Beyond electron impact: dissociation driven by molecular collisions in CO2 nanosecond pulsed plasmas

The efficient conversion of CO2 into value-added chemicals is a central challenge in green chemistry and sustainable process engineering. Non-thermal plasmas attract increasing interest as they enable chemical activation under mild conditions and offer direct compatibility with electrified, renewable-energy-driven processes. Recent experiments have shown that CO2 conversion in atmospheric pressure nanosecond pulsed discharges peaks on the microsecond timescale, when the electron density is already negligibly small. Elucidating the origin of this delayed conversion is essential for the development of energy-efficient plasma reactors for CO2 processing. In this work, we develop a 0.5D kinetic model, where the species’ concentrations and the plasma properties are spatially averaged over a volume of varying radius, that expands/contracts as the pressure in the discharge channel is higher/lower than the background gas pressure. We show that electronic and vibrational excitation by electron impact during the discharge initiate a cascade of energy-transfer processes that ultimately increase the gas temperature, allowing high-temperature chemistry to occur microseconds after discharge. Moreover, an explicit treatment of channel dynamics is essential, as it strongly influences the recombination kinetics during the afterglow. Our results challenge the conventional picture of electron-impact dissociation as the dominant mechanism in atmospheric pressures CO2 nanosecond discharges. These findings open new perspectives to attain operating regimes with high CO2 yield and competitive energy efficiency, for example by optimizing the pulsing patterns, specially in the context of future devices integrating plasma decomposition with product separation.