Abstract
Ti-V-based metal hydrides have decent overall performance as hydrogen storage materials, but V is expensive and it is therefore tempting to replace it by less expensive ferrovanadium containing about 20% Fe. In the present work we have investigated how Fe influences the structure and hydrogen storage properties of (Ti0.7V0.3)1−zFez alloys with e r r o r t y p e c e z ∈ { 0 , 0.03, 0.06, 0.1, 0.2, 0.3} using synchrotron radiation powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and manometric measurements performed in a Sieverts apparatus. The alloys form body-centered cubic (bcc) crystal structures for all considered values of z, and the addition of Fe causes the unit cell to contract. When exposed to hydrogen gas, the bcc alloys form face-centered cubic (fcc) hydrides if e r r o r t y p e c e z ≤ 0 . 1 while other hydrogen-containing phases are formed for higher Fe-contents. The hydrogen capacities of the fcc hydrides at 20 bar are not significantly influenced by the addition of Fe and reach 3.2(3) wt% in (Ti0.7V0.3)0.9Fe0.1H1.6(2). For higher Fe contents the hydrogen capacity is decreased. The absorption kinetics are fast and the reactions are complete within minutes when the alloys are exposed to 20 bar H2 at room temperature. Increasing Fe content reduces the desorption enthalpy, onset temperature and activation energy.
Highlights
Hydrogen is considered a promising energy carrier for the future as it possesses the highest gravimetric energy density of any known substance
Storage in metal hydrides is an interesting solution as such systems achieve very high volumetric hydrogen densities in the range 100–150 kg H2 /m3 at ambient conditions [1,2]
Applications are often prevented by unfavourable kinetics, thermodynamics and/or non-reversibility [3,4]
Summary
Hydrogen is considered a promising energy carrier for the future as it possesses the highest gravimetric energy density of any known substance. Hydrogen assumes a diatomic gas phase with very low density at ambient conditions This makes compact and safe storage a technological challenge. In this regard, storage in metal hydrides is an interesting solution as such systems achieve very high volumetric hydrogen densities in the range 100–150 kg H2 /m3 at ambient conditions [1,2]. Body-centered cubic (bcc) solid solutions based on Ti and V is one class of interstitial hydrides with potential for hydrogen storage applications. It should be noted that replacing V by ferrovanadium in Ti0.7 V0.3 corresponds to choosing z ≈ 0.07
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