Facile synthesis of NiCo2O4-anchored reduced graphene oxide nanocomposites as efficient additives for improving the dehydrogenation behavior of lithium alanate

Abstract

Lithium alanate (LiAlH₄), as a prototypical high-capacity complex hydride, has attracted intense interest as a promising hydrogen storage material. However, the drawbacks of high dehydrogenation temperatures and slow kinetics in the dehydrogenation process limit its practical applications. Herein, we have successfully synthesized NiCo₂O₄ nanorods anchored on rGO through a low-temperature solution method coupled with annealing treatment, and efficient effects derived from the NiCo₂O₄@rGO composite towards the dehydrogenation of LiAlH₄ are demonstrated. The ball-milled LiAlH₄ + 7 wt% NiCo₂O₄@rGO sample starts to decompose at 62.7 °C and releases a total of 6.28 wt% hydrogen, which is 118 °C lower than that of as-received LiAlH₄, and 42.8 °C lower than that of ball-milled LiAlH₄. The isothermal dehydrogenation kinetics show that the LiAlH₄ + 7 wt% NiCo₂O₄@rGO sample could release approximately 4.0 wt% hydrogen within 20 min at 150 °C, whereas less than 0.04 wt% hydrogen release was detected for LiAlH₄ under identical conditions within 100 min. Kinetic measurements reveal 21.9% and 37.1% reduction in the apparent activation energy of the two-step dehydrogenation of undoped LiAlH₄, respectively, in the presence of a 7 wt% NiCo₂O₄@rGO additive. It is reasonable to conclude that the large surface area and mesoporous structures provided by NiCo₂O₄@rGO nanocomposites play a synergistic role in remarkably improving the dehydrogenation properties of LiAlH₄.