Fabric liquid diode for electricity generation and self-cooling

Fabric liquid diode for electricity generation and self-cooling | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Fabric liquid diode for electricity generation and self-cooling Xiaoming Tao, Renbo Zhu, Zhongliang Zhang, Kitming Ma, Yonghui Luo, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7190787/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Energy harvesting devices with great breathability facilitate continuous operation of healthcare applications and are the critical components in the self-power wearable microelectronic systems. However, the insufficient electric outputs largely diminish the effectiveness of generators as wearable power supply and the lack of moisture/thermal management causes discomfort in the practical electronic application. Herewith we report a self-powered and self-cooling fabric that enhances electric outputs and provides good wear comfort simultaneously, for the first time, by a synergistic effect of directional water transport and ion migration. The water evaporation on the fabric liquid diode with gradient wetting channels reaches 0.56 g·h − 1 for dehumidification, dissipating body heat with a temperature drop of 6.3°C for self-cooling. The devices deliver a DC current output of 0.40 mA·cm − 2 , twice that of devices without liquid diode and is sufficient to power a wide variety of practical wearable electronics. Physical sciences/Energy science and technology/Energy harvesting/Devices for energy harvesting Physical sciences/Materials science/Materials for devices/Electronic devices Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction The increasing demands of green and wearable power supply have been a great global concern as a wide variety of electronic devices are emerging for “Internet of Things” (IoTs), such as human activity monitoring and human-machine interaction 1 , 2 , 3 , 4 . The power supply devices are the key components in the electronic systems that guarantee the stable operation of integrated units. Tremendous efforts have been made in the energy harvesting technologies (e.g., solar cell, piezoelectric generator, thermoelectric generator) for power supply, which achieve electricity generation by exposing generators to the energy sources of light, motion and temperature gradient 5 , 6 , 7 . The operation of energy harvesting strongly depends on the working environments and is insufficient to support real-time and continuous monitoring in the varied environments. Besides, the wear comfort, especially regulating moisture/sweat and body heat, is critical in the long-term wearability of wearable electronic textiles 8 , 9 . The reported power supply devices covering the fabric or human skin inhibit the release of moisture/sweat and body heat into environment 10 , 11 , 12 , 13 . Thus, the wearable power supplies exhibit unsatisfied electric outputs and wearability, impeding their practical applications and mass production. One promising approach to maintaining wearable power supplies with continuous outputs is collecting abundant moisture and converting chemical potential energy from moisture into electricity 14 , 15 , 16 , 17 . The sustainable electric outputs have been demonstrated with hygroelectric generators as the moisture is a ubiquitous energy source in the various environments 18 , 19 , 20 . By absorbing moisture with hydrophilic layers and forming asymmetrical water and ion gradient, the hygroelectric generators achieve ion migration and charge separation for sustainable electricity generation. The high moisture absorption of hydrophilic layer is often considered, but moisture management for directional ion transport and enhanced current outputs is generally not considered 21 , 22 . Therefore, the electric outputs (several microamperes) of hygroelectric generators are insufficient to power practical application as only a limited number of devices with a low power consumption can be driven by hygroelectric generators 23 , 24 . Besides, the moisture was absorbed and confined inside hydrophilic layer 25 , 26 , the waterproof substrates on the fabrics also blocked water transport in the direction from human body to the environment 12 , 27 , 28 . Thus, the poor water regulation of hygroelectric generators without moisture and thermal management is detrimental to users’ wear comfort (Fig. 1a). Here, we propose a rationally designed self-powered and self-cooling fabric (SSF) to simultaneously improve wear comfort and electric outputs (Fig. 1b) by the synergistic effect of directional water transport and ion migration. The liquid diode spontaneously pumps sweat from skin surface to the external side of the fabric and blocks environmental water infiltration, contributing to a fast water transport rate of 0.012 cm·s − 1 for dehumidification and good wear comfort. The water evaporation on the nylon fabrics improves by two times (from 0.28 g·h − 1 to 0.56 g·h − 1 ) and dissipates body heat with a skin temperature drop of 6.3°C for self-cooling. Besides, the devices with grid sandwich structures are designed and are printed on the liquid diode to allow fast and directional water evaporation through the generator, which triggers fast ion migration for the enhanced charge separation and electricity generation (0.40 mA·cm − 2 ). The efficient moisture management and enhanced electric outputs of SSF improve human comfort and solve a series of critical challenges of wearable power supply. 2. Results 2.1 Designs for self-cooling and electricity generation We elaborated SSF by printing hygroelectric generators (aluminium, polyvinyl alcohol/lithium chloride and graphene as bottom electrode, functional layer and top electrode, respectively) with grid sandwich structures (Supplementary Fig. 1) on the liquid diode for self-cooling and electricity generation (Fig. 1 c). The printed areas and unprinted areas in the grid structure are mainly responsible for electricity generation and moisture/thermal management, respectively. The liquid diode of gradient fabric (G-fabric) can transport sweat on the skin surface to external environment directionally for dehumidification and good wear comfort. The water evaporation on the large surfaces of gradient fabric dissipates body heat for self-cooling. The water transport also drives directional ion migration inside functional layer of hygroelectric generators for electricity generation. Moreover, SSF shows good comprehensive performance as wearable power supply in terms of breakthrough pressure (BP) ratio, electric outputs, temperature reduction (ΔT) and stretch cycles, which are significantly improved in comparison with other reported generators based on water evaporation (Fig. 1 d and table S1 ). The nylon fabrics are endowed with gradient wetting channels by hydrophobic titanium dioxide (TiO 2 ) nanoparticles with gradient distribution along the water flow channels (Fig. 1 e), which are achieved by spraying TiO 2 nanoparticles on the one side of fabric (Supplementary Fig. 1). The amount of TiO 2 nanoparticles along the channels of nylon fibers is decreased from the bottom to the top side to guarantee the one-way water movement of in the channel with varied width. The morphology of nylon fibers and element distribution (Fig. 1 f, Supplementary Fig. 2) confirm the exist of the hollow channel among nylon fibers and the vertical gradient distribution of TiO 2 nanoparticles. The Ti element of pristine nylon, hydrophilic (“I”) side, hydrophobic (“O”) side is 0.0%, 10.4% and 20.5%, respectively (table S2). The enhanced electricity generation is attributed to the enhanced ion migration with fast water evaporation rate in the hydrophilic layer. The hydrophilic layer is consisted of polyvinyl alcohol (PVA) chains as skeleton and Li + /Cl − ions as charge carriers. The water (H 2 O) molecules are bonded to Li + /Cl − ions and carry ions with different migration rates for charge separation (Fig. 1 g) in the water transport. The 2.5×2.5 cm 2 gradient fabric with 0.2 g water evaporation shows an evaporation rate of 1.4 kg·m − 2 ·h − 1 and a highest temperature drop of 6.3°C (Fig. 1 h), almost two times performance of fabric without modification. The SSF delivers an open-circuit voltage of 0.86 V and a short-circuit current of 0.40 mA·cm − 2 (Fig. 1 i). The electric power and cooling capacity are 0.42 J and 7.6 J, respectively, which are attributed to water evaporation in each operation cycle (Supplementary Note 1). 2.2 Moisture and thermal management The directional water transport is critical to regulate wear comfort of wearable electronics by moisture/thermal managemen 30 , 31 . The underlying principles of directional water transport in the varied channels and hydrophilicity are illustrated in the different configurations (Fig. 2 a). The water in the hydrophilic channels tends to wet on the large surfaces of fabric in the evaporation, while the water in the hydrophobic channels moves towards the narrow channels by the capillary pressure and is locked inside the fabric. By constructing gradient wetting channels in the liquid diode, water transports from hydrophobic side to hydrophobic side in a one-way direction. Thus, the liquid water is pumped from skin and is expelled to the external environment by evaporation. To achieve gradient wetting channels, the hydrophobic TiO 2 nanoparticles were sprayed on the one side of nylon fabric. The water contact angles (Supplementary Note 2 and Supplementary Fig. 3) increase with the amount of TiO 2 nanoparticles for a higher breakthrough pressure (BP). The fabrics modified with 0.94–3.58 wt.% (“direction range”) TiO 2 are capable of blocking water by top side and transporting water from bottom side when 0.5 cm H 2 O of BP is set as a boundary between “Block” and “Pass” zones (Fig. 2 b and Supplementary Fig. 4). Thus, a liquid diode is achieved by conducting water flow in one direction, with low flow resistance (low BP) in the “Ⅰ” direction and high flow resistance (high BP) in the “Ⅱ” direction (Supplementary Fig. 5). Otherwise, the water wets all fabric surfaces ( 3.58 wt.% TiO 2 ). The TiO 2 content on different sides follows: “O” > “I” >pristine nylon (Fig. 2 c) when 3.58 wt.% TiO 2 was sprayed on the fabric to conduct water asymmetrically. The liquid diode is demonstrated by water transport rate (V T ) along thickness with different water height (H T ) applied on the fabric surface (Fig. 2 d). The liquid diode shows a higher V T when water is applied on the “O” side (positive direction), while blocks water with a threshold of ~ 5 cm when water is applied on the “I” side (negative direction). The directional water transport model is also established to verify moisture management in the liquid diode. The water droplet dyed with methylene blue dropped on the “I” side (Fig. 2 e and Supplementary Movie 1) wets immediately and spreads to a larger surface area of “I” side, with no water observed on the “O” side. Thus, the external water is prohibited from wetting on the “O” side or skin surface and evaporates into the environment by the “I” side. Meanwhile, water dropped on the “O” side penetrates the fabric and spreads on the “I” side within a larger area for dehumidification (Fig. 2 f and Supplementary Movie 2), leaving a dry surface of “O” side for the dehumidification and good wear comfort. According to Gibbs pinning criterion 32 , the expansion/contraction angle (α) of flow channels and water contact angle (θ) guarantee the advancement of water flow when α + θ < 90°, which is satisfied in the “Pass” zones and is unsatisfied in the “Block” zone (Supplementary Note 3 and Supplementary Fig. 5). The water evaporation rate (Fig. 2 g) of gradient fabric is 0.56 g·h − 1 , twice that of pristine fabric (0.28 g·h − 1 ). The faster water evaporation (Supplementary Note 4 and Supplementary Fig. 6) as well as good air/moisture permeability (Supplementary Fig. 7) are also demonstrated by the SSF devices with gradient fabric. The significantly improved drying rate by the gradient fabric is attributed to the directional water transport toward “I” side and the wetting on a larger area. The wetting area of “O” side and “I” side (Fig. 2 h) is 0.8 cm 2 and 7.0 cm 2 , respectively, indicating that the evaporation area is increased by more than 8 times after water passes through the gradient fabric (“O” to “I”). The vertical water transport rate from “O” side to “I” side is 0.012 cm·s − 1 for dehumidification, while the horizontal water transport rate on the “I” side is 0.05 cm·s − 1 for wetting and water evaporation. The skin surface covered with gradient fabric is dry after 1 min operation and exhibits a better dehumidification performance, compared with wet skin without gradient fabric (Fig. 2 i). The surface temperature is reduced from 33.1°C to 26.8°C after evaporation and heat dissipation on the sweating arms in room conditions without convection (Fig. 2 j and Supplementary Fig. 8). 2.3 Electricity generation with high electric outputs In addition to good wear comfort, the directional water transport facilitates energy harvesting by the synergistic effect of water transport and ion migration in the functional layer (Fig. 3 a). Once the functional layer absorbs liquid water, water molecules transport from bottom side to top side under water gradient and drive ion migration by forming hydrated ion cluster for charge separation 33 . The strength difference of ν(‒OH) at ~ 3300 cm − 1 on the top and bottom surface of functional layer (Supplementary Fig. 9a) indicates that vertical water gradient exists during operation. The increasing water content in the functional layer contributes to more mobilized ions, that is charge carriers, which are beneficial in achieving high electric outputs. The water gradient and ion migration vanish after water is fully evaporated on the top side to achieve a full operation cycle. The SSF exposed to symmetrical relative humidity (RH) and asymmetrical RH show no current output and 0.15 mA·cm − 2 , respectively (Supplementary Note 5 and Supplementary Fig. 10). Thus, the water transport with hydrated ion clusters contributes to the formation of internal electric field (Supplementary Fig. 11). The current output of device is significantly improved from 0.19 mA·cm − 2 to 0.40 mA·cm − 2 by designing internal directional water transport (Fig. 3 b, Supplementary Fig. 12 and Supplementary Movie 3). The SSF device with gradient nylon also delivers a faster current response due to the fast vertical water transport, compared with device without moisture management. The devices without fabrics show a transient current peak of 0.15 mA·cm − 2 after absorbing water owing to the rapid vanish of water gradient without fabric (Supplementary Fig. 13). Thus, the design of directional water transport not only improves wear comfort of hygroelectric generator but also enhances ion migration for higher electric outputs. The SSF achieves continuous electric outputs with sufficient water sources by placing the bottom side of SSF onto the water tank over a week (Fig. 3 c). Besides, the graphene was printed as top electrode to facilitate water evaporation 34 for higher electric outputs, while aluminium (Al) with a higher electric conductivity was printed as bottom electrode to improve electric outputs (Supplementary Note 6, Supplementary Figs. 14 and 15). No chemical reaction between electrode and functional layer is detected from cyclic voltammetry curve and element distribution in Supplementary Fig. 16. The interaction between charge carriers and functional layer is closely related to the electricity generation. The SSF delivers no electric output without lithium chloride (LiCl), owing to no charge carrier available. By increasing the ratio of LiCl and PVA in the functional layer, the electric outputs of devices improve (Fig. 3 d). With the addition of LiCl, the ratio of intermediate water increases (Supplementary Note 7 and Supplementary Fig. 17), which can be vaporized with less energy and a higher evaporation rate compared with free water in the functional layer 35 . Besides, the increased contents of LiCl endow the functional layers with more charge carriers and lower ionic resistance (Fig. 3 e) in the electrochemical impedance spectroscopy (EIS). Moreover, the added LiCl salts in the PVA chains contribute to a higher electrostatic gradient along the PVA chains for charge separation and a wider electrostatic potential (ESP) distribution for water absorption in the density functional theory calculation (Supplementary Note 8 and Supplementary Fig. 18). An ultrahigh output of 0.48 mA·cm − 2 in the water evaporation was achieved (Fig. 3 f), which is higher than the output (0.40 mA·cm − 2 ) with D.I. water and salts provides more carriers (Supplementary Note 9 and Supplementary Fig. 19) for electricity generation. Unlike the common reported hygroelectric generators with several microamperes 15 , the significantly enhanced current output (hundreds of microamperes) with liquid water in this work is more promising as practical power supply. Various models were carried out to reveal the mechanism of electricity generation with water transport and ion migration. Once SSF absorbs water from bottom side, the surface potential by Kelvin probe force microscopy (KPFM) on the top side of hydrophilic layer becomes more negative with the extended operation time (Fig. 3 g), which demonstrates that more Cl − ions are accumulated on the top side to achieve charge separation by the water transport. The water molecules with greater polarity are also demonstrated to be a better carrier of ion migration for electricity generation (Supplementary Fig. 20). The faster ion migration of Cl − ions than that of Li + ions constructs a negative charge surface on the top side and a positive charge surface on the bottom side along the direction of water transport. The detailed 3D snapshot of functional layer was performed from molecular dynamics (MD) simulation by stacking two gel layers together, which starts with the top layer (LiCl:H 2 O:PVA = 100:1200:70) and the bottom layer (LiCl:H 2 O:70 = 100:6000:70) at t = 0 ns (Fig. 3 h, Supplementary Note 10 and Supplementary Fig. 21). The water transport and ion migration from bottom layer to top layer under water gradient were observed (t = 10 ns) in the same polarity with electric outputs of SSF (Fig. 3 h). The diffusion coefficient of Li + and Cl − from mean squared displacement (MSD) calculation is 0.38×10 − 5 cm 2 ·s − 1 and 2.54×10 − 5 cm 2 ·s − 1 , respectively, indicating that Cl − ions can be separated from Li + ions by water transport (Fig. 3 i). From density functional theory (DFT) calculation, the energy barrier of Li + and Cl − migration along PVA chain is 0.40 eV and 0.18 eV (Supplementary Fig. 22), respectively, as Li + ions shows a higher binding energy with PVA/H 2 O in the functional layer (Supplementary Fig. 23). Thus, polymer chains can work as ion migration paths for charge separation of Li + and Cl − ions (Fig. 3 j) for electricity generation. Radial distribution function (RDF) and coordination number (CN) of Li + ions dispersed in the functional layer is lower than that of Li + ions dispersed in the pure water (Supplementary Fig. 24), which also demonstrates that polymer chains occupy inner solvent sheath of hydrated Li + ions and provide transportation paths for Li + ions. The current outputs of devices fabricated with other salts (e.g., NaCl) are lower (0.3 mA·cm − 2 in Supplementary Fig. 25a) and can be attributed to the lower electric conductivity by a lower ion migration rate (Supplementary Fig. 25b). Li + ions show a higher electrostatic force with water to form more hydrated ions for a faster ion migration rate (Supplementary Fig. 26). 2.4 Simultaneous self-cooling and electricity generation The self-cooing and electricity generation are evaluated simultaneously for good comprehensive performance. The higher porosity of grid-structure device represents a higher ratio of unprinted area on the liquid diode of gradient fabric for an overall faster water evaporation rate, leading to the better self-cooling performance with lower temperature (Fig. 4 a). The faster water evaporation in the device with a higher porosity also facilitates ion migration for higher electric outputs. However, the higher porosity represents a smaller printed area for current collection 31 . Therefore, the current output and released charges of SSF increases and then decreases with the increasing porosity (Fig. 4 b and Supplementary Fig. 27). The smaller pore size, instead of pore shape, contributes to more uniform water evaporation and higher electric outputs (Supplementary Fig. 28). Besides, the SSF shows similar thermal resistance (2–3 m 2 ·K·W − 1 ) with different porosity and gel thickness in the equivalent thermal resistance network (Supplementary Note 11 and Supplementary Fig. 29). The printed layers are relatively thin in thickness (0.17 mm) compared with fabrics (0.5 mm), and lead to no obvious increased thermal resistance after printing various layers. By dropping water in the different spots of bottom side, the performance of devices shows no significant variation in the various spots (Fig. 4 c) owing to the high wetting areas of gradient fabric (Fig. 2 g). The faster water evaporation in the thinner fabrics and functional layers enhances electric outputs of SSF (Supplementary Fig. 30). The strategy of simultaneous self-cooling and electricity generation is also applicable to other commonly used fabrics (Fig. 4 d). The nylon fabrics show a lower moisture regain and a higher water evaporation rate 36 , which are better than wool, silk and cotton in terms of electric outputs and cooling performance. The electric output and cooling performance also improve with more water dropped onto the bottom side (Fig. 4 e). No further improvement is observed with excess water content (> 0.03 g·cm − 2 ) as excess water covers the whole device without water gradient. The devices can operate in a wide range of temperatures and deliver increased electric outputs in the higher operation temperatures due to faster water evaporation and ion migration (Fig. 4 f). Besides, the faster evaporation in the lower RH and the greater water absorption in the higher RH are beneficial to achieving high current outputs (Supplementary Fig. 31). The stable wearability is demonstrated with repeated stretch cycles, where no obvious performance decline occurs after 10000 cycles (Fig. 4 g). Stable electric outputs are achieved in the various mechanical tests with 0‒50% strain, 0‒150° bending angle and 10000 bending cycles (Supplementary Fig. 32). The devices also exhibit stable operation cycles for long-term application (Fig. 4 h). In an operation cycle, the electric outputs start with dropping water and last until devices are fully dried. The SSF devices achieve a linear increase of accumulated released charges in the repeated operation cycles (1.36 C charge released for each cycle). No chemical leakage or electric performance decline occurs in the operation cycles or long-term storage period (Supplementary Fig. 33). The SSF achieves a highest output of 77.5 µW with 0.42 J when the resistance of the external load is 2 kΩ (Fig. 4 i). Moreover, the integrated device units deliver linearly increased electric outputs by printing multiple units connected in series or parallel (17.16 V and 7.90 mA with 20 device units in Supplementary Fig. 34). 2.5 Practical wearable application demonstrations Our devices can be integrated into the wearable electronic system for practical application. The devices were printed onto different types of clothes (Fig. 5 a), which demonstrates that SSF is applicable to various fabrics and body parts for a wide range of practical application. The device was printed with a large-scale area (14.5×14.5 cm 2 ) on the clothes and shows a uniform temperature drop of 6.3°C on the large-scale area with sweat (Fig. 5 b). The skin temperature drops from 33.1°C to 26.8°C in 16 mins (Fig. 5 c) to achieve a quick wear comfort. Two device units were printed in series and powered a flexible LED strip directly for a flexible and wearable LED display with various letters (Fig. 5 d). The wearable monitoring system is critical for the health care of infants or disable people with insufficient communication ability 37 . Owing to the specific relation between leaked water content and current outputs in this work, the SSF integrated with diaper delivers immediate information of the amount of the leaked urine by generating corresponding current (Fig. 5 e). The wireless monitoring system consists of SSF, diaper, wireless current sensor, monitor (Fig. 5 f and Supplementary Movie 4). The urgency level of help in need is described as “Comfort”, “Low”, “Moderate”, “High”, “Immediate” according to maximum current output in the range of 0‒0.1, 0.1‒0.2, 0.2‒0.3, 0.3‒0.4, > 0.4, respectively (Fig. 5 g). Besides, the harvested energy by SSF can be stored in the various power storage devices (Supplementary Fig. 35) as power supply. The wireless detection of body signals is also demonstrated with a battery charged by SSF, wireless sensor and monitor (Fig. 5 h and Supplementary Fig. 36) to transmit immediate signals of skin temperature and heart rate (Fig. 5 i). 3. Discussion We have developed a self-cooling and self-powered fabric that achieves moisture/thermal management and enhanced electricity generation by directional water transport and ion migration. The gradient wetting channels in the liquid diode are designed to absorb water from skin surface and block external water by directional water transport. The asymmetrical water evaporation on a large area contributes to a fast water evaporation rate of 0.56 g·h − 1 and a considerable temperature drop of 6.3°C for good wear comfort. The different ion migration rates of Li + /Cl − ions in the directional water transport boost charge separation for the enhanced electric output of 0.40 mA·cm − 2 . The temperature drops and electric outputs are also balanced to deliver good comprehensive performance by rationally designing composite and structure of grid sandwiched SSF. Meanwhile, the device exhibits good operation stability and is integrated with multiple practical electronic devices to provide health care and monitor human activity. Our designs introduce a novel and effective approach to provide good wear comfort and enhanced electric outputs simultaneously, a good solution that not only encourages good wearability but also holds the potential for energy harvest and power supply. Methods Liquid diode preparation. The plain knitted nylon fabrics with 83% Tactel and 17% Lycra (Sunikorn Knitters Limited, HongKong) were used as substrates of liquid diode for good elasticity and low hysteresis. The nylon fabrics were designed with a yarn density of 43 courses·m − 1 and 22 wales·m − 1 . The weight of the nylon fabric is 195 g·m − 2 , the linear density of the Tactel yarn and Lycra yarn is 702 denier/68 filaments and 40 denier/5 filaments, respectively, fiber diameter is 12–24 µm. The nylon fabrics were cleaned with improved hydrophilicity by the plasma (Plasma Etch PE-25) with O 2 for 10 min before their use. The fabrics with wetting channels were fabricated by spraying hydrophobic particles on the bottom side of fabrics. To get sprayable dispersion with hydrophobic nanoparticles, the mixture of 1H,1H,2H,2H-Perfluorooctyltriethoxysilane (98%, Sigma), TiO 2 (particle size 95%, Sigma) were mixed at a mass ratio of 1:5:200 and were stirred for 5 h before spraying. The dispersion was uniformly sprayed onto the bottom side of the fabrics with a constant distance. Then, the fabrics were dried at 50°C for 10 min before testing and printing. Device preparation. The graphene pastes ( 95%, < 15 µm) were mixed at a mass ratio of 5:1 by stirring for 2 h. The mixed pastes were printed onto the top side of fabrics by screen printing and were dried at 50°C for 10 min to work as bottom electrodes. The printable gels were fabricated by heating and stirring PVA (Mw ~ 61000, Sigma) in the LiCl (> 99%, Sigma) solution at 90°C for 2 h (mass ratio of LiCl:PVA:H 2 O = 1:2.5:17). Then, the gels were printed onto the bottom electrode by screen printing and were dried at 50°C in the vacuum oven for 2 h. The graphene pastes were printed onto the gels, followed by drying at 50°C for 10 min. Thermal measurement. Thermal images and videos were collected by the thermal imaging camera (Fluke Ti400U Thermal Imager, precision: ± 2°C or 2%) at room temperature of 25°C and 55% RH. The temperature was recorded by K-type thermocouples and Anbat AT4516 (Applent Instruments Ltd.) on the bottom side of SSF. The temperature of SSF or human skin on the forearm was collected after it reaches the minimum value. The distilled water was stored at same temperature as the forearm surface. 0.2 g distilled water was sprayed onto the forearm to mimic sweat evaporation before the operation of SSF. The artificial sweat (pH = 4.7) was prepared with 2 wt.% NaCl, 1.8 wt.% NH 4 OH, 0.5 wt.% acetic acid, and 1.5 wt.% actic acid, according to International Organization for Standardization (ISO) 3160-2. Electrical measurement. The relative humidity of electrical measurement was adjusted in an environmental chamber. The electric outputs of self-powered and self-cooling fabric (SSF) were collected by Keithley 2400 (Tektronix, USA). The surface potentials of device surface were recorded by Kelvin probe force microscopy (KPFM) with Bruker Dimension Icon machine. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry curve were performed by Autolab PGSTAT302N platform with two-electrode test at room humidity (RH = 55%). Characterizations. The morphology and element distribution of devices were characterized by the field-emission scanning electron microscope (FE-SEM, Tescan MAIA3) equipped with an energy dispersive spectroscopy (EDS). The elements in the different sides of fabrics were characterized by X-ray photoelectron spectroscopy (XPS) with the Al-Kα radiation (8.34 Å) as a power source in the ESCALAB 250Xi (Thermo Fisher) spectrometer. Fourier-transform infrared spectroscopy (FTIR, PerkinElmer, Spectrum 100) was used to record wetting strates of different surfaces. The breakthrough pressure of water flow through fabrics from was recorded by home-made platform in Supplementary Fig. 4. The wetting area of saline droplet with 0.9 wt.% NaCl on the fabric was obtained by moisture management tester (MMT, SDL ATLAS Ltd., China). The planar wetting area with time was used to calculate planar water transport rates. The water contact angle was measured by a drop shape analyzer (Krüss, Hamburg, Germany). to calculate vertical water transport rates. The permeability tests were performed by using a MO21S permeability tester (SDL Americ, Inc.). The water states of intermediate water (IW) and free water (FW) in the functional layer were revealed with Raman spectrometer (Renishaw inVia Reflex) at the wavelength of 532 nm. Declarations Competing interests The authors declare no conflict of interest. Author contributions X.T. and R.Z. conceived the idea. R.Z. carried out sample preparation, characterizations, testing and writing. Z.Z. designed the integrated electronic systems for application. Y.L. and K.M. modified parameters in the sample preparation and helped with SEM characterization. J.Y. performed the calculations in this work. S.L. helped with indoor and outdoor experiments. All authors discussed the results and reviewed the manuscript. Acknowledgments The project is partially sponsored by Innovation and Technology Commission of Hong Kong SAR Government (No. MRP/020/21), Hong Kong Research Grants Council (No. 15302121 and 15201922) and Hong Kong Polytechnic University (No. 847A and P0036628-49621). Data availability The data that support the findings of this paper are available from the corresponding authors upon reasonable request. References Lee H et al (2018) Toward all-day wearable health monitoring: An ultralow-power, reflective organic pulse oximetry sensing patch. Sci Adv 4:eaas9530 Haight R, Haensch W, Friedman D (2016) Solar-powering the internet of things. Science 353:124–125 Li DF et al (2022) Touch iot enabled by wireless self-sensing and haptic-reproducing electronic skin. Sci Adv 8:eade2450 Wood CS et al (2019) Taking connected mobile-health diagnostics of infectious diseases to the field. 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Energy Environ Sci 12:972–978 Sun ZY, Wen X, Wang LM, Yu JY, Qin XH (2022) Capacitor-inspired high-performance and durable moist-electric generator. Energy Environ Sci 15:4584–4591 Liu C et al (2022) Hydrovoltaic energy harvesting from moisture flow using an ionic polymer-hydrogel-carbon composite. Energy Environ Sci 15:2489–2498 Qin YS et al (2020) Constant electricity generation in nanostructured silicon by evaporation-driven water flow. Angew Chem Int Edit 59:10619–10625 Guo CY et al (2024) Radiative cooling assisted self-sustaining and highly efficient moisture energy harvesting. Nat Commun 15:6100 Zhang YF et al (2024) Thermal and moisture managing e-textiles enabled by janus hierarchical gradient honeycombs. Adv Mater 36:2311633 Zhang BB et al (2024) A three-dimensional liquid diode for soft, integrated permeable electronics. Nature 628:84–92 Shou DH, Fan JT (2018) An all hydrophilic fluid diode for unidirectional flow in porous systems. Adv Funct Mater 28:1800269 Zhu R, Liu T, Balilonda A, Luo Y, Ma K, Tao X (2025) Green, safe, durable, printed fabric hygroelectric generators for wearable systems. Adv Mater, 2502091 Zhao F, Guo YH, Zhou XY, Shi W, Yu GH (2020) Materials for solar-powered water evaporation. Nat Rev Mater 5:388–401 Zhou XY, Zhao F, Guo YH, Rosenberger B, Yu GH (2019) Architecting highly hydratable polymer networks to tune the water state for solar water purification. Sci Adv 5:eaaw5484 Alberghini M et al (2021) Sustainable polyethylene fabrics with engineered moisture transport for passive cooling. Nat Sustain 4:715–724 Mahato K, Saha T, Ding SC, Sandhu SS, Chang AY, Wang JS (2024) Hybrid multimodal wearable sensors for comprehensive health monitoring. Nat Electron 7:735–750 Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.pdf Supplementary Information SupplementaryMovie1.mp4 Supplementary Movie 1 SupplementaryMovie2.mp4 Supplementary Movie 2 SupplementaryMovie3.mp4 Supplementary Movie 3 SupplementaryMovie4.mp4 Supplementary Movie 4 Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7190787","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":499274506,"identity":"1a2993ee-b6ae-48cf-acf4-9affda42fbc3","order_by":0,"name":"Xiaoming Tao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFUlEQVRIiWNgGAWjYDACZjApAeVVMDDwgRlsDAwGPAS1gFhnwIoJaEHRzNhGhBaD48wPHzDmWOTJO/Af/PBx3h05NokcA4YPZYcZzHkOYNUi2cxmbMC4TaLY8AAzs+TMbc+MQVoYZ5w7zGDZ24BVCz8zg5n0320SiRsbmBmkebcdTmwDamHmbTvMYHAeu8PYmNm/STBCtDD/5p0D1fIXjxZ+Zh4zsJb5DMxs0rwNUC2MIC1nsTtMspmnGOSXxA3MzGaWM44B/cLzrOBgz7l0HoMz2L1vcP74xgeM2+oS57c3Pr7xoeaOHD978sYHP8qs5QzOJGB3GVzvYTAFNFggAUQyEI5I+QaYFn7s7hkFo2AUjIKRCwBNDFYvox/TjAAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-2406-0695","institution":"Hong Kong Polytechnic University","correspondingAuthor":true,"prefix":"","firstName":"Xiaoming","middleName":"","lastName":"Tao","suffix":""},{"id":499274507,"identity":"d2f41359-19ce-44e8-8a18-cfd66437a49f","order_by":1,"name":"Renbo Zhu","email":"","orcid":"","institution":"Hong Kong Polytechnic University","correspondingAuthor":false,"prefix":"","firstName":"Renbo","middleName":"","lastName":"Zhu","suffix":""},{"id":499274508,"identity":"02d75355-1cb1-455b-a8a9-6a1e9cf85087","order_by":2,"name":"Zhongliang Zhang","email":"","orcid":"","institution":"Hong Kong Polytechnic University","correspondingAuthor":false,"prefix":"","firstName":"Zhongliang","middleName":"","lastName":"Zhang","suffix":""},{"id":499274509,"identity":"7266b1ea-7178-4dc6-968e-220d6481a58e","order_by":3,"name":"Kitming Ma","email":"","orcid":"","institution":"Hong Kong Polytechnic University","correspondingAuthor":false,"prefix":"","firstName":"Kitming","middleName":"","lastName":"Ma","suffix":""},{"id":499274510,"identity":"29f983c6-a9ab-4493-bb2c-7598de6d8773","order_by":4,"name":"Yonghui Luo","email":"","orcid":"","institution":"Hong Kong Polytechnic University","correspondingAuthor":false,"prefix":"","firstName":"Yonghui","middleName":"","lastName":"Luo","suffix":""},{"id":499274511,"identity":"6abcbfad-31f4-467b-b75d-6716b0feeb0a","order_by":5,"name":"Ying Yang","email":"","orcid":"","institution":"THe Hong Kong Polytechnic University","correspondingAuthor":false,"prefix":"","firstName":"Ying","middleName":"","lastName":"Yang","suffix":""},{"id":499274512,"identity":"40b206ee-136a-409f-91c0-37cc70a8f208","order_by":6,"name":"Su Liu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Su","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2025-07-22 23:55:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7190787/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7190787/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89040607,"identity":"cf57b6ab-6352-4e4f-9115-70263b5e1232","added_by":"auto","created_at":"2025-08-14 05:36:38","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":3449670,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eConcept and advantage of the SSF.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Schematic illustration of regular fabrics without moisture/thermal management. \u003cstrong\u003eb\u003c/strong\u003e, Schematic illustration of SSF with moisture/thermal management and electricity generation for self-cooling and electricity generation. \u003cstrong\u003ec\u003c/strong\u003e, Illustration of the SSF device for self-cooling and electricity generation by directional sweat evaporation on the human skin. \u003cstrong\u003ed\u003c/strong\u003e, Performance comparison of reported generators based on water evaporation\u003csup\u003e13, 14, 15, 28, 29\u003c/sup\u003e. The BP ratio is defined as the ratio of water breakthrough pressure in the different sides of liquid diode. \u003cstrong\u003ee\u003c/strong\u003e, Mechanism illustration of directional water transport and evaporation through fiber channels with gradient TiO\u003csub\u003e2\u003c/sub\u003e particles in the gradient fabric. \u003cstrong\u003ef\u003c/strong\u003e, Morphology of gradient fabric, C and Ti element distribution in the gradient fabric. \u003cstrong\u003eg\u003c/strong\u003e, Mechanism analysis of charge separation for electricity generation by the migration of different ions with water in the hygroelectric generators. \u003cstrong\u003eh\u003c/strong\u003e, Evaporation rate and temperature difference by nylon fabric and gradient nylon fabric. \u003cstrong\u003ei\u003c/strong\u003e, Open-circuit voltage and short-circuit current of SSF devices fabricated with nylon fabric and gradient nylon fabric.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/7002d79eae127e97d44b5a0b.png"},{"id":89040609,"identity":"874d574f-85e6-402e-8bd5-577fef2af24c","added_by":"auto","created_at":"2025-08-14 05:36:38","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2794067,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLiquid diode with directional water transport for dehumidification and self-cooling. a\u003c/strong\u003e, Water transport in the channels of fibers with different hydrophilicity. \u003cstrong\u003eb\u003c/strong\u003e, Breakthrough pressure of hydrophilic and hydrophobic side in the gradient fabric with different TiO\u003csub\u003e2\u003c/sub\u003e contents in the spraying process. \u003cstrong\u003ec\u003c/strong\u003e, The element distribution of pristine, hydrophilic and hydrophobic nylon by X-ray photoelectron spectroscopy analysis. \u003cstrong\u003ed\u003c/strong\u003e, Water transport rate along the thickness with different applied water height. The water transport from “O” side and “I” is positive and negative, respectively. \u003cstrong\u003ee\u003c/strong\u003e,\u003cstrong\u003ef\u003c/strong\u003e, Water transport through gradient fabric by dropping dyed water on the hydrophilic side (\u003cstrong\u003ee\u003c/strong\u003e) and hydrophobic side (\u003cstrong\u003ef\u003c/strong\u003e). \u003cstrong\u003eg\u003c/strong\u003e, Water evaporation on the nylon fabric and gradient nylon fabric by dropping water on the hydrophobic side. \u003cstrong\u003eh\u003c/strong\u003e, Wetting rates in the different directions of water transport in the gradient fabric. \u003cstrong\u003ei\u003c/strong\u003e, Photos of dehumidification by gradient fabric on the sweating arm. \u003cstrong\u003ej,\u003c/strong\u003e Optical and infrared image of self-cooling by gradient fabric on a sweating arm.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/ff840d7fb56ec5b470e59530.png"},{"id":89041641,"identity":"1a2c5d62-667f-42d8-b0e7-4941a2bedafa","added_by":"auto","created_at":"2025-08-14 05:44:39","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2558146,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectricity generation of SSF. a\u003c/strong\u003e, Schematical illustration of ion migration by water transport in the functional layer. \u003cstrong\u003eb\u003c/strong\u003e, Current outputs of SSF fabricated with nylon fabric and gradient nylon fabric. 0.2 g water was dropped on the bottom side of devices. \u003cstrong\u003ec\u003c/strong\u003e, Voltage/current retention of SSF with bottom side in contact with liquid water over a week. \u003cstrong\u003ed\u003c/strong\u003e, Electric outputs of SSF with different ratios of LiCl and PVA. \u003cstrong\u003ee\u003c/strong\u003e, EIS of functional layers with different ratios of LiCl and PVA. \u003cstrong\u003ef\u003c/strong\u003e, Current outputs of SSF with different water as energy sources. \u003cstrong\u003eg\u003c/strong\u003e, Potential variation on the top side of functional layers with different wetting time from KPFM tests. \u003cstrong\u003eh\u003c/strong\u003e, 3D snapshots from MD simulations at 0 ns and 10 ns. \u003cstrong\u003ei\u003c/strong\u003e, MSDs versus time by ion migration of Li\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e-\u003c/sup\u003e. \u003cstrong\u003ej\u003c/strong\u003e, Li\u003csup\u003e+\u003c/sup\u003e ion and Cl\u003csup\u003e-\u003c/sup\u003e ion in the functional layer at 0 ns and 10 ns.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/150361c09add0b1987ae178e.png"},{"id":89040616,"identity":"06ab3388-4932-4b27-94a8-bbf56dc6e4cd","added_by":"auto","created_at":"2025-08-14 05:36:39","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1773010,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThermal and electrical performance of SSF. a\u003c/strong\u003e, Evaporation rate and temperature of SSF on the wet skin. \u003cstrong\u003eb\u003c/strong\u003e, Current output and charges released by SSF on the wet skin. \u003cstrong\u003ec\u003c/strong\u003e, Electric outputs and temperature of SSF by dropping water in the different spots of gradient fabric. \u003cstrong\u003ed\u003c/strong\u003e, Temperature and current output of SSF fabricated with various fabrics. \u003cstrong\u003ee\u003c/strong\u003e, Charges and temperature of SSF exposed to the different water contents. \u003cstrong\u003ef\u003c/strong\u003e, Electric outputs of SSF operating in the different environmental temperatures. \u003cstrong\u003eg\u003c/strong\u003e, The temperature and current output of SSF with different stretch cycles. \u003cstrong\u003eh\u003c/strong\u003e, Accumulated released charges and current output of SSF with periodic water drop. \u003cstrong\u003ei\u003c/strong\u003e, Power output and electric energy of external loads by connecting SSF to the loads with different resistance.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/4b44130657f9f86c1e24c5e9.png"},{"id":89040620,"identity":"53c705a6-89f5-44f6-a96a-e871e3ad1bb9","added_by":"auto","created_at":"2025-08-14 05:36:39","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":4424856,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eApplication demonstration of wearable electronic systems. a\u003c/strong\u003e, Photos of SSF printed on the different clothes. \u003cstrong\u003eb\u003c/strong\u003e, Photo and infrared images of 14.5×14.5 cm\u003csup\u003e2\u003c/sup\u003e SSF with sweat. \u003cstrong\u003ec\u003c/strong\u003e, Temperature curve of 14.5×14.5 cm\u003csup\u003e2\u003c/sup\u003e SSF with and without sweat. \u003cstrong\u003ed\u003c/strong\u003e, The self-powered wearable display system with 2 device units and a LED stripe as power supply and display, respectively. \u003cstrong\u003ee\u003c/strong\u003e, Schematical illustration of disposable wearable system to detect bio-markers in the urine. \u003cstrong\u003ef\u003c/strong\u003e, Photo of urine detection system with SSF, diaper, monitor and wireless current sensor. \u003cstrong\u003eg\u003c/strong\u003e, The evaluation of health care by the relation between current output of SSF and urgency level. \u003cstrong\u003eh\u003c/strong\u003e, Photo of body signal detection system with monitor, wireless sensor and a battery charged by SSF. \u003cstrong\u003ei\u003c/strong\u003e, Schematical operation illustration of vital-sign monitoring system. \u003cstrong\u003ej\u003c/strong\u003e, Body signals with skin temperature and heart rate from the monitoring system.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/adabb26d05ee56344c1a2b89.png"},{"id":89043344,"identity":"ca23e31e-e9cd-4d21-ac6b-00443447230f","added_by":"auto","created_at":"2025-08-14 06:08:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":14881877,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/3ba596ca-9dea-423c-a8f9-bcffe863d51c.pdf"},{"id":89040610,"identity":"4dfd029b-6065-4b7e-8d2a-4bb4ef04c251","added_by":"auto","created_at":"2025-08-14 05:36:38","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":4464472,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/adf7eaf1462b3ce99770c47c.pdf"},{"id":89042477,"identity":"52797538-f52d-4f2d-a125-8e7df2f2b4f7","added_by":"auto","created_at":"2025-08-14 06:00:39","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3978691,"visible":true,"origin":"","legend":"Supplementary Movie 1","description":"","filename":"SupplementaryMovie1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/6919fb0c7ddeebc549d67a7b.mp4"},{"id":89041643,"identity":"3c264773-5241-47ce-9966-cf77fed73066","added_by":"auto","created_at":"2025-08-14 05:44:39","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":11886075,"visible":true,"origin":"","legend":"Supplementary Movie 2","description":"","filename":"SupplementaryMovie2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/3f15ffed1589e81376e6185a.mp4"},{"id":89040628,"identity":"8c08bc33-a156-4ae7-9913-c81c169bcd59","added_by":"auto","created_at":"2025-08-14 05:36:39","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":21308112,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 3\u003c/p\u003e","description":"","filename":"SupplementaryMovie3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/659b812ea664df5c3f9c78af.mp4"},{"id":89040632,"identity":"ec0f0943-c625-4b71-94a7-02223474988b","added_by":"auto","created_at":"2025-08-14 05:36:39","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":20107168,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 4\u003c/p\u003e","description":"","filename":"SupplementaryMovie4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7190787/v1/19dbe5d8b3a0140fdc40379c.mp4"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Fabric liquid diode for electricity generation and self-cooling","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe increasing demands of green and wearable power supply have been a great global concern as a wide variety of electronic devices are emerging for \u0026ldquo;Internet of Things\u0026rdquo; (IoTs), such as human activity monitoring and human-machine interaction\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. The power supply devices are the key components in the electronic systems that guarantee the stable operation of integrated units. Tremendous efforts have been made in the energy harvesting technologies (e.g., solar cell, piezoelectric generator, thermoelectric generator) for power supply, which achieve electricity generation by exposing generators to the energy sources of light, motion and temperature gradient\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. The operation of energy harvesting strongly depends on the working environments and is insufficient to support real-time and continuous monitoring in the varied environments. Besides, the wear comfort, especially regulating moisture/sweat and body heat, is critical in the long-term wearability of wearable electronic textiles\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. The reported power supply devices covering the fabric or human skin inhibit the release of moisture/sweat and body heat into environment\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Thus, the wearable power supplies exhibit unsatisfied electric outputs and wearability, impeding their practical applications and mass production.\u003c/p\u003e\u003cp\u003eOne promising approach to maintaining wearable power supplies with continuous outputs is collecting abundant moisture and converting chemical potential energy from moisture into electricity\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. The sustainable electric outputs have been demonstrated with hygroelectric generators as the moisture is a ubiquitous energy source in the various environments\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. By absorbing moisture with hydrophilic layers and forming asymmetrical water and ion gradient, the hygroelectric generators achieve ion migration and charge separation for sustainable electricity generation. The high moisture absorption of hydrophilic layer is often considered, but moisture management for directional ion transport and enhanced current outputs is generally not considered\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. Therefore, the electric outputs (several microamperes) of hygroelectric generators are insufficient to power practical application as only a limited number of devices with a low power consumption can be driven by hygroelectric generators\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Besides, the moisture was absorbed and confined inside hydrophilic layer\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, the waterproof substrates on the fabrics also blocked water transport in the direction from human body to the environment\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Thus, the poor water regulation of hygroelectric generators without moisture and thermal management is detrimental to users\u0026rsquo; wear comfort (Fig.\u0026nbsp;1a).\u003c/p\u003e\u003cp\u003eHere, we propose a rationally designed self-powered and self-cooling fabric (SSF) to simultaneously improve wear comfort and electric outputs (Fig.\u0026nbsp;1b) by the synergistic effect of directional water transport and ion migration. The liquid diode spontaneously pumps sweat from skin surface to the external side of the fabric and blocks environmental water infiltration, contributing to a fast water transport rate of 0.012 cm\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for dehumidification and good wear comfort. The water evaporation on the nylon fabrics improves by two times (from 0.28 g\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 0.56 g\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and dissipates body heat with a skin temperature drop of 6.3\u0026deg;C for self-cooling. Besides, the devices with grid sandwich structures are designed and are printed on the liquid diode to allow fast and directional water evaporation through the generator, which triggers fast ion migration for the enhanced charge separation and electricity generation (0.40 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). The efficient moisture management and enhanced electric outputs of SSF improve human comfort and solve a series of critical challenges of wearable power supply.\u003c/p\u003e"},{"header":"2. Results","content":"\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Designs for self-cooling and electricity generation\u003c/h2\u003e\u003cp\u003eWe elaborated SSF by printing hygroelectric generators (aluminium, polyvinyl alcohol/lithium chloride and graphene as bottom electrode, functional layer and top electrode, respectively) with grid sandwich structures (Supplementary Fig.\u0026nbsp;1) on the liquid diode for self-cooling and electricity generation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). The printed areas and unprinted areas in the grid structure are mainly responsible for electricity generation and moisture/thermal management, respectively. The liquid diode of gradient fabric (G-fabric) can transport sweat on the skin surface to external environment directionally for dehumidification and good wear comfort. The water evaporation on the large surfaces of gradient fabric dissipates body heat for self-cooling. The water transport also drives directional ion migration inside functional layer of hygroelectric generators for electricity generation. Moreover, SSF shows good comprehensive performance as wearable power supply in terms of breakthrough pressure (BP) ratio, electric outputs, temperature reduction (ΔT) and stretch cycles, which are significantly improved in comparison with other reported generators based on water evaporation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed and table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe nylon fabrics are endowed with gradient wetting channels by hydrophobic titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e) nanoparticles with gradient distribution along the water flow channels (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee), which are achieved by spraying TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles on the one side of fabric (Supplementary Fig.\u0026nbsp;1). The amount of TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles along the channels of nylon fibers is decreased from the bottom to the top side to guarantee the one-way water movement of in the channel with varied width. The morphology of nylon fibers and element distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef, Supplementary Fig.\u0026nbsp;2) confirm the exist of the hollow channel among nylon fibers and the vertical gradient distribution of TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles. The Ti element of pristine nylon, hydrophilic (\u0026ldquo;I\u0026rdquo;) side, hydrophobic (\u0026ldquo;O\u0026rdquo;) side is 0.0%, 10.4% and 20.5%, respectively (table S2).\u003c/p\u003e\u003cp\u003eThe enhanced electricity generation is attributed to the enhanced ion migration with fast water evaporation rate in the hydrophilic layer. The hydrophilic layer is consisted of polyvinyl alcohol (PVA) chains as skeleton and Li\u003csup\u003e+\u003c/sup\u003e/Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions as charge carriers. The water (H\u003csub\u003e2\u003c/sub\u003eO) molecules are bonded to Li\u003csup\u003e+\u003c/sup\u003e/Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions and carry ions with different migration rates for charge separation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg) in the water transport. The 2.5\u0026times;2.5 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e gradient fabric with 0.2 g water evaporation shows an evaporation rate of 1.4 kg\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a highest temperature drop of 6.3\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh), almost two times performance of fabric without modification. The SSF delivers an open-circuit voltage of 0.86 V and a short-circuit current of 0.40 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ei). The electric power and cooling capacity are 0.42 J and 7.6 J, respectively, which are attributed to water evaporation in each operation cycle (Supplementary Note 1).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Moisture and thermal management\u003c/h2\u003e\u003cp\u003eThe directional water transport is critical to regulate wear comfort of wearable electronics by moisture/thermal managemen\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. The underlying principles of directional water transport in the varied channels and hydrophilicity are illustrated in the different configurations (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). The water in the hydrophilic channels tends to wet on the large surfaces of fabric in the evaporation, while the water in the hydrophobic channels moves towards the narrow channels by the capillary pressure and is locked inside the fabric. By constructing gradient wetting channels in the liquid diode, water transports from hydrophobic side to hydrophobic side in a one-way direction. Thus, the liquid water is pumped from skin and is expelled to the external environment by evaporation. To achieve gradient wetting channels, the hydrophobic TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles were sprayed on the one side of nylon fabric. The water contact angles (Supplementary Note 2 and Supplementary Fig.\u0026nbsp;3) increase with the amount of TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles for a higher breakthrough pressure (BP). The fabrics modified with 0.94\u0026ndash;3.58 wt.% (\u0026ldquo;direction range\u0026rdquo;) TiO\u003csub\u003e2\u003c/sub\u003e are capable of blocking water by top side and transporting water from bottom side when 0.5 cm H\u003csub\u003e2\u003c/sub\u003eO of BP is set as a boundary between \u0026ldquo;Block\u0026rdquo; and \u0026ldquo;Pass\u0026rdquo; zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;4). Thus, a liquid diode is achieved by conducting water flow in one direction, with low flow resistance (low BP) in the \u0026ldquo;Ⅰ\u0026rdquo; direction and high flow resistance (high BP) in the \u0026ldquo;Ⅱ\u0026rdquo; direction (Supplementary Fig.\u0026nbsp;5). Otherwise, the water wets all fabric surfaces (\u0026lt;\u0026thinsp;0.94 wt.% TiO\u003csub\u003e2\u003c/sub\u003e) or is locked inside flow channels (\u0026gt;\u0026thinsp;3.58 wt.% TiO\u003csub\u003e2\u003c/sub\u003e). The TiO\u003csub\u003e2\u003c/sub\u003e content on different sides follows: \u0026ldquo;O\u0026rdquo; \u0026gt; \u0026ldquo;I\u0026rdquo; \u0026gt;pristine nylon (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec) when 3.58 wt.% TiO\u003csub\u003e2\u003c/sub\u003e was sprayed on the fabric to conduct water asymmetrically.\u003c/p\u003e\u003cp\u003eThe liquid diode is demonstrated by water transport rate (V\u003csub\u003eT\u003c/sub\u003e) along thickness with different water height (H\u003csub\u003eT\u003c/sub\u003e) applied on the fabric surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). The liquid diode shows a higher V\u003csub\u003eT\u003c/sub\u003e when water is applied on the \u0026ldquo;O\u0026rdquo; side (positive direction), while blocks water with a threshold of ~\u0026thinsp;5 cm when water is applied on the \u0026ldquo;I\u0026rdquo; side (negative direction). The directional water transport model is also established to verify moisture management in the liquid diode. The water droplet dyed with methylene blue dropped on the \u0026ldquo;I\u0026rdquo; side (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee and Supplementary Movie 1) wets immediately and spreads to a larger surface area of \u0026ldquo;I\u0026rdquo; side, with no water observed on the \u0026ldquo;O\u0026rdquo; side. Thus, the external water is prohibited from wetting on the \u0026ldquo;O\u0026rdquo; side or skin surface and evaporates into the environment by the \u0026ldquo;I\u0026rdquo; side. Meanwhile, water dropped on the \u0026ldquo;O\u0026rdquo; side penetrates the fabric and spreads on the \u0026ldquo;I\u0026rdquo; side within a larger area for dehumidification (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef and Supplementary Movie 2), leaving a dry surface of \u0026ldquo;O\u0026rdquo; side for the dehumidification and good wear comfort. According to Gibbs pinning criterion\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e, the expansion/contraction angle (α) of flow channels and water contact angle (θ) guarantee the advancement of water flow when α\u0026thinsp;+\u0026thinsp;θ\u0026thinsp;\u0026lt;\u0026thinsp;90\u0026deg;, which is satisfied in the \u0026ldquo;Pass\u0026rdquo; zones and is unsatisfied in the \u0026ldquo;Block\u0026rdquo; zone (Supplementary Note 3 and Supplementary Fig.\u0026nbsp;5). The water evaporation rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg) of gradient fabric is 0.56 g\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, twice that of pristine fabric (0.28 g\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The faster water evaporation (Supplementary Note 4 and Supplementary Fig.\u0026nbsp;6) as well as good air/moisture permeability (Supplementary Fig.\u0026nbsp;7) are also demonstrated by the SSF devices with gradient fabric. The significantly improved drying rate by the gradient fabric is attributed to the directional water transport toward \u0026ldquo;I\u0026rdquo; side and the wetting on a larger area. The wetting area of \u0026ldquo;O\u0026rdquo; side and \u0026ldquo;I\u0026rdquo; side (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh) is 0.8 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e and 7.0 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, respectively, indicating that the evaporation area is increased by more than 8 times after water passes through the gradient fabric (\u0026ldquo;O\u0026rdquo; to \u0026ldquo;I\u0026rdquo;). The vertical water transport rate from \u0026ldquo;O\u0026rdquo; side to \u0026ldquo;I\u0026rdquo; side is 0.012 cm\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for dehumidification, while the horizontal water transport rate on the \u0026ldquo;I\u0026rdquo; side is 0.05 cm\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for wetting and water evaporation. The skin surface covered with gradient fabric is dry after 1 min operation and exhibits a better dehumidification performance, compared with wet skin without gradient fabric (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei). The surface temperature is reduced from 33.1\u0026deg;C to 26.8\u0026deg;C after evaporation and heat dissipation on the sweating arms in room conditions without convection (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej and Supplementary Fig.\u0026nbsp;8).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Electricity generation with high electric outputs\u003c/h2\u003e\u003cp\u003eIn addition to good wear comfort, the directional water transport facilitates energy harvesting by the synergistic effect of water transport and ion migration in the functional layer (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Once the functional layer absorbs liquid water, water molecules transport from bottom side to top side under water gradient and drive ion migration by forming hydrated ion cluster for charge separation\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. The strength difference of ν(‒OH) at ~\u0026thinsp;3300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e on the top and bottom surface of functional layer (Supplementary Fig.\u0026nbsp;9a) indicates that vertical water gradient exists during operation. The increasing water content in the functional layer contributes to more mobilized ions, that is charge carriers, which are beneficial in achieving high electric outputs. The water gradient and ion migration vanish after water is fully evaporated on the top side to achieve a full operation cycle. The SSF exposed to symmetrical relative humidity (RH) and asymmetrical RH show no current output and 0.15 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively (Supplementary Note 5 and Supplementary Fig.\u0026nbsp;10). Thus, the water transport with hydrated ion clusters contributes to the formation of internal electric field (Supplementary Fig.\u0026nbsp;11).\u003c/p\u003e\u003cp\u003eThe current output of device is significantly improved from 0.19 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e to 0.40 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e by designing internal directional water transport (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, Supplementary Fig.\u0026nbsp;12 and Supplementary Movie 3). The SSF device with gradient nylon also delivers a faster current response due to the fast vertical water transport, compared with device without moisture management. The devices without fabrics show a transient current peak of 0.15 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e after absorbing water owing to the rapid vanish of water gradient without fabric (Supplementary Fig.\u0026nbsp;13). Thus, the design of directional water transport not only improves wear comfort of hygroelectric generator but also enhances ion migration for higher electric outputs. The SSF achieves continuous electric outputs with sufficient water sources by placing the bottom side of SSF onto the water tank over a week (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Besides, the graphene was printed as top electrode to facilitate water evaporation\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e for higher electric outputs, while aluminium (Al) with a higher electric conductivity was printed as bottom electrode to improve electric outputs (Supplementary Note 6, Supplementary Figs.\u0026nbsp;14 and 15). No chemical reaction between electrode and functional layer is detected from cyclic voltammetry curve and element distribution in Supplementary Fig.\u0026nbsp;16.\u003c/p\u003e\u003cp\u003eThe interaction between charge carriers and functional layer is closely related to the electricity generation. The SSF delivers no electric output without lithium chloride (LiCl), owing to no charge carrier available. By increasing the ratio of LiCl and PVA in the functional layer, the electric outputs of devices improve (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). With the addition of LiCl, the ratio of intermediate water increases (Supplementary Note 7 and Supplementary Fig.\u0026nbsp;17), which can be vaporized with less energy and a higher evaporation rate compared with free water in the functional layer\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. Besides, the increased contents of LiCl endow the functional layers with more charge carriers and lower ionic resistance (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee) in the electrochemical impedance spectroscopy (EIS). Moreover, the added LiCl salts in the PVA chains contribute to a higher electrostatic gradient along the PVA chains for charge separation and a wider electrostatic potential (ESP) distribution for water absorption in the density functional theory calculation (Supplementary Note 8 and Supplementary Fig.\u0026nbsp;18). An ultrahigh output of 0.48 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in the water evaporation was achieved (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef), which is higher than the output (0.40 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) with D.I. water and salts provides more carriers (Supplementary Note 9 and Supplementary Fig.\u0026nbsp;19) for electricity generation. Unlike the common reported hygroelectric generators with several microamperes\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, the significantly enhanced current output (hundreds of microamperes) with liquid water in this work is more promising as practical power supply.\u003c/p\u003e\u003cp\u003eVarious models were carried out to reveal the mechanism of electricity generation with water transport and ion migration. Once SSF absorbs water from bottom side, the surface potential by Kelvin probe force microscopy (KPFM) on the top side of hydrophilic layer becomes more negative with the extended operation time (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg), which demonstrates that more Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions are accumulated on the top side to achieve charge separation by the water transport. The water molecules with greater polarity are also demonstrated to be a better carrier of ion migration for electricity generation (Supplementary Fig.\u0026nbsp;20). The faster ion migration of Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions than that of Li\u003csup\u003e+\u003c/sup\u003e ions constructs a negative charge surface on the top side and a positive charge surface on the bottom side along the direction of water transport. The detailed 3D snapshot of functional layer was performed from molecular dynamics (MD) simulation by stacking two gel layers together, which starts with the top layer (LiCl:H\u003csub\u003e2\u003c/sub\u003eO:PVA\u0026thinsp;=\u0026thinsp;100:1200:70) and the bottom layer (LiCl:H\u003csub\u003e2\u003c/sub\u003eO:70\u0026thinsp;=\u0026thinsp;100:6000:70) at t\u0026thinsp;=\u0026thinsp;0 ns (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh, Supplementary Note 10 and Supplementary Fig.\u0026nbsp;21). The water transport and ion migration from bottom layer to top layer under water gradient were observed (t\u0026thinsp;=\u0026thinsp;10 ns) in the same polarity with electric outputs of SSF (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh). The diffusion coefficient of Li\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e from mean squared displacement (MSD) calculation is 0.38\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2.54\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively, indicating that Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions can be separated from Li\u003csup\u003e+\u003c/sup\u003e ions by water transport (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei). From density functional theory (DFT) calculation, the energy barrier of Li\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e migration along PVA chain is 0.40 eV and 0.18 eV (Supplementary Fig.\u0026nbsp;22), respectively, as Li\u003csup\u003e+\u003c/sup\u003e ions shows a higher binding energy with PVA/H\u003csub\u003e2\u003c/sub\u003eO in the functional layer (Supplementary Fig.\u0026nbsp;23). Thus, polymer chains can work as ion migration paths for charge separation of Li\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej) for electricity generation. Radial distribution function (RDF) and coordination number (CN) of Li\u003csup\u003e+\u003c/sup\u003e ions dispersed in the functional layer is lower than that of Li\u003csup\u003e+\u003c/sup\u003e ions dispersed in the pure water (Supplementary Fig.\u0026nbsp;24), which also demonstrates that polymer chains occupy inner solvent sheath of hydrated Li\u003csup\u003e+\u003c/sup\u003e ions and provide transportation paths for Li\u003csup\u003e+\u003c/sup\u003e ions. The current outputs of devices fabricated with other salts (e.g., NaCl) are lower (0.3 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in Supplementary Fig.\u0026nbsp;25a) and can be attributed to the lower electric conductivity by a lower ion migration rate (Supplementary Fig.\u0026nbsp;25b). Li\u003csup\u003e+\u003c/sup\u003e ions show a higher electrostatic force with water to form more hydrated ions for a faster ion migration rate (Supplementary Fig.\u0026nbsp;26).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Simultaneous self-cooling and electricity generation\u003c/h2\u003e\u003cp\u003eThe self-cooing and electricity generation are evaluated simultaneously for good comprehensive performance. The higher porosity of grid-structure device represents a higher ratio of unprinted area on the liquid diode of gradient fabric for an overall faster water evaporation rate, leading to the better self-cooling performance with lower temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). The faster water evaporation in the device with a higher porosity also facilitates ion migration for higher electric outputs. However, the higher porosity represents a smaller printed area for current collection\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Therefore, the current output and released charges of SSF increases and then decreases with the increasing porosity (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;27). The smaller pore size, instead of pore shape, contributes to more uniform water evaporation and higher electric outputs (Supplementary Fig.\u0026nbsp;28). Besides, the SSF shows similar thermal resistance (2\u0026ndash;3 m\u003csup\u003e2\u003c/sup\u003e\u0026middot;K\u0026middot;W\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) with different porosity and gel thickness in the equivalent thermal resistance network (Supplementary Note 11 and Supplementary Fig.\u0026nbsp;29). The printed layers are relatively thin in thickness (0.17 mm) compared with fabrics (0.5 mm), and lead to no obvious increased thermal resistance after printing various layers. By dropping water in the different spots of bottom side, the performance of devices shows no significant variation in the various spots (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec) owing to the high wetting areas of gradient fabric (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg). The faster water evaporation in the thinner fabrics and functional layers enhances electric outputs of SSF (Supplementary Fig.\u0026nbsp;30). The strategy of simultaneous self-cooling and electricity generation is also applicable to other commonly used fabrics (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). The nylon fabrics show a lower moisture regain and a higher water evaporation rate\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, which are better than wool, silk and cotton in terms of electric outputs and cooling performance. The electric output and cooling performance also improve with more water dropped onto the bottom side (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). No further improvement is observed with excess water content (\u0026gt;\u0026thinsp;0.03 g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) as excess water covers the whole device without water gradient. The devices can operate in a wide range of temperatures and deliver increased electric outputs in the higher operation temperatures due to faster water evaporation and ion migration (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). Besides, the faster evaporation in the lower RH and the greater water absorption in the higher RH are beneficial to achieving high current outputs (Supplementary Fig.\u0026nbsp;31).\u003c/p\u003e\u003cp\u003eThe stable wearability is demonstrated with repeated stretch cycles, where no obvious performance decline occurs after 10000 cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). Stable electric outputs are achieved in the various mechanical tests with 0‒50% strain, 0‒150\u0026deg; bending angle and 10000 bending cycles (Supplementary Fig.\u0026nbsp;32). The devices also exhibit stable operation cycles for long-term application (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh). In an operation cycle, the electric outputs start with dropping water and last until devices are fully dried. The SSF devices achieve a linear increase of accumulated released charges in the repeated operation cycles (1.36 C charge released for each cycle). No chemical leakage or electric performance decline occurs in the operation cycles or long-term storage period (Supplementary Fig.\u0026nbsp;33). The SSF achieves a highest output of 77.5 \u0026micro;W with 0.42 J when the resistance of the external load is 2 kΩ (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ei). Moreover, the integrated device units deliver linearly increased electric outputs by printing multiple units connected in series or parallel (17.16 V and 7.90 mA with 20 device units in Supplementary Fig.\u0026nbsp;34).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Practical wearable application demonstrations\u003c/h2\u003e\u003cp\u003eOur devices can be integrated into the wearable electronic system for practical application. The devices were printed onto different types of clothes (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), which demonstrates that SSF is applicable to various fabrics and body parts for a wide range of practical application. The device was printed with a large-scale area (14.5\u0026times;14.5 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) on the clothes and shows a uniform temperature drop of 6.3\u0026deg;C on the large-scale area with sweat (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). The skin temperature drops from 33.1\u0026deg;C to 26.8\u0026deg;C in 16 mins (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec) to achieve a quick wear comfort. Two device units were printed in series and powered a flexible LED strip directly for a flexible and wearable LED display with various letters (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed).\u003c/p\u003e\u003cp\u003eThe wearable monitoring system is critical for the health care of infants or disable people with insufficient communication ability\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. Owing to the specific relation between leaked water content and current outputs in this work, the SSF integrated with diaper delivers immediate information of the amount of the leaked urine by generating corresponding current (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). The wireless monitoring system consists of SSF, diaper, wireless current sensor, monitor (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef and Supplementary Movie 4). The urgency level of help in need is described as \u0026ldquo;Comfort\u0026rdquo;, \u0026ldquo;Low\u0026rdquo;, \u0026ldquo;Moderate\u0026rdquo;, \u0026ldquo;High\u0026rdquo;, \u0026ldquo;Immediate\u0026rdquo; according to maximum current output in the range of 0‒0.1, 0.1‒0.2, 0.2‒0.3, 0.3‒0.4, \u0026gt;\u0026thinsp;0.4, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg). Besides, the harvested energy by SSF can be stored in the various power storage devices (Supplementary Fig.\u0026nbsp;35) as power supply. The wireless detection of body signals is also demonstrated with a battery charged by SSF, wireless sensor and monitor (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eh and Supplementary Fig.\u0026nbsp;36) to transmit immediate signals of skin temperature and heart rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ei).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Discussion","content":"\u003cp\u003eWe have developed a self-cooling and self-powered fabric that achieves moisture/thermal management and enhanced electricity generation by directional water transport and ion migration. The gradient wetting channels in the liquid diode are designed to absorb water from skin surface and block external water by directional water transport. The asymmetrical water evaporation on a large area contributes to a fast water evaporation rate of 0.56 g·h\u003csup\u003e− 1\u003c/sup\u003e and a considerable temperature drop of 6.3°C for good wear comfort. The different ion migration rates of Li\u003csup\u003e+\u003c/sup\u003e/Cl\u003csup\u003e−\u003c/sup\u003e ions in the directional water transport boost charge separation for the enhanced electric output of 0.40 mA·cm\u003csup\u003e− 2\u003c/sup\u003e. The temperature drops and electric outputs are also balanced to deliver good comprehensive performance by rationally designing composite and structure of grid sandwiched SSF. Meanwhile, the device exhibits good operation stability and is integrated with multiple practical electronic devices to provide health care and monitor human activity. Our designs introduce a novel and effective approach to provide good wear comfort and enhanced electric outputs simultaneously, a good solution that not only encourages good wearability but also holds the potential for energy harvest and power supply.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cb\u003eLiquid diode preparation.\u003c/b\u003e The plain knitted nylon fabrics with 83% Tactel and 17% Lycra (Sunikorn Knitters Limited, HongKong) were used as substrates of liquid diode for good elasticity and low hysteresis. The nylon fabrics were designed with a yarn density of 43 courses·m\u003csup\u003e− 1\u003c/sup\u003e and 22 wales·m\u003csup\u003e− 1\u003c/sup\u003e. The weight of the nylon fabric is 195 g·m\u003csup\u003e− 2\u003c/sup\u003e, the linear density of the Tactel yarn and Lycra yarn is 702 denier/68 filaments and 40 denier/5 filaments, respectively, fiber diameter is 12–24 µm. The nylon fabrics were cleaned with improved hydrophilicity by the plasma (Plasma Etch PE-25) with O\u003csub\u003e2\u003c/sub\u003e for 10 min before their use. The fabrics with wetting channels were fabricated by spraying hydrophobic particles on the bottom side of fabrics. To get sprayable dispersion with hydrophobic nanoparticles, the mixture of 1H,1H,2H,2H-Perfluorooctyltriethoxysilane (98%, Sigma), TiO\u003csub\u003e2\u003c/sub\u003e (particle size \u0026lt; 100 nm, Sigma), and ethanol (\u0026gt; 95%, Sigma) were mixed at a mass ratio of 1:5:200 and were stirred for 5 h before spraying. The dispersion was uniformly sprayed onto the bottom side of the fabrics with a constant distance. Then, the fabrics were dried at 50°C for 10 min before testing and printing.\u003c/p\u003e\u003cp\u003e\u003cb\u003eDevice preparation.\u003c/b\u003e The graphene pastes (\u0026lt; 15 Ω·cm\u003csup\u003e− 1\u003c/sup\u003e) and Al powders (\u0026gt; 95%, \u0026lt; 15 µm) were mixed at a mass ratio of 5:1 by stirring for 2 h. The mixed pastes were printed onto the top side of fabrics by screen printing and were dried at 50°C for 10 min to work as bottom electrodes. The printable gels were fabricated by heating and stirring PVA (Mw ~ 61000, Sigma) in the LiCl (\u0026gt; 99%, Sigma) solution at 90°C for 2 h (mass ratio of LiCl:PVA:H\u003csub\u003e2\u003c/sub\u003eO = 1:2.5:17). Then, the gels were printed onto the bottom electrode by screen printing and were dried at 50°C in the vacuum oven for 2 h. The graphene pastes were printed onto the gels, followed by drying at 50°C for 10 min.\u003c/p\u003e\u003cp\u003e\u003cb\u003eThermal measurement.\u003c/b\u003e Thermal images and videos were collected by the thermal imaging camera (Fluke Ti400U Thermal Imager, precision: ± 2°C or 2%) at room temperature of 25°C and 55% RH. The temperature was recorded by K-type thermocouples and Anbat AT4516 (Applent Instruments Ltd.) on the bottom side of SSF. The temperature of SSF or human skin on the forearm was collected after it reaches the minimum value. The distilled water was stored at same temperature as the forearm surface. 0.2 g distilled water was sprayed onto the forearm to mimic sweat evaporation before the operation of SSF. The artificial sweat (pH = 4.7) was prepared with 2 wt.% NaCl, 1.8 wt.% NH\u003csub\u003e4\u003c/sub\u003eOH, 0.5 wt.% acetic acid, and 1.5 wt.% actic acid, according to International Organization for Standardization (ISO) 3160-2.\u003c/p\u003e\u003cp\u003e\u003cb\u003eElectrical measurement.\u003c/b\u003e The relative humidity of electrical measurement was adjusted in an environmental chamber. The electric outputs of self-powered and self-cooling fabric (SSF) were collected by Keithley 2400 (Tektronix, USA). The surface potentials of device surface were recorded by Kelvin probe force microscopy (KPFM) with Bruker Dimension Icon machine. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry curve were performed by Autolab PGSTAT302N platform with two-electrode test at room humidity (RH = 55%).\u003c/p\u003e\u003cp\u003e\u003cb\u003eCharacterizations.\u003c/b\u003e The morphology and element distribution of devices were characterized by the field-emission scanning electron microscope (FE-SEM, Tescan MAIA3) equipped with an energy dispersive spectroscopy (EDS). The elements in the different sides of fabrics were characterized by X-ray photoelectron spectroscopy (XPS) with the Al-Kα radiation (8.34 Å) as a power source in the ESCALAB 250Xi (Thermo Fisher) spectrometer. Fourier-transform infrared spectroscopy (FTIR, PerkinElmer, Spectrum 100) was used to record wetting strates of different surfaces. The breakthrough pressure of water flow through fabrics from was recorded by home-made platform in Supplementary Fig.\u0026nbsp;4. The wetting area of saline droplet with 0.9 wt.% NaCl on the fabric was obtained by moisture management tester (MMT, SDL ATLAS Ltd., China). The planar wetting area with time was used to calculate planar water transport rates. The water contact angle was measured by a drop shape analyzer (Krüss, Hamburg, Germany). to calculate vertical water transport rates. The permeability tests were performed by using a MO21S permeability tester (SDL Americ, Inc.). The water states of intermediate water (IW) and free water (FW) in the functional layer were revealed with Raman spectrometer (Renishaw inVia Reflex) at the wavelength of 532 nm.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eCompeting interests\u003c/h2\u003e\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e\u003cp\u003eX.T. and R.Z. conceived the idea. R.Z. carried out sample preparation, characterizations, testing and writing. Z.Z. designed the integrated electronic systems for application. Y.L. and K.M. modified parameters in the sample preparation and helped with SEM characterization. J.Y. performed the calculations in this work. S.L. helped with indoor and outdoor experiments. All authors discussed the results and reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThe project is partially sponsored by Innovation and Technology Commission of Hong Kong SAR Government (No. MRP/020/21), Hong Kong Research Grants Council (No. 15302121 and 15201922) and Hong Kong Polytechnic University (No. 847A and P0036628-49621).\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e\u003cp\u003eThe data that support the findings of this paper are available from the corresponding authors upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLee H et al (2018) Toward all-day wearable health monitoring: An ultralow-power, reflective organic pulse oximetry sensing patch. Sci Adv 4:eaas9530\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHaight R, Haensch W, Friedman D (2016) Solar-powering the internet of things. 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Nat Electron 7:735\u0026ndash;750\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7190787/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7190787/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEnergy harvesting devices with great breathability facilitate continuous operation of healthcare applications and are the critical components in the self-power wearable microelectronic systems. However, the insufficient electric outputs largely diminish the effectiveness of generators as wearable power supply and the lack of moisture/thermal management causes discomfort in the practical electronic application. Herewith we report a self-powered and self-cooling fabric that enhances electric outputs and provides good wear comfort simultaneously, for the first time, by a synergistic effect of directional water transport and ion migration. The water evaporation on the fabric liquid diode with gradient wetting channels reaches 0.56 g\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for dehumidification, dissipating body heat with a temperature drop of 6.3\u0026deg;C for self-cooling. The devices deliver a DC current output of 0.40 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, twice that of devices without liquid diode and is sufficient to power a wide variety of practical wearable electronics.\u003c/p\u003e","manuscriptTitle":"Fabric liquid diode for electricity generation and self-cooling","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-14 05:36:34","doi":"10.21203/rs.3.rs-7190787/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"29b8fd9e-a41d-4493-af0a-d15d150c9f22","owner":[],"postedDate":"August 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":53029478,"name":"Physical sciences/Energy science and technology/Energy harvesting/Devices for energy harvesting"},{"id":53029479,"name":"Physical sciences/Materials science/Materials for devices/Electronic devices"}],"tags":[],"updatedAt":"2026-03-04T07:42:10+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-14 05:36:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7190787","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7190787","identity":"rs-7190787","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}