Ultra-Low Power Electrochromic Heat Shutters Through Tailoring Diffusion-Controlled Behaviors

3D Printable Supramolecular Viologen-Cationic Polyurethane Ionotronics for Multimodal Sensing and Displays

Ionic polyurethanes with excellent properties have garnered significant attention in flexible wearables. However, it is still challenging to achieve ionic polyurethane ionotronics with both excellent mechanical properties and functionalization. Here, a series of hydroxypropyl viologen (HDPV) cationic-based supramolecular polyurethane with tunable strength (7.6-76.6 MPa), toughness (29.1-285.3 MJ m-3), and elongation (499.8%-1102.3%) are developed by balancing HDPV cations and dynamic sextuple hydrogen bonds into the polyurethane. Dynamic modulation of the mechanical and electrochromic properties of the polyurethane can be achieved by adjusting the content of HDPV cations and dynamic sextuple bonds. Strong electrostatic interactions between the HDPV cationic-based polyurethane and the ionic liquid resulted in the preparation of ionogels with excellent pressure/strain and temperature sensing properties. Additionally, benefiting from the redox properties of the polycationic backbone, electrochromic devices fabricated from HDPV cationic-based polyurethane demonstrated a high modulation range of 79.1%, a certain degree of color memory effect, and excellent cycling stability. Shape customization of flexible electrochromic devices of HDPV cationic-based polyurethane can be achieved by 3D printing technology. The study paves a new avenue for the fabrication of flexible visual ionotronics with high stability and versatility.

Full Spectrum Electrochromic WO3 Mechanism and Optical Modulation via Ex Situ Spectroscopic Ellipsometry: Effect of Li+ Surface Permeation

Tungsten oxide (WO3) electrochromic devices are obtaining increasing interest due to their color change and thermal regulation. However, most previous work focuses on the absorption or transmission spectra of materials, rather than the optical parameters evolution in full spectrum in the electrochromic processes. Herein, we developed a systematic protocol of ex situ methods to clarify the evolutions of subtle structure changes, Raman vibration modes, and optical parameters of WO3 thin films in electrochromic processes as stimulated by dosage-dependent Li+ insertion. We obtained the below information by ex situ spectroscopic ellipsometry. (1) Layer-by-layer Li+ embedding mechanism demonstrated by individual film thickness analysis. (2) The details of its optical leap in the Brillouin zone in the full spectral. (3) The optical constants varied with the Li+ insertion in the ultraviolet, visible, and near-infrared bands, demonstrating the potential for applications in chip fabrication, deep-sea exploration, and optical measurements. (4) Simulated angular modulation laws of WO3 films for full spectra in different Li+ insertion states. This ex situ method to study the optical properties of electrochromic devices are important for monitoring phase transition kinetics, the analysis of optical leaps, and the study of ion diffusion mechanisms and the stoichiometry-dependent changes in optical constants over the full spectral. This work shows that electrochromic films in Li+ surface permeation can be applied in the field of zoom lenses, optical phase modulators, and other precision optical components. Our work provides a new solution for the development of zoom lenses and a new application scenario for the application of electrochromic devices.

Employing polyaniline/viologen complementarity to enhance coloration and charge dissipation in multicolor electrochromic display with wide modulation range

Multicolor electrochromic devices have gained attention widely. To support the development of multicolor electrochromic devices, we studied complementary combinations of a multicolor switchable polyaniline (PANI) electrode and 1-methyl-4,4'-bipyridyl iodide (MBI). In particular, MBI acting as an electrolyte and cathodic electrochromic layer can not only simplify the architecture of a device, but also support the color richness of the device simultaneously. Wide band optical modulation in visible light (58.1% at 550 nm) and near-infrared light (35% at 800 nm) confirms the advantageous optical properties of the combination, possessing a wide color gamut range over a range of working voltages adjustable for red, yellow, green, blue, and purple, each having a high color contrast of up to 73.8. This is accompanied by the excellent electrochemical performances of the mentioned combination, such as a fast response time of 1 s/1.9 s (modulating 77%-colored/bleached) with good cycle stability, and high coloration efficiency of 140.63 cm2/C. In addition, utilizing a screen-printed polyvinyl alcohol (PVA) as a masking barrier layer, it is possible to display patterned anti-counterfeit information within the application. Given these electrochromic performance properties, it is considered a readily feasible strategy to utilize PANI and MBI combination to develop novel electrochromic devices, which can be used widely in the areas of smart packaging, smart labels, and flexible smart windows associated with specific application scenarios.

High-Voltage Pulse-Assisted Operation of Single-Layer Electrochromic Systems for High Performance and Reliability

A single-layer electrochromic device (SL-ECD) based on ionic conductors containing EC chromophores provides a very simple platform that can be readily fabricated by sandwiching the EC layer between two electrodes. The operation of SL-ECDs is governed by the diffusion of redox species due to their SL structure, which causes a relatively slow dynamic response. In this study, we propose an effective high-voltage pulse injection strategy to improve the performance of SL-ECDs. Applying a programmed voltage wave composed of DC and high-voltage pulses promotes coloration/bleaching switching without degrading device stability, which is more advantageous than applying high DC voltages. We modified the input voltage profile by considering fundamental parameters, such as the amplitude and duty ratio of additional voltage pulses. The coloration and bleaching dynamic responses with the optimized voltage wave are ∼62 and ∼20% faster, respectively, compared with those with the simple DC input. Furthermore, the additionally injected pulse aids in increasing the coloration efficiency from ∼95.3 to ∼168.6 cm2 C-1. Another notable feature of this system is that the device operates stably when a programmed voltage wave is used. These results indicate that the concept of high-voltage pulse-assisted operation of SL-ECDs is a straightforward but effective method for improving device performance without changing the EC chromophore or device structure.

Silver Nanoparticle-Embedded Conductive Hydrogels for Electrochemical Sensing of Hydroquinone

In this work, a conductive hydrogel was successfully synthesized, taking advantage of the high number density of active amino and hydroxyl groups in carboxymethyl chitosan and sodium carboxymethyl cellulose. These biopolymers were effectively coupled via hydrogen bonding with the nitrogen atoms of the heterocyclic rings of conductive polypyrrole. The inclusion of another biobased polymer, sodium lignosulfonate (LS), was effective to achieve highly efficient adsorption and in-situ reduction of silver ions, leading to silver nanoparticles that were embedded in the hydrogel network and used to further improve the electro-catalytic efficiency of the system. Doping of the system in the pre-gelled state led to hydrogels that could be easily attached to the electrodes. The as-prepared silver nanoparticle-embedded conductive hydrogel electrode exhibited excellent electro-catalytic activity towards hydroquinone (HQ) present in a buffer solution. At the optimum conditions, the oxidation current density peak of HQ was linear over the 0.1-100 μM concentration range, with a detection limit as low as 0.12 μM (signal-to-noise of 3). The relative standard deviation of the anodic peak current intensity was 1.37% for eight different electrodes. After one week of storage in a 0.1 M Tris-HCl buffer solution at 4 °C, the anodic peak current intensity was 93.4% of the initial current intensity. In addition, this sensor showed no interference activity, while the addition of 30 μM CC, RS, or 1 mM of different inorganic ions does not have a significant impact on the test results, enabling HQ quantification in actual water samples.

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.

Investigating Formate, Sulfate, and Halide Anions in Reversible Zinc Electrodeposition Dynamic Windows

Reversible metal electrodeposition (RME) is an emerging and promising method for designing dynamic windows with electrically controllable transmission, excellent color neutrality, and wide dynamic range. Zn is a viable option for metal-based dynamic windows due to its fast switching kinetics and reversibility despite its very negative deposition voltage. In this manuscript, we study the effect of the supporting electrolyte anions for Zn electrodeposition on transparent tin-doped indium oxide. Through systematic additions or removal of components of the electrolytes, we are able to establish a link between the anions and the effectiveness of Zn RME. This insight allows us to design practical two-electrode 25 cm² Zn dynamic windows that switch to <1% within 20 s. Lastly, we demonstrate that the accumulation of Zn(OH)₂ species on the working electrode degrades the optical contrast of Zn windows during long-term cycling. However, the elimination of these species through acid immersion allows the windows to cycle at least 500 times. Reversible Zn electrodeposition in the presence of a polyethylene glycol additive further improves the cycle life to greater than 1000 cycles. Taken together, these studies highlight important design principles for the construction of robust dynamic windows based on Zn RME.

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.

Heat-Insulating Black Electrochromic Device Enabled by Reversible Nickel-Copper Electrodeposition

An electrochromic device (ECD), which can switch between black and transmissive states under electrical bias, is a promising candidate for smart windows due to its color neutrality and excellent durability. Most of the black ECDs are achieved through a reversible electrodeposition and dissolution mechanism; however, they typically suffer from relatively poor cycling stability and a slow coloration/bleaching time. Herein, we present a heat-insulating black ECD with a gel electrolyte that operates via reversible Ni-Cu electrodeposition and dissolution. With the adoption of a Cu alloying strategy and a compatible gel electrolyte, this two-electrode ECD (5.0 cm × 2.5 cm) can achieve a cycling stability of 1500 cycles with transmittance modulation up to 55.2% in short coloration (6.2 s) and bleaching times (13.2 s) at a wavelength of 550 nm. Additionally, the ECD can be switched from the transparent state (visible light transmittance: 0.566) to the opaque state (visible light transmittance: 0.003) within 1 min, reaching transmittance less than 5% across the visible-near-infrared spectrum (400-2000 nm) to efficiently block solar heat. Besides, in the voltage-off state, the black Ni-Cu alloy film can be sustained for more than 60 min (at room temperature, λ = 550 nm). Under infrared irradiation (170 W/m²) for 30 min, the black ECD blocks up to 35.0% of infrared radiation, which not only effectively prevents the heat transmission for energy management but also finds potential applications for promoting indoor human health and indoor farming.

DNA Optoelectronics: Versatile Systems for On-Demand Functional Electrochemical Applications

Herein, we propose innovative deoxyribonucleic acid (DNA)-based gels and their applications in diverse optoelectronics. We prepared the optoelectronic DNA-based gels (^OpDNA Gel) through molecular complexation, that is, groove binding and ionic interactions of DNA and 1,1'-diheptyl-4,4'-bipyridinium (DHV). This process is feasible even with sequence-nonspecific DNA extracted from nature (e.g., salmon testes), resulting in the expansion of the application scope of DNA-based gels. ^OpDNA Gel possessed good mechanical characteristics (e.g., high compressibility, thermoplasticity, and outstanding viscoelastic properties) that have not been observed in typical DNA hydrogels. Moreover, the electrochromic (EC) characteristics of DHV were not lost when combined with ^OpDNA Gel. By taking advantage of the facile moldability, voltage-tunable EC behavior, and biocompatibility/biodegradability of ^OpDNA Gel, we successfully demonstrated its applicability in a variety of functional electrochemical systems, including on-demand information coding systems, user-customized EC displays, and microorganism monitoring systems. The ^OpDNA Gel is a promising platform for the application of DNA-based biomaterials in electrochemical optoelectronics.

Wide-Spectrum Modulated Electrochromic Smart Windows Based on MnO2/PB Films

Inorganic materials have been extensively studied for visible electrochromism in the past few decades. However, the single inorganic electrochromic (EC) material commonly exhibits a single color change, leading to a narrow spectrum of modulation, which offsets or limits the maximally energy-saving ability. Here, we present a wide-spectrum modulated EC device designed by combining the complementary EC nanocomposite of manganese dioxide (MnO₂) and Prussian blue (PB) for enhanced energy savings. Porous MnO₂ nanostructures serve as host frameworks for the templated growth of PB, resulting in MnO₂/PB nanocomposites. The complementary optical modulation ranges of MnO₂ and PB enable a widen-spectrum modulation across the solar region with the development of the MnO₂/PB nanocomposite. The colored MnO₂/PB device exhibited an optical modulation of 32.1% in the wide solar spectrum range of 320-1100 nm and blocked 72.0% of the solar irradiance. Furthermore, fast switching responses (2.7 s for coloration and 2.1 s for bleaching) and a high coloration efficiency (83.1 cm²·C^-1) of the MnO₂/PB EC device are also achieved. The high EC performance of the MnO₂/PB nanocomposite device provides a new strategy for the design of high-performance energy-saving EC smart windows.

Electrochromism of Viologen/Polymer Composite: From Gel to Insulating Bulk for High-Voltage Applications

Power equipment operates under high voltages, inducing space charge accumulation on the surface of key insulating structures, which increases the risk of discharge/breakdown and the possibility of maintenance workers experiencing electric shock accidents. Hence, a visualized non-equipment space charge detection method is of great demand in the power industry. Typical electrochromic phenomenon is based on redox of the material, triggered by a voltage smaller than 5 V with a continuous current in μA~mA level, which is not applicable to high electric fields above 10⁶ V/m with pA~nA operation current in power equipment. Until now, no naked-eye observation technique has been realized for space charge detection to ensure the operation of power systems as well as the safety of maintenance workers. In this work, a viologen/poly(vinylidene fluoride-co-hexafluoropropylene)(P(VDF–HFP)) composite is investigated from gel to insulating bulk configurations to achieve high-voltage electrical-insulating electrochromism. The results show that viologen/P(VDF–HFP) composite bulk can withstand high electric fields at the 10⁷ V/m level, and its electrochromism is triggered by space charges. This electrochromism phenomenon can be visually extended by increasing viologen content towards 5 wt.% and shows a positive response to voltage amplitude and application duration. As viologen/P(VDF–HFP) composite bulk exhibits a typical electrical insulating performance, it could be attached to the surface of insulating structures or clamped between metal and insulating materials as a space charge accumulation indicator in high-voltage power equipment.

Polymeric Ion Conductors Based on Sono-Polymerized Zwitterionic Polymers for Electrochromic Supercapacitors with Improved Shelf-Life Stability

Monolithic electrochromic supercapacitors (ECSs) have attracted increasing interest in recent electrochemical electronics due to their simplicity and unique ability to visually indicate stored energy levels. One crucial challenge for practical use is the improvement of shelf-life. Herein, zwitterionic (ZI) ionogels are proposed as effective electrolytes to reduce the self-discharging decay of ECSs. All-in-one ZI electrochromic (EC) gels are produced by one-pot sono-polymerization. The presence of ZI moieties in the gel does not affect the EC characteristics of chromophores. In addition, excellent capacitive properties in areal capacitance and coulombic efficiency are presented owing to the alignment of ZI units under an electric field and the formation of ion migration channels where rapid ion transport is allowed. Furthermore, the shelf-life of the ZI gel-based ECS is significantly improved by adjusting the interaction between polymeric gelators and ion species. The ZI gel-based ECS is expected to be a key platform for future smart energy storage devices.

Ru(II)-Based Metallo-Supramolecular Polymer with Tetrakis(N-methylbenzimidazolyl)bipyridine for a Durable, Nonvolatile, and Electrochromic Device Driven at 0.6 V

Low-voltage operation, high durability, and long memory time are demanded for electrochromic (EC) display device applications. Metallo-supramolecular polymers (MSPs), composed of a metal ion and ditopic ligand, are one of the recently developed EC materials, and the ligand modification is expected to tune the redox potential of MSP. In order to lower the redox potential of MSP, tetrakis(N-methylbenzimidazolyl)bipyridine (L_Bip) was designed as an electronically rich ligand. Ru-based MSP (polyRu-L_Bip) was successfully synthesized by 1:1 complexation of RuCl₂(DMSO)₄ with L_Bip. The molecular weight (M_w) was high (8.8 × 10⁶ Da) enough to provide a simple ¹H NMR spectrum, of which the proton peaks could be assigned by the comparison with the spectrum of the corresponding mono-Ru complex. The redox potential (E_1/2) between Ru(II/III) was 0.51 V versus Ag/Ag⁺, which was much lower than the redox potential of previously reported Ru-based MSP with bis(terpyridyl)benzene (0.95 V vs Ag/Ag⁺). The polymer film exhibited reversible, distinct color changes between violet and light green-yellow upon applying very low potentials of 0 and 0.6 V vs Ag/Ag⁺, respectively. The appearance and disappearance of the metal-to-ligand charge transfer absorption by the electrochemical redox between Ru(II/III) were confirmed using in situ spectro-electrochemical measurement. A solid-state EC device with polyRu-L_Bip was revealed to have large optical contrast (ΔT 54%), fast response time (1.37 s for bleaching and 0.67 s for coloration), remarkable coloration efficiency (571 cm²/C), and high durability for the repeated color changes more than 20,000 cycles. The device also showed a long optical memory time of up to 19 h to maintain 40% to the initial contrast under the open circuit conditions. It is considered that the stabilization of the Ru(III) state by L_Bip suppressed the self-coloring to Ru(II) inside the device.

Liquid/Liquid Interfacial Suzuki Polymerization Prepared Novel Triphenylamine-Based Conjugated Polymer Films with Excellent Electrochromic Properties

Preparing conjugated polymer films via interfacial Suzuki polymerization is a promising method for obtaining desirable electrochromic materials with desired structures. Here, a series of aryl boronic esters and triphenylamine-based aryl bromides were applied as precursors, and several polymer films were finally obtained via the liquid/liquid interfacial Suzuki polymerization reaction under mild conditions. FT-IR, UV, and Raman as well as electrochemistry, SEM, and EDS results all provide strong evidence for the formation of the desired polymer structures. Among them, the TPA-Wu (containing triphenylamine and alkyl-fluorene) film exhibits the best film-forming quality. Besides, these polymer films were applied in electrochromic applications. The results show that electrochromic properties can be affected by the quality of film formation. It is worth mentioning that the TPA-Wu film could achieve excellent electrochromic properties with reversible multicolor changes from transparent yellow to orange-red to blue-green under varying potentials. Compared to other triphenylamine-based electrochromic materials, the TPA-Wu film possessed the most desirable coloring efficiency, higher optical contrast, and shorter switching time. This work provides an existing general approach of liquid/liquid interfacial Suzuki polymerization for constructing conjugated polymer films toward electrochromic applications.

Reliable, High-Performance Electrochromic Supercapacitors Based on Metal-Doped Nickel Oxide

Herein, high-performance, reliable electrochromic supercapacitors (ECSs) are proposed based on tungsten trioxide (WO₃) and nickel oxide (NiO) films. To maximize device performance and stability, the stoichiometric balance between anode and cathode materials is controlled by carefully adjusting the thickness of the anodic NiO film while fixing the thickness of WO₃ to ∼660 nm. Then, a small amount (≤10 mol %) of metal (e.g., copper) is doped into the NiO film, improving the electrical conductivity and electrochemical activity. At a Cu doping level of 7 mol %, the resulting ECS exhibited the highest performance, including a high areal capacitance (∼14.9 mF/cm²), excellent coulombic efficiency (∼99%), wide operating temperature range (0-80 °C), reliable operation with high charging/discharging cyclic stability (>10,000 cycles), and good self-discharging durability. Simultaneously, the change in transmittance of the device is well synchronized with the galvanostatic charging/discharging curve by which the real-time energy storage status is visually indicated. Furthermore, the practical feasibility of the device is successfully demonstrated. These results imply that the ECS fabricated in this work is a promising potential energy storage platform and an attractive component for future electronics.