Zuoxiang Zhou

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.

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.

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.%).

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.

Calcium Zincate Synthesized by Ballmilling as a Negative Material for Secondary Alkaline Batteries

Calcium zincate has been successfully synthesized by a high-energy ballmilled method. The crystal structure, chemical composition, surface morphology, granularity distribution, and electrochemical performance have been investigated to compare with that prepared by a conventional chemical precipitation method. X-ray powder diffraction results revealed that the calcium zincate prepared by the two methods had a well-defined monoclinic structure using a Rietveld refinement method. Scanning electron microscope images and granularity analysis indicated that the ballmilled material was a finer powder with a higher specific surface area. The thermogravimetric and differential thermal analysis showed that there was a slight difference in the crystalline water content in the chemical composition of the powders prepared by the two methods. The galvanostatic charge and discharge results showed that the ballmilled powder had a promising cyclic behavior due to the better electrochemical stability as revealed from the cyclic voltammetry. It is suggested that the ballmilled calcium zincate is more suitable for applications in secondary alkaline batteries.

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.