Chemical Synthesis And Characteristic Of Vanadium-based Hydrogen Storage Alloys

Vanadium-based solid solution alloy is a kind of important hydrogen storage materials. It has become hotspot in research with high hydrogen storage capacity(3.8wt%) and excellent diffusion rate of hydrogen. (V_0.9Ti_0.1)_1-xFe_x(x=0⁰.06) alloys were synthesized by coprecipitation-reduction method in this work. It's expected that vanadium-based hydrogen storage alloys would obtain large-scale exploitation.NH₄VO₃, TiO₂ and Fe₂O₃ were chosen as raw materials because of their cheapness. Above all, VO²⁺, TiO²⁺ and Fe³⁺ were prepared. And then, vanadium-based solid solution alloys were synthesized by coprecipitation-reduction method with suitable precipitating agent and CaH₂ as reductant. Finally, the structure and hydrogen storage performance of alloy samples were studied.Firstly, precipitation effect of VO²⁺, TiO²⁺ and Fe³⁺ was good respectively with NH₃·H₂O or mixture solution (NH₄HCO₃/NH₃·H₂O=1/3, molar ratio) as the precipitating agent in suitable pH=8¹0. Then, the exploration of coprecipitation- reduction craft of alloys was studied. The hydrogen storage alloys were synthesized in the condition as below: chosen NH₃·H₂O as the precipitating agent, controlled pH=9, required excessive 50¹00% CaH₂, precursors fired and reduced about 4h at 900℃.Secondly, the structure and performance of alloy samples were studied. (V_0.9Ti_0.1)_0.94Fe_0.06 alloy is taken as an example. Its particle size is 7.026μm. The alloy consists of a single vanadium-based solid solution phase with BCC structure. It has excellent activation performance and hydrogen absorption kinetics performance. Compared with the same alloy prepared by melting method, its hydrogen absorption speed is faster. The alloy sample's maximum hydrogen absorption capacity is 3.47wt% at 20℃. But its hydrogen desorption rate is only about 40% at 40℃.Thirdly, the optimization of coprecipitation-reduction conditions of alloys was studied. (V_0.9Ti_0.1)_0.94Fe_0.06 alloy was chosen as the optimization object. The results show that alloy sample's particle size is 6.705μm; the yield of alloy is 86%; alloy sample's reduction-diffusion process has been thoroughly for firing 3h at 900℃.Finally, the structure and performance of (V_0.9Ti_0.1)_1-xFe_x(x=0⁰.06) alloys were studied. The results have shown that all of the alloys consist of a single vanadium-based solid solution phase with BCC structure; from x=0 to x=0.06, the lattice parameter and unit cell volume decrease; with the increase of Fe content, the activation times decreases from 3 cycles to 2 cycles, but the maximum hydrogen absorption capacity at 20℃decreases from 3.63wt% to 3.47wt%; while x=0.04, alloy sample has a better overall hydrogen desorption performance with the 1.81wt% effective hydrogen desorption capacity at 40℃; all of the alloys have a good cycle stability performance. Additionally, it was studied that 10% NH₄Cl was added to reaction in the firing-reduction stage. The results indicate that the alloy sample's particle size is becoming smaller, and the hydrogen absorption kinetics performance of alloy sample is better.