Synergistic Effect of LiBH4 and LiAlH4 Additives on Improved

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Synergistic Effect of LiBH and LiAlH Additives on Improved Hydrogen Storage Properties of Unexpected High Capacity Magnesium Hydride Yiwen Zhang, Xuezhang Xiao, Bosang Luo, Xu Huang, Meijia Liu, and Lixin Chen J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b11222 • Publication Date (Web): 22 Jan 2018 Downloaded from http://pubs.acs.org on January 22, 2018

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The Journal of Physical Chemistry

Synergistic Effect of LiBH4 and LiAlH4 additives on Improved Hydrogen Storage Properties of Unexpected High Capacity Magnesium Hydride Yiwen Zhang ab, Xuezhang Xiao*ab, Bosang Luo ab, Xu Huang ab, Meijia Liu ab, Lixin Chen*abc a

State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, P.R. China b

School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, P.R. China

c

Key Laboratory of Advanced Materials and Applications for Batteries of Zhejiang Province, Hangzhou 310013, P.R. China

Abstract A significant improvement in reversible de/rehydrogenation properties of MgH2 doped with 2.5 wt% LiAlH4 and 2.5 wt% LiBH4 additives is achieved by reactive ball milling. Careful comparison studies show that the small amount (total mass ratio ≤ 5 wt%) addition of LiBH4 and/or LiAlH4 can improve the hydrogen desorption performances of MgH2 in term of reducing hydrogen desorption temperature, enhancing hydrogen desorption kinetics and increasing hydrogen capacity. In particular, the MgH2 co-doped with LiAlH4-LiBH4 exhibits best dehydrogenation properties, which starts to release hydrogen at about 280 °C and releases a high hydrogen capacity of 7.62 wt% with superior reaction kinetics. The activation energy of hydrogen desorption is decreased from 187.8 kJ/mol (ball-milled MgH2) to 155.8 kJ/mol. It can also uptake 7.7 wt% H2 within 15 min at 300 °C with a stable hydrogen absorption kinetics in the first 10 cycles. This synergistic effect of LiBH4 and LiAlH4 additives on improved hydrogen absorption/desorption properties are attributed to the in-situ formation of Li3Mg7, Mg17Al12 and MgAlB4 new phases acting as the “catalytic active sites” to facilitate the

*

Corresponding author. Tel./fax: +86 571 87951152. E-mail address: [email protected] (X.Z. Xiao); [email protected] (L.X. Chen). 1

ACS Paragon Plus Environment

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diffusion of hydrogen through the reaction barriers in the de/hydrogenation cycles of MgH2. Moreover, these new phases can be rehydrogenated into MgH2, LiBH4 and Li3AlH6 hydrides, which further enhance the hydrogen capacity of co-doped sample more than the theoretical capacity of primitive MgH2.

1. Introduction Magnesium-based hydrides are regarded as one of the very promising hydrogen storage materials due to its high hydrogen weight density (7.6 wt%), low cost and good cycle reversibility1-4. However, MgH2 exists the disadvantages of high thermodynamic stability as well as slow kinetics for hydrogen storage process5. During recent decades, various modified strategies, such as nanostructuring6-12, alloying13-20 and adding catalyst21-28, have been studied to improve the hydrogen storage performances. One of the general methods is to decrease the grain/particle sizes by ball milling MgH2 or Mg, hence reducing its de/rehydrogenation activation energy. Another very effective strategy is utilizing transition metals (Ni, Ti, V, Cu, Nb)26, 29, transition metal oxides (Nb2O5,V2O5,CeO2,TiO2)21, 30-33, halides (TiCl3, TiF3)34-36 and hydrides (TiH2, NbH2, CeH2/CeH2.73)24, 37 as additives/catalysts, which can improve the de/rehydrogenation kinetics of the MgH2 system. However, the hydrogen storage capacity such as transition metal catalyzed MgH2 system would be considerably reduced because transition metal additives/catalysts are short of hydrogen storage ability. Recently, it was reported that the thermodynamics and kinetics of MgH2 could be effectively modified via mixing with complex hydrides, such as the MgH2-NaAlH438, MgH2-LiAlH439, MgH2-LiBH440. Complex hydrides as sources of LiBH4 and LiAlH4 have high hydrogen capacity and the products of Al or B-based alloy have a significant catalytic effect during the decomposition of hydrogen storage system38, 41, 42. Moreover, it was ever reported that there was a mutual destabilization among the LiAlH4-MgH2-LiBH4 (molar ratio 1:1:1) ternary hydride system, which had showed superior hydrogen desorption properties compared with unary sample (LiAlH4, MgH2 and LiBH4) or binary mixtures (LiAlH42


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MgH2, LiAlH4-LiBH4 and MgH2-LiBH4)42. However, the addition of LiAlH4 and/or LiBH4 in MgH2 system is a double-edged sword. On one hand, they can destabilize system and improve hydrogen capacity of MgH2. On the other hand, the reversibility of LiBH4 and LiAlH4 are too poor to meet the reversibility requirement in the mild condition. Although the properties of MgH2 are improved by mixing LiAlH4 or LiBH4 at a constant molar rate, it still doesn’t meet the requirements for practical application. Therefore, it is very important to find out an appropriate additive that can improve the hydrogen storage properties and maintain the hydrogen storage capacity of MgH2. Furthermore, fundamental mechanisms of hydrogen desorption/absorption reaction path and improved effect of LiAlH4/LiBH4 on MgH2 are still unknown. In the present study, the MgH2, MgH2-5wt%LiAlH4, MgH2-5wt%LiBH4, MgH22.5wt%LiAlH4-2.5wt%LiBH4, MgH2-10wt%LiAlH4-10wt%LiBH4 composites were prepared by reactive ball milling in order to investigate the effect of LiAlH4/LiBH4 on microstructure evolution and hydrogen storage behavior of MgH2 system. To the best of our knowledge, this is the first study using LiAlH4 and LiBH4 as additives to synergistically improve the hydrogen desorption/absorption properties of MgH2 system. It is found that the MgH2 doped with LiAlH4-LiBH4 composite starts to release hydrogen at 280 °C and exhibits a high reversible hydrogen capacity more than 7.6 wt%. The superior hydrogen desorption/absorption kinetics is also achieved in MgH2 doped with LiAlH4-LiBH4 composite. Herein, the synergistic mechanism of LiBH4 and LiAlH4 on improved hydrogen storage properties of MgH2 and the de/rehydrogenation performance have been investigated in detail.

2. Experimental section 2.1 Sample preparation The samples were synthesized from following starting materials: Mg (99.5%, Aladdin), LiBH4 (95%, Aladdin), LiAlH4 (≥95%, Alfa Aesar). The ball milling process was performed in a planetary ball mill (QM-3SP4, Nanjing). The MgH2 sample was first 3



synthesized by ball-milling the Mg powder in a 100 ml stainless steel jar under a 1 MPa H2 atmosphere and the ball-milled sample was further heat treated at 350 – 500 ºC under a 8 MPa H2 atmosphere for 24 h to obtain the high yield MgH2. Subsequently, the assynthesized MgH2 sample was mixed with LiAlH4 (mass ratio of 5% vs. MgH2), LiBH4 (mass ratio of 5% vs. MgH2), LiAlH4 (mass ratio of 2.5% vs. MgH2)-LiBH4 (mass ratio of 2.5% vs. MgH2) additives, respectively. The as-synthesized MgH2, MgH2-LiAlH4, MgH2-LiBH4 and MgH2-LiAlH4-LiBH4 composites were ball milled for 10 h under 0.1MPa hydrogen with a ball-to-powder weight ratio of 30:1 and rotation rate of 400 rpm. For simplicity, the above ball-milled MgH2-LiAlH4, MgH2-LiBH4, MgH2-LiAlH4LiBH4 composites are denoted as M-LA5, M-LB5, M-LAB5. In order to reveal the hydrogen storage reaction path of LiAlH4 and LiBH4 doped MgH2 system, the MgH2 doped with LiAlH4 (mass ratio of 10% vs. MgH2)-LiBH4 (mass ratio of 10% vs. MgH2) sample was prepared in the same conditions, which is denoted as M-LAB20. All sample handling was carried out in a glovebox (MIKROUNA) with O2 and H2O vapor levels under 0.1 ppm.

2.2 De/rehydrogenation property, structural and morphological characterization The hydrogen desorption/absorption properties and pressure composition-temperature (PCT) measurement were executed in a commercial Sievert’s type apparatus (PCTpro2000, Hy-Energy) and the sample was loaded in a vessel in the glove box. Temperature programmed desorption (TPD) measurements were heated from room temperature to 380 °C with a heating rate of 5 °C/min. The isothermal desorption measurements were carried out at the required temperature with an initial pressure of 0.9 bar. The reversible hydrogen storage capacity was measured through the way that the consecutive ten times re/de-hydrogenation cycles experiments executing at 300 °C, 10 MPa (rehydrogenation) and 310 °C, 0.09 MPa (dehydrogenation). Differential scanning calorimetry (DSC) measurements were carried out on a Netzsch STA 449F3 instrument with 0.1 MPa Ar as the purge gas with a rate of 40 ml/min. The sample of 2-8 mg was test with automatic program for the DSC data. The amount of dehydrogenated hydrogen was calculated in weight percent on the basis of the hydrogen 4


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volume and pressure changes in the reactor, which could confirm the initial decomposition temperature. XRD experiments of the samples were performed using X’Pert-PRO diffractometer with Cu Kα radiation. The diffraction angle is ranged from 20°to 80°with a speed of 2.00 °/min. Before the experiment, the samples wrapped in a plastic shade with Ar atmosphere were prepared in the glove box in order to avoid air and water contamination. An airtight container filled with Ar was used to protect samples during transferring and scanning. The morphology of the samples was got from Scanning Electron Microscope (SEM, HitachiSU-70, 3.0kV) and transmission electron microscopy (TEM, Tecnai G2F30, 200 kV, 350 A/m2, 0.3 s), high resolution transmission electron microscopy (HRTEM, Tecnai G2F30, 200 kV) with an EDX detector (Oxford Microanalysis 6767, 200 kV, 1.1×103 A/m2, 0.03 s). Fourier transform infrared (FTIR) spectra were recorded on a Bruker Tensor 27 Fourier Transform Infrared Spectrometer. Each FTIR spectrum was created from an average of 32 scans.

3. Results and discussion 3.1 Characterization of ball-milled MgH2, M-LB5, M-LA5, M-LAB5 samples Figure 1a shows the XRD patterns of ball-milled MgH2, M-LB5, M-LA5, M-LAB5 composites. It can be seen that the primary phase is MgH2 in the ball-milled MgH2 composite, while amounts of the additives of LiAlH4 and LiBH4 are too little to be detected for the ball-milled composites (M-LB5, M-LA5, M-LAB5). Moreover, amorphous boron element is difficult to be identified by XRD, executing the FTIR measurement and element mapping to analysis characterized frequencies of B-H spectra and existing of LiAlH4, respectively. Figure 1b is the FTIR spectrum of M-LB5, M-LA5 and M-LAB5 samples. The FTIR spectra of [BH4]– ion in LiBH4 has characteristic bands at 2224, 2293, 2363 cm-1, which is obvious in the M-LB5 and MLAB5 composites. Thus, it is confirmed that LiBH4 is existed in M-LB5 and M-LAB5 composites after ball-milling. At the same time, uniform distributions of Mg and Al can be detected in elemental mapping measurement (Figure 2), indicating that LiAlH4 or its 5



decomposition products (Li3AlH6/Al) can be well mixed in MgH2 matrix. FTIR analysis was further carried out to verify the existence of LiAlH4 in M-LAB5 and M-LA5 samples. As shown in Figure S1, several peaks appeared in the spectra of three samples after ball milling. Due to the amount of LiAlH4 is small, the peak is not so sharp. However, we can see that peak between 1600 and 1650 cm-1 is existed in the M-LAB5 and M-LA5 samples, which could be assigned to the stretching vibration of LiAlH4, in accordance with the previous reports43, 44. It indicates that LiAlH4 is existed in the MLAB5 and M-LA5 samples after ball milling. Yet, the corresponding peak did not appear in the M-LB5 sample. Thus, the existence of LiAlH4 is well confirmed.



 MgH2

 







M-LAB5



 



 



 



Transmittance/a.u.











M-LA5 

   



M-LA5



2363 2224 2293

ball-milled MgH2

 

 

30

40

50 60 2  (degree)

70

M-LB5

B-H



1500

20

2293

M-LB5 



2363

2224

 

M-LAB5

B-H



Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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2000

2500

3000

-1 Wavenumber (cm )

80

Figure 1. (a) XRD patterns of ball-milled MgH2, M-LB5, M-LA5, M-LAB5 composites. (b) FTIR test results of M-LB5, M-LA5, M-LAB5 composites.

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Figure 2. Elemental mapping images of M-LAB5 composite.

3.2 Hydrogen storage properties of as-synthesized MgH2, ball-milled MgH2, MLB5, M-LA5, M-LAB5 samples To elucidate the effect of LiBH4 and LiAlH4 on the hydrogen desorption/absorption properties of MgH2, a series of experiments were performed. Figure 3a exhibits the DSC curves of as-synthesized MgH2, ball-milled MgH2, M-LB5, M-LA5 and M-LAB5 composites. Obviously, the as-synthesized MgH2 sample releases most of its hydrogen at 376.8 °C, while the ball-milled MgH2 exhibits a dehydrogenation peak at 355.4 °C, which confirms that ball milling could reduce the dehydrogenation temperatures of MgH2, that is in good agreement with previous studies45. The peak temperatures of MLB5 and M-LA5 are corresponding to 348.5 °C and 335.5 °C, decreasing by 28.3 °C and 41.3 °C compared with the as-synthesized MgH2, respectively. Thus, mixing with LiBH4 or LiAlH4 complex has a good effect on decreasing desorption temperature of MgH2. Moreover, M-LAB5 shows the best hydrogen desorption properties according to the peak temperature of 314.1 °C, with values 62.7, 41.3, 34.4 and 21.4 °C lower than the as-synthesized MgH2, ball-milled MgH2, M-LB5 and M-LA5, respectively. From the above results, it can be concluded that the hydrogen desorption temperature 7



of MgH2 can be significantly decreased by ball-milling with LiBH4 and LiAlH4. Moreover, it is obvious that doping with LiAlH4-LiBH4 component exhibits a synergistic improvement for the dehydrogenation properties of MgH2, compared to the sample doped with LiAlH4 or LiBH4 solely data. Subsequently, TPD tests were carried out using a Sieverts-type apparatus to in-depth understand the kinetics of desorption of ball-milled MgH2, M-LB5, M-LA5, M-LAB5 composites, as shown in Figure 3b. It is also clearly shown that the LiAlH4 and/or LiBH4 doped MgH2 composites (M-LA5, MLB5, M-LAB5) exhibit the faster desorption behaviors than that of ball-milled MgH2, and M-LAB5 sample shows best desorption properties among the doping MgH2 composites. It is in complete consistent with DSC results according the starting desorption temperature of TPD data. At the same time, it also shows that the M-LAB5 composite starts to release hydrogen at about 280 °C and decreases by approximately 70 °C compared with the ball-milled MgH2. Regarding the hydrogen storage capacity, the M-LAB5 composite could release about 7.62 wt% of H2 within 10 min, which is higher than the theoretical hydrogen storage capacity of pure MgH2 because of the high hydrogen capacity of additives (LiBH4 and LiAlH4). Although a negative effect might be caused by the H-H exchange between LiBH4 (or LiAlH4) and MgH246, the LiBH4 and LiAlH4, acted as strong reductants, can possibly eliminate surface oxidation layer of pure MgH2 and meliorate desorption temperature and kinetics47. It also could be attributed to the reaction between MgH2 and LiBH4, LiAlH4 via the addition of LiBH4 and LiAlH4. Moreover, it was reported that the hydrogen desorption property of MgH2 could be greatly enhanced with the melting of LiBH4 due to the fast diffusion of H in liquid LiBH448.

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8

400

(b)

(a) 7

314.1℃

M-LA5 335.5℃

M-LB5 348.5℃

ball-milled MgH2

355.4℃

as-synthesized MgH2

exo

376.8℃

250

300

350 Temperature (C)

400

6

350

5 4

300

3

ball-milled MgH2 M-LB5 M-LA5 M-LAB5

2 1

250

Time-temperature dependence

0 40

450

Temperature (C)

Hydrogen desorbtion capacity (wt%)

M-LAB5

DSC (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60

80

100

200 120

Time (min)

Figure 3. (a) DSC profiles of as-synthesized MgH2, ball-milled MgH2, M-LB5, M-LA5, M-LAB5 at a heating rate of 5°C/min. (b) TPD curves of ball-milled MgH2, M-LB5, M-LA5, M-LAB5 at a heating rate of 5°C /min.

The comparison of isothermal hydrogen desorption behaviors of the ball-milled MgH2 and M-LAB5 at 300 °C, as shown in Figure 4. It can be found that the ball-milled MgH2 exhibits an obvious dehydrogenation behavior at 300 ºC, which can release 7.40 wt% H2 within 265 min. In contrast, the M-LAB5 composite shows the superior desorption kinetics to ball-milled MgH2 sample. The M-LAB5 composite is capable of releasing 7.69 wt% H2 within 17 min, and desorption rate is more 15 times than the result of the ball-milled MgH2. It should be noted that the hydrogen capacity of M-LAB5 sample is more than theoretical hydrogen capacity of MgH2 (7.6 wt%) due to the high gravimetric hydrogen density of LiAlH4 (10.6 wt%) and LiBH4 (18.5 wt%) in the M-LAB5 composite. These results reveal that the addition of LiAlH4 and LiBH4 can improve the dehydrogenation kinetics of MgH2 and magnify the hydrogen capacity of the system.

9



8 7

Hydrogen desorbtion (wt%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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6 5 4 3 2

ball-milled MgH2

1

M-LAB5

0 0

50

100

150

200

250

300

Time (min)

Figure 4. Isothermal hydrogen desorption curves of the ball-milled MgH2 and M-LAB5 under 0.01 MPa of hydrogen pressure at 300 °C.

In order to investigate the influence of temperature on the hydrogen desorption performance of M-LAB5 composite, isothermal hydrogen desorption at various temperature were measured and shown in Figure 5. It can be seen that the M-LAB5 sample can release a large amount of hydrogen even at 280 °C. The hydrogen desorption kinetics could gradually accelerate as the temperature increases from 280 to 340 °C. For example, the sample achieves a high hydrogen desorption capacity of 7.6 wt% within 53 min at 280 °C, 7.68 wt% within 22 min at 300 °C, 7.65 wt% within 9 min at 320 °C, 7.5 wt% within 7.5 min at 340 °C. The reasons of properties improvement might be the synergetic mechanism reaction between LiBH4, LiAH4 and MgH2, meantime, producing new phases in the system, which can be confirmed in the latter part.

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8 7 6

Hydrogen desorbed (wt%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5 4 3

280C 300C 320C 340C

2 1 0 0

10

20

30

40

50

60

Time (min)

Figure 5. Isothermal desorption hydrogen curves of M-LAB5 composite under 0.01 MPa of hydrogen pressure at different temperatures.

Since M-LAB5 is the new Mg-based composite system, the detailed mechanism of hydrogen desorption kinetics remains unclear. We employed Jone’s method to indentify the rate-controlling step during the hydrogen desorption process. The description of the reaction rate follows with the following equation49: 𝑑𝛼 𝑑𝑡

= 𝑘𝑓(𝛼)

(1)

Where k is a reaction rate constant influenced by temperature, 𝛼 is a reaction friction and 𝑓(𝛼) is a function relating to the reaction mechanism. Moreover, 𝑓(𝛼) is using the following equation for the models studied by Sharp et al.27 : 𝑓(𝛼) = 𝐴(𝑡⁄𝑡0.5 )

(2)

Where A is the constant which is related to the kinetic model and 𝑡0.5 is the time when 𝛼 is 0.5. Via plotting the experimental value of (t/t0.5)exp against the theoretical value (t/t0.5)theo, we can get the reliable kinetic model when the slope of the linear plot is closest to 1. The details of the models are list in Table 1. Isothermal dehydrogenation curves of M-LAB5 composite at 300, 320, 340 °C are shown in Figure 6a. Figure 6c shows the plot based on the isothermal desorption data under 320 °C, which can be seen that the fitting line slope of A2 model (Avarami-Erofe’ev) is the best fitting the hydrogen desorption process. Hence, the desorption reaction model of the M-LAB5 is 11



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assigned as Avarami-Erofe’ev50. The mechanism of A2 model is that the nucleation step occurs virtually instantaneously, so that the surface of each particle is covered with a layer of product. Nucleation of the byproduct is followed by a random process, not by rapid surface growth. As the nuclei grow larger, it will impinge on other nucleus, so the growth will cease during they touch each other. Moreover, friction ranging from 0.05 to 0.7 is utilized to further verify the model by time dependence of the A2 model equation at different temperatures. A nice linearity with a linear coefficient R2 are all more than 0.96 at different temperatures, signifying that the dehydrogenation reaction for both samples could be interpreted by the A2 model in the temperature range investigated.

Table 1. Common solid-state rate expressions for different reaction models40, 51

Symbol

Model

g(α)

D1 D2 D3

one-dimensional diffusion two-dimensional diffusion three-dimensional diffusion (Jander equation) three-dimensional diffusion (Ginstling-Braunsshtein equation) First-order reaction two-dimension phase boundary three-dimension phase boundary Avarami-Erofe’ev Avarami-Erofe’ev

𝛼2 𝛼 + (1 − 𝛼) 𝑙𝑛(1 − 𝛼) [1 − (1 − 𝛼)1⁄3 ]2

Sharp’ expression 0.2500(t⁄t 0.5) 0.1534(t⁄t 0.5) 0.0426(t⁄t 0.5)

(1 − 2𝛼 ⁄3) − (1 − 𝛼)2⁄3

0.0367(t⁄t 0.5)

−ln(1 − α) 1 − (1 − 𝛼)1⁄2

-0.6931(t⁄t 0.5 ) 0.2929(t⁄t 0.5)

1 − (1 − 𝛼)1⁄3

0.2063(t⁄t 0.5)

[−ln(1 − α)]1⁄2 [−ln(1 − α)]1⁄3

0.8326(t⁄t 0.5) 0.8850(t⁄t 0.5)

D4 F1 R2 R3 A2 A3

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1.0

8

(b)

(a) 0.8 6 5

Fraction

Hydrogen desorbed（wt.%)

7

4 3 2

300 C 320 C 340 C

1 0

0

5

10

15

20

0.6

0.4

300C 320C 340C

0.2

0.0

25

0

5

10

7

1.6

(c)

D1 slope=2.44477 D2 slope=3.14731 D3 slope=4.39745 D4 slope=3.52407 F1 slope=2.21971 R2 slope=1.60526 R3 slope=1.77922 A2 slope=1.03753 A3 slope=0.69435

4 3

(d)

1.2 1/2

5

2

1.0

300C 320C 340C

0.8 y=0.0998x-0.02628 2

0.6

R =0.96029 y=0.21328x-0.02023

1

2

R =0.9815 y=0.37672x+0.15169

0.4

2

0 0.0

20

1.4

g(a)=[-ln(1-a)]

6

15

Time (min)

Time (min)

(t/t0.5)theo

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


R =0.99898

0.2

0.4

0.6

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1.0

(t/t0.5)exp

1.2

1.4

0.2

1.6

0

2

4

6

8

Time/min

10

12

14

16

Figure 6. Isothermal dehydrogenation curves (a) and normalized isothermal dehydrogenation curves (b) of M-LAB5 at different temperatures under 0.01bar of H2, (t/t0.5)theo vs. (t/t0.5)exp of MLAB5 at 320°C for various kinetic models (c), time dependence of kinetic modeling equations g(α) for M-LAB5 with 0.05

Synergistic Effect of LiBH4 and LiAlH4 Additives on Improved

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