Modeling hydrogen storage on Mg–H2 and LiNH2 under variable temperature using multiple regression analysis with respect to ANOVA

https://doi.org/10.1016/j.ijhydene.2017.05.101Get rights and content

Highlights

  • Investigating Mg–H2 and LiNH2 as a hydrogen storage materials.

  • Generating new mathematical models.

  • Design and fabrication of a new hydrogen storage testing unit.

Abstract

The world is facing a major problem due to the depletion of conventional energy sources. Hydrogen is considered one of the most promising sources of energy. Recently, one of the problems facing utilization of hydrogen energy is the storage. Therefore, finding materials to store hydrogen based on the adsorption/desorption methodology (i.e. metal hydrides) is considered extremely vital issue. During this work two candidate materials (i.e. Mg–H2 and LiNH2) were investigated at different temperatures (25–45 °C). The results revealed that both candidate materials possessed long cycle life and cyclibility which opens the wide door to use these materials in vehicular applications. On the other hand the generated mathematical models based on the multiple regression analysis with respect to ANOVA showed that increasing temperature will increase the weight of hydrogen adsorption for both candidate materials.

Introduction

Hydrogen fuel is an attractive alternative source of energy since it is clean, non-toxic and renewable especially when it is produced from renewable resources (i.e. Sea Water and Solar Energy) [1], making it as a substitute for petroleum derived fuels in vehicular applications. However, the greatest challenge in making hydrogen available for use in transportation lies in the development of safe, compact, portable and cost effective hydrogen storage systems. Hydrogen can be stored as (i) pressurized gas, (ii) cryogenic liquid, (iii) solid fuel as chemical or physical combination with materials, such as metal hydrides and Metal Organic Frameworks (MOFs). Metal hydrides compose of metal atoms that constitute a host lattice and hydrogen atoms. Hydrogen storage in metal hydrides depends on different parameters and consists of several mechanistic steps. Metals differ in the ability to dissociate hydrogen, this ability being dependent on:

  • A.

    Surface structure.

  • B.

    Morphology and purity.

An optimum hydrogen-storage material is required to have the following properties [2], [3]:

  • A.

    High hydrogen capacity per unit mass and unit volume which determines the amount of available energy.

  • B.

    Low dissociation temperature.

  • C.

    Moderate dissociation pressure.

  • D.

    Low heat of formation in order to minimize the energy necessary for hydrogen release.

  • E.

    Low heat dissipation during the exothermic hydride formation.

  • F.

    Reversibility.

  • G.

    Limited energy loss during charge and discharge of hydrogen.

  • H.

    Fast kinetics.

  • I.

    High stability against O2 and moisture for long cycle life.

  • J.

    Cyclibility.

  • K.

    Low cost of recycling and charging infrastructures.

  • L.

    High safety.

There is considerable research on magnesium and its alloys due to their high hydrogen storage capacity by weight and low cost. Besides, the Mg-based hydrides possess good-quality functional properties, such as heat-resistance, vibration absorbing, reversibility and recyclability. Several researchers have investigated magnesium and its alloys from various angles. Fry et al. [4] have improved hydrogen cycling kinetics of nano-structured magnesium/transition metal multilayer thin films, while Shahi et al. [5] have conducted studies on de/rehydrogenation characteristics of nanocrystalline Mg–H2 co-catalysed with Ti, Fe and Ni. James Jr. et al. [6] have studied the fundamental environmental reactivity testing and analysis of the hydrogen storage material 2LiBH4·MgH2. Utke et al. [7] have investigated the effect of using 2LiBH4–MgH2 for reversible hydrogen storages. Mustafa et al. [8] have studied the influence of adding K2TiF6 on the hydrogen sorption properties of MgH2. Song et al. [9] have investigated the improvement of hydrogen-storage properties of MgH2 by adding Ni, LiBH4, and Ti. Gattia et al. [10] have studied the effect of hydrogen cycling on the microstructure and morphological changes in MgH2. Korablov et al. [11] have investigated activation effects during hydrogen release and uptake from MgH2. It is worth of mention that Shao et al. [12] have studied the hydrogen storage and thermal conductivity of Mg–based materials while Rusman et al. [13] have conducted a review on the current progress of metal hydrides for solid-state hydrogen storage applications. Tran et al. [14] have investigated the dehydriding mechanism of Mg2NiH4 using in-situ ultra-high voltage transmission electron microscopy (TEM) combined with Synchrotron powder X-ray diffraction (XRPD) and differential scanning calorimetry (DSC).They found that the hydrogen release is based on a mechanism of nucleation and growth of Mg2NiHx (x ∼ 0–0.3) solid solution grains which is greatly enhanced in the presence of crystal defects occurring as a result of the polymorphic phase transformation. Li et al. [15] investigated the hydrogen storage properties and mechanisms of the Ca (BH4)2-added 2LiNH2–MgH2 system. The results indicated that the dehydrogenated 2LiNH2–MgH2–0.1Ca (BH4)2 sample could absorb 4.7 wt% of hydrogen at 160 °C and 100 atm while only 0.8 wt% of hydrogen was recharged into the dehydrogenated pristine sample under the same conditions. Lin et al. [16] have studied the Mg (NH2)2–LiNH2–4LiH composite in order to improve its kinetics, thermodynamics and cycling properties. While Barison et al. [17] studied the influence of different high energy milling times and of the addition of catalysts such as Nb2O5, TiCl3 and graphite on the hydrogen absorption/desorption (A/D) kinetics of a mixture of 2LiNH2 + 1.1MgH2 in the temperature range (220–240) °C. Lan et al. [18] investigated the characteristics of hydrogen storage of LiNH2/MgH2 (1:1). Albanesi et al. [19] improved the hydrogen sorption kinetics by adding 1 mol% AlCl3 to LiNH2-LiH. They showed that Al+3 is incorporated into the LiNH2 structure by partial substitution of Li+ forming a new amide in the Li–Al–N–H system, which is reversible under hydriding/dehydriding cycles. They assured that the substituted amide improved hydrogen storage properties with respect to LiNH2–LiH. As a result a stable hydrogen storage capacity of about 4.5–5.0 wt% under cycling and completely desorbed in 30 min at 275 °C for the Li–Al–N–H system. Burger et al. [20] studied several material properties, like bulk density and thermodynamic data, isothermal absorption and desorption experiments. They have generated two-step model equations to be utilized to capture the experimentally measured reaction rates and can be used for model validation of the design simulations.

Varin et al. [21] studied the dehydrogenation rate of synthesized hydride nanocomposites of (LiNH2 + nMgH2). Zhang et al. [22] studied the effect of adding LiNH2 on the hydrogen absorption/desorption capacities of the Li3N–MgH2. Albanesi et al. [23] investigated the hydrogen sorption kinetics and the reactions between LiNH2–LiH and AlCl3 additive with a multitechnique approach involving differential scanning calorimetry (DSC), hydrogen volumetric measurements, X-ray powder diffraction (XRPD), Fourier transform infrared analysis (FTIR) and solid-state nuclear magnetic resonance (NMR).

During the current work a special reactor connected to a fully computerized system was designed and fabricated in order to fulfil the needs to study the effect of varying the temperature on the adsorption of hydrogen using Mg–H2 and LiNH2 at low temperatures (i.e. 25, 30, 35, 40 and 45 °C) based on the gravimetric method. Two mathematical models were generated based on the multiple regression analysis with respect to ANOVA to show the effect of low temperature on hydrogen adsorption for the given candidate materials.

Section snippets

Experimental work

The adsorption of hydrogen using commercial magnesium hydride (i.e. Mg–H2) supplied by Sigma Aldrich and lithium amide (i.e. LiNH2) supplied by ChemCruz at low temperatures as mentioned previously was investigated using a special hydrogen storage unit which was designed and fabricated in situ. This unit consisted of three major parts, the first part is a reactor made from stainless steel 316 L as shown in Fig. 1, connected to the second part which consisted of piping network made also of

Hydrogen storage behaviour of Mg–H2 and LiNH2

Twenty cycles were implemented to measure the adsorption of hydrogen using Mg–H2 at 25, 30, 35, 40 and 45 °C. These cycles were divided into two parts. The first part contained fifteen cycles using the first sample of Mg–H2 (i.e. three cycles per each temperature). Followed by another five cycles using the second sample of Mg–H2 (i.e. one cycle per each temperature) in order to investigate the performance and efficiency of the mentioned material. The results reflected good performance and

Conclusions

Investigating the hydrogen adsorption at the proposed range of temperatures (25–45° C) using Mg–H2 and LiNH2 showed that both candidate materials possessed long cycle life and cyclibility which opens the wide door to store hydrogen at ambient conditions which is considered very crucial in hydrogen vehicles powered by PEM fuel cells. On the other hand the generated mathematical models based on the multiple regression analysis with respect to ANOVA revealed that increasing temperature will

Acknowledgements

The authors would like to thank the ‘Support to Research, Technological Development & Innovation in Jordan’ (SRTD – II), an EU funded project managed by the Higher Council for Science & Technology of Jordan for financing the research activities of the current work under the grant no. SRTD/2014/GRT/AR/2321.

Nomenclature

ANOVA
analysis of variance
MOFs
metal organic frameworks
TEM
transmission electron microscopy
XRPD
X-ray powder diffraction
DSC
differential scanning calorimetry
PI
pressure indicator
GBTS
glove box temperature sensor for hydrogen
LC
load cell to measure the change in weight of the sample
TC
temperature controller
DES
desorption tank
ADS
adsorption tank
PC
pressure controller
TCNT
temperature controller
NV
needle valve
SV
solenoid valve
PT
pressure transmitter
VT
vacuum transmitter
PRT
proportional pressure transmitter
FM
flow

References (32)

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