Yunshi Zhang

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.

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.

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.

Oxygen evolution reaction on Ni hydroxide film electrode containing various content of Co

Abstract The effects of 0–52.6% Co coprecipitated into thin film nickel hydroxide electrodes, with emphasis on the oxygen evolution reaction (OER), were studied by SEM, XRD, stationary polarization and linear potential sweep (LPS) techniques. The film electrodes were prepared by cathodic codeposition from Ni(NO3)2 solutions containing various Co contents. The Co and Ni can be codeposited homogeneously in hydroxide state. The Co in the film has an evident effect on the OER, which varies with its content, but does not change the mechanism. During LPS, after the Co(OH)2 being oxidized to CoOOH, it no longer participates in the oxidation and reduction process, but it reduces the Ni(OH)2/NiOOH reaction potential significantly and the higher the Co content, the more the potential is reduced.

Electrochemical characteristics of Mg2−xAlxNi (0≤x≤0.5) alloys

Abstract The Mg-based hydrogen storage alloy Mg 2− x Al x Ni (0≤ x ≤0.5) have been successfully synthesized by a diffusion method (DM). The structures of these alloys have been examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical characteristics have also been investigated, such as corrosion resistance and electrochemical capacity. It is found that a new phase appears when Al is added to the Mg–Ni system. It can be observed that there are a large number of defects on the alloy surface, which strongly affect its characteristics. The electrochemical capacity and cycle lives of Al-containing alloys increase strongly compared to the Al-free alloy. With increasing Al concentration in the alloys, the capacity also increases due to the increase of the amount of the new phase.

Spherical nickel hydroxide composite electrode

Abstract A planar Ni(OH) 2 composite electrode was devised. The electrode was applied in the experiments of cyclic voltammetry and stationary polarization to investigate the electrochemical properties of spherical Ni(OH) 2 rapidly. It was found that the Ni(OH) 2 particles were dispersed homogeneously and properly adhered to the substrate. The performance of the electrode during the measurements was very satisfying.

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.%).

Characteristics of Mg2Ni0.75M0.25 (M=Ti, Cr, Mn, Fe, Co, Ni, Cu and Zn) alloys after surface treatment

The ternary Mg2Ni0.75M0.25 (M=Ti, Cr, Mn, Fe, Co, Ni, Cu and Zn) alloys have been successfully synthesized by the ball milling diffusion method (BDM). XRD results show that they all have a hexagonal crystal structure. We show that the alloys after fluorination treatment show good performance: the hydrogen desorption capacity reaches the highest value after only two adsorption–desorption cycles. The ratio of H/M is about 1.18 (≈3.3 wt.%) on desorption at 250°C. The hydrides have monoclinic phases. The larger the unit volume, the more unstable is the hydride. The dissociation enthalpies and temperatures of the hydrides in an open system are decreased with increasing unit cell volume. Replacement of Ni in Mg2Ni by Cr, Mn and Co has the same effect on Mg2Ni: they lower the decomposition plateau pressure; Ti and Cu have the opposite effect and Fe and Zn have little effect.

Electrochemical behaviour of Ni(OH)2 ultrafine powder

Abstract Ultrafine Ni(OH)2 powder is prepared by converting a Ni2C2O4 precipitate in NaOH solution which contained Tween-80. The sample prepared by this method is β(II)-type phase and its particle size is about 30 nm. The electrochemical behaviour of nickel foam electrodes using this ultrafine Ni(OH)2 powder as active material is studied and compared with micron-sized spherical Ni(OH)2 by means of a galvanostatic charge–discharge method, cyclic voltamperommetry (CV) and electrochemical impedance spectroscopy (EIS). It is found that ultrafine Ni(OH)2 powder has superior electrochemical properties, such as lower polarization, better reversibility, and smaller reaction resistance.

Study on the multi-composition AB5 alloys including Li, made by the diffusion method, and their electrodes

The mischmetal-based hydrogen storage alloys MlNi3.8Co0.5Mn0.4Al0.3Lix (Ml=La-rich mischmetal, 0<x<0.2) have been successfully synthesized by the diffusion method (DM). The properties of these alloys have been carefully investigated by means of XRD, PAT, PCT and the measurement of electrochemical capacity. Experimental results show that the Li-containing alloy, whose defects increase greatly, has excellent discharge efficiency and its utilization ratio increases greatly at high discharging current density. The results show that the alloy can be used as the negative material in a Ni-MH battery.