Dominant role of CaCl2 in integrated CO2 capture and utilization (ICCU-RWGS) in chloride-based molten salts

Integrated CO 2 capture and utilization (ICCU) in chloride-based molten salts provides a promising solar-driven pathway toward carbon-neutral syngas production, yet the mechanistic role of chloride components remains poorly understood. Here, we demonstrate that CaCl 2 governs both reaction kinetics and pathway selection by tuning the solubility equilibrium of CaO and CaCO 3 . In CaCl 2 -NaCl-KCl molten systems, moderate CaCl 2 contents (40–60 wt%) markedly enhance CO yield (from 2.4 to 5.8 mmol g −1 ) and CO 2 conversion (up to 78%), whereas excessive CaCl 2 (>60 wt%) suppresses both capture and conversion. In situ spectroscopy and kinetic analysis reveal that CaCl 2 -mediated dissolution of carbonate species shifts the reaction mechanism from the solid-state formate route to a homogeneous RWGS pathway, accelerating CO formation. These findings uncover a previously overlooked function of molten salts as active chemical regulators rather than passive heat carriers and establish a solubility-governed framework for designing solar-compatible ICCU systems with tunable performance and enhanced stability.