Influence of the carbonate ion on characteristics of electrochemically synthesized layered (α+β) nickel hydroxide

• Main Authors: Vadym Kovalenko, Valerii Kotok
• Format: Article
• Language: English
• Published: PC Technology Center 2019-02-01
• Series: Eastern-European Journal of Enterprise Technologies
• Subjects: nickel hydroxide; layered (α+β) structure; specific capacity; alkaline accumulator; slit-diaphragm electrolyzer; carbonate
• Online Access: http://journals.uran.ua/eejet/article/view/155738

Nickel hydroxide is widely used as the active material of supercapacitors. The most active are samples of Ni(OH)2 with (α+β) layered structure, synthesized in the slit diaphragm electrolyzer. Influence of carbonate anion on the structure and electrochemical properties of nickel hydroxide samples has been studied by means of sample synthesis in the slit-diaphragm electrolyzer with the use of the diaphragm and cation-exchange membrane as chamber separator. The experiment revealed that when the diaphragm is used, there is a filtration flow from the anodic chamber (alkali with carbonate) into the cathodic chamber. Thus, the samples synthesized with the diaphragm are formed in the presence of carbonates, while the samples synthesized with the cation-exchange membrane – in the absence of carbonates. Crystal structure of the samples was studied by means of X-ray diffraction analysis, electrochemical characteristics – by means of cyclic voltammetry and galvanostatic charge-discharge cycling in the accumulator regime. Comparative analysis of the samples synthesized in the presence or absence of carbonates has been conducted. By means of X-ray diffraction and cyclic voltammetry, the key role of carbonate ions in the formation of monophase layered (α+β) structure has been revealed. The absence of carbonate resulted in lower crystallinity, α-phase content, the formation of the bi-phase system, composed of the mixture of β-form and (α+β)-structure, at high current densities (12 and 15.7 A/dm2). The study of electrochemical characteristics revealed a decrease in specific capacity by 14.7–31.4 % for hydroxide samples formed in the absence of carbonate ions. The highest specific capacity was obtained for the samples synthesized in the SDE at i=10 A/dm2 with the diaphragm (in the presence of carbonates) and with the membrane (in the absence of carbonates), and are 216.8 and 185 mA·h/g respectively. To increase specific capacity, it is recommended to conduct synthesis in the SDE with the use of the diaphragm and introduce an additional quantity of sodium carbonate into the anolyte