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 LiBH₄ nanoconfined in MFe₂O₄ (M=Co, Ni) ferrite-catalyzed graphene host. Composites of LiBH₄-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/H₂) and the effect on hydrogen storage parameters are discussed. The thermodynamic parameters for the most promising composite LiBH₄-graphene-NiFe₂O₄ (Ar) were investigated by Kissinger plot method, revealing an EA = 127 kJ/mol, significantly lower than that of neat LiBH₄ (170 kJ/mol). The reversible H₂ content of LiBH₄-graphene-NiFe₂O₄ (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 H₂/Ar.