 Supporting information for          Seiji Kasahara, † Keisuke Natsui, † Takeshi Watanabe, ‡ Yasuyuki Yokota, § Yousoo Kim, § Shota Iizuka, # Yoshitaka Tateyama, # Yasuaki Einaga* ,†,¶ † Department of Chemistry, Keio University, 3)14)1 Hiyoshi, Yokohama, Kanagawa 223)8522, Japan ‡ Department of Electrical Engineering and Electronics, Aoyama Gakuin University, 5)10)1 Fuchinobe, Sagamihara, Kanagawa 252)5258, Japan § Surface and Interface Science Laboratory, RIKEN, 2)1 Hirosawa, Wako, Saitama 351)0198, Japan # Center for Green Research on Energy and Environmental Materials (GREEN) and Research and Services Division of Materials Data and Integrated System (MaDIS), National Institute of Materials Science (NIMS), 1)1 Namiki, Tsukuba, Ibaraki 305)0044, Japan ¶ ACCEL, Japan Science and Technology Agency, 5)3 Yonbancho, Chiyoda)ku, Tokyo 102)8666, Japan *To whom correspondence should be addressed. E)mail: einaga@chem.keio.ac.jp; Tel: +81)45)566)1704; Fax: +81)45)566)1697 Table of Contents 1. Characterization of boron)doped diamond (BDD) electrodes: Raman spectroscopy, glow discharge optical emission spectrometry (GD)OES), and scanning electron microscopy (SEM). 2. Investigation into the processing time for anodic oxidation treatment. 3. Surface analyses of BDD electrodes after cathodic reduction treatments by X)ray photoelectron spectroscopy (XPS). 4. Effects of buffer solution on surface hydrogenation. 5. Comparison between as)grown BDD and BDD after cathodic reduction. 6. Theoretical calculation. 7. References