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Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

Mass transfer is an essential factor determining photocatalytic performance, which can be modulated by fluid field via manipulating the kinetic characteristics of photocatalysts and photocatalytic intermediates. Past decades have witnessed the efforts and achievements made in manipulating mass transfer based on photocatalyst structure and composition design, and thus, a critical survey that scrutinizes the recent progress in this topic is urgently necessitated. This review examines the basic principles of how mass transfer behavior impacts photocatalytic activity accompanying with the discussion on theoretical simulation calculation including fluid flow speed and pattern. Meanwhile, newly emerged viable photocatalytic micro/nanomotors with self-thermophoresis, self-diffusiophoresis, and bubble-propulsion mechanisms as well as magnet-actuated photocatalytic artificial cilia for facilitating mass transfer will be covered. Furthermore, their applications in photocatalytic hydrogen evolution, carbon dioxide reduction, organic pollution degradation, bacteria disinfection and so forth are scrutinized. Finally, a brief summary and future outlook are presented, providing a viable guideline to those working in photocatalysis, mass transfer, and other related fields.

Coronavirus disease 2019 (COVID-19) as a severe acute respiratory syndrome infection has spread rapidly across the world since its emergence in 2019 and drastically altered our way of life. Patients who have recovered from COVID-19 may still face persisting respiratory damage from the virus, necessitating long-term supervision after discharge to closely assess pulmonary function during rehabilitation. Therefore, developing portable spirometers for pulmonary function tests is of great significance for convenient home-based monitoring during recovery. Here, we propose a wireless, portable pulmonary function monitor for rehabilitation care after COVID-19. It is composed of a breath-to-electrical (BTE) sensor, a signal processing circuit, and a Bluetooth communication unit. The BTE sensor, with a compact size and light weight of 2.5 cm3 and 1.8 g respectively, is capable of converting respiratory biomechanical motions into considerable electrical signals. The output signal stability is greater than 93% under 35%-81% humidity, which allows for ideal expiration airflow sensing. Through a wireless communication circuit system, the signals can be received by a mobile terminal and processed into important physiological parameters, such as forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC). The FEV1/FVC ratio is then calculated to further evaluate pulmonary function of testers. Through these measurement methods, the acquired pulmonary function parameters are shown to exhibit high accuracy (>97%) in comparison to a commercial spirometer. The practical design of the self-powered flow spirometer presents a low-cost and convenient method for pulmonary function monitoring during rehabilitation from COVID-19.

Molecular dynamics simulations have revealed the important roles of hydration shells of ions transported through ultrathin carbon nanotubes (CNTs). In particular, ions driven by electric fields tend to drag their hydration shells behind them, while for ions transported by pressure, their hydration shells can actively drive them. Given the different binding strengths of hydration shells to ions of different sizes, these active roles of hydration shells affect the relative entry rates and driving speeds of ions in CNTs. [ABSTRACT FROM AUTHOR]

Contact electrification (triboelectrification) (CE) is a universal phenomenon in ambient environment and has been recorded for more than 2600 years. Nonetheless, the intrinsic mechanism of CE still remains controversial. Herein, based on first‐principles theory, the underlying mechanism in CE is systematically investigated between metallic MXenes and semiconductive MoS2. The results show that the work functions of contacting materials dominate the direction of electron transfer during CE process. That is, the electron will be transferred from the material with low work function to the one with high work function. The theoretical prediction is verified experimentally through investigating triboelectric probes based on MXenes and MoS2 nanomaterials. Additionally, it is noted that the interfacial potential barrier and the work function difference together modulate the amount of transferred electron. Electron transfer mainly occurs in the repulsive forces region where the interaction distance between the two materials is shorter than the normal bonding length. The quantum calculation results agree well with the Wang transition theory. Furthermore, it is also noticed that, due to the wave‐particle duality of electron, electron transfer will obviously occur at the attractive force region when the two contacting materials exhibit a larger work function difference. [ABSTRACT FROM AUTHOR]

Profited from the rapid development of flexible skin‐like electronic materials and artificial intelligent technology, remarkable achievements have been witnessed in wearable health monitoring devices in recent years. The wearable intelligent systems featured with tailored structures and compositions as well as enriched functions enable human beings to access to next‐generation closed‐loop platform for early disease prevention and diagnosis. In this context, this mini‐review focuses on the recent progress and applications of flexible wearable intelligent health monitoring devices. Specifically, the basic sensing mechanisms and corresponding property requirements for wearable healthcare devices are examined firstly. Secondly, the versatile applications of advanced wearable devices for detecting temperature, heart rate, blood pressure and glucose are scrutinized exclusively. Finally, a brief summary is presented accompanying with future outlook in terms of material preparation, mechanism development and integration design of monitoring systems. This manuscript is expected to provide critical guidelines to those working in skin‐like electronics, flexible sensors, wearable intelligent devices, health monitoring and other related disciplines, especially for the beginners. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) have high potential in self-powered sensing and energy harvesting applications. In general, TENGs' internal source resistance is high, and their output power varies under different load resistance values. Therefore, a resistance box is required to evaluate their energy harvesting performance and obtain the power curve under different load values. The load tuning process is usually performed by hand. This repetitive process is time-consuming and error-prone. Consequently, an Automated Power Evaluation Workbench (APEW) is developed, making the resistance switching and power measuring process program-controlled. The resistance value is resolved using the Octal decomposition principle. In addition, a resistance synthesis algorithm is proposed to alter the resistance value with a minimum step of 1 Ohm. The target resistance value is physically synthesized by relay switching, while digital lines control the relays. The proposed APEW is then evaluated experimentally, and the obtained results are compared with those of the traditional manual switching approach. It is deduced that the two power curves are almost identical. Therefore, it is believed that the proposed APEW will play a crucial role in TENG's further development. [ABSTRACT FROM AUTHOR]

Highlights: [•] Metal-semiconductor-metal (MSM) structure detectors with diverse finger spacings were fabricated on the sputtered TiO2 films. [•] High quality TiO2 films and good Au/TiO2 Schottky contacts were achieved. [•] The detectors exhibit lower dark current and higher UV-to-visible rejection ratio. [•] The mechanism of diverse finger spacing on the device performances is analyzed. [•] The detectors are promising in commercial production due to low cost and ease of fabrication process. [ABSTRACT FROM AUTHOR]