Droplet-Based Direct-Current Electricity Generation Induced by Dynamic Electric Double Layers

Harvesting energy from water droplets has received tremendous attention due to the pursuit of sustainable and green energy resources. The droplet-based electricity generator (DEG) provides an admirable strategy to harvest energy from droplets into electricity. However, most of the DEGs merely generate electricity of alternating current (AC) output rather than direct current (DC) without the utilization of rectifiers, impeding its practical applications in energy storage and power supply. Here, a direct current droplet-based electricity generator (DC-DEG) is developed by the simple configuration of the electrodes. The DC output originates from the dynamical electric double layer (EDL) formed at two electrodes and droplet interfaces where the charging/discharging process of EDL capacitance occurs. Several experiments are exhibited to demonstrate the rationality of the proposed principle. The influence of some factors on the output is investigated for further insight into the DC-DEG device. This work provides a novel strategy to harvest energy from water droplets directly into DC electricity and may expand the application of DEGs in powering electronic devices without the help of rectifiers.

Hierarchical porous dual-mode thermal management fabrics achieved by regulating solar and body radiations

Personal thermal management (PTM) of fabrics is vital for human health; the ever-changing location of the human body poses a big challenge for fabrics to maintain a favorable metabolic temperature. Herein, a dual-mode thermal management fabric is designed to achieve both cooling and heating functions by regulating simultaneously solar and body radiations. The cooling or heating mode can be exchanged by flipping the fabric without an external energy supply. The passive cooling side consists of an electrospun polyacrylonitrile (PAN) fabric with a hierarchical porous structure, exhibiting high sunlight reflectance (91.42%) and an ∼14 °C temperature decrease under direct sunlight irradiation. The co-existence of nanoscale and microscale pores is proven to be essential for improved cooling performances. The other heating side, coated with an MXene layer, shows high photothermal conversion efficiency (37.5%) and outstanding heating capability outdoors. Furthermore, the contrary mid-infrared emissivity of the two sides (high emissivity of the cooling side while low emissivity of the heating side) leads to the dual-mode passive regulation of body thermal energy. Besides, this fabric demonstrates satisfactory wearability and excellent stability. Our work proposes an energy-saving and cost-effective approach for PTM fabrics potentially suitable for various scenarios (e.g., indoors/outdoors, summer/winter, low/high latitude areas).

Critical Roles of Acidic Residues in Loop Regions of the Structural Surface for the Salt Tolerance of a GH39 β-d-Xylosidase

Xylan is the main component of hemicellulose. Complete hydrolysis of xylan requires synergistically acting xylanases, such as β-d-xylosidases. Salt-tolerant β-d-xylosidases have significant application benefits, but few reports have explored the critical amino acids affecting the salt tolerance of xylosidases. Herein, the site-directed mutation was used to demonstrate that negative electrostatic potentials generated by 19 acidic residues in the loop regions of the structural surface positively correlated with the improved salt tolerance of GH39 β-d-xylosidase JB13GH39P28. These mutants showed reduced negative potentials on structural surfaces as well as a 13-43% decrease in stability in 3.0-30.0% (w/v) NaCl. Six key residue sites, D201, D259, D297, D377, D395, and D474, were confirmed to influence both the stability and activity of GH39 β-d-xylosidase. The activity of the GH39 β-d-xylosidase was found promoting by SO42- and inhibiting by NO3-. Values of Km and Kcat/Km decreased aggravatedly in 30.0% (w/v) NaCl when mutation operated on residues E179 and D182 in the loop regions of the catalytic domain. Taken together, mutation on acidic residues in loop regions from catalytic and noncatalytic domains may cause the deformation of catalytic pocket and aggregation of protein particles then decrease the stability, binding affinity, and catalytic efficiency of the β-d-xylosidase.

Screening Selection of Hydrogen Evolution-Inhibiting and Zincphilic Alloy Anode for Aqueous Zn Battery

The hydrogen evolution reaction (HER) and Zn dendrites growth are two entangled detrimental effects hindering the application of aqueous Zn batteries. The alloying strategy is studied to be a convenient avenue to stabilize Zn anodes, but there still lacks global understanding when selecting reliable alloy elements. Herein, it is proposed to evaluate the Zn alloying elements in a holistic way by considering their effects on HER, zincphilicity, price, and environmental-friendliness. Screening selection sequence is established through the theoretical evaluation of 17 common alloying elements according to their effects on hydrogen evolution and Zn nucleation thermodynamics. Two alloy electrodes with opposite predicted effects are prepared for experimental demonstration, i.e., HER-inhibiting Bi and HER-exacerbating Ni. Impressively, the optimum ZnBi alloy anode exhibits one order of magnitude lower hydrogen evolution rate than that of the pure Zn, leading to an ultra-long plating/stripping cycling life for more than 11 000 cycles at a high current density of 20 mA cm-2 and 81% capacity retention for 170 cycles in a Zn-V2O5 pouch cell. The study not only proposes a holistic alloy selection principle for Zn anode but also identifies a practically effective alloy element.

A high-current hydrogel generator with engineered mechanoionic asymmetry

Mechanoelectrical energy conversion is a potential solution for the power supply of miniaturized wearable and implantable systems; yet it remains challenging due to limited current output when exploiting low-frequency motions with soft devices. We report a design of a hydrogel generator with mechanoionic current generation amplified by orders of magnitudes with engineered structural and chemical asymmetry. Under compressive loading, relief structures in the hydrogel intensify net ion fluxes induced by deformation gradient, which synergize with asymmetric ion adsorption characteristics of the electrodes and distinct diffusivity of cations and anions in the hydrogel matrix. This engineered mechanoionic process can yield 4 mA (5.5 A m-2) of peak current under cyclic compression of 80 kPa applied at 0.1 Hz, with the transferred charge reaching up to 916 mC m-2 per cycle. The high current output of this miniaturized hydrogel generator is beneficial for the powering of wearable devices, as exemplified by a controlled drug-releasing system for wound healing. The demonstrated mechanisms for amplifying mechanoionic effect will enable further designs for a variety of self-powered biomedical systems.

A Wearable Multidimensional Motion Sensor for AI-Enhanced VR Sports

Regular exercise paves the way to a healthy life. However, conventional sports events are susceptible to weather conditions. Current motion sensors for home-based sports are mainly limited by operation power consumption, single-direction sensitivity, or inferior data analysis. Herein, by leveraging the 3-dimensional printing technique and triboelectric effect, a wearable self-powered multidimensional motion sensor has been developed to detect both the vertical and planar movement trajectory. By integrating with a belt, this sensor could be used to identify some low degree of freedom motions, e.g., waist or gait motion, with a high accuracy of 93.8%. Furthermore, when wearing the sensor at the ankle position, signals generated from shank motions that contain more abundant information could also be effectively collected. By means of a deep learning algorithm, the kicking direction and force could be precisely differentiated with an accuracy of 97.5%. Toward practical application, a virtual reality-enabled fitness game and a shooting game were successfully demonstrated. This work is believed to open up new insights for the development of future household sports or rehabilitation.

Recent Advances in Triboelectric Nanogenerators: From Technological Progress to Commercial Applications

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

Nonepitaxial Electrodeposition of (002)-Textured Zn Anode on Textureless Substrates for Dendrite-Free and Hydrogen Evolution-Suppressed Zn Batteries

Nontoxic and safe aqueous Zn batteries are largely restricted by the detrimental dendrite growth and hydrogen evolution of Zn metal anode. The (002)-textured Zn electrodeposition, demonstrated as an effective approach for solving these issues, is nevertheless achieved mainly by epitaxial or hetero-epitaxial deposition of Zn on pre-textured substrates. Herein, the electrodeposition of (002)-textured and compact Zn on textureless substrates (commercial Zn, Cu, and Ti foils) at a medium-high galvanostatic current density is reported. According to the systematic investigations on Zn nucleation and growth behaviors, this is ascribed to two reasons: i) the promoted nonepitaxial nucleation of fine horizontal (002) nuclei at increased overpotential and ii) the competitive growth advantages of (002)-orientated nuclei. The resulting freestanding (002)-textured Zn film exhibits significantly suppressed hydrogen evolution and prolonged Zn plating-stripping cycling life, achieving over 2100 mAh cm^-2 cumulative capacity under a current density of 10 mA cm^-2 and a high depth of discharge (DOD) of 45.5%. Therefore, this study provides both fundamental and practical insights into long-life Zn metal batteries.

Tuning pyridinic-N and graphitic-N doping with 4,4'-bipyridine in honeycomb-like porous carbon and distinct electrochemical roles in aqueous and ionic liquid gel electrolytes for symmetric supercapacitors

Doping engineering in nanostructured carbon materials is an effective approach to modify heteroatom species and surface electronic structures. Herein, an advanced electrode material based on a honeycomb-like porous carbon matrix with tunable N-doped configurations is prepared via 4,4'-bipyridine (4,4'-bpy)-assisted pyrolysis of SiO₂@ZIF-8 templates and subsequent etching treatment. Interestingly, the amounts of pyridinic-N and graphitic-N can be controlled by rationally varying the content of 4,4'-bpy which acts as the N source in the pyrolysis process. Both experimental results and density functional theory calculations have revealed that synergistically with 3D interconnected porous architecture, pyridinic-N and graphitic-N have different effects on the electrochemical performances in aqueous and ionic liquid gel electrolytes for symmetric supercapacitors. Highly exposed pyridinic-N endows the carbon electrode with a strengthened pseudocapacitance contribution manifested as a high specific capacitance of 436.1 F g^-1 and exceptional stability of almost 100% capacitance retention after 5000 cycles at 10 A g^-1 in the KOH/polyvinyl alcohol (PVA) electrolyte. By contrast, graphitic-N is propitious for reinforced electrical double-layer capacitance contribution, reflected by a maximum energy density of 125.4 Wh kg^-1 in the 1-ethyl-3-methylimidazolium tetrafluoroborate/poly(vinylidene fluoride-co-hexafluoropropylene) (EMIMBF₄/PVDF-HFP) electrolyte. This work offers an in-depth insight into the understanding of the energy storage mechanism of N-rich carbon electrodes in different electrolyte media.

Suppressing the Exacerbated Hydrogen Evolution of Porous Zn Anode with an Artificial Solid-Electrolyte Interphase Layer

Rechargeable Zn batteries are widely studied as aqueous, safe, and environmentally friendly alternatives to Li-ion batteries. The 3D porous Zn anode has been extensively reported for suppressing Zn dendrite growth and accelerating the electrode kinetics. However, we demonstrate herein that the undesirable hydrogen evolution reaction (HER) is also exacerbated for porous Zn electrode. Therefore, a polytetrafluoroethylene (PTFE) coating is further applied on the porous Zn serving as the artificial solid-electrolyte interphase (SEI), which is demonstrated to effectively inhibit the hydrogen evolution and maintain the Zn plating kinetics. By utilizing the synergistic effects of the porous morphology and artificial SEI layer, better performances are obtained over porous Zn or bare Zn foil, including dendrite-free Zn plating/stripping up to 2000 h at 2 mA cm^-2 and extended cycling in the Zn||V₂O₅ cell. This work suggests two complementary strategies for achieving simultaneously dendrite-free and side-reaction-suppressed Zn batteries.

Elastic Kernmantle E-Braids for High-Impact Sports Monitoring

The kernmantle construction, a kind of braiding structure that is characterized by the kern absorbing most of the stress and the mantle protecting the kern, is widely employed in the field of loading and rescue services, but rarely in flexible electronics. Here, a novel kernmantle electronic braid (E-braid) for high-impact sports monitoring, is proposed. The as-fabricated E-braids not only demonstrate high strength (31 Mpa), customized elasticity, and nice machine washability (>500 washes) but also exhibit excellent electrical stability (>200 000 cycles) during stretching. For demonstration, the E-braids are mounted to different parts of the trampoline for athletes' locomotor behavior monitoring. Furthermore, the E-braids are proved to act as multifarious intelligent sports gear or wearable equipment such as electronic jump rope and respiration monitoring belt. This study expands the kernmantle structure to soft flexible electronics and then accelerates the development of quantitative analysis in modern sports industry and athletes' healthcare.

Triboelectric nanogenerators as wearable power sources and self-powered sensors

Smart wearable technologies are augmenting human bodies beyond our biological capabilities in communication, healthcare and recreation. Energy supply and information acquisition are essential for wearable electronics, whereas the increasing demands in multifunction are raising the requirements for energy and sensor devices. The triboelectric nanogenerator (TENG), proven to be able to convert various mechanical energies into electricity, can fulfill either of these two functions and therefore has drawn extensive attention and research efforts worldwide. The everyday life of a human body produces considerable mechanical energies and, in the meantime, the human body communicates mainly through mechanical signals, such as sound, body gestures and muscle movements. Therefore, the TENG has been intensively studied to serve as either wearable sources or wearable self-powered sensors. Herein, the recent finding on the fundamental understanding of TENGs is revisited briefly, followed by a summary of recent advancements in TENG-based wearable power sources and self-powered sensors. The challenges and prospects of this area are given as well.

Topological Gradients for Metal Film-Based Strain Sensors

Metal film-based stretchable strain sensors hold great promise for applications in various domains, which require superior sensitivity-stretchability-cyclic stability synergy. However, the sensitivity-stretchability trade-off has been a long-standing dilemma and the metal film-based strain sensors usually suffer from weak cyclic durability, both of which significantly limit their practical applications. Here, we propose an extremely facile, low-cost and spontaneous strategy that incorporates topological gradients in metal film-based strain sensors, composed of intrinsic (grain size and interface) and extrinsic (film thickness and wrinkle) microstructures. The topological gradient strain sensor exhibits an ultrawide stretchability of 100% while simultaneously maintaining a high sensitivity at an optimal topological gradient of 4.5, due to the topological gradients-induced multistage film cracking. Additionally, it possesses a decent cyclic stability for >10 000 cycles between 0 and 40% strain enabled by the gradient-mixed metal/elastomer interfaces. It can monitor the full-range human activities from subtle pulse signals to vigorous joint movements.

Hollow Ni3Se4 with High Tap Density as a Carbon-Free Sulfur Immobilizer to Realize High Volumetric and Gravimetric Capacity for Lithium-Sulfur Batteries

Despite that the practical gravimetric energy density of lithium sulfur batteries has exceeded that of the traditional lithium-ion battery, the volumetric energy density still pales due to the low density of carbonaceous materials. Herein, hollow polar nickel selenide (Ni₃Se₄) with various architectures was designed and employed as a carbon-free sulfur immobilizer. Among them, hollow sea urchins like Ni₃Se₄ with high porosity (0.39 cm³ g^-1) and large specific surface area (82.7 m² g^-1) exhibit abundant adsorptive and electrocatalytic sites, which pledge excellent electrochemical performances of the Li-S battery. Correspondingly, the Ni₃Se₄-based sulfur electrode presents excellent rate endurability (581 mAh g^-1_-composite at 2.0 C) and superior cycle stability (ultralow fading rate of 0.042% per cycle during the 1000 cycles at 1.0 C). More importantly, thanks to the higher tap density (Ni₃Se₄/S: 1.57 g cm^-3 vs super P/S: 0.7 g cm^-3), the volumetric specific capacity of Ni₃Se₄-based cathodes is as high as 1699 mAh cm^-3_-composite at 0.1 C, which is almost 2.8 times that of the carbonaceous electrode. Hence, rational transition metal selenide architecture design with synergistic function of good conductivity, well-defined catalyst and adsorption, as well as high tap density provide a promising route toward high gravimetric and volumetric energy density of Li-S batteries.

Bioinspired soft electroreceptors for artificial precontact somatosensation

Artificial haptic sensors form the basis of touch-based human-interfaced applications. However, they are unable to respond to remote events before physical contact. Some elasmobranch fishes, such as seawater sharks, use electroreception somatosensory system for remote environmental perception. Inspired by this ability, we design a soft artificial electroreceptor for sensing approaching targets. The electroreceptor, enabled by an elastomeric electret, is capable of encoding environmental precontact information into a series of voltage pulses functioning as unique precontact human interfaces. Electroceptor applications are demonstrated in a prewarning system, robotic control, game operation, and three-dimensional object recognition. These capabilities in perceiving proximal precontact events can lenrich the functionalities and applications of human-interfaced electronics.

Ultralight Iontronic Triboelectric Mechanoreceptor with High Specific Outputs for Epidermal Electronics

The pursuit to mimic skin exteroceptive ability has motivated the endeavors for epidermal artificial mechanoreceptors. Artificial mechanoreceptors are required to be highly sensitive to capture imperceptible skin deformations and preferably to be self-powered, breathable, lightweight and deformable to satisfy the prolonged wearing demands. It is still struggling to achieve these traits in single device, as it remains difficult to minimize device architecture without sacrificing the sensitivity or stability. In this article, we present an all-fiber iontronic triboelectric mechanoreceptor (ITM) to fully tackle these challenges, enabled by the high-output mechano-to-electrical energy conversion. The proposed ITM is ultralight, breathable and stretchable and is quite stable under various mechanical deformations. On the one hand, the ITM can achieve a superior instantaneous power density; on the other hand, the ITM shows excellent sensitivity serving as epidermal sensors. Precise health status monitoring is readily implemented by the ITM calibrating by detecting vital signals and physical activities of human bodies. The ITM can also realize acoustic-to-electrical conversion and distinguish voices from different people, and biometric application as a noise dosimeter is demonstrated. The ITM therefore is believed to open new sights in epidermal electronics and skin prosthesis fields.

Electricity Generation and Self-Powered Sensing Enabled by Dynamic Electric Double Layer at Hydrogel-Dielectric Elastomer Interfaces

The electric double layer (EDL) at liquid-solid interfaces is fundamental to many research areas ranging from electrochemistry and microfluidics to colloidal chemistry. Here, we demonstrate the electricity generation by mechanically modulating the EDL at the hydrogel-dielectric polymer interfaces. It is found that contact electrification between the hydrogel and the dielectric polymer could charge the dielectric polymer surface at first; the mechanical deformation of the pyramid-shaped hydrogel results in the periodic variation of the EDL area and capacitance, which then induces an alternative current in the external circuits. This mechano-to-electrical energy conversion mechanism is then utilized to construct soft stretchable self-powered pressure sensors by designing dynamic EDL at hydrogel-dielectric elastomer interfaces. The sensitivity is optimized to 1.40 kPa^-1 in the low-pressure range of 31-300 Pa by increasing the elastomer roughness. Its antifreeze performance is also improved by adding ethylene glycol into the hydrogel. The capability in detecting subtle human activities is further demonstrated. This mechano-electrical energy conversion and the corresponding self-powered sensor can be widely applied in future soft electronics.

Triboelectric-optical responsive cholesteric liquid crystals for self-powered smart window, E-paper display and optical switch

Intelligent responsive devices are crucial for a variety of applications ranging from smart electronics to robotics. Electro-responsive cholesteric liquid crystals (CLC) have been widely applied in display panels, smart windows, and so on. In this work, we realize the mechanical stimuli-triggered optical responses of the CLC by integrating it with a triboelectric nanogenerator (TENG), which converts the mechanical motion into alternating current electricity and then tunes the different optical responses of the CLC. When the voltage applied on the CLC is relatively low (15-40 V), the TENG drives the switching between the bistable planar state and focal conic state of the CLC, which shows potential applications in self-powered smart windows or E-paper displays. When the voltage supplied by the TENG is larger than 60 V, a self-powered optical switch is demonstrated by utilizing the transformation between focal conic state and instantons homeotropic state of the CLC. This triboelectric-optical responsive device consumes no extra electric power and suggests a great potential for future smart electronics.

Self-Healing Solid Polymer Electrolyte for Room-Temperature Solid-State Lithium Metal Batteries

Poor room-temperature ionic conductivities and narrow electrochemical stable windows severely hinder the application of conventional poly(ethylene oxide)-based (PEO-based) solid polymer electrolytes (SPEs) for high-energy-density lithium metal batteries (LMBs). Herein, we designed and synthesized a PEO-based self-healing solid polymer electrolyte (SHSPE) via dynamically cross-linked imine bonds for safe, flexible solid LMBs. The constructed dynamic networks endow this SPE with fascinating intrinsic self-healing ability and excellent mechanical properties (extensibility > 500% and stress >130 kPa). More importantly, this SHSPE exhibits ultrahigh ionic conductivity (7.48 × 10^-4 S cm^-1 at 25 °C) and wide ESW (5.0 V vs Li/Li⁺). As a result, Li||Li symmetrical cells with the SHSPE showed reliable stability in a >1200 h cycling test under room temperature. The assembled Li|SHSPE|LiFePO₄ cell maintained a discharge capacity of 126.4 mAh g^-1 after 300 cycles (0.1C, 27 °C). This work highlights a promising strategy for next-generation room-temperature solid-state LMBs.

Dynamically Crosslinked Dry Ion-Conducting Elastomers for Soft Iontronics

Soft ionic conductors show great promise in multifunctional iontronic devices, but currently utilized gel materials suffer from liquid leakage or evaporation issues. Here, a dry ion-conducting elastomer with dynamic crosslinking structures is reported. The dynamic crosslinking structures endow it with combined advantageous properties simultaneously, including high ionic conductivity (2.04 × 10^-4 S cm^-1 at 25 °C), self-healing capability (96% healing efficiency), stretchability (563%), and transparency (78%). With this ionic conductor as the electrode, two soft iontronic devices (electroluminescent devices and triboelectric nanogenerator tactile sensors) are realized with entirely self-healing and stretchable capabilities. Due to the absence of liquid materials, the dry ion-conducting elastomer shows wide operational temperature range, and the iontronic devices achieve excellent stability. These findings provide a promising strategy to achieve highly conductive and multifunctional soft dry ionic conductors, and demonstrate their great potential in soft iontronics or electronics.

Ultra-stretchable and healable hydrogel-based triboelectric nanogenerators for energy harvesting and self-powered sensing

The next-generation multifunctional soft electronic devices require the development of energy devices possessing comparable functions. In this work, an ultra-stretchable and healable hydrogel-based triboelectric nanogenerator (TENG) is prepared for mechanical energy harvesting and self-powered sensing. An ionic conductive hydrogel was developed with graphene oxide and Laponite. as the physical cross-linking points, exhibiting high stretchability (∼1356%) and healable capability. When using the hydrogel as the electrode, the TENG can operate normally at 900% tensile strain, while the electrical output of the TENG can fully recover to the initial value after healing the damage. This hydrogel-based TENG is demonstrated to power wearable electronics, and is used as a self-powered sensor for human motion monitoring and pressure sensing. Our work shows opportunities for multifunctional power sources and potential applications in wearable electronics.

An ultra-stretchable and self-healing hydrogel is developed with graphene oxide and Laponite as collaborative physical crosslinking points, which is utilized in triboelectric nanogenerators for mechanical energy harvesting and self-powered sensing.

Textile Triboelectric Nanogenerators Simultaneously Harvesting Multiple "High-Entropy" Kinetic Energies

Distributed renewable kinetic energies are ubiquitous but with irregular amplitudes and frequencies, which, as one category of "high-entropy" energies, are crucial for next-generation self-powered electronics. Herein, we present a flexible waterproof dual-mode textile triboelectric nanogenerator (TENG), which can simultaneously scavenge multiple "high-entropy" kinetic energies, including human motions, raindrops, and winds. A freestanding-mode textile TENG (F-TENG) and a contact-separation-mode textile TENG (CS-TENG) are integrated together. The structure parameters of the textile TENG are optimized to improve the output performances. The raindrop can generate a voltage of up to ∼4.3 V and a current of about ∼6 μA, while human motion can generate a voltage of over 120 V and a peak power density of ∼500 mW m^-2. The scavenged electrical energies can be stored in capacitors for powering small electronics. Therefore, we demonstrated a facile preparation of a TENG-based energy textile that is highly promising for kinetic energy harvesting and self-powered electronics.

Boosting the Power and Lowering the Impedance of Triboelectric Nanogenerators through Manipulating the Permittivity for Wearable Energy Harvesting

Triboelectric nanogenerators (TENGs), which hold great promise for sustainably powering wearable electronics by harvesting distributed mechanical energy, are still severely limited by their unsatisfactory power density, small capacitance, and high internal impedance. Herein, a materials optimization strategy is proposed to achieve a high performance of TENGs and to lower the matching impedance simultaneously. A permittivity-tunable electret composite film, i.e., a thermoplastic polyurethane (TPU) matrix with polyethylene glycol (PEG) additives and polytetrafluoroethylene (PTFE) nanoparticle inclusions, is employed as the triboelectric layer. Through optimizing the dielectric constant of the composite, the injected charge density and internal capacitance of the TENG are significantly enhanced, thus synergistically boosting the output power and reducing the impedance of the TENG. The optimal output power reaches 16.8 mW at an external resistance of 200 kΩ, showing a 17.3 times enhancement in output power and a 90% decline in matching impedance. This work demonstrates a significant progress toward the materials optimization of a triboelectric generator for its practical commercialization.

Wearable Antifreezing Fiber-Shaped Zn/PANI Batteries with Suppressed Zn Dendrites and Operation in Sweat Electrolytes

Fiber-shaped Zn batteries are promising candidates for wearable electronics owing to their high energy and low cost, but further studies are still required to address the issues related to detrimental Zn dendrite growth and limited low-temperature performances. Here, we report an antifreeze, long-life, and dendrite-free fiber-shaped Zn battery using both nanoporous Zn and polyaniline (PANI) electrodeposited on carbon nanofibers (CFs) as the cathode and anode, respectively. The fiber-shaped Zn anode achieves stable plating/stripping for 1000 mAh cm^-2 accumulative capacity with low polarization (30 mV) at a current density of 2 mA cm^-2. The dendrite-free Zn electrodes also enable the stable cycling of the fiber battery with 75.1% capacity retention after 1000 cycles. With an antifreeze agent added in the gel electrolyte, the fiber battery maintains excellent performance at temperatures as low as -30 °C. Lastly, by utilizing the doping/dedoping mechanism of Cl^- in the PANI electrode, we achieve, for the first time, a Zn battery using human sweat as a harmless electrolyte. Our work provides a long-life and antifreeze fiber-shaped battery that is highly promising for future wearable energy storage devices.

Self-charging power system for distributed energy: beyond the energy storage unit

Power devices for the smart sensor networks of Internet of things (IoT) are required with minimum or even no maintenance due to their enormous quantities and widespread distribution. Self-charging power systems (SCPSs) refer to integrated energy devices with simultaneous energy harvesting, power management and effective energy storage capabilities, which may need no extra battery recharging and can sustainably drive sensors. Herein, we focus on the progress made in the field of nanogenerator-based SCPSs, which harvest mechanical energy using the Maxwell displacement current arising from the variation in the surface-polarized-charge-induced electrical field. Prototypes of different nanogenerator-based SCPSs will be overviewed. Finally, challenges and prospects in this field will be discussed.

[Current situation of screening, prevention and treatment of bleeding esophageal varices in cirrhotic portal hypertension in Tibet region: a multicenter study]

Objective: To investigate and analyze the current situation, screening, clinical characteristics, prevention and treatment of bleeding esophageal varices in cirrhotic patients with portal hypertension in Tibet region. Methods: Clinical data of cirrhotic patients with portal hypertension through March 2017 to February 2020 from Tibet region were collected and analyzed retrospectively. Results: 511 cases with liver cirrhosis were included in the study, of which 185 cases (36.20%) had compensated cirrhosis and 326 cases (63.80%) had decompensated cirrhosis. Further analysis of the etiological data of liver cirrhosis showed that 306 cases (59.88%) were of chronic hepatitis B, 113 cases (22.11%) of alcoholic liver disease, and 68 cases (13.31%) of chronic hepatitis B combined with alcoholic liver disease. Among patients with compensated liver cirrhosis, 48 cases (25.95%) underwent endoscopic examination of which 33 diagnosed as high-risk variceal bleeding. However, none of these 33 cases had received non-selective β-blocker therapy, and only four patients had received endoscopic variceal banding therapy. Among patients with decompensated liver cirrhosis, 83 cases (25.46%) had a history of upper gastrointestinal bleeding, 297 cases (91.10%) had ascites, 23 cases (7.05%) had hepatic encephalopathy, and 3 cases (0.92%) had hepatorenal syndrome. Among the patients with a history of upper gastrointestinal bleeding, 42 cases (50.60%) had received secondary preventive treatment for bleeding esophageal varices, including 39 cases of endoscopic treatment, 1 case of endoscopic combined drug treatment, 3 cases of interventional treatment, and 2 cases of surgical treatment. Conclusion: Chronic hepatitis B and alcoholic liver diseases are the main causes of liver cirrhosis in Tibet region. Moreover, this region lacks screening, prevention and treatment for bleeding esophageal varices in cirrhotic patients with portal hypertension. Therefore, it is necessary to increase the screening of high-risk groups to prevent and improve the first-time bleeding, and promote multidisciplinary team to prevent and treat re-bleeding.

A flexible triboelectric nanogenerator based on a super-stretchable and self-healable hydrogel as the electrode

Stretchable electronic devices nowadays have become more and more necessary in our daily lives, and most of the present electronic devices are based on inorganic materials. The obtained electronic devices can hardly bear various deformations in practical applications because of the poor flexibility and stretchability of these conventional inorganic materials. However, the biggest challenge for producing flexible and stretchable electronic devices is that each component of the device should endure deformations, and in the meantime, ensure that the whole electronic devices not only have excellent flexibility and stretchability, but also maintain excellent electrical output performances even under the situation of being deformed. In this work, a kind of super-stretchable, self-healable, and conductive hydrogel which could bear about sixty times stretching compared with its original state (∼ 6000%) is prepared; it could self-heal in about 10 min after being cut. More importantly, the hydrogel can greatly enhance the output performances of the TENG compared with the conventional copper foil as the electrode. Furthermore, when used as the electrode in flexible TENGs, relatively stable and excellent electrical output performances could be maintained even after being seriously stretched. Consequently, this study provides an ideal candidate for the electrode material of electric devices.

Stretchable Coplanar Self-Charging Power Textile with Resist-Dyeing Triboelectric Nanogenerators and Microsupercapacitors

The integration between energy-harvesting and energy-storage devices into a self-charging power unit is an effective approach to address the energy bottleneck of wearable/portable/wireless smart devices. Herein, we demonstrate a stretchable coplanar self-charging power textile (SCPT) with triboelectric nanogenerators (TENGs) and microsupercapacitors (MSCs) both fabricated through a resist-dyeing-analogous method. The textile electrodes maintain excellent conductivity at 600% and 200% tensile strain along course and wale directions, respectively. The fabric in-plane MSC with reduced graphene oxides as active materials reaches a maximum areal capacitance of 50.6 mF cm^-2 at 0.01 V s^-1 and shows no significant degradation at 50% of tensile strain. The stretchable fabric-based TENG can output 49 V open-circuit voltage and 94.5 mW m^-2 peak power density. Finally, a stretchable coplanar SCPT with one-batch resist-dyeing fabrication is demonstrated for powering small electronics intermittently without extra recharging. Our approach is also compatible with conventional textile processing and suggests great potential in electronic textiles and wearable electronics.

Vertically aligned NiS2/CoS2/MoS2 nanosheet array as an efficient and low-cost electrocatalyst for hydrogen evolution reaction in alkaline media

Recently, the rational design of non-precious metal electrocatalysts for highly efficient hydrogen evolution reaction (HER) in alkaline media has received considerable interests in sustainable and renewable energy researches. Herein, vertically aligned and interconnected NiS₂/CoS₂/MoS₂ nanosheet arrays on Ni foam were prepared by a two-step procedure that conducted by the hydrothermal synthesis of Ni-Co molybdate nanosheet array as the precursor and followed by the vapor phase sulfurization to achieve in situ conversion. Basing on the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations, it can be found that the honeycomb-like structure of the Ni-Co molybdate nanosheet array was well preserved after the sulfurization process. The high-resolution TEM (HRTEM) characterization reveals that the NiS₂/CoS₂/MoS₂ nanosheet array provided abundant well-exposed active edge sites and multiple heterointerfaces towards enhanced alkaline HER performance. Electrochemical studies demonstrated that the ultrathin NiS₂/CoS₂/MoS₂ nanosheets exhibited excellent HER performance with an overpotential of 112 mV at 10 mA cm^-2 and a smaller Tafel slope of 59 mV dec^-1 in comparison with NiS₂/MoS₂ (155 mV and 89 mV dec^-1) and CoS₂/MoS₂ (124 mV and 75 mV dec^-1) samples by taking the advantage of the well-exposed multiple heterointerfaces. This work presents a facile and reliable synthetic strategy for the rational design of highly efficient electrocatalysts for the HER in alkaline solution based on non-precious metal sulfide nanocomposite.

Boosting performances of triboelectric nanogenerators by optimizing dielectric properties and thickness of electrification layer

Triboelectric nanogenerators (TENGs) with excellent flexibility and high outputs are promising for powering wearable/wireless electronics with electricity converted from ubiquitous mechanical energies in the working environment. In this work, the effects of the dielectric properties and thickness of the electrification film on the performance of the TENG are discussed. BaTiO₃ nanoparticles are added into poly(vinylidene fluoride) (PVDF) to improve the dielectric constant of the composite film. The TENG using a BaTiO₃/PVDF nanocomposite film with 11.25 vol% BaTiO₃ as the tribo-negative electrification layer is demonstrated to be the optimized one, and generates an open-circuit voltage of 131 V and transferred short-circuit charge density of 89 μC m⁻², 6.5 fold higher than those of a TENG using bare a PVDF layer. Furthermore, by reducing the thickness of the BaTiO₃/PVDF film to 5 μm, the voltage and charge density increase to 161 V and 112 μC m⁻², respectively, and an instantaneous peak power density of 225.6 mW m⁻² is obtained.

Enhanced output performances of a triboelectric nanogenerator (TENG) are achieved by optimizing the high-dielectric-constant filler content in the electrification layer and decreasing its thickness.

A flower-like CoS2/MoS2 heteronanosheet array as an active and stable electrocatalyst toward the hydrogen evolution reaction in alkaline media

CoS₂/MoS₂ heteronanosheet arrays (HNSAs) with vertically aligned flower-like architectures are fabricated through in situ topotactic sulfurization of CoMoO₄ nanosheet array (NSA) precursors on conductive Ni foam. CoMoO₄ NSAs are prepared by a self-template hydrothermal method without using any hard template and surfactant. Benefiting from a 3D flower-like architecture constituted by ultrathin nanosheets with abundant exposed heterointerfaces as highly active sites and predesigned void spaces, the as-synthesized CoS₂/MoS₂ HNSAs exhibit an excellent hydrogen evolution reaction (HER) performance with a low overpotential of 50 mV at 10 mA cm⁻², and a small Tafel slope of 76 mV dec⁻¹ in 1.0 M KOH, which outperforms most previously reported CoS₂ and MoS₂ based electrocatalysts with compositional or morphological similarity. This work demonstrates the great potential in developing high-efficiency and earth-abundant electrocatalysts for alkaline HER through heterointerface engineering and morphological design by utilizing transition metal molybdate as a promising platform.

CoS₂/MoS₂ heteronanosheet arrays with vertically aligned flower-like architecture are fabricated through in situ topotactic sulfurization of CoMoO₄ nanosheet arrays.

Revisiting the positive roles of liquid polysulfides in alkali metal-sulfur electrochemistry: from electrolyte additives to active catholyte

Polysulfide dissolution and shuttling in liquid organic electrolytes are considered as the most challenging detrimental effects of an Li-S cell, which is one of the most promising next-generation high-energy-density batteries. Therefore, considerable efforts have been devoted to confining solid sulfur or sulfide so as to avoid the formation and diffusion of dissolved polysulfides. However, the positive roles played by the liquid polysulfides in Li-S electrochemistry should not be overlooked. Polysulfide dissolution can promote the cell kinetics and sulfur utilization; as electrolyte additives, polysulfides can help stabilize the Li metal anode, redistribute the active mass in the cathode and act as extra back-up active sulfur sources. After being applied directly as active catholytes, a novel Li-polysulfide redox flow battery (Li-PS RFB) and an Li-polysulfide battery (Li-PS battery) have been developed. This review revisited these beneficial effects of polysulfides and provided a summary of the recent progress on Li-PS RFB and Li-PS batteries, especially with a more comprehensive emphasis on the latter. Furthermore, dissolved polysulfides applied as active catholytes in Na-S and K-S systems and as catholytes or anolytes in aqueous batteries were also briefly discussed. Hopefully, the Li-S electrochemistry can be better understood so as to overcome challenging issues in the way of the practical commercialization of the Li-S batteries.

Shape-Adaptive, Self-Healable Triboelectric Nanogenerator with Enhanced Performances by Soft Solid-Solid Contact Electrification

The viable application of soft electronics/robotics relies on the development of power devices which are desired to be flexible, deformable, or even self-healable. We report here a shape-adaptive, self-healable triboelectric nanogenerator (SS-TENG) for harvesting biomechanical energies. The use of a viscoelastic polymer, normally known as Silly Putty, as the electrification material and as the matrix of a carbon-nanotube-filled composite (CNT-putty) electrode endows the SS-TENG the capability of adapting to arbitrary irregular surfaces and instantaneous healing from mechanical damage (almost completely recovered in 3 min without extra stimuli). Furthermore, the output performances of the SS-TENG have also been significantly improved because (i) the ideal soft contact is achieved at the solid-solid interfaces for more effective contact electrification and (ii) the introduced cation dopants make the putty even more tribo-negative than polytetrafluoroethylene. The SS-TENG can be adhered to any curvy surface, tailored, and reshaped into arbitrary configurations and utilized as a power supply for small electronics, suggesting promising applications in soft electronics/robotics in the future.