Carbon nanotubes (CNTs) possess exceptional physical and chemical properties, including the highest tensile strength of any known material, superior conductivity, and impressive catalytic activity. However, the high cost and significant carbon footprint associated with conventional chemical vapor deposition (CVD) methods for synthesizing CNTs have hindered their widespread adoption. The price of commercially available CVD-synthesized CNTs ranges from $50,000 to $500,000, depending on factors such as purity and quantity. The inexpensive synthesis of a wide variety of high-purity carbon nanotubes (CNTs), by the transition metal nucleated electrolytic splitting of CO2 in molten carbonates, is reported resulting in two orders of magnitude lower production cost. Notably, CO₂ serves as the only reactant in this process, making it an effective method for both carbon utilization and decarbonization. The high-purity CNTs produced through this technique include a variety of structures and macro CNT assemblies. The process can also produce magnetic and doped CNTs. The synthesis of these diverse CNT types is achieved by adjusting electrochemical parameters, including the composition of the anode, cathode, and carbonate electrolyte, as well as controlling temperature and current density.