Effect of temperature on the CO₂ splitting rate in a DBD microreactor

A novel plate-to-plate dielectric barrier discharge microreactor (micro DBD) has been demonstrated in CO₂ splitting. In this design, the ground electrode has a cooling microchannel to maintain the electrode temperature in the 263-298 K range during plasma operation. A small gap size between the electrodes of 0.50 mm allowed efficient heat transfer from the surrounding plasma to the ground electrode surface to compensate for heat released in the reaction zone and maintain a constant temperature. The effect of temperature on CO₂ conversion and energy efficiency was studied at a voltage of 6-9 kV, a frequency of 60 kHz and a constant CO₂ flow rate of 20 ml min^-1. The CO₂ decomposition rate first increased and then decreased as the electrode temperature decreased from 298 to 263 K with a maximum rate observed at 273 K. Operation at lower temperatures enhanced the vibrational dissociation of the CO₂ molecule as opposed to electronic excitation which is the main mechanism at room temperature in conventional DBD reactors, however it also reduced the rate of elementary reaction steps. The counterplay between these two effects leads to a maximum in the reaction rate. The power consumption monotonously increased as the temperature decreased. The effective capacitance of the reactor increased by 1.5 times at 263 K as compared to that at 298 K changing the electric field distribution inside the plasma zone.