Abstract
Nickel hydroxide is widely used as the active material in chemical power sources. The formation mechanism of nickel hydroxide includes two fast phases of the formation of an initial amorphous particle and slow aging (crystallization) stage. Characteristics of nickel hydroxide can be improved by slowing down the first stage through the reaction of nickel cation with «soft» ligand and formation of a weak complex. It is proposed to use acetate ion as a «soft» ligand, which forms a complex with Ni2+ without the outer sphere. The influence of acetate ion on the crystal structure, particle morphology and electrochemical properties of nickel hydroxide chemically precipitated at high supersaturation using nickel sulfate in the presence and absence of sodium acetate is studied. The crystal structure of the samples is studied by means of X-ray diffraction analysis and sample morphology – by means of scanning electron microscopy, electrochemical properties – cyclic voltammetry. A comparative analysis of the characteristics of the samples prepared in the presence and absence of sodium acetate is carried out. The results of XRD analysis revealed that synthesis in the presence of acetate ion leads to the formation of a bi-phase system that contains low crystallinity β-Ni(OH)2 and α-Ni(OH)2. This also leads to a higher content of smaller particles with a larger surface area. The comparative analysis of electrochemical characteristics revealed the formation of a more active samples in the presence of acetate ions, which predominantly behaves like the α-form. The sample activity increased during cycling. Synthesis in the presence of acetate ion results in the increase of specific discharge peak current (equivalent to electrochemical activity) by 1.93 times, in comparison to the sample synthesized under the same condition but in the absence of acetate ions
Highlights
Owing to high electrochemical activity [1], nickel hydroxides are used in various electrochemical devices.Ni(OH)2, double nickel hydroxides are used as the active material of nickel oxide electrode for alkaline batteries [2, 3], and as oxide after sintering – in lithium batteries [4]
Samples of nickel hydroxide were chemically precipitated at high supersaturation using nickel sulfate in the presence and absence of sodium acetate (25 % molar relative to Ni2+)
The results of X-ray diffraction analysis (XRD) analysis revealed that synthesis in the presence of acetate ion leads to the formation of a biphase system that contains low crystallinity β-Ni(OH)2 and α-Ni(OH)2
Summary
Owing to high electrochemical activity [1], nickel hydroxides are used in various electrochemical devices. Ni(OH), double nickel hydroxides are used as the active material of nickel oxide electrode for alkaline batteries [2, 3], and as oxide after sintering – in lithium batteries [4]. Various Ni(OH) modifications are used as the active material of the Faradic electrode of hybrid supercapacitors. Nickel hydroxide is used in electrochromic devi ces [11, 12] because thin layers of Ni(OH) are almost transparent, while NiOOH has a dark-brown color. It is used for the electrochemical oxidation of various organic compounds [13, 14] and in sensors [15, 16]. Determining the influence of synthesis parameters on structural parameters and electrochemical properties of Ni(OH) is a relevant problem
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