All‐Printed Porous Carbon Film for Electricity Generation from Evaporation‐Driven Water Flow

Converting environmental “waste energies” into electricity via a natural process is an ideal strategy for environmental energy harvesting and supplying power for distributed energy‐consuming devices. This paper reports that evaporation‐driven water flow within an all‐printed porous carbon film can reliably generate sustainable voltage up to 1 V with a power density of ≈8.1 µW cm^?3 under ambient conditions. The output performance of the device can be easily scaled up and used to power low‐power consumption electronic devices or for energy storage. Furthermore, the device is successfully used without electric storage as a direct power source for electrodeposition of silver microstructures. Because of the ubiquity of water evaporation in nature and the low cost of materials involved, the study presents a novel avenue to harvest ambient energy and has potential applications in low‐cost, green, self‐powered devices and systems.     

Rationally Engineered Electrodes for a High‐Performance Solid‐State Cable‐Type Supercapacitor

Wire‐shaped electrodes for solid‐state cable‐type supercapacitors (SSCTS) with high device capacitance and ultrahigh rate capability are prepared by depositing poly(3,4‐ethylenedioxythiophene) onto self‐doped TiO₂ nanotubes (D‐TiO₂) aligned on Ti wire via a well‐controlled electrochemical process. The large surface area, short ion diffusion path, and high electrical conductivity of these rationally engineered electrodes all contribute to the energy storage performance of SSCTS. The cyclic voltammetric studies show the good energy storage ability of the SSCTS even at an ultrahigh scan rate of 1000 V s^?1, which reveals the excellent instantaneous power characteristics of the device. The capacitance of 1.1 V SSCTS obtained from the charge–discharge measurements is 208.36 µF cm^?1 at a discharge current of 100 µA cm^?1 and 152.36 µF cm^?1 at a discharge current of 2000 µA cm^?1, respectively, indicating the ultrahigh rate capability. Furthermore, the SSCTS shows superior cyclic stability during long‐term (20 000 cycles) cycling, and also maintains excellent performance when it is subjected to bending and succeeding straightening process.     

General Method for Large‐Area Films of Carbon Nanomaterials and Application of a Self‐Assembled Carbon Nanotube Film as a High‐Performance Electrode Material for an All‐Solid‐State Supercapacitor

Rational assembly of carbon nanostructures into large‐area films is a key step to realize their applications in ubiquitous electronics and energy devices. Here, a self‐assembly methodology is devised to organize diverse carbon nanostructures (nanotubes, dots, microspheres, etc.) into homogeneous films with potentially infinite lateral dimensions. On the basis of studies of the redox reactions in the systems and the structures of films, the spontaneous deposition of carbon nanostructures onto the surface of the copper substrate is found to be driven by the electrical double layer between copper and solution. As a notable example, the as‐assembled multiwalled carbon nanotube (MWCNT) films display exceptional properties. They are a promising material for flexible electronics with superior electrical and mechanical compliance characteristics. Finally, two kinds of all‐solid‐state supercapacitors based on the self‐assembled MWCNT films are fabricated. The supercapacitor using carbon cloth as the current collector delivers an energy density of 3.5 Wh kg^?1 and a power density of 28.1 kW kg^?1, which are comparable with the state‐of‐the‐art supercapacitors fabricated by the costly single‐walled carbon nanotubes and arrays. The supercapacitor free of foreign current collector is ultrathin and shows impressive volumetric energy density (0.58 mWh cm^?3) and power density (0.39 W cm^?3) too.     

High‐Performance On‐Chip Thermionic Electron Micro‐Emitter Arrays Based on Super‐Aligned Carbon Nanotube Films

An important advancement towards the realization of miniaturized and fully integrated vacuum electronic devices will be the development of on‐chip integrated electron sources with stable and reproducible performances. Here, the fabrication of high‐performance on‐chip thermionic electron micro‐emitter arrays is demonstrated by exploiting suspended super‐aligned carbon nanotube films as thermionic filaments. For single micro‐emitter, an electron emission current up to ≈20 µA and density as high as ≈1.33 A cm^?2 are obtained at a low‐driven voltage of 3.9 V. The turn‐on/off time of a single micro‐emitter is measured to be less than 1 µs. Particularly, stable (±1.2% emission current fluctuation for 30 min) and reproducible (±0.2% driven voltage variation over 27 cycles) electron emission have been experimentally observed under a low vacuum of ≈5 × 10^?4 Pa. Even under a rough vacuum of ≈10^?1 Pa, an impressive reproducibility (±2% driven voltage variation over 20 cycles) is obtained. Moreover, emission performances of micro‐emitter arrays are found to exhibit good uniformity. The outstanding stability, reproducibility, and uniformity of the thermionic electron micro‐emitter arrays imply their promising applications as on‐chip integrated electron sources.     

A Self‐Branched Lamination of Hierarchical Patronite Nanoarchitectures on Carbon Fiber Cloth as Novel Electrode for Ionic Liquid Electrolyte‐Based High Energy Density Supercapacitors

The developments of rationally designed binder‐free metal chalcogenides decorated flexible electrodes are of paramount importance for advanced energy storage devices. Herein, binder‐free patronite (VS₄) flower‐like nanostructures are facilely fabricated on a carbon cloth (CC) using a facile hydrothermal method for high‐performance supercapacitors. The growth density and morphology of VS₄ nanostructures on CC are also controlled by varying the concentrations of vanadium and sulfur sources along with the complexing agent in the growth solution. The optimal electrode with an appropriate growth concentration (VS₄‐CC@VS‐3) demonstrates a considerable pseudocapacitance performance in the ionic liquid (IL) electrolyte (1‐ethyl‐3‐methylimidazolium trifluoromethanesulfonate), with a high operating potential of 2 V. Utilizing VS₄‐CC@VS‐3 as both positive and negative electrodes, the IL‐based symmetric supercapacitor is assembled, which demonstrates a high areal capacitance of 536 mF cm^?2 (206 F g^?1) and excellent cycling durability (93%) with superior energy and power densities of 74.4 µWh cm^?2 (28.6 Wh kg^?1) and 10154 µW cm^?2 (9340 W kg^?1), respectively. As for the high energy storage performance, the device stably energizes various portable electronic applications for a long time, which make the fabricated composite material open up news for the fabrication of fabrics supported binder‐free chalcogenides for high‐performance energy storage devices.     

A Nonmetallic Stretchable Nylon‐Modified High Performance Triboelectric Nanogenerator for Energy Harvesting

As a new energy harvesting strategy, triboelectric nanogenerators which have a broad application prospect in collecting environmental energy, human body mechanical energy, and supplying power for low‐power electronic devices, have attracted extensive attention. However, technology challenges still exist in the stretchability for the preparation of some high‐performance triboelectric materials. In this work, a new strategy for nonmetallic nylon‐modified triboelectric nanogenerators (NM‐TENGs) is reported. Nylon is introduced as a high performance friction material to enhance the output performance of the stretchable TENG. The uniform matrix reduces the difficulty of heterogeneous integration and enhances the structural strength. The open‐circuit voltage (V_OC) and short‐circuit current (I_SC) of NM‐TENG can reach up to 1.17 kV and 138 µA, respectively. The instantaneous power density reaches 11.2 W m^?2 and the rectified output can directly light ≈480 LEDs. The transferred charge density is ≈100 µC m^?2 in one cycle when charging the capacitor. In addition, a low‐power electronic clock can be driven directly by the rectified signal without additional circuits. NM‐TENG also has high enough strain rate and can be attached to the human body for energy harvesting effectively. This work provides a new idea for fabrication of stretchable TENGs and demonstrates their potential application.     

Novel Approach for Alternating Current (AC)‐Driven Organic Light‐Emitting Devices

A novel approach for alternating current (AC)‐driven organic light‐emitting devices is reported, which uses the concept of molecular doping in organic semiconductors. Doped organic charge‐transport layers are used to generate charge carriers within the device, hence eliminating the need for injecting charge carriers from external electrodes. Bright luminance of up to 1000 cd m^?2 is observed when the device is driven with an AC bias. The luminance observed is attributed to charge‐carrier generation and recombination, leading to the formation of excitons within the device, without injection of charge carriers through external electrodes. A mechanism for internal charge‐carrier generation and the device operation is proposed.     

Solution‐Processable Hole‐Generation Layer and Electron‐Transporting Layer: Towards High‐Performance,Alternating‐Current‐Driven,Field‐Induced Polymer Electroluminescent Devices

The effect of solution‐processed p‐type doping of hole‐generation layers (HGLs) and electron‐transporting layer (ETLs) are systematically investigated on the performance of solution‐processable alternating current (AC) field‐induced polymer EL (FIPEL) devices in terms of hole‐generation capability of HGLs and electron‐transporting characteristics of ETLs. A variety of p‐type doping conjugated polymers and a series of solution‐processed electron‐transporting small molecules are employed. It is found that the free hole density in p‐type doping HGLs and electron mobility of solution‐processed ETLs are directly related to the device performance, and that the hole‐transporting characteristics of ETLs also play an important role since holes need to be injected from electrode through ETLs to refill the depleted HGLs in the positive half of the AC cycle. As a result, the best FIPEL device exhibits exceptional performance: a low turn‐on voltage of 12 V, a maximum luminance of 20 500 cd m^?2, a maximum current and power efficiency of 110.7 cd A^?1 and 29.3 lm W^?1. To the best of the authors' knowledge, this is the highest report to date among FIPEL devices driven by AC voltage.     

A High‐Power Symmetric Na‐Ion Pseudocapacitor

Batteries and supercapacitors are critical devices for electrical energy storage with wide applications from portable electronics to transportation and grid. However, rechargeable batteries are typically limited in power density, while supercapacitors suffer low energy density. Here, a novel symmetric Na‐ion pseudocapacitor with a power density exceeding 5.4 kW kg^?1 at 11.7 A g^?1, a cycling life retention of 64.5% after 10 000 cycles at 1.17 A g^?1, and an energy density of 26 Wh kg^?1 at 0.585 A g^?1 is reported. Such a device operates on redox reactions occurring on both electrodes with an identical active material, viz., Na₃V₂(PO₄)₃ encapsulated inside nanoporous carbon. This device, in a full‐cell scale utilizing highly reversible and high‐rate Na‐ion intercalational pseudocapacitance, can bridge the performance gap between batteries and supercapacitors. The characteristics of the device and the potentially low‐cost production make it attractive for hybrid electric vehicles and low‐maintenance energy storage systems.     

Direct Conversion of Fe2O3 to 3D Nanofibrillar PEDOT Microsupercapacitors

Microsupercapacitors (µSCs) are attractive electrochemical energy storage devices serving as alternatives to batteries in miniaturized portable electronics owing to high‐power density and extended cycling stability. Current state‐of‐the‐art microfabrication strategies are limited by costly steps producing materials with structural defects that lead to low energy density. This paper introduces an electrode engineering platform that combines conventional microfabrication and polymerization from the vapor phase producing 3D µSCs of the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT). A sputtered Fe₂O₃ precursor layer enables deposition of a 250 nm thick polymer coating comprised of a high packing density of vertically aligned PEDOT nanofibers possessing exceptional electrical conductivity (3580 S cm^?1). The 3D µSCs exhibit state‐of‐the‐art volumetric energy density (16.1 mWh cm^?3) as well as areal (21.3 mF cm^?2) and volumetric (400 F cm^?3) capacitances in 1 m H₂SO₄ aqueous electrolyte. These figures of merit represent the highest values among conducting polymer‐based µSCs. Electrochemical performance is controlled by investigating coating thickness, gap distance, fractal geometry, and gel electrolyte (1 m H₂SO₄/polyvinyl alcohol). The quasisolid‐state µSCs exhibit extended rate capability (50 V s^?1), retain 94% of original capacitance after 10 000 cycles and remain thermally stable up to 60 °C.     

Inkjet Printed Large‐Area Flexible Few‐Layer Graphene Thermoelectrics

Graphene‐based organic nanocomposites have ascended as promising candidates for thermoelectric energy conversion. In order to adopt existing scalable printing methods for developing thermostable graphene‐based thermoelectric devices, optimization of both the material ink and the thermoelectric properties of the resulting films are required. Here, inkjet‐printed large‐area flexible graphene thin films with outstanding thermoelectric properties are reported. The thermal and electronic transport properties of the films reveal the so‐called phonon‐glass electron‐crystal character (i.e., electrical transport behavior akin to that of few‐layer graphene flakes with quenched thermal transport arising from the disordered nanoporous structure). As a result, the all‐graphene films show a room‐temperature thermoelectric power factor of 18.7 µW m^?1 K^?2, representing over a threefold improvement to previous solution‐processed all‐graphene structures. The demonstration of inkjet‐printed thermoelectric devices underscores the potential for future flexible, scalable, and low‐cost thermoelectric applications, such as harvesting energy from body heat in wearable applications.     

Touch‐Interactive Flexible Sustainable Energy Harvester and Self‐Powered Smart Card

Sustainable and safe energy sources combined with cost effectiveness are major goals for society when considering the current scenario of mass production of portable and Internet of Things (IoT) devices along with the huge amount of inevitable e‐waste. The conceptual design of a self‐powered “eco‐energy” smart card based on paper promotes green and clean energy, which will bring the zero e‐waste challenge one step closer to fruition. A commercial raw filter paper is modified through a fast in situ functionalization method, resulting in a conductive cellulose fiber/polyaniline composite, which is then applied as an energy harvester based on a mechano‐responsive charge transfer mechanism through a metal/conducting polymer interface. Different electrodes are studied to optimize charge transfer based on contact energy level differences. The highest power density and current density obtained from such a paper‐based “eco‐energy” smart card device are 1.75 W m^?2 and 33.5 mA m^?2 respectively. This self‐powered smart energy card is also able to light up several commercial light‐emitting diodes, power on electronic devices, and charge capacitors.     

Anhydride‐Assisted Spontaneous Room Temperature Sintering of Printed Bioresorbable Electronics

Bioresorbable electronic devices are promising replacements for conventional build‐to‐last electronics in implantable biomedical systems and consumer electronics. However, bioresorbable devices are typically achieved by complex complementary metal oxide semiconductor fabrication processes that minimize exposure to humidity. Emerging printable techniques for bioresorbable electronics demand further improvement in electrical conductivity and mechanical robustness. This paper presents a room‐temperature spontaneous sintering method of bioresorbable inks that contain zinc nanoparticles and anhydride. The entire process can be conducted in atmosphere environment under 90% humidity within 300 min. It has minimum requirement for external heating and special ambient conditions, allowing humidity to trigger the surface chemistry of zinc nanoparticles and spontaneous welding between neighboring nanoparticles. The resulting bioresorbable patterns are highly conductive (σ = 72 400 S m^?1) and mechanically robust (>1500 bending cycles) to enable practical applications. A radio circuit achieved through the above method can operate stably over 14 days in air and disappear in water for less than 30 min. The spontaneous room‐temperature sintering represents a rapid and energy‐efficient approach to achieve high‐performance bioresorbable electronics with improved mechanical robustness and electrical performance, leading to broader impacts in the areas of healthcare, information security, and consumer electronics.     

Fully Transparent p‐MoTe2 2D Transistors Using Ultrathin MoOx/Pt Contact Media for Indium‐Tin‐Oxide Source/Drain

Since transition metal dichalcogenide (TMD) semiconductors are found as 2D van der Waals materials with a discrete energy bandgap, many 2D‐like thin field effect transistors (FETs) and PN diodes are reported as prototype electrical and optoelectronic devices. As a potential application of display electronics, transparent 2D FET devices are also reported recently. Such transparent 2D FETs are very few in report, yet no p‐type channel 2D‐like FETs are seen. Here, 2D‐like thin transparent p‐channel MoTe₂ FETs with oxygen (O₂) plasma‐induced MoO_x/Pt/indium‐tin‐oxide (ITO) contact are reported for the first time. For source/drain contact, 60 s short O₂ plasma and ultrathin Pt‐deposition processes on MoTe₂ surface are sequentially introduced before ITO thin film deposition and patterning. As a result, almost transparent 2D FETs are obtained with a decent mobility of ≈5 cm² V^?1 s^?1, a high ON/OFF current ratio of ≈10⁵, and 70% transmittance. In particular, for normal MoTe₂ FETs without ITO, O₂ plasma process greatly improves the hole injection efficiency and device mobility (≈60 cm² V^?1 s^?1), introducing ultrathin MoO_x between Pt source/drain and MoTe₂. As a final device application, a photovoltaic current modulator, where the transparent FET stably operates as gated by photovoltaic effects, is integrated.     

High‐Performance Flexible Thermoelectric Devices Based on All‐Inorganic Hybrid Films for Harvesting Low‐Grade Heat

The fabrication of a flexible thermoelectric (TE) device that contains flexible, all‐inorganic hybrid thin films (p‐type single‐wall carbon nanotubes (SWCNTs)/Sb₂Te₃ and n‐type reduced graphene oxide (RGO)/Bi₂Te₃) is reported. The optimized power factors of the p‐type and n‐type hybrid thin films at ambient temperature are about 55 and 108 µW m^?1 K^?2, respectively. The high performance of these films that are fabricated through the combination of vacuum filtration and annealing can be attributed to their planar orientation and network structure. In addition, a TE device, with 10 couples of legs, shows an output power of 23.6 µW at a temperature gradient of 70 K. A prototype of an integrated photovoltaic‐TE (PV‐TE) device demonstrates the ability to harvest low‐grade “waste” thermal energy from the human body and solar irradiation. The flexible TE and PV‐TE device have great potential in wearable energy harvesting and management.     

Highly Conductive Ordered Mesoporous Carbon Based Electrodes Decorated by 3D Graphene and 1D Silver Nanowire for Flexible Supercapacitor

Ordered mesoporous carbon (OMC) is considered one of the most promising materials for electric double layer capacitors (EDLC) given its low‐cost, high specific surface area, and easily accessed ordered pore channels. However, pristine OMC electrode suffers from poor electrical conductivity and mechanical flexibility, whose specific capacitance and cycling stability is unsatisfactory in flexible devices. In this work, OMC is coated on the surface of highly conductive three‐dimensional graphene foam, serving as both charge collector and flexible substrate. Upon further decoration with silver nanowires (Ag NWs), the novel architecture of Ag NWs/3D‐graphene foam/OMC (Ag‐GF‐OMC) exhibits exceptional electrical conductivity (up to 762 S cm^?1) and mechanical robustness. The Ag‐GF‐OMC electrodes in flexible supercapacitors reach a specific capacitance as high as 213 F g^?1, a value five‐fold higher than that of the pristine OMC electrode. Moreover, these flexible electrodes also exhibit excellent long‐term stability with >90% capacitance retention over 10 000 cycles, as well as high energy and power density (4.5 Wh kg^?1 and 5040 W kg^?1, respectively). This study provides a new procedure to enhance the device performance of OMC based supercapacitors, which is a promising candidate for the application of flexible energy storage devices.     

Nanoarchitectured Graphene/CNT@Porous Carbon with Extraordinary Electrical Conductivity and Interconnected Micro/Mesopores for Lithium‐Sulfur Batteries

The sp²‐hybridized nanocarbon (e.g., carbon nanotubes (CNTs) and graphene) exhibits extraordinary mechanical strength and electrical conductivity but limited external accessible surface area and a small amount of pores, while nanostructured porous carbon affords a huge surface area and abundant pore structures but very poor electrical conductance. Herein the rational hybridization of the sp² nanocarbon and nanostructured porous carbon into hierarchical all‐carbon nanoarchitectures is demonstrated, with full inherited advantages of the component materials. The sp² graphene/CNT interlinked networks give the composites good electrical conductivity and a robust framework, while the meso‐/microporous carbon and the interlamellar compartment between the opposite graphene accommodate sulfur and polysulfides. The strong confinement induced by micro‐/mesopores of all‐carbon nanoarchitectures renders the transformation of S₈ crystal into amorphous cyclo‐S₈ molecular clusters, restraining the shuttle phenomenon for high capacity retention of a lithium‐sulfur cell. Therefore, the composite cathode with an ultrahigh specific capacity of 1121 mAh g^?1 at 0.5 C, a favorable high‐rate capability of 809 mAh g^?1 at 10 C, a very low capacity decay of 0.12% per cycle, and an impressive cycling stability of 877 mAh g^?1 after 150 cycles at 1 C. As sulfur loading increases from 50 wt% to 77 wt%, high capacities of 970, 914, and 613 mAh g^?1 are still available at current densities of 0.5, 1, and 5 C, respectively. Based on the total mass of packaged devices, gravimetric energy density of GSH@APC‐S//Li cell is expected to be 400 Wh kg^?1 at a power density of 10 000 W kg^?1, matching the level of engine driven systems.     

Ultrathin Nickel–Cobalt Phosphate 2D Nanosheets for Electrochemical Energy Storage under Aqueous/Solid‐State Electrolyte

2D materials are ideal for constructing flexible electrochemical energy storage devices due to their great advantages of flexibility, thinness, and transparency. Here, a simple one‐step hydrothermal process is proposed for the synthesis of nickel–cobalt phosphate 2D nanosheets, and the structural influence on the pseudocapacitive performance of the obtained nickel–cobalt phosphate is investigated via electrochemical measurement. It is found that the ultrathin nickel–cobalt phosphate 2D nanosheets with an Ni/Co ratio of 4:5 show the best electrochemical performance for energy storage, and the maximum specific capacitance up to 1132.5 F g^?1. More importantly, an aqueous and solid‐state flexible electrochemical energy storage device has been assembled. The aqueous device shows a high energy density of 32.5 Wh kg^?1 at a power density of 0.6 kW kg^?1, and the solid‐state device shows a high energy density of 35.8 Wh kg^?1 at a power density of 0.7 kW kg^?1. These excellent performances confirm that the nickel–cobalt phosphate 2D nanosheets are promising materials for applications in electrochemical energy storage devices.     

Scrutinizing Design Principles toward Efficient,Long‐Term Stable Green Light‐Emitting Electrochemical Cells

Enhancing the efficiency and lifetime of light emitting electrochemical cells (LEC) is the most important challenge on the way to energy efficient lighting devices of the future. To avail this, emissive Ir(III) complexes with fluoro‐substituted cyclometallated ligands and electron donating groups (methyl and tert ‐butyl)‐substituted diimine ancillary (N^{^}N) ligands and their associated LEC devices are studied. Four different complexes of general composition [Ir(4ppy)₂(N^{^}N)][PF₆] (4Fppy = 2‐(4‐fluorophenyl)pyridine) with the N^{^}N ligand being either 2,2′‐bipyridine ( 1 ), 4.4′‐dimethyl‐2,2′‐bipyridine ( 2 ), 5.5′‐dimethyl‐2,2′‐bipyridine ( 3 ), or 4.4′‐di‐tert ‐butyl‐2,2′‐bipyridine ( 4 ) are synthesized and characterized. All complexes emit in the green region of light with emission maxima of 529–547 nm and photoluminescence quantum yields in the range of 50.6%–59.9%. LECs for electroluminescence studies are fabricated based on these complexes. The LEC based on ( 1 ) driven under pulsed current mode demonstrated the best performance, reaching a maximum luminance of 1605 cd m^?2 resulting in 16 cd A^?1 and 8.6 lm W^?1 for current and power efficiency, respectively, and device lifetime of 668 h. Compared to this, LECs based on ( 3 ) and ( 4 ) perform lower, with luminance and lifetime of 1314 cd m^?2, 45.7 h and 1193 cd m^?2, 54.9 h, respectively. Interestingly, in contrast to common belief, the fluorine content of the Ir‐iTMCs does not adversely affect the LEC performance, but rather electron donating substituents on the N^{^}N ligands are found to dramatically reduce both performance and stability of the green LECs. In light of this, design concepts for green light emitting electrochemical devices have to be reconsidered.