Alloying Effect On The Hydrogenation Properties Of V-Fe-based Alloys

The V-based BCC solid solution alloys show high reversible hydrogen capacity in ambient condition. Substituting pure vanadium with cheap commercial ferrovanadium is an effective approach to lower the cost. This study was carried out basing on the V-Fe binary alloy with the ratio of V/Fe equal to that of commercial ferrovanadium. To gain an alloy with high capacity and low cost, the structures and hydrogenation properties of alloying effect on V-Fe-based alloys were studied by XRD, SEM, DSC and PCT tests.The hydrogenation property of V85Fe15 binary alloy with V/Fe approximately equal to commercial ferrovanadium was firstly studied. The result of PCT tests show a large decrease of hydrogen capacity and plateau pressure compared to V-1 at.%Ce. The maximum hydrogen absorption of V85Fe15-1 at.%Ce is no more than 1.8 wt.%.and the plateau of absorption is 0.0096 IMPa. The decomposition enthalpy of hydride is about-45.01 kJ/mol, which is more negative than pure V.In order to rise the plateau of V85Fe15-1 at.%Ce, the effect of different kind of M (M=Cr, Mo, Al) with different contents (x=l,3,5) on the structure and hydrogenation properties of V85Fe15-1 at.%Ce were investigated. As the lattice of BCC changes not much with the addition of minor M, the hydrogen capacities of (V0.85Fe0.15)100-xMx-1 at% Ce change little with M and none of them exceeds 2.0 wt.%. But the plateau pressure shows remarkable linearly variation with the amount of M and the lattice parameter of BCC matrix. The additions of Cr, Mo and Al raise the plateau but the linearly relation of plateau vs. BCC lattice parameter of Mo/Al-added alloys is opposite to Cr-added alloys and many other conventional hydrogen storage alloys. The radius of hydrogen site was introduced to explain the inconsistent. The plateau pressure of (V0.85Fe0.15)100-xMx-1 at%Ce with any kind of M we added rises with the contraction of the hydrogen site. The (V0.85Fe0.15)95Al5-1 at.%Ce with desorption plateau around 1.49MPa, a relatively higher plateau was optimized.To enlarge the hydrogen capacities of (V0.85Fe0.15)95-xAl5Tix-1 at.%Ce and V85Fe15-1 at.%Ce, the effects of different contents of Ti on the structures and hydrogenation properties of (V0.85Fe0.15)95-xAl5Tix-1 at.%Ce and V85Fe15-1 at.%Ce were studied. Alloys with x<20 maintain the phase composition consisting of BCC and CeO2. But the third Ti-riched phase appears when Ti content exceeds 20 at.%. The lattice parameter of BCC matrix increases linearly with Ti content. So the maximum hydrogen capacity of (V0.85Fe0.15)95-xAl5Tix-1 at.%Ce rises with Ti content firstly but decreases when x>20 for the effect of the third Ti-riched phase. The plateaus of both alloys (V0.85Fe0.15)95-xAl5Tix-1 at.%Ce and (V0.85Fe0.15)100-xTix-1 at.%Ce fluctuate with Ti content and appear an extreme point at x=20. V0.85Fe0.15)80Ti20-1 at.%Ce with a maximum capacity of 3.74 wt.% and desorption plateau of 0.06 MPa at 303 K was detected for the next stage research.The effect of Mo and Cr on the hydrogenation properties of (V0.85Fe0.15)80Ti20-1 at.%Ce were discussed for rising the plateau of V0.85Fe0.15)80Ti20-1 at.%Ce. Similar to V-Fe-M, the plateau pressure remarkably changed with Mo/Cr content. But the hydrogen capacity decrease because of the contraction of interstice of Cr substitution and the heavier of Mo atom. The decrease of capacity of [(V0.85Fe0.15)80Ti20]95Mo5-1 at.%Ce also related to the residual of elemental Mo.The hydrogenation properties of (V0.85Fe0.15)100-x-y-zTixMoyAlz-1 at.%Ce were investigated through an orthogonal tests around the composition of V0.85Fe0.15)80Ti20-1 at.%Ce. The direct analysis results show that the level of significance on the hydrogenation properties conform to Ti>Al>Mo. The factor of Al content is effective on rising plateau pressure and a 20 at.%Ti content is favorable for proper hydrogenation property.