Determination of the Tafel slope for oxygen evolution on boron-doped diamond electrodes

It has been reported that the oxygen evolution reaction (OER) on boron-doped diamond (BDD) electrodes appears at high overpotential and results in unusually high Tafel slope. In this work, we have studied the OER in 1 M HClO4 on BDD macroelectrode and microelectrodes-array (MEA). The correction of the anodic polarization curve for ohmic drop has been performed on BDD macroelectrode taking into account the total uncompensated resistance of the studied system. On BDD MEA, no correction of the polarization curve was necessary due to the small contribution of ohmic drop to the measured potential. At low overpotential (<1.2 V), abnormally high Tafel slopes (340 and 680 mV dec−1 on BDD MEA and BDD, respectively) have been observed. Such high slopes may result from the presence of surface redox couples/functional groups which act as a barrier for OER on BDD. In this potential region, the Tafel slope depends strongly on the state of the electrode surface. In the high overpotential region (>1.2 V), the Tafel slope has been found equal to 120 mV dec−1, which is the theoretical value considering a first or a second electron transfer step as the rate determining step.