Gold's crucial role in economic and technological developments has driven the industry towards underground mining, with air quality concerns challenging workers' safety. Currently, commercial solutions to assess air quality and safety in underground mines often suffer from low accuracy, high installation and maintenance costs, without providing data on noxious gases. To address these limitations, we developed a triboelectric self-powered sensing-platform (TESS) employing two distinct triboelectric nanogenerators (TENGs) modules to achieve power generation and wind-speed sensing function, with an ultra-low starting wind speed (0.32 m s<sup>-1</sup>), capable of operating for up to 3 months in underground mining tunnels. Wind-sensing capabilities are accrued by a horizontal turbine based on non-contact TENGs. Meanwhile, the TESS is powered by a distinct array of TENGs that operates via a new working mode, balancing the advantages of contact-separation and free-standing modes. Assisted by an optimized self-driven power management system, the TESS attains a charging power density of 16.36 mW m<sup>-2</sup>; this power is delivered every 166 s to a sensor node (temperature, relative humidity, pressure, and concentrations of CO, NO<sub>2</sub>, NH<sub>3</sub>), a data processing unit, and a LoRa transmitter. This work represents a leap forward in developing robust, cost-effective, battery-free, and wireless TENG-based environmental sensing platforms.
Contact electrification (CE) has been known for more than 2600 years, but its mechanism remains ambiguous, especially for liquid–solid cases. In previous studies on liquid–solid CE, the charges on a dielectric surface in a liquid environment have not been discussed due to the lack of proper measurement techniques, which may be responsible for the poor understanding on the liquid–solid CE. Here, the CE between dielectrics and different liquids, including deionized (DI) water, benzene, and cyclohexane (CYH), is performed by using dual harmonic Kelvin probe force microscopy (DH-KPFM). We focus on the transferred charges on the dielectric surface when it keeps in contact with a liquid. It is observed that the CE surface charges are screened in DI water, but not in organic solutions, suggesting that the electric double layer (EDL) is responsible for the screening of the surface charges. Moreover, it is revealed that the charge transfer in liquid–solid CE occurs not only in the contact but also during the separation process. Based on the observations, a model is proposed to describe the whole process of liquid–solid CE, in which the electron transfer plays a dominant role, and the adsorption of counterions in the EDL on the dielectric surface during separation is considered.
Inspired by the contact-separation mode triboelectric nanogenerator (TENG), we propose a technique for local surface charge density measurement based on atomic force microscopy. It is named as scanning TENG, in which a conductive tip tapping above a charged dielectric surface produces an AC between the tip and the dielectric bottom electrode due to electrostatic induction. The Fourier analysis shows that the amplitude of the first harmonic of the AC is linearly related to surface charge density. The results demonstrate that the scanning TENG is a powerful tool for probing nanoscale charge transfer in contact-electrification.
The conductance of multiwalled carbon nanotubes (MWNTs) was found to be quantized. The experimental method involved measuring the conductance of nanotubes by replacing the tip of a scanning probe microscope with a nanotube fiber, which could be lowered into a liquid metal to establish a gentle electrical contact with a nanotube at the tip of the fiber. The conductance of arc-produced MWNTs is one unit of the conductance quantum G0 = 2e2/h = (12.9 kilohms)-1. The nanotubes conduct current ballistically and do not dissipate heat. The nanotubes, which are typically 15 nanometers wide and 4 micrometers long, are several orders of magnitude greater in size and stability than other typical room-temperature quantum conductors. Extremely high stable current densities, J > 10(7) amperes per square centimeter, have been attained.
