Self-powered Humidity Sensor Research Articles

Moisture electricity generation based self-powered humidity sensor for smart agriculture

With the rapid development of smart agriculture, it is of great significance to monitor soil moisture through humidity sensors to maintain suitable soil environmental conditions and improve crop yield and quality. This study reports a self-powered humidity sensor (SPHS) based on moisture electricity generation, which was designed by using a humidity-sensitive composite film composed of polystyrene sulfonic acid: polyvinyl alcohol doped LiCl as the electrolyte layer and combined with copper and aluminum electrodes. The SPHS easily adsorbs and diffuses water molecules in humid environment, and relies on the principles of ion diffusion and electrochemical reaction to realize the sensing of soil moisture, without the external power source, and with good reliability and durability. The SPHS can spontaneously generate current response over a relative humidity (RH) range of 33 %–91 %, with a current response of 2.6 μA at 33 % RH and up to 76.1 μA at 91 % RH, which provides excellent RH-current linear response characteristics (R2 = 0.988). SPHS can be successfully applied in the field of human wearable devices, such as integration into masks for human breathing monitoring, as well as having excellent application potential in contactless human-computer interfaces. By integrating smart sensing technology and IoT communication technology, a smart agricultural environment sensing system was built in conjunction with SPHS for in-situ monitoring of soil moisture, ambient temperature, and light intensity to achieve real-time monitoring of the farmland environment, which promotes the development of agricultural production in the direction of intelligence, efficiency, and sustainability.

Environmentally stable, Adhesive, Self-healing, Stretchable and Transparent Gelatin based Eutectogels for Self-Powered Humidity Sensors

Intrinsic environmental and stability limitations of hydrogels have inhibited their practical applications as a flexible wearable device due to water evaporation or freezing in complex environments such as low temperatures and arid environments. In this work, a multifunctional gelatin based ionic conductive eutectogel with double network structure is designed via ternary deep eutectic solvent (DES) (acrylic acid (AA), choline chloride (ChCl) and ethylene glycol (EG)). In this system, the introduction of ethylene glycol (EG) can be used to dissolve gelatin. The resulting DESG eutectogel exhibited excellent adhesion, mechanical robustness, anti-freeze, anti-drying, and self-healing. Interestingly, the DESG gels showed high humidity sensitivity in a wide humidity detection range (11 %–83 %), which can be assembled as a self-powdered humidity sensor to monitor human mouth and nose breathing. This work is expected to bring new prospect to construct high performance humidity sensors using gelatin based humidity-responsive materials for a wide range of potential applications in respiratory diagnostics, sleep monitoring, electronic skin and wearable electronics.

Two Birds with One Stone: Impedance-Voltage Dual-Mode Low Humidity Sensor Based on LiBr-MOF-801 with High Response.

Dual-mode humidity sensors have received wide attention in recent years due to their great potential in multifunction applications. Herein, following a "two birds with one stone" strategy, a dual-mode and self-powered low humidity sensor based on LiBr-MOF-801 with high response and power generation is proposed. The optimized LiBr-MOF-801-based sensor exhibits impedance-voltage dual-mode sensitivity in the low humidity range of 0-23% relative humidity (RH) with high response (57.1 and 0.61V), small hysteresis (0.3% RH) and good long-term stability at room temperature (20°C). Moreover, an integrated humidity power generator is obtained by series connection of the self-powered humidity sensor within 15cm2, and the output voltage reaches 2.6V with an output power density of 110 nW cm-2, and can be used as energy, supplying power to commercial electronic equipment even in low humidity. This work provides a new sight for fabricating high-performance, dual-mode, and self-powered low-humidity sensors.

Self-powered and degradable humidity sensors based on silk nanofibers and its wearable and human–machine interaction applications

Humidity sensors have received increasing attention due to their broad potential application in wearable devices, health monitoring, intelligent control, and other fields. However, traditional humidity sensors are prone to produce various toxic substances to pollute the environment after discarding. Also, they are prone to damage during use, which shortens their service life. Therefore, the development of eco-friendly, degradable, and repairable humidity sensors is of great significance for reducing e-waste and protecting the environment. Here, we started with the selection of materials by using silk nanofiber (SNF) film as the substrate material, copper/aluminum as electrodes, and calcium chloride as the electrolyte, combined with the working mechanism of the primary battery, to construct a self-powered humidity sensor. The humidity sensor exhibits excellent humidity sensing performance and good linearity within the range of 30–90 % relative humidity (RH). A single humidity sensor can output 346 mV at 90 % RH. After being damaged, the humidity sensor can be repaired with the help of water. When the ruptured SNF film encounters water molecules, the water molecules can prompt the hydrogen bonds between the SNFs to rearrange and connect, connecting the broken area. Young’s modulus retention rate of the repaired SNF film is over 85 %. The repaired humidity sensor can also output 328 mV. Additionally, an alkaline solution can completely degrade the humidity sensor in less than 80 min. The proposed humidity sensors have been applied to wearable self-powered wristbands, wireless monitoring systems, and non-contact human–machine interaction systems. Hence, we provide comprehensive research from the material level (SNFs) to the functional device level (the self-powered humidity sensor), and then to the system level (wearable and human–machine interface system). The research will open a new way for the design of the self-powered humidity sensor and have great potential applications in wearable electronics and human–machine interface applications.

β-enhanced humidity robust high performance triboelectric nanogenerator for energy harvesting and sensors

Limited output current and harsh environmental conditions are big challenges to harvesting electrical energy from triboelectric nanogenerators (TENG) in sensing applications. One contributing factor to this issue is matching the density of state between two layers of TENG for maximum charge transfer. To ensure a stable output performance, a superhydrophobic interface between the TENG's two layers has been achieved by applying a novel fluorescence enhanced hexamethyldisiloxane (HMDSO) dielectric barrier discharge (DBD) plasma. The plasma coating not only improve the hydrophobicity but also the interface contacts between the two layers of TENG and therefore a maximum charge transfer and ultra-high current density are obtained. The plasma treatment increases the surface roughness and introduces functional groups such as amino (-NH2), hydroxyl (-OH), and siloxane (-Si-O-Si) on the PMMA film, which increases the electron affinity difference between the two layers, increases humidity resistance. The modified TENG generates a maximum stable output voltage of 1400 V and a maximum current of 125 µA with a power density of 55 W/m2, which is significantly higher than those reported in previous studies. Therefore, the TENG has been used as a self-powered droplet detector with an ultra-fast response time of 1.8 ms and has the potential to be used as a self-powered humidity sensor.

A high performance triboelectric nanogenerator using assembled sugar naphthalimides for self-powered electronics and sensors

A new class of N-glycosyl naphthalimide ricinoleate (NGNR) amphiphiles were generated using environmentally friendly reaction conditions in good yields. To investigate the potential applications of NGNR amphiphiles within the realm of supramolecular materials, molecular self-assembly experiments were conducted extensively across a diverse range of solvents and oils and observed the gel formation. Molecular-level interactions and assembly patterns were investigated by employing FTIR, SAXRD, UV–vis, and fluorescence spectroscopy, and a plausible assembly mechanism was proposed. The morphology of the supramolecular architecture was identified by scanning electron microscopy. Additionally, rheological studies provided insight into these soft materials' strength and processability. Further, in the process of fabricating a triboelectric nanogenerator (TENG) device, silicone rubber serves as an electron acceptor and assembled NGNR serves as an electron donor. The developed TENG demonstrated a significant improvement in performance over TENG made with amorphous NGNR, with output voltage, current, and power density of 410 V, 100 µA, and 5.1 W/m2, respectively, highlighting the importance of the assembly process. Furthermore, TENG is used to continuously power up small electronic device (calculator), which is useful in building self-powered electronic devices. Lastly, due to its high sensitivity and stability, the TENG was used to detect the humidity of the environment in the food processing, textile, and agriculture sectors. The change in TENG response is notably significant up to 70 % relative humidity (RH). This work showcases the development of self-powered humidity sensors.

Self-Powered Humidity Sensor Driven by Triboelectric Nanogenerator Composed of Bio-Wasted Peanut Skin Powder.

The increasing number of IoT devices has led to more electronic waste production, which harms the environment and human health. Self-powered sensor systems are a solution, but they often use toxic materials. We propose using biocompatible peanut skin as the active material for a self-powered humidity sensor (PSP-SPHS) through integration with a peanut-skin-based triboelectric nanogenerator (PSP-TENG). The PSP-TENG was characterized electrically and showed promising results, including an open circuit voltage (162 V), short circuit current (0.2 µA), and instantaneous power (2.2 mW) at a loading resistance of 20 MΩ. Peanut skin is a great choice for the sensor due to its porous surface, large surface area, eco-friendliness, and affordability. PSP-TENG was further used as a power source for the PSP-humidity sensor. PSP-SPHS worked as a humidity-dependent resistor, whose resistance decreased with increasing relative humidity (%RH), which further resulted in decreasing voltage across the humidity sensor. This proposed PSP-SPHS exhibited a good sensitivity (0.8 V/RH%), fast response/recovery time (4/10 s), along with excellent stability and repeatability, making it a potential candidate for self-powered humidity sensor technology.

Asymmetric self-powered cellulose-based aerogel for moisture-electricity generation and humidity sensing

In view of the current problems of fossil consumption and environmental pollution, harvesting electricity from water to obtain renewable and clean energy has become a trend. Herein, an asymmetric self-powered cellulose-based aerogel generator (SMEG) was proposed by directional freeze-drying using quaternized cellulose nanofibril (Q-CNF), sodium carboxymethylcellulose (CMC) and single-walled carbon nanotube. When exposed to humid air, the prepared aerogel generated ionic ionization and directional flow, resulting in a potential difference. The single SMEG could separately produce a continuous voltage and current output of up to 668 mV and 6.4 μA, accompanied by a power density of 0.871 μW⋅cm−2 at high humidity (90 %). Meanwhile, connecting several SMEG devices could directly provide satisfied power for some commercial electronics including LED lights and calculators. More importantly, it was compatible for applications in contactless sensing and respiratory monitoring with high moisture sensitivity and good durability. This work provides a low-cost and environmentally friendly strategy for the optimal design of moisture-electricity generators and self-powered humidity sensors.

High performance triboelectric nanogenerator based on purified chitin nanopaper for the applications of self-powered humidity sensing, gait monitoring, and hyperhidrosis sensor

Pollution caused by electronic wastes (E-wastes) is a global problem due to the use of haordous materials and chemicals in electronic devices therefore, green materials should be used to reduce the burden on our ecological system. Triboelectric nanogenerators (TENGs) are among those electronic devices that have a huge scope of replacing currently used hazardous materials with green materials as their triboelectric layers and substrates. Herein, we used king mushroom powder as an electropositive layer of a TENG, but its output performance was compromised due to the presence of unwanted elements in it. Chitin was the most desirable element in mushroom powder for achieving triboelectricity therefore, we isolated it via non-acidic approach to fabricate a transparent thin film (234.5 μm) of chitin nanopaper (CN). A significant increase of 287% in the output performance was shown by isolated CN based TENG including higher voltage (151 V) and current (11.4 μA) with a maximum power density of 1.78 Wm−2. The fabricated CN-TENG was used to power micro electronic devices including (50 red LEDs) and charging/discharging 6 different capacitors ranging from 9.5 nF to 47 μF. Furthermore, the potential use of CN as a self-powered humidity sensor was explored by observing its response towards variations in relative humidity (RH). Analysis of obtained results verified the implication of isolated CN as the self-powered humidity sensor with a fast reaction/recovery time (7/10 s) and wide operating range (21–95 %RH). The fabricated device was successfully used for the practical applications of hyperhidrosis sensing and gait monitoring. Electronic devices like CN-TENG proved to be a substantial step-forward in contributing towards reduction of cost and global pollution caused by E-wastes.

Multifunctionally moist-electric generator for self-powered ultra-fast sensing based on laterally dual gradient

Multifunctional self-powered sensors play a crucial role in various applications, ranging from body healthcare monitoring to environmental sensing. Herein, we developed a multifunctional moist-electric generator (MMEG), integrating energy harvesting, power supply and sensing in a single device. Two electrodes are on the same side of the poly (4-styrensulfonic acid) active film to construct a laterally dual gradient device The exposed areas of active film and the areas covered with electrodes naturally create a humidity gradient upon moisture, and meanwhile an ion gradient is generated on the surface of the active layer by asymmetric electrodes. The MMEG device has a small effective exposed film area of only 0.01×1 cm2 and provides a stable electrical output of 1 V and an unparalleled power density of 874 μW·cm−2 in humid environments. Due to good linear response and remarkable sensitivity (85700%), the MMEG is applied in self-powered humidity sensors of various scenarios, such as humidity sensors, respiration monitoring, non-contact sensing, sweat monitoring, and ultra-fast tactile sensing with a response time of 0.05 s. This work demonstrates a high-performance self-powered humidity sensing from self-humidity energy, rather than other energy types, and provides a general and effective strategy for the development of next-generation multifunctional self-powered devices.

Self-powered humidity sensors based on zero-dimensional perovskite-like structures with fast response and high stability.

With the rapid development of technology, the development of self-powered sensors has garnered significant attention. The importance of monitoring humidity has grown significantly in various technological contexts, from environmental monitoring to biomedical applications. In this work, we have fabricated a low-cost and self-powered humidity sensor using zero-dimensional perovskite-like structures. Switching tests at different relative humidity levels have shown that the zero-dimensional perovskites have visible coloration at high humidities and discoloration upon reducing the humidity. The humidity sensor was fabricated by spin coating the zero-dimensional perovskites on a patterned fluorine doped tin oxide (FTO) substrate and the sensor not only shows high response values of around 500 mV and few micro amperes of short circuit current densities, but also shows good cycling performance and stability. Also high selectivity to humidity is observed in comparison to different gases and volatile organic compounds. The high selectivity to humidity arises due to the fact that the exclusion of MAI from the MA4PbI6 strucuture does not happen with all the other analytes which has been confirmed from the XRD studies. In addition, due to the low temperature fabrication they can be deposited on flexible substrates and the sensor displayed excellent resistance to bending and durability. Furthermore, the study explored the humidity monitoring capabilities of this sensor, revealing an outstanding response performance to human respiration. This observation suggests that the sensor holds significant potential for practical applications in the monitoring of human health and environmental conditions. This work paves the way for developing organic-inorganic hybrid perovskite materials for self-powered sensing applications.

Self-Powered, Highly Sensitive, and Flexible Humidity Sensor Based on Carboxymethyl Cellulose for Multifunctional Applications.

Self-powered humidity sensors based on friction electric and piezoelectric principles have been proposed in recent years. However, the complicated structure and preparation processes usually involved in these power generation humidity sensors limit their wider application. Herein, we developed a self-powered flexible humidity sensor with a simple structure and facile preparation process based on the primary battery principle. The self-powered humidity sensor consists of copper conductive tape as the positive electrode, nickel conductive tape as the negative electrode, and a carboxymethyl cellulose film dissolved with lithium chloride and sodium chloride as the sensing layer. The sensor exhibits good sensing linearity (R2 = 0.99791) in a wide relative humidity range (11-95%) with a satisfying response voltage of 41 mV (RH 95%) and excellent flexibility. Furthermore, the conduction mechanism of the sensing film was investigated by the complex impedance and phase angle-frequency spectral measurement and analysis. Multifunctional applications of human respiration monitoring to determine the respiratory rate and type, noncontact sensing, diaper and soil moisture detection, and power generation were demonstrated. The low-cost and facile preparation method in this work could provide a useful strategy for developing a self-powered, flexible, and multifunctional humidity sensor.

Nylon Fabric/GO Based Self-Powered Humidity Sensor Based on the Galvanic Cell Principle with High Air Permeability and Rapid-Response.

Flexible humidity sensors have received more and more attention in people's lives, and the problems of gas permeability and power supply issues of the device have long been areas in need of improvement. In this work, inspired by the high air permeability of daily wear clothing and galvanic batteries, a self-powered humidity sensor with high air permeability and fast response is designed. A nylon fabric/GO net (as a humidity sensitive layer and solid electrolyte) is obtained by spraying technique. This structure enables the sensor to have fast response/recovery (0.78s/0.93s, calculated at 90% of the final value), ultra-high response (0.83V) and excellent stability (over 150 cycles) at 35°C. Such sensors are useful for health monitoring, such as non-contact monitoring of human respiratory rate before and after exercise, and monitoring a level of humidity in the palms, arms, and fingers. This research provides an idea for developing a flexible wearable humidity sensor that is both breathable and self-powered and can also be mass-produced similar to wearable clothing.

In2O3 nanocubes and ZnWO4 nanorod-based triboelectric nanogenerator for self-powered humidity sensors

In this study, a self-powered photo-induced humidity sensor was developed using ZnWO4/In2O3 heterostructure based Triboelectric Nanogenerator (TENG). The ZnWO4/In2O3 heterostructure-based TENG generates 44 V voltage and 1 µA current by finger tapping. The ZnWO4/In2O3 heterostructures were synthesized via hydrothermal method. SEM analysis confirmed the In2O3 nanocubes grown on ZnWO4 nanorods. XRD analysis confirmed the polycrystalline nature of ZnWO4/In2O3 heterostructures and the average crystallite size was found to be 32.66 nm. XPS analysis confirmed the presence of Zn2+, In3+, W4+, and O2- oxidation states. Optical properties were analyzed by UV–visible spectroscopy and maximum absorbance was found in the region (315–400 nm) since it is capable of absorbing UV light. In this work, the effect of very low-intensity UV light (2 mW/cm2) on a battery-less moisture detection was investigated at different moisture levels (10–90%RH). The sensor response was around 27.50 at 90%RH of photo-induced self-powered humidity sensor. Also, the fast response and recovery times were observed as 260 ms and 620 ms respectively in the illumination of UV light. The photo-induced self-powered humidity sensor showed highly sensitive and stable for a long time and it can be commercialized for indoor and outdoor humidity detection.

Highly Sensitive Self-Powered Humidity Sensor Based on a TaS2/Cu2S Heterostructure Driven by a Triboelectric Nanogenerator.

Self-powered humidity sensors with high response and good stability have attracted extensive interest in environmental monitoring, medical and health care, and sentiment detection. Because of its high specific surface area and good conductivity, two-dimensional material has wide application in the field of humidity sensing. In this work, we proposed a novel self-powered high-performance TaS2/Cu2S heterostructure-based humidity sensor driven by a triboelectric nanogenerator (TENG) made with the same structure. The TaS2/Cu2S heterostructure was prepared via the chemical vapor deposition method, and then, electrolytic and ultrasound treatments were introduced to further increase the surface area. The fabricated humidity sensor showed ultrahigh sensitivity (S = 3.08 × 104), fast response (2 s), low hysteresis (3.5%), and great stability. First-principles calculation results demonstrated the existence of an electron transport channel with a low energy barrier (-0.156 eV) from the Cu2S to TaS2 layer in the heterostructure, which improves the surface charge transfer of the material. The TaS2/Cu2S heterojunction-based TENG can generate an output voltage of 30 V and an output current of 2.9 μA. Furthermore, the proposed self-powered humidity sensor verified the potential ability of detecting human respiratory frequency, skin humidity, and environmental humidity. This work provides a new and feasible path for research in the field of humidity sensors and promotes the application development of self-powered electronic devices.

Self-powered health monitoring with ultrafast response and recovery enabled by nanostructured silicon moisture-electric generator

Humidity sensors have been widely applied in health management, including respiration monitoring and non-contact sensing for human–machine interaction. Nevertheless, most existing monitoring systems hinging on moisture-sensitive materials require an additional external power source. In addition, the inferior sensitivity and long response/recovery time of the sensors still hinder their desirable healthcare applications. Here, we developed a self-powered humidity sensor built on the moisture-directly triggered electricity generation (MEG) effect, where silicon nanowire arrays (SiNWs) function as the sensing element, exhibiting an ultrafast response to humidity changes with high-level sensitivity. Humidity gradients induce charge directional transport in SiNWs nanochannels, directly actuating electricity signals generation without any additional power units for sensing. The enlarged surface area, oriented nanochannel structure, and superior electrical conductivity of SiNWs facilitate a robust dependence of the output voltage on humidity, enabling the sensor with quick response/recovery (∼0.10 s/∼0.17 s), ultra-high sensitivity, and broad detection range (3.94 mV/1% for 50–95% RH/1.13 mV/1% for 0–50% RH). Furthermore, we designed a smart respiratory monitoring system that can extract various respiration patterns and distinguish different language commands. We also constructed a non-contact human–machine interface leveraging the SiNWs sensor that can effectively disrupt virus propagation and bacterial infection. The elaborate self-powered humidity sensor proposed in our work could as well potentially be exploited for establishing wearable and integrated health monitoring platforms in the future.

Edible rice paper-based multifunctional humidity sensor powered by triboelectricity

Electronic wastes are causing unadorned burden on our environment due to the use of hazardous materials therefore, using naturally available green materials is necessary for sustainable and eco-friendly future. Biowastes can be used as functional materials of advanced electronic devices owing to their biocompatibility, low cost, and abundant availability. In this study, we have explored the multifunctional humidity sensitive response of a cellulose enriched edible rice paper (CERP). Presence of hydrophilic functional groups and highly porous surface of CERP made it a highly suitable sensing material for adsorbing/desorbing water molecules over a full relative humidity (RH) sensing range (0–100 %RH). Fast response/recovery times (5/16 s) were recorded along with a high sensitivity of 97%. CERP was also used as the electropositive layer of a triboelectric nanogenerator (TENG) for harvesting energy, making it a self-powered humidity sensor. High performance results were obtained including output voltage (162 V), output current (2 μA), and power density (3 μW/cm2), respectively. Electrical energy produced by TENG was enough to charge 3 commercial capacitors (1 μF, 4.7 μF, and 10 μF) and light 30 green LEDs. Obtained results were highly stable (1500 s) and repeatable with a long lifetime (3 months).

A humidity- and environment-resisted high-performance triboelectric nanogenerator with superhydrophobic interface for energy harvesting and sensing

Triboelectric nanogenerator (TENG) has been widely researched and used for sustainable energy, sensing and other applications in recent years due to its energy conversion properties. However, in practical applications, TENG is often exposed to complex and harsh environments, so ensuring its stable output performance is a significant challenge. Here, a flexible, superhydrophobic and environmentally resistant TENG for energy harvesting and self-powered sensing is proposed by a cost-effective surface modification and co-blending method. The roughness, hydrophobicity and surface potential of the composites are significantly enhanced by the introduction of surface modified BN (m-BN), resulting in excellent triboelectric output (43 W/m2) of the m-BN/TENG. Moreover, the m-BN/TENG not only maintains 90% initial electrical output at 80% humidity but also its output performance has no noticeable change after treatment with acid and alkali. Apart from energy harvesting, the TENG has been demonstrated as a self-powered humidity sensor with a sensitivity of − 80 nA RH−1 and a self-powered droplet detector with an ultra-fast response time of 0.6 ms. Our work provides a practical approach for stable energy harvesting and self-powered sensing of TENG in harsh environments.

Ultrafast response of self-powered humidity sensor of flexible graphene oxide film

Next-generation humidity sensor, as one of the smart devices in artificial skin or flexible electronics, will need to be self-powered, flexible, fast and accurately detecting in the microenvironment. Although various flexible humidity sensors have already been demonstrated, most of them rely on large external power sources to operate, and still suffer from slow response, poor selectivity in environmental stimuli, and expensive and complicated procedures. Here, we realize a self-powered humidity sensor with ultrafast response and recovery time of less than 0.3 s by flexible GO film. Importantly, of all state-of-the-art humidity sensors, this is the fastest response for humidity sensor. Moreover, the sensor has a high sensitivity within a wide range of RH from 33% to 98%, and an excellent selective response to humidity under multiple environmental stimuli, due to its moist-induced generator. Theoretical computations reveal that protons generated spontaneously from oxygen-containing groups and water molecules, have a fast diffusion behavior as Grotthuss hopping. In particular, we build four real-time measurement systems capable of respiration monitoring of human, smart leaf surface humidity sensor, and energy harvesting. Our work provides a simple way to fabricate next-generation self-powered sensor using GO film with outstanding humidity sensor performance.

Unravelling the impact of carbon allotropes in flexible polydimethylsiloxane film towards self-powered triboelectric humidity sensor

The influence of surface charge on tribo-layer is a crucial parameter in improving the performance of triboelectric nanogenerators (TENG). Nevertheless, most researchers focus on the structure and design of TENG rather than increasing the surface charge density, which is the main parameter for energy harnessing in nanogenerators. Herein, we tweaked the surface charge density of polydimethylsiloxane (PDMS) via incorporating different types of carbon allotropes to shift the charge density (positive to negative and vice versa) for high output TENG. The PDMS/GO TENG device generated a voltage of 234 V; higher compared to that of bare PDMS and other nanocomposite films, which is attributed to the high surface charge of PDMS/GO confirmed via Kelvin probe force microscopic (KPFM) analysis. As a proof concept, we have demonstrated the use of PDMS/GO-based TENG device for self-powered humidity sensor.