Energy-harvesting devices based on a single energy conversion mechanism generally have a low output and low conversion efficiency. To solve this problem, an energy harvester coupled with a triboelectric mechanism and electrostatic mechanism for biomechanical energy harvesting is presented. The output performances of the device coupled with a triboelectric mechanism and electrostatic mechanism were systematically studied through principle analysis, simulation, and experimental demonstration. Experiments showed that the output performance of the device was greatly improved by coupling the electrostatic induction mechanisms, and a sustainable and enhanced peak power of approximately 289 μW was produced when the external impedance was 100 MΩ, which gave over a 46-fold enhancement to the conventional single triboelectric conversion mechanism. Moreover, it showed higher resolution for motion states compared with the conventional triboelectric nanogenerator, and can precisely and constantly monitor and distinguish various motion states, including stepping, walking, running, and jumping. Furthermore, it can charge a capacitor of 10 μF to 3 V within 2 min and light up 16 LEDs. On this basis, a self-powered access control system, based on gait recognition, was successfully demonstrated. This work proposes a novel and cost-effective method for biomechanical energy harvesting, which provides a more convenient choice for human motion status monitoring and can be widely used in personnel identification systems.
Functional adjustment of graphene with metal oxide can in fact progress the affectability of graphene-based gas sensors. However, it could be a huge challenge to upgrade the detecting execution of nitrogen dioxide (NO 2 ) sensors at room temperature. The ultrasmall size of nanocrystals (NCs) and copious defects are two key variables for moving forward gas detecting execution. Herein, we provide an effective strategy that the hydrothermal reaction is combined with room-temperature oxygen plasma treatment to prepare Co 3 O 4 NCs and reduced graphene oxide (RGO) nanohybrids (Co 3 O 4 -RGO). Among all of Co 3 O 4 -RGO nanohybrids, Co 3 O 4 -RGO-60 W exhibits the most superior NO 2 sensing properties and achieves the low-concentration detection of NO 2 . The sensitivity of Co 3 O 4 -RGO-60 W to 20 ppm NO 2 at room temperature is the highest (72.36%). The excellent sensing properties can mainly depend on the change in the microstructure of Co 3 O 4 -RGO. Compared with Co 3 O 4 -RGO, Co 3 O 4 -RGO-60 W with oxygen plasma treatment shows more favorable properties for NO 2 adsorption, including the smaller size of Co 3 O 4 NCs, larger specific surface area, pore size, and more oxygen vacancies (OVs). Especially, OVs make the surface of NCs have a unique chemical state, which can increase active sites and improve the adsorption property of NO 2 . Besides, the agreeable impact of the p−p heterojunction (Co 3 O 4 and RGO) and the doping of N molecule contribute to the improved NO 2 detecting properties. It is demonstrated that the Co 3 O 4 -RGO-60 W sensor is expected to monitor NO 2 at room temperature sensitively.
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