title: Effects of halogen doping on nanocarbon catalysts synthesized by a solution plasma process for the oxygen reduction reaction.
abstract: Halogen-doped carbon nanoparticles (CNPs) were synthesized by a simple one-step solution plasma process at room temperature using a mixture of benzene (C6H6) and organics containing halogen atoms as the precursors (i.e., hexafluorobenzene (C6F6), hexachlorobenzene (C6Cl6), and hexabromobenzene (C6Br6)). The experimental results demonstrated that halogen doping, especially F and Cl, could lead to more efficient removal of residual hydrogen compared to carbon synthesized with pure benzene. This phenomenon was related to the different binding energies between hydrogen and halogens to form hydrogen halides. Their crystallinity and morphology did not change and remained the same as non-doped carbon. The electrochemical evaluation of oxygen reduction reaction (ORR) activity in an alkaline solution revealed that halogen doping did not play a significant role in shifting the onset potential for the ORR, while a slight enhancement in diffusion limited current density was observed at high overpotentials. Moreover, the electron transfer number involved in the ORR process determined from the Koutecky-Levich plot at -0.6 V was found to increase for halogen-doped carbons in the following order: F-CNPs > Br-CNPs > Cl-CNPs > CNPs. The improved ORR performance of F-CNPs could reasonably be attributed to the synergistic effects of specific bonding states between the halogen and carbon, structural defects and surface functional groups. Our results confirmed the validity of using halogen doping to improve the ORR catalytic activity of CNPs.
authors.affiliation: Department of Materials Science and Engineering, College of Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan. ishizaki@shibaura-it.ac.jp and Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ishizaki
authors.affiliation: Department of Materials Science and Engineering, Graduate School of Engineering and Science, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Wada
authors.affiliation: Department of Materials Science and Engineering, Graduate School of Engineering and Science, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Chiba
authors.affiliation: Department of Materials Science and Engineering, Graduate School of Engineering and Science, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan.
authors.forename: Sou
authors.initials: S
authors.lastname: Kumagai
authors.affiliation: Department of Materials Science and Engineering, Graduate School of Engineering and Science, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan.
authors.forename: Hoonseung
authors.initials: H
authors.lastname: Lee
authors.affiliation: Department of Materials Science and Engineering, College of Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan. ishizaki@shibaura-it.ac.jp.
authors.forename: Ai
authors.initials: A
authors.lastname: Serizawa
authors.affiliation: Department of Materials Science and Engineering, Graduate School of Engineering and Science, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan.
authors.forename: Oi Lun
authors.initials: OL
authors.lastname: Li
authors.affiliation: NU-PPC Plasma Chemical Technology Laboratory, The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, Soi Chulalongkorn 12, Phayathai Road, Pathumwan, Thailand.
authors.forename: Gasidit
authors.initials: G
authors.lastname: Panomsuwan