Physicochemical properties of fluorinated diamond electrodes

Although boron-doped diamond (BDD) is itself quite stable and chemically inert, some electrochemical applications could require further improvement, and fluorination could be one of the most promising methods. In the present paper, a characterization of diamond film electrodes surface-modified by fluorine insertion, through CF4 plasma treatment, has been carried out. X-ray photoelectron spectroscopy (XPS) analysis showed that the above preparation method most probably leads to the fluorination of the near-surface region of the diamond film. The electrochemical characterization showed that the fluorination of BDD shifts the cathodic water decomposition by about 2 V in the negative direction; this behavior could not be ascribed to problems of film conductivity and/or to a decrease in electronic density of states. The electron-transfer kinetics for model redox couples such as the Eu3+/Eu2+, Fe3+/Fe2+, and ferri/ferro cyanide redox systems has been found to be quite significantly affected by the surface modification, while the electrochemical behavior of methyl viologen remains practically unchanged. The exchange current densities for the aquo complexes are decreased about five times, while for the cyano complex of more than 3 orders of magnitude.