Advanced Electrochemistry with DiaChem^Ò Electrodes

Lothar Schäfer, Matthias Fryda, Dennie Herrmann, Inga Tröster

Fraunhofer Institute for Surface Engineering and Thin Films, IST
Bienroder Weg 54 E, 38108 Braunschweig, Germany
E-mail: schaefer@ist.fhg.de
Fax +49 (0) 531-2155-901
Phone +49 (0) 531-2155-520

Werner Hänni, André Perret

Centre Suisse d´Electronique et de Microtechnique SA CSEM
Jaquet-Droz 1, CH-2007 Neuchâtel, Switzerland

Abstract

Boron-doped conductive diamond films applied as electrode material exhibit unique properties in electrochemical processes. Beside the inherent extreme chemical stability of diamond, even at high doping levels, in particular, the high overpotential for water decomposition opens new opportunities for improved and also new electrochemical processes.

To investigate conductive CVD diamond for electrochemical processes under laboratory as well as industrial conditions we developed large-area conductive DiaChem^Ò deposition on a variety of electrode substrate materials. Because of the temperature sensitivity of substrate materials growth rates vary between 0.1 µm/h and 1.5 µm/h. For the investigations DiaChem^Ò electrodes with different geometries and dimensions have been fabricated using hot-filament CVD with diamond deposition areas up to (40 x 50) cm². Electrical conductivities are in the range of (5-100) mWcm using in-situ doping with diborane or trimethylboron, respectively, at doping levels of a few thousand ppm of boron.

The extreme chemical stability of DiaChem^Ò electrodes is demonstrated by high current density testing. In these experiments the electrodes are loaded with increasing current densities up to 10 A/cm² in sulfuric acid over several months without degradation of the electrode performance.

Electrochemical cells with DiaChem^Ò electrodes have been used for treatment of industrial waste water, synthesis of inorganic chemical products and in electroplating processes. Results of these predominantly positive industrial evaluation will be presented by representative examples for the different fields of application. The evaluation serves as a basis for the transfer of DiaChem^Ò electrodes into the market.

Keywords: large-area hot-filament CVD, diamond electrodes, electrochemistry, applications