There is an ongoing quest for finding a hydrogen storage material that provides both high storage density and good hydrogen sorption properties. Here, nanosized hydrides promise improved thermodynamics and kinetics. As for the structural characterization utilizing TEM, however, most materials degrade fast upon irradiation with high energy electrons due to radiolysis.
Due to its comparably high storage capacity of 7.6 wt.% H2, MgH2 is one of the best studied binary hydrides. Ball milled MgH2 was thus used as a reference material for in-situ TEM experiments. Hereto, electron energy loss spectroscopy (EELS) was conducted in a monochromated FEI Titan3 80-300 microscope. By monitoring the plasmonic absorptions we can follow the irradiation-induced conversion of nanocrystalline MgH2 into Mg (cf. Fig.). The temporal evolution of the EEL spectra can then be analyzed quantitatively to determine the fractions of pure and hydrogenated Mg at different stages of the reaction. MgH2 decomposes exponentially in time with a characteristic electron dose. A comparison of the characteristic doses of individual particles allows us to characterize their dehydrogenation kinetics. Conclusions drawn from such experiments are also crucial for TEM studies on other hydrides such as AlH3: