Unusual Electrochemical Properties of Low-Doped Boron-Doped Diamond Electrodes Containing sp² Carbon

Unexpected phenomena displayed by low-boron-doped diamond (BDD) electrodes are disclosed in the present work. Generally, the presence of sp² nondiamond carbon impurities in BDD electrodes causes undesirable electrochemical properties, such as a reduced potential window and increased background current, etc. However, we found that the potential window and redox reaction in normally doped (1%) BDD and low-doped (0.1%) BDD exhibited opposite tendencies depending on the extent of sp² carbon. Moreover, we found that contrary to the usual expectations, low-doped BDD containing sp² carbon hinders electron transfer, whereas in line with expectations, normally doped BDD containing sp² exhibits enhanced electron transfer. Surface analyses by X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS) and electrochemical methods are utilized to explain these unusual phenomena. This work indicates that the electrochemical properties of low-doped BDD containing sp² might be due partially to the high level of surface oxygen, the large work function, the low carrier density, and the existence of different types of sp² carbon.