Surface Chemistry Analysis of Carbon Nanotube Fibers by X‐Ray Photoelectron Spectroscopy

Abstract

Carbon nanotube (CNT) fibers are materials with an exceptional combination of properties, including higher toughness than carbon fibers, electrical conductivity above metals, large specific surface area (250 m2 g−1), and high electrochemical stability. As such, they are a key component in various multifunctional structures combining augmented mechanical properties with efficient interfacial energy storage/transfer processes. This work presents a thorough XPS study of CNT fibers subjected to different purification and chemical treatments, including spatially‐resolved micro XPS synchrotron measurements. The dominant feature is an inherently high degree of sp2 conjugation, leading to a strong plasmonic band and a semi‐metallic valence band lineshape. This high degree of CNT perfection in terms of longitudinal “graphitization” helps to explain reported bulk properties including the high electrical and thermal conductivity, and accessible quantum capacitance. There is also presence of organic impurities, mostly heavy carbonaceous molecules formed as by‐products during fiber synthesis and which are adsorbed on the CNTs. Sulfur, a promoter used in the CNT growth reaction, is found both in these surface impurities and associated with the Fe catalyst. The observation of strongly‐adsorbed surface impurities is consistent with the high ductility of CNT fibers, attributed to interfacial lubricity.

Origin of the electrocatalytic activity in carbon nanotube fiber counter-electrodes for solar-energy conversion

“…4.5 Â 10 À6 cm 2 s À1 are very close to the values obtained in the literature for highly efficient devices based on liquid electrolytes. 43,[60][61][62][63][64][65] This suggests that the electrodes are well-optimized; the typical mass transport limitation caused by the bulky nature of the Co 2+ /Co 3+ complexes is circumvented with the functionalisation of the CE. Regarding the electrochemical impedance spectroscopy study (EIS), 1-cells (Fig.…”

“…[16][17][18]27,28 In addition, the stability issue is even more critical in cobalt-based electrolytes, as they are prone to degrade. 42,43,[60][61][62][63][64][65] In this line, the low stability of Pt-cells is manifested by an increase of the redox potential and a decrease of J lim aer 10 LSV cycles -Fig. 2 and 3.…”

“…This is typically ascribed to the interaction with tert-butyl pyridine (TBP) and the ligand dissociation in ACN [74][75][76][77] along with Pt poisoning by air exposure. 42,43,[60][61][62][63][64][65] In contrast, 1-cells feature stable redox potentials over 30 cycles, showing a loss of J lim of <60% with respect to that of the fresh electrodes -Fig. 2.…”

“…4.5 × 10 -6 cm 2 /s are very close to the values obtained in literature for highly efficient devices based on liquid electrolytes. 43,[60][61][62][63][64][65] This suggests that the electrodes are well-optimized; the typical mass transport limitation caused by the bulky nature of the 𝐶𝑜 +2 /𝐶𝑜 +3 complexes is circumvented with the functionalisation of the CE. Regarding the electrochemical impedance spectrsocopy study (EIS), 1-cells (Figure S3) presents two semicircles of ≈250Ω and >400Ω in the Nyquist plot centered at 10 3 -10 4 Hz, corresponding to the charge transfer resistance (Rct) and at 10 -2 -1 Hz, corresponding to the bulk diffusion of the electrolkyte (Rdiff), respectively.…”

Fabrication of High Specific Electrical Conductivity and High Ampacity Carbon Nanotube/Copper Composite Wires

“…[ 8 ] However, when CNTs are combined to form a useable wire, these properties drop many order of magnitude. [ 9 ] Over the last decade there has been a great progress in creating CNTs wires using wet spinning (spinning using super‐acids [ 10–13 ] and surfactant‐based coagulation spinning [ 14–31 ] ) and dry spinning (aligned forest‐array spinning [ 32–54 ] and direct spinning of CNTs aerogel [ 40,55–87 ] ). Good quality CNTs wires are now commercially available.…”