A comparative in situ 195Pt electrochemical NMR investigation of PtRu nanoparticles supported on diverse carbon nanomaterials.
This paper reports a detailed in situ 195Pt electrochemical nuclear magnetic resonance (EC NMR) study of PtRu nanoparticles (NPs) that had a nominal atomic ratio of Pt Ru 1 1 and were supported on carbon nanocoils and carbon black (Vulcan XC 72) respectively. The particle sizes of the two samples were determined by X ray diffraction using the Sherrer equation: 3.6 nm for the former and 3.2 nm for the latter, which were further corroborated by transmission electron microscope measurements. By taking advantage of a unique correlation between the spectral frequency of the 195Pt NMR resonance and the radial atomic position in a particle, qualitatively and spatially resolved local Pt atomic fractions in the particles were deduced by using a Ruderman Kittel Kasuya Yosida (RKKY) J coupling based method as a function of different electrode potentials. The results indicated that both samples had Pt enriched cores and Pt deprived surfaces and, most importantly, the local Pt concentration varied as the electrochemical environment changed. The spatially resolved Fermi level local densities of states (E(f) LDOS) which are a measure of the electronic frontier orbitals in metals, were deduced across the NMR spectrum and correlated with the EC activity in methanol electro oxidation. The results were also compared to those obtained previously from Pt/Ru NPs supported respectively on carbon and graphite nanofibers.
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