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

• Thermodynamic and kinetic of NaBH4 thermochemical regeneration was studied.
• Equilibrium constant and Gibbs free energy for NaBH4 regeneration were estimated.
• A mathematical model for the quantification of NaBH4 regeneration was proposed.

NaBH4 is a candidate for H2 storage in solid phase. NaBH4 hydrolysis readily produces H2 gas and NaBO2 which can regenerate NaBH4 with pressurized hydrogen and the aid of a reducing agent like Magnesium above 500 °C. This paper deals with the NaBH4 thermochemical regeneration from the NaBO2–Mg–H2 ternary system at isothermal temperatures between 558 and 634 °C and H2 pressure in the range 2–31 bar. A simplified Langmuir adsorption model has been applied for the interpretation of the in-situ H2 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 (Keq), Gibbs free energy (ΔrG0) 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.