Effects of two-dimension MXene Ti3C2 on hydrogen storage performances of MgH2-LiAlH4 composite

Abstract

4MgH2-LiAlH4 composite exhibits reduced over-high thermal stability and enhanced de/re-hydrogenation kinetics in previous work. However, de/re-hydrogenation temperatures are still higher than the requirement of mobile fuel cell system. In this case, two-dimension lamellar Ti3C2 was introduced into the 4MgH2-LiAlH4 composite. The de-hydrogenation onset temperature of 4MgH2-LiAlH4-Ti3C2 composite is decreased by 64 K and 274 K from 4MgH2-LiAlH4 and as-milled MgH2, respectively. Its de-hydrogenation activation energy value is reduced by 47.8 kJ mol−1 from 176.2 kJ mol−1 of 4MgH2-LiAlH4. The re-hydrogenation activation energy (65.7 kJ mol−1) of 4MgH2-LiAlH4-Ti3C2 is also lowered by 33.5 kJ mol−1 from 4MgH2-LiAlH4 (99.2 kJ mol−1). Further study indicates that Ti3C2 partially decomposed itself during ball milling and was completely transformed to metallic Ti and carbon during de-hydrogenation. The identified TiH1.942 indicates that in-situ formed Ti should react with 4MgH2-LiAlH4 system and slightly destabilize the system. For this system, de-hydrogenation enthalpies in three stages (65.9 kJ mol−1 H2−1, 70.6 kJ mol−1 H2-1 and 74.3 kJ mol−1 H2−1, respectively) are all lower than as-milled MgH2 (76.2 kJ mol−1 H2−1). It means that introducing Ti3C2 into 4MgH2-LiAlH4 not only improves the reaction kinetics but also lowers its over-high thermal stability.