Thermodynamic and kinetic studies of NaBH4 regeneration by NaBO2-Mg-H2 ternary system at isothermal condition

NaBH4 is a candidate for H-2 storage in solid phase. NaBH4 hydrolysis readily produces H-2 gas and NaBO2 which can regenerate NaBH4 with pressurized hydrogen and the aid of a reducing agent like Magnesium above 500 degrees C. This paper deals with the NaBH4 thermochemical regeneration from the NaBO2 Mg H-2 ternary system at isothermal temperatures between 558 and 634 degrees C and H-2 pressure in the range 2-31 bar. A simplified Langmuir adsorption model has been applied for the interpretation of the in-situ H-2 pressure variations. The applied model is zero-dimensional but provides a reasonable approach to identify the rate determining step and acquire relevant thermodynamic and kinetic parameters such as equilibrium constant (K-eq), Gibbs free energy (Delta(r)G degrees) and reaction rate coefficients (k). The study provides an apparent activation energy and Gibbs free energy of this process of 29.2 kJ/mol and -76.9 kJ/mol, respectively. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.