Hydrogen Absorption/Desorption in Palladium and Metal Hydrides

Electrical generation from hydrogen, the element with higher energy density per unit mass, requires appropriated materials that can be used in its storage [1]. Palladium, with a high capacity to dissociate, absorb and desorb gaseous hydrogen, has been widely used for hydrogen storage [2], in separation membranes [3] and catalytic hydrogenation [4]. The present DFT calculations on clusters models reveal interesting details of the hydrogen absorption/desorption process in palladium and metal hydrides. The results point to the existence of a pre-absorption state of the hydrogen atom on palladium and indicate that occupation of the tetrahedral site is preferred at low hydrogen concentrations (-phase), whereas in -phase the octahedral site is the most stable. Taking the absorption and desorption energies of palladium as reference, we analyzed the properties of the metal hydrides AlH3, MgH2, Mg(BH4)2, Mg(BH4)(NH2) and Li2NH for hydrogen storage. Among these compounds, MgH2 most closely resembles the properties of palladium, but the complex hydrides in borohydrides (BH4 ) and amide (NH2 ) show better properties both in absorption and desorption. Furthermore we found that Cu and Pd doping of MgH2 can reduce the desorption energy, improving the hydrogen release. 12 a 17/Nov, 2017, Águas de Lindóia/SP, Brasil