Novel solid-state hydrolysis kinetics of NaBH₄ for stable and high-capacity on-line hydrogen production

Solid-state hydrolysis of NaBH₄ could achieve high-capacity on-line hydrogen production. However, the stability of hydrogen production in the solid-state hydrolysis process has been questioned. In this paper, a novel kinetic model is proposed for the solid-state hydrolysis behavior. The acceleration factor β is introduced into the traditional shrinking core model to reveal the relationship between “dissolution” and “catalytic hydrolysis” in the solid-state hydrolysis process. The comparison results show a good agreement between the model and experiment in the temperature range of 303.15–348.15 K. Meanwhile, the kinetics conclusions and by-products characterization indicated that the “excessive dissolution” of NaBH₄ and the “dehydration of by-products” are two important factors contributing to the uncontrolled reaction. Based on the parametric analysis and experimental verification, the optimum temperature for solid-state hydrolysis is approximately 323.15 K. Besides, the adjustment of the water intake strategy to intermittent intake reduced water consumption by 36.6 %. As a result, the hydrogen release capacity could be increased to as high as 5.49 wt% (close to the U.S. Department of Energy 2025 gravimetric hydrogen storage capacity of 5.5 wt%), even though the weight of water is taken into account as reactant.