Combining surface and gas phase in situ diagnostics to decouple plasma-surface interaction processes for CO2 conversion

Efficiently recycling CO2 through plasma processes requires preventing reverse reactions that reform CO2 from CO. To achieve this, it is possible to combine plasma with catalytic materials and/or ionic membranes (such as MIEC, Mixed Ionic Electronic Conductors or SOEC, Solid Oxide Electrolyzer Cells types). Whether they are catalysts or MIECs, these materials can be activated by heating. Consequently, when coupled with plasma, it can be challenging to distinguish the actual effect of the plasma on these materials from that of the simple heating induced by the plasma. In this work, in situ diagnostics of the gas phase (OES, in situ FTIR) and surface (transmission FTIR, Raman scattering) are used within a single low-pressure DC glow discharge plasma source to study plasma-surface interaction processes. Another radio frequency plasma source can also be used to achieve higher dissociation rates. Whether in the DC glow discharge or the RF discharge, the electric field can be determined either by floating probe measurements or by an emission line ratio method. Pellets of CeO2 (catalyst support) and BSFCo (MIEC-type membrane) or YSZ (SOEC type membrane) are exposed to CO2 and O2 plasmas to investigate the formation of carbonates and their desorption under plasma conditions. The lifetimes and densities of oxygen atoms are obtained by OES by modulating the discharge current. The gas temperatures, as well as the vibrational temperatures of CO2 and CO, are obtained by infrared absorption. Finally, the performance of CO2 conversion and oxygen permeation through the membranes are also evaluated using the same materials and under the same plasma conditions. By combining all these data, the role of heating, oxygen atom flux, and vibrational excitation of molecules on surface reactivity and membrane permeation flux can be evaluated.