Achieving high equilibrium pressure and low hysteresis of Zr–Fe based hydrogen storage alloy by Cr/V substitution

Abstract

Owing to fast kinetics, high equilibrium pressure and impressive volumetric hydrogen storage density at ambient temperature, ZrFe2 based alloys are promising candidates to composite with high pressure compressed hydrogen tanks and thus reduce the working pressure and volume of high pressure tanks. However, simple ZrFe2 alloy exhibits rather high de-/hydriding equilibrium pressure and large hysteresis, which are not coupled with the dis-/charging performances of high pressure tanks. In this work, to tune the plateau characteristics and hysteresis of ZrFe2 alloys for potential application in high-pressure hybrid hydrogen storage tanks, the effects of Cr/V element substitution for Fe on the phase structure and hydrogen storage behaviors were systematically investigated in Zr1.05Fe2-xCrx (0.1 ≤ x ≤ 0.3) and Zr1.05Fe1.85Cr0.15-xVx (x = 0.05, 0.075, 0.1). It has been found that the Cr and V substitution could effectively decrease the equilibrium pressure due to the enlarged unit cell of Laves phase, while the V substitution could greatly improve the hysteresis phenomenon. However, too high Cr addition (x = 0.3) led to structure transition from C15 to C14 for the Zr1.05Fe2-xCrx. The alloy Zr1.05Fe1.85Cr0.075V0.075 shows the best overall hydrogen storage properties with the capacity of 1.54 wt%, and the absorption and desorption equilibrium pressure of 13.63 atm and 9.73 atm respectively at 243 K. The equilibrium pressure of Zr1.05Fe1.85Cr0.075V0.075 at ambient temperature could meet the requirements of high-pressure hybrid hydrogen tanks.