Plasma-assisted CO 2 conversion: optimizing performance via microwave power modulation

Significant improvement in the energy efficiency of plasma-assisted CO 2 conversion is achieved with applied power modulation in a surfaguide microwave discharge. The obtained values of CO 2 conversion and energy efficiency are, respectively, 0.23 and 0.33 for a 0.95 CO 2 + 0.05 N 2 gas mixture. Analysis of the energy relaxation mechanisms shows that power modulation can potentially affect the vibrational–translational energy exchange in plasma. In our case, however, this mechanism does not play a major role, likely due to the low degree of plasma non-equilibrium in the considered pressure range. Instead, the gas residence time in the discharge active zone together with plasma pulse duration are found to be the main factors affecting the CO 2 conversion efficiency at low plasma pulse repetition rates. This effect is confirmed experimentally by the in situ time-resolved two-photon absorption laser-induced fluorescence measurements of CO molecular density produced in the discharge as a result of CO 2 decomposition.