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