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In this report, density functional theory (DFT) calculations of O and OH binding energies on triatomic surface ensembles of Pd x Ir (100−x) nanoalloys successfully predicted the overall trend in experimental oxygen reduction reaction (ORR) activity as a function of nanoparticle (NP) composition. Specifically, triatomic Pd 3 ensembles were found to possess optimal O and OH binding energies and were predicted to be highly active sites for the ORR, rivaling that of Pt(111). However, DFT calculations suggest that the O binding energy increases at active sites containing Ir, thereby decreasing ORR activity. Pd x Ir (100−x) nanoalloys were synthesized using a microwave-assisted method and their activity towards the ORR was tested using rotating disk voltammetry (RDV). As predicted, the bimetallic electrocatalysts exhibited worse catalytic activity than the Pd-only NPs. The strong qualitative correlation between the theoretical and experimental results demonstrates that the activity of individual active sites on the surface of NPs can serve as a proxy for overall activity. This is a particularly useful strategy for applying DFT calculations to electrocatalysts that are too large for true first-principle analysis. 

A microwave assisted method was used to synthesize RhAu nanoparticles (NPs). Characterization, based upon transmission electron microscopy (TEM), energy dispersive spectroscopy, and powder X-ray diffraction, provided the evidence of monomodal alloy NPs with a mean size distribution between 3 and 5 nm, depending upon the composition. Extended X-ray adsorption fine-structure spectroscopy (EXAFS) also showed evidence of alloying, but the coordination numbers of Rh and Au indicated significant segregation between the metals. More problematic were the low coordination numbers for Rh; values of ca. 9 indicate NPs smaller than 2 nm, significantly smaller than those observed with TEM. Additionally, no single-particle structural models were able to reproduce the experimental EXAFS data. Resolution of this discrepancy was achieved with high resolution aberration corrected scanning TEM imaging which showed the presence of ultra-small (<2 nm) pure Rh clusters and larger (∼3–5 nm) segregated particles with Au-rich cores and Rh-decorated shells. A heterogeneous model with a mixture of ultrasmall pure Rh clusters and larger segregated Rh/Au NPs was able to explain the experimental measurements of the NPs over the range of compositions measured. The combination of density functional theory, EXAFS, and TEM allowed us to quantify the heterogeneity in the RhAu NPs. It was only through this combination of theoretical and experimental techniques that resulted in a bimodal distribution of particle sizes that was able to explain all of the experimental characterization data.