Mechanistic Insights into CO₂ Adsorption of Li₄SiO₄ at High Temperature

The development of materials with high adsorption capacity for capturing CO₂ from industrial exhaust gases has proceeded rapidly in recent years. Li₄SiO₄ has attracted attention due to its low cost, high capture capacity, and good cycling stability for direct high-temperature CO₂ capture. Thus far, the CO₂ adsorption mechanism of Li₄SiO₄ is poorly understood, and detailed phase transformations during the CO₂ adsorption process are missing. Here, aided by in situ X-ray diffraction and in situ Raman spectroscopy, we find that Li₄SiO₄ reacts with CO₂ to form Li₂SiO₃ and Li₂CO₃ in CO₂ atmosphere at 973 K, with no detectable involvement of crystalline Li₂O during the adsorption process. Moreover, we observe a formation of stepped structures in the Li₄SiO₄ surface after CO₂ adsorption by scanning electron microscopy. To illustrate the formation of stepped structures, we propose a modified double-shell mechanism, suggesting a possible two-dimensional nucleation and growth of Li₂CO₃. This work provides a deeper understanding of the CO₂ adsorption mechanism and paves a way for further optimization of Li₄SiO₄-based adsorbents.