P.W. Shen

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 Hydrogen Storage of Nanocrystalline La2Mg17 Alloy Ballmilled with Ni Powders

La 2 Mg 1 7 -based nanocrystalline alloys were prepared by ballmilling La 2 Mg 1 7 alloy with Ni powders. Electrochemical charging and discharging of the ballmilled La 2 Mg 1 7 -based nanocrystalline alloy succeeded due to theformation of highly dispersed metallic Ni particles through the nanocrystalline alloy matrix. The first discharge capacity of the La 2 Mg 1 7 alloys ballmilled with Ni powders in a weight ratio of 1:2 was near 990 mAh/g, corresponding to a hydrogen storage capacity of 3.69 wt %. Inlaid metallic Ni at the surface layer of the nanocrystalline alloy matrix served as electrocatalytic reaction sites and hydrogen adsorption sites to accelerate the electrochemical charging and discharging process.

Electrochemical and surface properties of the Zr(V0.2Mn0.2Ni0.6)2.4 alloy electrode

Abstract In order to further improve the electrocatalytic activity and activation behaviour of the Zr(V 0.2 Mn 0.2 Ni 0.6 ) 2.4 alloy electrode, the alloy powder surface was treated by HF acid solution and the electrochemical properties of both electrodes were measured. It was found that the surface treatment by HF acid solution was significantly effective on improving the electrocatalytic activity and activation behaviour of the alloy electrode by means of electrochemical impedance spectroscopy. The surface properties of the untreated and treated alloy powders were investigated by scanning electron spectroscopy and X-ray photoelectron spectroscopy. The effected factors on the electrocatalytic activity such as the chemical state and composition of alloy powder surfaces before and after treatment by HF acid solution were discussed. Additionally, the crystallographic characterization and the hydrogen storage performance of the alloy were also examined.

Molecular dynamics simulation of LiTFSI-acetamide electrolytes: structural properties.

The liquid structures of nonaqueous electrolytes composed of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and acetamide, with LiTFSI/acetamide molar ratios of 1:2, 1:4, and 1:6, were studied by molecular dynamics simulations. The simulations indicate that the Li+ cations prefer to be six-coordinate by the sulfonyl oxygen atoms of the TFSI- anions and the carbonyl oxygen atoms of the acetamide molecules, rather than by the most electronegative nitrogen atom of the TFSI- anion. Therefore, close Li+-TFSI- contact pairs exist in the system. The TFSI- anion prefers to provide only one of four possible oxygen atoms to coordinate to the same Li+ cation. Three conformations (cis, trans, and gauche) of the TFSI- anions were found to coexist in the liquid electrolyte. At high salt concentrations, the TFSI- anions mainly adopt the gauche conformation in order to provide more oxygen atoms to coordinate to different Li+ cations, while simultaneously reducing the repulsion among the Li+ cations. On the other hand, the fraction of TFSI- anions adopting the cis conformation is largest for the system with the molar ratio of 1:6, in which many clusters, mainly composed of the Li+ cations and the TFSI- anions, are immersed in the acetamide molecules. The size and charge distribution of clusters were also investigated. In the system with the molar ratio of 1:2, nearly all of the ions in the PBC (periodic boundary conditions) box aggregate into a bulky cluster that gradually disassembles into small clusters with decreasing salt concentration. The addition of acetamide molecules was found to effectively relax the liquid electrolyte structure, and the system with the molar ratio of 1:4 was found to exhibit a more homogeneous liquid structure than the other two electrolyte systems with molar ratios of 1:2 and 1:6.

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.

Electrochemical hydrogen storage property of amorphous and crystalline Ml-Ni alloy films

Abstract Amorphous and crystalline MlNi1.79, MlNi2.52 and MlNi3.44 films were prepared by means of ion beam sputtering. Electrochemical properties such as discharge capacity, discharge capability and charge-discharge cycle life were examined. The results snowed that the crystalline films had higher discharge capacity than the corresponding amorphous counterparts. The high-rate dischargeability of amorphous samples was superior to the crystalline counterparts. This could be ascribed to high electrocatalytic activity of amorphous electrodes. In addition, the amorphous film electrode also exhibited longer cycle life and excellent antipulverizability.

Characteristics of the superstoichiometric C15-type Laves phase alloys and their hydride electrodes

Abstract Laves phase alloy hydrides have some promising properties as electrode materials in reversible metal hydride batteries. In this work, the hydrogen storage performance, crystallographic parameters, surface state and electrochemical characteristics of the superstoichiometric Zr(V Mn Ni Mo) 2.4 alloys were examined. These as-cast pseudobinary alloys were found to have mainly a cubic C15-type Laves phase structure by X-ray diffraction analysis. The plateau pressure of the hydrides obtained from desorption P-C isotherms was in the range 10 −3 −0.1 MPa at 30°C with [H]/[M] capacities of about 1.0. Some electrodes exhibited electrochemical capacities of about 300 mA h g −1 . Molybdenum-containing alloy hydride electrodes showed a better electrocatalytic activity by means of electrochemical impedance spectroscopy. This was attributed to both the improvement of the alloy surface state and the synergism of molybdenum and nickel in the electrocatalytic reaction. The discharge capacity and high rate capability of the alloy electrodes were correlated not only to the electrocatalytic activity of the electrodes but also to the hydrogen storage performance of the hydrides.