Field parameters investigation of CO2 splitting in atmospheric DBD plasma by multi-physics coupling simulation and emission spectroscopy measurements

Abstract

CO2 dissociation in DBD plasma was thoroughly studied by combining dissociation experiments, multi-physics coupling simulation and in-situ emission spectroscopy measurements. Evolution of spatial–temporal distributions of key field parameters such as discharge mode, electron density (Ne), electron temperature (Te), intermediate concentration and reaction rates were analyzed in depth, to uncover the underlying reaction mechanism. The specific energy input (SEI) had a large impact on CO2 conversion and energy efficiency, and there was a trade-off between plasma power and gas flow rate. The highest CO2 conversion was achieved a maximum of 15.5% at SEI = 177 J·cm−3 in this work. Meanwhile, the spectrum shows that there was a large amount of CO2+, CO, O, and O2 in the plasma. In addition, we proposed and validated a reduced CO2 splitting plasma chemistry set to explore the field parameter and key reactin rates distributions. According to the multiphysics modelling, the discharge gap greatly affected the discharge form of DBD, which will subsequently influence CO2 splitting. In discharge gap > 1.75 mm formation of discharge channels remarkably decreased, and an over small discharge gap (δg < 1.25 mm) would restrain the electric field range, causing shorter motion path of charged particles and less free electrons, both of which hindered the conversion of CO2. A thinner dielectric layer can promote CO2 conversion, due to the reduction in breakdown field strength and increase of high-energy electrons. Electron impact reactions (e + CO2 → CO + O−, e− + CO2 → CO + O + e−), reactions of the excited CO2* (CO2 + CO2* → CO2 + CO + O, CO2*+O → CO + O2) mainly contributed to the CO2 dissociation.