Abstract
Nickel hydroxides are widely used as the active material in supercapacitors. To improvise electrochemical activity, activators, namely Co and Al compounds, are introduced into the structure of nickel hydroxide. The most effective is the introduction of activators directly into the structure of nickel hydroxide. Characteristics of double Ni–Co (Ni:Co=8:1) and triple Ni–Co–Al (Ni:Co:Al=8:1:2) hydroxides, synthesized by single-stage reverse titration method were studied. Crystal structure of the samples was studied by means of X-ray diffraction analysis, thermogravimetry and differential scanning calorimetry, electrochemical characteristics were studied by means of cyclic voltammetry and galvanostatic charge-discharge cyclic in supercapacitor regime. Comparative analysis of characteristics of double Ni–Co and triple Ni–Co–Al hydroxide was conducted. By means of XRD analysis, thermogravimetry, and differential scanning calorimetry it was found that Ni–Co–Al is layered triple hydroxide with the structure of α-Ni(OH) 2 with high crystallinity. Ni-Co hydroxide is double Ni–Co hydroxide with the crystal lattice of β-Ni(OH) 2 , in which part of Ni 2+ is isostructurally substituted by Co 2+ , and low crystallinity. By means of cyclic voltammetry and galvanostatic charge-discharge cycling, high electrochemical activity of Ni–Co hydroxide was found. By means of cyclic voltammetry, an abnormal, α-like behavior of Ni–Co with β-Ni(OH) 2 lattice was found . The electrochemical activity of triple Ni–Co–Al hydroxide was found to be significantly lower than that of double Ni–Co hydroxide (maximum specific capacities are 550.4 F/g and 741.5 F/g, respectively), despite the structure of pure layered double hydroxide and presence of two activators. A hypothesis was proposed on the poisoning of Ni–Co–Al LTH with free aluminum compounds during reverse titration synthesis
Highlights
Nickel hydroxide and its different modifications possess high electrochemical activity [1]
The analysis shows that there are different opinions regarding the form of cobalt and nickel hydroxide that are to be used for the active material
Synthesis of layered double hydroxides (LDH) and layered triple hydroxide (LTH) samples Analytical grade reagents were used in the study with the exception of NaOH
Summary
Nickel hydroxide and its different modifications possess high electrochemical activity [1]. Monohydroxide and double hydroxides of nickel are used as the active material of nickel oxide electrode in alkaline Ni–Cd, Ni–Fe and Ni–MeH accumulators [3, 4]. Nickel hydroxide is used as cathode material in lithium batte ries [5]. Hydroxides of nickel are used as the active material of Faradic electrode of hybrid supercapacitors. Ni(OH) is used on its own [6, 7] and in the form of a composite with nanocarbon materials [8]. A nickel film can be formed on the conductive substrate [10]. Nickel hydroxides are used as electrochromic material [11, 12]. Ni(OH) has high electrocatalytic activity and is used for electrooxidation of various organic compounds [13], sensor applications [14]
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