title: Particle-size effect of nanoscale platinum catalysts in oxygen reduction reaction: an electrochemical and 195Pt EC-NMR study.
abstract: Oxygen reduction reaction (ORR) measurements and (195)Pt electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy were combined to study a series of carbon-supported platinum nanoparticle electrocatalysts (Pt/CB) with average diameters in the range of roughly 1-5 nm. ORR rate constants and H(2)O(2) yields evaluated from hydrodynamic voltammograms did not show any particle size dependency. The apparent activation energy of 37 kJ mol(-1), obtained for the ORR rate constant, was identical to that obtained for bulk platinum electrodes. Pt/CB catalysts on Nafion produced only 0.7-1% of H(2)O(2), confirming that the direct four-electron reduction of O(2) to H(2)O is the predominant reaction. NMR spectral features showed characteristic size dependence, and the line shapes were reproduced by using the layer-deconvolution model. Namely, the variations in the NMR spectra with particle size can be explained as due to the combined effect of the layer-by-layer variation of the s-type and d-type local density of states. However, the surface peak position of (195)Pt NMR spectra and the spin-lattice relaxation time of surface platinum atoms showed practically no change with the particle size variation. We conclude that there is a negligible difference in the surface electronic properties of these Pt/CB catalysts due to size variations and therefore, the ORR activities are not affected by the differences in the particle size.
authors.affiliation: Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Clean Energy Research Center, Takeda 4, Kofu 400-8511, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yano
authors.forename: Junji
authors.initials: J
authors.lastname: Inukai
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Uchida
authors.forename: Masahiro
authors.initials: M
authors.lastname: Watanabe
authors.forename: Panakkattu K
authors.initials: PK
authors.lastname: Babu
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Jong Ho
authors.initials: JH
authors.lastname: Chung
authors.forename: Eric
authors.initials: E
authors.lastname: Oldfield
authors.forename: Andrzej
authors.initials: A
authors.lastname: Wieckowski
mesh_terms: D002384:Catalysis; D004563:Electrochemistry; D007554:Isotopes; D009682:Magnetic Resonance Spectroscopy; D046529:Microscopy, Electron, Transmission; D036103:Nanotechnology; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010316:Particle Size; D010984:Platinum / Q000737:chemistry*; D013696:Temperature
chemical_list: D007554:Isotopes; D010984:Platinum; D010100:Oxygen