Study On Surface Modifications And Electrochemical Properties Of Nanodiamond

Nanodiamond, as a novel electrode material, possesses potential applications in many electrochemical fields. However, its poor conductivity and activity significantly embarrass its application. Surface modification was regarded as an effective way to resolve the problems.The detonation-synthesized nanodiamond was used as raw material in this study. The electrochemical properties was investigated both in aqueous and non-aqueous electrolytes. Three kinds of surface modifications were carried on nanodiamond: fluorination and amination; surface graphitization; nano Pt modification. The means of Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction and transmission electron microscopy were used to characterize the surface structure and morphology of the modified nanodiamond. The electrochemical properties were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry.The results showed that nanodiamond powder electrode had wide potential window and low background current in tetrabutylammonium tetrafluoroborate and acetonitrile. The electrode reaction was quasi-reversible in non-aqueous electrolytes containing the ferrocene redox system, and the electrochemical process was diffusion controlled, which had similar electrode kinetics with the aqueous electrolytes. The peak current increased linearly with the increase of the ferrocene concentration. Compared with the pristine nanodiamond, the electrical conductivity of fluoro-nanodiamond reduced in aqueous electrolytes, and the reversibility of Fe(CN)₆^3-/4- redox became worse. The conductivity of amino-nanodiamond increased in aqueous electrolytes, but an irreversible reaction ocurrured at amino-nanodiamond powder electrode in Fe^3+/2+ solutions. Surface graphitization process was carried out by heat treatment at the temperature of 550¹000°C in vacuum. When the temperature was below 800 °C, the electrical conductivity of nanodiamond was reduced as the temperature increasing. While the temperature was higher 800°C, graphitized-nanodiamond which had a diamond core covered with thin graphene shell was obtained. The graphitized-nanodiamond exhibited good electrical conductivity and electrochemical activity. Microwave-assisted method was used to deposit Pt nanoparticles on nanodiamond support. Pt particles with the size of 3⁵ nm were well-dispersed on the surface of nanodiamond supports. The Pt/nanadiamond and Pt/graphitized-nanodiamond catalysts exhibited good electrocatalytic activities for methanol electrooxidation. Compared with Pt/nanodiamond catalyst, the Pt/graphitized-nanodiamond catalyst exhibited better electrocatalytic activity and stability.