Time-resolved optical emission spectroscopy in CO2 nanosecond pulsed discharges

Nanosecond repetitively pulsed discharges at atmospheric pressure have shown comparatively high performances for CO2 reduction to CO and O-2. However, mechanisms of CO2 dissociation in these transient discharges are still a matter of discussion. In the present work, we have used time-resolved optical emission spectroscopy to investigate the CO2 discharge progression from the initial breakdown event to the final post-discharge. We discover a complex temporal structure of the spectrally resolved light, which gives some insights into the underlying electron and chemical kinetics. We could estimate the electron density using the Stark broadening of O and C lines and the electron temperature with C+ and C++ lines. By adding a small amount of nitrogen, we could also monitor the time evolution of the gas temperature using the second positive system bands of N-2. We conclude that the discharge evolves from a breakdown to a spark phase, the latter being characterised by a peak electron density around 10(18) cm(-3) and a mean electron temperature around 2 eV. The spark phase offers beneficial conditions for vibrationally enhanced dissociation, which might explain the high CO2 conversion observed in these plasma discharges.

Automated summary

Nanosecond repetitively pulsed discharges at atmospheric pressure show high performances for CO2 reduction to CO and O-2. Using time-resolved optical emission spectroscopy, the study reveals a complex spectral structure and evolution from breakdown to spark phase with beneficial conditions for high CO2 conversion. The spark phase is characterized by peak electron density and temperature, aiding vibrationally enhanced dissociation.