Deying Song

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.

Surface modification and electrochemical studies of spherical nickel hydroxide

Electroless cobalt on the surface of spherical nickel hydroxide has been used as a surface modifying method of active material for positive electrodes of rechargeable alkaline batteries. Cyclic voltammetric studies show that the electrodes exhibit higher oxygen overpotential and much more reversibility than ones of pure nickel hydroxide or nickel hydroxide with 5 wt.% cobalt added as a conductor. The discharge behaviour of the electrodes is also similar.

Dehydriding properties of ternary Mg2Ni1-xZrx hydrides synthesized by ball milling and annealing

Abstract The ternary hydrogen-storage alloys Mg 2 Ni 1− x Zr x (0 x ≤0.3) have been successfully synthesized by ball milling followed by annealing. Studies of the synthesis conditions of the ternary alloys and their dehydriding properties have been carried out. The results show that the ternary Mg 2 Ni 1− x Zr x (0 x ≤0.3) alloys have the same hexagonal crystal structure as that of Mg 2 Ni. Compared with a Mg 2 Ni alloy, they have a larger specific surface (∼1.20 m 2 g −1 ), more promising dehydriding kinetics, lower enthalpy of formation of hydrides than that of Mg 2 NiH 4 , and lower decomposition temperatures in an open system. An optimum desorption storage capacity of about 3.3 wt.% is observed.

Pressure-composition isotherms of the Mg2Ni0.75Fe0.25-Mg system synthesized by replacement-diffusion method

Abstract The hydrogen-storage system Mg2Ni0.75Fe0.25-Mg (molar ratio is 2:1) has been successfully synthesized by the replacement-diffusion method (RDM). A study of the hydrogen desorption process was carried out. The results indicated that the pressure-composition isotherm (P-C-T) characteristics, plateau pressure and storage capacity change with temperature. The present system corresponds to a new hydrogen storage material with an optimum storage-capacity (3.3 wt.%).

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.

Hydrogen adsorption of metal nickel and hydrogen storage alloy electrodes

Abstract An improvement in the electrocatalytic activity of the hydrogen storage alloy electrodes is essential to ensure a high rate capability of an Ni–MH battery. Previous experimental results showed that there was a hydrogen adsorption phenomenon on the alloy surface and the activation energy barrier of the electrochemical reaction process should be reduced by hydrogen adsorption. Therefore, the hydrogen adsorption is of benefit in improving the electrocatalytic activity of the alloy electrode. In this work, the hydrogen adsorption performance on the surfaces of Zr(V0.2Mn0.2Ni0.6)2.4, MmNi3.6Mn0.4Co0.75Al0.25 alloy electrodes and carbonyl nickel electrode was measured by means of cyclic voltammetry. In addition, the hydrogen adsorption performance of the metal nickel ribbon was performed by electrochemical impedance spectra. The results showed that the Ni sites on the surface of the metal hydride electrodes play an important role in the hydrogen adsorption.

Electrode properties of amorphous nickel-iron-molybdenum alloy as a hydrogen electrocatalyst in alkaline solution

Abstract Amorphous Ni/Fe/Mo alloys were obtained by electrodeposition from an alkaline citrate bath. The effect of the cathodic current density on the chemical composition, surface morphology of the Ni/Fe/Mo alloys, and the current efficiency of the deposition process was determined. The activity of the Ni/Fe/Mo alloy for the hydrogen evolution reaction (HER) was investigated under various electrolysis conditions in 30 wt.% KOH at 70 °C. The results showed that the Ni 41.49 Fe 23.02 Mo 35.49 alloy had the best activity for HER and excellent stability under continuous electrolysis. When accompanied by some current interruptions of various durations, the ternary alloy electrode still maintained good activity for HER.

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.

Electrochemical impedance spectra study of the hydrogen storage electrode

The hydrogen storage electrode (MH) has been investigated by a.c. impedance measurements. The electrode impedance has been measured by superimposing an a.c. voltage of 5 mV amplitude ranging between 104 and 10−2 Hz. The impedance experiment result indicated that Cole-Cole plot for the electrode consisted of two obviously comparable semicircles and a slope related to Warburg impedance, and the semicircle in the high frequency region was very different from that in the low frequency region. The very small semicircle in the high frequency region was probably a typical double-layer capacitance; the large semicircle in the low frequency region which exhibited marked dependence on the hydrogen content was attributed to the electrochemical Heyrovsky reaction. The two semicircles were both affected by the electrode activation numbers and the depth of discharge. The impedance experiment also indicated that the semicircle in the high frequency region was almost independent of activation number, but that in the low frequency region was not. On increasing the depth of discharge, the two semicircles both reduced at first and increased later.

The surface decoration and electrochemical hydrogen storage of carbon nanofibers

Abstract The tube-like CNFs with cone-shaped structure were synthesized by catalytic pyrolysis of methane. The outer surface of purified CNFs was decorated with Ni–P alloy particles having polycrystalline or nanocrystalline structure instead of amorphous structure. The low Ni–P content appeared to be more efficient to cover the outer surface of CNFs. The electrochemical discharge capacity increased with increasing the Ni–P content on the outer surface of CNFs owing to the synergistic effect between metal and carbon in the electrochemical reaction. The heat treatment contributed to the higher crystallization of surface alloy and improvement of the electrochemical capacity of the composite.