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 electrochemistry owing to the wide potential range accessible, low background currents, extreme hardness, and the ease of chemical modification of diamond surfaces. It is shown here that, although the electrodeposition of silver metal is known to yield very poorly adhering films with a poor electrical contact, a silver oxysalt deposit formed on anodically pre-treated diamond surfaces adheres strongly with good electrical contact. The deposit is stable even in the presence of ultrasound. Voltammetric and XPS studies reveal that the silver oxide deposit, in contrast to the silver metal deposit, is efficiently stripped from the diamond surface by applying a sufficiently negative potential. The silver oxysalt Ag₇O₈NO₃, deposited onto two types of borondoped diamond electrodes, a 50 μm thick polycrystalline thin film deposited on a tungsten substrate and a polished free standing diamond plate, is shown to act as an electrocatalyst for oxygen evolution and for the oxidation of toluene. This development opens up the possibility of boron-doped diamond being 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.