BORON-DOPED DIAMOND TITANIUM COMPOSITE ELECTRODES FOR ELECTROCHEMICALGAS GENERATION FROM AQUEOUS-ELECTROLYTES/

Titanium substrates were coated by 2-5 mu m thick boron doped diamond layers through the HFCVD-process from an activated H-2/CH4 gas phase. The doping level was 50-230 atom ppm B. The surface was saturated with drop CH2 groups. A TIC interphase was formed in situ. Stationary curr ent-voltage curves up to j(+/-\) = 0.1 A cm(-2) were measured in three aqueous electrolytes, 1 M H2SO4, 1M NaOH and 3 M NaCl. Very high over voltages of \eta\ = 1-2 V at 0.1 A cm(-2) were found for the relevant gas evolution reactions. An appreciable, potential dependent portion o f the Galvani voltage seems to be due to a voltage drop in a space cha rge layer in the semiconductor. Tafel plots yield no straight lines th erefore. An additional reason is the inertness of the electrode surfac e due to the drop CH2 groups in the negative and drop C=O groups in th e positive reg:on. Electrochemical transformations between these surfa ce structures seem to be possible. (C) 1998 Published by Elsevier Scie nce Ltd. All rights reserved.