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