Controllable Electrochemical Activities by Oxidative Treatment toward Inner-Sphere Redox Systems at N-Doped Hydrogenated Amorphous Carbon Films

Yoriko Tanaka,Hiroshi Naragino,Akira Fujishima,Kohsuke Yoshinaga,Akira Nakahara,Kensuke Honda,Takeshi Kondo

doi:10.1155/2012/369130

Abstract

The electrochemical activity of the surface of Nitrogen-doped hydrogenated amorphous carbon thin films (a-CNH, N-doped DLC) toward the inner sphere redox species is controllable by modifying the surface termination. At the oxygen plasma treated N-doped DLC surface (O-DLC), the surface functional groups containing carbon doubly bonded to oxygen (C=O), which improves adsorption of polar molecules, were generated. By oxidative treatment, the electron-transfer rate for dopamine (DA) positively charged inner-sphere redox analyte could be improved at the N-doped DLC surface. For redox reaction of 2,4-dichlorophenol, which induces an inevitable fouling of the anode surface by forming passivating films, the DLC surfaces exhibited remarkably higher stability and reproducibility of the electrode performance. This is due to the electrochemical decomposition of the passive films without the interference of oxygen evolution by applying higher potential. The N-doped DLC film can offer benefits as the polarizable electrode surface with the higher reactivity and higher stability toward inner-sphere redox species. By making use of these controllable electrochemical reactivity at the O-DLC surface, the selective detection of DA in the mixed solution of DA and uric acid could be achieved.

Highlights

Boron-doped diamond (BDD) thin film is an ideal polarizable electrode material because it possesses superior electrochemical properties such as a wide working potential range, low background current, and high stability toward electrochemical reaction
It has been shown that amorphous carbon (a-C):N has a wide potential window and low back current in aqueous media that are comparable with those observed at the BDD electrode
The methods employed for fabricating a-C:N electrodes were a filtered cathodic vacuum arc (FCVA) [3,4,5,6,7,8], radio-frequency cathodic sputtering from graphite target [9, 10], and direct ion beam deposition [11]

Summary

Introduction

Boron-doped diamond (BDD) thin film is an ideal polarizable electrode material because it possesses superior electrochemical properties such as a wide working potential range, low background current, and high stability toward electrochemical reaction. As a simple method of nitrogen-doped hydrogenated amorphous carbon thin film (N-doped DLC) synthesis, our research group proposed microwave-assisted plasmaenhanced chemical vapor deposition method using the vapor of nitrogen-containing hydrocarbon as carbon and nitrogen sources [12]. This method is widely used for the diamondlike carbon coating. N-doped DLC thin films exhibited a wide working potential range over 3 V, low double-layer capacitance, high resistance to electrochemically induced corrosion in strong acid media, and reversible electron transfer kinetics for inorganic redox analytes (Fe2+/3+, [Fe(CN)6]3−/4−, and Ru(NH3)26+/3+), which were on the same level as those of BDD [12]. The N-doped DLC films could be an ideal polarizable electrode material with physical stability and chemical inertness, alternative to BDD

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