Study on surface termination of boron-doped diamond electrodes under anodic polarization in H2SO4 by means of dynamic impedance technique

Abstract

Anodic oxidation is a popular way to modify termination bonds at boron doped diamond electrodes altering their electrochemical and physicochemical properties. Our studies, performed with dynamic electrochemical impedance spectroscopy technique, supported with X-ray photoelectron spectroscopy and ellipsometry analysis prove its utility in continuous on-line monitoring of impedance changes on the electrode surface under polarization conditions, which may be of great use for the optimization of working conditions of the process. Based on our results, it can be observed that oxidation of termination bonds is a multistep process, each stage initiated at different anodic polarization potential. The factors influencing oxidation of termination bonds are presented and discussed. It was also possible to draw a conclusion about the removal of sp2 carbon impurities from the electrode surface as a precondition to activate the oxidation process. The depth and time of polarization, boron uptake at the grain boundaries, as well as crystallographic orientation of individual grains influence the heterogeneity of the oxidation process. Its partial reversibility was observed as a result of cathodic polarization in the range of hydrogen evolution, however due to irreversible corrosion of sp2 impurities, hydrogenation is not complete. This form of hydrogenation additionally contaminates the electrode surface with sulphur.