Capacitance and potentiodynamic measurements were conducted on single crystal (homoepitaxial) and polycrystalline boron-doped diamond thin-film electrodes. The impedance characteristics and kinetic data in the Ce3+/4+ redox system, even if having a great deal of variability, appeared to be similar for the two kinds of diamond electrodes, whereas the kinetics of redox reactions on crystalline diamond and amorphous diamond-like carbon films differ significantly. These data in aggregate lead to a tentative conclusion that the electrochemical behaviour of polycrystalline diamond is determined by the diamond crystallites proper, rather than by the disordered carbon of the intercrystallite boundaries. The concentration of uncompensated accepters in diamond was estimated from the linear and non-linear impedance data. The ways of presentation of Mott-Schottky plots for semiconductor electrodes are discussed for the case of frequency-dependent differential capacitance.