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.

MXene-based all-solid flexible electrochromic microsupercapacitor.

With the increasing demand for multifunctional optoelectronic devices, flexible electrochromic energy storage devices are being widely recognized as promising platforms for diverse applications. However, simultaneously achieving high capacitance, fast color switching and large optical modulation range is very challenging. In this study, the MXene-based flexible in-plane microsupercapacitor was fabricated via a mask-assisted spray coating approach. By adding electrochromic ethyl viologen dibromide (EVB) into the electrolyte, the device showed a reversible color change during the charge/discharge process. Due to the high electronic conductivity of the MXene flakes and the fast response kinetics of EVB, the device exhibited a fast coloration/bleaching time of 2.6 s/2.5 s, a large optical contrast of 60%, and exceptional coloration efficiency. In addition, EVB acted as a redox additive to reinforce the energy storage performance; as a result, the working voltage window of the Ti3C2-based symmetric aqueous microsupercapacitor was extended to 1 V. Moreover, the device had a high areal capacitance of 12.5 mF cm-2 with superior flexibility and mechanical stability and showed almost 100% capacitance retention after 100 bending cycles. The as-prepared device has significant potential for a wide range of applications in flexible and wearable electronics, particularly in the fields of camouflage, anticounterfeiting, and displays.

Breakthrough application of electrochromism: Multifunctional artificial muscle.

In the article (Advanced Materials 2023; 2305914, https://doi.org/10.1002/adma.202305914) reported by Wang et al., electrochemically driven multifunctional electrochromic artificial muscles (EAMs) are demonstrated with intricate actuation and eye-catching color-change behaviors, which were assembled from V2O5 nanowires-carbon nanotube fibers-based high-twist electrochromic artificial muscle yarn (EAMY). With combined wet winding and wet twisting, excellent mechanical properties and uniform color change were achieved in the core-sheath EAMYs. Followed by hot pouring and molding of gel electrolyte, the contact problem between electrode and electrolyte was resolved and EAMs were fabricated with stable operation in the air, harvesting a high shrinkage stroke of 12% and a high reflectivity contrast of 51%. The judicious device architecture design and integration of multifunctionality will open new avenues for electrochromic technology.

Adaptive Thermal Management Radiative Cooling Smart Window with Perfect Near-Infrared Shielding.

The architectural window with spectrally selective features and radiative cooling is an effective way to save building energy consumption. However, architectural windows that combine both functions are currently based on micro-nano photonic structures, which undoubtedly hinder their commercial application due to the complexity of manufacture. Herein, a novel tunable visible light transmittance radiative cooling smart window (TTRC smart window) with perfect near-infrared (NIR) shielding ability is manufactured via a mass-producible scraping method. TTRC smart window presents high luminous transmittance (Tlum = 56.8%), perfect NIR shielding (TNIR = 3.4%), bidirectional transparency adjustment ability unavailable in other transparent radiative coolers based on photonic structures (ΔTlum = 54.2%), and high emittance in the atmospheric window (over 94%). Outdoor measurements confirm that smart window can reduce 8.2 and 6.6 °C, respectively, compared to ordinary glass and indium tin oxide (ITO) glass. Moreover, TTRC smart window can save over 20% of annual energy in the tropics compared to ITO and ordinary glass. The simple preparation method employed in this work and the superior optical properties of the smart window have significantly broadened the scope of application of architectural windows and advanced the commercialization of architectural windows.

Quadruple Control Electrochromic Devices Utilizing Ce4W9O33 Electrodes for Visible and Near-Infrared Transmission Intelligent Modulation.

Electrochromic smart windows are promising for building energy savings due to their dynamic regulation of the solar spectrum. Restricted by materials or traditional complementary device configuration, precisely and independently controlling of visible (VIS) and near-infrared (NIR) light is still on the drawing board. Herein, a novel Zn2+ electrochemically active Ce4W9O33 electrode is reported, which demonstrates three distinct states, including VIS and NIR transparent "bright and warm" state, VIS and NIR opaque "dark and cool" state, VIS transparent and NIR opaque "bright and cool" state. A dual-operation mode electrochromic platform is also presented by integrating Ce4W9O33/NiO complementary device and Zn anode-based electrochromic device (Ce4W9O33/Zn/NiO device). Such a platform enables an added VIS opaque and NIR transparent "dark and warm" state, thus realizing four color states through individually controlling Ce4W9O33 and NiO electrodes, respectively. These results present an effective approach for facilitating electrochromic windows more intelligent to weather/season conditions and personal preferences.

A hydrophobic alloy-coated Zn anode for durable electrochromic devices.

To mitigate Zn corrosion, dendrite growth and hydrogen evolution reactions (HER) in Zn-anode based electrochromic devices, hydrophobic CuZn5 alloy was coated on Zn@CuZn with lower nucleation potential, high coulombic efficiency, inhibited HER, and prolonged reversibility, enabling improved switching kinetics and cycling stability in an electrochromic Zn@CuZn||Prussian Blue (PB) device.

Transparent metal oxide interlayer enabling durable and fast-switching zinc anode-based electrochromic devices.

Growing energy and environmental challenges have imposed higher requirements for the development of novel multifunctional energy storage and energy-saving devices. Electrochromic devices having similar configurations and working mechanisms with secondary batteries exhibit promising applications in dual-functional electrochromic-energy storage (ECES) devices. Electrochromic Prussian blue (PB) as typical battery cathodes are of great interest for ECES devices although they suffer from poor stability and limited capacity. In this study, a transparent metal oxide (NiO nanosheets) interlayer was incorporated to enhance the structural stability and capacity of PB while offering enlarged optical modulation (ΔT) and accelerated switching kinetics in the NiO/PB film. Impressively, the NiO/PB nanocomposite film exhibited a high areal capacity of 50 mA h m-2 and excellent electrochemical stability, simultaneously manifesting a large ΔT (73.2% at 632.8 nm), fast switching time (tc = 1.4 s, tb = 2.6 s) and higher coloration efficiency (CE = 54.9 cm2 C-1), surpassing those of the bare PB film (ΔT = 69.1% at 632.8 nm, tc = 1.6 s, tb = 4.1 s, CE = 50.9 cm2 C-1). Finally, a prototype zinc anode-based electrochromic device assembled with NiO/PB nanocomposite film exhibited a self-bleaching function and ΔT retention of up to 92% after 1000 cycles, and a 100 cm2 large area device was also demonstrated for high performance. Such a transparent metal oxide interlayer has enabled the construction of durable and fast-switching dual-functional zinc anode-based electrochromic devices and will inspire more efforts in designing novel multifunctional ECES devices.

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.

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.

Reversible Zn2+ Insertion in Tungsten Ion-Activated Titanium Dioxide Nanocrystals for Electrochromic Windows.

Zinc-anode-based electrochromic devices (ZECDs) are emerging as the next-generation energy-efficient transparent electronics. We report anatase W-doped TiO2 nanocrystals (NCs) as a Zn2+ active electrochromic material. It demonstrates that the W doping in TiO2 highly reduces the Zn2+ intercalation energy, thus triggering the electrochromism. The prototype ZECDs based on W-doped TiO2 NCs deliver a high optical modulation (66% at 550 nm), fast spectral response times (9/2.7 s at 550 nm for coloration/bleaching), and good electrochemical stability (8.2% optical modulation loss after 1000 cycles).

Transparent Zinc-Mesh Electrodes for Solar-Charging Electrochromic Windows.

Newly born zinc-anode-based electrochromic devices (ZECDs), incorporating electrochromic and energy storage functions in a single transparent platform, represent the most promising technology for next-generation transparent electronics. As the existing ZECDs are limited by opaque zinc anodes, the key focus should be on the development of transparent zinc anodes. Here, the first demonstration of a flexible transparent zinc-mesh electrode is reported for a ZECD window that yields a remarkable electrochromic performance in an 80 cm2 device, including rapid switching times (3.6 and 2.5 s for the coloration and bleaching processes, respectively), a high optical contrast (67.2%), and an excellent coloration efficiency (131.5 cm2 C-1 ). It is also demonstrated that such ZECDs are perfectly suited for solar-charging smart windows as they inherently address the solar intermittency issue. These windows can be colored via solar charging during the day, and they can be bleached during the night by supplying electrical energy to electronic devices. The ZECD smart window platform can be scaled to a large area while retaining its excellent electrochromic characteristics. These findings represent a new technology for solar-charging windows and open new opportunities for the development of next-generation transparent batteries.

Transparent inorganic multicolour displays enabled by zinc-based electrochromic devices.

Electrochromic displays have been the subject of extensive research as a promising colour display technology. The current state-of-the-art inorganic multicolour electrochromic displays utilize nanocavity structures that sacrifice transparency and thus limit their diverse applications. Herein, we demonstrate a transparent inorganic multicolour display platform based on Zn-based electrochromic devices. These devices enable independent operation of top and bottom electrochromic electrodes, thus providing additional configuration flexibility of the devices through the utilization of dual electrochromic layers under the same or different colour states. Zn-sodium vanadium oxide (Zn-SVO) electrochromic displays were assembled by sandwiching Zn between two SVO electrodes, and they could be reversibly switched between multiple colours (orange, amber, yellow, brown, chartreuse and green) while preserving a high optical transparency. These Zn-SVO electrochromic displays represent the most colourful transparent inorganic-based electrochromic displays to date. In addition, the Zn-SVO electrochromic displays possess an open-circuit potential (OCP) of 1.56 V, which enables a self-colouration behaviour and compelling energy retrieval functionality. This study presents a new concept integrating high transparency and high energy efficiency for inorganic multicolour displays.

Simultaneously enabling dynamic transparency control and electrical energy storage via electrochromism.

Transparency-switchable electrochromic devices (ECDs) offer promising applications, including variable optical attenuators, optical shutters, optical filters, and smart windows for energy-efficient buildings. However, the operation of conventional ECDs requires external voltages to trigger coloration/de-coloration processes, which makes them far from being an optimal energy-efficient technology. Electrochromic batteries that incorporate electro-optical modulation and electrical energy storage functionalities in a single platform, are highly-promising in the realization of energy-efficient ECDs. Herein, we report a novel Zn-Prussian blue (PB) system for aqueous electrochromic batteries. By utilizing different dual-ion electrolytes with various cations (e.g. Zn2+-K+ and Zn2+-Al3+), the Zn-PB electrochromic batteries demonstrate excellent performance. We show that the K+-Zn2+ dual-ion electrolyte in the Zn-PB configuration endows a rapid self-bleaching time (2.8 s), a high optical contrast (83% at 632.8 nm), and fast switching times (8.4 s/3 s for the bleaching/coloration processes). Remarkably, the aqueous electrochromic battery exhibits a compelling energy retrieval of 35.7 mW h m-2, where only 47.5 mW h m-2 is consumed during the round-trip coloration-bleaching process. These findings may open a new direction for developing advanced net-zero energy-consumption ECDs.

Oxygen-Vacancy-Tunable Electrochemical Properties of Electrodeposited Molybdenum Oxide Films.

Molybdenum oxides have been widely studied in recent years, owing to their electrochromic properties, electrocatalytic activities for hydrogen evolution reactions (HERs) and excellent energy storage performance. These characteristics strongly depend on the valence states of Mo in the oxides such as IV, V, and VI, which can be efficiently altered through oxygen deficiencies within the oxides. Here, we present a colloidal electrodeposition method to introduce oxygen vacancies in such Mo oxide films. We prepared uniform MoO x films and investigated their electrochemical characteristics under different valence states IV, V, and VI. In this paper, we demonstrate that MoO2+ x films, where Mo in valence states IV and V, can be used for high-performance supercapacitor electrodes. Due to their high conductivity, they exhibit an areal capacitance of 89 mF cm-2 at 1 mA cm-2 and negligible capacitance loss within 600 cycles. Additionally, we demonstrate that, in a complementary electrochromic device configuration, the introduction of an MoO2+ x counter electrode remarkably lowers the activation potential of WO3 from -2 to -0.5 V and achieves a fully bleached state at 0.5 V. These properties make the MoO2+ x film an ideal counter electrode to store ions for an electrochromic device. Furthermore, MoO3- y films, where Mo in the valence states V and VI, are obtained by annealing the electrodeposited MoO2+ x film under 200 °C for 24 h. Such films exhibit an excellent catalytic for the HER with an overpotential of 201 mV. Furthermore, we show that MoO3 films, where Mo at its highest oxidation state (VI), can be obtained via annealing the MoO2+ x film at 300 °C for 6 h, and the resulting films exhibit battery characteristics. Our research provides a new and facile strategy to fabricate substoichiometric molybdenum oxide nanofilms and reveals the effect of different valences on the electrochemical performance of molybdenum oxide films, which opens new doorways for future research in the electrochemical applications of transition metal oxides.

Rechargeable Aqueous Electrochromic Batteries Utilizing Ti-Substituted Tungsten Molybdenum Oxide Based Zn2+ Ion Intercalation Cathodes.

Batteries are used in every facet of human lives. Desirable battery architectures demand high capacity, rechargeability, rapid charging speed, and cycling stability, all within an environmentally friendly platform. Many applications are limited by opaque batteries; thus, new functionalities can be unlocked by introducing transparent battery architectures. This can be achieved by incorporating electrochromic and energy storage functions. Transparent electrochromic batteries enable new applications, including variable optical attenuators, optical switches, addressable displays, touch screen devices, and most importantly smart windows for energy-efficient buildings. However, this technology is in the incipient state due to limited electrochromic materials having satisfactory optical contrast and capacity. As such, triggering electrochromism via Zn2+ intercalation is advantageous: Zn is abundant, safe, easily processed in aqueous electrolytes and provides two electrons during redox reactions. Here, enhanced Zn2+ intercalation is demonstrated in Ti-substituted tungsten molybdenum oxide, yielding improved capacity and electrochromic performance. This technique is employed to engineer cathodes exhibiting an areal capacity of 260 mAh m-2 and high optical contrast (76%), utilized in the fabrication of aqueous Zn-ion electrochromic batteries. Remarkably, these batteries can be charged by external voltages and self-recharged by spontaneously extracting Zn2+ , providing a new technology for practical electrochromic devices.

Rechargeable Zn2+/Al3+ dual-ion electrochromic device with long life time utilizing dimethyl sulfoxide (DMSO)-nanocluster modified hydrogel electrolytes.

Despite recent advances in hydrogel electrolytes for flexible electrochemical energy storage, ion conductors still exhibit some major shortcomings including low ionic conductivity and short lifetimes. As such, for applications in electrochromic batteries, a transparent, highly conductive electrolyte based on a dimethyl-sulfoxide (DMSO) modified polyacrylamide (PAM) hydrogel is being developed and implemented in a dual-ion Zn2+/Al3+ electrochromic device consisting of a Zn anode and WO3 cathode. Gelation in a DMSO : H2O mixed solvent leads to highly increased electrolyte retention in the hydrogel and prolonged life time for ionic conduction. The hydrogel-based electrochromic device offers a specific charge capacity of 16.9 µAh cm-2 at a high current density of 200 µA cm-2 while retaining 100% coulombic efficiency over 200 charge-discharge cycles. While the DMSO-modified electrolyte shows ionic conductivities up to 27 mS cm-1 at room temperature, the formation of DMSO : H2O nanoclusters enables ionic conduction even at temperatures as low as -15 °C and retention of ionic conduction over more than 4 weeks. Furthermore, the electrochromic WO3 cathode gives the device a controllable absorption with up to 80% change in transparency. Based on low-cost, earth abundant materials like W (tungsten), Zn (zinc) and Al (aluminum) and a scalable fabrication process, the introduced hydrogel-based electrochromic device shows great potential for next-generation flexible and wearable energy storage systems.

Correction: Rechargeable Zn2+/Al3+ dual-ion electrochromic device with long life time utilizing dimethyl sulfoxide (DMSO)-nanocluster modified hydrogel electrolytes.

[This corrects the article DOI: 10.1039/C9RA06785J.].

Solution-Processed Interfacial PEDOT:PSS Assembly into Porous Tungsten Molybdenum Oxide Nanocomposite Films for Electrochromic Applications.

Electrochromic devices (ECDs) have received increased attention for applications including optoelectronics, smart windows, and low-emission displays. However, it has been recognized that the ECDs with transition-metal oxide (TMO) electrodes possess a high charge transport barrier because of their poor electrical conductivity, which limits their electrochromic performance. In this work, we addressed this limitation by utilizing a conjugated polymer to fabricate an organic-inorganic nanocomposite film that decreases the charge transport barrier of typical TMO electrodes. Using a conventional spray-layer-by-layer (spray-LbL) deposition technique, we demonstrate an electrochromic film composed of porous layers of tungsten molybdenum oxide (W0.71Mo0.29O3) nanorods permeated with an interconnected conductive layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The introduction of PEDOT:PSS is shown to significantly reduce the charge transport barrier, allowing the nanocomposite W0.71Mo0.29O3/PEDOT:PSS electrode to exhibit significantly improved electrochromic switching kinetics compared with the deposited W0.71Mo0.29O3 films. Furthermore, the optical contrast of the nanocomposite electrode was observed to be superior to both pure PEDOT:PSS and W0.71Mo0.29O3 electrodes, with a performance that exceeded the linearly predicted contrast of combining the pure films by 23%. The enhanced performance of the PEDOT:PSS-intercalated porous W0.71Mo0.29O3 nanocomposite electrodes and the facile synthesis through a spray-LbL method demonstrate a viable strategy for preparing fast assembling high-performance nanocomposite electrodes for a wide variety of electrochemical devices.