Dehydrogenation Reaction Pathway of the LiBH₄–MgH₂ Composite under Various Pressure Conditions

Abstract

This paper investigates dehydrogenation reaction behavior of the LiBH4–MgH2 composite at 450 °C under various hydrogen and argon back-pressure conditions. While the individual decompositions of LiBH4 and MgH2 simultaneously occur under 0.1 MPa H2, the dehydrogenation of MgH2 into Mg first takes place and subsequent reaction between LiBH4 and Mg into LiH and MgB2 after an incubation period under 0.5 MPa H2. Under 1 MPa H2, enhanced dehydrogenation kinetics for the same reaction pathway as that under 0.5 MPa H2 is obtained without the incubation period. However, the dehydrogenation reaction is significantly suppressed under 2 MPa H2. The formation of Li2B12H12 as an intermediate product during dehydrogenation seems to be responsible for the incubation period. The degradation in hydrogen capacity during hydrogen sorption cycles is not prevented with the dehydrogenation under 1 MPa H2, which effectively suppresses the formation of Li2B12H12. The overall dehydrogenation behavior under argon pressure conditions is similar to that at hydrogen pressure conditions, except that under 2 MPa Ar.