Lili Zhang

Understanding the catalyst-assisted etching mechanisms of carbon nanotubes (CNTs) is essential for structure tailoring and stability enhancement. This process occurs in an oxidizing atmosphere with catalyst nanoparticles (NPs) in direct contact with the nanotubes, however, its atomic-scale mechanisms have long been overlooked due to the challenge of capturing real-time dynamics at the CNT-NP interface. Using atmospheric-pressure environmental transmission electron microscopy, we grow CNTs directly from cobalt NPs to construct a well-defined CNT-NP interface, enabling us to investigate the etching dynamics in real time. We demonstrate that catalytic oxidation at this interface efficiently etches CNTs under mild oxidative conditions, with etching rates approximately six times higher than those of direct oxidation and an activation energy of 1.9 eV. Orthorhombic Co₃C is precisely identified as the active phase of the catalysts during oxidative etching, and it remains stable until the CNT is completely consumed. Contrary to the conventional solid-vapor gasification mechanism, we reveal a solid-solid-vapor (SSV) catalytic etching mechanism for CNT oxidation, which inherently involves metal-mediated carbon gasification. Moreover, even when starting as an oxide, the NP is converted into a carbide via the SSV mechanism through chemical reaction with the attached CNT.

Carbon nanotubes (CNTs) have attracted intense research interest owing to their unique one-dimensional structure and exceptional properties. However, when individual CNTs are assembled to macrostructures such as films and fibers, their electrical performance often deteriorates significantly. This review offers a comprehensive look at the recent progress in the electrical properties and measurement techniques of CNTs, ranging from individual nanotubes to their assemblies. Firstly, we explore the methods for measuring the electrical properties of individual CNTs, including scanning tunnelling microscopy, electron microscope-based nanoprobes, and measurements using nanodevices. Secondly, we examine how structural characteristics of CNTs (e.g., chirality, diameter, and defects) influence their electrical behaviors. A critical comparison between individual CNTs and their assemblies reveals the difficulties in transferring the electrical properties from nanoscale to bulk materials. Finally, we put forward strategies to boost the electrical conductivity of CNT assemblies and also sketch out future research and development directions.

Phase-pure ultrafine W₂C nanostructures are promising electrocatalysts but face synthesis challenges due to unclear formation mechanisms and harsh thermodynamics. Here, we reveal the formation mechanism of ultrathin W₂C nanowires (NWs) confined in the cavity of single-wall carbon nanotubes (SWCNTs) at the atomic scale by combined in situ transmission electron microscopy and density functional theory calculations. It was found that the hollow core of SWCNTs can control the phase, axial orientation, and diameter of W₂C NWs. Leveraging this mechanism, we synthesized SWCNT-encapsulated W₂C NWs, WS₂-W₂C heterostructures, and WS₂ NWs (1D@1D), which assembled into free-standing hybrid films. The integrated W₂C NWs@SWCNT membrane was primarily tested, exhibiting a low overpotential of 44 mV to reach a current density of 10 mA cm^-2 and outstanding durability (500 h at a high current density of 250 mA cm^-2 in acidic conditions).