High-Performance Asymmetric Electrochromic-Supercapacitor Device Based on Poly(indole-6-carboxylicacid)/TiO2 Nanocomposites

Nano Aerogel-Based VIS-NIR Switchable Electrochromic Supercapacitor: Energy Storage and Heat-Shielding Device

Power-efficient electrochromic devices that can exhibit multifunctional applications, especially in the areas of energy storage and savings, are increasingly in demand. Here, an inorganic-organic electrochromic smart window has been designed in which a self-supporting aerogel-type network of tin-doped indium oxide (a-ITO) nanoparticles was doped to enable applications in supercapacitive energy storage. The devices based on poly(3-hexylthiophene-2,5-diyl) (doped with incorporated a-ITO) and viologen exhibit bias-induced color modulation in the visible and infrared range. This function can be employed to prevent the transmission of latter radiation to maintain a temperature difference on the two sides of the device when it is turned ON with a bias voltage of 1.6 V. The device exhibits an electrochromic supercapacitor property with a maximum coloration efficiency of 966 cm2/C with a switching time of only 0.5 s, color contrast of 61%, and high specific capacitance of 17 F/g. Potential applications of the device in temperature shielding are discussed, and a maximum cooling efficiency of 32% is demonstrated. Overall, a recipe is developed to design energy-storing and energy-saving multicolor-switchable smart windows for application in designing energy-efficient smart windows/buildings.

Recent Advances of Electrode Materials Applied in an Electrochromic Supercapacitor Device

An electrochromic supercapacitor device (ESD) is an advanced energy storage device that combines the energy storage capability of a supercapacitor with the optical modulation properties of electrochromic materials. The electrode materials used to construct an ESD need to have both rich color variations and energy storage properties. Recent advances in ESDs have focused on the preparation of novel electrochromic supercapacitor electrode materials and improving their energy storage capacity, cycling stability, and electrochromic performance. In this review, the research significance and application value of ESDs are discussed. The device structure and working principle of electrochromic devices and supercapacitors are analyzed in detail. The research progress of inorganic materials, organic materials, and inorganic/organic nanocomposite materials used for the construction of ESDs is discussed. The advantages and disadvantages of various types of materials in ESD applications are summarized. The preparation and application of ESD electrode materials in recent years are reviewed in detail. Importantly, the challenges existing in the current research and recommendations for future perspectives are suggested. This review will provide a useful reference for researchers in the field of ESD electrode material preparation and application.

Stoichiometrically Optimized Electrochromic Complex [V2O2+ξ(OH)3-ξ] Based Electrode: Prototype Supercapacitor with Multicolor Indicator

The systematic structure modification of metal oxides is becoming more attractive, and effective strategies for structural tunning are highly desirable for improving their practical color-modulating energy storage performances. Here, the ability of a stoichiometrically tuned oxide-hydroxide complex of porous vanadium oxide, namely [V2O2+ξ(OH)3-ξ]ξ = 0:3 for multifunctional electrochromic supercapacitor application is demonstrated. Theoretically, the pre-optimized oxide complex is synthesized using a simple wet chemical etching technique in its optimized stoichiometry [V2O2+ξ(OH)3-ξ] with ξ = 0, providing more electroactive surface sites. The multifunctional electrode shows a high charge storage property of 610 Fg-1 at 1A g-1, as well as good electrochromic properties with high color contrast of 70% and 50% at 428 and 640 nm wavelengths, faster switching, and high coloration efficiency. When assembled in a solid-state symmetric electrochromic supercapacitor device, it exhibits an ultrahigh power density of 1066 mWcm-2, high energy density of 246 mWhcm-2, and high specific capacitance of 290 mFcm-2 at 0.2 mAcm-2. A prepared prototype device displays red when fully charged, green when half charged, and blue when fully discharged. A clear evidence of optimizing the multifunctional performance of electrochromic supercapacitor by stoichiometrical tuning is presented along with demonstrating a device prototype of a 25 cm2 large device for real-life applications.

Homogeneous and Nanogranular Prussian Blue to Enable Long-Term-Stable Electrochromic Devices

The increasing demand for the state-of-the-art electrochromic devices has received great interest in synthesizing Prussian blue (PB) nanoparticles with a uniform diameter that exhibit excellent electrochromism, electrochemistry, and cyclability. Herein, we report the controllable synthesis of sub-100 nm PB nanoparticles via the coprecipitation method. The diameter of PB nanoparticles can be modulated by adjusting the reactant concentration, the selection of a chelator, and their purification. The self-assembled nanogranular thin films, homogeneously fabricated by using optimized PB nanoparticles with an average diameter of 50 nm as building blocks via the blade coating technique enable excellent performance with a large optical modulation of 80% and a high coloration efficiency of 417.79 cm2 C-1. It is also demonstrated by in situ and ex situ observations that the nanogranular PB thin films possess outstanding structural and electrochemical reversibility. Furthermore, such nanogranular PB thin films can enjoy the enhanced long-term cycling stability of the PB-WO3 complementary electrochromic devices having a 91.4% optical contrast retention after 16,000 consecutive cycles. This work provides a newly and industrially compatible approach to producing a complementary electrochromic device with extraordinary durability for various practical applications.

Electrode materials for electrochromic supercapacitors

Smart energy storage systems, such as electrochromic supercapacitor (ECSC) integrated technology, have drawn a lot of attention recently, and numerous developments have been made owing to their reliable performance. Developing novel electrode materials for ECSCs that embed two different technologies in a material is an exciting and emerging field of research. To date, the research into ECSC electrode materials has been ongoing with excellent efforts, which need to be systematically reviewed so that they can be used to develop more efficient ECSCs. This mini-review provides a general composition, main evaluation parameters and future perspectives for electrode materials of ECSCs as well as a brief overview of the published reports on ECSCs and performance statistics on the existing literature in this field.

C-Rich Carbon Nitride Conjugated Polymer Enabling Ion-Migration-Induced Precise Electrochromic Display

The development of electrochromic (EC) displays has been in the challenge of displaying precise patterns, such as characters or high-resolution images of small size. High-performance EC materials as well as efficient, precise-display strategies are still urgent. To enable a microfactor-guided strategy for highly precise display, I3-/I- ion-migration-induced localized electrochromism is developed in an EC device based on the C-rich polymeric carbon nitride (CPCN). The CPCN material with an extended conjugated backbone of individual aromatic nuclei and heptazine rings has been reported possessing remarkable photorechargeable performance. Owing to the self-charging behavior, the CPCN exhibits color switching by the interfacial charge recombination with I3- ions in electrolyte and serves as the EC material with a coloration efficiency of 210.2 cm2 C-1 and an optical contrast of 48.6%. Material synthesis, electrode preparation, device design and fabrication, mechanism analysis, and performance evaluation of the CPCN-based EC display device are described.

Preparation of a TiO2/PEDOT nanorod film with enhanced electrochromic properties

The designed growth of titanium dioxide (TiO₂)/poly(3,4-ethylenedioxythiophene) (PEDOT) nanorod arrays has been achieved by the combination of hydrothermal and electrodeposition methods. Due to the use of one-dimensional (1D) TiO₂ nanorod arrays as the template of the nanocomposites (TiO₂/PEDOT), the surface area of the active materials is enlarged and the diffusion distance of the ions is shortened. The nanorod structure also contributes to increasing the length of PEDOT conjugated chains and facilitates the transfer of electrons in the conjugated chains. Consequently, the TiO₂/PEDOT film delivers a shorter response time (∼0.5 s), higher transmittance contrast (∼55.5%) and long-cycle stability compared to the pure PEDOT film. In addition, the TiO₂/PEDOT electrode is further developed to be a smart bi-functional electrochromic device exhibiting energy storage performance. We expect that this work may lead to new designs for powerful intelligent electrochromic energy storage devices.

Nanostructured TiO2 Arrays for Energy Storage

Because of their extensive specific surface area, excellent charge transfer rate, superior chemical stability, low cost, and Earth abundance, nanostructured titanium dioxide (TiO₂) arrays have been thoroughly explored during the past few decades. The synthesis methods for TiO₂ nanoarrays, which mainly include hydrothermal/solvothermal processes, vapor-based approaches, templated growth, and top-down fabrication techniques, are summarized, and the mechanisms are also discussed. In order to improve their electrochemical performance, several attempts have been conducted to produce TiO₂ nanoarrays with morphologies and sizes that show tremendous promise for energy storage. This paper provides an overview of current developments in the research of TiO₂ nanostructured arrays. Initially, the morphological engineering of TiO₂ materials is discussed, with an emphasis on the various synthetic techniques and associated chemical and physical characteristics. We then give a brief overview of the most recent uses of TiO₂ nanoarrays in the manufacture of batteries and supercapacitors. This paper also highlights the emerging tendencies and difficulties of TiO₂ nanoarrays in different applications.

Synthesis Strategies and Applications for Pitch-Based Anode: From Industrial By-Products to Power Sources

It is significant for saving energy to manufacture superb-property batteries. Carbon is one of the most competitive anode materials in batteries, but it is hard for commercial graphite anodes to meet the increasingly higher energy-storage requirements. Moreover, the price of other better-performing carbon materials (such as graphene) is much higher than graphite, which is not conducive to massive production. Pitch, the cheap by-product in the petroleum and coal industries, has high carbon content and yield, making it possible for commercialization. Developing pitch-based anodes can not only lower raw material costs but also realize the pitch's high value-added utilization. We comprehensively reviewed the latest synthesis strategies of pitch-derived materials and then introduced their application and research progress in lithium, sodium, and potassium ion batteries (LIBs, SIBs, and PIBs). Finally, we summarize and suggest the pitch's development trend for anodes and in other fields.

A multi-chromic supercapacitor of high coloration efficiency integrating a MOF-derived V2O5 electrode

Modern technological trends in smart electronic devices demand more intelligent automation. Simultaneous integration of energy storage and multicolor electrochromism in a single device improves user-device interfacing based on a salient human-readable output. In this work, primarily metal-organic framework (MOF) derived V₂O₅ was synthesized which, as an electrochromic material, shows high optical modulation of 35% at 485 nm, with very fast switching speeds (2.9/3.4 s for coloring/bleaching). The multiple coloration states of the V₂O₅ electrode make it worthy for further integration as a smart negative electrode in a multicolored electrochromic asymmetric supercapacitor, where the electrochromic polyaniline electrode serves as the counter electrode. The device demonstrates a high coloration efficiency of 137.2 cm² C^-1 and an areal capacitance of 12.27 mF cm^-2 and an energy density of 2.21 × 10^-3 mW h cm^-2 at a current density of 0.05 mA cm^-2. By virtue of its different chromatic states during charging and discharging, smart visual tracking of the state of charge of the supercapacitor can be realized. Such a design of energy storage devices will have promising practical application in futuristic smart multifunctional electronic devices.

Recent progress in electrochromic energy storage materials and devices: a minireview

Integration of several functionalities into one isolated electrochemical body is necessary to realize compact and tiny smart electronics. Recently, two different technologies, electrochromic (EC) materials and energy storage, were combined to create a single system that supports and drives both functions simultaneously. In EC energy storage devices, the characteristic feature of EC materials, their optical modulation depending on the applied voltage, is used to visually identify the stored energy level in real time. Moreover, combining energy-harvesting and EC storage systems by sharing one electrode facilitates the realization of further compact multifunction systems. In this minireview, we highlight recent groundbreaking achievements in EC multifunction systems where the stored energy levels can be visualized using the color of the device.

Organic electrochromic energy storage materials and device design

While not affecting electrochemical performance of energy storage devices, integrating multi-functional properties such as electrochromic functions into energy storage devices can effectively promote the development of multifunctional devices. Compared with inorganic electrochromic materials, organic materials possess the significant advantages of facile preparation, low cost, and large color contrast. Specifically, most polymer materials show excellent electrochemical properties, which can be widely used in the design and development of energy storage devices. In this article, we focus on the application of organic electrochromic materials in energy storage devices. The working mechanisms, electrochemical performance of different types of organics as well as the shortcomings of organic electrochromic materials in related devices are discussed in detail.

Stimuli-Responsive Electrochemical Energy Storage Devices

Electrochemical energy storage (EES) devices have been swiftly developed in recent years. Stimuli-responsive EES devices that respond to different external stimuli are considered the most advanced EES devices. The stimuli-responsive EES devices enhanced the performance and applications of the EES devices. The capability of the EES devices to respond to the various external stimuli due to produced advanced EES devices that distinguished the best performance and interactions in different situations. The stimuli-responsive EES devices have responsive behavior to different external stimuli including chemical compounds, electricity, photons, mechanical tensions, and temperature. All of these advanced responsiveness behaviors have originated from the functionality and specific structure of the EES devices. The multi-responsive EES devices have been recognized as the next generation of stimuli-responsive EES devices. There are two main steps in developing stimuli-responsive EES devices in the future. The first step is the combination of the economical, environmental, electrochemical, and multi-responsiveness priorities in an EES device. The second step is obtaining some advanced properties such as biocompatibility, flexibility, stretchability, transparency, and wearability in novel stimuli-responsive EES devices. Future studies on stimuli-responsive EES devices will be allocated to merging these significant two steps to improve the performance of the stimuli-responsive EES devices to challenge complicated situations.

Electropolymerized 1D Growth Coordination Polymer for Hybrid Electrochromic Aqueous Zinc Battery

Organic materials are always viewed as promising electrochromic (EC) materials due to their synthetic versatility, color tunability, ready processability, and derivability from sustainable feedstocks. Most organic materials, however, are prone to undesirable redox side reactions in the presence of oxygen and water. As such, redox-active organic layers are often used in tandem with organic electrolytes to preserve their electrochemical stability. With the growing interest in electronics that are environmentally sustainable and biologically safe, developing aqueous-compatible organic materials is gaining growing interest. Herein, a rationally designed iron terpyridyl coordination polymer (CP) is prepared by controlled electropolymerization for realization of aqueous compatible EC and energy storage applications. Detailed analysis is established, showing that the CP grows in a 1D fashion and exhibits a predominant capacitive behavior which is reflected from its rapid charge-transfer kinetics. Taking this as an advantage, an integrated hybrid electrochromic zinc battery device is demonstrated with high color contrast, fast response time, and good endurance.

Reducing the resistance for the use of electrochemical impedance spectroscopy analysis in materials chemistry

Electrochemical impedance spectroscopy (EIS) is a highly applicable electrochemical, analytical, and non-invasive technique for materials characterization, which allows the user to evaluate the impact, efficiency, and magnitude of different components within an electrical circuit at a higher resolution than other common electrochemical techniques such as cyclic voltammetry (CV) or chronoamperometry. EIS can be used to study mechanisms of surface reactions, evaluate kinetics and mass transport, and study the level of corrosion on conductive materials, just to name a few. Therefore, this review demonstrates the scope of physical properties of the materials that can be studied using EIS, such as for characterization of supercapacitors, dye-sensitized solar cells (DSSCs), conductive coatings, sensors, self-assembled monolayers (SAMs), and other materials. This guide was created to support beginner and intermediate level researchers in EIS studies to inspire a wider application of this technique for materials characterization. In this work, we provide a summary of the essential background theory of EIS, including experimental design, signal responses, and instrumentation. Then, we discuss the main graphical representations for EIS data, including a scope of the foundation principles of Nyquist, Bode phase angle, Bode magnitude, capacitance and Randles plots, followed by detailed step-by-step explanations of the corresponding calculations that evolve from these graphs and direct examples from the literature highlighting practical applications of EIS for characterization of different types of materials. In addition, we discuss various applications of EIS technique for materials research.

Energy storage electrochromic devices in the era of intelligent automation

The current intelligent automation society faces increasingly severe challenges in achieving efficient storage and utilization of energy. In the field of energy applications, various energy technologies need to be more intelligent and efficient to produce, store, transform and save energy. In addition, many smart electronic devices facing the future also require newer, lighter, thinner and even transparent multi-functional power supplies. The unique properties of electrochromic energy storage devices (ECESDs) have attracted widespread attention. In the field of energy applications, they have high potential value and competitiveness. This review focuses on the electrochromic basic principles, and the latest technological examples of ECESDs, which are related to materials and device structures. Simultaneously, this review makes a detailed comparison and summary of example performances. Moreover, the review compares the current mainstream energy storage devices: lithium batteries and supercapacitors, and the main challenges of ECESDs are discussed. Finally, the future development directions in the field of electrochromic energy storage are predicted.

Fused Heterocyclic Molecule-Functionalized N-Doped Reduced Graphene Oxide by Non-Covalent Bonds for High-Performance Supercapacitors

Indole molecules with fused heteroaromatic structures can be adsorbed on the N-doped graphene surface through the π-π interaction. Therefore, the indole-functionalized N-doped graphene (InFGN) with mesopores is successfully fabricated by a simple hydrothermal method and subsequent vacuum freeze-drying process. The microstructure, thickness, element composition, pore structure, and electrochemical performance of InFGN are analyzed via SEM, TEM, AFM, BET, UV-vis, FT-IR, XPS, Raman, XRD, and electrochemical technologies. Since the five-membered aromatic heterocycles are electron-rich, the indole molecules fixed on the N-doped graphene surface can repair the structural defects generated by N doping. Electrochemical measurements show that the InFGN electrode highlights an excellent capacitance of 622.3 F g^-1 at 2 A g^-1 and a durable cycling life of 100.5% after 5000 charging/discharging cycle times. For further practical application, a symmetric device has been assembled by using InFGN electrodes, which realizes high-power and energy densities (18.8-20.6 Wh kg^-1 at 800-8000 W kg^-1). This study provides a shortcut for building green supercapacitors with enhanced energy storage performance.

An Efficient Electrochromic Supercapacitor Based on Solution-Processable Nanoporous Poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine}

A new green synthetic route to tris[4-(3,4-ethylenedioxythiophene)phenyl]amine (TEPA) monomer has been developed and the molecular structure of TEPA has been determined by using single-crystal XRD. Solution-processable nanoporous poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine} (PTEPA) is prepared by a chemical oxidative polymerization in a microemulsion. Based on the distorted structure of TEPA in the solid state, it is proposed that dendritic PTEPA has a distorted 3 D conformation with multiple twisted channels and pores that are narrowed and blocked by bifurcation and distortion of PTEPA, which is consistent with the observed hierarchical pore structure. As a cathode material, PTEPA exhibits a discharge capacity of 89.5 mAh g-1 in the initial cycle with a highly sloping two-stage discharge curve and relatively stable cycling performance. Beyond its excellent energy storage properties, PTEPA also shows relatively good electrochromic performance. Furthermore, an efficient all-solid-state electrochromic supercapacitor (ECSC) with good electrochromic performance and high energy storage capacity (13.3 mF cm-2 ) is assembled from PTEPA and nanoporous graphene films. During charge-discharge processes, the color of the ECSC changes between yellow-green and steel blue. Thus, the energy storage level of the ECSC can be monitored by the corresponding color changes. The fabricated ECSC may have practical applications, for example, in self-powered electrochromic smart windows.

An electrochromic supercapacitor based on an MOF derived hierarchical-porous NiO film

Nickel oxide (NiO) is a promising candidate for future electrochromic supercapacitors due to its pronounced electrical properties and low cost. Unfortunately, the weak interaction between NiO films and conductive substrates results in poor cycling stability. In addition, the long color-switching time and low capacitance by the small lattice spacing in dense NiO impede its practical applications seriously. Herein, a hierarchical porous NiO film/ITO glass bifunctional electrode has been prepared via the solvothermal and subsequent calcination process of growing MOF-74 in situ on ITO, which shows outstanding cycle reversibility, excellent capacitance, high coloration efficiency and short color-switching time. Because of the strong binding force between the NiO film and substrate, and large surface areas with a hierarchical porous structure which are beneficial to the ion transport, the NiO film demonstrates perfect capacitive and electrochromic properties. As a bifunctional electrode, the NiO film shows a specific capacitance of 2.08 F cm-2 at 1 mA cm-2, large optical modulation of 41.08% and about 86% of optical modulation retention after 10 000 cycles. Furthermore, we assembled a bifunctional device whose energy condition can be roughly estimated according to the color state of the device. This finding can provide us with a new application of MOFs in the dual device of electrochromic supercapacitors.

Intelligent electrochromic-supercapacitor based on effective energy level matching poly(indole-6-carboxylicacid)/WO3 nanocomposites

A high-quality electrochromic-supercapacitor based on poly(indole-6-carboxylicacid)/WO₃ nanocomposites can intelligently monitor the energy storage state by changing the color of the device.

Electrochromic polymers with multiple redox couples applied to monitor energy storage states of supercapacitors

Electrochromic polymers with multiple separate redox couples are used to monitor the energy storage states of supercapacitors by appearance colour.

In situ preparation and determination of electrochemical and electrochromic properties of copper phthalocyanine-polyaniline nanocomposite films

Copper phthalocyanine (CuPc) films with different morphologies were electrodeposited on the surfaces of ITO electrodes. Then, in each case, a polyaniline (PANI) film was electrochemically polymerized in situ on the surface of the copper phthalocyanine film to form a CuPc-PANI composite film. The electrochemical properties of the CuPc-PANI composite film were observed to be much better than those of the film without CuPc. With the modification involving the CuPc nanowires, the composite film formed a finer particle surface and an increased interface area between the PANI and the electrolyte. Compared to the single-component PANI film, the CuPc-PANI composite film exhibited better performance with a higher optical contrast (58% at 730 nm), a faster response speed (coloring time of 1.02 s, discoloring time of 1.96 s), and better cycling stability (68.71% of the initial electrochemical activity after 500 cycles, in contrast to only about 48.02% for PANI). Moreover, the CuPc-PANI film shows a new feature that can be used as a supercapacitor (specifically a capacitance value of about 5.4 mF cm-2 at typical currents). Our results demonstrate that the prepared CuPc-PANI composite film is one of the best candidates for multiple potential applications such as high-performance polymer electrochromic materials and supercapacitors.

Electrochemical and electrochromic properties of bilayer polymer films prepared by electrochemical polymerization based on star-shaped thiophene derivatives

Electrochemical and EC properties of bilayer films prepared by electropolymerization prove that charge-transport has important effects on switching speed of materials.