Characteristics of a corona discharge ignited by a MgO/NiO/Ni sandwich cathode with high secondary electron emission for VOC degradation

Abstract

In this paper, an improved corona discharge in air at atmospheric pressure is ignited by a MgO/NiO/Ni sandwich cathode with high secondary electron emission and is then employed for volatile organic compound degradation. Current–voltage characteristics, discharge images, and spectroscopic investigations are compared for two corona discharges with a MgO/NiO/Ni cathode and a Ni cathode, respectively. The discharge current with the MgO/NiO/Ni cathode is about 2.5–3.3 times larger than the one with the Ni cathode at various applied voltages from 12 to 19 kV. Besides, discharge images show that, as well as the expected glow discharge around the needle tips, luminous points also occur on the surface of the MgO/NiO/Ni cathode simultaneously, indicating that ionization and excitation processes take place around the cathode surface. This is attributed to the fact that an internal field within the oxide layer calculated by the measured surface potential, which is induced by positive charges accumulated on the oxide layers, is sufficient to induce field emission and further cause the improved corona discharge generation. Such improved corona discharge with the MgO/NiO/Ni cathode is then applied to toluene degradation, and the toluene degradation efficiency and energy yield are much higher than those with the Ni cathode, respectively.