Enhanced cyclic durability of low-cost Ti–V–Cr hydrogen storage alloys by elemental alloying

Low-cost low vanadium (low-V) hydrogen storage materials have high reversible capacities (>2.0 wt.%) under moderate conditions, however, they suffer from drastic capacity decay during cycling. In this work, a series of TiCr1.1M0.1(V–Fe)0.6 (M = Mn, Mo and Nb) alloys are prepared by elemental alloying on the basis of the low-cost, low-V alloy TiCr1.2(V–Fe)0.6 alloy, and the modification mechanism of the elemental alloying on the cycling durability of the alloy is systematically investigated. In 100 cycles, the results demonstrated that the original alloy TiCr1.2(V–Fe) 0.6 suffered from poor desorption capacity (1.13 wt.%) and lowly capacity retention rate (60.43%). Compared to the addition of Mn and Nb, TiCr1.1Mo0.1(V–Fe)0.6 obtained higher cyclic hydrogen storage capacity (1.32 wt.%) and capacity retention (68.04%). In addition, it is found that the addition of Mo can inhibit the formation of the secondary phase during the cycling, and the abundance of the C14 Laves phase maintained at only 2.47% after 100 cycles. According to the microstructural analysis of the alloys during cycling, it is found that the decrease in grain size, the accumulation of micro strain and dislocation density, and the degree of particle pulverization seriously affect the cycling durability of the alloys, resulting in a drastic decrease in the dehydrogenation cycling capacity. Finally, it should be noted that although the improvement in cycle durability with Mo alloying is limited, it is still a positive reference for developing low-cost low-V alloys with good cycle durability.