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calculationsShimoyama, Iwao; Baba, Yuji
DV-X Kenkyu Kyokai Kaiho, 28(1&2), p.62 - 69, 2016/03
We studied electronic structures at phosphorus sites doped in graphite to clarify the dopant effect on catalytic activity of P-doped graphite using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A sample prepared by high-temperature doping at 700 
C showed graphite-like clear polarization dependence of P K-edge NEXAFS spectra indicating planar structure at phosphorus sites. We calculated electronic structures at phosphorus sites in carbon model clusters using the DV-X method and compare them with NEXAFS. The electronic structure at planar phosphorus site with three carbon coordination reproduced the NEXAFS spectra. On the other hand, samples prepared by room-temperature doping and post annealing at 800 C showed deterioration of polarization dependence of NEXAFS. We clarified that an electronic structure of a curved carbon model cluster with a pentagon reproduced change of polarization dependence and spectral shape of NEXAFS. This means local structures at phosphorus sites can be controlled by substrate temperatures during ion dopings.
Shimoyama, Iwao; Hakoda, Teruyuki; Shimada, Akihiko; Baba, Yuji
Carbon, 81, p.260 - 271, 2015/01
Times Cited Count：23 Percentile：58.72(Chemistry, Physical)The relationship between catalytic activity and local structure at dopant sites of phosphorus-doped graphite prepared by ion implantation was studied by electrochemical measurements and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The P K-edge NEXAFS spectra of samples doped at room temperature and high temperature showed different polarization dependences, with graphite-like clear polarization dependence observed for the sample prepared by high-temperature doping. NEXAFS spectra were analyzed by density functional theory calculations to reveal the chemical-bonding states of P sites. In electrochemical measurements with an acid solution, samples with relatively small polarization dependence of NEXAFS exhibited marked catalytic activity in oxygen reduction reactions while those with larger polarization dependence showed lower catalytic activity. This indicates the influence of the configuration at dopant sites on catalytic activity and suggests that the introduction of curved structures is one way to design carbon catalysts with high catalytic activity.
