Impedance of Al-substituted α-nickel hydroxide electrodes

Al-substituted α-nickel hydroxide were used as active materials in pasted nickel hydroxide electrodes for rechargeable alkaline batteries. The electrochemical impedance spectra of α-nickel hydroxide electrodes with different Al contents were measured. An equivalent circuit model was applied to simulate the experimental results. Some equivalent circuit parameters for different electrodes were determined. The reason why the α-nickel hydroxide electrode with 25% Al shows a better performance was discussed using these parameters.     

The cobalt content effect on the electrochemical behavior of nickel hydroxide electrodes

In this paper, the study of nickel hydroxide porous electrodes containing different concentrations of cobalt as additive (2–10%), polytetrafluoroethylene (PTFE) as binder material and prepared by chemical impregnation on nickel sintered substrate, are presented. The characterization of the different electrodes is performed using optical techniques such as scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrochemical techniques as cyclic voltammetry, charge-discharge curves and electrochemical impedance spectroscopy (EIS). The results indicate that the concentration of 5% metallic Co improves the electrochemical behavior of the active material.     

Effect of cobalt electroless deposition on nickel hydroxide electrodes

The effects of cobalt additive on the positive electrode surface of nickel alkaline batteries are investigated. Electrode surface modifications by electroless cobalt deposits were made at different immersion times. The performance of nickel hydroxide electrodes was studied by optical techniques, such as scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrochemical methods as cyclic voltammetry, charge–discharge curves and electrochemical impedance spectroscopy (EIS). According to these results, electroless cobalt deposits obtained with 5 min of immersion time in the electroless-bath exhibit a better electrode performance.     

Effect of cobalt addition to nickel hydroxide as a positive material for rechargeable alkaline batteries

Nickel hydroxide powder is used widely as an active material in pasted-type nickel electrodes. The effect on the electrochemical behaviour of cobalt addition (0.19–9.9 wt.%) to the nickel hydroxide powder is investigated. The physical properties of several nickel hydroxide powders containing different amounts of cobalt compound are examined by inductively coupled spectroscopy, laser diffraction, BET, X-ray diffraction and scanning electron microscopy measurements. The interlayer distance of the layered nickel hydroxide diminishes to a small value with increase in cobalt content. Moreover, the charge and discharge potentials of nickel hydroxide samples decrease with an increase in cobalt content. The chemical diffusion coefficients of the proton (D̄) in the nickel hydroxide samples with different amounts of cobalt are measured by a current-pulse relaxation technique. The D̄ and D₀ values increase with an increase in cobalt content, and the activation energy for proton diffusion is in the 0.20–0.33 eV range.     

Size effect investigation on battery performance: Comparison between micro- and nano-particles of β-Ni(OH)2 as nickel battery cathode material

In this work we report on the comparison between nano- and micro-particles of β-Ni(OH)₂ as cathode material of Ni battery. The synthesis of nano- and micro-particles of nickel hydroxide is done by two different procedures: sonication process and stirrer. Nano-particles of β-Ni(OH)₂ are synthesized by chemical precipitation from a solution containing NiCl₂·6H₂O and surfactant under ultrasonic irradiation. Micro-particles of β-Ni(OH)₂ are synthesized by a similar procedure while applying magnetic stirring instead of ultrasonic. The products are characterized by scanning electron microscopy and X-ray powder diffraction. Under the optimized conditions nickel hydroxide nano-particles, with an average particle size of 18 nm, are obtained. Cyclic voltammetric (CV) studies show a pair of well-defined peaks for Ni(OH)₂/NiOOH redox reaction, along with faster proton diffusion coefficient and higher oxygen evolution potential for nano-particles of nickel hydroxide compared to that of micro-particles. Electrochemical impedance spectroscopy (EIS) studies of Ni(OH)₂ electrodes show that the reaction occurring at the nickel hydroxide is controlled by charge transfer and Warburg diffusion. The β-Ni(OH)₂ nano-particles are found to exhibit a superior cycling reversibility and improved capacity when they are used as positive electrode materials of alkaline rechargeable batteries.     

Stability enhancement of the CoOOH conductive network of nickel hydroxide electrodes

Nickel hydroxide is used as the electrochemically active material in positive electrodes of rechargeable alkaline batteries. Well-spread CoOOH is used as the conductive network to enhance the utilization of the nickel hydroxide. If the nickel hydroxide electrode is subjected to a negative potential it may display an enduring capacity loss due to an irreversible electrochemical reduction of CoOOH. In this paper it has been demonstrated that the addition of MnO₂ to nickel hydroxide pressed powder electrodes ensures 100% capacity retention after imposing reducing conditions.     

Mathematical modeling of lithium-ion and nickel battery systems

A review of mathematical models of lithium and nickel battery systems developed at the University of South Carolina is presented. Models of Li/Li-ion batteries are reviewed that simulated the behavior of single electrode particles, single electrodes, full cells and batteries (sets of full cells) under a variety of operating conditions (e.g. constant current discharge, pulse discharge, impedance and cyclic voltammetry). Models of nickel battery systems are reviewed that simulate the performance of full cells, as well as the behavior of the nickel hydroxide active material. The ability of these models to predict reality is demonstrated by frequent comparisons with experimental data.     

Fe-Cu coated nickel mesh usage as cathode catalyst for hydrogen evolution reaction

Nickel mesh electrodes were used as the working electrode. Iron and copper were electrochemically deposited on the nickel mesh in different amounts. When electrochemical coatings had been carried out, different currents were passed from the circuit at different times and coatings were accumulated at constant load. The prepared electrodes called as FexCux, FexCu3x and FexCu9x and these electrodes have been used for hydrogen evolution reaction (HER). The surface morphologies were investigated by scanning electron microscopy. The HER activity is assessed by recording cathodic current–potential curves, cyclic voltammetry, electrochemical impedance spectroscopy. The results show that FexCu9x catalysts have a compact and porous structure as well as good electrocatalytic activity for the HER in alkaline media.     

Nickel hydroxide/activated carbon composite electrodes for electrochemical capacitors

In this paper, a nickel hydroxide/activated carbon (AC) composite electrode for use in an electrochemical capacitor was prepared by a simple chemical precipitation method. The structure and morphology of nickel hydroxide/AC were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that nano-sized nickel hydroxide was loading on the surface of activated carbon. Electrochemical performance of the composite electrodes with different loading amount was studied by cyclic voltammetry and galvanostatic charge/discharge measurements. It was demonstrated that the introduction of a small amount of nickel hydroxide to activated carbon could promote the specific capacitance of a composite electrode. The composite electrodes have good electrochemical performance and high charge–discharge properties. Moreover, when the loading amount of nickel hydroxide was 6 wt.%, the composite electrode showed a high specific capacitance of 314.5 F g⁻¹, which is 23.3% higher than pure activated carbon (255.1 F g⁻¹). Also, the composite electrochemical capacitor exhibits a stable cyclic life in the potential range of 0–1.0 V.     

Electrochemical properties of the pasted nickel electrode using surface modified Ni(OH)2 powder as active material

Nickel hydroxide powder was modified by immersing the mixture of nickel hydroxide powder with cobalt compounds in an alkali solution or by chemical deposition. Electrochemical properties of the pasted nickel electrodes consisting of surface modified Ni(OH)₂ powder in a porous nickel substrate were studied. The results show that the active material utilization of the modified nickel electrodes greatly increases due to the uniform distribution of a Co(OH)₂ layer on the surface of the nickel hydroxide powder resulting in the improvement of the electrochemical activity and conductivity. The EIS results show that the Co(OH)₂ layer decreases the charge-transfer resistance and increases the active surface area of the nickel electrode.     

Performance characterization of sintered iron electrodes in nickel/iron alkaline batteries

A nickel/iron storage battery with a porous, sintered, iron negative electrode and a nickel positive electrode is a high power system by virtue of its low internal resistance. A dry-powder sintering procedure is used to fabricate negative and positive electrodes. Negative iron electrodes are activated with various salt solutions such as CdSO₄, BaCl₂, HgCl₂ and sulfur. Positive electrodes are impregnated with nickel hydroxide by a chemical method. Tests are performed in 10 Ah capacity nickel/iron cells and two types of activated iron electrodes are used. The present work deals with electrode fabrication, charge/discharge studies, self-discharge, temperature performance and cycle life. Finally, the best iron electrodes are coupled with nickel electrodes to obtain a 1.37 V, 75 Ah nickel/iron cell. The performance of this cell is discussed.     

Synthesis and characterization of high-density non-spherical Ni(OH)2 cathode material for Ni–MH batteries

Positive electrode active materials of non-spherical nickel hydroxide powders with a high tap-density for alkaline Ni–MH batteries have been successfully synthesized using a polyacrylamide (PAM) assisted two-step drying method. The tap-density of the powders reaches 2.32 g cm⁻³, which is significantly higher than that of nickel hydroxide powders obtained by the conventional co-precipitation method. X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG-DTA), Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, tap-density testing, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge–discharge test were used to characterize the physical and electrochemical properties of the synthesized material. The results show that the as-prepared nickel hydroxide materials have an irregular tabular shape, a high density of structural disorder, and a high specific surface area. The charge–discharge tests indicate that nickel hydroxide powders synthesized by the new method have better electrochemical performance than those obtained by the conventional co-precipitation method. This performance improvement could be attributable to a more compact electrode microstructure, a lower amount of intercalated anions, better reaction reversibility, a higher proton diffusion coefficient, and lower electrochemical impedance, as indicated by TG-DTA, CV, and EIS. The results clearly show that better electrochemical activity can be achieved using nickel hydroxide that has a higher tap-density. Moreover, the new synthesis process is simple, cost-effective, and facile for large-scale production.     

Cyclic voltammetric studies of stabilized α-nickel hydroxide electrode

Substitution of aluminum for nickel in the lattice of nickel hydroxide, prepared by co-precipitation, leads to hydrofalcite-like compound of α-nickel hydroxide. This compound has been used as the electrochemical active material in the positive electrodes of rechargeable alkaline batteries. Cyclic voltammetric studies suggest that α-nickel hydroxide displays better reversibility of the Ni(OH)₂/NiOOH redox couple. The mechanism of the electrode reaction is still found to be controlled by proton diffusion, and the proton diffusion coefficient differs with the content of aluminium.     

Effects of γ-CoOOH coating on the high-temperature and high-rate performances of spherical nickel hydroxide electrodes

To improve the high-temperature and high-rate performances of nickel hydroxide electrodes in nickel–metal hydride (Ni/MH) batteries, γ-CoOOH is coated onto spherical Ni(OH)₂ through surface modification. X-ray diffraction, scanning electron microscopy with energy dispersive X-ray, and X-ray photoelectron spectroscopy are used to characterize the synthesized products. The effects of γ-CoOOH on the electrochemical performance of nickel electrodes are investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and a charge/discharge test. It is found that the spherical γ-CoOOH-coated Ni(OH)₂ electrode without adding any conductive additives exhibits superior electrode properties including excellent high-temperature and high-rate discharge abilities, and superior cycling reversibility. These performance improvements are ascribed to the enhancement of oxygen evolution over-potential, slower oxygen evolution rate and lower charge transfer resistance resulting from the high conductivity coating of γ-CoOOH.     

Study on the in situ sulfidation and electrochemical performance of spherical nickel hydroxide

In this paper, atmospheric reflux in water is used to directly form a nickel sulfide layer in-situ with excellent conductivity sulfide on the surface of spherical nickel hydroxide particles, significantly improving the conductivity of nickel hydroxide particles. The experimental results show that the spherical Ni(OH)₂@NiS material synthesized by the in situ sulfurization method. As the cathode active material of nickel-iron batteries exhibits excellent electrochemical performance, especially high-rate discharge and cycle performance, which are better than nickel hydroxide electrodes with cobalt oxide. The atmospheric reflux method in water has a simple process and equipment and has no pollution to the environment. Spherical Ni(OH)₂@NiS materials synthesized by in situ vulcanization can completely replace nickel hydroxide material with cobalt, and they have great commercial application value and market competitiveness as cathode active materials for alkaline nickel-based batteries.     

Effects of different electrolytes containing Na2WO4 on the electrochemical performance of nickel hydroxide electrodes for nickel–metal hydride batteries

To improve the high-temperature performance of the nickel hydroxide electrodes in nickel–metal hydride batteries, sodium tungstate (Na₂WO₄) used as an electrolyte additive has been added into two types of binary electrolytes (KOH–LiOH and NaOH–LiOH) in this study. The effects of electrolyte composition on the electrochemical performance of nickel electrodes have been systematically investigated via a combination of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and charge/discharge tests. It is found that by adding (1.0 wt.%) Na₂WO₄, the performance of nickel electrodes is significantly improved in both NaOH and KOH electrolytes at 70 °C. The improved performance can be attributed to the deposition of WO₃·2H₂O solid film on the surface of nickel electrode, which is beneficial to the increase in oxygen evolution overpotential, the slow-down of oxygen evolution rate and the decrease in charge-transfer resistance.     

Effect of cupric oxide addition on the performance of nickel electrode

Nickel hydroxide is widely used as the active material in positive electrodes of rechargeable alkaline batteries. In this paper, the effects of cupric oxide additive on the characteristics of the nickel electrode have been investigated. The results indicate that the addition of cupric oxide in the nickel electrode can prevent swelling of the nickel electrode during charging and thus prolong the cycle-life of rechargeable batteries. Cupric oxide additive can also promote the transformation from cobalt powder to β-CoOOH and make cobalt additive be well-spread on nickel hydroxide particles, thus facilitate the charging process in the initial stage.     

Nickel hydroxide deposited indium tin oxide electrodes as electrocatalysts for direct oxidation of carbohydrates in alkaline medium

In this work, the direct electrochemical oxidation of carbohydrates using nickel hydroxide modified indium tin oxide (ITO) electrodes in alkaline medium is demonstrated; suggesting the feasibility of using carbohydrates as a novel fuel in alkaline fuel cells applications. The chosen monosaccharides are namely glucose and fructose; disaccharides such as sucrose and lactose; and sugar acid like ascorbic acid for this study. ITO electrodes are chemically modified using a hexagonal lyotropic liquid crystalline phase template electrodeposition of nickel. Structural morphology, growth, orientation and electrochemical behaviour of Ni deposits are characterized using SEM, XRD, XPS and cyclic voltammetry (CV), respectively. Further electrochemical potential cycling process in alkaline medium is employed to convert these Ni deposits into corresponding nickel hydroxide modified electrodes. These electrodes are used as novel platform to perform the electrocatalytic oxidation of various carbohydrates in alkaline medium. It was found that bare and Ni coated ITO electrodes are inactive towards carbohydrates oxidation. The heterogeneous rate constant values are determined and calculated to be two orders of magnitude higher in the case of template method when compared to non-template technique. The observed effect is attributed to the synergistic effect of higher surface area of these deposits and catalytic ability of Ni(II)/Ni(III) redox couple.     

The influences of some additives on electrochemical behaviour of nickel electrodes

Nickel hydroxide is used as an active material in positive electrodes of rechargeable alkaline batteries. Since the nickel hydroxide electrode exhibits a poor performance which results not only from the competitive reactions of the oxidation of the active material but also from the evolution of oxygen. Its reduced charge acceptance is suspected to be related to a relatively long distance between nickel hydroxide particles and the nearest portion of the substrate. The practical capacity of the positive nickel electrode depends on the efficiency of the conductive network connecting the Ni(OH)₂ particle with the current collector.     

The hydrogen evolution reaction on nickel-polyaniline composite electrodes

The electrolytic codeposition of nickel composite coatings with different amounts of polyaniline particles (PAni) was used to produce electrodes for the catalytic hydrogen evolution reaction (HER). The electrodes produced were imaged by scanning electron microscopy, and their catalytic activities for HER were determined by linear Tafel polarization and electrochemical impedance spectroscopy (EIS) in a 0.5 M H₂SO₄ solution. The electron micrographs showed that the amount of exposed polyaniline surface was directly related to the polyaniline concentration in the solution used for the electrolytic codeposition. The linear Tafel polarizations indicated that the HER was limited by the Volmer step, and the EIS measurements showed that the presence of PAni on the electrode surface affected the HER. Electrodes with higher composite contents exhibited enhanced catalytic activity.