A dehydrogenation mechanism through substitution of H by D in LiBH4-MgD2 mixture

In this work, a new substitution mechanism was proposed to describe the dehydrogenation of the hand-mixed LiBH4-MgD2 mixture. Above the melting point of LiBH4, the free D atoms originated from the decomposition of MgD2 would replace the H atoms of liquid LiBH4, leading to the formation of BD bond, and major release of H2 and HD other than D2 gas. The hydrogen substitution mechanism would play the role above the melting point of LiBH4. Similar hydrogen substitution effect was found in the LiBH4-VD2 mixture, not in the NaBH4-MgD2 mixture. Due to the substitution mechanism, the dehydrogenation kinetics of MgD2 in the LiBH4-MgD2 mixture is enhanced, which is contrary to the retarding effect due to hydrogen exchange mechanism previously proposed in the ball-milled LiBH4-MgD2 composite.