Effect of dehydrogenation depth on cyclic hydrogen desorption properties of V40Ti25.5Cr26.5Fe8 alloy

Abstract

The cyclic stability of hydrogen absorption and desorption is an important indicator of hydrogen storage alloy. The decay mechanism was roundly investigated by controlling the depth of dehydrogenation (DOD) of the V40Ti25.5Cr26.5Fe8 alloy during the process of hydrogen ab/desorption cycles. The V40Ti25.5Cr26.5Fe8 alloy exhibits the hydrogen desorption capacity of 2.36 wt% at 323 K in the first cycle. After 30 cycles, the decay rate of the hydrogen desorption capacity is only 4.37 % at 40 % DOD, but rises to 8.74 % at 100 % DOD. The hydrogen desorption capacity (C), plateau pressure (P) and micro-strains (S) all show an “acceleration followed by slowing” exponential variation trend with the increase of cycle number (x). Additionally, any two of C, P and S show linear correlation. It is considered that the micro-strains in the crystal lattice is the main factor for the decay of the hydrogen desorption capacity and the plateau pressure. On the premise of ensuring the valid hydrogen storage capacity to meet the requirements of the application, properly reducing DOD per cycle can effectively reduce the micro-strains accumulation and cell volume expansion, thus improving the cyclic stability of the alloy. Moreover, the application of this alloy in a fuel cell bicycle was investigated, and the total range and mileage per unit weight of the alloy are up to 100.8 km and 15.7 km/kg, respectively. Compared with the lead-acid battery, lithium-ion battery and LaNi5-based hydrogen fuel cell, the V-Ti-Cr-Fe-based fuel cell shows significant advantages.