量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果(学会誌発表論文、学会発表、研究開発報告書、特許等)を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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Pt nanoparticle electrocatalysts on an Ar+-irradiated glassy carbon (GC) substrate were recently found to show a higher oxygen reduction reaction (ORR) activity than those on the non-irradiated one [1]. This finding suggests that the Pt nanoparticles would be electronically modified by the lattice defects in irradiated GC. Our theoretical research previously revealed that vacancies in graphite would lower a d-band center of the supported Pt nanoparticles; this is probably the reason for the higher activity [2]. We investigated here the electronic states of the interface between the Pt nanoparticles and the irradiated carbon support by X-ray absorption fine structure (XAFS) measurements in order to get an insight into the mechanism of the activity enhancement.
Highly oriented pyrolytic graphite (HOPG) and glassy carbon (GC) substrates were irradiated with 380 keV Ar+. The HOPG substrate was employed so that the electronic structure could be resolved into orbital components ( and bonds). The Pt nanoparticles were then deposited by RF magnetron sputtering. The Pt deposition was also done on the non-irradiated HOPG and GC substrates for comparison. The XAFS spectra were measured at BL14B1 in SPring-8 and at BL-8 of the SR Center, Ritsumeikan University.
Figure 1 shows the C K XAFS spectra for the pristine HOPG, the irradiated HOPG, Pt/non-irradiated HOPG, and Pt/irradiated HOPG. This spectral measurement was made at the X-ray incident angle of 30° to obtain the X-ray absorption due to C-C * and * orbitals with almost the same cross-section. The pristine and irradiated HOPG substrates exhibited three peaks from a C-C * orbital (285.3 eV), C-C *, 1 orbital (291.5 and 292.5 eV), and surface carbon with adsorbates (287.5 eV). The shoulder structure around 284 eV was observed for Pt/non-irradiated HOPG, indicating the occurrence of Pt-C interaction at the interface. The intensity of this shoulder increases for Pt/irradiated HOPG as shown by the arrow. Therefore, the vacancies in the irradiated carbon support would induce the change of Pt-C interaction, leading to the different electronic structure at the interface.
Our previous paper reported that the Pt nanoparticles on the irradiated carbon support were distorted [3]. According to the result of Fig. 1, the Pt-C interaction could be an origin of the observed distortion of the Pt nanoparticles, which lowered the d band center and then improved their ORR activity. In this presentation, we will additionally clarify the electronic structure of Pt nanoparticles based on the XAFS results of Pt L edge.