Non‐oxidative methane conversion in diffuse, filamentary, and spark regimes of nanosecond repetitively pulsed discharge with negative polarity

Abstract Methane conversion for higher hydrocarbons was carried out in the diffuse, filamentary, and spark regimes of nanosecond repetitively pulsed discharge with negative polarity in a pin‐to‐plate reactor. The diffuse discharge was characterized as a regime with low‐plasma energy, and only trace hydrogen and C 2 H 6 were found in this regime. In filamentary regime, the conversion rate reached 2.2–7.6% with energy conversion efficiency (ECE) of 8.8–12.7%. Meanwhile the selectivity of C 2 H 6 , C 2 H 4 , C 2 H 2 , and C 3 were 24.3–18.6%, 9.3–7%, 5.6–7.3%, and 0–5%, respectively. As for the spark regime, C 2 H 2 became the main hydrocarbon product with the selectivity of 12.8%, conversion rate of 44.7–74.4% and ECE of 12.3%. Electrical measurements and ICCD photographs showed that the short pulse could prevent the streamer turning into spark discharge, and thus realize smooth transitions among each regime. Optical emission spectroscopy was used to investigate the plasma chemistry in each regime. It found that the highest spectral line, gas temperature, and electron density varied in these regimes. These results suggested that, comparing with electron impact reactions, the thermal chemistry became more and more important as the plasma energy increased.