Diffusion controlled hydrogen desorption reaction for the LiBH 4/2LiNH 2 system

Abstract

The hydrogen desorption kinetic mechanism of the Li–B–N–H system and the catalytic role of metallic Co in this process were investigated systematically. It is found that ca. 10 wt% hydrogen can be released from a 5 wt% Co-doped LiBH 4/2LiNH 2 sample to form a plate-like Li 3BN 2 product with dramatically improved kinetics. A diffusion controlled kinetic mechanism for the dehydrogenation reaction was identified by analyzing isothermal hydrogen desorption processes with the Johnson–Mehl–Avrami equation. Introduction of metallic Co into the LiBH 4/2LiNH 2 system decreased the melting temperature of the α phase, catalyzed the formation of B–N bonds and facilitated nucleation and growth of the dehydrogenated product. As a consequence, lower apparent activation energy (∼94.8 kJ/mol) for the sample with the Co additive was obtained relative to the pristine sample (∼128.0 kJ/mol). This lower activation energy is responsible for the significant enhancement of the dehydrogenation kinetics.