Design of a New Energy‐Harvesting Electrochromic Window Based on an Organic Polymeric Dye,a Cobalt Couple,and PProDOT‐Me2

A new design for an energy‐harvesting electrochromic window (EH‐ECW) based on the fusion of two technologies, organic electrochromic windows and dye‐sensitized solar cells (DSSCs), is presented. Unlike other power‐generating smart windows, such as photoelectrochromic devices that are passive and only contain two states (i.e., a closed‐circuit colored state and an open‐circuit bleaching state), EH‐ECW allows active tuning of the transmittance by varying the applied potential and it functions as a photovoltaic cell based on a DSSC. The resulting device demonstrates a fast switching rate of 1 s in both the bleaching and coloring processes through the use of an electrochromic polymer as a counter electrode layer. To increase the transmittance of the device, a cobalt redox couple and a light‐colored, yet efficient, organic dye are used. The organic dye contains a polymeric structure that contributes to the high cyclic stability. The device exhibits a power conversion efficiency (PCE) of 4.5% (100 mW cm^‐2) under AM 1.5 irradiation, a change in transmittance of 34% upon applied potential, and shows only 3% degradation in the PCE after 5000 cycles.     

Inkjet Printed Large Area Multifunctional Smart Windows

Multifunctional smart windows are successfully fabricated by assembling inkjet printed CeO₂/TiO₂ and WO₃/poly(3,4‐ethylenedioxythiophene)‐poly(styrene sulfonate) films as the anode and cathode, respectively. Large optical modulation (more than 70% at 633 nm), fast switching (12.7/15.8 s), high coloration efficiency (108.9 cm² C^?1), and excellent bistability are achieved by the assembled smart windows. The multifunctional smart window not only can be used as typical electrochromic window, which can change its color to dynamically control the solar radiation transmittance through windows or protect privacy during the day, but also can be used as energy‐storage device simultaneously. The designed smart window releases the stored energy to light the bulbs and power other electronic devices at night while its color gradually reverts to transparent state. Moreover, the level of stored energy can be monitored via the visually detectable reversible color variation of the window. The fascinating multifunctional smart windows exhibit promising features for a wide range of applications in buildings, airplanes, automobiles, etc.     

Empowering Semi‐Transparent Solar Cells with Thermal‐Mirror Functionality

Device architectures for semi‐transparent perovskite solar cells are proposed that are not only highly efficient but also very effective in thermal‐mirror operation. With the optimal top transparent electrode design based on thin metal layer capped with a high‐index dielectric layer for selective transmittance in visible and high reflectance in near‐infrared (NIR) region, the proposed see‐through devices exhibit average power conversion efficiency as large as 13.3% and outstanding NIR rejection of 85.5%, demonstrating their great potential for ideal “energy‐generating and heat‐rejecting” solar windows that can make a smart use of solar energy.     

High‐Performance Suspended Particle Devices Based on Copper‐Reduced Graphene Oxide Core–Shell Nanowire Electrodes

Smart windows are one of the key components of so‐called “green” buildings. These windows are based on an actively switchable electro‐optic material that is sandwiched between two transparent electrodes. Although great progress has been made in identifying the optimal materials for such active windows, there is still a great need to improve their key elements, especially the performance of the transparent electrodes. Here, a new suspended particle device (SPD), holding a great potential for smart window applications, which is built upon copper‐reduced graphene oxide (Cu‐rGO) core–shell nanowire (NW) films as a transparent conductive electrode is reported. With the wrapping of rGO, the Cu NW electrodes demonstrate both high optical transparency and electrical conductivity, as well as significantly improved stability under various testing conditions. The novel sandwich‐structured SPDs, based on these electrodes, show a large change in their optical transmittance (42%) between “on” and “off” states, impressively fast switching time and superior stability. These high performances are comparable to those of the SPDs based on indium tin oxide electrodes. These promising results pave the way for the electrodes to be an integral part of a variety of optoelectronic devices, including energy‐friendly and flexible electronics.     

High‐Performance,Transparent, Dye‐Sensitized Solar Cells for See‐Through Photovoltaic Windows

Dye‐sensitized solar cells (DSCs) have attracted great interest as one of the most promising photovoltaic technologies, and transparent DSCs show potential applications as photovoltaic windows. However, the competition between light absorption for photocurrent generation and light transmittance for obtaining high transparency limits the performance of transparent DSCs. Here, transparent DSCs exhibiting a high light transmittance of 60.3% and high energy conversion efficiency (3.66%) are reported. The strategy is to create a cocktail system composed of ultraviolet and near‐infrared dye sensitizers that selectively and efficiently harvest light in the invisible or low‐eye‐sensitivity region while transmitting light in high‐eye‐sensitivity regions. This new design provides a reasonable approach for realizing high efficiency and transparency DSCs that have potential applications as photovoltaic windows.     

Nature‐Inspired Electrochemical Energy‐Storage Materials and Devices

Currently, tremendous efforts are being devoted to develop high‐performance electrochemical energy‐storage materials and devices. Conventional electrochemical energy‐storage systems are confronted with great challenges to achieve high energy density, long cycle‐life, excellent biocompatibility and environmental friendliness. The biological energy metabolism and storage systems have appealing merits of high efficiency, sophisticated regulation, clean and renewability, and the rational design and fabrication of advanced electrochemical energy‐storage materials and smart devices inspired by nature have made some breakthrough progresses, recently. In this review, we summarize the latest developments in the field of nature‐inspired electrochemical energy‐storage materials and devices. Specifically, the nature‐inspired exploration, preparation and modification of electrochemical energy‐storage related materials including the active materials, binders, and separators are introduced. Furthermore, nature‐inspired design and fabrication of smart energy‐storage devices such as self‐healing supercapacitors, supercapacitors with ultrahigh operating voltage, and self‐rechargeable batteries are also discussed. The review aims to provide insights and expanded research perspectives for further study in this exciting field based on our comprehensive discussions.     

All Pseudocapacitive MXene‐RuO2 Asymmetric Supercapacitors

2D transition metal carbides and nitrides, known as MXenes, are an emerging class of 2D materials with a wide spectrum of potential applications, in particular in electrochemical energy storage. The hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions is the key for high‐rate pseudocapacitive energy storage in MXene electrodes. However, symmetric MXene supercapacitors have a limited voltage window of around 0.6 V due to possible oxidation at high anodic potentials. In this study, the fact that titanium carbide MXene (Ti₃C₂T_x) can operate at negative potentials in acidic electrolyte is exploited, to design an all‐pseudocapacitive asymmetric device by combining it with a ruthenium oxide (RuO₂) positive electrode. This asymmetric device operates at a voltage window of 1.5 V, which is about two times wider than the operating voltage window of symmetric MXene supercapacitors, and is the widest voltage window reported to date for MXene‐based supercapacitors. The complementary working potential windows of MXene and RuO₂, along with proton‐induced pseudocapacitance, significantly enhance the device performance. As a result, the asymmetric devices can deliver an energy density of 37 µW h cm^?2 at a power density of 40 mW cm^?2, with 86% capacitance retention after 20 000 charge–discharge cycles. These results show that pseudocapacitive negative MXene electrodes can potentially replace carbon‐based materials in asymmetric electrochemical capacitors, leading to an increased energy density.     

High‐Temperature Shock Enabled Nanomanufacturing for Energy‐Related Applications

Functional nanomaterials are playing a crucial role in the emerging field of energy‐related devices. Recently, as a novel synthesis method, high‐temperature shock (HTS), which is rapid, low cost, eco‐friendly, universal, scalable, and controllable, has provided a promising option for the rational design and synthesis of various high‐quality nanomaterials. In this report, the HTS technique, including the equipment setup and operating principle, is systematically introduced, and recent progress in the synthesis of nanomaterials for energy storage and conversion applications using this HTS method is summarized. The growth mechanisms of nanoparticles and carbonaceous nanomaterials are thoroughly discussed, followed by the summary of the characteristic advantages of the HTS strategy. A series of nanomaterials prepared by the HTS method, including carbon‐based films, metal nanoparticles and compound nanoparticles, show high performance in the diverse applications of storage energy batteries, highly active catalysts, and smart energy devices. Finally, the future perspectives and directions of HTS in nanomanufacturing for broader applications are presented.     

An Ultrathin Flexible Single‐Electrode Triboelectric‐Nanogenerator for Mechanical Energy Harvesting and Instantaneous Force Sensing

The trends in miniaturization of electronic devices give rise to the attention of energy harvesting technologies that gathers tiny wattages of power. Here this study demonstrates an ultrathin flexible single electrode triboelectric nanogenerator (S‐TENG) which not only could harvest mechanical energy from human movements and ambient sources, but also could sense instantaneous force without extra energy. The S‐TENG, which features an extremely simple structure, has an average output current of 78 μA, lightening up at least 70 LEDs (light‐emitting diode). Even tapped by bare finger, it exhibits an output current of 1 μA. The detection sensitivity for instantaneous force sensing is about 0.947 μA MPa^?1. Performances of the device are also systematically investigated under various motion types, press force, and triboelectric materials. The S‐TENG has great application prospects in sustainable wearable devices, sustainable medical devices, and smart wireless sensor networks owning to its thinness, light weight, energy harvesting, and sensing capacities.     

Electrochromic Smart Windows Can Achieve an Absolute Private State through Thermochromically Engineered Electrolyte

Smart windows regulate the indoor solar radiation by adjusting their optical transmissive properties, offering an efficient way toward energy‐saving buildings, vehicles, etc. Electrochromism is one of the most promising solutions due to its simple control, versatile colors. Yet, electrochromics cannot give zero‐transmission through the whole visible range, leading to the windows that can always be looked through and limited for applications in the public sector. In this work, poly(N‐isopropylacrylamide) (PNIPAm) hydrogel, which undergoes temperature‐stimulated phase transition from a highly transparent state to a highly scattered zero‐transmission state through the whole visible range is used in the electrolyte of the electrochromic devices without affecting their electrochromic performance. It can be universally applied to inorganic and organic electrochromic devices, and the phase transition temperature can be easily tuned by the ion concentration. Therefore, apart from its ion conductive function, the electrolyte performs the chromatic transition function as well, allowing the electrochromic devices to achieve a zero‐transmissive, absolute “private” state. This chromatic engineering of the electrolyte can significantly broaden the industrial market of electrochromic smart window applications from public to private circumstances and bring much more flexibility in building façades design, which is a remarkable pavement for further industrial applications.     

Water Splitting Progress in Tandem Devices: Moving Photolysis beyond Electrolysis

Water photolysis is a sustainable technology to convert natural solar energy and water into chemical fuels and is thus considered a thorough solution to the forthcoming energy crises. Unassisted water splitting that could directly harvest solar light and subsequently split water in a single device has become an important research theme. Three types of tandem devices including photoelectrochemical (PEC), photovoltaic (PV) cell/PEC and PV/electrolyser tandem cells are proposed to realize water photolysis at different levels of integration and component. Recent progress in tandem water splitting devices is summarized, and crucial issues on device optimization from the perspective of each photo‐absorber functionalities in band edge potential, light absorptivity and transmittance are discussed. By increasing the performances of stand‐alone PEC or PV devices, a 20% solar to hydrogen efficiency is predicted that is a significant value towards further application in practice. Accordingly, the challenges for materials development and configuration optimization are further outlined.     

Immobilization of lanthanide doped aluminate phosphor onto recycled polyester toward the development of long-persistent photoluminescence smart window

Smart window can be defined as switchable material whose light transmission is altered upon exposure to light, voltage, or heat. However, smart windows are usually produced from expensive and breakable glass materials. Herein, transparent smart window with long-persistent phosphorescence, high optical transmittance, ultraviolet (UV) protection, rigid, high photostability and durability, an d superhydrophobicity was developed from recycled polyester (PET). Recycled polyester waste (RBW) was simply immobilized with different ratios of lanthanide-doped aluminate nanoparticles (LdAN) to provide a long-persistent phosphorescent polyester smart window (LdAN@PET) with an abili ty to persist emitting light for extended time periods. The solid-state high temperature technique was used to prepare lanthanide-doped aluminate (LdA) micro-scale powder. Then, the top-down technique was applied to afford the corresponding LdAN. Recycled shredded recycled polyester bottles were charged into a hot bath to provide a clear plastic shred bulk, which was then well-mixed with LdAN and drop-casted to provide long-persistent luminescent smart window. In order to improve the phosphor dispersion in the PET bulk, LdAN was synthesized in the nanoparticle form which was characterized utilizing transmission electron microscopy (TEM). For better preparation of translucent smart window of long-persistent phosphorescent polyester, LdAN must be homogeneously dispersed in the PET matrix without agglomeration. The morphology and chemical composition were studied by Fourier-transform infrared (FTIR) spectra), X-ray fluorescence (XRF) analysis, scanning electron microscopy (SEM), and energy-dispersion X-ray spectroscopy (EDX). In addition, spectral profiles of excitation and emission, and decay and lifetime were used to better understand the photoluminescence properties. The hardness properties were also investigated. The developed phosphorescent transparent polyester smart window demonstrated a color switch to intense green underneath UV irradiation and greenish-yellow under darkness as verified by CIELab color parameters. The afterglow polyester smart window showed an absorption wavelength at 365 nm and two phosphorescence intensities at 442 and 512 nm. An enhanced UV protection, photostability and hydrophobic activity were detected. The luminescent polyester substrates with lower LdAN ratios demonstrated rapid and reversible fluorescent photochromic activity beneath the UV light. The luminescent polyester substrates with higher LdAN contents displayed long-persistent phosphorescence afterglow. The current strategy can be simply applied for the production of smart windows, low thickness anti-counterfeiting films and warning signs.     

Emerging 3D‐Printed Electrochemical Energy Storage Devices: A Critical Review

Three‐dimensional (3D) printing, a layer‐by‐layer deposition technology, has a revolutionary role in a broad range of applications. As an emerging advanced fabrication technology, it has drawn growing interest in the field of electrochemical energy storage because of its inherent advantages including the freeform construction and controllable 3D structural prototyping. This article focuses on the topic of 3D‐printed electrochemical energy storage devices (EESDs), which bridge advanced electrochemical energy storage and future additive manufacturing. Basic 3D printing systems and material considerations are described to provide a fundamental understanding of printing technologies for the fabrication of EESDs. The performance metrics of 3D‐printed EESDs are then given and the related performance optimization strategies are discussed. Next, the recent advances of 3D‐printed EESDs, including sandwich‐type and in‐plane architectures, are summarized. Conclusions and future perspectives with some unique challenges and important directions are then discussed. It can be expected that, with the help of 3D printing technology, the development of advanced electrochemical energy storage systems will be greatly promoted.     

Biomechanical Energy‐Driven Hybridized Generator as a Universal Portable Power Source for Smart/Wearable Electronics

The fast growth of smart electronics requires novel solutions to power them sustainably. Portable power sources capable of harvesting biomechanical energy are a promising modern approach to reduce battery dependency. Herein, a novel elastic impact‐based nonresonant hybridized generator (EINR‐HG) is reported to effectively harvest biomechanical energy from diverse human activities outdoors. Through the rational integration of a nonlinear electromagnetic generator with two contact‐mode triboelectric nanogenerators, the proposed EINR‐HG generates hybrid electrical output simultaneously under the same mechanical excitations. By introducing a flux‐concentrator with a nanowire‐nanofiber surface modification, significant improvement in the energy harvesting efficiency of the EINR‐HG is achieved. After optimizing using simulations and vibration tests, the as‐fabricated EINR‐HG delivers an outstanding normalized power density of 3.13 mW cm^?3 g^?2 across a matching resistance of 1.5 kΩ at 6 Hz under 1 g acceleration. Under human motion testing, the EINR‐HG generates an optimal output power of 131.4 mW with horizontal handshaking. With a customized power management circuit, the EINR‐HG serves as a universal power source that successfully drives commercial smart electronics, including smart bands and smartphones. This work shows the massive potential of biomechanical energy‐driven hybridized generators for powering personal electronics and portable healthcare monitoring devices.     

Combining Nature‐Inspired,Graphene‐Wrapped Flexible Electrodes with Nanocomposite Polymer Electrolyte for Asymmetric Capacitive Energy Storage

Two kinds of free‐standing electrodes, reduced graphene oxide (rGO)‐wrapped Fe‐doped MnO₂ composite (G‐MFO) and rGO‐wrapped hierarchical porous carbon microspheres composite (G‐HPC) are fabricated using a frozen lake‐inspired, bubble‐assistance method. This configuration fully enables utilization of the synergistic effects from both components, endowing the materials to be excellent electrodes for flexible and lightweight electrochemical capacitors. Moreover, a nonaqueous HPC‐doped gel polymer electrolyte (GPE‐HPC) is employed to broad voltage window and improve heat resistance. A fabricated asymmetric supercapacitor based on G‐MFO cathode and G‐HPC anode with GPE‐HPC electrolyte achieves superior flexibility and reliability, enhanced energy/power density, and outstanding cycling stability. The ability to power light‐emitting diodes also indicates the feasibility for practical use. Therefore, it is believed that this novel design may hold great promise for future flexible electronic devices.     

Watchband‐Like Supercapacitors with Body Temperature Inducible Shape Memory Ability

Smart watches have gained worldwide popularity because they can integrate diverse functions all in one. However, their energy storage devices currently being used are placed in the watches, and this design seriously limited the energy support ability and the future boost space. Herein, for the first time, a strategy to integrate energy storage device with watchband is put forward, which is realized by the preparation of watchband‐like solid‐state supercapacitors using graphene coated on TiNi alloy flake as the negative electrode, ultrathin MnO₂/Ni film as the positive electrode, and different gel electrolytes as the separator. Statical and dynamical bending tests both verify that the as‐fabricated devices have excellent electrochemical performance reliability during bending process. The devices also exhibit the distinctive shape memory ability owing to the use of TiNi shape memory alloy. As a state of the art, such a watchband‐like supercapacitor is connected with an electronic watch to show its potential application. Interestingly, this “watchband” can not only support power to the watch, but also can maintain the shape memory property which can be automatically induced by touching it with the human wrist. In addition, it exhibits excellent biocompatibility. Thus, the smart supercapacitor is qualified for a promising candidate for the next‐generation smart watches.     

Gel Polymer Electrolytes for Electrochemical Energy Storage

With the booming development of flexible and wearable electronics, their safety issues and operation stabilities have attracted worldwide attentions. Compared with traditional liquid electrolytes, gel polymer electrolytes (GPEs) are preferred due to their higher safety and adaptability to the design of flexible energy storage devices. This review summarizes the recent progress of GPEs with enhanced physicochemical properties and specified functionalities for the application in electrochemical energy storage. Functional GPEs that are capable to achieve unity lithium‐ion transference number and offer additional pseudocapacitance to the overall capacitance are carefully discussed. The smart GPEs with self‐protection, thermotolerant, and self‐healing abilities are particularly highlighted. To close, the future directions and remaining challenges of the GPEs for application in electrochemical energy storages are summarized to provide clues for the following development.     

Novel Metal@Carbon Spheres Core–Shell Arrays by Controlled Self‐Assembly of Carbon Nanospheres: A Stable and Flexible Supercapacitor Electrode

The high performance of electrochemical energy‐storage devices relies largely on scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. Carbon nanopsheres (CNSs) are widely used for energy storage and conversion devices. Here, the directional assembly of CNSs on a vertical‐standing metal scaffold into a core/shell array structure is reported. The method uses a three‐step all‐solution synthesis strategy (chemical bath deposition, electrodeposition, and hydrothermal) and begins from ZnO microrod arrays as a sacrificial template. The self‐assembly of CNSs can be correlated to a simultaneous etching effect to the ZnO accompanying the polymerization of glucose precursor. The Ni microtube/CNSs arrays are selected as an example for structural and electrochemical characterizations. The novel type of metal/CNSs arrays is demonstrated to be a highly stable electrode for supercapacitors. The electrodes of metal/CNSs arrays are assembled into symmetric supercapacitors and exhibit high capacitances of 227 F g^?1 (at 2.5 A g^?1) and an outstanding cycling stability with capacitance retention of 97% after 40 000 cycles.     

The "windows", scales, and bristles of the tropical moth Rothschildia lebeau (Lepidoptera: Saturniidae)

The common Spanish name of the moth Rothschildia lebeau (Saturniidae) is cuatro ventanas (four 'windows'), because it exhibits a transparent oval path in each wing. The scales of the colored areas and the bristles from the "window" were analyzed. We developed a simple device to measure transmittance across the "windows" with an spectrophotometer. A square section of "window" was mounted onto a flat black card and placed onto a clamp that hung in the path of the light - beam of the spectrophotometer. Absorbance was measured at 350 and 550 nm, with the "window" positioned perpendicular to the light beam (incidence of 90 degrees); then the measurements were repeated with the "window" moved at an angle of 45 degrees. Each measurement was replicated 5 times. Wing color spots were analyzed with a light dissection microscope (stereoscope) and with scanning electron microscopy. The scales have a minimum of 4 morphological types, 3 of them showed the typical appearance of unspecialized scales described for other butterflies; whereas the fourth has features particular to this species. On the "window" the scales are transformed in hair-like bristles that do not interfere with light, conferring the transparency that characterizes the "windows". However, if the wing is illuminated at an almost grazing-incidence, they reflect the light as a mirror. Two hypothetical functional explanation for the windows are mimicry and interspecies communication.     

Hybrid Piezo/Triboelectric‐Driven Self‐Charging Electrochromic Supercapacitor Power Package

The rapid development of personal electronics imposes a great challenge on sustainable and maintenance‐free power supplies. The integration of nanogenerators (NG) and electrochromic supercapacitors (SC) offers a promising solution to efficiently convert mechanical energy to stored electrical energy in a predictable and noticeable manner. In this paper, by integrating hybrid NGs and electrochromic micro‐SCs (µ‐SCs) array, the authors demonstrate a smart self‐charging power package capable of indicating the charging state with color change. The electrochromic µ‐SC employs Ag nanowires/NiO as electrode materials, exhibiting high capacitance (3.47 mF cm^?2) and stable cycling performance (80.7% for 10000 cycles). The hybrid NG can produce a high output voltage of 150 V and an enhanced output current of 20 µA to satisfy the self‐charging requirements. The integrated electrochromic µ‐SCs array is capable of self‐charging to 3 V to light up a LED under human palm impact. The charging states can be estimated according to the color differences with the naked eye during the self‐charging process. Moreover, it is possible to design the planar interdigitated electrodes into different shapes according to user demand. The proposed simple and cost‐effective approaches for smart self‐charging power package may pave the way for future intelligent, independent and continuous operation of daily electronics.