Bifunctional Li₄SiO₄ nanowires via one-pot synthesis for low-concentration CO₂ capture and thermochemical energy storage

The practical application of lithium silicate (Li₄SiO₄) in high-temperature CO₂ capture is limited by its deteriorated sorption performance under low-concentration CO₂ atmospheres and poor long-term cycling stability. Additionally, its inherent powder form poses significant challenges for industrial implementation. Meanwhile, as a thermochemical energy storage material, its stability is equally crucial. To address these issues, this study developed a novel Li₄SiO₄ sorbent featuring nanowire-like Li₄SiO₄ crystallites on the particle surface by utilizing mixed lithium sources (LiOH/LiNO₃) and pumice (PU). The synthesized Li₄SiO₄ not only retains the porous granular structure of pumice but also exhibits excellent sorption performance and regeneration stability under low CO₂ concentrations. The results demonstrate that when the molar ratio of LiOH/LiNO₃ is 7:3, the synthesized Li₄SiO₄ particles (PU-Li₄SiO₄-0.7LH/0.3LN) exhibit nanowire-like Li₄SiO₄ crystallites on the particle surface. Under conditions of 600 °C and 20 vol% CO₂ concentration, it achieves a sorption capacity of 29.5 wt% and a thermochemical storage capacity of 629.2 kJ/kg, significantly surpassing pure Li₄SiO₄. Moreover, PU-Li₄SiO₄-0.7LH/0.3LN demonstrates remarkable sorption-regeneration stability. After 150 cycles of reaction at 20 vol% CO₂ concentration, the sorption capacity of PU-Li₄SiO₄-0.7LH/0.3LN decreased only from 21.4 wt% to 19.9 wt%. This excellent performance is attributed not only to the nanowire-like Li₄SiO₄ crystallites providing abundant sorption sites, but also to the natural porous structure of pumice offering stable gas transport channels.