Analytical Sciences

Suppression of Surface Oxygen on Nanocarbon Film Electrodes for Maintaining Electrode Activity

Mitsunobu TAKEMOTO,*,** Tomoyuki KAMATA,*** Motoki HAISHI,* Dai KATO,*** and Masahiko HARA**

*Nitto Denko Corporation, 1-1-2 Shimohozumi, Ibaraki, Osaka 567-8680, Japan
**School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8502, Japan
***Health and Medical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan

We investigated sputtered nanocarbon films with respect to the effect of suppressing surface oxygen on their electrochemical properties. The nanocarbon film consisted of nanocrystallites with mixed sp² and sp³ bonds formed by unbalanced magnetron sputtering. Ultraviolet/ozone (UV/O₃) irradiation and electrochemical pretreatment (ECP) were conducted to change the surface oxygen concentration of nanocarbon film. X-ray photoelectron spectroscopy (XPS) measurements revealed that nanocarbon films with different amounts of surface oxygen could be prepared. In addition, we observed no significant increase of the surface roughness (R_a) at the angstrom level after treatments, owing to a stable structure containing 40% of sp³ bonds. The electrode characteristics, including the potential window and electrochemical properties for some redox species, such as Ru(NH₃)₆^3+/2+, were investigated. Some electrochemical measurements of zinc ions (Zn²⁺) and hydrogen peroxide (H₂O₂) showed that the electrochemical reaction was improved by suppressing the surface oxygen. These results clearly indicated that the low surface oxygen concentration plays an important role in these electrochemical reactions.

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