Effects of CNTs, graphene, and organic additives on hydrogen storage performance of severely deformed ZK60 alloy

Abstract

The commercial ZK60 (Mg-5.7 wt%Zn-0.6 wt%Zr) magnesium alloy was used to investigate the effects of organic solvents along with CNTs and graphene on hydrogen absorption characteristics. The ZK60 alloy was plastically deformed via equal channel angular pressing using route BA at 300 °C and processed for 12 passes. The mechanically removed chips of deformed ZK60 alloy were milled with 5 wt% graphene or 5 wt% CNTs along with organic solvents (toluene and cyclohexane) in a high energy ball mill at 1725 rpm for 20 h. The kinetics and hydrogen storage were measured using Sievert's apparatus for five cycles at different absorption/desorption temperatures. At 320 °C/320 °C absorption/desorption temperature, the maximum hydrogen absorption with 5 wt% CNTs and 5 wt% graphene was 7.13 wt% and 7.28 wt%, respectively, reaching more than 98% within 10 min. The additions of CNTs and graphene could significantly reduce the hydrogenation temperature because the hydrogen storage and kinetics at 280 °C/280 °C were very close to 320 °C/320 °C. At 320 °C/320 °C absorption/desorption temperature, the maximum hydrogen absorption of 5 wt% CNTs or 5 wt% graphene with the addition of 1 ml toluene was about 6.5 wt%, and the hydrogen absorption with the addition of 2 ml toluene was reduced to 5.5 wt%. The addition of 2 ml cyclohexane along with CNTs and graphene had maximum hydrogen absorption of 6.3 wt% and 6.9 wt%, respectively, after five cycles of hydrogen absorption/desorption at 320 °C/320 °C. At the same absorption/desorption temperature, the number of cycles had no obvious effect on hydrogen storage and kinetics, indicating the absorbed hydrogen was completely released during the desorption process.