Monolayer NbSe2 Favors Ultralow Friction and Super Wear Resistance.

The urgent demand for atomically thin, superlubricating, and super wear-resistant materials in micro/nanoelectromechanical systems has stimulated the research of friction-reducing and antiwear materials. However, the fabrication of subnanometer-thick films with superlubricating and super wear-resistant properties under ambient conditions remains a huge challenge. Herein, high-quality monolayer (ML) NbSe2 (∼0.8 nm) with ultralow friction and super wear resistance in an atmospheric environment was successfully grown by chemical vapor deposition (CVD) for the first time. Moreover, compared with few-layered (FL) NbSe2, ML NbSe2 has a lower friction coefficient and better wear resistance. On the basis of density function theory (DFT) calculations, the adhesion and the degree of charge transfer between ML NbSe2 and the substrate is larger than that of the topmost layer to the underlying layers of NbSe2 with two or more layers, which can be used to explain that the ML NbSe2 favors ultralow friction and super wear resistance.

A New Reversible Thermosensitive Liquid-Solid TENG Based on a P(NIPAM-MMA) Copolymer for Triboelectricity Regulation and Temperature Monitoring.

Intelligent and highly precise control of liquid-solid triboelectricity is of great significance for energy collection and electrostatic prevention. However, most of the traditional methods are irreversible and complex, greatly limiting their applicability. Here, a reversible thermosensitive liquid-solid triboelectric nanogenerator (L-S TENG) is assembled based on P(NIPAM-MMA) (PNM) copolymer for tunable triboelectrification. Through temperature regulation, the conformation between acylamino and isopropyl groups changes with the interfacial wettability and triboelectricity of PNM. When the temperature rises from 20 to 60 °C, the contact angle of PNM rises from 22.49° to 82.08°, and the output of the PNM-based L-S TENG shows a 27-fold increase. In addition, this transformation is reversible and repeatable with excellent durability for up to 60 days. Other organic liquids, such as glycol, exhibit positive response to temperature for this PNM-based L-S TENG. Polymers including polymethylmethacrylic, polytetrafluoroethylene, and polyimide are verified to not have such thermo-sensitivity properties. In addition, a droplet-based wireless warning system based on PNM is designed and actuated for monitoring specific temperature. The introduction of thermal PNM not only provides new material for reversible manipulation of L-S TENG, but also provides a new method for designing highly sensitive temperature warning sensors.

High-Output Triboelectric Nanogenerator Achieved through Conductive Layer Strategy for Motion Step Sensing.

As an emerging high-efficiency energy conversion device, improving the output of triboelectric nanogenerators (TENGs) is still a key method to promote practical application of TENGs. This paper systematically investigated the influence of component composition, thickness, and surface morphology of the metal conducting layer on the performance of triboelectric nanogenerators. It has been established that these three factors have a significant influence on the output performance of TENGs. Among the four common metals Au, Pt, Ag, and Cu, the triboelectric nanogenerator achieves its maximum output when utilizing Ag as the conducting layer, with optimal performance observed at a thickness of 278 nm. TENGs with nanostructured conducting layers have better output as the nanostructure amplifies the induction charging area, thereby effectively augmenting the performance of TENGs. In particular, when contrasted with a triboelectric nanogenerator utilizing copper foil as the conducting layer alongside poly(vinylidene difluoride) and Nylon-11 as friction layers in the common work, the short-circuit current of the triboelectric nanogenerator increased by 2.3 times, and the maximum short-circuit current reached 149 µA when the conducting layer was replaced with Ag, and the enhanced triboelectric nanogenerator successfully illuminated 1536 commercial LEDs. In addition, the TENG-based smart insoles combined with pedometers can realize signal sensing and the real-time recording of steps during exercise. This research provides a new simple and reliable method to further improve the output of the TENG.

Macroscale Superlubricity with Ultralow Wear and Ultrashort Running-In Period (∼1 s) through Phytic Acid-Based Complex Green Liquid Lubricants.

Liquid superlubricity has attracted much attention, due to its ability to significantly reduce friction on the macroscale. However, the severe wear caused by the long running-in period is still one of the bottlenecks restricting the practical application of liquid superlubricating materials. In this work, the obtained polyethylene glycol-phytic acid (PEG-PA) composite liquid lubricants showed outstanding superlubricating properties (µ ≈ 0.006) for Si3N4/glass friction pairs with an ultrashort running-in period (∼1 s) under high Hertzian contact pressure of ∼758 MPa. More importantly, even after up to 12 h (∼700 m of travel), only about 100 nm deep wear scars were found on the surface of the glass sheet (wear rate = 2.51× 10-9 mm3 N-1 m-1). From the molecular point of view, the water molecules anchored between the two friction pairs have extremely low shear force during the friction process, and the strong hydrogen bond interaction between PEG and PA greatly improves the bearing capacity of the lubricant. This work addresses the challenge of liquid superlubricant simultaneously exhibiting low shear force and high load-carrying capacity and makes it possible to obtain liquid superlubrication performance with an extremely short running-in time.