Sonoelectrochemistry at highly boron-doped diamond electrodes: silver oxide deposition and electrocatalysis in the presence of ultrasound

The use of boron-doped diamond has a considerable impact in electrochemistr y owing to the wide potential range accessible, low background currents, ex treme hardness, and the ease of chemical modification of diamond surfaces. It is shown here that, although the electrodeposition of silver metal is kn own to yield very poorly adhering films with a poor electrical contact, a s ilver oxysalt deposit formed on anodically pre-treated diamond surfaces adh eres strongly with good electrical contact. The deposit is stable even in t he presence of ultrasound. Voltammetric and XPS studies reveal that the sil ver oxide deposit, in contrast to the silver metal deposit, is efficiently stripped from the diamond surface by applying a sufficiently negative poten tial. The silver oxysalt Ag7O8NO3, deposited onto two types of boron-doped diamond electrodes, a 50 mu m thick polycrystalline thin film deposited on a tungsten substrate and a polished free standing diamond plate, is shown t o act as an electrocatalyst for oxygen evolution and for the oxidation of t oluene. This development opens up the possibility of boron-doped diamond be ing applied as an inert and conducting substrate material for a wide range of oxidic materials, which can then be utilised as active electrocatalysts at high applied potentials.