| Density Functional Theory Studies on a Reversible Hydrogen Storage "Li-Mg-B-N-H" System | ||
| Nianthrini Balakrishnan, Pabitra Choudhury, Venkat R. Bhethanabotla and Babu Joseph, Chemical and Biomedical Engineering, University of South Florida, 4202 E. Fowler Ave., ENB 118, Tampa, FL 33620
Many experimental and theoretical studies have been carried out to find materials with reversible properties, low desorption temperatures1, accelerated kinetics1 and optimum hydrogen storage capacity (at 298 K, the US DOE target for gravimetric hydrogen storage capacity is 6.5 wt %)3. Experiments suggest that complex hydrides of Li, Na, Mg, B, Al and N have such properties1. In this study, a density functional theory study with the local density approximation (LDA) and augmented plane wave method (PAW) is performed to find the hydrogen storage properties for different molar ratios X of MgH2 in the complex storage material (LiNH2)2 - LiBH4 - (MgH2)X. Experimentally proposed multistep hydrogen release pathway for the intermediate quaternary phase Li4(NH2)3(BH4)1 that is formed will be examined, and the impact of MgH2 in the storage material for X = 0, 0.25, 0.5, 0.75 and 1.0 will be calculated. Using ab-initio methods, the stability of the structures are confirmed and thermodynamic properties such as heat of reaction and Gibbs energy are found for each reactant and product in the reaction step. These are compared with the literature values to validate the proposed reaction pathways. The reversibility and storage capacity of these materials will be verified from the desorption behavior observed at different temperatures. The kinetic barrier which negatively impacts this system with increasing fraction of MgH2 will be identified. These theoretically obtained data can be used to validate the suggested mechanism from experimental observations for the reaction. These efforts are expected to contribute towards identification of suitable hydrogen storage materials. References: 1Andrea Sudik, Jun Yang, Devin Halliday and Christopher Wolverton, J. Phys. Chem. C 2008, 112, 4384. 2 G.J.Lewis, J.W.A.Sachtler, J.J.Low, D.A.Lesch, S.A.Faheem, P.M.Dosek, L.M.Knight, L.Halloran, C.M.Jensen, Jun Yang, Andrea Sudik, Donald J.Seigel, Christopher Wolverton, Vidvuds Ozolins and Shu Zhang, J. Alloys Compd. 2007, 446-447, 355. 3You Fa Yin, Tim Mays, and Brian McEnaney, Langmuir 2000, 16, 10521. Extended Abstract Status: Not Uploaded | ||