Determination of the Dependence of the Structure of Zn-Al Layered Double Hydroxides, as A Matrix for Functional Anions Intercalation, on Synthesis Conditions

Layered double hydroxides, especially Zn-Al, are valuable matrices for intercalation with various functional anions: dyes, medicines, food additives, etc. For the purposeful development and optimization of the technology for the synthesis of Zn-Al hydroxides intercalated with functional anions, the phase composition and crystal structure of Zn-Al nitrate layered double hydroxide samples (Zn:Al=4:1) synthesized at solution flow rates of 0.8 and 1.6 l/h, pH=7, 8, 9, 10 and t=10, 20, 30, 40, 50 and 60 °С were studied. XRD showed that all samples synthesized at different temperatures, pH, and solution flow rates were Zn-Al layered double hydroxides with an α-Zn(OH)2 crystal lattice of medium crystallinity, with an admixture of an oxide phase with a ZnO lattice. Three sections of the dependence of the crystallite size of the sample on the synthesis temperature were distinguished: 10–20 °C, 30–50 °C, and 60 °C, within which an increase in temperature led to an increase in crystallinity. A hypothesis was put forward about a change in the mechanism or kinetics of LDH formation at temperatures of 30 °C and 60 °C. An increase in the pH of the synthesis and the flow rate of solutions led to an increase in crystallinity. A retrospective comparative analysis of the phase composition and crystal structure of Zn-Al-nitrate and Zn-Al-tripolyphosphate (tartrazine or Orange Yellow S) LDH samples was carried out. It was found that the use of large and multi-charged functional anions caused significant adsorption on precipitate nuclei and difficult intercalation. As a result, low crystallinity was formed (Tartrazine anion) or a significant part of LDH was decomposed to oxide (tripolyphosphate and Orange Yellow S anions)

Effect of Variable Temperature Loads on Characteristics of Electrochrome Composite Ni (OH)2-PVA Films

Electrochromic coating is the basis of smart windows with variable optical characteristics. Nevertheless, despite the obvious advantages of using smart windows in construction, their cost is high.We have considered the coatings obtained by the cathodic template method, which are more economical in production. The presented studies are devoted to tests at cyclic temperature loads – repeated cooling and heating. The paper shows the influence of the medium and the method of heat supply (removal) to an electrochromic electrode based on a composite Ni(OH)2-PVA coating as well as the effect of surface preparation before its application.As a medium for cyclic temperature loads, we used air or a working electrolyte – 0.1 M KOH. As a preliminary preparation of the transparent electrically conductive base, we used electrochemical etching of a part of the layer of the electrically conductive transparent coating of tin oxide doped with fluorine in a solution of 1 M HCl.The result of a series of experiments was the discovery of a strong influence of temperature cyclic loads on the final characteristics of electrochromic films. The electrochromic film on the sample, which was subjected to cyclic temperature changes in air and on the substrate without etching, almost completely lost its electrochromic characteristics and adhesion. The sample, which was subjected to thermal stress in an alkali solution, lost its uniformity during coloring.On the other hand, both films, which were deposited on etched substrates, had generally better characteristics than samples deposited without etching and subjected to thermal stress in the air and in alkali. In this case, the sample, which was obtained on the substrate with pretreatment by etching and subjected to temperature cycling in alkali, had even slightly better characteristics than the reference sampl

Determination of the Effect of Exposure Conducted in KOH Solutions at Different Temperatures on the Properties of Electrochromic Ni(OH)2-PVA Films

To determine the effect of exposure of film composite electrodes based on Ni(OH)2-polyvinyl alcohol to an alkaline solution at high temperatures on the electrochromic and electrochemical characteristics, a series of films was obtained. The films were obtained on a glass substrate coated with fluorine-doped tin oxide. The coating of the substrates was carried out by the cathodic template method under the same conditions. The resulting precipitates were treated by keeping them in an alkali solution at different temperatures: 30, 40, 50, 60, and 70 °C for 8 hours, thereby simulating the operating conditions of an electrochromic device in a hot climate. It was found that the exposure temperature directly affected the electrochemical and electrochromic properties of the treated films. In this case, the cyclic volt-ampere curves showed a decrease in the peak values of the current densities and a lower rate of establishment of characteristics with an increase in the treatment temperature. At a maximum treatment temperature of 70 °C, the properties of the film significantly changed towards deterioration. According to the results of the experiments, three temperature ranges of treatment were identified. The first one was in the range up to 40 °C, in which the films showed significant electrochromic and electrochemical activity after treatment. The second interval was between 40 and 60 °C, in which the coatings showed a reversible deterioration in electrochromic and electrochemical activity. After treatment in the second interval, the films gradually restored their performance during electrochemical cycling. The third interval was from 70 °C and above. The films treated in this temperature range irreversibly lost their electrochemical and electrochromic activity. The study also proposed mechanisms to explain changes in the characteristics of electrodes during treatment, as well as possible ways to combat temperature degradation

Efficiency Definition of the Deposition Process of Electrochromic Ni(OH)2-PVA Films Formed on A Metal Substrate From Concentrated Solutions

Electrochemical devices based on nickel hydroxide electrodes are used in different areas. The main ones are chemical current sources, variable transparency “smart” windows, devices for carrying out electrocatalytic reactions, sensors for determining various substances. In this regard, methods of nickel hydroxide synthesis are of great interest, especially those that allow forming nickel hydroxide directly on the surface of electrodes. One of these methods is electrochemical deposition with cathodic current polarization. The available information on nickel hydroxide synthesis from nickel solutions was considered. It was shown that the available data mainly covered information on dilute solutions from 0.01 to 0.25 mol/L Ni(NO3)2. In addition, no comparison was found in the literature for the efficiency of the cathodic formation of Ni(OH)2 at different concentrations of nickel nitrate. To eliminate the lack of information, the dependence of the current efficiency on the concentration of nickel nitrate in the electrodeposition solution was determined at a constant cathode current density of 0.625 mA/cm2. The resulting dependence decreased nonlinearly with increasing concentration. The nickel hydroxide deposit formed in this case had an X-ray amorphous structure, and it depended little on the Ni(NO3)2 concentration. In addition, the current efficiency reached zero at concentrations of 1.5 mol/L Ni(NO3)2 and higher. However, with polyvinyl alcohol in the solution and at Ni(NO3)2 concentrations of 1.5 and 2 mol/L, electrochemically and electrochromically active Ni(OH)2 films were deposited. The current efficiency calculated indirectly for 1.5 and 2 mol/L Ni(NO3)2 solutions was 3.2 and 2.3 %, respectively. Thus, it was concluded that polyvinyl alcohol affected the mechanism of nickel hydroxide electrodeposition from aqueous solutions of nickel nitrate

A Study of Physico-chemical Characteristics of Electrochromic Ni(OH)2-PVA Films on Fto Glass with Different Deposition Duration

The use of electrochromic elements in “smart” windows leads to significant savings in electricity required for cooling premises. However, the high cost of these devices does not allow the technology to be widely used. Since the cost is determined by costly vacuum deposition methods, the development of other cheaper methods of deposition of electrochromic element layers is urgent. Aspects of alternative to vacuum formation methods – cathode template electrochemical deposition of composite electrochromic Ni(OH)2-PVA films were investigated. The study is devoted to determining the effect of the duration of deposition of the electrochromic layer on their physicochemical characteristics, in particular, on the optical and electrochemical properties. The deposition was carried out on fluorine-doped tin oxide glasses (FTO glasses). The time of deposition was chosen equal to 5, 10, 20, 40, 60, and 80 minutes. As a result of the experiments, it was shown that the optimal duration of deposition under the selected conditions of the electrochromic layer formation was the interval from 5 to 20 minutes, inclusive. The deposition time of 40 minutes did not improve the optical characteristics of the film. At the same time, with the deposition duration of 60 and 80 minutes, the electrochemical and optical parameters sharply decreased, the coloration depth and irreversibility during bleaching, as well as the specific capacitances of the processes decreased. In the course of data processing, the film thickness was calculated depending on the duration of deposition in several ways. Comparison of the graphs obtained made it possible to determine the approximate amount of polyvinyl alcohol in the electrochromic composite coating, as well as to estimate the current efficiency of the electrodeposition and oxidation-reduction process of the electrochromic material. In this case, the volume of polyvinyl alcohol in the composite was approximately equal to the volume of nickel hydroxide, and the efficiency of Ni(OH)2 deposition and coloration-bleaching processes was approximately 100