关键词: 介质阻挡放电, 交流弧放电, 氢气, 氨气, 发射光谱

Abstract:

At ambient pressure, the effect of plasma discharge mode and reactor structure on ammonia decomposition to hydrogen was investigated. Dielectric barrier discharge (DBD) and alternating current (AC) arc discharge were produced upon adjusting the structure of the plasma reactor. By studying the discharge images, the voltage-current waveforms and the optical emission spectra in two discharge modes, we found that the AC arc discharge was a spatially partially stronger discharge compared with DBD. The AC arc discharge had a higher power efficiency and higher electron density than the dielectric barrier discharge. The ammonia molecules were mainly transformed into NH₃^* in an electronic excited state, and the N―H bond ruptured upon collision with a high-energy electron in DBD. However, electrons with a high average electron energy upon AC arc discharge can rupture the N―H bond directly to form highly active NH₂ and NH species, which can enhance the ammonia decomposition reaction. Results show that AC arc discharge had better performance toward ammonia decomposition than dielectric barrier discharge. The ability of different reactor structures to decompose ammonia under AC arc discharge increased in the following order: tube-tube>tube-flat>point-flat>flat-flat. The ammonia conversion can be as high as 60% under the tube-tube AC arc discharge with an input power of 30 W and a gap distance of 6 mm, while it was only 4% under the flat-flat dielectric barrier discharge.

Key words: Dielectric barrier discharge, AC arc discharge, Hydrogen, Ammonia, Optical emission spectrum