Hydrogen storage on LaNi 5−x Sn x . Experimental and phenomenological Model-based analysis

OLIVA, D.G.; FUENTES, M.; BORZONE, E.M.; MEYER, G.O.; AGUIRRE, P.A.

ENERGY CONSERVATION AND MANAGEMENT

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2018 vol. 173 p. 113 - 122

0196-8904

Three hydride-forming metals (LaNi5, LaNi4.73Sn0.27, and LaNi4.55Sn0.45) have been studied as solid phase hydrogenstorage material in batch experiments using pure hydrogen and temperatures ranging from 300 K to340 K. This process mainly involves: physisorption of hydrogen gas molecules; chemisorption and dissociation ofhydrogen molecules; surface penetration of hydrogen atoms; hydride formation; and diffusion of hydrogenatoms through hydride-forming metal. In case the material is fully hydrided, hydride formation ceases anddiffusion proceeds on the fully hydrided material.A phenomenological model was developed by aggregating the first four mechanisms in a single sorptionkinetic term involving a first-order driving force, the remaining mechanism being the atomic diffusion in thehydride-forming material. The driving force is computed between external partial pressure and equilibriumpressure according to the Pressure-Composition-Temperature model (PCT). The corresponding parameters for anempirical PCT were estimated from equilibrium data. This equation is more suitable for process engineeringoptimization due to the smoothness in its concentration domain. Specific sorption rate and diffusion coefficientsof the process were also estimated from dynamic data. From a sensitivity analysis, productivity proved to berelated to particle diameter. In the frame of batch processes, the global rate is dominated by the sorption kineticterm at the beginning of the experiments with the material being free from hydride, whereas with more than5?10% of the material being hydrided, diffusion dominates the process. LaNi5 shows higher hydrogen storagecapacity than LaNi4.73Sn0.27 and LaNi4.55Sn0.45 within the investigated temperature and pressure ranges.Diffusion and sorption kinetic limited regions were identified from a sensitivity analysis of process productivityand normalized marginal values. The present work is oriented to modeling, designing, and optimizing storageand purification devices.