High-performance Humidity Research Articles

High performance humidity sensor based on crystalline copper tungstate nanoparticles at room temperature

This work demonstrates the synthesis and fabrication of Copper tungstate (CuWO4) nanoparticles-based humidity sensor. The as synthesized sample was characterized by X-ray diffraction, Raman spectroscopy, photoluminescence and high resolution transmission electron microscopy to study structural and morphological nature. The humidity sensing performance of CuWO4 nanoparticles based sensor device was tested at room temperature which was exposed to 11%-97% relative humidity levels. The sensitivity of the device was found to be ∼767 at 97% relative humidity level. The CuWO4 nanoparticles sensing device showed ultra-low response and recovery time of ∼39 sec and ∼18 sec respectively. The high sensitivity and response/recovery was likely due to the high adsorption energy, fast charge transfer rate and low bonding energy of water molecules with CuWO4 nanoparticles. Our results indicate that CuWO4 nanoparticles-based humidity sensor device has great promising application as a portable device for control humidity detection.

High Sensitive Humidity Sensors Based on Biomass Ionogels

This work proposes humidity sensors based on ionic liquid loaded in situ crosslinked ionogels. Stable ionogels were constructed by the synergistic effect of k-carrageenan and gelatin to ensure the uniformly dispersion of ionic liquid, which is conducive to the stability of humidity sensors. The humidity sensitive electrolyte with different contents were introduced into the ionogels. By controlling the ratio of ionic liquid in the crosslinked ionogels, the optimal sensor exhibits a high sensitivity in the low humidity range (5% - 35% RH). The resultant sensors exhibit excellent repeatability, and possess good stability in long-term tests up to 60 days. The introduction of ionic liquid to the sensing film is beneficial for enhancing the water adsorption capacity and ionic conductivity, which is of great significance for high-performance humidity sensors.

Carbon nanodot-based humidity sensor for self-powered respiratory monitoring

Developing low-cost, portable, and high-performance humidity sensors for respiratory monitoring has received considerable attention in recent years. Herein, humidity sensors have been fabricated based on carbon nanodots (CDs), which exhibit high sensitivity (5318%) at 94% relative humidity (RH) and excellent long-time stability under the RH range of 11% to 94%. The high sensitivity can be attributed to the adsorption of the water molecules by the massive hydrophilic functional groups on the surface of CDs. By introducing a breath-driven triboelectric nanogenerator (TENG), the self-powered humidity sensor is developed for the first time, exhibiting a wide sensing range (11–94% RH) and excellent stability. The maximum output voltage of the TENG is up to 200 V and the maximum short-circuit current is about 9.2 μA. Furthermore, the self-powered humidity sensor further demonstrates the potential ability for real-time respiration monitoring, which can detect different breathing statuses. This work provides a convenient and low-cost strategy for constructing sensitive CDs-based humidity sensors, and prospects their applications in respiratory monitoring systems.

High-performance humidity sensor for multipurpose applications by recycling of potato peel bio-waste

This study suggests the development of a biocompatible and eco-friendly humidity sensor fabricated by using a naturally available potato peel bio-waste as the substrate and the humidity sensitive material. Entire fabrication process of this potato peel-based humidity sensor (PPHS) took less than two minutes owing to the facile and handmade patterning of silver interdigitated electrodes on the surface of dry potato peel. The fabricated humidity sensor yielded a high sensitivity (70 kΩ/ % RH) due to the presence of abundant polar hydrophilic functional groups. The achieved results were stable for more than seven days and repeatable data was obtained for three different samples. Furthermore, a quick response/recovery time of 0.96/1.65 s was recorded for nose breathing with a small hysteresis of only 0.21 % for adsorption and desorption process. The sensor exhibited a good linearity (R2 = 0.997) in the practical applications-based humidity sensing range of 40–85 % RH. Efficient use of PPHS was successfully demonstrated in multiple applications including medical diagnosis, skin care, real-time environment monitoring and touchless sensing owing to its biocompatibility and nonhazardous nature. In addition to the above listed multifunctional applications of PPHS, economic use of potato peel in commercial devices can help in recycling the worldwide wastage of this bio-waste.

In-Plane Oriented Two-Dimensional Conjugated Metal–Organic Framework Films for High-Performance Humidity Sensing

In-Plane Oriented Two-Dimensional Conjugated Metal–Organic Framework Films for High-Performance Humidity Sensing

Ultrafast, highly sensitive, flexible textile-based humidity sensors made of nanocomposite filaments

Wearable electronics are promising next-generation smart textiles for human-computer interaction, health monitoring, and other applications. However, integrating electronic functions into strong, highly deformable electronic textiles and maintaining their functionalities during wear is a great challenge. Herein, we report ultrafast, highly sensitive, textile-based humidity sensors made of single-walled carbon nanotube (SWNT)/polyvinyl alcohol (PVA)/lithium chloride (LiCl) nanocomposite filaments fabricated via a wet-spinning and a solvent exchange process. The SWNT/PVA/LiCl textile-based humidity sensors exhibited excellent stabilities during deformation and high sensitivities with 6-fold resistance variations over a wide range of relative humidity (RH) conditions. The ultrafast responses of the sensors were attributed to the quick deliquescence of LiCl during contact with water molecules and the simultaneous conductivity change caused by the generated ions. The as-prepared sensors responded well to human breathing and real-time humidity changing, which could distinguish different breaths and microclimate changes. Such outstanding sensing performances of our textile-based sensors, in combination with their mechanical flexibilities, enable the facile integration of high-performance humidity sensors onto textile substrates for real-time microclimate monitoring.

Printing assembly of flexible devices with oxidation stable MXene for high performance humidity sensing applications

Transition metal carbides and carbonitrides MXenes have developed to be attractive nanomaterials for humidity-sensitive materials due to abundant hydrophilic active sites on their chemically active surfaces. Nevertheless, the low stability exhibited by MXenes in moist air or water limits their long-term storage and wide applications. This work proposes a composite of sodium ascorbate-decorated MXene (SA-MXene) by combining ascorbate ions with Ti3C2Tx MXene synthesized through a minimally intensive layer delamination (MILD) process. The synthesizing and decoration of MXene with SA to obtain SA-MXene had been shown to be a viable method for avoiding Ti3C2Tx MXene materials from oxidizing. The as-prepared SA-MXene was formulated as screen-printing ink with high stability and oxidation resistance despite being stored at ambient temperature after 30 days. Furthermore, a flexible humidity sensor was assembled by screen-printing technology with SA-MXene ink as the humidity-sensitive layer on the copper interdigital electrode prepared by the electrodeless deposition (ELD) process. Consequently, the SA-MXene sensor showed remarkable potential in humidity sensing with an ultrahigh relative capacitance response (131.4% to 97% RH) and rapid response time across a wide detection range. This work represents a promising strategy of developing SA-MXene to fabricate high sensitivity sensors derived from MXene.

Morphology-controlled BaTiO3 nanostructures with high sensitivity and fast response for respiratory monitoring

As a typical perovskite oxide, BaTiO3 has been fully proved to be an excellent impedance humidity sensing material, meanwhile its application in human respiratory monitoring needs to be further researched. In this contribution, BaTiO3 nanorods (BT-NR), nanowires (BT-NW) and micron particle (BT-MP) were successfully synthesized by the molten salt synthesis (MSS) method. Various characterization techniques were used to analyze the structure, morphology and composition of these materials. As-synthesized BaTiO3 samples had been assembled as impedimetric humidity sensors and then tested systematically under relatively humidity (RH) range of 11%–97%. All the three sensors exhibited high response values greater than three orders of magnitude, which are much higher than the commercial BaTiO3 (BT-C) sensor (S97% = 4.90 × 102). Thereinto, the BT-NR humidity sensor holds the fastest response-recovery times (1 s and 22 s) and the smallest hysteresis (ΔH = 0.67%). Excellent sensing performance of BT-NR can be attributed to synergistic effects of larger specific surface area and smaller pore size. In addition, the BT-NR humidity sensor shows considerable potential in the field of human respiratory monitoring. This work provides a new perspective to high-performance humidity sensors for human body-related detection through morphology-controlled perovskite nanostructures.

Aerosol-Printed MoS2 Ink as a High Sensitivity Humidity Sensor.

Molybdenum disulfide (MoS2) is attractive for use in next-generation nanoelectronic devices and exhibits great potential for humidity sensing applications. Herein, MoS2 ink was successfully prepared via a simple exfoliation method by sonication. The structural and surface morphology of a deposited ink film was analyzed by scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM). The aerosol-printed MoS2 ink sensor has high sensitivity, with a conductivity increase by 6 orders of magnitude upon relative humidity increase from 10 to 95% at room temperature. The sensor also has fast response/recovery times and excellent repeatability. Possible mechanisms for the water-induced conductivity increase are discussed. An analytical model that encompasses two ionic conduction regimes, with a percolation transition to an insulating state below a low humidity threshold, describes the sensor response successfully. In conclusion, our work provides a low-cost and straightforward strategy for fabricating a high-performance humidity sensor and fundamental insights into the sensing mechanism.

A Nb2CTx/sodium alginate-based composite film with neuron-like network for self-powered humidity sensing

Existing wearable sensing electronics generally require to connect a battery for the power supply. Despite many years of effort, it still remains a great challenge to develop self-powered sensing systems without external power supplies. Herein, we develop a neuron-like MXene Nb2CTx/sodium alginate (Nb2CTx/SA) composite films prepared by an electrospinning approach. The Nb2CTx/SA composite film not only can be used to fabricate a high-performance electronic humidity sensor, but also to construct a moisture-triggered nanogenerator with a sustainable voltage output. Importantly, the humidity sensor is demonstrated to be portable and compatible for applications in respiration assessment, noncontact monitoring and intelligent alarm. More importantly, by simply integrating the Nb2CTx/SA film-based sensor/nanogenerator with a capacitor and light-emitting diode (LED), a prototype of self-powered sensing system capable of indicating different relative humidity (i.e., low, medium or high) through the LED’s brightness without external power supplies is demonstrated. This work not only demonstrates the design and fabrication of a smart self-powered humidity sensing system, but also opens a new avenue for development of next-generation intelligent wearable electronics.

Highly Conductive and Mechanically Robust Cellulose Nanocomposite Hydrogels with Antifreezing and Antidehydration Performances for Flexible Humidity Sensors.

Conductive hydrogels are emerging as an appealing material platform for flexible electronic devices owing to their attractive mechanical flexibility and conductive properties. However, the conventional water-based conductive hydrogels tend to inevitably freeze at subzero temperature and suffer from continuous water evaporation under ambient conditions, leading to a decrease in their electrical conductivities and mechanical properties. Thus, it is extremely necessary, but generally challenging, to create an antifreezing and antidehydration conductive gel for maintaining high and stable performances in terms of electrical conductivity and mechanical properties. Herein, we fabricated a cellulose nanofibril (CNF)-reinforced and highly ion-conductive organogel featuring excellent antifreezing and antidehydration performances by immersing it in the CaCl2/sorbitol solution for solvent displacement. The incorporation of a rigid CNF serving as a dynamic connected bridge provided a hierarchical honeycomb-like cellular structure for the obtained CS-nanocomposite (NC) organogel networks, facilitating significant mechanical reinforcement. The synergy effects of sorbitol and CaCl2 allowed high-performance integration with excellent antifreezing tolerance, antidehydration ability, and ionic conductivity. Strong hydrogen bonds were formed between water molecules and sorbitol molecules to impede the formation of ice crystals and water evaporation, thereby imparting the CS-NC organogels with extreme-temperature tolerance as low as -50 °C and pre-eminent antidehydration performance with over 90% weight retention. Furthermore, this CS-NC organogel exhibited high humidity sensitivity in a wide humidity detection range (23∼97% relative humidity) because of the ready formation of hydrogen bonds between water molecules and numerous hydrophilic groups in the binary solvent and elaborated polymer chains, which can be assembled as a stretchable humidity sensor to monitor human respiration with a fast response. This work provides a new prospect for fabricating intrinsically stretchable and high-performance humidity sensors using cellulose-based humidity-responsive materials for the emerging wearable applications.

Polyimide-Sputtered and Polymerized Films with Ultrahigh Moisture Sensitivity for Respiratory Monitoring and Contactless Sensing.

Respiratory monitoring and contactless sensing using the moisture produced by respiration and perspiration have garnered considerable attention in recent years. In this study, we fabricated polyimide-sputtered and polymerized (PSP) humidity sensors with ultrahigh capacitive sensitivity, fast response, and a wide working range of relative humidity (RH). The sensors produced >40 000 times increment in the sensing signal over the 10-95% RH range at 10 Hz and exhibited good performance at low RH levels (<40%) as well. These sensors displayed excellent sensing properties with small hysteresis, long-time stability, and fast response and recovery times (2.4 and 1.2 s, respectively). In the mechanism study of PSP humidity sensors, we found that the high sensitivity can be attributed to massive hydrophilic functional groups formed on the polymer chains by moist aging with oxidation and the fast response speed is due to the mesoporous structure of PSP films. We also fabricated a 5 × 5 array of PSP humidity sensors to identify the shapes of wet objects and of leaves during transpiration. Thus, we reported a novel and effective method for fabricating high-performance humidity polymer films, channeling new pathways for the development of advanced humidity and gas sensors.

High-performance humidity sensor based on GO/ZnO/plant cellulose film for respiratory monitoring

High-performance humidity sensor based on GO/ZnO/plant cellulose film for respiratory monitoring

High-Performance Humidity Sensing in π-Conjugated Molecular Assemblies through the Engineering of Electron/Proton Transport and Device Interfaces.

The development of systems capable of responding to environmental changes, such as humidity, requires the design and assembly of highly sensitive and efficiently transducing elements. Such a challenge can be mastered only by disentangling the role played by each component of the responsive system, thus ultimately achieving high performance by optimizing the synergistic contribution of all functional elements. Here, we designed and synthesized a novel [1]benzothieno[3,2-b][1]benzothiophene derivative equipped with hydrophilic oligoethylene glycol lateral chains (OEG-BTBT) that can electrically transduce subtle changes in ambient humidity with high current ratios (>104) at low voltages (2 V), reaching state-of-the-art performance. Multiscale structural, spectroscopical, and electrical characterizations were employed to elucidate the role of each device constituent, viz., the active material's BTBT core and OEG side chains, and the device interfaces. While the BTBT molecular core promotes the self-assembly of (semi)conducting crystalline films, its OEG side chains are prone to adsorb ambient moisture. These chains act as hotspots for hydrogen bonding with atmospheric water molecules that locally dissociate when a bias voltage is applied, resulting in a mixed electronic/protonic long-range conduction throughout the film. Due to the OEG-BTBT molecules' orientation with respect to the surface and structural defects within the film, water molecules can access the humidity-sensitive sites of the SiO2 substrate surface, whose hydrophilicity can be tuned for an improved device response. The synergistic chemical engineering of materials and interfaces is thus key for designing highly sensitive humidity-responsive electrical devices whose mechanism relies on the interplay of electron and proton transport.

High performance humidity sensor based on 3D mesoporous Co3O4 hollow polyhedron for multifunctional applications

In this work, the three-dimensional (3D) hollow mesoporous Co3O4 was successfully prepared by calcining the Co-based zeolitic imidazolate framework-67 (ZIF-67). As-obtained Co3O4 inherited the rhombohedral framework structure of ZIF-67 and possessed mesoporous and hollow structure. Further, the humidity sensor based on Co3O4 was fabricated, and its humidity sensing properties were investigated at room temperature (25 °C). The results indicated that the Co3O4 humidity sensor exhibited high humidity sensing performance with a wide linear detection range (10%−95% relative humidity (RH)), small humidity hysteresis (2.6% RH), and fast response/recovery times (1.0/13.5 s). In particular, the Co3O4 humidity sensor was of high detection resolution (1% RH). The excellent performance was attributed to the strong hydrophilicity and the unique 3D porous structure of Co3O4. In addition, the potential applications of the fabricated Co3O4 humidity sensor in skin humidity, simulated diaper, human breathing, and non-contact switch were demonstrated. This work provides a promising humidity sensing material for fabricating high-performance humidity sensors.

Microwave-assisted synthesis of Co-doped SnO2/rGO for indoor humidity monitoring

The evaluation of indoor humidity is challenging compared to other environmental parameters such as light intensity, temperature, sound and so forth. The proper selection of sensing materials and structural tuning will lead to high-performance humidity sensors. Herein, the SnO2/rGO and SnO2/rGO doped with Co nanocomposite were produced by microwave route. The obtained nanocomposite was characterized by XRD, SEM, EDAX, DTA, TGA, FTIR, Raman, and HRTEM. The successful incorporation of Co onto the rGO/SnO2 is affirmed by the XRD and supported with matching SEM and TEM outcomes where nanoscale particles exist. FTIR reveals the existence of the CC stretching band at ∼1570 cm−1 indicating graphene network sustaining upon reduction. Micro-pores presence is claimed by the adsorption-desorption isotherm curve. The humidity sensing behavior of both structures was evaluated in a wide range of humidity (11–97% RH). The obtained results confirmed that best working frequency for highest humidity change is 50 Hz. Furthermore, upon doping the SnO2/rGO composite with Co, sensitivity, the response time and recovery time has improved reaching 52 s and 100 s respectively.

A Printed Flexible Humidity Sensor with High Sensitivity and Fast Response Using a Cellulose Nanofiber/Carbon Black Composite

In the emerging Internet of Things (IoT) society, there is a significant need for low-cost, high-performance flexible humidity sensors in wearable devices. However, commercially available humidity sensors lack flexibility or require expensive and complex fabrication methods, limiting their application and widespread use. We report a high-performance printed flexible humidity sensor using a cellulose nanofiber/carbon black (CNF/CB) composite. The cellulose nanofiber enables excellent dispersion of carbon black, which facilitates the ink preparation and printing process. At the same time, its hydrophilic and porous nature provides high sensitivity and fast response to humidity. Significant resistance changes of 120% were observed in the sensor at humidity ranging from 30% RH to 90% RH, with a fast response time of 10 s and a recovery time of 6 s. Furthermore, the developed sensor also exhibited high-performance uniformity, response stability, and flexibility. A simple humidity detection device was fabricated and successfully applied to monitor human respiration and noncontact fingertip moisture as a proof-of-concept.

IOT Based Wireless Data Technology Using LORA and GSM

Traditional agriculture is converting into smart agriculture due to the bulge of the IoT (Internet of things). An agriculture services platform is developed to support environmental monitoring and to improve the efficiency of agriculture management. Contemporary the Internet of things (IoT) is one of the highest promising application areas in information technology for forthcoming products and services. And, the agriculture field is changing expeditiously pointing to the future of automated and embedded systems with a bunch of sensors to monitor and curb the flourishing plants in a way to profit associated with it. However, one of the major issues of IoT is still a conversion between devices, notably on long-range. LoRa is lately accepted as auspicious communication technology, due to its properties such as long-range, two-way communication, and low cost. In this work, the LoRa technology is applied in the agriculture sector for making long-distance, low-cost communication. This work includes sensing and monitoring the parameters such as level, temperature, and humidity and also controlling the said parameters with the help of a remote unit. The proposed system is based on a high-performance microcontroller, integrated temperature and humidity sensor on real-time data analysis. The use of Data collection, pattern classification and apply strategic analysis then control execution for the final result.

Hierarchical spindle structures of Li+-doped ZnO for a high performance humidity sensor

Li+-doped ZnO hierarchical spindle structures have been prepared on FTO conductive glass via a simple hydrothermal synthesis. The sensing performance of the sensor based on Li+-doped ZnO was improved by controlling the Li+ doping concentration.

Printing Assembly of Flexible Devices with Oxidation Stable Mxene for High Performance Humidity Sensing Applications

Printing Assembly of Flexible Devices with Oxidation Stable Mxene for High Performance Humidity Sensing Applications