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Journal Articles

Impact of heterometallic cooperativity of iron and copper active sites on electrocatalytic oxygen reduction kinetics

Kato, Masaru*; Fujibayashi, Natsuki*; Abe, Daiki*; Matsubara, Naohiro*; Yasuda, Satoshi; Yagi, Ichizo*

ACS Catalysis, 11(4), p.2356 - 2365, 2021/02

https://doi.org/10.1021/acscatal.0c04753

Times Cited Count：37 Percentile：89.44(Chemistry, Physical)

Fe-N-C oxygen reduction reaction catalyst is a key materials in polymer electrolyte fuel cell. However, the many Fe-N-C electrocatalysts still suffer from product selectivity due to the production of H $_{2}$ O $_{2}$ as the byproduct. In this work, we synthesized an ORR electrocatalyst of Cu $^{-}$ , Fe $^{-}$ , and N-doped carbon nanotubes. This heterobimetallic catalyst showed the selective four electron reduction of O $_{2}$ to H $_{2}$ O. Kinetic analysis of the electrocatalytic ORR and hydrogen peroxide reduction reaction in acidic media revealed that Cu, Fe-N-doped catalyst showed two orders of magnitude higher rate constants for the direct four electron reduction of O $_{2}$ to H $_{2}$ O than those for the two electron reduction of O $_{2}$ to H $_{2}$ O $_{2}$ , whereas a monometallic Fe-N-doped catalyst showed the same order of magnitude, indicating that the heterometallic cooperativity had a drastic impact on the ORR kinetics.

Journal Articles

Precise chemical state analyses of ultrathin hafnium films deposited on clean Si(111)-77 surface using high-resolution core-level photoelectron spectroscopy

Kakiuchi, Takuhiro*; Matoba, Tomoki*; Koyama, Daisuke*; Yamamoto, Yuki*; Kato, Daiki*; Yoshigoe, Akitaka

Surface Science, 701, p.121691_1 - 121691_8, 2020/11

https://doi.org/10.1016/j.susc.2020.121691

Times Cited Count：1 Percentile：5.82(Chemistry, Physical)

Ultrathin hafnium films on Si(111)-77 were studied using synchrotron radiation photoelectron spectroscopies to reveal the chemical states at interface and surface. Ultrathin Hf layers grow on clean Si(111)-77 surface by lever rule. Surface and interface of Hf/Si(111) contain three components (metallic Hf layers, Hf monosilicide (HfSi) and Si-rich Hf silicide). Ultrathin Hf layers changes HfSi $_{2}$ islands on bared Si(111)-77 surface after annealing at 1073 K. It was found that the long axes of the rectangle islands expand the direction connecting the corner holes in DAS model of clean Si(111)-77 surface.