A study of the increased temperature influence on the electrochromic and electrochemical characteristics of Ni(OH)2-PVA composite films

2020

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Nickel hydroxide is widely used in supercapacitors, alkaline batteries, for the electrocatalytic oxidation of organic contaminants, etc. Due to their electrochemical activity, Ni(OH) 2 (α+β) samples of a layer structure synthesized in a slit diaphragm electrolyzer are the most promising. The effect of the thermal field on the structural characteristics of layered (α+β) Ni(OH) 2 was studied. The effect was assessed in two ways: 1) internal (in situ) cooling directly in the electrolyzer by cooling the cathode from the rear side; 2) external (ex situ) heating directly after the electrolyzer when passing through a spiral heat exchanger heated to 90 °C. The crystal structure of the samples was studied by X-ray phase analysis. It was shown that the base sample obtained without changing the thermal field was a monophase layered (α+β) structure with a high content of α-modification and a gradient transition from α to β through a number of intermediate structures. The crystallinity of the sample was not high. During the internal cooling of the cathode, the crystallinity decreased and the fraction of the α-modification increased. External heating of the nickel hydroxide suspension immediately after leaving the electrolyzer led to the recrystallization of the samples with the decomposition of the (α+β) layered structure and formation of β-Ni(OH) 2 with high crystallinity. It was found that external 6-minute heating did not change the crystal structure. This is explained by the fact that the aging process of nickel hydroxide at an elevated temperature is a crystal-chemical transformation, which is characterized by an induction period, during which the rate of the process is minimal. As a result, the study has shown the possibility of controlling the type of forming crystalline modification of nickel hydroxide and its crystallinity by changing the internal (in situ) or external (ex situ) thermal field

“…2, c). Based on the published data, this can lead to a decrease in the electrochemical activity of the sample [58][59][60]. However, this increases stability.…”

Section: Discussion Of the Results Of The Thermal Field Effect On Thementioning

confidence: 99%

Section: Literature Review and Problem Statementmentioning

confidence: 99%

Changes in the nickel hydroxide properties under the influence of thermal field in situ and ex situ during electrochemical synthesis

2020

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“…It is assumed that laser radiation removes a part of the coating, and the nearest layers to the point of the laser impact melt and increase adhesion to the substrate surface [37]. This is due to the fact that the coating contains polyvinyl alcohol with a glass transition temperature of about 85 °C.…”

Section: Discussion Of the Characteristics Of Processed And Unprocessmentioning

confidence: 99%

A study of the possibility of conducting selective laser processing of thin composite electrochromic Ni(OH)2-PVA films

2021

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The surfaces of thin composite electrochromic Ni(OH)2-polyvinyl alcohol films, deposited by the cathodic template method on FTO glass substrates, were proposed to be processed using laser radiation. The processing of these films was carried out in a colored state with a laser beam of a semiconductor emitter with a wavelength of 650 nm (red) with a pulse duration of 3,000 μs, the beam diameter was about 40 μm. The energy at a single point was 37.5 J/cm2. The result was a film with microholes of about 80 μm. The transparent areas of the surface did not exhibit electrochromic properties, which indicated the absence of the original electrochromic coating. The study of the properties of the laser-processed film following a certain pattern showed that the characteristics of composite Ni(OH)2-polyvinyl alcohol coatings had changed significantly. On the one hand, the coloration depth of the films decreased by several percent, on the other hand, the specific electrochemical characteristics increased significantly. The study also showed that laser processing did not lead to significant changes in the main properties of the transparent electrically conductive layer – color and resistance. Before and after laser processing, the surface resistance of FTO glasses was 12.1±0.9 and 14.4±1.2 Ohm/sq., respectively. In addition, it was found that the processing of Ni(OH)2-polyvinyl alcohol films improved the adhesion of the latter to the surface of FTO glass. Based on the data obtained, a selective method was proposed for modifying thin colored films deposited on transparent conductive oxides (FTO, ITO, AZO) by visible laser radiation. This approach to changing the properties of films can be useful for areas related to the development of sensors, microelectronics, solar cells, small-sized current sources, electrodes with high efficiency, etc.

“…Raising the temperature initially improves the characteristics of the α-Ni(OH) 2 film. However, a further increase in temperature leads to a significant deterioration in the electrochemical and electrochromic characteristics of the film, probably as a result of an increase in crystallinity [60]. For the chemical synthesis method, the temperature is also the main factor in controlling the type and crystallinity of the product [61].…”

Section: Introductionmentioning

confidence: 99%

Improvement of continuous technology of electrochemical synthesis of nickel hydroxide by implementation of solution recycling

2021

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Nickel hydroxide is widely used in supercapacitors, alkaline batteries, for the electrocatalytic oxidation of organic contaminants, etc. Due to their electrochemical activity, Ni(OH)2 (α+β) samples with a layer structure synthesized in a slit diaphragm electrolyzer are the most promising. To improve the continuous technology of electrochemical synthesis of nickel hydroxide, the possibility of recycling the spent catholyte containing sodium sulfate was determined. For this, samples of nickel hydroxide were synthesized from a solution of nickel sulfate in the presence of sodium sulfate with concentrations of 40, 60, 80, 100, and 120 g/L. The crystal structure of the samples was studied by X-ray phase analysis; the electrochemical properties were studied by the method of cyclic voltammetry. It was shown that the base sample obtained without the presence of sodium sulfate was a monophase layered (α+β) structure with a high content of α-modification. The crystallinity of the sample was not high. It was revealed that the presence of sodium sulfate led to a decrease in the crystallinity of nickel hydroxide due to an increase in the electrical conductivity of the solution and a decrease in the voltage in the electrolyzer. Cyclic voltramperometry showed that synthesis in a slit diaphragm electrolyzer in the presence of Na2SO4 (40–80 g/L) did not lead to a significant change in the electrochemical activity of nickel hydroxide samples. An increase in the concentration of sodium sulfate in the catholyte to 100–120 g/L led to an increase in electrochemical activity – the specific current of the discharge peak was 3.7–3.9 A/g (compared to 2.1 A/g for the reference sample).A comprehensive analysis of the characteristics of nickel hydroxide samples synthesized in the presence of sodium sulfate revealed the possibility and prospects of recycling the spent catholyte in a continuous technology for producing Ni(OH)2 in a slit diaphragm electrolyzer. It was revealed that when introducing recycling, it was recommended to maintain a high concentration of sodium sulfate (80–100 g/L)