Boron-doped diamond electrodes in organic media: Electrochemical activation and selectivity effects

This study highlights the effects of the electrochemical surface pre-treatment of polished polycrystalline boron-doped diamond electrodes in ethanol on electron transfer to organic redox systems. A novel ‘‘activation’’ procedure based on cathodic polarisation in ethanol (0.01 M NBu4PF6) is proposed and shown to be highly effective in promoting electron transfer to the aqueous FeðCNÞ =4 6 redox system. For redox systems in acetonitrile, effects on electron transfer processes are strongly dependent on the type of electron transfer process. For decamethylferrocene, decamethylcobaltocene, methyviologen, and for methylviologen redox systems essentially reversible electron transfer is observed irrespective of the pre-treatment of the boron-doped diamond electrode. For the benzoquinone redox system insignificant changes occur but for the benzoquinone /2 process a more dramatic change in electron transfer kinetics is observed (after cathodic polarisation in ethanol) consistent with an improved interfacial electron transfer (a 4.6 · increase in peak current occurs). Finally, the tetraethyl-ethylenetetracarboxylate system is investigated as a model olefin redox system. Again changes in reactivity occur (a 4.0 · increase in peak current) at the cathodically pre-treated boron-doped diamond electrode. XPS surface analysis data reveal only insignificant changes in the chemical composition of the boron-doped diamond surface before and after activation and therefore a predominantly electronic mechanism for the ‘‘activation’’ process is proposed. In future selectivity effects for electron transfer at borondoped diamond electrode surfaces could be introduced intentionally and used beneficially for chemo-selective electro-organic processes. 2007 Elsevier B.V. All rights reserved.