Electron transfer kinetics on composite diamond (sp3)-graphite (sp2) electrodes

The concept of non-diamond sp(2) impurity states as charge transfer mediators on boron-doped diamond (BDD) surface was suggested as an explanation for the electrochemical behavior of synthetic diamond based electrodes. In order to verify this concept, graphite particles (sp(2)) were deposited on diamond electrodes (sp(3)) by mechanical abrasion. The behavior of the so prepared diamond-graphite composite electrodes were compared with those of as-grown (BDDag) and those after mild anodic polarization (BDDmild). Outer-sphere electron transfer processes such as ferri/ferrocyanide (Fe(CN)(6)III/II) and inner-sphere charge transfer reactions such as 1.4-benzoquinone/hydroquinone (Q/H(2)Q) were chosen in order to investigate the electrochemical properties of these composite electrodes. Both redox systems became more reversible as the graphite (sp(2)) loading increased. A strong analogy existed between as-grown diamond electrodes and diamond-graphite composite electrodes. Finally a model is proposed which describes the BDD electrode surface as a diamond matrix in which non-diamond (sp(2)) impurity states are dispersed. These non-diamond sp(2) states on BDD surface acts as charge mediators for both inner-sphere and outersphere reactions. (C) 2003 Published by Elsevier B.V.