Mechanistic understanding of the direct air capture and conversion of CO₂ using Ru-K₂CO₃ based dual functional materials

Dual functional materials (DFMs) are an emerging class of materials that integrate a CO₂ capture and conversion functionality into a hybrid material. We present a DFM for direct air capture and conversion comprising of carbon nanofiber supported Ru nanoclusters with a homogeneous K₂CO₃ coverage. Investigation into the capture and conversion phases using gas analysis, in-situ XRD, operando quick-EXAFS, and density functional theory revealed an adsorption mechanism where CO₂ capture from air proceeds through the formation of KHCO₃. During conversion, desorbed CO₂ is activated by K-promoted Ru which acts as a recyclable intermediate, effectively re-adsorbing CO₂ as stable carbonyl species that are further converted to CH₄ at higher temperatures. We further reveal the previously unidentified trade-offs this mechanism imposes. Finally, an integrated heat exchange between endo- and exothermic processes during the conversion phase was demonstrated using operando reaction calorimetry.