The construction of advanced electrode materials is key to the field of energy storage. Herein, a free-standing anatase titania (TiO₂) nanocrystal/carbon nanotube (CNT) film is reported using a simple and scalable sol-gel method, followed by calcination. This unique free-standing film comprises ultra-small TiO₂ nanocrystals (~ 5.9 nm) and super-aligned CNTs, with ultra-dispersed TiO₂ nanocrystals on the surfaces of the CNTs. On the one hand, these TiO₂ nanocrystals can significantly decrease the diffusion distance of the charges and on the other hand, the cross-linked CNTs can act as a three-dimensional (3D) conductive network, allowing the fast transport of electrons. In addition, the film is free-standing, without requiring electrode fabrication and additional conductive agents and binders. Owing to these above synergistic effects, the film is directly used as an anode in Li-ion batteries, and delivers a high discharge capacity of ~ 105 mAh·g^-1 at high rate of 60 C (1 C = 170 mA·g^-1) and excellent cycling performance over 2,500 cycles at 30 C. These results indicate that the free-standing anatase TiO₂ nanocrystal/CNT film affords a superior performance among the various TiO₂ materials and can be a promising anode material for fast-charging Li-ion batteries. Moreover, the TiO₂/CNT film exhibits an areal capacity of up to 2.4 mAh·cm^-2, confirming the possibility of its practical use.

Two-dimensional (2D) heterostructures based on the combination of transition metal dichalcogenides (TMDs) and transition metal oxides (TMOs) have aroused growing attention due to their integrated merits of both components and multiple functionalities. However, nondestructive approaches of constructing TMD-TMO heterostructures are still very limited. Here, we develop a novel type of lateral TMD-TMO heterostructure (NbS₂-Nb₂O₅-NbS₂) using a simple lithography-free, direct laser-patterning technique. The perfect contact of an ultrathin TMO channel (Nb₂O₅) with two metallic TMDs (NbS₂) electrodes guarantee strong electrical signals in a two-terminal sensor. Distinct from sensing mechanisms in separate TMOs or TMDs, this sensor works based on the modulation of surface conduction of the ultrathin TMO (Nb₂O₅) channel through an adsorbed layer of water molecules. The sensor thus exhibits high selectivity and ultrahigh sensitivity for room-temperature detection of NH₃ (ΔR/R = 80% at 50 ppm), superior to the reported NH₃ sensors based on 2D materials, and a positive temperature coefficient of resistance as high as 15%-20%/°C. Bending-invariant performance and high reliability are also demonstrated in flexible versions of sensors. Our work provides a new strategy of lithography-free processing of novel TMD-TMO heterostructures towards high-performance sensors, showing great potential in the applications of future portable and wearable electronics.