Kinetics of High-Pressure CO₂ Splitting in Nanosecond Pulsed Discharges

We investigate CO₂ splitting using nanosecond repetitively pulsed discharges (NRP) in a high-pressure (5-12 bar) batch reactor. Product species were measured using gas chromatography. The yield and energy efficiency were determined for a range of processing times, pulse energy, and fill pressures. A zero-dimensional kinetic model was developed to understand the key reaction pathways for CO₂ conversion. Experimental results reveal, for long processing times, a saturation in yield and drop in efficiency, attributed to the increasing role of three-body recombination reactions. Detailed modeling reveals the presence of three-stage kinetics between pulses, controlled by electron-impact CO₂ dissociation, vibrational relaxation, and reversible neutral elementary kinetics. Transport effects are shown to be important at high pressures. Enhancing mixing at high pressures can avoid dissociating generated CO and increase efficiency. For fill pressures beyond 10 bar, CO₂ may transit into local supercritical states, where the plasma kinetics may bypass atomic oxygen pathways and directly convert CO₂ into O₂. This work provides an analysis of plasma-based high-pressure CO₂ conversion, which is of great relevance to future large-scale sustainable carbon capture, utilization, and storage.