Electrochemical properties of new electrode material, synthetic diamond compacts with the boron (dopant) level approaching the upper limit, are studied for the first time. Cylinder-shaped polycrystalline samples, 3.5-4 mm in diameter and 2.5 mm in height, were prepared by thermobaric processing of graphite-boron carbide mixtures in the diamond thermodynamic stability region (at the pressure of 8-9 GPa and temperature of similar to 2500 K). Their diamond nature, in particular, the absence of graphite, was confirmed by Raman spectroscopy and XRD technique. The compacts' electrode behavior is studied by using cyclic voltammetry and electrochemical impedance spectroscopy. The cyclic voltammograms showed that the compacts are very much similar to conventional chemical-vapor-deposited thin-film diamond electrodes in their electrode characteristics. In particular, they have wide potential window, low background current in indifferent electrolytes (KCl, K2SO4) and good reproducibility. Moreover, their extremely high doping level makes them somewhat more electroactive. Anodic oxidation of benzene is accompanied by electrode-surface blocking phenomena. To conclude, the compacts are well comparable to the CVD-diamond electrodes. One might think that they can equally be used, e.g., as electrodes in electrosynthesis, electroanalysis, water treatment, etc. Moreover, they could be more robust in electrochemical devices (sensors, etc.). (C) 2015 Elsevier Ltd. All rights reserved.