Comparison of Approaches for CO ₂ Sequestration as Solid Carbon Products

The growing global climate crisis linked to the rising atmospheric CO₂ levels calls for urgent and innovative solutions. Fixing CO₂ as valuable solid carbon products, such as carbon nanofibers or nanotubes (CNFs or CNTs), offers a promising way to potentially achieve net-negative CO₂ emissions. However, direct CO₂-to-solid carbon faces significant thermodynamic and kinetic constraints, especially under mild reaction conditions. This mini-review compares three emerging approaches for CO₂ conversion into solid carbon: 1) using molten salt at high temperatures to produce CNFs or CNTs, 2) converting CO₂ to amorphous carbon with pyrophoric liquid metals at near room temperature, and 3) employing an electrocatalytic-thermocatalytic tandem process to produce CNFs at relatively mild temperatures. We examine the underlying principles, thermodynamic driving forces, and recent advances of each approach, and discuss the challenges and opportunities in catalyst development, reactor design, and energy management. We aim to highlight CO₂ fixation, facilitate net-negative CO₂ emissions, and stimulate more innovations for both environmental and economic benefits.