs, it is reasonable to explore the viability of studying reactions at individual, well-defined NPs. Here, we focus specifically on electrocatalysis at single NPs.…”

“…Indeed, a small subpopulation of NP structures can sometimes dominate catalytic activity. 23,24 To avoid the intrinsic heterogeneity discussed above, and hence to better understand the relationship between surface structure and catalytic activity for NPs, it is reasonable to explore the viability of studying reactions at individual, well-defined NPs. Here, we focus specifically on electrocatalysis at single NPs.…”