Fabrication, characterization, and electrocatalytic activity of metal/diamond composite electrodes

This dissertation is devoted to a new research area of diamond electrochemistry: application of boron-doped diamond thin-film electrodes in the field of electrocatalysis. The main focus is on the fabrication and characterization of Pt/diamond composite electrodes and on the investigation of their electrocatalytic activities.; Dimensionally stable Pt/diamond composite electrodes are fabricated by a sequential diamond growth/ Pt deposition/ diamond growth procedure. In this multistep process, a continuous boron-doped diamond thin film is first deposited on a conductive substrate (e.g. Pt, Si or W). DC magnetron sputtering or electrodeposition is next used to deposit a discontinuous layer of Pt particles on the surface. The Pt-coated diamond film is then subjected to a short, secondary diamond growth in order to anchor the metal particles into the diamond surface microstructure.; The resulting Pt/diamond composite films are characterized by SEM, EDX, AFM, AES, XRD, SIMS, Raman spectroscopy, and cyclic voltammetry. The metal particles range in diameter from 10 to 500 rim. In the electrodeposition approach, the number of exposed metal particles, particle size, and distribution can be controlled, to some extent, by adjusting the electrodeposition and secondary diamond growth conditions. The second, short diamond deposition serves to entrap many of the metal particles into the diamond microstructure by surrounding their base. Consequently, there is little catalyst detachment or particle aggregation during use under extreme conditions. The catalytic activity of the composite electrodes is extremely stable, as no microstructural alterations or activity losses were observed during a 2 h anodic polarization in 85% H ₃PO₄ at 0.1 A·cm−2 and 170°C.; The electrode's catalytic activity is evaluated using the oxygen reduction reaction and methanol oxidation reaction, at room temperature in acidic media. The catalytic activities of the composite electrode are found to be comparable to those for a polycrystalline and carbon-supported Pt catalyst. The results suggest that there is little alteration of the physicochemical properties of the Pt catalyst during secondary diamond growth. The diamond film exhibits metal-like electrical conductivity as both a support material and a current collector.; As part of the groundwork for my research, copper electrodeposition is investigated in order to gain a fundamental understanding of metal nucleation/growth on diamond surface. The electrodeposition of copper is strongly influenced by the electronic properties (i.e., doping level) of the diamond film. An increase in the boron-doping level significantly increases the number density of nucleation sites and alters the nucleation mechanism. The size of the metal deposits, their spatial distribution and number density are potentially to be controlled by adjusting the applied overpotential, deposition time and electrical conductivity (i.e., boron doping level) of the diamond film.