Reaction of hydrogen with sodium oxide: A reversible hydrogenation/dehydrogenation system

Sodium oxide, Na2O, reversibly absorbs hydrogen, H2, to form sodium hydride, NaH, and sodium hydroxide, NaOH, which possesses a potential to find its application to reversible hydrogen storage. X-ray diffraction measurements illustrate reversible phase and composition changes during the hydrogen absorption and desorption in the Na–O–H system. Pressure–composition (P–C) isotherm and thermogravimetric (TG) measurements exhibit a hydrogen capacity up to 3.0 wt.%. Temperature-programmed desorption (TPD) measurements demonstrate that mixing NaOH to NaH significantly shifts the hydrogen desorption of NaH towards lower temperature, to which TiCl3 and SiO2 show catalytic activity. A reaction intermediate, NaHδ−Hδ′+ONa, involving dihydrogen bonding between the negatively charged hydrogen atom bonded to sodium and the positively charged hydrogen atom bonded to oxygen is proposed for the reaction mechanism.