Catalytic Twist‐Spun Yarns of Nitrogen‐Doped Carbon Nanotubes

The treatment of free‐standing sheets of multiwalled carbon nanotubes (MWNTs) with a NH 3 /He plasma results in self‐supporting sheets of aligned N‐doped MWNTs (CN x ). These CN x sheets can be easily twist spun in the solid state to provide strong CN x yarns that are knottable, weavable, and sewable. The CN x yarns exhibit tunable catalytic activity for electrochemically driven oxygen reduction reactions (ORR), as well as specific capacitances (up to 39 F·g −1 ) that are 2.6 times higher than for the parent MWNTs. Due to a high degree of nanotube alignment, the CN x yarns exhibit specific strengths (451 ± 61 MPa·cm 3 ·g −1 ) that are three times larger than observed for hybrid CN x /MWNT biscrolled yarns containing 70 wt.% CN x in the form of a powder. This difference in mechanical strength arises from substantial differences in yarn morphology, revealed by electron microscopy imaging of yarn cross‐ sections, as well as the absence of a significant strength contribution from CN x nanotubes in the biscrolled yarns. Finally, the chemical nature and abundance of the incorporated nitrogen within the CN x nanotubes is studied as function of plasma exposure and annealing processes using X‐ray photoelectron spectroscopy and correlated with catalytic activity.