Chemical Engineering Journal, Vol.362, 339-348, 2019
An improved corona discharge ignited by oxide cathodes with high secondary electron emission for toluene degradation
An improved corona discharge ignited by oxide cathodes (MgO/NiO/Ni cathode and NiO/Ni cathode) with high secondary electron emission is proposed for toluene degradation. The overall aim of this investigation is to explore the discharge characteristics and toluene degradation performance with oxide cathodes. Current-voltage characteristics results show that discharge currents with MgO/NiO/Ni cathode and NiO/Ni cathode are 2.6-17.4 times (applied voltage of 10.5-13.0 kV) and 1.2-13.5 times (applied voltage of 11.5-14.0 kV) larger, respectively, than the one with Ni cathode. Besides, from the discharge images and optical analysis, the ionization and excitation processes also take place around the oxide cathodes surface, except for the normal corona discharge around the discharge electrode (wires). Moreover, discharges with oxide cathodes exhibit remarkably better toluene degradation, mineralization, and energy performance than the one with Ni cathode. The toluene degradation efficiency, CO2 selectivity, and energy yield in the discharge with MgO/NiO/Ni cathode (P = 5.2 W) are 36.2%, 15.3%, 0.39 g.kWh(-1) higher, respectively, than with Ni cathode (P = 6.2 W), and they are 19.4%, 7.9%, 0.15 g.kWh(-1) higher, respectively, with NiO/Ni cathode (P = 5.5 W). It is believed that abundant secondary electrons emitted from oxide cathodes, which are induced by the intense electric field within the oxide layers caused by positive charges accumulated on the oxide layer surface, resulting the remarkable increase of discharge current. Besides, the emitted electrons cause extra gas discharge on the oxide layer surface, increasing the number and spatial distribution of electrons/reactive species in the whole discharge gap for good toluene degradation performance.