Synthesis of Nickel and Cobalt Ferrite-Doped Graphene as Efficient Catalysts for Improving the Hydrogen Storage Kinetics of Lithium Borohydride.

Featuring a high hydrogen storage content of up to 20 wt%, complex metal borohydrides remain promising solid state hydrogen storage materials, with the real prospect of reversible behavior for a zero-emission economy. However, the thermodynamic barriers and sluggish kinetics are still barriers to overcome. In this context, nanoconfinement has provided a reliable method to improve the behavior of hydrogen storage materials. The present work describes the thermodynamic and kinetic enhancements of LiBH nanoconfined in MFeO (M=Co, Ni) ferrite-catalyzed graphene host. Composites of LiBH-catalysts were prepared by melt infiltration and investigated by X-ray diffraction, TEM, STEM-EDS and TPD. The role of ferrite additives, metal precursor treatment (Ar, Ar/H) and the effect on hydrogen storage parameters are discussed. The thermodynamic parameters for the most promising composite LiBH-graphene-NiFeO (Ar) were investigated by Kissinger plot method, revealing an E = 127 kJ/mol, significantly lower than that of neat LiBH (170 kJ/mol). The reversible H content of LiBH-graphene-NiFeO (Ar) after 5 a/d cycles was ~6.14 wt%, in line with DOE's target of 5.5 wt% storage capacity, while exhibiting the lowest desorption temperature peak of 349 °C. The composites with catalysts treated in Ar have lower desorption temperature due to better catalyst dispersion than using H/Ar.