Plasma for nitrogen fixation by using N₂/O₂ mixture: Reaction pathway, energy flow, and plasma reactor

Abstract

When N2/O2 mixture is used for nitrogen fixation (NF), researchers believe that the Zeldovich mechanism is the main pathway for NO formation. However, there is still debate on whether N2 participates in the Zeldovich mechanism through vibrational excitation or electronic excitation of the N2(A) state. This ambiguity has led to uncertainty regarding which type of plasma can achieve higher efficiency. Furthermore, the most significant obstacle to plasma‐assisted NF is the high energy consumption. Gaining a deeper understanding of the energy flow in the discharge process is crucial for improving NF energy efficiency in the future. Therefore, this paper provides an overview of the research on these topics. Finally, various new plasma NF devices reported in recent years will also be discussed.

Importance of geometric effects in scaling up energy-efficient plasma-based nitrogen fixation

“…In order to operate their reactor efficiently, only ¼ of the gas had to pass through the plasma and the remaining ¾ acted as quenching gas. As a result, their NO concentration was lower but produced quite efficiently, 6,7 just like in our upscaled reactor.…”

“…In our reactors the gas is heated more uniformly through DC current, which allows for better control of the gas flow dynamics. 6,7…”

“…5,6 Additionally, Liu et al reviewed the reaction pathways, energy flow and performance of different plasma reactors for NO x production from N 2 /O 2 mixtures. 7 They discussed four different mechanisms playing a key role toward NO x production, i.e. , with dominant role of either electronically or vibrationally excited N 2 molecules, or a combination of both, and a dominant role of N( 2 D) excited atoms, dependent on the type of discharge generated in the plasma reactor.…”

“…Finally, they concluded that there is a need to develop new plasma devices where one can independently adjust the electron and gas temperature, to gain more insight in the mechanisms. 7 The reported NO x concentration and EC for plasma-based NO x production at various SEI values for different plasma types are summarized in Fig. 1.…”

Gliding arc discharge in combination with Cu/Cu2O electrocatalysis for ammonia production

“…As the arc slides downwards, the distance between the electrodes gradually increases, resulting in a decrease in the density of electron ions between the electrodes. This increases the relative resistance, ultimately leading to insufficient input power energy to sustain the continuous combustion of the arc channel [43]. At the end of the arc cycle, a new arc will be excited again at the narrowest point of the electrode, generating conductive particles and repeating this process [28,29].…”