A flexible, large-area three-dimensional porous N-doped carbon microtube (NCMT) sponge was prepared via a simple and low-cost process of pyrolyzing facial cotton. Due to its unique structure with a micron-scale hollow core and well-graphitized and interconnected porous walls, the NCMT sponge exhibits incomparable electrocatalytic activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) with a small potential difference of 0.63 V between the OER current density at 10 mA cm⁻² and the ORR current density at −3 mA cm⁻², which is the best to date.

Single-wall carbon nanotubes (SWCNTs) are ideal for fabricating transparent conductive films because of their small diameter, good optical and electrical properties, and excellent flexibility. However, a high intertube Schottky junction resistance, together with the existence of aggregated bundles of SWCNTs, leads to a degraded optoelectronic performance of the films. We report a network of isolated SWCNTs prepared by an injection floating catalyst chemical vapor deposition method, in which crossed SWCNTs are welded together by graphitic carbon. Pristine SWCNT films show a record low sheet resistance of 41 ohm □⁻¹ at 90% transmittance for 550-nm light. After HNO₃ treatment, the sheet resistance further decreases to 25 ohm □⁻¹. Organic light-emitting diodes using this SWCNT film as anodes demonstrate a low turn-on voltage of 2.5 V, a high current efficiency of 75 cd A⁻¹, and excellent flexibility. Investigation of isolated SWCNT-based field-effect transistors shows that the carbon-welded joints convert the Schottky contacts between metallic and semiconducting SWCNTs into near-ohmic ones, which significantly improves the conductivity of the transparent SWCNT network. Our work provides a new avenue of assembling individual SWCNTs into macroscopic thin films, which demonstrate great potential for use as transparent electrodes in various flexible electronics.