Defect engineering is widely applied in transition metal dichalcogenides (TMDs) to achieve electrical, optical, magnetic, and catalytic regulation. Vacancies, regarded as a type of extremely delicate defect, are acknowledged to be effective and flexible in general catalytic modulation. However, the influence of vacancy states in addition to concentration on catalysis still remains vague. Thus, via high throughput calculations, the optimized sulfur vacancy (S-vacancy) state in terms of both concentration and distribution is initially figured out among a series of MoS2 models for the hydrogen evolution reaction (HER). In order to realize it, a facile and mild H2O2 chemical etching strategy is implemented to introduce homogeneously distributed single S-vacancies onto the MoS2 nanosheet surface. By systematic tuning of the etching duration, etching temperature, and etching solution concentration, comprehensive modulation of the S-vacancy state is achieved. The optimal HER performance reaches a Tafel slope of 48 mV dec–1 and an overpotential of 131 mV at a current density of 10 mA cm–2, indicating the superiority of single S-vacancies over agglomerate S-vacancies. This is ascribed to the more effective surface electronic structure engineering as well as the boosted electrical transport properties. By bridging the gap, to some extent, between precise design from theory and practical modulation in experiments, the proposed strategy extends defect engineering to a more sophisticated level to further unlock the potential of catalytic performance enhancement.

1wileyonlinelibrary.com schemes, the fl exible functional sensors are competitive and attractive candidates for promoting the advancement of sensing system. Recently, for the achievement of sensing devices, the printing technique has attracted widespread attention and been pursued to deposit various materials, like carbon materials, [ 13,23,24 ] polymers, [ 25,26 ] metals, [ 12,27 ] and semiconductors, [ 28,29 ] because the process is low energy consumption while maintaining the unique properties of the materials. By this way, the fl exible devices can be cheaper and easily produced.Graphite, one of carbon allotropes, has been increasing wide and keen interests of researchers, due to a wonder material of graphene. [ 9,[30][31][32] Pencil, a day-to-day material, is a nanocomposite of graphite and intercalated clay. [33][34][35] Being layered or pelleted, pencil lead can be exfoliated by using a gentle force. The drawing process can easily deposit graphite onto a rough paper, which contains massive amounts of cellulose fi bers and offer a naturally porous structure. [ 13,36 ] Pencil-trace drawn on printing papers is perhaps the simplest and easiest way of constructing graphite-based devices. The pen-on-paper (PoP) approach, a basic printing technique, offers a unique method to fabricate fl exible devices, such as strain sensors, [ 35 ] biosensors, [ 19,37 ] microfl uidic chips, [ 38 ] electronic devices, [ 34,39 ] photoconductive sensors, [ 29,40 ] and energy-storage devices. [ 33,41,42 ] Most of these devices have a response to force-induce changes in capacitance [ 33 ] and resistivity. [ 35 ] The microcontact-reversible sensing can effectively translate the microstructural deformations into electrical signals on active fl exible substrates. [ 6,9,43,44 ] As the potential to make fl exible, lightweight, portable, biocompatible, economical, and environment-friendly products, the PoP approach has an important role on the breakthroughs toward fl exible and wearable sensing devices.Herein, we demonstrate that the application of PoP approach can be expanded further to crucial fl exible sensing devices. We evaluated the repeatability of bending-unbending and the robustness of the strain sensors applied by loading. The strain sensors have a rapid respond to microdeformation changes and can be used to monitor various structural change and even human motion through facilitative and effective installing designs. Typically, the microdeformation of <0.13% strain can be detected. Compared with the recently reported fl exible sensing devices, the strain sensors behave signifi cant Flexible and Highly Sensitive Strain Sensors Fabricated by Pencil Drawn for Wearable MonitorXinqin Liao , Qingliang Liao , Xiaoqin Yan , Qijie Liang , Haonan Si , Minghua Li , Hualin Wu , Shiyao Cao , and Yue Zhang * Functional electrical devices have promising potentials in structural health monitoring system, human-friendly wearable interactive system, smart robotics, and even future multifunctional intelligent room. Here, a low-cost fabrication s...

We establish a powerful poly(4-styrenesulfonate) (PSS)-treated strategy for sulfur vacancy healing in monolayer MoS2 to precisely and steadily tune its electronic state. The self-healing mechanism, in which the sulfur vacancies are healed spontaneously by the sulfur adatom clusters on the MoS2 surface through a PSS-induced hydrogenation process, is proposed and demonstrated systematically. The electron concentration of the self-healed MoS2 dramatically decreased by 643 times, leading to a work function enhancement of ∼150 meV. This strategy is employed to fabricate a high performance lateral monolayer MoS2 homojunction which presents a perfect rectifying behaviour, excellent photoresponsivity of ∼308 mA W−1 and outstanding air-stability after two months. Unlike previous chemical doping, the lattice defect-induced local fields are eliminated during the process of the sulfur vacancy self-healing to largely improve the homojunction performance. Our findings demonstrate a promising and facile strategy in 2D material electronic state modulation for the development of next-generation electronics and optoelectronics.

Stretchable and multifunctional sensors can be applied in multifunctional sensing devices, safety forewarning equipment, and multiparametric sensing platforms. However, a stretchable and multifunctional sensor was hard to fabricate until now. Herein, a scalable and efficient fabrication strategy is adopted to yield a sensor consisting of ZnO nanowires and polyurethane fibers. The device integrates high stretchability (tolerable strain up to 150%) with three different sensing capabilities, i.e., strain, temperature, and UV. Typically achieved specifications for strain detection are a fast response time of 38 ms, a gauge factor of 15.2, and a high stability of >10 000 cyclic loading tests. Temperature is detected with a high temperature sensitivity of 39.3% °C−1, while UV monitoring features a large ON/OFF ratio of 158.2. With its fiber geometry, mechanical flexibility, and high stretchability, the sensor holds tremendous prospect for multiparametric sensing platforms, including wearable devices.

A stretchable‐rubber‐based (SR‐based) triboelectric nanogenerator (TENG) is developed that can not only harvest energy but also serve as self‐powered multifunctional sensors. It consists of a layer of elastic rubber and a layer of aluminum film that acts as the electrode. By stretching and releasing the rubber, the changes of triboelectric charge distribution/density on the rubber surface relative to the aluminum surface induce alterations to the electrical potential of the aluminum electrode, leading to an alternating charge flow between the aluminum electrode and the ground. The unique working principle of the SR‐based TENG is verified by the coupling of numerical calculations and experimental measurements. A comprehensive study is carried out to investigate the factors that may influence the output performance of the SR‐based TENG. By integrating the devices into a sensor system, it is capable of detecting movements in different directions. Moreover, the SR‐based TENG can be attached to a human body to detect diaphragm breathing and joint motion. This work largely expands the applications of TENG not only as effective power sources but also as active sensors; and opens up a new prospect in future electronics.

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Strain sensors with both of stretchability and ultrahigh sensitivity have been designed and fabricated for various wearable monitoring applications.