Cost reduction possibilities of vanadium-based solid solutions – Microstructural, thermodynamic, cyclic and environmental effects of ferrovanadium substitution

Microstructural changes, thermodynamic and cyclic properties, total material cost and the cumulative energy demand of V_(40−40·x)Fe_(8−8·x)Ti₂₆Cr₂₆(FeV)_(48·x) with 0 ≤ x ≤ 0.9 using commercial ferrovanadium (FeV) are investigated. The substitution of V + Fe by FeV (x = 0.9) raises the equilibrium hydrogen pressure at 298 K from p_a = 1 MPa to p_a = 6 MPa during absorption of H₂ and p_d = 0.2 MPa and p_d = 1 MPa during desorption. The reversible hydrogen storage capacity is determined after 50 pressure-swing cycles and is reduced from 2.2 mass% to 1.7 mass% for the unsubstituted alloy (x = 0) compared to 1.7 mass% to 1.3 mass% for the FeV substituted alloy (x = 0.9). This corresponds to a loss of capacity of approx. 23% for both samples. After taking into account the capacity loss caused by FeV substitution, the raw material cost per 100 kg of stored H is reduced to 1/3 of the original price of the unsubstituted alloy. The cumulative energy demand of pure V depends on the number of purification steps. Ferrovanadium shows a cumulative energy demand which is reduced at least by a factor of 1.4 as compared to high-purity vanadium. - Highlights: • Effect of FeV on microstructure and H storage properties of V–Fe–Ti–Cr alloys. • Increasing FeV content increases the equilibrium pressure from 1 to 6 MPa. • Cyclic effects: degradation by 23% for both pristine and FeV-substituted alloys. • FeV substitution reduces the overall material cost to 1/3 of the original cost. • High-purity V production requires 1.4 times more energy than FeV production