Elucidating reaction equations of TiFx (x = 4,3,2) catalysts for hydrogen storage applications

Abstract

In the never ending quest for clean energy, storing chemical energy in the form of hydrogen molecules in solid state materials is a premier choice. The release of H2 from the H-storage (absorbent) material is hindered by the on-set of reaction mechanism which depends on the energy barrier. In a search for efficient onset (re)hydrogenation temperature, stimuli like catalysts have drawn more attention in the hydrogen fuel economy. It is laborious to down-select the aspirant candidates by screening their material properties and the thermochemical energy which are required for bond breaking. An understanding on perceptible energies involved in breaking/creating bonds has been obtained using the novel “Interface Reaction tool”. To enlighten the underpinning catalytic reaction mechanism to the absorbent, the energetics of interactions between the catalyst and the solid metal hydrides have been derived. For this test study, a leading catalyst TiFx (x = 4,3, and 2) has been added to the well-studied high gravimetric metal hydrides such as MgH2, Mg(BH4)2, and Mg(AlH4)2. The reaction equation at ambient condition has been validated using the total energies from Kohn-Sham density-functional-theory, and the outcome emphasizes the importance of bonding analysis. Hence, we exemplified the bonding states of all the Ti–F derivatives namely TiF4, TiF3 and TiF2 in an effort to elucidate the role of fluorine for the onset of catalytic reaction. Our detailed analysis of reaction pathways indicate the vitality of TiF4 as an additive before and after the H2 release. Our work pioneers the study on often overlooked reaction possibilities at ambient condition. The calculated reaction energy of less than 40 kJ/mol and 4.64 wt % of H2 release for TiF4 and TiF3 underscores their catalytic activity and meet the system targets set by DoE for the year 2020. This work presents “significant disclosures” on the hydrogen decomposition mechanism and provides a platform for the feasibility study of a new material. This proposes an innovative methodology for predicting the suitability of a new material for efficient production of H2 fuel.