Y.S. Zhang

Physical and electrochemical characteristics of aluminium-substituted nickel hydroxide

Substitution of 20 aluminium for nickel in the lattice of nickel hydroxide, prepared by coprecipitation, leads to a hydrotalcite-like compound of formula Ni0.8Al0.2(OH)2(CO3)0.1.0.66H2O. It has been found that the compound has prolonged stability in 6m KOH solution and can be used as the positive electrode material in rechargeable alkaline batteries. The structure, morphology and composition of the compound have been investigated by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. The electrode comprising the aluminium-substituted nickel hydroxide has greater discharge capacity and higher utilization of active material than the β-Ni(OH)2 electrode. Cyclic voltammetry suggest that the aluminium-substituted nickel hydroxide has better reversibility of the Ni(OH)2/NiOOH redox couple and higher oxygen evolution overpotential than β-Ni(OH)2. The mechanism of the electrode reaction has also been discussed and the proton diffusion coefficient in the compound has been determined.

Impedance studies of nickel hydroxide microencapsulated by cobalt

Abstract Nickel hydroxide is used as an active material in pasted-type nickel hydroxide electrodes for rechargeable alkaline batteries. The electrochemical impedance spectroscopes of different nickel hydroxide electrodes were measured. The results were analyzed using a standard equivalent circuit model including a Warburg impedance term. The Nyquist plots were used to interpret the characteristics of the different electrodes. The nickel hydroxide electrode deposited by cobalt has shown lower charge transfer resistance and higher electronic and protonic conductivity.

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.

Electrochemical properties of the Zr(V0.4Ni0.6)2.4 hydrogen storage alloy electrode

Abstract In order to improve the electrocatalytic activity, hydrogen adsorption performance and activation behaviour of the Zr(V 0.4 Ni 0.6 ) 2.4 alloy electrode, the alloy powder surface was modified by HF acid solution treatment. It was found that the alloy surface was transformed from a Zr-rich layer to a Ni-rich layer after the treatment and the electrocatalytic activity, hydrogen adsorption performance and activation behaviour of the alloy electrodes were significantly improved. An electrode reaction mechanism on the alloy surface (i.e. the mechanism of nickel-catalysis, hydrogen adsorption and hydrogen-transference) has been suggested. The Ni sites on the surface are not only the electrocatalytic reaction centre but also the hydrogen adsorption centre. In addition, the impedance spectra were fitted to an equivalent circuit using a non-linear, least squares fitting program.

The chemical preparation of Mo(W)Co(Ni) and their influence on hydrogen storage electrode

Alloys with cooperative effects such as MoCo3 and WCo3 attract researchers because of their high electrocatalytic property. These alloys prepared by melting are very difficult to pulverize, and it is considerably difficult to prepare them as second phase in a hydrogen storage alloy. The alloy powders of MoCo3, WCo3 and MoNi3 with large surface area were prepared by solid state chemistry in this paper, then mixed with a hydrogen storage alloy. The mixed hydrogen storage alloy electrodes were measured with electrochemical methods. The results showed that the mixed hydrogen storage alloy electrode had advantages such as higher activation rate, higher discharge capacity and better high rate discharge characteristics.

Application of ion beam sputtering to electrocatalysts of hydrogen storage alloy

Abstract LaNi 3.94 Si 0.54 film cathodes are prepared by ion beam sputtering on iron substrates. The electrocatalytic behaviours of the film cathodes are investigated in 30wt % KOH at 70 °C. The results show that the amorphous film cathode has good catalytic activity for HER and excellent resistance to hydrogen embrittlement. The ion beam sputtering has the potential for surface modification on a cathode substrate.

Effect of Zn on the hydrogen storage characteristics of multi-component AB5-type alloys

The mischmetal-based hydrogen storage alloy systems MlNi3.8Co0.5Mn0.4Al0.3Znx (Ml, La-rich mischmetal; 0<x<0.2) have been successfully synthesized by the diffusion method (DM). The characteristics of these alloys have been carefully investigated by means of XRD, PAT, PCT, EIS and measurement of electrochemical capacity. Experimental results show that the unit cell volume becomes larger and the point defect density increases strongly due to the diffusion of Zn. The presence of Zn decreases the desorption plateau and prevents losing the capacity to a certain degree at high discharge current density. Electrochemical impedance spectra (EIS) results show that the rate-determining step is the charge-transfer reaction on the alloy/electrolyte interface. The charge-transfer resistance of the electrode increases with increasing Zn concentration due to the formation of an oxide layer and the reduction of active sites on the electrode surface. So the concentration of Zn in the alloy should be limited to below x=0.1. The Zn-free multicomponent AB5 alloy has also been examined for comparison.

Characteristics of Mg2−xTixNi1−yCuy–H2 (0<x<2, 0<y<1) alloys

Abstract The Mg 2− x Ti x Ni 1− y Cu y (0 x y 2 system with and without the treatment of F-solution. A study of the hydrogen desorption process was also carried out. The results show that the main phase of the alloys is an Mg 2 Ni structure. The gas–solid phase reaction can occur without detailed surface treatment and activation. A study on the anti-corrosion properties in alkaline solution of Mg 2− x Ti x Ni 1− y Cu y (0 x y

The characteristics of mixed hydrogen storage electrode with Bi2(MoO4)3

Abstract Bi 2 (MoO 4 ) 3 could be used to catalyze the oxidation–reduction reaction related to hydrogen, so we tried to use Bi 2 (MoO 4 ) 3 and P 2 O 5 –MoO 3 –Bi 2 O 3 –SiO 2 as catalyst to catalyze the reaction of absorption and desorption of hydrogen storage electrodes. In this paper, Bi 2 (MoO 4 ) 3 and P 2 O 5 –MoO 3 –Bi 2 O 3 –SiO 2 were prepared in order to improve the electrochemical activity of the hydrogen storage alloy electrodes. The results showed that the electrochemical capacity and high rate discharge characteristics were improved.

Structure and electrochemical properties of Zr(V0.2Mn0.2Ni0.6 − xCox)2.4 hydrogen storage alloys

Abstract The structure and hydrogen absorbed properties of a series of the multicomponent Zr(V 0.2 Mn 0.2 Ni 0.6 − x Co x ) 2.4 alloys have been investigated as a negative electrode in the metal hydride batteries. The crystal structure turned out to change as a function of substituted cobalt from a cubic C15 type structure to a hexagonal C14 type structure. There were anomalies in the relation among the hydrogen plateau pressure from PCT, electronic factor of the alloy and A 2 B 2 tetrahedral interstice for hydrogen occupation. The Zr(V 0.2 Mn 0.2 Ni 0.5 Co 0.1 ) 2.4 electrode was used to evaluate the electrochemical characteristics including activation, cycle life, electrocatalytic activity and hydrogen adsorption. It was found that both the hydrogen adsorption process and hydrogen diffusion process took place in the electrochemical impedance spectra of the electrode used here.