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

This paper investigates dehydrogenation reaction behavior of the LiBH4-MgH2 composite at 450 degrees C under various hydrogen and argon back-pressure conditions. While the individual decompositions of LiBH4 and MgH2 simultaneously occur under 0.1 MPa H-2, 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 H-2. Under 1 MPa H-2, enhanced dehydrogenation kinetics for the same reaction pathway as that under 0.5 MPa H-2 is obtained without the incubation period. However, the dehydrogenation reaction is significantly suppressed under 2 MPa H-2. 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 dehydrogenation under 1 MPa H-2, 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.