Electrochemical reactions at conductive diamond electrodes

The preparation of synthetic, highly conductive, diamond thin films has been achieved by different research groups from the end of the Eighties. Different papers appeared, together with many patents (relating both on semi-conducting and insulating films); however, a number of questions remains still open. In order to further elucidate this topic, highly boron-doped diamond (BDD) electrodes have been studied, both physically and by means of electrochemical investigations. This thesis work starts with a brief introduction on diamond, from a mineralogical as well as a jeweler point of view (chapter one). Chapter two deals with the synthesis of diamond: both the HP-HT (high pressure, high temperature) and the CVD (chemical vapor deposition) method of preparation have been reviewed and thoroughly discussed [1]. The electric / electronic properties of BDD are summarized in chapter three; although a lot of work has been reported on semi-conducting diamond thin films, little is known about the highly-doped material. Chapter four concerns with the BDD physical characterization, illustrating the most commonly adopted techniques; in particular, a non-exhaustive collection of papers, dealing with X-ray Photoelectron Spectroscopy, is reported and briefly evaluated. Starting with chapter five, original results are reported, relating to BDD films synthesized at CSEM (Neuchâtel, Switzerland); firstly, the properties of the material has been investigated through SEM, AFM, XRD, Raman, XPS and CV analyses. The behavior of some simple electron transfer reactions (ironIII/ironII [2], ferri/ferro-cyanide [2], ceriumIV/ ceriumIII [3] and europiumIII/ europiumII) has been investigated, and results are reported in chapter six. Extending the investigation on multi step electrode processes, chapter seven contains data on the chlorine evolution reaction (chl.e.r.) at BDD [4]. Finally, chapter eight takes profit of the unique chemical and electrochemical stability of conductive diamond, reporting data on modified BDD films: physical and electrochemical characterizations of noble-metal oxide nanoparticles are described, together with the discussion of a radical-spillover mechanism possibly occurring, during the chl.e.r., at slightly modified BDD films [5-7]. [1] S. Ferro, “Synthesis of Diamond”, Journal of Materials Chemistry, Accepted for publication. [2] S. Ferro and A. De Battisti, “Electron Transfer Reactions at Conductive Diamond Electrodes”, Electrochimica Acta, 47 (10), 1637-1645 (2002). [3] S. Ferro and A. De Battisti, “Electrochemistry of the aqueous Ceric/Cerous redox couple at conductive diamond and gold electrodes”, Physical Chemistry Chemical Physics, 4 (10), 1915-1920 (2002). [4] S. Ferro, A. De Battisti, I. Duo, Ch. Comninellis, W. Haenni and A. Perret, “Chlorine evolution at highly boron-doped diamond electrodes”, Journal of the Electrochemical Society, 147 (7), 2614-2619 (2000). [5] A. De Battisti, S. Ferro and M. Dal Colle, “Electrocatalysis at conductive diamond modified by noble-metal oxides”, Journal of Physical Chemistry B, 105 (9), 1679-1682 (2001). [6] S. Ferro and A. De Battisti, “Electrocatalysis and chlorine evolution reaction at ruthenium dioxide deposited on conductive diamond”, Journal of Physical Chemistry B, 106 (9), 2249-2254 (2002). [7] Duo, S. Ferro, A. De Battisti and Ch. Comninellis, “Conductive Metal-Oxide nanoparticles on synthetic boron-doped diamond surfaces”, in “Catalysis of Nanoparticles Surfaces”; A. Wieckowski, E. R. Savinova and C. G. Vayenas Eds.; Marcel Dekker, Inc.; Projected publication date: 2002 (in press).