Circadian humidity fluctuation induced capillary flow for sustainable mobile energy

Leaf-based energy harvesting and storage utilizing hygroscopic iron hydrogel for continuous power generation

In the era of big data, developing next-generation self-powered continuous energy harvesting systems is of great importance. Taking advantage of fallen leaves' specific structural advantage gifted by nature, we propose a facile approach to convert fallen leaves into energy harvesters from ubiquitous moisture, based on surface treatments and asymmetric coating of hygroscopic iron hydrogels. Upon moisture absorption, a water gradient is established between areas with/without hydrogel coating, and maintained due to gel-like behaviors and leaf veins for water retention and diffusion restriction, thus forming electrical double layers over the leaf surface and showing capacitance-like behavior for energy charging and discharging. Besides, the specific leaf cell structures with small grooves enabled uniform carbon coatings instead of aggregations, and high electrical conductivity, resulting in 49 μA/cm2 and 497 μW/cm3 electrical output, achieving competitive performance with the state-of-art and potential for lower environmental impact compared to other types of energy harvesters.

Hermetic hydrovoltaic cell sustained by internal water circulation

Numerous efforts have been devoted to harvesting sustainable energy from environment. Among the promising renewable resources, ambient heat exhibits attractive prospects due to its ubiquity and inexhaustibility, and has been converted into electricity through water evaporation-induced hydrovoltaic approaches. However, current hydrovoltaic approaches function only in low-humidity environments and continuously consume water. Herein, we fabricate a hermetic hydrovoltaic cell (HHC) to harvest ambient heat, and have fully addressed the limitations posed by environmental conditions. Meanwhile, for the first time we develop an internal circulation hydrovoltaic mechanism. Taking advantage of the heterogeneous wicking bilayer structure, we verify that inside the hermetic cell, the ambient temperature fluctuation-induced evaporation and further the water circulation can persist, which sustains the hydrovoltaic effect to convert ambient heat into electricity. More importantly, the hermetic design enables the cell to work continuously and reliably for 160 h with negligible water consumption, unaffected by external influences such as wind and light, making it an excellent candidate for extreme situations such as water-scarce deserts, highly humid tropical rain forests, rainy days, and dark underground engineering. These findings provide an easily accessible and widely applicable route for stably harnessing renewable energy, and more notably, offer a novel paradigm toward leveraging low-grade ambient heat energy via circulation design.

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.

Selective ion migration in a polyelectrolyte driving a high-performance flexible moisture-electric generator

We propose a novel moisture-electric generator that utilizes the unique properties of a blended poly(4-styrene sulfonic acid) and poly(vinyl alcohol) with phytic acid by screen printing and scrape coating, achieving an impressive open-circuit voltage of 0.88 V from ambient humidity. This innovative design significantly enhances ion transport, moisture adsorption, and flexibility, making a marked improvement in converting environmental humidity to electrical energy.

Correlating Structural Disorder in Metal (Oxy)hydroxides and Catalytic Activity in Electrocatalytic Oxygen Evolution

Understanding the correlation between the structural evolution of electrocatalysts and their catalytic activity is both essential and challenging. In this study, we investigate this correlation in the context of the oxygen evolution reaction (OER) by examining the influence of structural disorder during and after dynamic structural evolution on the OER activity of Fe-Ni (oxy)hydroxide catalysts using operando X-ray absorption spectroscopy, alongside other experiments and theoretical calculations. The Debye-Waller factors obtained from extended X-ray absorption fine structure analyses reflect the degree of structural disorder and exhibit a robust correlation with the intrinsic OER activities of the electrocatalysts. The enhanced OER activity of in situ-generated metal (oxy)hydroxides derived from different pre-catalysts is linked to increased structural disorder, offering a promising approach for designing efficient OER electrocatalysts. This strategy may inspire similar investigations in related electrocatalytic energy-conversion systems.

Nanofluid-Guided Janus Membrane for High-Efficiency Electricity Generation from Water Evaporation

Harvesting electricity from widespread water evaporation provides an alternative route to cleaner power generation technology. However, current evaporation power generation (EPG) mainly depends on the dissociation process of certain functional groups (e.g., SO3 H) in water, which suffers from low power density and short-term output. Herein, the Janus membrane is prepared by combining nanofluid and water-grabbing material for EPG, where the nanoconfined ionic liquids (NCILs) serve as ion sources instead of the functional groups. Benefiting from the selective and fast transport of anions in NCILs, such EPG demonstrates excellent power performance with a voltage of 0.63 V, a short-circuit current of 140 µA, and a maximum power density of 16.55 µW cm-2 while operating for at least 180 h consistently. Molecular dynamics (MD) simulation and surface potential analysis reveal the molecular mechanism, that is, the diffusion of Cl- anions during evaporation is much faster than that of cations, generating the voltage and current across the membrane. Furthermore, the device performs well in varying environmental conditions, including different water temperatures and sources of evaporating water, showcasing its adaptability and integrability. Overall, the nanofluid-guided Janus membrane can efficiently transform low-grade thermal energy in evaporation into electricity, showing a competitive advantage over other sustainable applied approaches.

Vertical Phase-Engineering MoS2 Nanosheet-Enhanced Textiles for Efficient Moisture-Based Energy Generation

Flexible moisture-electric generators (MEGs) capture chemical energy from atmospheric moisture for sustainable electricity, gaining attention in wearable electronics. However, challenges persist in the large-scale integration and miniaturization of MEGs for long-term, high-power output. Herein, a vertical heterogeneous phase-engineering MoS2 nanosheet structure based silk and cotton were rationally designed and successfully applied to construct wearable MEGs for moisture-energy conversion. The prepared METs exhibit ∼0.8 V open-circuit voltage, ∼0.27 mA/cm2 current density for >10 h, and >36.12 μW/cm2 peak output power density, 3 orders higher than current standards. And the large-scale device realizes a current output of 0.145 A. An internal phase gradient between the 2H semiconductor MoS2 in carbonized silks and 1T metallic MoS2 in cotton fibers enables a phase-engineering-based heterogeneous electric double layer functioning as an equivalent parallel circuit, leading to enhanced high-power output. Owing to their facile customization for seamless adaptation to the human body, we envision exciting possibilities for these wearable METs as integrated self-power sources, enabling real-time monitoring of physiological parameters in wearable electronics.

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.

Humidity-Tolerant Moisture-Driven Energy Generator with MXene Aerogel-Organohydrogel Bilayer

Free-standing and film-type moisture-driven energy generators (MEGs) that harness the preferential interaction of ionized moisture with hydrophilic materials are interesting because of their wearability and portability without needing a water container. However, most such MEGs work in limited humidity conditions, which provide a substantial moisture gradient. Herein, we present a high-performance MEG with sustainable power-production capability in a wide range of environments. The bilayer-based device comprises a negatively surface-charged, hydrophilic MXene (Ti₃C₂T_x) aerogel and polyacrylamide (PAM) ionic hydrogel. The preferential selection on the MXene aerogel of positive charges supplied from the salts and water in the hydrogel is predicted by the first-principle simulation, which results in a high electric output in a wide relative humidity range from 20% to 95%. Furthermore, by replacing the hydrogel with an organohydrogel of PAM that has excellent water retention and structural stability, a device with long-term electricity generation is realized for more than 15 days in a broad temperature range (from -20 to 80 °C). Our MXene aerogel MEGs connected in series supply sufficient power for commercial electronic components in various outdoor environments. Moreover, an MXene aerogel MEG works as a self-powered sensor for recognizing finger bending and facial expression.