(283c) A Computational Study of the NaBH4 Hydrolysis Reaction for Hydrogen Production | AIChE

(283c) A Computational Study of the NaBH4 Hydrolysis Reaction for Hydrogen Production

Authors 

Henkelman, G., University of Texas at Austin
Johnson, K., University of Pittsburgh



NaBH4 is a promising hydrogen storage material due to its high hydrogen content (10.7 wt%), relative safety, and low cost. The NaBH4 hydrolysis reaction: NaBH4 + 4H2O → NaBO2·2H2O + 4H2 has found application in niche markets such as portable energy generation. The rate of hydrolysis reaction without catalyst is very low in aqueous solution, so a great deal of work has been focused on catalyst design and application.1,2 Additionally, the aqueous hydrolysis reaction also suffers from low system hydrogen storage capacity due to excess water used as solvent for NaBH4 and byproducts. Recently, Matthews and coworkers demonstrated that steam hydrolysis of NaBH4 can be used to release hydrogen with both fast kinetics and high extent of reaction without the use of any catalyst and with reduced water consumption.3-5 Despite a long history of research and development, the basic mechanism of NaBH4 hydrolysis reaction is not understood on a molecular level. We have performed first-principles density functional theory calculations to investigate the elementary reaction steps in aqueous NaBH4 hydrolysis. Detailed understanding of these steps would be useful for reaction condition optimization, catalyst design, and ultimately for precise control of the reaction in practical applications. Representative minimum energy pathways have been characterized from the family of mechanisms that exist in the real system by using the conventional nudged elastic band method6 and the solid-state nudged elastic band method.7 We identified energy barriers and reaction intermediates for each elementary step. Taken together, these steps provide a full picture of the NaBH4hydrolysis reaction at the molecular level.

References

                (1)          Schlesinger, H. I.; Brown, H. C.; Finholt, A. E.; Gilbreath, J. R.; Hoekstra, H. R.; Hyde, E. K. Journal of the American Chemical Society 1953, 75, 215-219.

                (2)          Liu, B. H.; Li, Z. P.; Suda, S. Journal of Alloys and Compounds 2006, 415, 288-293.

                (3)          Aiello, R.; Sharp, J. H.; Matthews, M. A. International Journal of Hydrogen Energy 1999, 24, 1123-1130.

                (4)          Marrero-Alfonso, E. Y.; Gray, J. R.; Davis, T. A.; Matthews, M. A. International Journal of Hydrogen Energy 2007, 32, 4717-4722.

                (5)          Marrero-Alfonso, E. Y.; Gray, J. R.; Davis, T. A.; Matthews, M. A. International Journal of Hydrogen Energy 2007, 32, 4723-4730.

                (6)          Henkelman, G.; Uberuaga, B. P.; Jonsson, H. J. Chem. Phys. 2000, 113, 9901-9904.

                (7)          Sheppard, D.; Xiao, P.; Chemelewski, W.; Johnson, D. D.; Henkelman, G. J. Chem. Phys. 2012, 136, 074103-074108.