Atomically thin lubrication materials with anti-friction properties are crucial for reducing energy consumption and extending the service life of micro/nanoelectromechanical systems (MEMS/NEMS). However, achieving atomically thin films with ultra-low friction properties at the atomic/nanoscale even at the micrometer scale presents significant challenges. In this study, large-size and high-quality monolayer MoS₂ (ML MoS₂) was grown on SiO₂/Si substrate by chemical vapor deposition (CVD) method. Compared with mechanically exfoliated ML MoS₂, the CVD-grown ML MoS₂ (CVD-MoS₂) exhibits an ultra-lower friction coefficient (0.00904). Based on the stick–slip effect and Prandtl–Tomlinson (P–T) model, the reduction of puckering effect indicates stronger interaction and lower interface potential barrier in tip, CVD-MoS₂, and SiO₂/Si substrate system. Moreover, combining with the density functional theory calculations, the stronger interface adhesion and higher overall charge redistribution degree of CVD-MoS₂ can also be used to explain its ultralow friction state. This work will provide theoretical guidance for designing ultra-thin lubricating materials with ultra-low friction properties.

The stable operation of friction pairs is one of the most critical factors to maintain the stable operation of mechanical equipment. The real-time monitoring of lubrication state of the friction pair is very important to ensure the normal operation of machinery and realize early warning of wear failure, but it is also a big challenge. In this article, a new lubrication in-situ monitoring system is designed, which can monitor the lubrication and wear state of friction pairs through triboelectrification. The current acquisition module and friction coefficient acquisition module are integrated into a high vacuum hydrodynamic oil film thickness measuring instrument to explore the intrinsic relationship between triboelectricity and friction coefficient curves. When severe wear occurs, the oil film at the interface of the friction pair is no longer complete, and the accumulated triboelectric charge at the interface of the friction pair breaks down the air and causes discharge, the friction current suddenly increases from nanoampere level to microampere level. The time node when discharge occurs at the steel ball interface is well consistent with the time node when the friction pair suffers serious wear. According to the corresponding relationship between the triboelectric current and the friction and wear status of the friction pair, an early wear warning monitoring system is designed to monitor the operating status of the friction pair in real time through triboelectric signals. When the mechanical friction pair is worn, the early warning system will send out sound and light alarm signals and send real-time warnings to the mobile terminal through the Internet of Things, providing a new and reliable method for real-time monitoring of friction and wear of grease-lubricated machinery.

Ultra-low friction is crucial for the anti-friction, anti-wear, and long-life operation of nanodevices. However, very few two-dimensional materials can achieve ultra-low friction, and they have some limitations in their applications. Therefore, exploring novel materials with ultra-low friction properties is greatly significant. The emergence of ternary two-dimensional materials has opened new opportunities for nanoscale ultra-low friction. This study introduced nickel phosphorous trisulfide (NiPS₃, referred to as NPS), a novel two-dimensional ternary material capable of achieving ultralow friction in a vacuum, into the large nanotribology family. Large-size and high-quality NPS crystals with up to 14 mm × 6 mm × 0.3 mm dimensions were grown using the chemical vapor transport method. The NPS nanosheets were obtained using mechanical exfoliation. The dependence of the NPS nanotribology on layer, velocity, and angle was systematically investigated using lateral force microscopy. Interestingly, the coefficient of friction (COF) of NPS with multilayers was decreased to about 0.0045 under 0.005 Pa vacuum condition (with load up to 767.8 nN), achieving the ultra-low friction state. The analysis of the frictional dissipation energy and adhesive forces showed that NPS with multilayers had minimum frictional dissipation energy and adhesive forces since the interlayer interactions were weak and the meniscus force was excluded under vacuum conditions. This study on the nanoscale friction of a ternary two-dimensional material lays a foundation for exploring the nanoscale friction and friction origin of other two-dimensional materials in the future.

Superlubricating materials can greatly reduce the energy consumed and economic losses by unnecessary friction. However, a long pre-running-in period is indispensable for achieving superlubricity; this leads to severe wear on the surface of friction pairs and has become one of the important factors in the wear of superlubricating materials. In this study, a polyethylene glycol-tannic acid complex green liquid lubricant (PEG10000-TA) was designed to achieve macroscale superlubricity with an ultrashort running-in period of 9 s under a contact pressure of up to 410 MPa, and the wear rate was only 1.19 × 10^–8 mm³·N⁻¹·m⁻¹. This is the shortest running-in time required to achieve superlubricity in Si₃N₄/glass (SiO₂). The results show that the strong hydrogen bonds between PEG and TA molecules can significantly reduce the time required for the tribochemical reaction, allowing the lubricating material to reach the state of superlubrication rapidly. Furthermore, the strong hydrogen bond can share a large load while fixing free water molecules in the contact zone to reduce shear interaction. These findings will help advance the use of liquid superlubricity technology in industrial and biomedical.

Two-dimensional compounds combining group IV A element and group V A element were determined to integrate the advantages of the two groups. As a typical 2D group IV–V material, SiP has been widely used in photodetection and photocatalysis due to its high carrier mobility, appropriate bandgap, high thermal stability, and low interlayer cleavage energy. However, its adhesion and friction properties have not been extensively grasped. Here, large-size and high-quality SiP crystals were obtained by using the flux method. SiP nanosheets were prepared by using mechanical exfoliation. The layer-dependent and velocity-dependent nanotribological properties of SiP nanosheets were systematically investigated. The results indicate the friction force of SiP nanosheets decreases with the increase in layer number and reaches saturation after five layers. The coefficient of friction of multilayer SiP is 0.018. The mean friction force, frictional vibrations, and the friction strengthening effect can be affected by sliding velocity. Specially, the mean friction force increases with the logarithm of sliding velocity at nm/s scale, which is dominated by atomic stick-slip. The influence of frequency on frictional vibration is greater than speed due to the different influences on the change in contact quality. The friction strengthening saturation distance increases with the increase in speed for thick SiP nanosheets. These results provide an approach for manipulating the nanofriction properties of SiP and serve as a theoretical basis for the application of SiP in solid lubrication and microelectromechanical systems.

Polyaniline nanofibers (PANI NFs) are introduced to construct a wind-driven triboelectric nanogenerator (TENG) as a new power source for self-powered cathodic protection. PANI NFs serve as a friction layer to generate charges by harvesting wind energy as well as a conducting layer to transfer charges in TENG. A PANI NFs-based TENG exhibits a high output performance with a maximum output voltage of 375 V, short current circuit of 248 μA, and corresponding power of 14.5 mW under a wind speed of 15 m/s. Additionally, a self-powered anticorrosion system is constructed by using a PANI-based TENG as the power source. The immersion experiment and electrochemical measurements demonstrate that carbon steel coupled with the wind-driven TENG is effectively protected with an evident open circuit potential drop and negative shift in the corrosion potential. The smart self-powered device is promising in terms of applications to protect metals from corrosion by utilizing wind energy in ambient conditions.

Despite one-dimensional (1D) semiconductor nanostructure arrays attracting increasing attention due to their many advantages, highly ordered TiO₂ nanorod arrays (TiO₂ NR) are rarely grown in situ on Ti substrates. Herein, a feasible method to fabricate TiO₂ NRs on Ti substrates by using a through-mask anodization process is reported. Self-ordered anodic aluminum oxide (AAO) overlaid on Ti substrate was used as a nanotemplate to induce the growth of TiO₂ NRs. The NR length and diameter could be controlled by adjusting anodization parameters such as electrochemical anodization voltage, anodization time and temperature, and electrolyte composition. Furthermore, according to the proposed NR formation mechanism, the anodized Ti ions migrate and deposit in the AAO nanochannels to form Ti(OH)₄ or amorphous TiO₂ NRs under electric field, owing to the confinement effect of the template. Photoelectrochemical tests indicated that, after hydrogenation, the TiO₂ NRs presented higher photocurrent density under simulated sunlight and visible light illuminations, suggesting their potential use in photoelectrochemical water splitting, photocatalysis, solar cells, and sensors.