Microstructure and electrochemical performance of vanadium-containing AB5-type low-Co intermetallic hydrides

The effects of the vanadium substitution for nickel on the microstructure and electrochemical behaviors of as-cast and melt-spun compounds of Mm(NiCoMnAIV)5 with low Co content were studied at -20 to 80 degrees C. The substitution of V improved the capacity and cycling stability of the compounds. Melt-spinning reparation enhanced the cycling stability significantly due to the change of the microstructures. Phase structure analysis and SEM observation shows that the substitution of V for Ni plays an important role in suppressing the crystal grain growth and increasing texture. The melt-spinning technique is favorable to the formation of the fine columnar structure. ICP-AES analysis indicates that the corrosive resistance of the compounds is improved remarkably by the melt-spinning technique. In addition, the substitution of V for Ni and melt-spinning preparation increased the electrochemical capacity at higher temperature (more than 60 degrees C due to high potential difference between hydride-formation and hydrogen evolution reactions and the decrease in the charge transfer impedance, while the reduced capacity at lower temperature (less than 0 degrees C owing to the lower hydrogen evolution potential and earlier hydrogen evolution reaction as well as lower hydrogen diffusion coefficient. (c) 2005 Elsevier B.V. All rights reserved.