Mass-selected nanoparticles of PtxY as model catalysts for oxygen electroreduction

Abstract

Low-temperature fuel cells are limited by the oxygen reduction reaction, and their widespread implementation in automotive vehicles is hindered by the cost of platinum, currently the best-known catalyst for reducing oxygen in terms of both activity and stability. One solution is to decrease the amount of platinum required, for example by alloying, but without detrimentally affecting its properties. The alloy PtxY is known to be active and stable, but its synthesis in nanoparticulate form has proved challenging, which limits its further study. Herein we demonstrate the synthesis, characterization and catalyst testing of model PtxY nanoparticles prepared through the gas-aggregation technique. The catalysts reported here are highly active, with a mass activity of up to 3.05 A mgPt(-1) at 0.9 V versus a reversible hydrogen electrode. Using a variety of characterization techniques, we show that the enhanced activity of PtxY over elemental platinum results exclusively from a compressive strain exerted on the platinum surface atoms by the alloy core.

Exploring the phase space of time of flight mass selected PtxY nanoparticles

“…The ISS spectra confirm that, at least on the surface, the nanoparticles produced from the Pt 3 Y are richer in Y than the ones prepared from the Pt 9 Y target. Furthermore, under the assumption that the composition of the Pt x Y alloy is uniform throughout the particle, 48 XPS after ORR show that the NPs produced from the Pt 3 Y target are richer in Y than the NPs produced from the Pt 9 Y. This is similar to what was observed by Gan et al in an earlier study on Pt x Ni nanoparticles.…”

“…This is similar to what was observed by Gan et al in an earlier study on Pt x Ni nanoparticles. 58 As we proposed recently, 48 the presence of Y in the Pt lattice induces a compressive surface strain in the Pt overlayer of the NP (Fig. 1a), destabilising OH intermediates of the ORR.…”

“…[39][40][41] In our laboratory we have taken a different approach, namely to study alloys of Pt and rare earths such as Y, Gd, Ce and La. 33,[42][43][44][45][46][47][48] These alloys have a particularly negative heat of formation, which should provide them with long term-kinetic stability against dealloying at the cathode of a fuel cell. Extended surfaces of Pt 3 Y and Pt 5 Gd show particularly high activity for oxygen reduction.…”

“…The activity increases monotonically with particle size; we attributed this to an increased degree of compressive strain exerted by the alloy core onto the pure Pt shell. 48 Importantly, size effects are not the only significant characteristics of nanoparticles. Improvements can be made to catalysts by forming non-equilibrium morphologies.…”

A DFT Study on the O2 Adsorption Properties of Supported PtNi Clusters

“…However, the slope of the linear fit is less pronounced, compared to supported PtNi clusters, due to elemental differences between the mono-and bi-metallic system. Figure 5a,b value dispersion can be understood due to drastic changes in the Pt-Pt bond lengths at the adsorption site, as both PtNi and Pt clusters try to accommodate the incoming O 2 molecule, thus directly effecting the GCN at the adsorption site (see Figure 6a Figure 6c,d shows both the calculated core and shell supported PtNi, Pt and Ni cluster strain, as it has been recently shown a direct link between the NP reactivity and its compressive strain, particularly in bimetallic cases [8,44,54]. The most dramatic effects are observed for supported PtNi as they are characterised by a large core compressive strain (between −4% and −10%).…”