Stable hydrogen storage of lithium borohydrides via the catalytic effect of Ni2B induced by thermodynamic destabilization reaction

Abstract

Lithium borohydride (LiBH4) is regarded as a potential hydrogen storage material due to its high gravimetric and volumetric capacity, but its practical application suffers from high operating temperature and poor reversibility. Herein, porous hollow carbon microspheres composed of carbon-coated Ni nanoparticles with high content (denoted as Ni/C) are rationally designed as functional support, which not only induces effective nanoconfinement of LiBH4 but also promotes efficiently homogeneous destabilization reaction between LiBH4 and Ni nanoparticles. The introduction of Ni nanoparticles leads to the decrease of the Gibbs free energy change for H2 desorption of LiBH4 based on the formation of Ni2B down to −0.95 eV while this value reaches 1.19 eV for bulk LiBH4, validating the effective role of Ni in thermodynamically destabilizing H2 desorption. Impressively, the average B–H bond length of LiBH4 on Ni2B reaches 1.291 Å and thus the corresponding dissociation energy of removing one H atom from LiBH4 is lowered to 1.00 eV, much lower than bulk LiBH4 (4.22 eV) and even LiBH4 on Ni (1.27 eV), which verifies superior role of Ni2B than Ni in catalytically enhancing H2 desorption. Therefore, a capacity of 8.86 wt.% is obtained for LiBH4 confined into Ni/C at 320 °C after 10 cycles.