Electrochromic Energy Storage Research Articles

Copper complex/polyoxometalate‐based tunable multi‐color film for energy storage

AbstractPolyoxometalates (POMs) are considered as an attractive option for electrochromic energy storage (EES) system due to their unique electrochemical feature. Herein, a composite film NW/P2W17/Cu (phen)2 based on Dawson‐type monolacunary POMs K10P2W17O61 (abbreviated as P2W17) and copper complex [CuII (phen)2](NO3)2 (abbreviated as Cu (phen)2) formed on TiO2 nanowire (abbreviated as NW) array substrate was fabricated by hydrothermal process and layer‐by‐layer self‐assembly combination method. This rational designed film NW/P2W17/Cu (phen)2 exhibits excellent tunable multicolor electrochromic behavior and improved pseudocapacitive performance with large optical modulation (43.7% at 600 nm), fast switching time (tc = 2.9 s, tb = 9.5 s), and high volumetric capacitance (228.0 F cm−3 at 0.3 mA cm−2). In the process of charge and discharge, the composite film can realize the transformation from light green to orange, green, and finally to blue‐green color, successfully achieve the bridge between electrochromic behavior and energy storage, and monitor the level of stored energy by color change. This work showed great potential of POMs‐based electrode materials for integrated electrochromism and energy storage applications.

Electrochemically co-deposited WO3-V2O5 composites for electrochromic energy storage applications

In this study, a W-V mixed metal oxide composite thin-film structure comprising tungsten oxide (WO3) and vanadium oxide (V2O5) is prepared using a one-step electrochemical co-deposition method. The electrochromic and electrochemical energy storage applications of the prepared thin films comprising different compositions of WO3 and V2O5 are systematically investigated. The films of the W-V mixed composite, comprising WO3 and V2O5 in the ratio of 1:1, exhibits remarkable electrochromic properties, such as an optimum optical contrast of 60%, a fast coloration response of 4.9 s, and the highest coloration efficiency of 61.5 cm2/C. Furthermore, for the electrochemical energy storage application, a maximum areal capacitance of 38.75 mF/cm2 at an applied current of 0.5 mA/cm2 is obtained. Furthermore, it displays a capacitive retention of 78.5%, even after 5000 charge/discharge cycles. The ameliorated characteristics of both electrochromic and electrochemical energy storage applications are attributed to the (a) unique morphology containing more active sites introduced by both WO3 and V2O5, (b) fast charge transfer kinetics, and (c) redox behavior of both metal ions present in the synthesized W-V mixed metal composite.

High-performance electrochromic supercapacitor based on quinacridone dye with good specific capacitance, fast switching time and robust stability

• QA dyes were designed and firstly prepared into electrochromic polymers. • The polymers with three donor units show different electrochemical behaviors. • pC10QA-2EDOT film exhibits remarkable electrochromic properties. • The device based on pC10QA-2EDOT exhibits robust cyclic stability. • The electrochromic supercapacitor can make a LED light for more than 85 s. Quinacridone (QA) dye with large π-conjugation system exhibit excellent optical, thermal and chemical properties. A series of QA derivatives (C10QA-2T, C10QA-2EDOT, C10QA-2DT) were designed and synthesized with different donor units (including thiophene, EDOT and bithiophene) in this work. Three monomers show different HOMO energy levels and onset oxidation potentials. Their corresponding polymer films were obtained by electrochemical polymerization. Compared to pC10QA-2T and pC10QA-2DT, pC10QA-2EDOT exhibits better integrated electrochromic properties in terms of multicolor showing (yellow, gray and blue), higher optical contrast (more than 40% in the visible region), larger coloration efficiency (498 cm 2 /C at 455 nm), faster switching time (less than 1 s) and better cyclic stability. It is intriguing that the electrochromic device based on pC10QA-2EDOT exhibits robust stability over 50,000 cycles with almost no decay of its original optical contrast. In addition, pC10QA-2EDOT film possesses large volume specific capacitance of up to 322 F/cm 3 , which should be ascribed to that the loose and porous structures owing to large dihedral angles caused by the steric hindrance of oxygen on the EDOT may facilitate the ion diffusion during the doping/dedoping process. Hence, the electrochromic supercapacitor can supply power to a green LED for 85 s. This work pioneers QA dye in the electrochromic field and further develops a new electrochromic energy storage device with visual color display, which may have potential prospects in portable and wearable electronic devices.

Attaining remarkable switching speed of nickel oxide-based electrode for electrochromic energy storage devices

Integrating the electrochromic (EC) with energy storage devices (EC-ESDs) can considerably drop the energy-storing cost. In this direction, Nickel oxide (NiO) is considered a potential electrode material for EC devices owing to its superior coloration efficiency (CE), wide dynamic range, excellent cycling capability, and cost-effectiveness. On the flip side, NiO-based EC-ESDs experience low CE, slow switching speed, and soft chromatic contracts. To this end, a highly porous NiO nano-sheets (NSs) of thickness < 20 nm are grown on the hydrophilic surface of the FTO glass using a hydrothermal process. With this, an extremely low series (1.68 Ω) and marginal charge transfer (85.96 Ω) resistances are obtained. Thus, the switching speeds for coloration and bleach are significantly reduced to 0.85 and 0.30 s, respectively. Furthermore, the achieved optical modulation is 66.9%; whereas, the CE is 48.51 cm2/C. The obtained areal capacitance is 129.32 mF/cm2 at the scan rate of 5 mV/s. Admirable capacity retention (92.3% at 10 mV/s) is observed after 1000 cycles. The obtained outcomes suggest that NiO can be a potential candidate for EC-ESDs.

Tunable Intracrystal Cavity in Tungsten Bronze‐Like Bimetallic Oxides for Electrochromic Energy Storage (Adv. Energy Mater. 5/2022)

Electrochromic Energy Storage In article number 2103106, Guofa Cai, Pooi See Lee and co-workers report that Nb18W16O93 nanomaterials with superstructure motifs show fast Li+ intercalation–deintercalation kinetics and robust stability for both electrochromic and rechargeable energy storage applications. A complementary smart window is further fabricated based on the Nb18W16O93 film, which can dynamically regulate the sunlight and solar radiant heat input of buildings while electrical energy can be stored in the smart window, providing a multifunctional system consisting of electrochromism, energy storage and an indicator.

Nanostructured materials for electrochromic energy storage systems

This review highlights the recent progress in electrochromic energy storage (EES) systems. EES bifunctional devices can be incorporated with characteristics such as flexibility, stretchability, self-healing properties, etc. making them convenient for everyday applications.

In situ grown hierarchical NiO nanosheet@nanowire arrays for high-performance electrochromic energy storage applications.

Electrodes with hierarchical nanoarchitectures could promote electrochemical properties due to their largely exposed active sites and quick charge transfer. Herein, in situ grown hierarchical NiO nanosheet@nanowire films are reported by a one-step hydrothermal process followed by heat treatment. The unique NiO hierarchical nanostructures, which are composed of NiO nanowires grown on the surface of a nanosheet array, show improved electrochromic properties such as large optical modulation in different light regions (95% at 550 nm and 50.6% at 1000 nm), fast color change (9.8/5.4 s) and better coloring efficiency (91.2 cm2 C-1) with long-term cycling properties (82.2% after 700 cycles). Simultaneously, the hierarchical nanostructures possess optimal areal capacitance (117.2 mF cm-2), rate performance and cycling properties. The enhanced electrochemical properties are due to the pretreated seed layer and the synergistic effect between the unique in situ grown ultrathin nanowire and the underlying vertical nanosheet layer which can strengthen the mechanical adhesion of the nanoarray film to the substrate and make both nanosheets and nanowires more exposed to the electrolyte, enhancing charge transfer and mass diffusion. This work provides a promising pathway towards developing high quality electrochromic energy storage 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.

High performance electrochromic energy storage devices based on Mo-doped crystalline/amorphous WO3 core-shell structures

The crystal structure and architecture of electrochromic (EC) materials are the key factors for their performance. In this paper, Mo-doped crystalline/amorphous WO 3 (c/a-WO 3 ) are fabricated via facile hydrothermal and electrodeposition methods, which combine the advantages of excellent cycle stability (c-WO 3 nanobars) and fast switching speed and high coloring efficiency (Mo-doped a-WO 3 thin films) of different WO 3 structure. By optimizing the hydrothermal and electrodeposition parameters, the core-shell c/a-WO 3 EC material shows a significant optical modulation (67.8%) owing to the low energy barrier and rapid ion migration in Mo-doped a-WO 3 shell. More importantly, the EC devices based on Mo-doped c/a-WO 3 exhibit fast switching speeds and high coloration efficiency (104.98 cm 2 /C) due to enhanced Li + diffusivity. These great electrochemical performances could be attributed to the amorphous shell and the proper structure distortion caused by doped atoms. Meanwhile, the EC devices exhibit good cycling stability as the transmittance modulation has no decrease after 23000 s. As an energy storage device, the EC supercapacitor delivers a high energy density of 10.8 Wh/kg at a power of 117.6 W/kg and long cycle life (72.8% capacitance retention over 1500 cycles). The metal-doped core-shell structure can provide a reliable solution to produce high-performance EC materials and devices such as energy-saving smart windows, outdoor static displays and other energy-efficient applications. • Mo-doped crystalline/amorphous WO 3 are fabricated via facile methods. • The core-shell c/a-WO 3 EC material shows a significant optical modulation (67.8%). • The EC devices exhibit fast switching speeds and high coloration efficiency. • Devices exhibit good stability (72.8% capacitance retention over 1500 cycles). • The great electrochemical performance could be attributed to structure distortion.

A fast self-charging and temperature adaptive electrochromic energy storage device

ECESDs exhibit a wide operating temperature range. They can be chemically self-charged through a spontaneous redox reaction and the energy status could be estimated by the naked eye according to the obvious color during the charge/discharge process.

Interfacial Charge Transfer and Zinc Ion Intercalation and Deintercalation Dynamics in Flexible Multicolor Electrochromic Energy Storage Devices

Bifunctional electrochromic devices integrating electrochromism and energy storage have attracted extensive attention in recent years. Here, zinc-ion-intercalation-based multicolor electrochromic energy storage devices (EESDs) based on a free-standing Zn2+-based polymeric electrolyte membrane (ZPEM) and a nanocrystal-in-glass V2O5 thin film were constructed. Evolution of the interlayer spacing, V–O-related bonds, and chemical compositions of the V2O5 thin films with zinc ion intercalation and deintercalation is elaborated in a liquid Zn(CF3SO3)2-propylene carbonate (PC) electrolyte. Impressively, highly reversible multi-electrochromism among greenish-blue, yellowish-green, greenish-yellow, faint-yellow, yellowish-orange, and reddish-orange colors is observed in both flexible V2O5 thin films and flexible ZPEM/V2O5/indium tin oxide (ITO) EESDs, which enjoy the benefits from the free channel originating from the large interlayer spacing, the buffering effect of the amorphous phase in the host nanocrystal-in-glass V2O5 matrix, the robust electrostatic interactions between the host V2O5 and guest Zn2+, and Faradaic redox reactions at the Zn2+/V2O5 active interface. The flexible multicolor EESD based on zinc ion intercalation and deintercalation exhibits remarkable electrochromic and energy storage performance with a high transmittance modulation of 57.88%, an excellent coloration efficiency of 36.91 cm2 C–1, a superior specific capacitance of 51 μF cm–2, an enhanced rate capacity, and a pseudocapacitive feature, making it a promising candidate for cost-efficient, environmentally friendly, and bifunctional electrochromic devices.

Effect of the electrical formation of electrochromic devices based on tungsten oxide

Electrochromic energy storage systems have high potential value and competitiveness. However, the problems related to the operation of such electro-optic devices are still not fully solved. The aim of our study was to increase the operational lifetime of electrochromic devices using preoperational electrical action. We discovered an effect of electrical formation of electrochromic devices based on tungsten oxide previously observed only for other types of chemical current sources. The electrical formation comprised multistage action of galvanostatic stabilized current in the stability range of the oxidation–reduction potential. The new approach made it possible to reduce the power consumption of electrochromic devices in the coloration and bleaching stages by approximately 3 times and by 30%–40%, respectively, and achieve an increase in their operational lifetime by 2–3 times.

Tunable Intracrystal Cavity in Tungsten Bronze‐Like Bimetallic Oxides for Electrochromic Energy Storage

AbstractDesigning materials with appropriate crystal and electronic structures to enhance ionic and electronic transport simultaneously are highly desirable for both electrochromic and electrochemical energy storage devices. It remains a great challenge to simultaneously meet these requirements. Here, a Nb18W16O93 nanomaterial is successfully synthesized with superstructure motifs and uniform self‐supported electrochromic films are prepared on a transparent conductive substrate. The results show that the films can effectively accommodate lithium ions and facilitate intercalation–deintercalation on transparent fluorine‐doped tin oxide (FTO) substrates at high current density. Mechanistic insights into the excellent electrochromic and rechargeable energy storage properties are provided by density functional theory (DFT) calculations. Specifically, the Nb18W16O93 film displays a large optical modulation (up to 93% at 633 nm and 89% at 1200 nm), high coloration efficiency (105.6 cm2 C−1), high energy storage capacity (151.4 mAh g−1 at 2 A g−1), excellent rate capability, and long‐term electrochemical stability (6000 cycles). As a demonstration of its application, an energy storage indicator is illustrated and a complementary electrochromic energy storage smart window is fabricated based on the Nb18W16O93 film. The results demonstrate that the Nb18W16O93 nanomaterial has a promising application in the field of high‐performance electrochromic and energy storage devices.

Optimal Rule-of-Thumb Design of Nickel-Vanadium Oxides as an Electrochromic Electrode with Ultrahigh Capacity and Ultrafast Color Tunability.

The use of electrodes capable of functioning as both electrochromic windows and energy storage devices has been extended from green building development to various electronics and displays to promote more efficient energy consumption. Herein, we report the electrochromic energy storage of bimetallic NiV oxide (NiVO) thin films fabricated using chemical bath deposition. The best optimized NiVO electrode with a Ni/V ratio of 3 exhibits superior electronic conductivity and a large electrochemical surface area, which are beneficial for enhancing electrochemical performance. The color switches between semitransparent (a discharged state) and dark brown (a charged state) with excellent reproducibility because of the intercalation and deintercalation of OH- ions in an alkaline KOH electrolyte. A specific capacity of 2403 F g-1, a coloration efficiency of 63.18 cm2 C-1, and an outstanding optical modulation of 68% are achieved. The NiVO electrode also demonstrates ultrafast coloration and bleaching behavior (1.52 and 4.79 s, respectively), which are considerably faster than those demonstrated by the NiO electrode (9.03 and 38.87 s). It retains 91.95% capacity after 2000 charge-discharge cycles, much higher than that of the NiO electrode (83.47%), indicating that it has significant potential for use in smart energy storage applications. The superior electrochemical performance of the best NiVO compound electrode with an optimum Ni/V compositional ratio is due to the synergetic effect between the high electrochemically active surface area induced by V-doping-improved redox kinetics (low charge-transfer resistance) and fast ion diffusion, which provides a facile charge transport pathway at the electrolyte/electrode interface.

Studies on transmittance modulation and ions transfer kinetic based on capacitive-controlled 2D V2O5 inverse opal film for electrochromic energy storage application

Two-dimensional vanadium pentoxide inverse opal (2D V2O5 IO) architecture was fabricated by polystyrene (PS) sphere template assisted electrodeposition process. In comparison to the un-templated V2O5 film, the 2D V2O5 IO film exhibited a highly ordered hexagonal close-packed bowel-like array, as well as noticeable electrochromism, such as transmittance modulation up to 42.6% at 800 nm, high coloration efficiency (28.6 cm2 · C−1), fast ions transfer kinetic (t b = 7.2 s, t c = 2.5 s). These improvements of electrochromic performance were attributed to the ordered morphology with larger surface areas, which considerably shortened the ions diffusion paths and accelerated ions migration. An electrochromic energy storage device assembled from the 2D V2O5 IO film with simultaneous electrochromic and pseudocapacitive performance could not only show transmittance modulation accompanied by multicolor variations but also powered an LCD screen and an LED bulb, demonstrating a promising potential for practical applications.

Repairable electrochromic energy storage devices: A durable material with balanced performance based on titanium dioxide/tungsten trioxide nanorod array composite structure

Electrochromic-capacitive bifunctional materials have been widely developed in recent years due to their broad application prospects. However, the failure to achieve all-round excellent performance simultaneously, as well as the limited stability restricted their large-scale commercialization. Here, we prepared a TiO2/WO3 nanorod composite material, which showed balanced electrochromic and capacitive properties without any significant shortcoming in all aspects. Generally, the material possessed excellent coloration efficiency (153.1 cm2 C−1), fast color switching response (10/10s) and high capacitance (557.7 F g−1 at 1 A g−1). In addition, a new concept of “stability in industrial sense” was firstly proposed to redefining the durability of materials. The decline of material stability during cycles was fully explained by a theoretical model of “ion trap”, which contained two categories: (1) eliminable trap and (2) non-eliminable trap. The eliminable trap could be removed by a de-trapping treatment, so that all the properties of declined materials could be restored, while the non-eliminable trap couldn’t be removed.

A high-performance electrochromic battery based on complementary Prussian white/Li4Ti5O12 thin film electrodes

Electrochromic energy storage devices (EESDs) have a wide range of applications from static displays to building windows. However, it is a great challenge to assemble EESDs with both high performance of energy storage and electrochromism. In this work, we design a multifunctional EESD composed of a Li4Ti5O12 and a Prussian white. Li4Ti5O12 (E = 1.55 V vs Li/Li+) film with excellent lithium-ion storage performance is used as the anode, and Prussian white film (E = 3.2 V vs Li/Li+) as the cathode. Thanks to the complementary electrochromic behavior, the suitable redox voltage gap, and the intrinsic electrochemical stability of Li4Ti5O12 film and Prussian white film, the as-assembled EESD exhibits excellent electrochromic performances including broad optical modulation (55.3% at 529 nm), high coloration efficiency (170.1 cm2 C−1), and long-term cycling stability (retention of 95.8% of initial optical modulation after 1000 cycles). And the EESD shows high energy density of 127.2 mWh cm−2 and exceptionally high power density of 24 mW cm−2. This EESD with an output voltage of 1.5 V and Coulombic efficiency of 98.8% is promising for applications of electrochromic smart windows and static displays to significantly reduce their energy consumption.

A Systematic Review of the Most Recent Concepts in Smart Windows Technologies with a Focus on Electrochromics

In the context of sustainability and in the face of ambitious goals towards the reduction of CO2 emission, the modification of transparency in architecture becomes an important tool of energy flow management into the building. Windows that dim to stop the energy transfer reduce the cooling load in the building. Recently, however, the latest achievements in the development of electrochromic materials allowed us to integrate some additional—previously unknown—functionalities into EC devices. The purpose of this paper is to provide a systematic review of recent technological innovations in the field of smart windows and present the possibilities of recently established functionalities. This review article outlines recent general progress in electrochromic but concentrates on multicolour and neutral black electrochromism, spectrally selective systems, electrochromic energy storage windows, hybrid EC/TC systems, OLED lighting integrated with the EC device, and EC devices powered by solar cells. The review was based on the most recent publication from the years 2015–2020 recorded in the databases WoS and Scopus.

Robust Cu-Au alloy nanowires flexible transparent electrode for asymmetric electrochromic energy storage device

Flexible electrochromic energy storage (EES) systems have attracted tremendous attention because of their combined advantages of color-changing and energy-storing. Although copper nanowires (Cu NWs) flexible transparent electrodes (FTEs) have been considered as one of the most promising candidates for next-generation flexible electronics, its instinct electrochemical instability hindered its application in flexible electrochemical energy system, including EES device. Herein, we proposed a highly conductive electrochemically stable FTE based on Cu-Au alloy NWs network synthesized in a facile and simple electrochemical method. Compared with the pristine Cu NWs network that breaks into disconnected nanorods less than 10 s in 1 M H2SO4 solution during electrochemical anodic corrosion, the Cu-Au NWs network remained stable after 4000 s under the same condition. Furthermore, thanks to the forming of firm joints between the stacked NWs during inducting Au atoms, the optical-electrical performance (a sheet resistance of 23.2 Ohm/sq at a transmittance of 87%) and mechanical flexibility were highly improved. Based on these improvements, anodic PANI and cathodic WO3 layer were successfully deposited onto the Cu-Au NWs FTE by electrochemical method. An asymmetric-EES (AEES) device was assembled utilizing these complementary electrodes, which concurrently exhibited excellent electrochromic (coloration efficiency: 153.77 cm2/C at 633 nm) and energy storage performance (areal capacitance: 2.29 mF/cm2), demonstrating their potential for smart multifunctional flexible electronics.

Flexible conjugated polyfurans for bifunctional electrochromic energy storage application

The development of high-efficiency organic electronic energy storage materials is a necessary prerequisite for modern intelligent and environmentally friendly devices. Given that polymer molecular structure is always closely related to its arrangement conformation, morphological attributes and performances. Here, we electrodeposited and characterized series poly(2,2′-bifuran) (P2Fu), poly(2,2′:5′,2′'-terfuran) (P3Fu), and poly(2,2′:5′,2′':5′',2′''-quaterfuran) (P4Fu) based furan heterocycle to understand the molecular structure induce the changes of optical and electronic properties. As expected, flexible free-standing films were polymerized at low potential with improved stability. By virtue of its favorable electronic structure and inherent electrochromic, the tailored P4Fu reveals its potential for dual-function electrochromic-supercapacitor (DES) applications via systematic cyclic voltammetric and galvanostatic techniques, showing noticeable multicolor, high coloration efficiency (CE) of 330.5 cm2 C-1, and high specific capacitance (241.6F g−1/1.0 A g−1), which are much attractive than those of polythiophene derivatives, even superior to the heterocyclic counterparts. This is also the first time to explore the DES application potential of polyfuran. Furthermore, a DES device was successfully assembled by using P4Fu as the activation layers, which can monitor the energy storage level through color conversion. The research demonstrates an important step toward environmentally compatible electronics, and provides novel green material options for high-available organic smart devices.