Moisture-Enabled Electricity from Hygroscopic Materials: A New Type of Clean Energy

Dual-Scale Hydration-Induced Electrical and Mechanical Torsional Energy Harvesting in Heterophilically Designed CNT Yarns

Water holds vast potential for a useful energy source, yet traditional approaches capture only a fraction of it. This study introduces a heterophilically designed carbon nanotube (CNT) yarn with an asymmetric configuration. This yarn is capable of both electrical and mechanical torsional energy harvesting through dual-scale hydration. Fabricated via half-electrochemical oxidation, the yarn contains a hydrophilic region enriched with oxygen-containing functional groups and a hydrophobic pristine CNT region. Molecular-scale hydration triggers proton release in the hydrophilic region. Consequently, a concentration gradient is established that generates a peak open-circuit voltage of 106.0 mV and a short-circuit current of 20.6 mA cm-2. Simultaneously, microscale hydration induces water absorption into inter-bundle microchannels, resulting in considerable yarn volume expansion. This process leads to hydro-driven actuation with a torsional stroke of 78.8° mm-1 and a maximum rotational speed of 1012 RPM. The presented simultaneous harvesting results in electrical and mechanical power densities of 3.5 mW m-2 and 34.3 W kg-1, respectively, during a hydration cycle. By integrating molecular and microscale hydrations, the proposed heterophilic CNT yarns establish an unprecedented platform for simultaneous electrical and mechanical energy harvesting from water, representing a groundbreaking development for sustainable applications.

Enhancing the Performance of Fluorinated Graphdiyne Moisture Cells via Hard Acid-Base Coordination of Aluminum Ions

Moisture-enabled electric generators (MEGs) are emerging as a transformative energy technology, capable of directly converting ambient moisture into electrical energy without producing pollutants or harmful emissions. However, the widespread application of MEGs is hindered by challenges such as intermittent output and low current densities, which limit power density and prevent large-scale integration. Here, a novel moisture cell based on Al ion-F coordination-specifically, a fluorinated graphdiyne (FGDY) Al-ion moisture cell (FGDY AlMC) is introduced. This new moisture cell achieves an exceptionally high mass-specific power density of 371.36 µW g-¹, stable output (0.65 V for 15 h), and broad applicability across varying humid environments. Density functional theory (DFT) calculations reveal that the large-pore molecular structure of FGDY significantly reduces the diffusion barriers for Al ions compared to other 2D carbon materials. Furthermore, the F atoms as "hard base" on FGDY effectively coordinate with "hard acid" Al ions, enhancing ionic conductivity, accelerating ion migration, and promoting the generation of a higher number of mobile cations. These combined advantages lead to a marked improvement in the performance of the FGDY AlMC. These findings position Al ion coordinated FGDY as a highly promising candidate for the development of high-performance MEG active materials.

Natural polysaccharides-based smart sensors for health monitoring, diagnosis and rehabilitation: A review

With the rapid growth of multi-level health needs, precise and real-time health sensing systems have become increasingly pivotal in personal health management and disease prevention. Natural polysaccharides demonstrate immense potential in healthcare sensors by leveraging their superior biocompatibility, biodegradability, environmental sustainability, as well as diverse structural designs and surface functionalities. This review begins by introducing a variety of natural polysaccharides, including cellulose, alginates, chitosan, hyaluronic acid, and starch, and analyzing their structural and functional distinctions, which offer extensive possibilities for sensor design and construction. Further, we summarize several principal sensing mechanisms, such as piezoresistivity, piezoelectricity, capacitance, triboelectricity, and hygroelectricity, which provide a theoretical and technological foundation for developing high-performance healthcare sensing devices. Additionally, the review discusses the most recent applications of natural polysaccharide-based sensors in diverse healthcare contexts, including human body motion tracking, respiratory and heartbeat monitoring, electrophysiological signal recording, body temperature variation detection, and biomarker analysis. Finally, prospective development directions are proposed, such as the integration of artificial intelligence for real-time data analysis, the design of multifunctional devices that combine sensing with therapeutic functionalities, and advancements in remote monitoring and smart wearable technologies. This review aims to provide valuable insights into the development of next-generation healthcare sensors and propose novel research directions for personalized medicine and remote health management.

A self-sustained moist-electric generator with enhanced energy density and longevity through a bilayer approach

Although MEG is being developed as a green renewable energy technology, there remains significant room for improvement in self-sustained power supply, generation duration, and energy density. In this study, we present a self-sustained, high-performance MEG device with a bilayer structure. The lower hydrogel layer incorporates graphene oxide (GO) and carbon nanotubes (CNTs) as the active materials, whereas the upper aerogel layer is comprised of pyrrole-modified graphene oxide (PGO). This design generates a dual-gradient structure (ion density gradient and relative humidity gradient), enabling continuous power generation from the intrinsic moisture in the hydrogel. The device can operate for up to 16 days without external water and extend its operation to 45 days with added moisture. Remarkably, encapsulating this MEG maintains its high performance output even after nearly three months. The short-circuit current of MEG reaches 1695 μA, with an energy density of 809.2 μW h cm-2, which is considerably higher than those reported in previous studies on MEG. This work highlights a promising approach for long-term, self-sustained power generation, with potential applications in environmental sensing and low-power devices.

Screen printing of ionic diode arrays for large-area uniform moist-electric generators

Developing moist-electric array device using screen printing technology that meets mass customization, high power output, and wearable capabilities is very attractive for sustainable mobile power. However, the design of sandwich stacked moist-electric array devices and their screen printing patterning manufacturing process are still challenging. Here, we developed a large-scale fine construction strategy for ion diode nano-channels compatible with screen printing process. A single moist-electric device can generate an open circuit voltage of 0.7 V and a short circuit current density of 56.69 μA/cm2. After large-area integrated manufacturing, the array can generate an open circuit voltage of 126 V and a short circuit current of 5.47 mA. In addition, compared with the spraying process, the performance deviation between different array units is greatly reduced using the screen printing process, which is the key to ensuring the application of moist-electric technology from a single prototype device to a functional integrated device.

Flexible Moisture-Driven Electricity Generators Based on Heterogeneous Gels and Carbon Nanotubes

Recently developed asymmetric heterogeneous moisture-driven electricity generators (AHMEGs) are advantageous for harvesting energy from ubiquitous moisture due to their superior output performance and possible flexibility. However, the regeneration of AHMEG has seldom been explored. Here, we report the fabrication of flexible AHMEGs with regeneration ability simply by asymmetrically incorporating carbon nanotubes into a bilayer-structured gel with heterogeneities of both hygroscopicity and charge. The bilayered gel consists of a Na+-containing macroporous aerogel and a highly hygroscopic Cl--containing hydrogel. After assembly, the resulting flexible AHMEG unit shows excellent output performance, with a stable voltage of 1.03 V, a current density of 23.8 μA cm-2, a power density of up to 9.12 μW cm-2 and a high stability over 7 days, resulting from a synergistic effect between hygroscopicity and charge heterogeneities of the bilayered gel. The regeneration of the AHMEGs has been realized via light irradiation of the aerogel containing carbon nanotubes, and the regeneration can be repeated for at least 30 cycles, significantly expanding the lifecycle of moisture-driven electricity generators. Regeneration imposed by carbon nanotubes, combined with flexibility, simple preparation, and excellent electrical performance, enables the AHMEGs to be excellent moisture-driven electricity generators for advantageous applications.

High-Performance and Anti-Freezing Moisture-Electric Generator Combining Ion-Exchange Membrane and Ionic Hydrogel

Moisture-electric generators (MEGs), which convert moisture chemical potential energy into electrical power, are attracting increasing attention as clean energy harvesting and conversion technologies. However, existing devices suffer from inadequate moisture trapping, intermittent electric output, suboptimal performance at low relative humidity (RH), and limited ion separation efficiency. This study designs an ionic hydrogel MEG capable of continuously generating energy with enhanced selective ion transport and sustained ion-to-electron current conversion at low RH by integrating an ion-exchange membrane (IEM-MEG). A single IEM-MEG exhibits a maximum open-circuit voltage (VOC) of 0.815 V and a short-circuit current (ISC) of 101 µA at 80% RH. Even at a low RH of 10%, a stable VOC of 0.43 V and ISC of 11 µA can be generated. Moreover, the antifreeze performance of the device is improved by adding LiCl, which significantly expands its operational range in low-temperature environments. Finally, a simple series-parallel connection of six IEM-MEGs can yield an enhanced VOC of 4.8 V and a ISC of ≈0.6 mA, and the scalable units can directly power commercial electronics. This study provides new insights into the design of MEGs that will advance the development of green energy conversion technologies in the future.

Long-Lasting and High-Power-Density Yarn-Based Moisture-Enabled Electric Generator for Self-powered Electronic Textiles

1D moisture-enabled electric generators (MEGs) hold great promise for powering electronic textiles, but their current limitations in power output and operational duration restrict their application in wearable technology. This study introduces a high-performance yarn-based moisture-enabled electric generator (YMEG), which comprises a carbon-fiber core, a cotton yarn active layer with a radial gradient of poly(4-styrensulfonic acid) and poly(vinyl alcohol) (PSSA/PVA), and an aluminum wire as the outer electrode. The unique design maintains a persistent moisture gradient between the interior and exterior electrodes, enhancing performance through the continuous proton diffusion from PSSA and Al3⁺ ions from the aluminum wire. The optimized 5-cm-long YMEG delivers an open-circuit voltage of 1.35 V and a short-circuit current density of 460 µA cm-2, sustaining over 300 µA cm-2 for more than 5 h. When woven into a 1 m long yarn containing 95 YMEGs, it generates 101.0 V at 60% relative humidity. Additionally, a configuration of 420 YMEGs connected in series and parallel can power a 1 W LED and a 40 mW motor. This innovative YMEG design paves the way for self-powered electronic textiles such as warning vests and headbands, capable of harnessing insensible sweat for energy.

Hollow Hydrogels for Excellent Aerial Water Collection and Autonomous Release

Air moisture is a valuable and omnipresent resource of fresh water. However, traditional water collectors come with an enduring problem of the water-release step, which requires special devices and additional energy to remove the water from the adsorbent, such as heat, sunlight, or both. Herein, we report the first composite conical hollow hydrogel architecture fabricated through a film-to-tube transforming protocol, designed to harvest water from aerial humidity. This hollow hydrogel device can rapidly collect water from humid air to a saturation point, whereupon it automatically and continually releases fresh water at room temperature. The entire water collection and release process does not require any external assistance. Therefore, this device is highly suitable for emergency water collection in arid areas. As an exemplary demonstration, positioning the hollow hydrogel device next to a plant turns into an individualized system for irrigation. Since the device is biodegradable, it eventually decomposes and becomes an organic fertilizer after the water supply is not required. For long-term application, the water-release process can be monitored in real time by an electronic device to indicate the amount of collected water. The hollow hydrogel combines the humidity-adsorbing capacity with autonomous water release that carries the potential for harvesting water from humidity to address the shortage of fresh water, especially in arid locations where other sources of water are scarce or inaccessible.

Recent Advances in Self-Powered Sensors Based on Ionic Hydrogels

After years of research and development, flexible sensors are gradually evolving from the traditional "electronic" paradigm to the "ionic" dimension. Smart flexible sensors derived from the concept of ion transport are gradually emerging in the flexible electronics. In particular, ionic hydrogels have increasingly become the focus of research on flexible sensors as a result of their tunable conductivity, flexibility, biocompatibility, and self-healable capabilities. Nevertheless, the majority of existing sensors based on ionic hydrogels still mainly rely on external power sources, which greatly restrict the dexterity and convenience of their applications. Advances in energy harvesting technologies offer substantial potential toward engineering self-powered sensors. This article reviews in detail the self-powered mechanisms of ionic hydrogel self-powered sensors (IHSSs), including piezoelectric, triboelectric, ionic diode, moist-electric, thermoelectric, potentiometric transduction, and hybrid modes. At the same time, structural engineering related to device and material characteristics is discussed. Additionally, the relevant applications of IHSS toward wearable electronics, human-machine interaction, environmental monitoring, and medical diagnostics are further reviewed. Lastly, the challenges and prospective advancement of IHSS are outlined.

Hybrid electromagnetic and moisture energy harvesting enabled by ionic diode films

Wireless energy-responsive systems provide a foundational platform for powering and operating intelligent devices. However, current electronic systems relying on complex components limit their effective deployment in ambient environment and seamless integration of energy harvesting, storage, sensing, and communication. Here, we disclose a coupling effect of electromagnetic wave absorption and moist-enabled generation on carrier transportation and energy interaction regulated by ionic diode effect. As demonstration, a wireless energy interactive system is established for electromagnetic-moist coupled energy harvesting and signal transmission through highly integrated polyelectrolyte/conjugated conductive polymer bilayer ionic diode films as dynamic energy-switching carriers. The gradient distribution of ions within the films, excited by moist energy, enables the ionic rectification and further endows the films with electromagnetic energy harvesting capability. In turn, the absorbed electromagnetic energy drives the directional migration of charge carriers and internal ionic current. By rationally regulating the electrolyte and dielectric properties of ionic diodes, it becomes feasible to control targeted electric signals and energy outputs under coupled electromagnetic-moist environment. This work is a step towards enabling enhanced smart interactivities for wirelessly driven flexible electronics.

Unveiling the Sorption Properties of Graphene Oxide-M13 Bacteriophage Aerogels for Advanced Sensing and Environmental Applications

GraPhage13 aerogels (GPAs) are ultralow density, porous structures fabricated through the self-assembly of graphene oxide (GO) and M13 bacteriophage. Given GPA's high surface area and extensive porous network, properties typically associated with highly adsorbent materials, it is essential to characterize its sorption capabilities, with a focus on unlocking its potential for advanced applications in areas such as biomedical sensing and environmental monitoring. Herein, the water, ethanol and acetone sorption properties of GPA were explored using dynamic vapor sorption (DVS). GPA was found to be highly hygroscopic, with a sorption capacity of 0.68 ± 0.02 g/g, double that of conventional desiccant silica gels and 20% higher than GO laminates. This remarkable sorption capacity, along with its sorption kinetics, was influenced by both GPA's morphology and the strong interactions between the water molecules and the functional groups on the GO within GPA. The low hysteresis and stability of GPA during repeated sorption-desorption cycles highlight the reversibility of water sorption. While GPA shows lower capacity for ethanol and acetone, its tuneability presents opportunities for improving acetone sorption, and its ethanol sorption capacity exceeds that of similar carbon-based materials. These findings underscore GPA's capability and versatility in vapor adsorption, paving the way toward its integration into graphene-based devices for sensing applications.

Neuron-Inspired Flexible Phase Change Materials for Ambient Energy Harvesting and Respiration Monitoring

The global energy crisis and climate change pose unprecedented challenges. Wearable devices with personal thermoregulation and energy harvesting hold great promise for achieving energy savings and human thermal comfort. Here, inspired by neurons, a novel phase change material (PCM) is reported for efficient energy harvesting and respiratory monitoring via a self-assembly strategy. The use of gum arabic (GA) enabled the encapsulation of polyethylene glycol (PEG) and the targeted distribution of carboxylated multi-walled carbon nanotubes (cMWCNTs) simultaneously in poly (ethylene vinyl acetate) (EVA) matrix. The material exhibits an outstanding toughness value of 14.88 MJ m-3 and high elongation at a break of 565.67%, exhibiting remarkable flexibility. The material with sufficient melting enthalpy (71.11 J g-1) demonstrates high photothermal conversion efficiency (95.27%) under 808 nm laser irradiation (105 mW cm-2). In addition, due to the synergistic effect of GA and PEG, especially the formation of microdome structures on the surface, the material demonstrates ultrasensitive humidity responsiveness for respiratory monitoring with high precision, excellent repeatability, and fast response/recovery time (50.4/50.5 ms). Notably, it shows great potential for moisture-electric generators (MEGs) with the function of non-contact sensing. This material opens the path toward next-generation wearable devices in energy conversion and health monitoring.

A Paper-Based Wearable Moist-Electric Generator for Sustained High-Efficiency Power Output and Enhanced Moisture Capture

Disposable wearable electronics are valuable for diagnostic and healthcare purposes, reducing maintenance needs and enabling broad accessibility. However, integrating a reliable power supply is crucial for their advancement, but conventional power sources present significant challenges. To address that issue, a novel paper-based moist-electric generator is developed that harnesses ambient moisture for power generation. The device features gradients for functional groups and moisture adsorption and architecture of nanostructures within a disposable paper substrate. The nanoporous, gradient-formed spore-based biofilm and asymmetric electrode deposition enable sustained high-efficiency power output. A Janus hydrophobic-hydrophilic paper layer enhances moisture harvesting, ensuring effective operation even in low-humidity environments. This research reveals that the water adsorption gradient is crucial for performance under high humidity, whereas the functional group gradient is dominant under low humidity. The device delivers consistent performance across diverse conditions and flexibly conforms to various surfaces, making it ideal for wearable applications. Its eco-friendly, cost-effective, and disposable nature makes it a viable solution for widespread use with minimal environmental effects. This innovative approach overcomes the limitations of traditional power sources for wearable electronics, offering a sustainable solution for future disposable wearables. It significantly enhances personalized medicine through improved health monitoring and diagnostics.

A core-shell fiber moisture-driven electric generator enabled by synergetic complex coacervation and built-in potential

Moisture-driven electricity generators (MEGs) have been extensively researched; however, high-performance flexible variants have seldom been demonstrated. Here we present a novel complex coacervation with built-in potential strategy for developing a high-performance uniaxial MEG, featuring a core of poly(3,4-ethylenedioxythiophene) (PEDOT) with a built-in charge potential and a gel shell composed of poly(diallyldimethylammonium chloride) (PDDA) and sodium alginate (NaAlg) coacervate. The complex coacervation of two oppositely charged polyelectrolytes produces extra mobile carriers and free volume in the device; meanwhile, the PEDOT core's surface charge significantly accelerates carrier diffusion. Consequently, the uniaxial fiber-based MEG demonstrates breakthrough performance, achieving an output voltage of up to 0.8 V, a maximum current density of 1.05 mA/cm2, and a power density of 184 μW/cm2 at 20% relative humidity. Moreover, the mechanical robustness is ensured for the PEDOT nanoribbon substrate without performance degradation even after 100,000 folding cycles, making it suitable for self-powered human interactive sensor and synapse. Notably, we have constructed the inaugural MEG-synapse self-powered device, with a fiber-based MEG successfully operating a synaptic memristor, thereby emulating autonomous human synapses linked with fibrous neurons. Overall, this work pioneers innovative design strategies and application scenarios for high-performance MEGs.

Enhancement of Water Productivity and Energy Efficiency in Sorption-based Atmospheric Water Harvesting Systems: From Material, Component to System Level

To address the increasingly serious water scarcity across the world, sorption-based atmospheric water harvesting (SAWH) continues to attract attention among various water production methods, due to it being less dependent on climatic and geographical conditions. Water productivity and energy efficiency are the two most important evaluation indicators. Therefore, this review aims to comprehensively and systematically summarize and discuss the water productivity and energy efficiency enhancement methods for SAWH systems based on three levels, from material to component to system. First, the material level covers the characteristics, categories, and mechanisms of different sorbents. Second, the component level focuses on the sorbent bed, regeneration energy, and condenser. Third, the system level encompasses the system design, operation, and synergetic effect generation with other mechanisms. Specifically, the key and promising improvement methods are: synthesizing composite sorbents with high water uptake, fast sorption kinetics, and low regeneration energy (material level); improving thermal insulation between the sorbent bed and condenser, utilizing renewable energy or electrical heating for desorption and multistage design (component level); achieving continuous system operation with a desired number of sorbent beds or rotational structure, and integrating with Peltier cooling or passive radiative cooling technologies (system level). In addition, applications and challenges of SAWH systems are explored, followed by potential outlooks and future perspectives. Overall, it is expected that this review article can provide promising directions and guidelines for the design and operation of SAWH systems with the aim of achieving high water productivity and energy efficiency.

Water-Triboelectrification-Complemented Moisture Electric Generator

Energy harvesting from ubiquitous natural water vapor based on moisture electric generator (MEG) technology holds great potential to power portable electronics, the Internet of Things, and wireless transmission. However, most devices still encounter challenges of low output, and a single MEG complemented with another form of energy harvesting for achieving high power has seldom been demonstrated. Herein, we report a flexible and efficient hybrid generator capable of harvesting moisture and tribo energies simultaneously, both from the source of water droplets. The moisture electric and triboelectric layers are based on a water-absorbent citric acid (CA)-mediated polyglutamic acid (PGA) hydrogel and porous electret expanded polytetrafluoroethylene (E-PTFE), respectively. Such a waterproof E-PTFE film not only enables efficient triboelectrification with water droplets' contact but also facilitates water vapor to be transferred into the hydrogel layer for moisture electricity generation. A single hybrid generator under water droplets' impact delivers a DC voltage of 0.55 V and a peak current density of 120 μA cm-2 from the MEG, together with a simultaneous AC output voltage of 300 V and a current of 400 μA from the complementary water-based triboelectric generator (TEG) side. Such a hybrid generator can work even under harsh wild environments with 5 °C cold and saltwater impacts. Significantly, an optical alarm and wireless communication system for wild, complex, and emergency scenarios is demonstrated with power from the hybrid generators. This work expands the applications of water-based electricity generation technologies and provides insight into harvesting multiple potential energies in the natural environment with high output.

Ionic Hydrogel-Based Moisture Electric Generators for Underwater Electronics

Ubiquitous moisture is of particular interest for sustainable power generation and self-powered electronics. However, current moisture electric generators (MEGs) can only harvest moisture energy in the air, which tremendously limits the energy harvesting efficiency and practical application scenarios. Herein, the operationality of MEG from air to underwater environment, through a sandwiched engineered-hydrogel device with an additional waterproof breathable membrane layer allowing water vapor exchange while preventing liquid water penetration, is expanded. Underwater environment, the device can spontaneously deliver a voltage of 0.55 V and a current density of 130 µA cm-2 due to the efficient ion separation assisted by negative ions confinement in hydrogel networks. The output can be maintained even under harsh underwater environment with 10% salt concentration, 1 m s-1 disturbing flow, as well as >40 kPa hydraulic pressure. The engineered hydrogel used for MEG also exhibits excellent self-healing ability, flexibility, and biocompatibility. As the first demonstration of practical applications in self-powered underwater electronics, the MEG device is successfully powering a wireless emitter for remote communication in water. This new type of MEG offers an innovative route for harvesting moisture energy underwater and holds promise in the creation of a new range of innovative electronic devices for marine Internet-of-Things.

Recent Advances in Fibrous Materials for Hydroelectricity Generation

Depleting fossil energy sources and conventional polluting power generation pose a threat to sustainable development. Hydroelectricity generation from ubiquitous and spontaneous phase transitions between liquid and gaseous water has been considered a promising strategy for mitigating the energy crisis. Fibrous materials with unique flexibility, processability, multifunctionality, and practicability have been widely applied for fibrous materials-based hydroelectricity generation (FHG). In this review, the power generation mechanisms, design principles, and electricity enhancement factors of FHG are first introduced. Then, the fabrication strategies and characteristics of varied constructions including 1D fiber, 1D yarn, 2D fabric, 2D membrane, 3D fibrous framework, and 3D fibrous gel are demonstrated. Afterward, the advanced functions of FHG during water harvesting, proton dissociation, ion separation, and charge accumulation processes are analyzed in detail. Moreover, the potential applications including power supply, energy storage, electrical sensor, and information expression are also discussed. Finally, some existing challenges are considered and prospects for future development are sincerely proposed.

Recent Advances on Two-Dimensional Nanomaterials Supported Single-Atom for Hydrogen Evolution Electrocatalysts

Water electrolysis has been recognized as a promising technology that can convert renewable energy into hydrogen for storage and utilization. The superior activity and low cost of catalysis are key factors in promoting the industrialization of water electrolysis. Single-atom catalysts (SACs) have attracted attention due to their ultra-high atomic utilization, clear structure, and highest hydrogen evolution reaction (HER) performance. In addition, the performance and stability of single-atom (SA) substrates are crucial, and various two-dimensional (2D) nanomaterial supports have become promising foundations for SA due to their unique exposed surfaces, diverse elemental compositions, and flexible electronic structures, to drive single atoms to reach performance limits. The SA supported by 2D nanomaterials exhibits various electronic interactions and synergistic effects, all of which need to be comprehensively summarized. This article aims to organize and discuss the progress of 2D nanomaterial single-atom supports in enhancing HER, including common and widely used synthesis methods, advanced characterization techniques, different types of 2D supports, and the correlation between structural hydrogen evolution performance. Finally, the latest understanding of 2D nanomaterial supports was proposed.

Wetting Behavior-Induced Interfacial transmission of Energy and Signal: Materials, Mechanisms, and Applications

Wetting behaviors can significantly affect the transport of energy and signal (E&S) through vapor, solid, and liquid interfaces, which has prompted increased interest in interfacial science and technology. E&S transmission can be achieved using electricity, light, and heat, which often accompany and interact with each other. Over the past decade, their distinctive transport phenomena during wetting processes have made significant contributions to various domains. However, few studies have analyzed the intricate relationship between wetting behavior and E&S transport. This review summarizes and discusses the mechanisms of electrical, light, and heat transmission at wetting interfaces to elucidate their respective scientific issues, technical characteristics, challenges, commonalities, and potential for technological convergence. The materials, structures, and devices involved in E&S transportation are also analyzed. Particularly, harnessing synergistic advantages in practical applications and constructing advanced, multifunctional, and highly efficient smart systems based on wetted interfaces is the aim to provide strategies.

Flexible electrochemical energy storage devices and related applications: recent progress and challenges

Given the escalating demand for wearable electronics, there is an urgent need to explore cost-effective and environmentally friendly flexible energy storage devices with exceptional electrochemical properties. However, the existing types of flexible energy storage devices encounter challenges in effectively integrating mechanical and electrochemical performances. This review is intended to provide strategies for the design of components in flexible energy storage devices (electrode materials, gel electrolytes, and separators) with the aim of developing energy storage systems with excellent performance and deformability. Firstly, a concise overview is provided on the structural characteristics and properties of carbon-based materials and conductive polymer materials utilized in flexible energy storage devices. Secondly, the fabrication process and strategies for optimizing their structures are summarized. Subsequently, a comprehensive review is presented regarding the applications of carbon-based materials and conductive polymer materials in various fields of flexible energy storage, such as supercapacitors, lithium-ion batteries, and zinc-ion batteries. Finally, the challenges and future directions for next-generation flexible energy storage systems are proposed.

Manipulating the Crystallization of Tin Halide Perovskites for Efficient Moisture-to-Electricity Conversion

Manipulating the crystallization of perovskite in thin films is essential for the fabrication of any thin-film-based devices. Fabricating tin-based perovskite films from solution poses difficulties because tin tends to crystallize faster than the commonly used lead perovskite. To achieve optimal device performance in solar cells, the preferred method involves depositing tin perovskite under inert conditions using dimethyl sulfoxide (DMSO), which effectively retards the formation of the tin-bromine network, which is crucial for perovskite assembly. We found that under ambient conditions, a DMSO-based tin perovskite salt solution resulted in the formation of a two-phase system, SnBr4(DMSO)2 and MABr, whereas a dimethylformamide-based solution resulted in the formation of vacancy-ordered double perovskite MA2SnBr6. Humidity is known to solvate MABr to form the solvated ions, and so we used the two-phase system for the application in moisture to electricity conversion. The importance of the presence of the scaffold can be seen with the negligible power output from the vacancy-ordered double perovskite obtained with MA2SnBr6. We have fabricated a device with two-phase system that can generate an open-circuit potential of 520 mV and a short-circuit current density of 30.625 μA/cm2 at 85% RH. Also, the device charges a 10 μF capacitor from 150 mV at 51% RH to 500 mV at 85% RH in 6 s at a rate of 52.5 mV/s. Moreover, the output can be scaled by connecting devices in series and parallel configurations. A 527 nm green LED was powered by connecting five devices in series at 75% RH. This indicates a potential for utilizing these moisture-to-electricity conversion devices in powering low-energy requirement devices.

Advances in Energy Harvesting Technologies for Wearable Devices

The development of wearable electronics is revolutionizing human health monitoring, intelligent robotics, and informatics. Yet the reliance on traditional batteries limits their wearability, user comfort, and continuous use. Energy harvesting technologies offer a promising power solution by converting ambient energy from the human body or surrounding environment into electrical power. Despite their potential, current studies often focus on individual modules under specific conditions, which limits practical applicability in diverse real-world environments. Here, this review highlights the recent progress, potential, and technological challenges in energy harvesting technology and accompanying technologies to construct a practical powering module, including power management and energy storage devices for wearable device developments. Also, this paper offers perspectives on designing next-generation wearable soft electronics that enhance quality of life and foster broader adoption in various aspects of daily life.

Hierarchical Bilayer Polyelectrolyte Ion Paper Conductor for Moisture-Induced Power Generation

Harvesting energy from air water (atmospheric moisture) promises a sustainable self-powered system without any restrictions from specific environmental requirements (e.g., solar cells, hydroelectric, or thermoelectric devices). However, the present moisture-induced power devices traditionally generate intermittent or bursts of energy, especially for much lower current outputs (generally keeping at nA or μA levels) from the ambient environment, typically suffering from inferior ionic conductivity and poor hierarchical structure design for manipulating sustained air water and ion-charge transport. Here, we demonstrate a universal strategy to design a high-performance bilayer polyelectrolyte ion paper conductor for generating continuous electric power from ambient humidity. The generator can produce a continuous voltage of up to 0.74 V and also an exceptional current of 5.63 mA across a single 1.0 mm-thick ion paper conductor. We discover that the sandwiched LiCl-nanocellulose-engineered paper promises an ion-transport junction between the negatively and positively charged bilayer polyelectrolytes for application in MEGs with both high voltage and high current outputs. Moreover, we demonstrated the universality of this bilayer sandwich nanocellulose-salt engineering strategy with other anions and cations, exhibiting similar power generation ability, indicating that it could be the next generation of sustainable MEGs with low cost, easier operation, and high performance.

Robustly and Intrinsically Stretchable Ionic Gel-Based Moisture-Enabled Power Generator with High Human Body Conformality

Direct harvesting of energy from moist air will be a promising route to supply electricity for booming wearable and distributed electronics, with the recent rapid development of the moisture-enabled electricity generator (MEG). However, the easy spatial distortion of rigid MEG materials under severe deformation extremely inconveniences the human body with intense physical activity, seriously hindering the desirable applications. Here, an intrinsically stretchable moisture-enabled electricity generator (s-MEG) is developed based on a well-fabricated stretchable functional ionic gel (SIG) with a flexible double-network structure and reversible cross-linking interactions, demonstrating stable electricity output performance even when stretched up to 150% strain and high human body conformality. This SIG exhibits ultrahigh tensile strain (∼600%), and a 1 cm × 1 cm SIG film-based s-MEG can generate a voltage of ∼0.4 V and a current of ∼5.7 μA when absorbing water from humidity air. Based on the strong adhesion and the excellent interface combination of SIG and rough fabric electrodes induced by the fabrication process, s-MEG is able to realize bending or twisting deformation and shows outstanding electricity output stability with ∼90% performance retention after 5000 cycles of bending tests. By connecting s-MEG units in series or parallel, an integrated device of "moisture-powered wristband" is developed to wear on the wrist of humans and drive a flexible sensor for tracking finger motions. Additionally, a comfortable "moisture-powered sheath" based on s-MEGs is created, which can be worn like clothing on human arms to generate energy while walking and flexing the elbow, which is promising in the field of wearable electronics.

Green moisture-electric generator based on supramolecular hydrogel with tens of milliamp electricity toward practical applications

Moisture-electric generators (MEGs) has emerged as promising green technology to achieve carbon neutrality in next-generation energy suppliers, especially combined with ecofriendly materials. Hitherto, challenges remain for MEGs as direct power source in practical applications due to low and intermittent electric output. Here we design a green MEG with high direct-current electricity by introducing polyvinyl alcohol-sodium alginate-based supramolecular hydrogel as active material. A single unit can generate an improved power density of ca. 0.11 mW cm-2, a milliamp-scale short-circuit current density of ca. 1.31 mA cm-2 and an open-circuit voltage of ca. 1.30 V. Such excellent electricity is mainly attributed to enhanced moisture absorption and remained water gradient to initiate ample ions transport within hydrogel by theoretical calculation and experiments. Notably, an enlarged current of ca. 65 mA is achieved by a parallel-integrated MEG bank. The scalable MEGs can directly power many commercial electronics in real-life scenarios, such as charging smart watch, illuminating a household bulb, driving a digital clock for one month. This work provides new insight into constructing green, high-performance and scalable energy source for Internet-of-Things and wearable applications.

Soft multi-layer actuators integrated with the functions of electrical energy harvest and storage

Soft multi-layer actuators are smart, lightweight, and flexible, which can be used in a wide range of fields such as artificial muscles, advanced medical devices, and wearable devices. The research on the actuation property of the soft actuators has made significant progress, paving the way for the controllable motions of the actuators. However, compared with the intelligence and adaptability of life in nature, these actuators still have the problem of insufficient intelligence. The phenomenon is reflected in a lack of continuous supply of energy. Therefore, it has become a development trend to combine functions such as energy harvesting, storage, and conversion with actuators to build intelligent actuators. This concept presents a synopsis of the advancements made in soft actuators that have been coupled with the capabilities of electrical energy harvesting and storage. The design concepts and typical applications of this soft smart actuators are introduced in detail. Finally, the future research directions and applications of smart actuators are prospected from our perspective.

Power Generation from the Interaction of a Carbon Foam and Water

Understanding the interaction mechanisms between the surface of carbon-based materials and water is of great significance for the development of water-based energy storage and energy conversion devices. Herein, a self-supporting electric generator is demonstrated based on water adsorption on the surface of the carbon foam (CF) that works with various water resources, including deionized (DI) water, tap water, wastewater, and seawater. It is revealed that the dissociation of oxygen-containing groups on the surface of CF after water molecule adsorption leads to a reduction of the surface potential of the CF. Through surface modulation techniques such as reduction and oxidation, a balance has been uncovered between the oxygen content and conductivity for the high-performance CFs. The generator can generate an open-circuit voltage of approximately 0.6 V in natural seawater with a power density of up to 0.77 mW g-1. A high voltage of more than 2 V can be achieved easily by assembling components connected in series to drive electronic devices, such as a light-emitting diode (LED). This work demonstrates a simple and low-cost method for electricity harvesting, offering an additional option for self-powered devices.

Modified Wood Fibers Spontaneously Harvest Electricity from Moisture

With the rapid development of modern society, our demand for energy is increasing. And the extensive use of fossil energy has triggered a series of problems such as an energy crisis and environmental pollution. A moisture-enabled electric generator (MEG) is a new type of energy conversion method, which can directly convert the ubiquitous moisture in the air into electrical energy equipment. It has attracted great interest for its renewable and environmentally friendly qualities. At present, most MEGs still have low power density, strong dependence on high humidity, and high cost. Herein, we report the development of a high-efficiency MEG based on a lignocellulosic fiber frame with high-power-density, all-weather, and low-cost characteristics using a simple strategy that optimizes the charge transport channel and ion concentration difference. The MEG devices we manufactured can generate the open-circuit voltage of 0.73 V and the short-circuit current of 360 μA, and the voltage can still reach 0.6 V at less than 30% humidity. It is possible to drive commercial electronic devices such as light-emitting diodes, electronic displays, and electronic calculators by simply connecting several electric generators in series. Biomass-based moisture-enabled electric generation has a low cost, is easy to integrate on a large scale, and is green and pollution-free, providing clean energy for low-humidity or high-electricity-cost areas.

Ion-Diode-Like Heterojunction for Improving Electricity Generation from Water Droplets by Capillary Infiltration

Water-droplet-based electricity generators are emerging hydrovoltaic technologies that harvest energy from water circulation through strong interactions between water and nanomaterials. However, such devices exhibit poor current performance owing to their unclear driving force (evaporation or infiltration) and undesirable reverse diffusion current. Herein, a water-droplet-based hydrovoltaic electricity generator induced by capillary infiltration with an asymmetric structure composed of a diode-like heterojunction formed by negatively and positively charged materials is fabricated. This device can generate current densities of 160 and 450 µA cm-2 at room temperature and 65 °C, respectively. The heterojunction achieves a rectification ratio of 12, which effectively suppresses the reverse current caused by concentration differences. This results in an improved charge accumulation of ≈60 mC cm-2 in 1000 s, which is three times the value observed in the control device. When the area of the device is increased to 6 cm2 , the current increases linearly to 1 mA, thus demonstrating the scale-up potential of the generator. It has been proven that the streaming potential originates from capillary infiltration, and the presence of ion rectification. The proposed method of constructing ion-diode-like structures provides a new strategy for improving generator performance.

Multistage coupling water-enabled electric generator with customizable energy output

Constant water circulation between land, ocean and atmosphere contains great and sustainable energy, which has been successfully employed to generate electricity by the burgeoning water-enabled electric generator. However, water in various forms (e.g. liquid, moisture) is inevitably discharged after one-time use in current single-stage water-enabled electric generators, resulting in the huge waste of inherent energy within water circulation. Herein, a multistage coupling water-enabled electric generator is proposed, which utilizes the internal liquid flow and subsequently generated moisture to produce electricity synchronously, achieving a maximum output power density of ~92 mW m-2 (~11 W m-3). Furthermore, a distributary design for internal water in different forms enables the integration of water-flow-enabled and moisture-diffusion-enabled electricity generation layers into mc-WEG by a "flexible building blocks" strategy. Through a three-stage adjustment process encompassing size control, space optimization, and large-scale integration, the multistage coupling water-enabled electric generator realizes the customized electricity output for diverse electronics. Twenty-two units connected in series can deliver ~10 V and ~280 μA, which can directly lighten a table lamp for 30 min without aforehand capacitor charging. In addition, multistage coupling water-enabled electric generators exhibit excellent flexibility and environmental adaptability, providing a way for the development of water-enabled electric generators.

Advances and Challenges for Hydrovoltaic Intelligence

In recent years, excessive exploitation and rapid population growth have posed numerous challenges. The climate crisis is deepening because of the unabated use of fossil fuels and the ascendance of greenhouse gas levels, so there is still an urgent need to seek different clean energy sources and electricity generating methods with the purpose of adjusting energy structures and solving environmental problems. In the ubiquitous hydrologic cycle, at least 60 petawatts (10¹⁵ W) energy can be supplied, but little of it has yet been utilized. Nowadays, hydrovoltaic intelligence has emerged and exhibited an ecofriendly concept of electricity generation compared with traditional methods with the rise of nanoscience and nanomaterials. Hence, it provides the prospect of upgrading the mode of water energy use, constructing a renewable energy industry, and alleviating environmental issues. In this review, starting by introducing different types of hydrovoltaic effect mechanisms─energy harvesting based on drawing potential of liquids; energy harvesting based on water evaporation, and energy harvesting based on moisture adsorption─we summarize the fabrication processes, material classifications, intelligent applications, and representative advances in detail. Moreover, the future development trends of hydrovoltaic intelligence and the challenges for improvement in electrical output are further discussed.

Self-chargeable supercapacitor made with MXene-bacterial cellulose nanofiber composite for wearable devices

The development of wearable electronics is restricted by the developments of supporting energy storage devices, especially flexible supercapacitors. Nowadays, miniaturized supercapacitors based on MXenes due to their obvious advantages in the specific capacity have received extensive attention. The energy existing in the surrounding environment has been used to directly charge energy storage devices. However, the hybrid wearable electronics integrated supercapacitors are mechanically connected through metal wires leading to non-compact devices. Thus, it is urgent to develop a general and universal method to fabricate high-performance robust MXene-based flexible electrodes with high electrical conductivity and apply them to self-chargeable supercapacitors and compact wearable devices. Herein, the bacterial cellulose (BC) nanofibers are used as a crosslinking agent to connect two-dimensional MXene nanosheets through the hydrogen bond, which greatly improves the mechanical strength of MXene-bacterial cellulose (MXene-BC) composite films (Young's modulus reaching 6.8 GPa). The supercapacitors made with the electrodes of MXene-BC composite films (BC content is 10%) present high capacitance behavior (areal capacitance up to 346 mF cm^-2) because the introduction of BC nanofibers increases the interlayer spacing of MXene nanosheets, providing more storage space for the ions in the electrolyte. Then, a self-chargeable supercapacitor is proposed based on the combination of a zinc-air (Zn-air) battery and a supercapacitor. The self-chargeable supercapacitor can realize self-charging after dropping a drop of electrolyte solution into the Zn-air battery. The charging voltage of a single self-chargeable supercapacitor can reach 0.6 V after adding artificial sweat as the electrolyte. Finally, a smart wristband with the function of self-charging is proposed, which can absorb the sweat generated by the human for self-chargeable supercapacitors to drive the pedometer integrated within the smart wristband to work. The proposed self-chargeable supercapacitors are simple and effective, not restricted by the use environment, providing a promising way for self-powered wearable electronics.