Modeling the kinetic behavior of the Li-RHC system for energy-hydrogen storage : ( I ) absorption

The LithiumeBoron Reactive Hydride Composite System (Li-RHC) (2 LiH þ MgB2/2 LiBH4- þ MgH2) is a high-temperature hydrogen storage material suitable for energy storage appli- cations. Herein, a comprehensive gas-solid kinetic model for hydrogenation is developed. Based on thermodynamic measurements under absorption conditions, the system's enthalpy DH and entropy DS are determined to amount to —34 ± 2 kJ∙mol H—2 1 and —70 ± 3 J∙K—1∙mol H—2 1, respectively. Based on the thermodynamic behavior assessment, the kinetic measurements' conditions are set in the range between 325 ◦C and 412 ◦C, as well as between 15 bar and 50 bar. The kinetic analysis shows that the hydrogenation rate-limiting-step is related to a one- dimensional interface-controlled reaction with a driving-force-corrected apparent activation energy of 146 ± 3 kJ∙mol H—2 1. Applying the kinetic model, the dependence of the reaction rate constant as a function of pressure and temperature is calculated, allowing the design of opti- mized hydrogen/energy storage vessels via finite element method (FEM) simulations.
The authors would like to thankfully acknowledge the Karl- Vossloh-Stiftung for the financial support provided for this project (Project Number S047/10043/2017). Also, the authors acknowledge Kristin Przybilla for the experimental work related to the PCI assessment and for previous experiments, which have led to the current developments. Lastly, we thank Oliver Metz for all the technical support. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and the Government of Catalonia's Agency for Business Competitiveness(ACCIÓ).