Angle-resolved optical characterisation of an electrochromic device

An electrochromic prototype with WO₃ and NiO as electrochromic layers was analysed in an absolute spectrophotometer. The electrochromic glazing was measured in combination with a clear float glass and a low-e glass in order to simulate a ‘real’ window. Similar measurements were performed on a commercial electrochromic product, i.e., a Gentex Night Vision Safety™ (NVS^®) mirror from Gentex Corporation, and the results were compared. The spectral transmittance was measured, in bleached and coloured state, over the solar wavelength range at the angles of incidence, φ=0, 40, 60 and 70°. The direct solar transmittance, T_sol, the visual transmittance, T_vis, and the angular dependence for these parameters were calculated.     

Proton diffusion in polyethylene oxide: Relevance to electrochromic device design

Polyethylene oxide is a frequently used component in polymer electrolytes developed for applications in electrochromic devices. The transmittance variation may occur as a result of either proton or lithium ion intercalation into the electrochromic films. Impedance spectroscopy data in the low-frequency space-charge relaxation regime can be used to obtain estimates of ion concentrations and ion diffusion coefficients in ion-conducting materials. We apply this method to literature data for pure polyethylene oxide where the residual conductivity is believed to be due to protons. The obtained diffusion coefficient is found to be in the order of, or higher than, reported lithium ion diffusion coefficients in low molecular weight polyethylene oxide. Hence it is likely that proton intercalation will be of importance for electrochromic devices, provided there is a significant amount of protons present.     

Synthesis of derivatives of polythiophene and their application in an electrochromic device

Poly(3-methylthiophene) (P3MT) and poly(3-octylthiophene) (P3OT) are conducting polymers with interesting optoelectronic properties and a wide variety of optoelectronic applications. In this work, 3-octylthiophene was synthesized through a Grignard reactive and was analyzed by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR). The morphology of electrosynthesized P3OT and P3MT thin films was analyzed by atomic force microscopy and different film morphologies were found for different electrodeposition technique and the solution temperature. Optical absorbance spectra of the two types of films confirm the bipolaron band structure and a starting π–π^* interband transition around 2 eV. Electrochromic performance of the polymers with both liquid and polymeric electrolytes showed a high switch potential for P3OT that for P3MT films. The kinetic optical response of a P3MT electrochromic device shows a good color contrast and a capacitive current characteristic under a square electrical potential.     

Relating cyclic voltammetry and impedance analysis in a viologen electrochromic device

Viologens are electrochromic materials that have a wide range of coloration depending on the radical substituents. The results for a new blue viologen-based device, that has recently been patented, with an active area of 8.5 cm² is presented in this paper. The characterization techniques used are based on optical measurements, chronoamperometry, cyclic voltammetry, and impedance spectroscopy analysis. A study of the results obtained from these measurements provides both an overview of the reactions taking place and has allowed an equivalent circuit to be developed which relates the different electrochemical parameters. The transmittance is observed to change from 80% to 15% in 600 nm for input voltages ranging from 0 to 2.5 V. However, increasing voltage beyond 1.8 V shows no optical change, thus, maintaining the voltage below this level optimizes the use of electrical current. Voltages and charges used for each redox reaction have been computed and are seen to be linearly related. The equivalent circuit generated to mimic the process has included parameters based on Warburg diffusion and double-layer capacitances. Results from this model are consistent with measurements for up to 1.8 V. Saturation of reduced species has been deduced for input voltages beyond this level.     

An all-thiophene electrochromic device fabricated with poly(3-methylthiophene) and poly(3,4-ethylenedioxythiophene)

A novel all-organic electrochromic device (ECD) is presented. By electrodepositing poly(3-methylthiophene) (PMeT) in boron fluoride ethyl ether (BFEE), a strong Lewis acid, a good-quality PMeT film was obtained. On the basis of studies of PMeT, it can be regarded as a pseudo-anodic coloring material for ECDs. On the other hand, poly(3,4-ethylenedioxythiophene) (PEDOT) is an ideal cathodic coloring electrochromic material known for its high optical contrast, long-term stability, and high coloration efficiency. By combining these two thiophene derivatives, the application potential of this device was determined. The color of the ECD switches between deep blue at −1.4 V (PEDOT vs. PMeT) and light red at 0.6 V. The device exhibits stable electrochromic performance, with a maximum optical attenuation (ΔT_max) at 655 nm reaching 46% (from 9% to 55%), and achieves a high coloration efficiency of 336 cm²/C. After 100 repeated cycles, the cell still retained at 91.3% of its ΔT_max at 655 nm.     

An all-solid-state electrochromic device based on NiO/WO3 complementary structure and solid hybrid polyelectrolyte

An all-solid-state electrochromic (EC) device based on NiO/WO₃ complementary structure and solid polyelectrolyte was manufactured for modulating the optical transmittance. The device consists of WO₃ film as the main electrochromic layer, single-phase hybrid polyelectrolyte as the Li⁺ ion conductor layer, and NiO film as the counter electrochromic layer. Indium tin oxide- (ITO) coated glass was used as substrate and ITO films act as the transparent conductive electrodes. The effective area of the device is 5×5 cm². The device showed an optical modulation of 55% at 550 nm and achieved a coloration efficiency of 87 cm² C⁻¹. The response time of the device is found to be about 10 s for coloring step and 20 s for bleaching step. The electrochromic mechanism in the NiO/WO₃ complementary structure with Li⁺ ion insertion and extraction was investigated by means of cyclic voltammograms (CV) and X-ray photoelectron spectroscopy (XPS).     

Characterization of ion diffusion and transient electrochromic performance in PECVD grown tungsten oxide thin films

Electrochromic tungsten oxide thin films were synthesized by plasma-enhanced chemical vapor deposition (PECVD). Film density and electrochromic performance were controlled by the degree of ion bombardment. A moderate degree of ion bombardment was optimal, and the refractive index was shown to be a sensitive indicator of electrochromic performance. Chronoamperometry in concert with optical transmission was used to determine diffusion and absorption coefficients using both H⁺ and Li⁺ containing electrolytes. The absorption coefficients were similar for both ions, scaling with the degree of intercalation to 50,000 cm⁻¹ in the opaque state. The diffusion coefficients for optimized films were found to be relatively insensitive to the degree of ion intercalation, with values of 10⁻⁹ and 10⁻¹⁰ cm²/s for H⁺ and Li⁺, respectively. These values are about an order of magnitude greater than values reported for vacuum-deposited films, which was attributed to low relative density in the PECVD films. The diffusion and absorption coefficients were incorporated into a model that successfully reproduced transient optical performance.     

压缩空气储能系统储气装置研究现状与发展趋势

压缩空气储能被认为是最具发展潜力的大规模物理储能技术,储气装置作为压缩空气储能系统的关键环节,对系统高效、稳定和安全运行具有重要影响.近些年来,随着压缩空气储能技术的快速发展,储气装置的研究备受人们关注.储气装置的特点主要取决于其材料属性,因此本文根据材料不同对储气装置进行分类,并着重论述了天然地下洞穴储气、人造洞室储...     

Development of a new self-powered electrochromic device for light modulation without external power supply

Despite considerable improvements within the last decades, electrochromic (EC) window coatings are still too expensive to be applied in buildings on a large scale. Beside the manufacturing costs, wiring costs have to be added which may exceed the fabrication expenses of the electrochromic window. Therefore, self-powered electrochromic windows have been considered, where a semi-transparent photovoltaic (PV) cell provides the power to activate an electrochromic system deposited on top of the solar cell. The whole PVEC device consists of up to eight layers which must be deposited on large scales without short circuits or other failures. Recently, we came up with a much simpler idea where power generation and electrochromic properties are combined rather than just added as in the case of the PVEC cell. The whole device now is obtained by the deposition of only three layers and is highly transparent in the bleached state. Exposing it to sunlight and completing an external circuit the device can be colored within a few minutes, reducing the transmission by about 40%. Bleaching occurs either spontaneously by blocking the sunlight or is induced by a small rechargeable battery which can be incorporated in the external circuit and is charged from the device when exposed to sunlight.     

Design, production and characterisation of an all solid state electrochromic medium size device

An electrochromic device based on a five layer coating deposited on a glass sheet was produced. The layers were all obtained by physical vapour deposition in the same vacuum environment, using a commercial apparatus capable of producing thin films on large area substrates. Small (50×50 mm²) and medium (300×300 mm²) size specimens were prepared for preliminary study, to establish the electrochemical and optical performances of the device. Electrochemical measurements were performed on each active material, as well as on the whole specimens, in order to relate electrochemical properties to process conditions. Also, luminous and solar parameters were obtained from (near) normal incidence spectrophotometry in both the bleached and coloured states, to confirm the values used in the design phase of the electrochromic device. One of the specimens was also submitted to variable angle photometric and radiometric measurements, using an integrating sphere. This data was then used to evaluate the room luminance distribution and energy loads using a building simulation code.     

Incorporation of a stable radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in an electrochromic device

A stable organic radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), was studied. We employed TEMPO as a cathodic radical provider in propylene carbonate (PC) and poly(3,4-propylenedioxythiophene) derivatives (PProDOT-Et₂) as an anodic electrochromic (EC) thin film, which was obtained through electropolymerization. On assembling them together in a device, the electrochemical and optical performances of this hybrid electrochromic device (ECD) showed reversible cycling stability and high absorbance attenuation in the visible range. By selecting proper electrolytes (LiClO₄/PC) and controlling the deposited charge of the PProDOT-Et₂ thin film, it was possible to obtain a transmittance change (ΔT) of up to 59% at 590 nm with no noticeable degradation after operating between 0 and 0.9 V for 1000 cycles. Furthermore, an electrochemical quartz crystal microbalance (EQCM) was used to investigate ion migrations in the PProDOT-Et₂ thin film, which influenced its long-term stability.     

First a-SiC : H photovoltaic-powered monolithic tandem electrochromic smart window device

We report on the first monolithic, amorphous-silicon-based, photovoltaic-powered electrochromic window coating. The coating employs a wide band gap a-Si_1−xC_x : H n–i–p photovoltaic (PV) cell as a semitransparent power supply, and an Li_yWO₃/LiAlF₄/V₂O₅ electrochromic (EC) device as an optical-transmittance modulator. The EC device is deposited directly on top of a PV device that coats a glass substrate. The a-Si_1−xC_x : H PV cell has a Tauc gap of 2.2 eV and a transmittance of 80% over a large portion of the visible light spectrum. We reduced the thickness of the device to about 600 Å while maintaining a 1-sun open-circuit voltage of 0.9 V and short-circuit current of 2 mA/cm². By employing the LiAlF₄ as the Li⁺ ion electrolyte, the parasitic electronic current through the device has been significantly reduced (<10 μA/cm² under 1 V bleaching voltage). By properly controlling y and the thickness of each layer, the coloration and bleaching voltage of the EC device could be adjusted within the range of −0.6 to −1.3 V (coloring) and 0.1–0.6 V (bleaching) for compatibility with the underlying PV cell. Our prototype 16 cm² PV/EC device modulates the transmittance by more than 60% over a large portion of the visible spectrum. Its color is pale yellow at bleached state and dark blue at colored state. The coloring and bleaching times of the electrochromic device are approximately 2 min under normal operating conditions (±1 V). The device is hermetically sealed for a long lifetime.     

Naturally occurring neem gum: An unprecedented green resource for bioelectrochemical flexible energy storage device

Naturally available neem tree gum consisting of bioelectrolyte and bioelectrode was fabricated for flexible energy storage device. Structural morphology, thermal stability, porosity and surface area of as prepared bioelectrode were characterized thoroughly by using scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) isotherm respectively. The bioelectrolyte conductivity was optimized under various concentrations of lithium ion salts and temperatures through electrochemical impedance spectroscopy (EIS). A flexible supercapacitor (SCs) was fabricated by using bioelectrodes and electrolyte and tested for its electrochemical properties. The supercapacitor displayed specific capacitance of 640 Fg^-1 and 200 Fg^-1 at a current density 0.5 Ag^-1 and 1.0 V operating potential window. The energy device has also demonstrated large operational window (2.0 V) and shown 102 Fg^-1 at a current density of 1.0 Ag^-1. The novelty of the present work lies in the simplified, cost-effective procedure for preparation of biomaterials, their remarkably high stability under strong mechanical bent and long-term charging-discharging cycles of the fabricated device.     

Thermodynamic optimization of a stratified thermal storage device

Thermodynamic optimization combines exergy analysis with dynamical modeling to determine optimal design parameters. In this work we apply exergy analysis to an analytically solvable model of a single-medium stratified thermal storage device. We consider a simple one-dimensional model that includes conductive losses to the environment. Competition between mixing and conductive losses gives rise to a thermodynamically optimum charging time for the system. The model can treat the full range of stratification from the fully-mixed limit to perfect stratification and we are therefore able to determine the effect of stratification on the thermodynamic optimum. We show that stratification increases the overall efficiency and shortens the thermodynamically optimum charging time.     

Photo-polymerized films of lithium ion conducting solid polymer electrolyte for electrochromic windows (ECWs)

Films of solid polymer electrolyte (spe) have been prepared by the photo-polymerization of the monomer: 2-hydroxyethylmethacrylate (HEMA) simultaneously accompanied by chemical crosslinking with neopentyl glycol which is dissolved in a liquid electrolyte, namely, 1 M LiClO₄ in EC:PC binary solvent mixed in two different volume ratios. The spe films exhibit ionic conductivities greater than 10⁻³ Scm⁻¹ at 25°C. Thermal and structural characteristics of the films have been determined by DSC and XRD, respectively. The electrochemical redox behavior of an electrochromic device (PWECD) fabricated with an electrodeposited tungsten oxide film as the primary electrode, a prussian blue film as the counter electrode and a poly(HEMA) based electrolyte film as well as that of the individual components of the device has been examined by cyclic voltammetry. Transmission modulation of 60% (λ=650 nm) shown by the PWECD renders it to be a promising candidate for electrochromic window applications.     

圆柱形等距螺旋盘管式相变蓄热装置蓄热性能研究

文章设计了一种以石蜡为相变材料的圆柱形等距螺旋盘管式相变蓄热装置,并通过实验分析了该装置的传热特性,以及传热流体入口温度、入口流量对石蜡的融化特性、相变蓄热装置的蓄热量及相变蓄热系统总传热系数的影响。分析结果表明:融化后期,石蜡的融化速率会明显加快;当传热流体入口温度一定时,随着入口流量逐渐增大,蓄热装置的最终显热蓄热量略微升高;与传热流体入口流量相比,传热流体入口温度对石蜡融化速率影响较大;相变阶段,石蜡的传热性能较强,传热流体入口温度越高,石蜡的传热性能越不稳定。     

All-solid-state electrochromic device based on poly(butyl viologen), Prussian blue, and succinonitrile

A new complementary electrochromic device (ECD) is described; it is based on poly(butyl viologen) (PBV) and Prussian blue (PB) confined to the electrode surfaces. PBV is a cathodically colored organic polymer, while PB is an anodically colored inorganic material. The two electrochromic materials were individually characterized in a 0.5 M KCl aqueous solution. On the basis of their properties, a PBV–PB ECD containing a solid-state electrolyte prepared by adding lithium tetrafluoroborate (LiBF₄) as a salt to succinonitrile (SN) was investigated. This all-solid-state ECD system showed good optical contrast with a coloration efficiency of ca. 163 cm²/C at 650 nm and good stability during 4000 cycles. The transmittance of the ECD at 650 nm changed from 73% (bleached) to 8% (darkened), with an applied potential of 1.7 V (−1.0 to 0.7 V) across the two electrodes. After 4000 cycles, the transmittance attenuation (ΔT) of the device was still at 86% of its original value, i.e. the ΔT value had decreased from 65% to 56%.     

Numerical simulation of hydrogen filling process in novel high-pressure microtube storage device

Novel high-pressure microtube hydrogen storage device has higher hydrogen storage density and safety than conventional hydrogen tanks. A one-dimensional numerical model for hydrogen filling process in microtubes is established, with reasonable calculation methods and accurate physical properties adopted. Based on the analysis of flow parameters variations, three stages of the filling process are summarized. At the beginning of the filling process, the maximum temperature appears at the inlet, but the average temperature does not rise significantly during the whole process. The effects of microtube length, filling pressure and environmental temperature are investigated and discussed. The results show that excessively long microtubes greatly increase the filling time and higher filling pressure reduces the filling time and improves the filling efficiency. The microtube hydrogen storage device achieves higher hydrogen storage density and filling efficiency in lower temperature mediums. It reveals that high filling pressure, low temperature encapsulation and reasonable microtube size design are the future development directions of microtube hydrogen storage for better application.     

一种太阳能储能装置的模拟计算与实验分析

利用太阳能相变储能技术提出一种新型太阳能储能装置,并搭建该装置的实验测试台,简要分析了该装置的结构和工作原理。将太阳能集热部分与储能一体化设计,在增强换热的同时降低了储能空间,具有良好的蓄放热性能。通过相关实验表明:装置蓄热时间为307 min,储能量为10.64 MJ;将流量为2.2 L/min、温度为33.2℃的冷水充入集热器,放热时长60 min,总出热水量为132 L,放热量为8.43 MJ,整体效率为64.7%。ANSYS模拟及相关实验验证,相变储能单元内部相变材料和装置放热过程中储能单元的温度变化对蓄热一体化集热器的设计具有参考价值。     

Cycling and at-rest stabilities of a complementary electrochromic device containing poly(3,4-ethylenedioxythiophene) and Prussian blue

PEDOT-based electrochromic devices (ECDs) have been investigated intensively in recent years. In order to obtain an ECD having long cycle life, the counter electrode and electrolyte used should be compatible in the electrochemical environment. Prussian blue (PB) is proven to be electrochemically stable when cycling in non-aqueous solutions. Thus a new organic-inorganic complementary ECD was assembled in combination with a PMMA-based gel polymer electrolyte. This ECD exhibited deep blue-violet when applying −2.1 V and became light blue when applying 0.6 V. Under these conditions, the transmittance of the ECD at 590 nm changed from 13.8% (−2.1 V) to 60.5% (+0.6 V) with a coloration efficiency of 338 cm²/C. The cell retained 55% of its maximum transmittance window (ΔT_max) after 50,640 repeated cycles. Moreover, the at-rest stability test revealed a transmittance window (ΔT) decay of 9.6% over a period of 107 days. Therefore, the proposed PEDOT-PB ECD may have potential for practical applications.