Self-powered Humidity Sensor Research Articles

Graphene Oxide Papers in Nanogenerators for Self-Powered Humidity Sensing by Finger Tapping

Triboelectric nanogenerators (TENGs) offer an emerging market of self-sufficient power sources, converting the mechanical energy of the environment to electricity. Recently reported high power densities for the TENGs provide new applications opportunities, such as self-powered sensors. Here in this research, a flexible graphene oxide (GO) paper was fabricated through a straightforward method and utilized as the electrode of TENGs. Outstanding power density as high as 1.3 W.m−2, an open-circuit voltage up to 870 V, and a current density of 1.4 µA.cm−2 has been extracted in vertical contact-separation mode. The all-flexible TENG has been employed as a self-powered humidity sensor to investigate the effect of raising humidity on the output voltage and current by applying mechanical agitation in two forms of using a tapping device and finger tapping. Due to the presence of superficial functional groups on the GO paper, water molecules are inclined to be adsorbed, resulting in a considerable reduction in both generated voltage (from 144 V to 14 V) and current (from 23 µA to 3.7 µA) within the range of relative humidity of 20% to 99%. These results provide a promising applicability of the first suggested sensitive self-powered GO TENG humidity sensor in portable/wearable electronics.

A triboelectric nanogenerator design for harvesting environmental mechanical energy from water mist

Abstract Mechanical energy is abundant in nature and its potential is yet to be fully explored. Despite intensive research, triboelectric nanogenerators (TENGs) can only collect the energy stored in bulk water; reports on harvesting environmental mechanical energy from small scale water sources, including water mist, are still lacking. In this research, which is inspired by how tapered micro-pillars collect water from the air, a solid-liquid TENG is proposed for harvesting mechanical energy from water mist. The contact area of a water droplet with a dielectric layer in the TENG was found to be the key factor influencing the performance of the TENG, and higher current and voltage were achieved using a tapered electrode with a large diameter or by setting multiple tapered electrodes in parallel. An increase in local ambient humidity was observed to cause a significant increase in the saturation voltage and reduce the voltage saturation time of the TENG. However, an increase in ambient temperature and the amount of unpurified water mist degraded the performance of the TENG. By optimizing the parameters, the TENG can produce a maximum open-circuit voltage of 9.5 V and a short-circuit current of 250 nA simultaneously. Seven commercial light-emitting diodes (LEDs) were easily lit by the TENG, and their brightness was sensitive to varied mist flow rates. These results could inform the design and fabrication of new self-powered humidity sensors and TENGs for collecting energy from air.

High-performance flexible self-powered tin disulfide nanoflowers/reduced graphene oxide nanohybrid-based humidity sensor driven by triboelectric nanogenerator

Flexible self-powered humidity sensors with high response and good flexibility have attracted extensive interest in wearable electronics, motion monitoring and personal healthcare. In this work, we reported a high-performance flexible tin disulfide nanoflowers/reduced graphene oxide (SnS2/RGO) nanohybrid-based humidity sensor driven by a poly(tetrafluoroethylene) triboelectric nanogenerator (TENG). The humidity sensitive film of SnS2/RGO was screen-printed on a flexible PET substrate with Au interdigital electrodes. The TENG has a peak-to-peak voltage of 500 V and maximum output power of 378 μW. The tribotronic constant voltage source is achieved by integrating TENG with voltage rectifier and stabilizer circuits to steadily power the humidity sensor. The performance of the self-powered triboelectric humidity sensor (TEHS) at different humidity levels was systematically investigated, which exhibits high steady output voltage (0–24 V), fast response/recovery time (4 s/3 s for 33%RH, 6 s/15 s for 97%RH), wide sensing range (0–97%RH), great stability, and ultralow power consumption (29.78 μW). Furthermore, the TEHS demonstrated the potential ability of monitoring human breath with differ frequency, human cough, and finger approach in various applications for humidity sensing. This work provides a novel thought to design the self-powered humidity sensor, and also proposes the promising applications of TENG for the self-powered electronic devices.

Multifunctional Conductive Copper Tape-Based Triboelectric Nanogenerator and as a Self-Powered Humidity Sensor

In recent years, triboelectric nanogenerators (TENGs) have been increasingly attracting attention owing to the ability for converting multiple mechanical energy into electricity. In this paper, we first propose a multifunctional conductive copper tape-based TENG (CCT-TENG) that is constructed completely using one piece of conductive copper tape. The triboelectric pairs, supporting structure, and conductive electrode were composed using bottom paper, silicone oil, and copper foil, all of which came from one roll of conductive copper tape. The approximate output power density of the CCT-TENG reached <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$240.1~\mu \text{W}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . By spraying the aqueous solution of LiCl onto the surface of the bottom paper, a CCT-TENG incorporating LiCl was fabricated and used as a self-powered active sensor to detect the relative humidity (RH) of the environment. The obtained results revealed that the humidity sensor had good humidity response, response linearity, and reversibility. In addition, the RH was reflected by the brightness of light-emitting diodes (LEDs) that was driven by the humidity sensor. This paper realizes a promising, affordable, and portable integration of power supply systems and sensing systems, which can promote the application of TENG in the field of electronic detection device and environment monitoring.

Graphene Oxide Film Based Moisture-driven Nanogenerator and Its Application as Self-powered Relative Humidity Sensor

A humidity sensor driven by self-powered graphene oxide film with in-plane proton transfer was successfully fabricated. A 5 × 5 humidity sensor array was built, and finger position was detected via monitoring the humidity change under zero bias voltage. ΔI/I0 was about 45 at finger distance of 0.8 cm, and reached 450 at distance of 0.2 cm. The facile device preparation procedure and fast current pulse upon exposure to moisture make it suitable for practical applications in smart self-powered humidity sensor systems.

AuNPs Hybrid Black ZnO Nanorods Made by a Sol-Gel Method for Highly Sensitive Humidity Sensing.

A highly sensitive self-powered humidity sensor has been realized from AuNPs hybrid black zinc oxide (ZnO) nanorods prepared through a sol-gel method. XRD pattern reveals that both ZnO and ZnO/AuNPs exhibit a wurtzite structure. ZnO/AuNPs nanorods grow in a vertical alignment, which possesses high uniformity and forms dense arrays with a smaller diameter than that of ZnO nanoparticles. All ZnO/AuNPs and pure black ZnO show lower band gap energy than the typically reported 3.34 eV of pure ZnO. Furthermore, the band gap of ZnO/AuNPs nanocomposites is effectively influenced by the amount of AuNPs. The humidity sensing tests clearly prove that all the ZnO/AuNPs humidity sensors exhibit much higher response than that of ZnO sensors, and the sensitivity of such ZnO/AuNPs nanorods (6 mL AuNPs) display a change three orders higher than that of pure ZnO with relative humidity (RH) ranging from 11% to 95% at room temperature. The response and recovery time of the ZnO/AuNPs are 5.6 s and 32.4 s, respectively. This study of the construction of semiconductor/noble metal sensors provides a rational way to control the morphology of semiconductor nanomaterials and to design a humidity sensor with high performance.

Realization of a room-temperature/self-powered humidity sensor, based on ZnO nanosheets

In this paper, we report the first use of ZnO nanosheet-based direct-current nanogenerators (NG), as a room-temperature self-powered humidity sensor. It has been shown that the networked ZnO nanosheets are structurally stable under external mechanical pressures; hence these 2D nanostructures can be proposed as an emerging/attractive candidate in the field of mechanical energy harvesting. Also, benefiting from the high surface adsorption activity and large surface-to-volume ratio of ZnO nanosheets, we propose the fabricated NG as a promising self-powered gas sensor. Our study demonstrates short circuit and open circuit sensitivities of about 43.4% and −2.96%, because of humidity exposure. It is notable that the achieved output short circuit sensitivity is more than 10 times higher than the maximum sensitivity of a recently reported self-powered humidity sensor, based on ZnO nanorods. High sensitivity and stability, as well as direct-current output current are attractive properties of the realized humidity sensor, which can be proposed as a promising self-powered sensor.

Induced Potential in Porous Carbon Films through Water Vapor Absorption.

Sustainable electrical potential of tens of millivolts can be induced by water vapor adsorption on a piece of porous carbon film that has two sides with different functional group contents. Integrated experiments, and Monte Carlo and ab initio molecular dynamics simulations reveal that the induced potential originates from the nonhomogeneous distribution of functional groups along the film, especially carboxy groups. Sufficient adsorbed water molecules in porous carbon facilitate the release of protons from the carboxy groups, resulting in a potential drop across the carbon film because of the concentration difference of the released free protons on the two sides. The potential utilization of such a phenomenon is also demonstrated by a self-powered humidity sensor.

Hydrothermal synthesis of Co–ZnO nanowire array and its application as piezo-driven self-powered humidity sensor with high sensitivity and repeatability

Self-powered humidity sensor with high sensitivity and repeatability has been fabricated from Co-doped ZnO NW arrays. Such a high performance can be attributed to the piezo-surface coupling effect and more active sites introduced by the Co dopants.

Bifacial Structures of ZnS Humidity Sensor and Cd-Free CIGS Photovoltaic Cell as a Self-Powered Device

In this letter, a ZnS humidity sensor was integrated with MgF 2 /ZnS/CuIn 1-x Ga x Se 2 (CIGS)/Mo photovoltaic cell as a self-powered device. Both the ZnS layers of this bifacial device were deposited at the same time by a one-step process. This ZnS layer not only serves as the buffer layer of the CIGS photovoltaic cell on the upside, but is also used as the humidity sensing material on the backside. Under 1-sun illumination, the humidity current increased monotonically from 0.045 to 12.63 nA as we increased the related humidity (RH) from 30% to 95%. At RH 95%, the humidity current decreased from 13.1 to 4.93 nA while the illumination decreased from 1 to 0.1 sun. These results indicate that this device is of practical use as a self-powered humidity sensor.

Self-powered humidity sensor based on graphene oxide composite film intercalated by poly(sodium 4-styrenesulfonate).

This Research Article reports self-powered humidity sensors based on graphene oxide (GO) and poly(sodium 4-styrenesulfonate) (PSS)-intercalated GO composite films used as the humidity-responsive dielectrics. A hydrophilic and electrically-insulating PSS polymer was used as an intercalant between the individual GO platelets to enhance the water permeation characteristics. Capacitive-type humidity sensors fabricated by forming metal electrodes on both sides of the GO and GO-PSS films were installed into the charge pumping system, which can produce a voltage output as a response to humidity sensing. While both sensors based on GO and GO-PSS dielectrics responded stably and reversibly to the changes in RH, the GO-PSS sensor showed enhanced sensing responses compared to the GO sensor, providing ∼5.6 times higher voltage output and 3 times faster responses in humidity sensing.

Integration of flower-like ZnO nanostructures with crystalline-Si interdigitated back contact photovoltaic cell as a self-powered humidity sensor

In this article, flower-like ZnO nanostructures were integrated with crystalline-Si interdigitated back contact photovoltaic cell by direct growth on its surface. These ZnO nanostructures not only possess the anti-reflective characteristics to increase the converting efficiency of photovoltaic cell but also serve as the humidity sensing material. For measurement of the self-powered humidity sensor, it can be seen that the measured current increased monotonically as we increased the related humidity (RH) from 40% to 95%. The plot of log-resistance as a function of RH also showed good linearity (Y = −0.0089X + 7.0914 and R2 = 0.9874).