Unlocking the impact of electrode porosity on CO₂ splitting efficiency in porous DBD plasma reactors

The existence of non-thermal plasma within porous electrodes remains a topic of considerable debate within the scientific community. This study examines this phenomenon in CO₂ splitting using a coaxial dielectric barrier discharge (DBD) reactor with a porous stainless steel (PSS) tube as the internal electrode. Four primary configurations were examined: smooth stainless-steel electrodes, porous electrodes with 0.2 µm and 0.5 µm pores diameter, and boehmite-coated porous electrodes, both with and without packing. A comprehensive range of gas flow rates (20–50 ml/min) and CO₂ feed compositions were investigated. The CO₂ conversion rates, specific energy input (SEI), and energy efficiency (η) were evaluated and compared across the configurations above. The findings revealed that the 0.5 µm porous electrode in an empty configuration achieved the highest CO₂ conversion rate of 22.0 mmol CO₂/h (CO₂ conversion of 17.6 %) at a flow rate of 50 ml/min. The addition of argon to the feed gas resulted in enhanced CO₂ conversion and energy efficiency, particularly in packed reactors. The boehmite-coated electrodes demonstrated an intermediate performance between the empty and packed configurations, combining the advantages of both. The superior performance of porous electrodes can be attributed to the intensified plasma interactions within the pores and amplified electric field effects at the electrode surfaces. This research underscores the potential of porous DBD reactors with optimised gas flows and electrode configurations to enhance CO₂ conversion and energy efficiency. The use of porous electrodes, particularly when coated with boehmite, represents a promising avenue for the development of efficient plasma catalysts. This approach has the potential to reduce the costs associated with reactors and to increase conversion rates, thereby making it a viable option for the implementation of sustainable industrial processes.