CO2 Reduction by Nanosecond-Plasma Discharges: Revealing the Dissociation's Time Scale and the Importance of Pulse Sequence

Power-to-chemical technologies with CO2 as feedstock recycle CO2 and store energy into value-added compounds. Plasma discharges fed by renewable electricity are a promising approach to CO2 conversion. However, controlling the mechanisms of plasma dissociation is crucial to improving the efficiency of the technology. We have investigated pulsed nanosecond discharges, showing that while most of the energy is deposited in the breakdown phase, CO2 dissociation only occurs after an order of microsecond delay, leaving the system in a quasi-metastable condition in the intervening time. These findings indicate the presence of delayed dissociation mechanisms mediated by CO2 excited states rather than direct electron impact. This "metastable" condition, favorable for an efficient CO2 dissociation, can be prolonged by depositing more energy in the form of additional pulses and critically depends on a sufficiently short interpulse time.