A comparative in situ Pt-195 electrochemical-NMR investigation of PtRu nanoparticles supported on diverse carbon nanomaterials

This paper reports a detailed in situ Pt-195 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 Pt-195 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.