CO₂ Conversion Performance of Pulse Micro-Gap Dielectric Barrier Discharge Reactor

The CO₂ concentration in the atmosphere is one of attributing factors to climate change. Therefore, many attempts have been made not only to reduce the CO₂ emission but also to utilize the CO₂ into valuable syngas. DBD reactors are of great interest for CO₂ conversion into CO and O₂ because they operate at atmospheric pressure and are simple to scale up for industrial application. However, the conversion and energy efficiency of CO₂ decomposition using DBD reactors are still limited. Several approaches have been investigated to achieve higher CO₂ conversion and energy efficiency, including modifying the reactor design such as discharge gap, discharge length, dielectric material, electrode material, and changing the plasma operating conditions such as applied frequency, applied power, and gas flow rate. Introducing packing materials into the DBD reactor has also been performed to increase CO₂ conversion and energy efficiency of the DBD reactor. However, it requires the use of high-cost catalytic materials. DBD reactor with discharge gap of micrometer range can enhance the plasma performance and increase CO₂ conversion. However, this higher CO₂ conversion comes at the cost of high specific energy input (SEI). Utilizing a pulse power supply can also enhance the CO₂ conversion by increasing the production of radical species on the plasma that performed the CO₂ decomposition.<br/>This study investigates the influence of micro-gap discharge length combined with a pulse power on the conversion and efficiency of CO₂ decomposition at various SEI. CO₂ decomposition was performed using a 250 µm gap cylindrical DBD plasma reactor powered by an impulse high voltage power supply. Pure CO₂ gas was sent through the DBD reactor as the feed gas, and its flow rate was controlled by mass flow controllers. A two-channel micro-gas chromatograph (GC) was employed to analyze the composition of feed gas and product gas. Micro-GC measurement data were then used to calculate the CO₂ conversion. The discharge power was controlled by varying the applied voltage to the DBD reactor. The applied voltage was measured by a high voltage probe, and the current was measured by a current probe. The voltage and current signal were subsequently recorded by a digital oscilloscope. These signals were then analyzed to determine the electrical characteristics of the discharge, such as discharge power, capacitance, transferred charge, burning voltage, and estimated reduced electric field. The ratio of the discharge power to the gas flow rate defines SEI, which determines the energy efficiency of CO₂ conversion. The electrical characteristics were further used to analyze the effect of plasma conditions on CO₂ con<br/>The micro-gap size seems to enhance the electric field inside the reactor while the use of a pulse power supply increases the energy efficiency, consequently allowing us to achieve a high value of CO₂ conversion at relatively low SEI. The highest CO₂ conversion of 51.42% was achieved at SEI of 154.74 kJ/L, corresponding to an energy efficiency of 4.15%. At a similar SEI value, it was found that lower gas flow rate and discharge power give better conversion performance than higher gas flow rate and discharge power. The results of this study also suggest that the gas flow rate, which controls the residence time, seems to be a more critical factor in achieving higher CO₂ conversion than discharge power, which controls the overall peak-to-peak value of discharge current. The comparable conversion value achieved from this study implies that pure CO₂ decomposition using a micro-gap DBD reactor could be more favorable than a DBD reactor with expensive packing material for industrial application.