59 research outputs found
Potentials and challenges of a Li-RHC based Tank
No full textThe potential of a LiBH4 - MgH2 hydrogen storage tank is discussed, on the basis of the Lab tests concerning the thermodynamic and kinetic properties of the composite and of the preliminary simulation results on the large scale capacity
Modeling the kinetic behavior of the Li-RHC system for energy-hydrogen storage: (I) absorption
Get PDFThe Lithium–Boron Reactive Hydride Composite System (Li-RHC) (2 LiH + MgB2/2 LiBH4 + MgH2) is a high-temperature hydrogen storage material suitable for energy storage applications. Herein, a comprehensive gas-solid kinetic model for hydrogenation is developed. Based on thermodynamic measurements under absorption conditions, the system's enthalpy ΔH and entropy ΔS are determined to amount to −34 ± 2 kJ∙mol H2−1 and −70 ± 3 J∙K−1∙mol H2−1, 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 H2−1. Applying the kinetic model, the dependence of the reaction rate constant as a function of pressure and temperature is calculated, allowing the design of optimized hydrogen/energy storage vessels via finite element method (FEM) simulations
Development of a new approach for the kinetic modeling of the lithium reactive hydride composite (Li-RHC) for hydrogen storage under desorption conditions
No full textAmong some promising candidates for high-capacity energy and hydrogen storage is the Lithium-Boron Reactive Hydride Composite System (Li-RHC: 2 LiH + MgB2/2 LiBH4 + MgH2). This system desorbs hydrogen only at relatively high temperatures and presents a two-step series of reactions occurring in different time scales: first, MgH2 desorbs, followed by LiBH4. Hitherto, the dehydrogenation kinetic behavior of such a system has been described for different temperatures at specific values of operative pressure. However, a comprehensive model representing its dehydrogenation kinetic behavior under different operative conditions has not yet been developed. Herein, the separable variable method is applied to develop a comprehensive kinetic model, including the two-step dehydrogenation series reaction. The MgH2 decomposition is described with the one-dimensional interface-controlled reaction rate Johnson-Mehl-Avrami-Erofeyev-Kholmogorov (JMAEK) with a (Pequilibrium/Poperative) pressure functionality and an Arrhenius temperature dependence activation energy of 63 ± 3 kJ/mol H2. The LiBH4 decomposition is modeled applying the autocatalytic Prout-Tompkins model. A novel approach to describe the Prout-Tompkins t0 parameter as a function of the operative temperature and pressure model is proposed. This second reaction step presented a (Pequilibrium – Poperative/Pequilibrium)2 pressure dependence and an Arrhenius temperature dependence with activation energy 94 ± 13 kJ/mol H2. The proposed approach is experimentally and computationally validated, successfully describing the decomposition kinetic behavior of MgH2 and LiBH4 under three-phase gas, liquid and solid environment and shows good agreement between experimental and modeled curves
Thermodynamic and kinetic characterization of the catalysed LiBH4 - MgH2 system
No full textThe LiBH4 – MgH2 system is of particular interest among the reactive hydride composites due to its high gravimetric capacity and the full reversibility of the sorption reactions. With the aim to realize a hydrogen storage tank based on this material, a full physico-chemical characterization of the 2:1 molar ratio composition has been undertaken, in order to obtain data fundamental for the simulation of the sorption processes and the design of the system. In particular, the reaction enthalpy, entropy and activation energy for all the sorption steps have been evaluated by PCT and coupled manometric – calorimetric measurements. Optical microscopy has been used to confirm the evolution of the different physico-chemical processes involving liquid and gas phases.
Concerning the response of the system to the exothermal absorption and endothermal desorption reaction, the thermal conductivity of the composite in the charged and discharged state has been measured by the transient source method as a function of the temperature and the density, modified by compaction, of the samples.
The effect of the density on the sorption properties and the cycling of the materials has been explored by kinetic measurements and scanning electron microscope investigations up to 20 full charging/discharging cycles on pellets compacted at pressure as high as 900 MPa. A strong effect has been noticed on the number of the so-called activation cycles and on the absorption kinetic performance, while no decrepitation and disaggregation effects have been observed, in spite of the presence of the borohydride liquid phase
Design and evaluation of a LiBH4 ‐ MgH2 storage system
No full textThe discovery of the reversible hydrogenation reaction of MgH2-borohydride based Reactive Hydride Composites (RHCs) in 2004 gave new impetus to the entire hydrogen storage research. RHCs combine high hydrogen storage capacities with relatively fast sorption rates at more moderate temperature and pressure conditions than in the case of the respective single borohydrides. In particular, for the promising combination of LiBH4 and MgH2, many investigations were carried out to gain a deeper understanding of the reaction pathways and optimize kinetic and cycling properties. However, a scaled up tank system containing the Li-based RHC has not been investigated until now. In this work we present the potentials and challenges of this system based on small scale investigations and compare these results with first experiences with two different tank systems, each of them filled with 250 g of LiH / MgB2 and TiCl3 as additive material. Compaction of the material plays a key role for technical application of RHCs regarding storage mass and volume as well as for heat transfer. The high potential of this system to meet DoE system targets will be discussed and possible solutions for the remaining challenges will be presented
Changing the dehydrogenation pathway of LiBH4-MgH2via nanosized lithiated TiO2
Get PDFNanosized lithiated titanium oxide (LixTiO2) noticeably improves the kinetic behaviour of 2LiBH4 + MgH2. The presence of LixTiO2 reduces the time required for the first dehydrogenation by suppressing the intermediate reaction to Li2B12H12, leading to direct MgB2 formation.Fil: Puszkiel, Julián Atilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Karimi, F.. Helmholtz-zentrum Geesthacht; AlemaniaFil: Santoru, A.. Helmholtz-zentrum Geesthacht; AlemaniaFil: Pistidda, C.. Helmholtz-zentrum Geesthacht; AlemaniaFil: Klassen, T.. Helmholtz-zentrum Geesthacht; AlemaniaFil: Bellosta von Colbe, J. M.. Helmholtz-zentrum Geesthacht; AlemaniaFil: Dornheim, M.. Helmholtz-zentrum Geesthacht; Alemani
Compaction pressure influence on density, sorption behaviour and surface morphology for LiBH4-MgH2 composite
No full textThe compaction pressure influence on the sorption behaviour, the thermal conductivity and the morphology of LiBH4 - MgH2 reactive hydride composite is studied by manometric, calorimetric, thermal conductivity and scanning electron microscopy measurements
Modeling and Parameterization of a PEM Fuel Cell Stack for a System Integration Into a Metal Hydride Based Hydrogen Storage System
No full textPower systems using renewable energy sources have emerged as a sustainable solution for decarbonizing the energy sector. Implementing such systems requires integrating them with an efficient storage medium to improve their reliability and flexibility. This work explores the modeling and parameterization of a fuel cell system, with the purpose of coupling it with a metal hydride-based hydrogen storage reservoir. An electrical and thermal 0D simulation model for a 1.6 kW air-cooled proton exchange fuel cell stack is developed to investigate its performance, heat transfer and temperature development. The model validation and simulation are done by testing it with four different steady-state power demand scenarios. Experimental results show an efficient thermal coupling between the fuel cell stack and the metal-hydride system. Simulations and experimental results show an excellent agreement. The developed modeling approach is also appliccable to the design of different gas-to-power configurations and sizes, for the design of fuel cell-metal hydride storage systems
NaAlH4 production from waste aluminum by reactive ball milling
No full textEfficient ways of storing renewable energies belong to the major research challenges of our time. Hydrogen as energy carrier is considered to be a promising option for future energy storage. Due to their high volumetric energy densities solid state hydrogen storage systems are regarded as effective storage media besides high pressure or liquefied gas tanks. An important issue for later mass production are production costs of such materials. Our work shows how the established hydrogen storage material sodium alanate (NaAlH4) [1,2] can be obtained from low cost starting materials. Thereby NaAlH4 is produced by reactive ball milling of commercial NaH and waste aluminum grains under 100 bar hydrogen atmosphere. The mechanochemical synthesis was followed stepwise by means of ex-situ PXD (powder X-ray diffraction) and DSC measurements (differential scanning calorimetry). Furthermore, the synthesis was investigated by in-situ monitoring of the milling vial’s temperature and pressure. The sorption properties of the synthesized material were characterized by Sievert’s method and in-situ SRPXD (synchrotron radiation powder X-ray diffraction). A complete conversion of the starting reactants was obtained
- …
