Electronic Alterations Caused by Ruthenium in Pt−Ru Alloy Nanoparticles as Revealed by Electrochemical NMR

We have carried out a series of 195Pt and 13C NMR spectroscopic and electrochemical experiments on commercial Pt−Ru alloy nanoparticles and compared the results with those on Pt-black samples having similar particle sizes. The Pt NMR spectrum of the alloy nanoparticles consists of a single Gaussian peak, completely different from the broad “multi-Gaussian” NMR spectra, which are generally observed for carbon-supported Pt catalysts. Spin−echo decay measurements show that the intrinsic spin−spin relaxation time (T2) is much larger in the alloy compared to Pt-black. A “slow-beat” is observed in the spin−echo decay curve of the alloy, implying that the NMR frequencies of spin−spin coupled Pt nuclei in the alloy nanoparticles are quite similar, unlike the situation found with Pt-black. These 195Pt NMR results strongly suggest that there is a surface enrichment of Pt atoms in the Pt−Ru alloy nanoparticles. The CO-stripping cyclic voltammogram (CV) of the Pt−Ru alloy nanoparticles is broader than that observed w...