A system and process for producing macro length carbon nanotubes is disclosed. A carbonate electrolyte including transition metal powder is provided between a nickel alloy anode and a nickel alloy cathode contained in a cell. The carbonate electrolyte is heated to a molten state. An electrical current is applied to the nickel alloy anode, nickel alloy cathode, and the molten carbonate electrolyte disposed between the anode and cathode. The resulting carbon nanotube growth is collected from the cathode of the cell.