Power Pulsing To Maximize Vibrational Excitation Efficiency in N2 Microwave Plasma: A Combined Experimental and Computational Study

TitlePower Pulsing To Maximize Vibrational Excitation Efficiency in N2 Microwave Plasma: A Combined Experimental and Computational Study
Publication TypeJournal Article
Year of Publication2020
AuthorsS. van Alphen, V. Vermeiren, T.D Butterworth, D.CM van den Bekerom, G.J van Rooij, A. Bogaerts
JournalJournal of Physical Chemistry C, The
Volume124
Issue3
Pagination1765-1779
Date Published01/2020
Abstract

Plasma is gaining increasing interest for N2 fixation, being a flexible, electricity-driven alternative for the current conventional fossil fuel-based N2 fixation processes. As the vibrational-induced dissociation of N2 is found to be an energy-efficient pathway to acquire atomic N for the fixation processes, plasmas that are in vibrational nonequilibrium seem promising for this application. However, an important challenge in using nonequilibrium plasmas lies in preventing vibrational-translational (VT) relaxation processes, in which vibrational energy crucial for N2 dissociation is lost to gas heating. We present here both experimental and modeling results for the vibrational and gas temperature in a microsecond-pulsed microwave (MW) N2 plasma, showing how power pulsing can suppress this unfavorable VT relaxation and achieve a maximal vibrational nonequilibrium. By means of our kinetic model, we demonstrate that pulsed plasmas take advantage of the long time scale on which VT processes occur, yielding a very pronounced nonequilibrium over the whole N2 vibrational ladder. Additionally, the effect of pulse parameters like the pulse frequency and pulse width are investigated, demonstrating that the advantage of pulsing to inhibit VT relaxation diminishes for high pulse frequencies (around 7000 kHz) and long power pulses (above 400 μs). Nevertheless, all regimes studied here demonstrate a clear vibrational nonequilibrium while only requiring a limited power-on time, and thus, we may conclude that a pulsed plasma seems very interesting for energy-efficient vibrational excitation.

DOI10.1021/acs.jpcc.9b06053
Division

MaSF

Department

NFC

PID

c79f0847e9db94a70cf6472a37661b14

Alternate TitleJ. Phys. Chem. C

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