Some effects of the addition of cobalt to the nickel hydroxide electrode

The action of cobalt upon the characteristics of the nickel hydroxide electrode has been investigated by constant current, linear potential sweep and EDAX methods. It was found that cobalt raises the oxygen overpotential and promotes greater utilization of the active material, although major additions of cobalt were observed to lower the working potential of the electrode. It was also found that cobalt prevented any significant loss of electrode capacity when the system was poisoned with iron.     

Cyclic voltammetric studies of pasted nickel hydroxide electrode microencapsulated by cobalt

Spherical nickel hydroxide microencapsulated by cobalt has been used as the electrochemically active material in pasted-type nickel electrodes of rechargeable alkaline batteries. Cobalt coating on the surface of nickel hydroxide particles can be converted to CoOOH during charge. Well distributed CoOOH forms the conductive network on the surface of nickel hydroxide particles, thereby leading to higher utilization of active material. Cyclic voltammetric studies suggest that nickel hydroxide microencapsulated by cobalt has better reversibility of the Ni(OH)2/NiOOH redox couple, greater discharge capacity and higher oxygen evolution overpotential than nickel hydroxide with added cobalt metal powder as a conductor. The mechanism of the electrode reaction is still found to be controlled by proton diffusion, and the proton diffusion coefficient is 1. 2×10–9cm2s–1.     

Non-equilibrium effects in the nickel hydroxide electrode

The electrochemical reaction Ni(OH)₂=NiOOH+H⁺+e occurring under potentiodynamic conditions in 1 N KOH using complex triangular potential sweep revealed the existence of non-equilibrium effects of both reactant and products which cause the splitting of the anodic current peak already known. By a suitable choice of the perturbation variables, the rate of the chemical change the Ni(OH)₂ species undergoes can be estimated. The reaction presenting the nickel hydroxide electrode is interpreted as two parallel electron transfer steps coupled to two chemical reactions through a square-type reaction model.     

The effect of lithium in preventing iron poisoning in the nickel hydroxide electrode

The effect of lithium in preventing poisoning of the nickel hydroxide electrode by soluble iron species has been investigated using constant current, X-ray diffraction and EDAX methods. Iron was found to decrease the oxygen overpotential preventing full charging of the electrode. It was found that lithium prevented this loss of capacity, probably due to an increase in the oxygen overpotential.     

Ball milled cobalt oxyhydroxide coat on the surface of nickel hydroxide

Cobalt oxyhydroxide coat on the surface of nickel hydroxide particles is finished employing a simple ball milling process. The structure, morphology, and surface composition of the coated Ni(OH)₂ particles is characterized by using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy tests. The results show that numerous strip-like particles of a mixture of Ni(OH)₂ and CoOOH aggregate on the surface of the Ni(OH)₂ particles, and a structure of β-Ni(OH)₂ is preserved. Compared to the Ni(OH)₂ electrodes with a mixed CoO additive, the electrochemical activity of the electrodes with ball milled CoOOH coat can be improved as shown by using electrochemical impedance spectroscopy test, thus resulting in charge–discharge and cycle life performance improvement of the electrodes.     

纳米氢氧化镍掺杂镍电极的电化学性能

介绍了一种通过合成草酸镍,进而生成纳米Ni(OH)2的新的合成路线.X射线衍射以及红外光谱测试结果表明,得到的Ni(OH)2为β型.通过透射电镜观察到,合成的Ni(OH)2样品呈针状,长度在100～200 nm之间,直径为10～20 nm.对掺杂质量分数8%纳米级氢氧化镍的电极的电化学性能进行了测试,可以发现:放电容量比未掺杂的球形氢氧化镍电极提高了9.6%,且经过10次循环以后放电容量仍能达到原来的94%.     

非晶相氢氧化镍电极材料的研究进展

非晶态材料原子排列无序性强、结构缺陷多,内部含有大量配位不饱和原子和表面活性中心,是理想的高性能电极材料.本文综述了非晶相氢氧化镍电极材料的制备方法,描述了非晶相氢氧化镍作为电极活性材料的电化学特性.提出了非晶相氢氧化镍进一步的研究方向.     

A study on the swelling of a sintered nickel hydroxide electrode

The swelling and blistering of a sintered nickel hydroxide electrode, which usually determine the life of the electrode, have been found to be dependent on the the change in the density of the active material during charge and discharge. In particular, the swelling after cycling has been related to the degree of formation of -NiOOH. The largest swelling, as represented by an increase in the thickness of the electrode, occurs when -NiOOH changes to -NiOOH during charging rather than discharging. Addition of cadmium, zinc and magnesium is effective in preventing the formation of -NiOOH. In particular, the swelling can be almost completely prevented by addition of cobalt and cadmium together, even with overcharging at the 1 C rate.     

The influence of temperature on the current peak multiplicity related to the nickel hydroxide electrode

The splitting of the anodic and cathodic potentiodynamic E/I display of the nickel hydroxide electrode in 1 N KOH between 0 and 75° C is reported. The formal first order rate constants for the chemical reactions which occur simultaneously with the electrochemical steps, and the corresponding activation energies are evaluated. The results are discussed on the basis of the reaction model recently proposed for the nickel hydroxide electrode.     

Electrochemical studies of the nickel electrode with cobalt modification

The electrochemical behaviour of the paste-type nickel hydroxide electrode with cobalt-modified nickel foam was investigated using galvanostatic charge–discharge, electrochemical impedance spectroscopy, cyclic voltammetry and current pulse relaxation methods. Experimental results showed that the performance of the nickel electrode with substrate deposition of a thin layer of cobalt was improved markedly. This improvement could be attributed to the enhanced electrical conduction between the substrate and the active material. The enhanced electrical conduction increases the charge efficiency and the discharge depth of the nickel electrodes and therefore increases the utilization of the active material. This suggests that the electrical conduction between the substrate and the active material is essential to the practical use of paste-type nickel hydroxide electrodes.     

Ageing and the diffusion process at the nickel hydroxide electrode

The ageing of α-Ni(OH)₂ causes changes in the characteristics of the electrode due to the formation of different oxyhydroxides on charging. The discharge process has been studied by potential step technique, and diffusion coefficients refined by extrapolation have shown little variation with ageing for measurements made at room temperature. An unusual temperature function has been recorded and its mechanistic implications are discussed.     

Studies on the lithium and potassium uptake of nickel hydroxide electrodes

The extent of lithium and potassium uptake by both- and-Ni(OH)₂ electrodes has been studied by atomic absorption/emission spectroscopy. It was found that lithium ions are preferentially taken up into the bulk of the electrodes. The increase in the end-of-charge potential on constant current charging in lithiated electrolyte compared with pure potassium hydroxide is attributed to the bulk incorporation of lithium into the Ni(OH)₂ electrodes. X-ray studies have indicated no change in the phases present in the lithiated electrolytes either in the charged or discharged states. Cyclic voltametric measurements to 100 cycles showed no significant benefit due to lithium ions in terms of charge retention.     

Performance improvement of pasted nickel electrodes with an addition of ball-milled nickel hydroxide powder

Spherical β-Ni(OH)₂ was modified by a low-cost method of normal ball milling (NBM), and the physical properties of both ball-milled and un-milled Ni(OH)₂ were characterized by transmission electron microscopy, specific surface area, particle size distribution and X-ray diffraction. It was found that NBM could obviously increase the surface area, decrease the particle and crystallite size, and reduce the crystallinity of β-Ni(OH)₂, which were advantageous to the improvement of the electrochemical activity of Ni(OH)₂. NBM also lowered the packing density and flowability of Ni(OH)₂, as revealed by the measurements of tapping density and angle of repose. Electrochemical performances of pasted nickel electrodes with an addition of ball-milled Ni(OH)₂ to spherical Ni(OH)₂ as the active material were investigated, and were compared with those of the pure spherical Ni(OH)₂ electrodes. Charge/discharge tests showed that ball-milled Ni(OH)₂ addition could enhance the charging efficiency, specific discharge capacity, discharge voltage and high-rate capability of the electrodes. This performance improvement could be attributed to a more compact electrode microstructure, better reaction reversibility and lower electrochemical impedance, as indicated by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Thus, it was an effective method to modify the microstructure and improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of ball-milled Ni(OH)₂ to spherical Ni(OH)₂ as the active material.     

The potentiodynamic investigations of the overcharge and self-discharge of nickel hydroxide electrode

Potentiodynamic investigations of the nickel hydroxide electrodes were carried out. We have tried to explain the mechanisms of the overcharge and self-discharge of these electrodes.     

Electrocatalytic oxidation of urea by nanostructured nickel/cobalt hydroxide electrodes

The present paper describes the catalytic oxidation of urea performed by nickel hydroxide and nickel/cobalt hydroxide modified electrodes by using both electrodeposited films and nanoparticles. The incorporation of Co foreign atoms leads to a slight increase in sensitivity besides the shift in redox process, avoiding the oxygen reaction. Nanostructured Ni₈₀Co₂₀(OH)₂ was synthesized by sonochemical route producing 5 nm diameter particles characterized by high-resolution transmission electron microscopy (HRTEM) being immobilized onto electrode by using the electrostatic Layer-by-layer technique, yielding attractive modified electrodes for sensor development.     

Structure and electrochemical properties of nickel hydroxide electrodes with cobalt additives

In this article,cobalt additives are introduced into nickel hydroxide electrodes by two incorporation methods—co-precipitated cobalt hydroxide during the nickel hydroxide synthesis or post-added CoO with nickel hydroxide. The results of X-ray diffraction, cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests indicate that (i) the diffraction peaks show a decrease in intensity and increase in the half peak breadths for Ni(OH)₂ with co-precipitated cobalt hydroxide; (ii) the electrochemical activity of nickel hydroxide can be improved by both incorporated cobalt and the effects of post-added CoO are more notable; (iii) CoOOH derived from post-added CoO is not stable in the KOH electrolyte when the potential of the Ni(OH)₂ electrode is lowered and its reduction product may be inactive, thus results in an irreversible capacity loss of nickel-metal-hydride battery after over-discharge-state storage.     

Electrochemical and chemical reactions involving non-equilibrium species at the nickel hydroxide electrode

The square-type reaction scheme proposed to interpret the behaviour of the nickel hydroxide electrode in KOH solutions under non-equilibrium conditions must include electrochemical as well as chemical crossed reactions between the different transient species. These reactions are evidenced by means of the triangularly-modulated triangular potential sweep technique. The contribution of the crossed reactions in the square-type reaction scheme becomes more relevant as the KOH concentrations decreased in the presence of K₂SO₄ supporting electrolyte.     

Theory of porous electrodes—XVI. The nickel hydroxide electrode

A model of the positive plate of a nickel—cadmium accumulator is proposed, based on the known electrochemical behaviour of hydrated nickel oxides and on transport equations similar to those used previously for the cadmium electrode. The mathematical treatment of this model allows to predict the theoretical discharge characteristics, which are compared with those measured on a real electrode. A comparison of the calculated and measured discharge time suggests that the composition of the oxidised form is intermediate between NiO_1.5 and NiO_1.8.     

A study of the electro-catalytic oxidation of methanol on a cobalt hydroxide modified glassy carbon electrode

Cobalt hydroxide modified glassy carbon electrodes (CHM/GC) prepared by the anodic deposition in presence of tartrate ions have been used for the electro-catalytic oxidation of methanol in alkaline solutions where the methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (IS) have been employed. In CV studies, in the presence of methanol the peak current of the oxidation of cobalt hydroxide increase is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of methanol is being catalysed through the mediated electron transfer across the cobalt hydroxide layer comprising of cobalt ions of various valence states. A mechanism based on the electro-chemical generation of Co(IV) active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. In this context the charge transfer resistance accessible both theoretically and through the IS studies have been used as a criteria. Under the CA regimes the reaction followed a Cottrellian behaviour.