Emerging Zn Anode‐Based Electrochromic Devices

2D Conjugated Metal-Organic Frameworks for New Generation Flexible Multicolor Electrochromic Devices

There has been considerable interest in 2D conductive conjugated MOFs (2D c-MOFs) for their potential applications in sensors, opto-electronics, catalysis, and energy storage, owing to their ultra-high specific surface area, relatively high electrical conductivity, and tunable pore channel sizes for ion/charge diffusion/adsorption. The unique advantages brought by systematic tunings in the metal nodes and organic ligands enable the creation of highly accessible and remarkable structures with diverse chemical and physical behaviors. While the 2D c-MOFs are being explored for the rapid widening spectrum of applications, in this work, the great potential of multicolor transitions and functional properties of these 2D c-MOFs are examined for the new generation of flexible multicolor electrochromic devices (FMEDs). Despite the rather limited and yet steady progress that has been made so far, 2D c-MOFs offer great opportunities in addressing the monotonous color switching, undesirable stability, as well as the sluggish kinetics of electron/ion transportation, which are typically encountered by the conventional electrochromic materials. Together with the main challenges that are being faced, this perspective provides a timely re-visit to the expected transition in the near future from the proof-of-concept demonstration to the eventual industrial-scale implementation of 2D c-MOFs in the new generation FEMDs.

High-Performance Complementary Electrochromic Batteries using Nb18W16O93 by the Synergistic Effects of Aqueous Al3+/K+ Dual-Ion

Multivalent ions, especially Al3+ in aqueous electrolyte contributes to higher capacity and color contrast for more sustainable post-lithium electrochromism and energy storages. However, the lack of suitable cathodic and anodic electrochromic materials is a major challenge for Al-ion electrochromic batteries, which limits their optical contrast and lifespan. Herein, we report that Wadsley-Roth phase Nb18W16O93 with open structure achieves Al3+ intercalation/extraction reversibly. The complementary electrochromic energy storage devices based on Nb18W16O93 coupled with Prussian blue using hybrid Al3+/K+ aqueous electrolytes show a fast response, a high capacity and a large coloring efficiency. The superior performances are due to the cations of Al3+ and K+ selectively insert/extract in the electrode of Nb18W16O93 and Prussian blue, respectively. This work provides an effective strategy for high-performance and low-cost electrochromic batteries with higher sustainability.

Innovative Energy Storage Smart Windows Relying on Mild Aqueous Zn/MnO2 Battery Chemistry

Rechargeable mild aqueous Zn/MnO2 batteries are currently attracting great interest thanks to their appealing performance/cost ratio. Their operating principle relies on two complementary reversible electrodeposition reactions at the anode and cathode. Transposing this operating principle to transparent conductive windows remains an unexplored facet of this battery chemistry, which is proposed here to address with the development of an innovative bifunctional smart window, combining electrochromic and charge storage properties. The proof-of-concept of such bifunctional Zn/MnO2 smart window is provided using a mild buffered aqueous electrolyte and different architectures. To maximize the device's performance, transparent nanostructured ITO cathodes are used to reversibly electrodeposit a high load of MnO2 (up to 555 mA h m-2 with a CE of 99.5% over 200 cycles, allowing to retrieve an energy density as high as 860 mA h m-2 when coupled with a zinc metal frame), while flat transparent FTO anodes are used to reversibly electrodeposit an homogenous coating of zinc metal (up to ≈280 mA h m-2 with a CE > 95% over 50 cycles). The implementation of these two reversible electrodeposition processes in a single smart window has been successfully achieved, leading for the first time to a dual-tinting energy storage smart window with an optimized face-to-face architecture.

Continuous Solar Energy Conversion Windows Integrating Zinc Anode-Based Electrochromic Device and IoT System

Integration of solar cells and electrochromic windows offers crucial contributions to green buildings. Solar-charging zinc anode-based electrochromic devices (ZECDs) present opportunities for addressing the solar intermittency issue. However, the limited energy storage capacity of ZECDs results in wasted harnessing of solar energy as well as overcharging. Herein, spectral-selective dual-band ZECDs that continuously transport solar energy to indoor appliances by remotely controlling the repeated bleached-tinted cycles during the daytime, are reported. Hexagonal phase cesium-doped tungsten bronze (h-Cs0.32WO3, CWO) nanocrystals are adopted for dual-band ZECDs due to their independent control ability of near-infrared (NIR) and visible (VIS) light transmittance (∆T = 73.0%, 700 nm; ∆T = 83.7%, 1200 nm) and excellent cycling stability (0.8% optical contrast decay at 1200 nm after 10 000 cycles). The prototype device (i.e., CWO//Zn//CWO) delivers extraordinary thermal insulation capability, displaying a 10 °C difference between "bright" and "dark" modes. Furthermore, an Internet of Things (IoT) controller to control the NIR and VIS lights of the CWO//Zn//CWO window wirelessly with a smartphone, empowering the continuous discharging of the solar-charged window during the daytime remotely, is developed. Such windows represent an intriguing potential technology whose future impact on green buildings may be substantial.

Electrochromic and Energy Storage Performance Enhancement by Introducing Jahn-Teller Distortion: Experimental and Theoretical Study

Aqueous electrochromic batteries (ECBs) have recently garnered significant attention within the realm of renewable rechargeable technology due to their potential applicability in diverse multifunctional devices featuring visible-level indicator batteries. However, there exists an imperative to comprehend the underlying structural factors that contribute to achieving an elevated electrochemical performance. In this context, we have synthesized and compared WO3·H2O (HWO) specifically for heightened ECB application as against the performance of a standard anhydrous WO3 (AWO). To unravel the underlying cause, a density functional theory (DFT) investigation is carried out, disclosing a structural deformation of HWO, unlike AWO, due to Jahn-Teller distortion induced by the presence of interlayer water. It results in a fully compatible HWO ion host to devise a zinc-ion aqueous electrolyte electrochromic battery, exhibiting superior redox reactivity, optical modulation (50%), capacity (200 mAh/m2), and cyclic stability. To glean insights into the dynamic structural alterations during the intercalation and deintercalation processes of Zn2+, ex situ X-ray diffraction and Raman spectroscopic studies are carried out. These investigations culminate in the determination that HWO films are better suited for the application than their AWO counterparts. This finding holds promise for advancing the applications of ECBs and represents a significant step forward in this field.

Resonant-Cavity-Enhanced Electrochromic Materials and Devices

With rapid advances in optoelectronics, electrochromic materials and devices have received tremendous attentions from both industry and academia for their strong potentials in wearable and portable electronics, displays/billboards, adaptive camouflage, tunable optics, and intelligent devices, etc. However, conventional electrochromic materials and devices typically present some serious limitations such as undesirable dull colors, and long switching time, hindering their deeper development. Optical resonators have been proven to be the most powerful platform for providing strong optical confinement and controllable lightmatter interactions. They generate locally enhanced electromagnetic near-fields that can convert small refractive index changes in electrochromic materials into high-contrast color variations, enabling multicolor or even panchromatic tuning of electrochromic materials. Here, resonant-cavity-enhanced electrochromic materials and devices, an advanced and emerging trend in electrochromics, are reviewed. In this review, w e will focus on the progress in multicolor electrochromic materials and devices based on different types of optical resonators and their advanced and emerging applications, including multichromatic displays, adaptive visible camouflage, visualized energy storage, and applications of multispectral tunability. Among these topics, principles of optical resonators, related materials/devices and multicolor electrochromic properties are comprehensively discussed and summarized. Finally, the challenges and prospects for resonant-cavity-enhanced electrochromic materials and devices are presented.

Fast and Stable Zinc Anode-Based Electrochromic Displays Enabled by Bimetallically Doped Vanadate and Aqueous Zn2+/Na+ Hybrid Electrolytes

Vanadates are a class of the most promising electrochromic materials for displays as their multicolor characteristics. However, the slow switching times and vanadate dissolution issues of recently reported vanadates significantly hinder their diverse practical applications. Herein, novel strategies are developed to design electrochemically stable vanadates having rapid switching times. We show that the interlayer spacing is greatly broadened by introducing sodium and lanthanum ions into V3O8 interlayers, which facilitates the transportation of cations and enhances the electrochemical kinetics. In addition, a hybrid Zn2+/Na+ electrolyte is designed to inhibit vanadate dissolution while significantly accelerating electrochemical kinetics. As a result, our electrochromic displays yield the most rapid switching times in comparison with any reported Zn-vanadate electrochromic displays. It is envisioned that stable vanadate-based electrochromic displays having video speed switching are appearing on the near horizon.

Electrochromic-Induced Rechargeable Aqueous Batteries: An Integrated Multifunctional System for Cross-Domain Applications

Multifunctional electrochromic-induced rechargeable aqueous batteries (MERABs) integrate electrochromism and aqueous ion batteries into one platform, which is able to deliver the conversion and storage of photo-thermal-electrochemical sources. Aqueous ion batteries compensate for the drawbacks of slow kinetic reactions and unsatisfied storage capacities of electrochromic devices. On the other hand, electrochromic technology can enable dynamically regulation of solar light and heat radiation. However, MERABs still face several technical issues, including a trade-off between electrochromic and electrochemical performance, low conversion efficiency and poor service life. In this connection, novel device configuration and electrode materials, and an optimized compatibility need to be considered for multidisciplinary applications. In this review, the unique advantages, key challenges and advanced applications are elucidated in a timely and comprehensive manner. Firstly, the prerequisites for effective integration of the working mechanism and device configuration, as well as the choice of electrode materials are examined. Secondly, the latest advances in the applications of MERABs are discussed, including wearable, self-powered, integrated systems and multisystem conversion. Finally, perspectives on the current challenges and future development are outlined, highlighting the giant leap required from laboratory prototypes to large-scale production and eventual commercialization.

Advances in electrochromic device technology through the exploitation of nanophotonic and nanoplasmonic effects

Research regarding electrochromic (EC) materials, such materials that change their color upon application of an electrochemical stimulus, has been conducted for centuries. However, most recently, increasing efforts have been put into developing novel solutions to utilize these on-off switching materials in advanced nanoplasmonic and nanophotonic devices. Due to the significant change in dielectric properties of oxides such as WO3, NiO, Mn2O3 and conducting polymers like PEDOT:PSS and PANI, EC materials have transcended beyond simple smart window applications and are now found in plasmonic devices for full-color displays and enhanced modulation transmission and photonic devices with ultra-high on-off ratios and sensing abilities. Advancements in nanophotonic ECDs have further decreased EC switching speed by several orders of magnitude, allowing integration in real-time measurement and lab-on-chip applications. The EC nature of such nanoscale devices promises low energy consumption with low operating voltages paired with bistability and long lifetimes. We summarize these novel approaches to EC device design, lay out the current short comings and draw a path forward for future utilization.

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.

Inkjet-Printed Dual-Mode Electrochromic and Electroluminescent Displays Incorporating Ecofriendly Materials

Displays and indicators are an integral component of everyday electronics. However, the short lifecycle of most applications is currently contributing to the unsustainable growth of electronic waste. In this work, we utilize ecofriendly materials in combination with sustainable processing techniques to fabricate inkjet-printed, ecofriendly dual-mode displays (DMDs). These displays can be used in a reflective mode or an emissive mode by changing between DC and AC operation due to the combination of an electrochromic (EC) and electrochemiluminescent (ECL) layer in a single device. The EC polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) serves as the reflective layer, while an ECL gel made of dimethylsulfoxide (DMSO), poly(lactic-co-glycolic acid) (PLGA), 1-butyl-3-methylimidazoliumbis(oxalato)borate (BMIMBOB), and tris(bipyridine)ruthenium(II) chloride (Ru²⁺(bpy)₃Cl₂) enables the emissive mode. The final dual-mode devices exhibited their maximum optical power output of 52 mcd/m² at 4 V and 40 Hz and achieved an EC contrast of 45% and a coloration efficiency of 244 cm²/C at a wavelength of 690 nm. The fabricated devices showed clear readability in dark and light conditions when operated in reflective or emissive modes. This work demonstrates the applicability of ecofriendly and potentially biodegradable materials to reduce the amount of hazardous components in versatile display technologies.

Self-Driven Electrochromic Window System Cu/WOx-Al3+/GR with Dynamic Optical Modulation and Static Graph Display Functions

Electrochromic devices with unique advantages of electrical/optical bistability are highly desired for energy-saving and information storage applications. Here, we put forward a self-driven Al-ion electrochromic system, which utilizes WO_x films, Cu foil, and graphite rod as electrochromic optical modulation and graph display electrodes, coloration potential supplying electrodes, and bleaching potential supplying electrodes, respectively. The inactive Cu electrode can not only realize the effective Al³⁺ cation intercalation into electrochromic WO_x electrodes but also eliminate the problem of metal anode consumption. The electrochromic WO_x electrodes cycled in Al³⁺ aqueous media exhibit a wide potential window (∼1.5 V), high coloration efficiency (36.0 cm²/C), and super-long-term cycle stability (>2000 cycles). The dynamic optical modulation and static graph display function can be achieved independently only by switching the electrode connection mode, thus bringing more features to this electrochromic system. For a large-area electrochromic system (10 × 10 cm²), the absolute transmittance value in its color-neutral state can reach about 41% (27%) at 633 nm (780 nm) by connecting the Cu and WO_x electrodes for 140 s. The original transparent state can be readily recovered by replacing the Cu foil with the graphite rod. This work throws light on next-generation electrochromic applications for optical/thermal modulation, privacy protection, and information display.

Recent Advances in Inorganic Electrochromic Materials from Synthesis to Applications: Critical Review on Functional Chemistry and Structure Engineering

For the assembly of electrochromic devices (ECDs) generally with multilayer structures, supportive components usually are needed to be incorporated with EC materials. The reasonable project and development of ECDs will achieve broad expected applications. In this study, we reviewed several impressive methods to design and fabricate ECDs with high-performance and versatility based on recent frontier research. The first part of the review is centered on the desirability and strengthening mechanism of nanostructured inorganic EC materials. The second part illustrates the recent advances in transparent conductors. We then summarize the demands and means to modify the formation of electrolytes for practicable ECDs. Moreover, efforts to increase the compatibility with the EC layer and ion capacity are delineated. In the end, the application prospects of inorganic ECDs are further explored, which offers a guideline for the industrialization process of ECDs.

Self-Driven Infrared Electrochromic Device with Tunable Optical and Thermal Management

Electrochromic devices (ECDs) exhibiting tunable optical and thermal modulation in the infrared (IR) region have attracted extensive attention in recent years due to their attractive application prospects in both military and civilian settings. However, considering the continuous energy supply needed for driving the device operation, it is desired to develop advanced IR-ECDs with low energy consumption. Herein, a flexible self-driven IR-ECD is constructed for achieving variable optical and thermal management in a low-energy mode. In this device, a built-in potential difference of 1.36 V exists between the EC polyaniline cathode and the aluminum foil anode. Consequently, there is a rapid and obvious increase in the IR reflectance of the device after connecting the two electrodes. Such a self-driven reflectance contrast is over 20% at the wavelength of 1500 nm, and the coloration efficiency of the device reaches up to 93.6 cm² C^-1. Meanwhile, the maximum apparent temperature modulation on the surface of the device reaches up to 5.6 °C. Then, the self-driven IR-ECD could recover to its original state driven by a solar cell, indicating good reversibility and stability. We anticipate that this work may provide a new insight into developing advanced self-driven IR-ECDs for applications in dynamic military camouflage and commercial thermal control.