Decomposition of magnesium hydride fiber observed using TEM and in-situ AFM

The thermodynamics and the decomposition behavior of an MgH₂ fiber of a single crystal synthesized by chemical vapor deposition were investigated using in-situ atomic force microscopy and transmission electron microscopy. The MgH₂ fiber without oxidation decomposed into polycrystalline Mg with a crystalline size of 20-50 nm. The polyciystalline Mg absorbed hydrogen at a pressure similar to the equilibrium pressure of bulk Mg. On the other hand, the MgH₂ fiber with surface oxidation decomposed into Mg crystals larger than 100 nm. The surface oxide layer affected the decomposition behavior of the MgH₂ fiber and prevented polycrystallization. These results suggest that surface oxidation increases the equilibrium pressure for hydrogen absorption of the MgH₂ fiber.