CO₂ Decomposition in CO₂ and CO₂ /H₂ Spark-like Plasma Discharges at Atmospheric Pressure

In this work, a spark-like plasma discharge is ignited in pure CO₂ and in CO₂ /H₂ mixtures to investigate CO formation. Power pulsing is used to limit arc formation to sustain a high current transient "spark-like" plasma consisting of a mixed mode discharge comprising an initial current pulse ("spark") followed by a longer-lived glow mode thorough each half cycle of the applied voltage. In pure CO₂ , the efficiency ranged between 20-50 % for CO₂ conversions between 9-18 % for gas residence times of 100-600 ms. Adding H₂ as a co-reactant was investigated for a wide range of mixture ratios. The outlet gas was found to produce O₂ -free mixtures of CO/H₂ /CO₂ . Conversion rates in CO₂ /H₂ mixtures are found to be similar to pure CO₂ at equivalent residence times. The primary role of H₂ as a co-reactant is therefore found to be the removal of O₂ formed during dissociation of CO₂ . The energy cost of this dilution resulted in reduced efficiency for CO₂ conversion (from 41 to 18 %), which is correlated to the efficiency drop found for pure CO₂ conversion at lower flows. Opportunities for optimising this small volume "unit-cell" spark reactor are encouraged by the results presented. This approach could enable deployment of serial or parallel combinations of such reactors capable of dealing cost-effectively with the conversion of the larger CO₂ and CO₂ /H₂ volumes required in future industry applications.