Q.D. Wang

The electrochemical properties of LaxMg3-xNi9 (x=1.0-2.0) hydrogen storage alloys

Abstract LaxMg3−xNi9 (x=1.0–2.0) alloys were prepared by a powder sintering method and the influence of partial substitution of Mg by La on the crystal structure and electrochemical performance of the alloys was investigated. The ternary alloys with different La/Mg ratio are related to the hexagonal PuNi3-type structure. The increase of La/Mg ratio in the alloys leads to a linear increase of the unit cell volume. The La-rich alloys (x=1.8–2.0) show promising electrode properties including a large discharge capacity (∼400 mAh/g), easy activation and good high-rate dischargeability, although the cycling stability needs further improvement.

The effect of Nd on the properties of ceria–zirconia solid solution and the catalytic performance of its supported Pd-only three-way catalyst for gasoline engine exhaust reduction

A series of ceria-zirconia-neodymia mixed oxides with different contents of neodymia and the supported Pd-only three-way catalysts before and after aging have been prepared and characterized. The influence of Nd doping on the structural/textural properties of ceria-zirconia (CZ) and the effect on the three-way catalytic performance are also investigated. The results demonstrate that the addition of neodymia results in the formation of ceria-zirconia-neodymia ternary solid solution (CZN) with better textural and structural properties as well as improved reducibility and redox behavior, leading to the promoted three-way catalytic activity and enlarged air/fuel operation window. The modified solid solution with 5 wt.% neodymia shows the preferable textural/structural properties considering that the capacity of foreign cation is limited in the crystal lattice of ceria-zirconia solid solution, and Pd/CZN5 shows the optimum three-way catalytic performance and wider air/fuel operation window, especially for the corresponding aged one.

Effect of Co content on the kinetic properties of the MlNi4.3-XCoXAl0.7 hydride electrodes

By means of linear polarization, Tafel polarization and galvanostatic discharge methods, the kinetic properties of MlNi4.3ˇXCoXAl0.7 (X=0.0, 0.3, 0.5, 0.7, 0.9, 1.1 and 1.3) hydride electrodes, including high rate dischargeability HRD, exchange current density I0, limiting current density IL, the symmetry factor b, and the apparent diAusion coeAcient of hydrogen in the a phase Da have been studied systematically. The results show that the HRD of the electrode with high Co content is lower than that with low Co content. For the MlNi4.3ˇXCoXAl0.7 hydride electrodes, with Co content increasing from 0.0 to 1.3, the values of I0, IL, b and Da decreased from 395 to 33 mA/ g, 2263 to 308 mA/g, 0.85 to 0.43, 1.42 10 ˇ10 to 2.1 10 ˇ11 cm 2 /s, respectively. In order to calculate the electrochemical polarization Ze and concentration polarization Zc based on anodic polarization curve, the experimental anodic polarization curve should be divided into three regions to discuss according to discharge current density Id, namely, Id If. The calculation of Ze and Zc should use diAerent formula in diAerent regions. When discharge current density Id is smaller than Ip, the traditional equation used to calculate the electrochemical overpotential can not be used, when Ip is between Ip and If, both equations used to calculate the electrochemical overpotential and concentration overpotential can be used, and when Id is larger than If, because there exists absorption and adsorption of hydrogen, the traditional equation used to calculate concentration overpotential can not be used in the system of hydride electrodes. # 1999 Elsevier Science Ltd. All

Application of Rare Earth Modified Zr-based Ceria-Zirconia Solid Solution in Three-Way Catalyst for Automotive Emission Control

Automotive exhaust emission is a major cause of air pollution. Three-way catalyst (TWC) which can eliminate CO, HC (hydrocarbons), and NO(x) simultaneously has been used to control exhaust emissions. Ceria-zirconia is a key component in TWC and most researchers pay attention to Ceria-Zirconia (Ce-rich) solid solution. The research presented in this paper is focused on the intrinsic structure of Ceria-Zirconia (Zr-based) solid solution and its application in TWC. A series of Ce(0.2)Zr(0.8)O(2) modified with rare earths (La, Nd, Pr, Sm, and Y) have been prepared by coprecipitation method combined with supercritical drying technique. All samples showed single tetragonal solid solution, indicating that the rare earth ion inserted into the lattice structure completely, and an approximately linearly relationship between lattice parameter a and the ionic radius of doped rare earth was observed. The catalytic performances of corresponding Pd-only catalysts were investigated in simulated exhaust gas. The presence of La, Nd, and Pr was favorable to the catalytic activity and wide air/fuel operation window. The relationship between the intrinsic structure of the Zr-based ceria-zirconia solid solution and catalytic activity was discussed in detail, which has some reference value for catalyst design and application.

Effects of Nb and Pd on the electrochemical properties of a Ti-Ni hydrogen-storage electrode

Abstract The effects of Nb and Pd on the electrochemical properties of a Ti-Ni hydrogen-storage electrode are studied. The results show that adding Pd or Nd to the alloy can slow down the rate of decay of the exchange current during charge-discharge cycling and is also useful in increasing the discharge capacity and cycle life of Ti-Ni electrodes.

The effect of Zr substitution for Ti on the microstructures and electrochemical properties of electrode alloys Ti1-xZrxV1.6Mn0.32Cr0.48Ni0.6

Abstract The effect of Zr substitution for Ti on the microstructures and electrochemical properties of the electrode alloys Ti 1− x Zr x V 1.6 Mn 0.32 Cr 0.48 Ni 0.6 ( x =0.2,0.3,0.4,0.5) has been studied. It is found by X-ray powder diffraction and energy dispersive X-ray spectroscope analyses that all the alloys consist of a C14 Laves main phase with hexagonal structure and a V-based solid solution secondary phase with b.c.c. structure. A small amount of TiNi-based third phase with b.c.c. structure has been found precipitated in the C14 Laves main phase in addition. With the increase in the amount of Zr substitution, the lattice parameters of the main phase and secondary phase are found increased and decreased, respectively. The electrochemical PCT curves indicate that the maximum hydrogen absorption capacity [H/M] max decreases with increasing Zr substitution, which may be attributed to the decrease in the content of V-based solid solution. The maximum discharge capacity and high rate dischargeability of the alloy electrodes both decrease, while the cyclic durability increases with the increasing amount of Zr substitution.

The recent research, development and industrial applications of metal hydrides in the People's Republic of China

Abstract Chief accomplishments in the research and development of hydrogen storage alloys and hydride technology in recent years in the Peoples Republic of China are summarized and reported.

Effect of alloys modified by an alkaline solution containing potassium borohydride on the kinetic properties of MlNi3.7Co0.6Mn0.4Al0.3 hydride electrode

This paper describes the effects of treating the alloy powder of an electrode with 6 M KOH solution containing y M KBH4 (y=0.0, 0.005, 0.01, 0.02 and 0.03) on the kinetic properties of the electrode, including high rate dischargeablilty HRD, exchange current density I0, symmetry factor β, limiting current density IL, diffusion coefficient of hydrogen in the α-phase Dα, and electrochemical polarization ηe and concentration polarization ηc. The results show that the kinetic parameters HRD, I0, IL and Dα increase markedly with the increase in the concentration of KBH4, the ηe and ηc decrease rapidly with increasing concentration of KBH4, but the symmetry factor β does not change.

Effect of iron doping into CeO2-ZrO2 on the properties and catalytic behaviour of Pd-only three-way catalyst for automotive emission control

Ce(0.67)Zr(0.33)O(2) doped with iron oxide was prepared and the corresponding Pd-only three-way catalysts were examined and characterized. Pd/CZFe(1%) catalyst exhibits the best catalytic performance for CO, HC, NO and NO(2) elimination and the widest operation window. The doping of iron oxide with 1% loading suggests the formation of more homogeneous Ce-Zr-Fe-O ternary solid solution, which seems to facilitate the reduction of Ce(4+)→Ce(3+) or the formation of oxygen vacancy and to promote the interaction between Ce-Zr and Fe. Moreover, the Ce redox behaviour for surface reduction suggests depending not only on the formation of homogeneous Ce-Zr-Fe-O but also on the surface property of the sample. The increase in the concentration of oxygen vacancies under all atmospheres for CZFe(1%) sample also results in the enhancement of oxygen storage complete capacity.

The hydriding kinetics of MlNi5—I. Development of the model

The hydriding kinetics of hydrogen storage materials in the two-phase regions have been studied. It is believed that the hydriding process is best classified into three steps: dissolution of hydrogen into the alloy or its hydride; diffusion of hydrogen atoms through the alloy or its hydride phase; and nucleation and growth of β-hydride (hydride depositing from supersaturated α-solid solution). Kinetics equations have been derived for the cases when one of the three steps is the rate-determining step.