The role of Ni in increasing the reversibility of the hydrogen release from nanoconfined LiBH4

Abstract

Nanoconfinement and the use of catalysts are promising strategies to enhance the reversibility of hydrogen storage in light metal hydrides. We combined nanoconfinement of LiBH₄ in nanoporous carbon with the addition of Ni. Samples were prepared by deposition of 5–6 nm Ni nanoparticles inside the porous carbon, followed by melt infiltration with LiBH₄. The Ni addition has only a slight influence on the LiBH₄ hydrogen desorption, but significantly enhances the subsequent uptake of hydrogen under mild conditions. Reversible, but limited, intercalation of Li is observed during hydrogen cycling. X-ray diffraction shows that the initial crystalline 5–6 nm Ni nanoparticles are not present anymore after melt infiltration with LiBH₄. However, transmission electron microscopy showed Ni-containing nanoparticles in the samples. Extended X-ray absorption fine structure spectroscopy proved the presence of Ni_xB phases with the Ni–B coordination numbers changing reversibly with dehydrogenation and rehydrogenation of the sample. Ni_xB can act as a hydrogenation catalyst, but solid-state ¹¹B NMR proved that the addition of Ni also enhanced the reversibility of the system by influencing the microstructure of the nanoconfined LiBH₄ upon cycling.