Material properties and empirical rate equations for hydrogen sorption reactions in 2 LiNH2–1.1 MgH2–0.1 LiBH4–3 wt.% ZrCoH3

Abstract

Abstract2 LiNH 2 -1.1 MgH 2 -0.1 LiBH 4 -3 wt.% ZrCoH 3 is a promising solid state hydrogen storage material with a hydrogen storage capacity of up to 5.3 wt.%. As the material shows sufficiently fast desorption rates at temperatures below 200 °C, it is used for a prototype solid state hydrogen storage tank that is coupled to a HT-PEM fuel cell. In order to perform design simulations for this prototype reactor with a hydrogen capacity of 2kWh el , model equations for the rate of hydrogen sorption reactions are required.Therefore, several material properties, like bulk density and thermodynamic data, have been measured and they are summarized in the present publication. Furthermore, isothermal absorption and desorption experiments are performed in a temperature and pressure range that is in the focus of the coupling procedure. Using this experimental data, two-step model equations have been fitted for the absorption and desorption reaction. These empirical model equations are able to capture the experimentally measured reaction rates and can be used for model validation of the design simulations. KeywordsLi-Mg-N-H hydride, reaction rate, model equations, hydrogen storage IntroductionDue to high theoretical storage densities, complex hydrides show the potential to improve the present state of the art of hydrogen storage for automotive applications [1]. As the hydrogen is strongly bonded to the powdered material, the amount of free gaseous hydrogen in equilibrium at room temperature and pressure is small. Therefore, hydrogen is just released when external heat is provided for the endothermal desorption reactions. In case the storage reactor is coupled to a fuel cell (FC), the required amount of hydrogen can be released by transfer of the waste heat from the FC. This kind of coupled system has already been studied by several simulations and experiments for conventional metal hydrides as well as NaAlH 4 [2,3].The present work has been developed within a framework of activities aiming to realize a hydrogen storage tank that is studied in technically relevant scale, i.e. allowing for 2 h coupled operation with a 1 kW el high temperature proton-exchange membrane (HT-PEM) fuel cell. As for an appropriate tank design modelling and simulation tools are used, reliable information on the properties of the selected

Recent Progress and New Perspectives on Metal Amide and Imide Systems for Solid-State Hydrogen Storage

“…2LiNH 2 + 1.1MgH 2 + 0.1LiBH 4 -3 wt. %ZrCoH 3 has been considered as one of the most promising materials for possible real scale applications owing to its excellent hydrogen storage properties [136][137][138]. A prototype tank to feed a 1 kW HT-PEM stack for an Auxiliary Power Unit (APU), was built using this ternary system as storage material.…”

Development of Hydrogen Storage Tank Systems Based on Complex Metal Hydrides

“…In the absorption step, the heat of absorption of the MH bed (low temperature) was transferred to the CH bed (higher temperature). The kinetics for the simulation was based on the model by Bürger et al [16]. The viability of the concept was demonstrated by comparing the temperature front in a pure CH bed and in a MH/CH combined bed.…”

Numerical investigation of hydrogen charging performance for a combination reactor with embedded metal hydride and coolant tubes

“…The combination reactor, initially at room temperature, is filled with hydrogen at 70 bar. Since the AB 5 material, LaNi 4.3 Al 0.4 Mn 0.3 is able to absorb hydrogen very quickly at these ranges of temperature and pressure, its reaction heat ensures the heat up of the complex hydride bed to temperatures above 130 o C. Furthermore, based on the kinetics measurements of the Li-Mg-N-H material at 70 bar, it has been shown that temperatures above 130 o C are required for achieving high hydrogen loading rates [14]. Accordingly, in a combination reactor, the complex hydride charging process is initiated without the need of external heat source integration.…”

“…Reaction kinetics of both, metal and complex hydrides are determined based on their measured hydrogen charging rates under different conditions of temperature and pressure as described in [14].…”