Electrochemical properties of undoped CVD diamond films

The electrochemical properties of undoped diamond polycrystalline films grown on tungsten wire substrates using methanol as a precursor are described. The diamond film quality was changed by introducing sp2-bonded non-diamond carbon impurity through adjustment of the methanol-to-hydrogen (C/H) source gas ratio used for diamond growth.The electrodes were characterized by Raman spectroscopy, scanning electronic microscopy (SEM) and cyclic voltammetry (CV).Diamond coated tungsten wires were then used as a working electrode to ascertain their electrochemical behavior in electrolytic medium. Electrochemical windows of these films were found to be suitable in the potential range of [−2.5 V, +2.2 V] vs. Ag/AgCl in acid medium (0.1 M KCl).The electrochemical behavior was evaluated also using the Fe(CN)63−/4−redox couple.The results demonstrate that the grain boundaries and sp2-hybridized carbon impurity can have a significant influence on electrochemical window of undoped diamond electrodes. It was observed that with increasing sp2 carbon impurity concentration the electrochemical window decreases.

► Physical and electrochemical properties of undoped polycrystalline diamond electrodes of different qualities prepared by HF CVD method investigated.
► A direct correlation was found between diamond quality and width of electrochemical window.
► Changes of potential window vs. FWHM goes in the same direction as that observed by J.A. Bennet et al. and our results are extension of that research.
► Diamond quality and the sp2-hybridized carbon phase content have a little effect on CV peak separation (ΔΔEp) for Fe(CN)63−/4 couple.