Regulation of CO₂ molten salt capture and electrolysis to elemental carbon

High-temperature molten salt capture and electrolysis technology of CO₂ for the effective preparation of elemental carbon materials are considered to be an exceedinglyare gaining traction as promising carbon capture utilization and storage technology. The reason is their excellent selectivity and ease of operation, making them suitable for the effective preparation of elemental carbon materials from CO₂. Nonetheless, the current research on the kinetic mechanism of CO₂ capture in high-temperature molten salt systems is inadequate. Furthermore, the energy consumption and production costs associated with the process of preparing elemental carbon materials through CO₂ molten salt electrolysis are relatively high. Therefore, achieving efficient CO₂ capture in high-temperature molten salts and low-energy consumption electrolysis is very crucial. This paper delves into the thermodynamics of CO₂ capture by various alkali metals/alkaline earth metal oxides. It also compares the theoretical decomposition voltage and energy consumption of various alkali metals/alkaline earth metal carbonates. The capture behavior of CO₂ in typical binary chloride molten salts is also examined. The study further explores the thermodynamics of CO₂ capture in molten salts to carbonates and calculates the theoretical voltage and power consumption during carbonate electrolysis in a high-temperature molten salt system. The kinetics of CO₂ capture in typical CaCl₂-based molten salts are examined by advanced technologies such as online gas mass spectrometry, carbon–sulfur analyzer, X-ray diffraction, and energy spectroscopy. The effects of temperature and voltage on the electrolysis process, electrolytic energy consumption, and product structure of elemental carbon materials prepared by CO₂ electrolysis are investigated in typical ternary Na₂CO₃–K₂CO₃–Li₂CO₃ molten salts and ternary CaCl₂–NaCl–CaO molten salts using scanning electron microscopy (SEM), Raman spectroscopy, and constant voltage electrolysis. The results indicate that CaO outperforms alkali metal oxide as a CO₂ capture agent, and CaCO₃ obtained by energy and conversion exhibits the lowest theoretical decomposition voltage and electrolytic energy consumption. In a typical CaCl₂–3.0% CaO (mass fraction) molten salt, the CO₂ capture capacity is 0.016 gCO₂·g⁻¹. Compared with the Na₂CO₃–K₂CO₃–Li₂CO₃ molten salt, the CaCl₂–NaCl–CaO molten salt has a lower electrolysis voltage and energy consumption. Moreover, the current efficiency of the electrolytic elemental carbon material reaches up to 95.3%, with the minimum electrolytic energy consumption being only 14.1 kW·h·kg⁻¹ under the optimal conditions of 750 ℃ and 1.5 V. Therefore, this study provides a foundation for exploring CO₂ molten salt capture materials that combine excellent performance, low cost, and environmental friendliness. It also offers theoretical and data support for optimizing the process and reducing the cost of the actual electrolysis.