Electronic-type-separated SWCNTs thin-films were used to demonstrate that the strength of the redox potential of dopants influences their electrical conductivity enhancement.

A process to fabricate carbon nanotube (CNT) wires with diameters greater than 1 cm and continuous current carrying capability exceeding 20 A is demonstrated. Wires larger than 5 mm are formed using a multi-step radial densification process that begins with a densified CNT wire core followed by successive wrapping of additional CNT material to increase the wire size. This process allows for a wide range of wire diameters to be fabricated, with and without potassium tetrabromoaurate (KAuBr4) chemical doping, and the resulting electrical and thermal properties to be characterized. Electrical measurements are performed with on/off current steps to obtain the maximum current before reaching a peak CNT wire temperature of 100 °C and before failure, yielding values of instantaneous currents in excess of 45 A for KAuBr4 doped CNT wires with a diameter of 6 mm achieved prior to failure. The peak temperature of the wires at failure (∼530 °C) is correlated with the primary decomposition peak observed in thermal gravimetric analysis of a wire sample confirming that oxidation is the primary failure mode of CNT wires operated in air. The in operando stability of doped CNT wires is confirmed by monitoring the resistance and temperature, which remain largely unaltered over 40 days and 1 day for wires with 1.5 mm and 11.2 mm diameters, respectively. The 100 °C continuous current rating, or ampacity, is measured for a range of doped CNT wire diameters and corresponding linear mass densities ρL. To describe the results, a new form of the fuse-law, where the critical current is defined as I∝ρL3/4, is developed and shows good agreement with the experimental data. Ultimately, CNT wires are shown to be stable electrical conductors, with failure current densities in excess of 50 A in the case of a convectively cooled 11.2 mm doped CNT wire, and amenable for use in applications that have long-term, high-current demands.

Densification and chemical doping with KAuBr 4 are shown to improve the electrical conductivity of commercially scaled CNT wires by a factor of 6 to values greater than 1 MS/m, while increasing the failure current density by 67% to 35 ± 3 MA/m 2 . The electrical conductivity retention is quantified via measuring changes in the conductivity during increasing applied current densities (working conductivity) and at room temperature after current exposure (resting conductivity). CNT wires doped with KAuBr 4 exhibit no change in resting conductivity after application of current densities up to 32 MA/m 2 , which exceeds that of the as-received material by more than 3 times. The mechanism by which KAuBr 4 doping improves the electrical stability of CNT conductors at higher current densities was probed via analysis of CNT wires treated with various thermal oxidation and doping procedures. Energy-dispersive X-ray spectroscopy was used to determine the elemental composition of KAuBr 4 -doped CNT wires after thermal oxidation to 400 °C, demonstrating the presence of residual chemical dopants near the onset temperature of CNT conductor failure. Therefore, enhanced KAuBr 4 -doped and densified CNT wire performance is attributed to the inherent thermal stability of KAuBr 4 and its decomposition cascade into other chemically active dopants. Overall, the thermal stability of the chemical dopant is a critical factor for high current CNT conductor applications.