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/H-2 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 H-2 as a co-reactant was investigated for a wide range of mixture ratios. The outlet gas was found to produce O-2-free mixtures of CO/H-2/CO2. Conversion rates in CO2/H-2 mixtures are found to be similar to pure CO2 at equivalent residence times. The primary role of H-2 as a co-reactant is therefore found to be the removal of O-2 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/H-2 volumes required in future industry applications.