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This paper is concerned with the study of the influence of electrochemical pre-treatments on the behavior of highly boron doped diamond electrodes. Anodic and cathodic preconditioning performed either with 10 -4 A.cm -2 or 10 -1 A.cm -2 , have been studied. Cyclic voltammetry at as-deposited, anodically and cathodically treated electrodes, in presence of 2 redox couples serving as electrochemical probes is analyzed in the light of the surface characterization given by XPS chemical analysis and wetting angle measurements. Ce 4+/3+ and Fe(CN) 6 3-/4-redox couples in 0.5 M H 2 SO 4 medium, have been studied before and after the different treatments. The results of Mott-Schottky plots and current voltage curves are reported and show that the electrochemical response of BDD electrodes is very dependent on the current density involved in the process. The modification of surface bond termination studied by XPS analyses and contact angle measurements is also strongly dependent on electrochemical pre-treatment. IntroductionDiamond presents a number of outstanding properties, attractive for many applications as electronic devices, biomedical applications and for preparing very stable electrodes for electrochemistry. Surfaces properties of diamond attracts increasing attention as the carbon dangling bonds at the surface can be terminated by different elements, the most important ones are oxygen and hydrogen. For oxygen termination, hydrophilic surfaces with positive electron affinity and insulating properties are observed (1), while hydrogen gives rises to hydrophobic surfaces with negative electron affinity and good conductivity (2). Among the different ways of surface preconditioning, electrochemical treatments are the subject of several studies. Anodic polarization in acidic solution has been widely studied: it induces the conversion of as-deposited hydrogen terminations in oxygen (3). However, the great diversity of results (3-6) proves that the effects of electrochemical treatments, on charge transfer are not completely understood. ExperimentalPolycrystalline boron ([B] =10 20 cm -3 ) doped diamond films (BDD) of 1.6 µm thickness were deposited on high conductivity (100) silicon substrates by hot filament chemical vapour deposition. Electrochemical experiments were performed using a classical three-electrode configuration: mercury sulfate electrode (MSE) as the reference, BDD working electrode and platinum counter electrode. Electrochemical treatments were performed in 0.5 M H 2 SO 4 , with a galvanostatic configuration. Two ranges of imposed current densities have been tested. The higher one