Bilayer Wood Membrane with Aligned Ion Nanochannels for Spontaneous Moist-Electric Generation

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.

Study of Electrode Design and Inclination Angle for Superior Droplet-Driven TENG Performance

The urgent need for efficient water energy harvesting has led to the development of triboelectric nanogenerators (TENGs). In this study, considering the droplet spreading dynamics and the capacitive effects in a droplet-driven TENG (DD-TENG) device, an inverse relationship between the width of the top electrode and the output voltage was derived for the first time through a circuit model and was experimentally verified. Additionally, key performance parameters were optimized, including the types and widths of top electrodes, dropping height, inclination angle of the device, and solution types. A nonmonotonic relationship between the inclination angle of the device and the output voltage was established. Under optimal conditions, the output voltage of the DD-TENG achieved a 1133% increase compared to that of the device without a top electrode. The power density reached 1265 mW·m-2, which is among the state-of-the-art DD-TENG devices. These findings provide valuable insights for the performance improvement of DD-TENGs.

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.

Moisture Power Generation: From Material Selection to Device Structure Optimization

Moisture power generation (MPG) technology, producing clean and sustainable energy from a humid environment, has drawn significant attention and research efforts in recent years as a means of easing the energy crisis. Despite the rapid progress, MPG technology still faces numerous challenges with the most significant one being the low power-generating performance of individual MPG devices. In this review, we introduce the background and underlying principles of MPG technology while thoroughly explaining how the selection of suitable materials (carbons, polymers, inorganic salts, etc.) and the optimization of the device structure (pore structure, moisture gradient structure, functional group gradient structure, and electrode structure) can address the existing and anticipated challenges. Furthermore, this review highlights the major scientific and engineering hurdles on the way to advancing MPG technology and offers potential insights for the development of high-performance MPG systems.

Polyelectrolyte Hydrogel-Functionalized Photothermal Sponge Enables Simultaneously Continuous Solar Desalination and Electricity Generation Without Salt Accumulation

Technologies that can simultaneously generate electricity and desalinate seawater are highly attractive and required to meet the increasing global demand for power and clean water. Here, a bifunctional solar evaporator that features continuous electric generation in seawater without salt accumulation is developed by rational design of polyelectrolyte hydrogel-functionalized photothermal sponge. This evaporator not only exhibits an unprecedentedly high water evaporation rate of 3.53 kg m-2 h-1along with 98.6% solar energy conversion efficiency but can also uninterruptedly deliver a voltage output of 0.972 V and a current density of 172.38 µA cm-2 in high-concentration brine over a prolonged period under one sun irradiation. Many common electronic devices can be driven by simply connecting evaporator units in series or in parallel without any other auxiliaries. Different from the previously proposed power generation mechanism, this study reveals that the water-enabled proton concentration fields in intermediate water region can also induce an additional ion electric field in free water region containing solute, to further enhance electricity output. Given the low-cost materials, simple self-regeneration design, scalable fabrication processes, and stable performance, this work offers a promising strategy for addressing the shortages of clean water and sustainable electricity.

Rational Design of Amorphous Carbon-Coated Laminar-Structured Wood for Integrating Repeatable Early Fire Detection and High-Temperature Affordable Flexible Pressure Sensing in One System

High-temperature affordable flexible polymer-based pressure sensors integrated with repeatable early fire warning service are strongly desired for harsh environmental applications, yet their creation remains challenging. This work proposed an approach for preparing such advanced integrated sensors based on silver nanoparticles and an ammonium polyphosphate (APP)-modified laminar-structured bulk wood sponge (APP/Ag@WS). Such integrated sensors demonstrated excellent fire warning performance, including a short response time (minimum of 0.44 s), a long-lasting alarm time (>750 s), and reliable repeatability. Moreover, it achieved high-temperature affordable flexible pressure sensing that exhibited an almost unimpaired working range of 0-7.5 kPa and a higher sensitivity (in the low-pressure range, maximum to 226.03 kPa-1) after fire. The high stability was attributed to reliable structural elasticity, and the wood-derived amorphous carbon is capable of repeatable fire warnings. Finally, a Ag@APP/WS-based wireless fire alarm system that realized reliable house fire accident detection was demonstrated, showing great promise for smart firefighting application.

The emerging chemistry of self-electrified water interfaces

Water is known for dissipating electrostatic charges, but it is also a universal agent of matter electrification, creating charged domains in any material contacting or containing it. This new role of water was discovered during the current century. It is proven in a fast-growing number of publications reporting direct experimental measurements of excess charge and electric potential. It is indirectly verified by its success in explaining surprising phenomena in chemical synthesis, electric power generation, metastability, and phase transition kinetics. Additionally, electrification by water is opening the way for developing green technologies that are fully compatible with the environment and have great potential to contribute to sustainability. Electrification by water shows that polyphasic matter is a charge mosaic, converging with the Maxwell-Wagner-Sillars effect, which was discovered one century ago but is still often ignored. Electrified sites in a real system are niches showing various local electrochemical potentials for the charged species. Thus, the electrified mosaics display variable chemical reactivity and mass transfer patterns. Water contributes to interfacial electrification from its singular structural, electric, mixing, adsorption, and absorption properties. A long list of previously unexpected consequences of interfacial electrification includes: "on-water" reactions of chemicals dispersed in water that defy current chemical wisdom; reactions in electrified water microdroplets that do not occur in bulk water, transforming the droplets in microreactors; and lowered surface tension of water, modifying wetting, spreading, adhesion, cohesion, and other properties of matter. Asymmetric capacitors charged by moisture and water are now promising alternative equipment for simultaneously producing electric power and green hydrogen, requiring only ambient thermal energy. Changing surface tension by interfacial electrification also modifies phase-change kinetics, eliminating metastability that is the root of catastrophic electric discharges and destructive explosions. It also changes crystal habits, producing needles and dendrites that shorten battery life. These recent findings derive from a single factor, water's ability to electrify matter, touching on the most relevant aspects of chemistry. They create tremendous scientific opportunities to understand the matter better, and a new chemistry based on electrified interfaces is now emerging.

Bioinspired Hierarchical Self-Assembled Nanozyme for Efficient Antibacterial Treatment

Along with the rapid development and ever-deepening understanding of nanoscience and nanotechnology, nanomaterials hold promise to mimic the highly evolved biological exquisite nanostructures and sophisticated functions. Here, inspired by the ubiquitous antibacterial nanostructures on the wing surfaces of some insects, a NiCo2 O4 nanozyme with self-adaptive hierarchical nanostructure is developed that can capture bacteria of various morphotypes via the physico-mechanical interaction between the nanostructure and bacteria. Moreover, the developed biomimetic nanostructure further exhibits superior peroxidase-like catalytic activity, which can catalytically generate highly toxic reactive oxygen species that disrupt bacterial membranes and induce bacterial apoptosis. Therefore, the mechano-catalytic coupling property of this NiCo2 O4 nanozyme allows for an extensive and efficient antibacterial application, with no concerns of antimicrobial resistance. This work suggests a promising strategy for the rational design of advanced antibacterial materials by mimicking biological antibiosis.

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

Water utilization is accompanied with the development of human beings, whereas gaseous moisture is usually regarded as an underexploited resource. The advances of highly efficient hygroscopic materials endow atmospheric water harvesting as an intriguing solution to convert moisture into clean water. The discovery of hygroelectricity, which refers to the charge buildup at a material surface dependent on humidity, and the following moisture-enabled electric generation (MEG) realizes energy conversion and directly outputs electricity. Much progress has been made since then to optimize MEG performance, pushing forward the applications of MEG into a practical level. Herein, the evolvement and development of MEG are systematically summarized in a chronological order. The optimization strategies of MEG are discussed and comprehensively evaluated. Then, the latest applications of MEG are presented, including high-performance powering units and self-powered devices. In the end, a perspective on the future development of MEG is given for inspiring more researchers into this promising area.

Harvesting Energy from Atmospheric Water: Grand Challenges in Continuous Electricity Generation

Atmospheric water is ubiquitous on earth and extensively participates in the natural water cycle through evaporation and condensation. This process involves tremendous energy exchange with the environment, but very little of the energy has so far been harnessed. The recently emerged hydrovoltaic technology, especially moisture-induced electricity, shows great potential in harvesting energy from atmospheric water and gives birth to moisture energy harvesting devices. The device performance, especially the long-term operational capacity, has been significantly enhanced over the past few years. Further development; however, requires in-depth understanding of mechanisms, innovative materials, and ingenious system designs. In this review, beginning with describing the basic properties of water, the key aspects of the water-hygroscopic material interactions and mechanisms of power generation are discussed. The current material systems and advances in promising material development are then summarized. Aiming at the chief bottlenecks of limited operational time, advanced system designs that are helpful to improve device performance are listed. Especially, the synergistic effect of moisture adsorption and water evaporation on material and system levels to accomplish sustained electricity generation is discussed. Last, the remaining challenges are analyzed and future directions for developing this promising technology are suggested.

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.

Electric-Eel-Type Bi-Ionic Gradient Battery

Electric eels generate electricity with a discharge voltage of up to 860 V under ionic gradients, providing a fascinating example to inspire viable and flexible power sources. However, hitherto reported eel-related devices are strictly restricted by complicated fabrication and environmental energy input. Herein, an electric-eel-type bi-ionic gradient battery (BGB) is performed by cationic and anionic polyelectrolyte hydrogels featuring simplified units and self-energy supply. Benefiting from ionic bonds with opposite charges in the polymer chain, bianion gradients as well as ion selective migration pathways are synchronously constructed and integrated units are enabled. As a result, an open-circuit voltage of 0.54 V and a short-circuit current density of 13 μA cm-2 are generated by a BGB unit. Moreover, a voltage output up to 60 V is derived from integrated BGB devices, demonstrating the potential to drive wearable and implantable electronics. In this case, these artificial electric systems could overcome the great challenges of environmentally friendly, biocompatible, low-cost, and soft power sources, providing in-depth insights into the development of clean and sustainable power generation technologies.

A Flexible Tough Hydrovoltaic Coating for Wearable Sensing Electronics

The lack of a strong binding mechanism between nanomaterials severely restricts the advantages of the evaporation-driven hydrovoltaic effect in wearable sensing electronics. It is a challenging task to observably improve the mechanical toughness and flexibility of hydrovoltaic devices to match the wearable demand without abandoning the nanostructures and surface function. Here, a flexible tough polyacrylonitrile/alumina (PAN/Al2 O3 ) hydrovoltaic coating with both good electricity generation (open-circuit voltage, Voc  ≈ 3.18 V) and sensitive ion sensing (2285 V M-1 for NaCl solutions in 10-4 to 10-3  m) capabilities is developed. The porous nanostructure composed of Al2 O3 nanoparticles is firmly locked by the strong binding effect of PAN, giving a critical binding force 4 times that of Al2 O3 film to easily deal with 9.92 m s-1 strong water-flow impact. Finally, skin-tight and non-contact device structures are proposed to achieve wearable multifunctional self-powered sensing directly using sweat. The flexible tough PAN/Al2 O3 hydrovoltaic coating breaks through the mechanical brittleness limitation and broadens the applications of the evaporation-induced hydrovoltaic effect in self-powered wearable sensing electronics.

Layer-by-Layer Nanofluidic Membranes for Promoting Blue Energy Conversion

Access to and use of energy resources are now crucial components of modern human existence thanks to the exponential growth of technology. Traditional energy sources provide significant challenges, such as pollution, scarcity, and excessive prices. As a result, there is more need than ever before to replace depleting resources with brand-new, reliable, and environmentally friendly ones. With the aid of reverse electrodialysis, the salinity gradient between rivers and seawater as a clean supply with easy and infinite availability is a viable choice for energy generation. The development of nanofluidic-based reverse electrodialysis (NRED) as a novel high-efficiency technology is attributable to the progress of nanoscience. However, understanding the predominant mechanisms of this process at the nanoscale is necessary to develop and disseminate this technology. One viable option to gain insight into these systems while saving expenses is to employ simulation tools. In this study, we looked at how a layer-by-layer (LBL) soft layer influences ion transport and energy production in charged nanochannels. We solved the steady-state Poisson-Nernst-Planck (PNP) and Navier-Stokes (NS) equations for three different types of nanochannels with a trumpet geometry, where the narrow part is covered with a built-up LbL soft layer and the rest is a hard wall with a surface charge density of σ = -10, 0, or +10 mC/m2. The findings show that in type (I) nanochannels, at NPEL/NA = 100 mol/m3 and pH = 7, the maximum power output rises 675-fold as the concentration ratio rises from 10 to 1000. The results of this study can aid in a better understanding of energy harvesting processes using nanofluidic-based reverse electrodialysis in order to identify optimal conditions for the design of an intelligent route with great controllability and minimal pollution.

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.