Reactive species distribution characteristics and toluene destruction in the three-electrode DBD reactor energized by different pulsed modes

This work describes the plasma degradation process of toluene in the sliding dielectric barrier discharge (DBD) reactor based on three-electrode configuration energized by + pulse, -pulse, and +/- pulse, respectively. The overall aim of this investigation is to explore the streamer propagation characteristic, spatial distribution of reactive species, and VOC degradation performance of the sliding DBD plasma under different pulsed energization conditions. The experimental result shows that the sliding DBD plasma can be ignited when the discharge electrode (electrode #1) and counter electrode (electrode #3) are energized by +/- pulse (or + pulse) and -DC, respectively, while the electrode #2 is grounded. However, the sliding DBD phenomenon cannot be observed when the two air-exposed electrodes are driven by -pulse and + DC, respectively, which can be explained on the basis of different evolution mechanisms of positive and negative streamers. Optical analysis results indicate that bipolar pulse is beneficial to the ignition of DBD plasma, which can generate more reactive species compared with unipolar pulse. The toluene degradation efficiency and energy yield increase in the sequence -pulse < + pulse < +/- pulse in the three-electrode DBD reactor. It is worth noting that remarkable improvements in toluene degradation efficiency, energy yield, and CO2 selectivity can be observed for positive pulsed discharge when a three-electrode DBD reactor is employed instead of a two-electrode one, which can be attributed to the increased amount of reactive species within the entire inter-electrode distance due to sliding DBD effect. The postdischarge gas was monitored by FT-IR analysis, the main decomposition products including CO, CO2, H2O, HCOOH and discharge products such as O-3, N2O, and HNO3 can be identified regardless of the pulsed power and discharge reactor used.