Bleached State Research Articles

Aqueous intelligent bi-functional electrochromic-energy storage device on heterostructured nanoarrays:In-situ repairability and Al3+ ion effect

In this paper, well oriented TiO2@WO3 nanorod arrays were synthesized and applied in AlCl3 aqueous (AlCl3-H2O) electrolyte for enhancing dual-function of single material. Benefiting from large specific surface area and stable structure of TiO2@WO3, as well as small ionic radius and trivalent characteristics of Al3+, the composite showed excellent electrochromic-capacitive properties and super stability, including large optical modulation (83.5% at 800 nm), excellent stability (the optical modulation only decreased by 2.3% after 3000 cycles; the specific capacitance value remained 92% after 1000 cycles at 5 A/g) and good energy storage level (248.3 F/g at 1A/g). Notably, the “ion trap” model was firstly applied to the Al3+ aqueous electrolyte to clarify the degradation and repair mechanisms of electrode. Different from Li + based organic electrolyte, only “eliminable trap” that eroded the colored state was generated after long cycles. The “non-eliminable trap” that reduced the transmittance of the bleached state was hardly produced, which was attributed to the limited voltage range of the aqueous solution and the characteristics of Al3+. In addition, the slightly reduced electrochromic and capacitive properties were both recovered in-situ through applying a constant voltage for de-trapping treatment, suggesting the novel construction of “TiO2@WO3 composite nanoarrays/AlCl3-H2O electrolyte” was the key for durable and repairable electrochromic-supercapacitor (ECSC). More importantly, real devices of TiO2@WO3-based ECSC were constructed and exhibited excellent bifunctional performance. Three devices with 3 × 4 cm2 in series could lit the LED light up, and its color changed with the power supply time, bringing a bright prospect in visual monitoring field.

Self‐Driven Ni‐Based Electrochromic Devices for Energy‐Efficient Smart Windows

AbstractElectrochromic devices (ECDs) with adjustable transmittance have opened new opportunities to the development of smart windows for energy‐efficiency building. However, the switching between colored and bleached state of conventional ECD will bring extra energy consumption, the design of high‐performance ECD with low consumption is still an elusive goal. To address this issue, a self‐driven and energy‐saving Ni anode‐based ECD using Prussian blue as electrochromic material is developed. During the day, it can be colored by solar energy. By contrast, it can spontaneously bleach when the ECD's anode and cathode are short‐circuiting using the internal redox potential during the night. It is worth noting that no extra energy is inputted in the coloring‐bleaching cycle. In comparison with the ECD using electrolyte with high Ni2+ (K+:Ni2+ = 1:9) or high K+ (K+:Ni2+ = 9:1) concentration with poor optical contrast and cyclic stability (failed <100 cycles), the Ni‐based ECD with the electrolyte containing equal amount of K+ and Ni2+ exhibits a high optical contrast (39.45%), good coloration response time (6 s), and excellent stability (1000 cycles). These properties suggest that the Ni‐based electrochromic configuration is expected to be a catalyst for the development of energy‐storage EC smart window in the future.

Tungsten-oxide/polypyrrole film for hybrid solid-state electrochromic smart window

An organic–inorganic hybrid electrochromic device was fabricated by combining the films of hydrothermally synthesized tungsten oxide (WO3) with electrodeposited polypyrrole. Before making a device, these deposited thin films were characterized using scanning electron microscopy, infrared spectroscopy, and Raman spectroscopy techniques. Thereafter, a solid-state organic–inorganic electrochromic device was fabricated, which shows reversible switching between coloration and bleaching states with a very small external bias voltage (±1 V) and excellent cyclic stability up to 500 s with a negligible amount of transmission loss. In situ electrochemical studies show that the device has enhanced switching speed (1.1/1.8 s), and optical contrast of more than 47% at the wavelength of 650 nm. Furthermore, the optimized electrochromic device displays enhanced coloration efficiency up to ∼304 cm2/C. All these results open a new door for increasing the performance of a single-layered device by combining it with complementary electrodes.

Absorption Coefficient and Optical Contrast Modulation through Side Chain Engineering of Electrochromic Polymers

Conjugated polymers can be electrochemically bleached to achieve colored-to-transmissive electrochromic switching. This work presents a side chain engineering approach to enhance colored state absorptivity of an electrochromic polymer, while maintaining high transmissivity in the bleached state. A series of dioxythiophene copolymers with systematic variations in their branched alkyl side chains have been used to understand side chain influence on solubility, aggregation, film morphology and optical constants. By increasing the chromophore density through an appropriate choice of side chains, the absorption coefficient of the colored polymer can be improved by almost 50%, with minimal influence on bleached-state absorption coefficients over the visible region. As such, solution-processed films of high absorbance can be prepared using thin polymer layers to achieve fast electrochromic switching and highly transmissive bleached states. Under optimized conditions, optical contrasts nearing 80% can be reached at the wavelength of maximum absorbance, among the highest reported for solution-processed, cathodically coloring electrochromic polymers. The improved absorption coefficients are especially useful in enhancing the electrochromic performance in the low transmittance regime (colored state transmittance <20%), providing useful insights for designing high contrast electrochromic materials.

Eradicating β-trap induced bleached-state degradation in amorphous TiO2 electrochromic films

Titanium dioxide (TiO2) draw great attention in developing electrochromic devices due to its low cost, dual-band optical modulation and wide potential window complementary to other EC films. Akin to other electrochromic oxides, TiO2 suffers from the tradeoff between cycling stability and large optical modulation because of the ion trapping effect. In this paper, we find formation of β-traps can be prevented through adjusting the applied duration time at high potential, thus β-traps induced bleached state degradation in amorphous TiO2 films can be eradicated. More importantly, we show the formed β-traps locate at the TiO2/electrolyte interface, and are independent of the employed electrolyte systems. The TiO2 based full electrochromic devices confirm β-traps can be suppressed in a full device fashion. This work paves the way to understand the electrochromic performance degradation for oxide films upon square wave cycling and lays the foundation for adaptation in EC devices.

Persistence of phenotypic responses to short-term heat stress in the tabletop coral Acropora hyacinthus.

Widespread mapping of coral thermal resilience is essential for developing effective management strategies and requires replicable and rapid multi-location assays of heat resistance and recovery. One- or two-day short-term heat stress experiments have been previously employed to assess heat resistance, followed by single assays of bleaching condition. We tested the reliability of short-term heat stress resistance, and linked resistance and recovery assays, by monitoring the phenotypic response of fragments from 101 Acropora hyacinthus colonies located in Palau (Micronesia) to short-term heat stress. Following short-term heat stress, bleaching and mortality were recorded after 16 hours, daily for seven days, and after one and two months of recovery. To follow corals over time, we utilized a qualitative, non-destructive visual bleaching score metric that correlated with standard symbiont retention assays. The bleaching state of coral fragments 16 hours post-heat stress was highly indicative of their state over the next 7 days, suggesting that symbiont population sizes within corals may quickly stabilize post-heat stress. Bleaching 16 hours post-heat stress predicted likelihood of mortality over the subsequent 3-5 days, after which there was little additional mortality. Together, bleaching and mortality suggested that rapid assays of the phenotypic response following short-term heat stress were good metrics of the total heat treatment effect. Additionally, our data confirm geographic patterns of intraspecific variation in Palau and show that bleaching severity among colonies was highly correlated with mortality over the first week post-stress. We found high survival (98%) and visible recovery (100%) two months after heat stress among coral fragments that survived the first week post-stress. These findings help simplify rapid, widespread surveys of heat sensitivity in Acropora hyacinthus by showing that standardized short-term experiments can be confidently assayed after 16 hours, and that bleaching sensitivity may be linked to subsequent survival using experimental assessments.

Colorimetric and coulometric dual-mode sensing based on electrochromic Prussian blue device for solid-contact ion-selective electrodes

The colorimetric and coulometric dual-mode sensing strategies based on electrochromic Prussian blue (PB) device are proposed for reading out the potentiometric responses of the solid-contact ion-selective electrodes (ISEs). The mechanism is that the transformation between the bleached state and the colored state for the PB-based electrochromic device is modulated by using the solid-contact Ca2+-ISE with changing the ion activities under the control of a constant potential, and a transient current related to the oxidation-reduction reaction of PB is also obtained. Results show that the concentration range of 1.0 × 10−6-1.0 × 10−2 Ca2+ can be qualitatively and semi-quantitatively detected through observing the color change via the naked eye or analyzing the red-green-blue (RGB) values by a smartphone and the corresponding integrated charges of the PB-based electrochromic device under the control of the applied potential. These proposed readout strategies are not only free from the influences of colored and turbid samples, but also can keep the inherent selectivity for the solid-contact Ca2+-ISE, since the signal detection based on the PB-based electrochromic device and the ion recognition based on the solid-contact Ca2+-ISE are separately placed. This work provides a simple, fast, and visual readout strategy for solid-contact ISEs, and expands the sensing concepts for reading out the potentiometric responses.

Preparation and electrochromic properties of NiO and ZnO-doped NiO thin films

Great optical contrast, high coloration efficiency, short response time, and good cycling stability have become the key to achieving large-scale application of electrochromic materials. In this paper, NiO thin films and ZnO-doped NiO thin films were prepared using magnetron sputtering technology. The microstructure and electrochromic properties of thin films were studied using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), electrochemical workstation and UV spectrophotometer, and the optimal preparation parameters of NiO thin films were found. The results show that NiO thin films with sputtering power of 150 W, Ar:O2 of 50:6, working pressure of 2.0 Pa and sputtering time of 20 min displayed the best electrochromic properties. In the electrolyte of 1 mol/L KOH, the optical contrast was 74.04% (@550 nm), the coloration efficiency was 8.73 cm2/C, the coloration time was 1.67 s, and the bleaching time was 1.26 s. ZnO-doped NiO thin films were prepared with the optimal parameters of NiO thin films. The results show that the ZnO-doped can improve the bleached state transmittance of the thin films. Moreover, the optical contrast reached 78.20% (@550 nm), the coloration efficiency was 11.20 cm2/C, and the cycling stability of the thin films was greatly improved. The results of electrochemical impedance measurement show that ZnO-doped in NiO thin films can reduce the charge transfer impedance and ion diffusion impedance, which is conducive to electrochromic reactions.

Ester decorated 1,2,4,5-tetraphenylbenzene electrochromic materials with AEE activity, high optical contrast, fast response, and good cycling stability

Multifunctional electrochromic materials are ideal candidates for applications in various commercial fields. In this work, a series of dual-functional materials, 1,2,4,5-tetrakis (4-carboxyphenyl)benzene esters (TCPBEs), were synthesized by decorating 1,2,4,5-tetraphenylbenzene with tetra-esters. TCPBEs exhibited aggregation-induced emission and distinct phenomenon of aggregation-enhanced emission in water/N-methyl pyrrolidone due to their polyphenyl substituted structures and electrochromic properties due to surrounding esters. TCPBEs underwent a two-step one-electron reduction process in the electrochemical behavior. The electrochromic devices based on TCPBEs showed good long-term cycling stability (i.e., Hex-TCPBE remained 90% of the initial optical contrast after 2350 cycles), high optical contrast (i.e., Et-TCPBE up to 64.5%) and coloration efficiency (i.e., Hex-TCPBE up to 261 cm2/C), rapid response (<3 s), and dual colored state. Significant changes in color from colorless bleached state to orange and brown colored states were observed. Each TCPBE demonstrated distinct electrochromic properties because of the electronic effects of different R-substituted ester groups. In general, Et-TCPBE, Hex-TCPBE, and CH3Ph-TCPBE performed better than Bn-TCPBE and CF3Ph-TCPBE. In summary, this study provides a strategy for the design of novel dual-functional electrochromic materials, which have broad application prospects in the field of multifunctional devices.

MoS2 doping and concentration optimization for application-specific design of P3HT-viologen-based solid state electrochromic device

Methods to improve the performance of solid state electrochromic devices (ECDs) need to be explored and the dynamic doping process must be optimized to achieve ideal device performance. Molybdenum disulphide (MoS2) doped ECD has been fabricated by using two conducting polymeric films, i.e. polythiophene (P3HT) and ethyl viologen (EV), to investigate the role of 2D material doping on the overall device performance. Hydrothermally grown MoS2 nanoflowers, characterized using x-ray diffraction, electron microscopy and Raman spectroscopy were used for this purpose. Furthermore, the effect of MoS2 dopant concentration on the performance of an EV/P3HT-based ECD was studied systematically. The prepared solid-state ECD shows improved electrochromic performance in terms of switching speed, color contrast and coloration efficiency while switching its color from one state to the other (magenta and blue) under a very small external bias (±1.4 V). The transition from colored to bleached state is fastest for the highest (0.3 wt%) MoS2-doped ECD, whereas the color contrast and coloration efficiency is maximum for the lowest (0.1 wt%) MoS2-doped device. The variation in electrochromic parameters as a function of dopant (MoS2) concentration reveals that an appropriate concentration must be chosen depending on the requirement

Theory of the metastable injection-bleached E3c center in GaAs

The $E3$ transition in irradiated GaAs observed in deep level transient spectroscopy (DLTS) was recently discovered in Laplace-DLTS to encompass three distinct components. The component designated $E3c$ was found to be metastable, reversibly bleached under minority carrier (hole) injection, with an introduction rate dependent upon Si doping density. It is shown through first-principles modeling that the $E3c$ must be the intimate Si-vacancy pair, best described as a Si sitting in a divacancy ${\mathrm{Si}}_{vv}$. The bleached metastable state is enabled by a doubly site-shifting mechanism: Upon recharging, the defect undergoes a second site shift rather returning to its original $E3c$-active configuration via reversing the first site shift. Identification of this defect offers insights into the short-time annealing kinetics in irradiated GaAs.

Smart window with grating optical filter: Comparison with smart windows fully coated with chromogenic layer

A comparative analysis is presented of a smart window with grating filter and a conventional smart window fully covered with switchable layer using the same chromogenic material in its colored and bleached states. The filter, formed by two thin-film gratings with alternating transmissive and chromogenic strips, has an angular-selective transmission of direct sunlight. Both gratings are sloped on the window plane at an angle to the horizontal, calculated taking into account the window azimuth to adapt to the solar trajectory relative to this window. The previously obtained calculation methods are modified and expanded, on the basis of which the temporal characteristics of light and solar transmittance, as well as direct and diffuse illuminance and irradiance indoors, of windows with two different southeast azimuths for June 15, September and December are calculated. The results show two main advantages of a grating smart window over a conventional one. Firstly, in active (colored) mode, due to angular selectivity of transmission it has self-adjusting light and solar transmittance throughout the day and year without using the daylight shading/redirecting devices, and in the bleached state, it has a higher transmittance. Secondly, by adjusting the transmission of direct sunlight, the filter transmits more than twice as much diffuse light in both colored and bleached states, thereby increasing indoor comfort in any season.

Electrochromic Performance Fading and Restoration in Amorphous TiO2 Thin Films

AbstractElectrochromic performance fading is inevitable upon extended cycling, and the limited lifetime greatly prevents large‐scale commercialization of electrochromism‐based devices. Here the origin of the performance degradation is uncovered and the performance restoration in TiO2 thin films is explored. It is shown that, depending on the applied potential windows, the inserted ions are immobilized in α‐traps resulting in a monotonous degradation of colored state, or immobilized in b‐ and modified α‐traps leading to mutual degradation of colored and bleached state of the films. It is found by releasing the resided ions in various traps, the initial performance can be restored accordingly. Moreover, reversible sites and all traps are demonstrated to be interconvertible through an ion trapping and detrapping process. These results provide a general scope in understanding the electrochromism in oxide thin films and offer the scheme for potential traps control or even elimination, aiming at superior electrochromic devices.

Substrate effect on electrochromic properties of Nb2O5:TiO2 nanocomposite thin films deposited by thermionic vacuum arc

In this paper, substrate effect on electrochromic properties of Nb2O5:TiO2 nanocomposite thin films have been investigated. Thin films have been deposited by thermionic vacuum arc deposition technology. Nb2O5 and TiO2 are known to be electrochromic materials. Nb/Ti rate was obtained 1.4. Average thicknesses of the films were found as 113 nm and 111 nm and band gap values for bleached states were calculated as 3.96 eV and 3.85 eV for the films deposited onto ITO and FTO coated glass substrates, respectively. The coloration efficiency values were calculated as 17 cm2/C and 26 cm2/C for the film onto ITO layered glass substrate and 31 cm2/C, 23 cm2/C and 24 cm2/C for the film onto FTO layered glass substrate at a different wavelength values in the visible region. The obtained results shows that films for each transparent conductive oxide material is promising material to obtain the high performance TiO2 active layer.

On the local atomic structure for swift coloration of chromogenic thin film

Chromogenic thin films used for smart windows have been intensively studied owing to their potential uses in sensors and their ability to increase the energy efficiency and interior comfort of buildings by controlling the amount of solar light that enters them. Many investigations have focused on the optical transmittance properties of smart windows. Herein, gasochromic bare and Mo-V2O5 thin films are used as model systems of a color-switchable window, which are fabricated by the sol–gel spin-coating route. The transmittance of colored states is much lower than that of bleached states for both films. The correlation between atomic/electronic structures and the coloration performance of smart windows are investigated using in situ soft X-ray absorption spectroscopy (XAS) in the total electron yield (TEY) mode. This method is used to monitor the evolutions of the local electronic and atomic structures of bare and Mo-V2O5 thin films during the gasochromic reaction. In situ soft XAS enables the cation and anion sites of a material to be identified in operando condition, and the vanadium L-edge measured in the TEY mode provides information that is complementary to the vanadium K-edge. Grazing incidence X-ray diffraction (GIXRD), and the Raman analysis of Mo-V2O5 thin films demonstrate that they have a larger interlayer distance than V2O5 thin films. These films undergo structural adjustments before the valence states of vanadium change. The symmetrical octahedral-like structure, adjusted bond length, and partial β-V2O5 phase of the Mo-V2O5 thin film promote fast coloration. The analytical results herein provide a deep insight into the coloration mechanism and pave the way to the development of advanced chromogenic smart windows.

Study of a Novel Electrochromic Device with Crystalline WO3 and Gel Electrolyte.

Most ECDs are coated with an electrochromic material on the transparent conductive oxide (TCO) substrate. A novel electrochromic device (ECD), having a variable optical performance, was prepared by using tungsten foil as a substrate in this study. It was found that the WO3 discoloration layer, having a monoclinic phase crystalline structure made of 600 °C calcined, had optimum charge transmission performance with PADA gel polymer electrolyte. Ionic conductivity of PADA gel polymer electrolyte was 2.3 × 10−3 S cm−1 at −20 °C, and it was possible to help Li+ to implement embedding and extraction from WO3 even in low-temperature conditions. The colored time (tc) and the bleached time (tb) of the electrochromic device were 15 s and 26 s, and it showed yellowish-brown in the colored state and navy blue in the bleached state. The ECD (WO3-600) exhibited good cycle stability reach at least 150 times.

Targeted enhancement of electrochromic memory in Fe(II) based metallo-supramolecular polymer using molybdenum disulfide quantum dots

Bistable electrochromic (EC) display with long EC memory has been a much-anticipated goal owing to its zero-energy consumption when maintaining the colored or bleached state when used in smart windows. However, it is very challenging to engineer the structure of the materials to accomplish a long EC memory along with high optical contrast, durability, switching fastness, and coloration efficiency which are of significance for fabricating the electrochromic devices with essentially power efficiency. Herein, we have judiciously incorporated the charge trapping MoS2 quantum dots (QDs) to prepare an electrochromic nanocomposite (polyFe-QD-10) of an Fe2+-based metallo-supramolecular EC polymer (polyFe) for the targeted enhancement of EC memory than the pristine polyFe polymer. The polyFe-QD-10 based electrochromic device (ECD) exhibits more cycle durability as it produced no loss in ΔT after the measurement of 100 cycle, while pristine polyFe-based ECD produced 14% loss in similar 100 cycle. The prototype ECD with polyFe-QD-10 film is also demonstrated with fast switching time (3.3 s for bleaching and 0.78 s for coloring), and good coloration efficiency (242.2 cm2 C−1). Remarkably, the ECD based on polyFe-QD-10 composite displays higher EC memory in open circuit condition as it takes 32 min for 90% reappearance of the original purple color after complete bleaching, while the pristine polyFe based ECD regains 90% of the transmittance of the color state only in 15 min. The strategy reported here presents the polyFe-MoS2 QD composite thin film an encouraging candidate for developing power efficient electrochromic information displays and smart windows.

Stable and reversible electrochromic behaviors in anodic NiO thin films

We report the synthesis and electrochromic behavior of nickel oxide (NiO) nanostructures deposited over conducting glass substrates by hot-filament metal vapor deposition (HFMVD). The NiO crystallized into rhombohedra structure with R3-m space group without any post-treatment. The cyclic voltammogram (CV) revealed the coloration and bleaching effect of NiO nanostructures with forward and reverse scans, respectively. The 85.05% reversibility for NiO films from the coloration state back to its bleached state was calculated from Chronocoulometry (CC) measurements. The highest optical transmittance difference obtained at 420 nm has resulted in a corresponding optical density of 1.016. The switching time between the coloration and bleaching cycles calculated from transmittance spectra unfolded the lowest coloration time of 4.96 sec at 354 nm, which increased up to 6.32 sec at 590 nm, whereas the bleaching time at all the wavelengths was estimated to be less than 0.5 sec.

Microbiomes of Healthy and Bleached Corals During a 2016 Thermal Bleaching Event in the Andaman Sea of Thailand

As seawater temperature rises, repeated thermal bleaching events have negatively affected the reefs of the Andaman Sea for over decades. Studies on the coral-associated microbial diversity of prokaryotes and microbial eukaryotes (microbiome) in healthy and bleached corals are important to better understand the coral holobionts that involved augmented resistance to stresses, and this information remains limited in the Andaman Sea of Thailand. The present study thereby described the microbiomes of healthy (unbleached) and bleached colonies of four prevalent corals, Acropora humilis, Platygyra sp., Pocillopora damicornis, and Porites lutea, along with the surrounding seawater and sediments, that were collected during a 2016 thermal bleaching event, using 16S and 18S rRNA genes next-generation sequencing (NGS). Both prokaryotic and eukaryotic microbes showed isolated community profiles among sample types (corals, sediment, and seawater) [analysis of similarities (ANOSIM): p = 0.038 for prokaryotes, p &amp;lt; 0.001 for microbial eukaryotes] and among coral genera (ANOSIM: p &amp;lt; 0.001 for prokaryotes and microbial eukaryotes). In bleached state corals, we found differences in microbial compositions from the healthy state corals. Prevalent differences shared among bleached coral genera (shared in at least three coral genera) included a loss of reported coral-beneficial microbes, such as Pseudomonadales, Alteromonadales, and Symbiodinium; meanwhile an increase of putative coral-pathogenic Malassezia and Aspergillus. This difference could affect carbon and nitrogen availability for coral growth, reflective of a healthy or bleached state. Our findings in part supported previously microbial dysbiosis knowledge of thermal bleaching coral microbiomes around South East Asia marine geography, and together ongoing efforts are to support the understanding and management of microbial diversity to reduce the negative impacts to corals in massive thermal bleaching events.

N-(thiophen-2-ylmethylene)aniline- and N-(thiazol-2-ylmethylene)aniline-containing poly(2,5-dithienylpyrrole)s as anodically coloring polymers for high contrast electrochromic devices

Two N-(thiophen-2-ylmethylene)aniline- and N-(thiazol-2-ylmethylene)aniline-containing poly(dithienylpyrrole)s (PTA and PZA) are deposited on indium tin oxide (ITO) glass substrates and their electrochemical, spectral, and electrochromic performances are characterized. PTA and PZA display reversible multicolor chromism in the UV–Vis–NIR region. PTA is ocher, olive, slate grey, and bluish-grey at −0.2, 0.8, 1.0, and 1.2 V, respectively, whereas PZA is terreous, coffee, grey, and deep grey at −0.2, 0.2, 1.0, and 1.4 V, respectively. Kinetic investigations of polymeric films display the transmittance change (ΔΤ) of PTA and PZA between the doped and undoped state is 35.4% at 1286 nm and 31.2% at 1218 nm, respectively. PZA attains a high coloration efficiency (η = 218.8 cm2 C−1 at 1218 nm) in a liquid solution. Bilayer electrochromic devices (ECDs) based on PTA (or PZA) as anodic polymer and PProDOTEt2 (or PProDOTBz2) as cathodic polymer were fabricated. The ΔT of PTA/PProDOTBz2 and PZA/PProDOTBz2 ECDs between the bleached and colored state is 70.2% at 622 nm and 64.7% at 622 nm, respectively. Moreover, four ECDs display short response time and multichromic reversible redox behaviors, indicating that PTA and PZA are promising candidates for future electrochromic and optoelectronic applications.