Self-supported one-dimensional materials for enhanced electrochromism

Full color control and patterned display device from cyan/magenta/yellow water-dispersed electrochromic polymer nanoparticles systems

Electrochromic polymers (ECPs) have great application potential in flexible displays, and there is an increasing expectation of using green methods to form ECP films. Herein, we propose a modified microemulsion method to prepare cyan/magenta/yellow (C/M/Y) water-dispersed electrochromic polymer nanoparticles (WDEN) systems. Three polymer films (WDECP-C/M/Y) maintain similar electrochemical properties compared to their corresponding organic solvent-based polymer films. It is intriguing that WDECP-C/M/Y exhibit better electrochromic properties in terms of higher cycling stability (97.24%, 95.05%, and 52.84%, respectively) and faster switching time (0.94 s, 1.09 s, and 1.34 s for coloring time, respectively) due to the introduction of nanoparticles. In addition, it can achieve various desired colors by blending the C/M/Y WDEN systems in different ratios. The calculated chromaticity coordinates of the blending polymer films show close values to the experimental observation, and the calculated ΔE*abvalues range from 2.6 to 10.3, which may provide theoretical guidance for precisely color control. Finally, large-scale and patterned devices were assembled, which can achieve colored-to-colorless reversible electrochromism at a low driving voltage of 0-1.5 V. This work puts forward a universal and environmentally sustainable strategy to prepare WDEN systems, demonstrating their wide range of applications in display devices and electronic tags.

Assessing the Influence of Confinement on the Stability of Polyoxometalate-Functionalized Surfaces: A Soft Sequential Immobilization Approach for Electrochromic Devices

A functionalization process has been developed and the experimental conditions optimized allowing the immobilization of first-row transition metal (Mn+) containing polyoxometalates (POMs) with the formula [M(H2O)P2W17O61](10-n)- on transparent indium-tin oxide (ITO) electrodes for electrochromic applications. Both flat ITO grafted with 4-sulfophenyl moieties and sulfonate-functionalized vertically oriented silica films on ITO have been used as electrode supports to evaluate possible confinement effects provided by the mesoporous matrix on the stability of the modified surfaces and their electrochromic properties. Functionalization involved a two-step sequential process: (i) the immobilization of hexaaqua metallic ions, such as Fe(H2O)63+, onto the sulfonate-functionalized materials achieved through hydrogen bonding interactions between the sulfonate functions and aqua ligands (water molecules) coordinated to the metallic ions facilitating and stabilizing the attachment of the metallic ions to the sulfonated surfaces; (ii) their coordination to [P2W17O61]10- species to generate "in situ" the target [Fe(H2O)P2W17O61]7- moieties. Comparison of the characterized surfaces clearly evidenced a significant improvement in the long-term stability of the nanostructured [Fe(H2O)P2W17O61]7--functionalized silica films compared to the less constrained flat [Fe(H2O)P2W17O61]7--modified ITO electrodes for which a rapid loss of [P2W17O61]10- species was observed. Concordantly, the [Fe(H2O)P2W17O61]7- POM confined in the mesoporous films coated on ITO gave rise to much better and stable electrochromic properties, with a transmittance modulation of 40% at 515 nm.

The frontier of tungsten oxide nanostructures in electronic applications

Electrochromic (EC) glazing has garnered significant attention recently as a crucial solution for enhancing energy efficiency in future construction and automotive sectors. EC glazing could significantly reduce the energy usage of buildings compared to traditional blinds and glazing. Despite their commercial availability, several challenges remain, including issues with switching time, leakage of electrolytes, production costs, etc. Consequently, these areas demand more attention and further studies. Among inorganic-based EC materials, tungsten oxide nanostructures are essential due to its outstanding advantages such as low voltage demand, high coloration coefficient, large optical modulation range, and stability. This review will summarize the principal design and mechanism of EC device fabrication. It will highlight the current gaps in understanding the mechanism of EC theory, discuss the progress in material development for EC glazing, including various solutions for improving EC materials, and finally, introduce the latest advancements in photo-EC devices that integrate photovoltaic and EC technologies.

Recent Progress of Self-Supported Metal Oxide Nano-Porous Arrays in Energy Storage Applications

The demand for high-performance and cost-effective energy storage solutions for mobile electronic devices and electric vehicles has been a driving force for technological advancements. Among the various options available, transitional metal oxides (TMOs) have emerged as a promising candidates due to their exceptional energy storage capabilities and affordability. In particular, TMO nanoporous arrays fabricated by electrochemical anodization technique demonstrate unrivaled advantages including large specific surface area, short ion transport paths, hollow structures that reduce bulk expansion of materials, and so on, which have garnered significant research attention in recent decades. However, there is a lack of comprehensive reviews that discuss the progress of anodized TMO nanoporous arrays and their applications in energy storage. Therefore, this review aims to provide a systematic detailed overview of recent advancements in understanding the ion storage mechanisms and behavior of self-organized anodic TMO nanoporous arrays in various energy storage devices, including alkali metal ion batteries, Mg/Al-ion batteries, Li/Na metal batteries, and supercapacitors. This review also explores modification strategies, redox mechanisms, and outlines future prospects for TMO nanoporous arrays in energy storage.

Self-Powered Flexible Multicolor Electrochromic Devices for Information Displays

The development of self-powered flexible multicolor electrochromic (EC) systems that could switch different color without an external power supply has remained extremely challenging. Here, a new trilayer film structure for achieving self-powered flexible multicolor EC displays based on self-charging/discharging mechanism is proposed, which is simply assembled by sandwiching an ionic gel film between 2 cathodic nickel hexacyanoferrate (NiHCF) and Prussian blue (PB) nanoparticle films on indium tin oxide substrates. The display exhibits independent self-powered color switching of NiHCF and PB films with fast responsive time and high reversibility by selectively connecting the Al wire as anodes with the 2 EC films. Multicolor switching is thus achieved through a color overlay effect by superimposing the 2 EC films, including green, blue, yellow, and colorless. The bleaching/coloration process of the displays is driven by the discharging/self-charging mechanism for NiHCF and PB films, respectively, ensuring the self-powered color switching of the displays reversibly without an external power supply. It is further demonstrated that patterns can be easily created in the self-powered EC displays by the spray-coating method, allowing multicolor changing to convey specific information. Moreover, a self-powered ionic writing board is demonstrated based on the self-powered EC displays that can be repeatedly written freehand without the need of an external power source. We believe that the design concept may provide new insights into the development of self-powered flexible multicolor EC displays with self-recovered energy for widespread applications.

Synergistic Electric and Thermal Effects of Electrochromic Devices

Electrochromic devices are the preferred devices for smart windows because they work independently of uncontrollable environmental factors and rely more on the user's personal feelings to adjust actively. However, in practical applications, the ambient temperature still has an impact on device performance, such as durability, reversibility and switching performance, etc. These technical issues have significantly slowed down the commercialization of electrochromic devices (ECDs). It is necessary to investigate the main reasons for the influence of temperature on the device and make reasonable optimization to enhance the effectiveness of the device and extend its lifetime. In recent years, with the joint efforts of various outstanding research teams, the performance of electrochromic devices has been rapidly improved, with a longer lifetime, richer colors, and better color contrast. This review highlights the important research on temperature-dependent electrochromic properties in recent years. Also, the reported structures, mechanisms, characteristics, and methods for improving electrochromic properties are discussed in detail. In addition, the challenges and corresponding strategies in this field are presented in this paper. This paper will inspire more researchers to enrich the temperature-dependent properties of ECDs and their related fields with innovative means and methods to overcome the technical obstacles faced.

Emerging Electrochromic Materials and Devices for Future Displays

With the rapid development of optoelectronic fields, electrochromic (EC) materials and devices have received remarkable attention and have shown attractive potential for use in emerging wearable and portable electronics, electronic papers/billboards, see-through displays, and other new-generation displays, due to the advantages of low power consumption, easy viewing, flexibility, stretchability, etc. Despite continuous progress in related fields, determining how to make electrochromics truly meet the requirements of mature displays (e.g., ideal overall performance) has been a long-term problem. Therefore, the commercialization of relevant high-quality products is still in its infancy. In this review, we will focus on the progress in emerging EC materials and devices for potential displays, including two mainstream EC display prototypes (segmented displays and pixel displays) and their commercial applications. Among these topics, the related materials/devices, EC performance, construction approaches, and processing techniques are comprehensively disscussed and reviewed. We also outline the current barriers with possible solutions and discuss the future of this field.

Applications of Viologens in Organic and Inorganic Discoloration Materials

Viologen derived from 4,4'-bipyridine has attracted much attention because of its color changing properties with electron transfer, unique redox stability and structural diversity. These characteristics have led to its successful use in various applications, in particular in color-changing materials. In the past few years, researchers have been working on the syntheses of viologen-based color-changing functional materials, and such materials have been widely used in many fields. In photochromic materials, it is used as anti-counterfeiting material; in thermochromic, it is used as memory storage material, and in electrochromic, it is used as a battery material. This Review discusses the progress of viologen in organic and inorganic discoloration materials in recent years. The syntheses of viologen and its derivatives are summarized, and its application in the field of discoloration materials is introduced.

Pd Doped Co3O4 Loaded on Carbon Nanofibers as Highly Efficient Free-Standing Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions

Self-supporting electrodes usually show excellent electrocatalytic performance which does not require coating steps, additional polymer binders, and conductive additives. Rapid in situ growth of highly active ingredient on self-supporting electric conductors is identified as a straight forward path to prepare binder-free and integrated electrodes. Here, Pd-doped Co₃O₄ loaded on carbon nanofiber materials through electrospinning and heat treatment was efficiently synthesized, and used as a free-standing electrode. Benefiting from its abundant active sites, high surface area and effective ionic conduction capability from three-dimensional (3D) nanofiber framework, Pd-Co₃O₄@CNF works as bifunctional oxygen electrode and exhibits superior activity and stability superior to commercial catalysts.

Studies on transmittance modulation and ions transfer kinetic based on capacitive-controlled 2D V2O5inverse opal film for electrochromic energy storage application

Two-dimensional vanadium pentoxide inverse opal (2D V₂O₅IO) architecture was fabricated by polystyrene (PS) sphere template assisted electrodeposition process. In comparison to the un-templated V₂O₅film, the 2D V₂O₅IO 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 V₂O₅IO 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.

Evidence of oxygen bubbles forming nanotube embryos in porous anodic oxides

Anodic TiO2 nanotubes have been studied widely for two decades because of their regular tubular structures and extensive applications. However, the formation mechanism of anodic TiO2 nanotubes remains unclear, because it is difficult to find convincing evidence for popular field-assisted dissolution or field-assisted injection theories and the oxygen bubble model. Here, in a bid to find direct evidence that oxygen bubbles form nanotube embryos, a new method is applied to handle this challenge. Before nanotube formation, a dense cover layer was formed to make nanotubes grow more slowly. Many completely enclosed nanotube embryos formed by oxygen bubbles were found beneath the dense cover layer for the first time. The formation of these enclosed and hollow gourd-shaped embryos is convincing enough to prove that the nanotubes are formed by the oxygen bubble mold, similar to inflating a football, rather than by field-assisted dissolution. Based on the 'oxygen bubble model' and ionic current and electronic current theories, the formation and growth process of nanotube embryos is explained clearly for the first time. These interesting findings indicate that the 'oxygen bubble model' and ionic current and electronic current theories also apply to anodization of other metals.

Prussian Blue and Carbon-Dot Hybrids for Enhanced Electrochromic Performance

In this study, Prussian blue@Carbon-dot (PB@C-dot) hybrids have been developed by one-step hydrothermal method. The incorporation of C-dots into Prussian blue thin film as a way of improving its electrochromic performance was investigated. The structure of the PB@C-dot hybrid was characterized through X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The electrochromic properties showed that incorporation of 10 mL C-dots into the film showed higher optical contrast of 1.6 and superior coloration/bleaching response of 10 and 3 s. It is proposed that the C-dots component used in the construction of the PB@C-dot hybrid plays a key role to achieve superior electrochromic performance.

3D texturing of the air-water interface by biomimetic self-assembly

A simple, insoluble monolayer of fatty acid is shown to induce 3D nanotexturing of the air-water interface. This advance has been achieved through the study of monolayers of a methyl-branched long chain fatty acid, analogous to those found on the surface of hair and wool, directly at the air-water interface. Specular neutron reflectometry combined with AFM probing of deposited monolayers shows pronounced 3D surface domains, which are absent for unbranched analogues and are attributed to hydrocarbon packing constraints. The resulting surface topographies of the water far exceed the height perturbation that can be explained by the presence of capillary waves of a free liquid surface. These have hitherto been considered the only source of perturbation of the flatness of a planar water interface under gravity in the absence of topographical features from the presence of extended, globular or particulate matter. This amounts to a paradigm shift in the study of interfacial films and opens the possibility of 3D texturing of the air-water interface.

Advances in nanomaterials for electrochromic devices

This review article systematically highlights the recent advances regarding the design, preparation, performance and application of new and unique nanomaterials for electrochromic devices.

Electrochemistry and Rapid Electrochromism Control of MoO3/V2O5 Hybrid Nanobilayers

MoO3/V2O5 hybrid nanobilayers are successfully prepared by the sol-gel method with a spin- coating technique followed by heat -treatment at 350 °C in order to achieve a good crystallinity. The composition, morphology, and microstructure of the nanobilayers are characterized by a scanning electron microscope (SEM) and X-ray diffractometer (XRD) that revealed the a grain size of around 20-30 nm, and belonging to the monoclinic phase. The samples show good reversibility in the cyclic voltammetry studies and exhibit an excellent response to the visible transmittance. The electrochromic (EC) window displayed an optical transmittance changes (ΔT) of 22.65% and 31.4% at 550 and 700 nm, respectively, with the rapid response time of about 8.2 s for coloration and 6.3 s for bleaching. The advantages, such as large optical transmittance changes, rapid electrochromism control speed, and excellent cycle durability, demonstrated in the electrochromic cell proves the potential application of MoO3/V2O5 hybrid nanobilayers in electrochromic devices.

Highly Transparent Conductive Reduced Graphene Oxide/Silver Nanowires/Silver Grid Electrodes for Low-Voltage Electrochromic Smart Windows

Transparent conductive electrodes (TCEs) based on hybrid structures (silver nanowires) have been compressively reconnoitered in next-generation electronics such as flexible displays, artificial skins, smart windows, and sensors because of their admirable conductivity as well as flexibility, which make them favorable substitutes to replace ITO (indium tin oxide) as a transparent conductor. Nevertheless, silver-based TCEs grieve from poor stability because of the corrosion and oxidation of silver in electrolytes. To overcome these issues, a RGO (reduced graphene oxide) layer on silver was promoted to resolve the difficulties of corrosion and oxidation in the electrolyte. Moreover, we successfully designed and demonstrated low-voltage WO₃-based electrochromic devices (ECDs) with fabricated hybrid TCEs. The hybrid electrodes with RGO/silver nanowires/metal grid/PET (RAM) electrode exhibited improvements in the switching stability and optoelectronic properties, such as the sheet resistance (0.714 ohm/sq) as well as optical transparency of 90.9%. The coloration and bleaching behavior of the ECD was observed in an applied low-voltage range of -1.0 to 0.0 V with a maximum optical difference of 72% at 700 nm, which yielded a coloration efficiency (η) of ∼33.4 cm²/C. The highly conductive hybrid TCEs exhibit favorable features for numerous embryonic flexible electronics and optoelectronic devices.

Erasable memory properties of spectral selectivity modulated by temperature and bias in an individual CdS nanobelt-based photodetector

Single CdS nanobelt-based photodetectors are strongly dependent on bias and temperature. They not only show a strong photoresponse to close bandgap energy light with ultrahigh responsivity of approximately 10⁷ A W^-1, large photo-to-dark current ratio of 10⁴, photoconductive gain of 10⁷, and fast response and recovery speed at a large bias of 20 V, but can also show a weak photoresponse to above- and below-bandgap energy light. Moreover, their spectral response range can show tunable selectivity to above- and below-bandgap light, which can be accurately controlled by temperature and bias. More importantly, the modulated spectral response characteristics show excellent memory behaviour after reversible writing and erasing by using temperature and bias. In nanostructures, abundant surface states and stacking fault-related traps play a vital role in the ultrahigh photoresponse to bandgap light and the erasable memory effect on spectral response range selectivity. Given the erasable memory of the spectral response selectivity with excellent photoconduction performance, the CdS NBs possess important applications in new-generation photodetection and photomemory devices.

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

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

A CuPc-PANI composite film with good electrochromic properties and obvious pseudocapacitance performance was successfully prepared using in situ electrochemical methods.

Engineering Morphologies of Cobalt Pyrophosphates Nanostructures toward Greatly Enhanced Electrocatalytic Performance of Oxygen Evolution Reaction

Herein, a surfactant- and additive-free strategy is developed for morphology-controllable synthesis of cobalt pyrophosphate (CoPPi) nanostructures by tuning the concentration and ratio of the precursor solutions of Na4 P2 O7 and Co(CH3 COO)2 . A series of CoPPi nanostructures including nanowires, nanobelts, nanoleaves, and nanorhombuses are prepared and exhibit very promising electrocatalytic properties toward the oxygen evolution reaction (OER). Acting as both reactant and pseudo-surfactant, the existence of excess Na4 P2 O7 is essential to synthesize CoPPi nanostructures for unique morphologies. Among all CoPPi nanostructures, the CoPPi nanowires catalyst renders the best catalytic performance for OER in alkaline media, achieving a low Tafel slope of 54.1 mV dec-1 , a small overpotential of 359 mV at 10 mA cm-2 , and superior stability. The electrocatalytic activities of CoPPi nanowires outperform the most reported non-noble metal based catalysts, even better than the benchmark Ir/C (20%) catalyst. The reported synthesis of CoPPi gives guidance for morphology control of transition metal pyrophosphate based nanostructures for a high-performance inexpensive material to replace the noble metal-based OER catalysts.