Enhanced electrochemical response of boron-doped diamond electrodes brought on by a cathodic surface pre-treatment

The effect of surface pre-treatment on the electrochemical response of boron-doped diamond (BDD) electrodes is reported. Initially, several examples from published works illustrate the dramatic changes observed when a cathodic polarisation is applied before measurements instead of the classically adopted anodic treatment. In particular, electroanalytical determinations of pesticides in pure and contaminated waters could only be possible after holding the BDD electrode at -3.0 V versus Ag/AgCl for 30 min. Cyclic voltammetry of well-known reversible systems such as K(4)Fe(CN)(6) and ferrocene in aqueous solutions rendered the expected behaviour after the cathodic pre-treatment while for the usual anodic treatment considerable distortions were recorded. Electrochemical impedance spectroscopy carried out in the presence and in the absence of the mentioned electroactive species confirmed the previously observed differences. Nyquist plots showed that in both cases the resistance associated to a high-frequency element diminishes from over 300 to about 4 Omega cm(2) when a cathodic pre-treatment replaces the anodic pre-treatment. Moreover, Mott-Schottky plots in the absence of electroactive species revealed that the flat-band potential decreases by ca. 250 mV when measurements are carried out after the cathodic pre-treatment. All these effects could be explained in terms of the presence of a discontinuous passive layer on the BDD surface but they still require further studies for a definite conclusion. (C) 2004 Elsevier Ltd. All rights reserved.