Improved Hydrogen Storage Properties of MgH2 Co-Doped with

Improved Hydrogen Storage Properties of MgH2 Co-Doped withFeCl3 and Carbon NanotubesM. Ismail,* N. Juahir, and N. S. Mustafa

School of Ocean Engineering, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Malaysia

ABSTRACT: A MgH2/FeCl3/carbon nanotubes (CNTs)composite was prepared by dry ball milling, and its hydrogenstorage properties were investigated. The CNT additionresulted in both a decreased desorption temperature andimproved sorption kinetics compared to the undoped MgH2−FeCl3 composite. The desorption temperature of the 5 wt %CNT-added MgH2−FeCl3 composite was decreased to 230 °Ccompared with 275 °C for undoped MgH2−FeCl3. For thedehydrogenation kinetics, the 5 wt % CNT-added MgH2−FeCl3 sample released about 4.3 wt % hydrogen at 320 °C after4 min of dehydrogenation, while the MgH2−FeCl3 compositereleased about 3.1 wt % hydrogen under the same conditions.Meanwhile, for the rehydrogenation kinetics, the 5 wt % CNT-added MgH2−FeCl3 sample absorbed about 5.21 wt % hydrogenat 300 °C after 1 min of rehydrogenation, but the MgH2−FeCl3 composite only absorbed about 4.8 wt % hydrogen. Theapparent activation energy, Ea, for dehydrogenation decreased from 130 kJ/mol for the MgH2−FeCl3 composite to 112 kJ/molby the addition of 5 wt % CNTs. It is believed that the enhancement of the hydrogenation performance of the MgH2/FeCl3/CNTs composite is due to the active Fe-containing species and the function of the Cl anions, as well as the unique structure ofthe CNTs.

1. INTRODUCTIONStoring hydrogen in a solid state has become a promisingoption due to the favorable safety considerations and the highvolumetric hydrogen capacity of storage materials. Among thesolid-state hydrogen storage material based on chemisorptions,such as metal hydrides1 and complex hydrides,2,3 MgH2 hasattracted much attention due to its high hydrogen storagecapacity (7.6 wt %), good reversibility, and low cost. AlthoughMgH2 has become an attractive candidate for on-boardhydrogen storage, the high thermodynamic stability andsluggish sorption kinetics hinder the practical application ofMgH2. Over the past several decades, these disadvantages havebeen overcome by reducing the grain size,4,5 introducing acatalyst,6−8 and reactions with other metal or metal hydrides(the so-called destabilization concept).9−17 Among these threemethods, the introduction of a catalyst into MgH2 has played avital role in the development of hydrogen storage materials.Many studies have shown that by using various additives orcatalysts, the hydrogenation properties of MgH2 could beimproved. In these studies, different kinds of additives orcatalysts have been mixed with MgH2 by ball milling, such asmetals,18,19 metal oxides,20−22 metal halides,23,24 and car-bon.25−28

Previous studies have shown that the carbon nanotube(CNT) is a good catalyst for MgH2.

29,30 In addition, acombination of transition metals with CNTs as mixed dopantshas been found to lead to significant improvement of hydrogendissociation and diffusion in nanostructured magnesium.31−34

This indicates that the synergistic interaction among CNTs and

metals may be an effective approach to improve the hydrogenstorage properties of MgH2. Although the hydrogen storageproperties of MgH2 were improved, it still does not satisfy all ofthe requirements for practical applications. Moreover, the exactmechanism of the metal or metal halide combined with CNTsas a catalyst in the enhancement of hydrogen storage propertiesof MgH2 is still a matter of debate. Therefore, it is an importantissue to further explore and develop the synergistic effects ofother metallic or metal halide catalysts with CNTs that canimprove the hydrogen storage properties of MgH2 and to gain adeeper understanding of the modification of the hydrogensorption process of MgH2.We recently demonstrated that the hydrogenation perform-

ance of MgH2 was enhanced after catalyzing with FeCl3.35 It is

believed that the significant improvement of MgH2 sorptionproperties in the MgH2/FeCl3 composite is due to the catalyticeffects of in-situ-generated Fe species and MgCl2 that wereformed during the heating process. Therefore, in this study,with the aim of combining CNTs with transition metals ormetal halides, we investigate the effects of the CNTs as a co-dopant on the hydrogen storage properties of MgH2−FeCl3composites. To the best of our knowledge, no studies havebeen reported on MgH2 co-doped with FeCl3 and CNTs. Thehydrogen storage performance of the MgH2−FeCl3 compositein the presence of CNTs was investigated by temperature-

Received: May 12, 2014Revised: July 24, 2014Published: July 24, 2014

Article

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© 2014 American Chemical Society 18878 dx.doi.org/10.1021/jp5046436 | J. Phys. Chem. C 2014, 118, 18878−18883

programmed desorption (TPD), isothermal sorption measure-ments, and differential scanning calorimetry (DSC). X-raydiffraction (XRD) was used to clarify the reaction mechanismafter the de/rehydrogenation process, and scanning electronmicroscopy (SEM) was used to investigate the surfacemorphology. The possible mechanism behind the catalyticeffect of CNTs in the MgH2−FeCl3 composite is also discussed.

2. EXPERIMENTAL SECTION

All of the necessary materials, namely, MgH2 powder (≥95%pure), FeCl3 (reagent grade, 97%), and MWCNT (diameter =110−170 nm, length = 5−9 μm, 90+%), were purchased fromSigma-Aldrich. All of the materials were used as receivedwithout further purification. All handling of the samples wasconducted under an Ar atmosphere in an MBraun Unilabglovebox. About 400 mg of MgH2 was mixed with 10 wt % ofFeCl3 and 5 wt % of CNT. For comparison, pure MgH2 andMgH2 + 10 wt % FeCl3 samples were also prepared under thesame conditions. Each sample was put into a sealed stainlesssteel vial together with four hardened stainless steel balls. Thesample was then milled in a planetary ball mill (NQM-0.4) for1 h at 400 rpm, with a ball to powder ratio of 30:1.The experiments for TPD and de/rehydrogenation kinetics

were performed in a Sievert-type pressure−compositiontemperature apparatus (Advanced Materials Corporation).About 100 mg of sample was loaded into a sample vessel inthe glovebox. For TPD, the sample was heated in a vacuumchamber from room temperature to 450 °C, and the heatingrate was 5 °C/min. For the rehydrogenation kinetic purposes,after complete dehydrogenation at 450 °C, the samples werekept at 300 °C under 3.0 MPa of hydrogen pressure for 1 h.The dehydrogenation kinetic measurements were conducted at320 °C with initial hydrogen pressures of 0.01 MPa.The morphology of the samples was investigated by using a

JEOL JSM-6360LA scanning electron microscope with thesamples set on carbon tape and then coated with gold sprayunder vacuum. The phase structure for the as-milled and afterde/rehydrogenation was determined by a Rigaku MiniFlex X-ray diffractometer with Cu Kα radiation. The patterns werescanned in steps of 0.02° (2θ) over diffraction angles from 20to 80° with a speed of 2.00°/min.DSC analysis was carried out using a Mettler Toledo TGA/

DSC 1. About 2−6 mg of sample was loaded into an aluminacrucible in the glovebox. The samples were heated from roomtemperature to 500 °C under an argon atmosphere, anddifferent heating rates were used.

3. RESULTS AND DISCUSSION

Figure 1 shows the TPD patterns for the dehydrogenation ofthe as-received MgH2, as-milled MgH2, MgH2 + 10 wt % FeCl3,and MgH2 + 10 wt % FeCl3 + 5 wt % CNT. The as-receivedMgH2 started to decompose at about 410 °C, with a totaldehydrogenation capacity of 7.0 wt % H2 by 430 °C. Aftermilling, the onset desorption temperature of MgH2 decreasedto about 340 °C, indicating that the milling process alsoinfluenced the onset decomposition temperature of the MgH2.The curve shows that no reduction occurred in the hydrogenreleased capacity of the MgH2 after milling. The addition ofFeCl3 markedly improved the onset decomposition temper-ature for the MgH2. The addition of 10 wt % FeCl3 causeddecreases in the decomposition onset temperature of about 65and 155 °C compared with that of the as-milled and as-received

MgH2, respectively, but the amount of hydrogen releasedcapacity slightly dropped to about 6.4 wt % H2. Furthermore,the FeCl3 and CNT co-doped MgH2 samples started to releasehydrogen at about 230 °C, which was a decrease of about 45,110, and 200 °C compared with the MgH2 + 10 wt % FeCl3, as-milled MgH2 and as-received MgH2, respectively. The FeCl3and CNT co-doped MgH2 sample also demonstrated a totalhydrogen released capacity of 6.3 wt % H2, which was almostthe same as the hydrogen desorption capacity of the FeCl3-doped MgH2. These results show the synergistic effectsbetween CNT and FeCl3 as a mixed dopant.Figure 2 shows the results of the isothermal dehydrogenation

kinetic measurements for the as-milled MgH2, MgH2 + 10 wt %

FeCl3, and MgH2 + 10 wt % FeCl3 + 5 wt % CNT at a constanttemperature of 320 °C. The results show that the samplesdoped with 10 wt % FeCl3 and 10 wt % FeCl3 + 5 wt % CNTreleased 3.9 wt % hydrogen and 4.8 wt % hydrogen,respectively, at 320 °C in 5 min under 0.1 MPa of pressure.In contrast, almost no hydrogen was desorbed at thistemperature from the as-milled MgH2 over the same timeperiod. This result further suggests that a synergistic catalyticeffect from the combination of FeCl3 and CNT exists forMgH2.The results of the isothermal rehydrogenation kinetics at 300

°C under 3.0 MPa of hydrogen pressure (shown in Figure 3)show that the MgH2 + 10 wt % FeCl3 and MgH2 + 10 wt %FeCl3 + 5 wt % CNT samples absorbed hydrogen faster thanthe pure MgH2 and that the MgH2 + 10 wt % FeCl3 + 5 wt %

Figure 1. TPD patterns for the dehydrogenation of the as-receivedMgH2, as-milled MgH2, MgH2 + 10 wt % FeCl3, and MgH2 + 10 wt %FeCl3 + 5 wt % CNT.

Figure 2. Isothermal dehydrogenation kinetics at 320 °C of the as-milled MgH2, MgH2 + 10 wt % FeCl3, and MgH2 + 10 wt % FeCl3 + 5wt % CNT.

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CNT had the fastest kinetics rate. The as-milled MgH2 sampleabsorbed 3.42 wt % at this temperature after 1 min. In contrast,the hydrogen absorbed by the MgH2 + 10 wt % FeCl3 andMgH2 + 10 wt % FeCl3 + 5 wt % CNT samples at 300 °Creached 4.8 and 5.21 wt % hydrogen, respectively, within 1 min.Taken together, these results suggest that the CNT alsoimproves the rehydrogenation kinetics of the MgH2−FeCl3composite.Figure 4 shows the SEM images of the as-received MgH2, the

as-milled MgH2 + 10 wt % FeCl3, and the as-milled MgH2 + 10

wt % FeCl3 + 5 wt % CNT. The particle size of the as-receivedMgH2 was larger than 100 μm (Figure 4a). The SEM imagesshowed the FeCl3-doped MgH2 powders (Figure 4b) to beirregularly shaped and agglomerated, which is the typicalmorphology for ball-milled powders, and their particle size wasbetween 1 and 10 μm. Figure 4c shows the SEM images of thesample ball-milled with FeCl3 and CNT. This image confirmsthat the CNT was not destroyed after the short milling process,which is in accordance with the findings reported in theliterature.36 The length of the nanotube was about 5−9 μm,which is in agreement with the information provided by thesupplier. In addition, the results indicate that the sample withCNT appeared to have less agglomeration. It is already well-known that the hydrogen storage properties of light metal

hydrides is improved with reduced particle agglomeration andgrowth.37 From the morphology results, it is speculated that thehydrogen storage properties of the MgH2 + 10 wt % FeCl3 + 5wt % CNT sample were improved as a result of the reducedparticle agglomeration.The thermal properties of the as-received and as-milled

MgH2, MgH2 + 10 wt % FeCl3, and MgH2 + 10 wt % FeCl3 + 5wt % CNT samples were further investigated by DSC, with theresults as shown in Figure 5. Clearly, the curve for the as-

received MgH2 shows only one strong endothermic process,namely, a peak at 440.69 °C, which corresponds to thedecomposition of the MgH2. As a whole, the DSC curves forthe as-milled MgH2, MgH2 + 10 wt % FeCl3, and MgH2 + 10wt % FeCl3 + 5 wt % CNT samples were similar to those of theas-received MgH2 sample, displaying only one endothermicpeak at 424.62, 353.35, and 325.35 °C, respectively, whichcorresponded to the decomposition of the MgH2 but with thepeaks having moved to lower temperatures. This phenomenonfurther suggested the synergistic effect of FeCl3 and CNT onthe decomposition of MgH2.The enhancement of the dehydrogenation property is related

to the energy barrier for the H2 release from the MgH2. Theactivation energy for dehydrogenation of the MgH2 wasreduced by ball milling and doping with the catalyst. Tocompare the activation energy of the FeCl3-doped sample andthe FeCl3 and CNT co-doped samples, the Kissinger analysis38

was used as follows

β = − +⎡⎣⎢⎢

⎤⎦⎥⎥T

ERT

Alnp

2a

p (1)

where β, Tp, and R are the heating rate, the peak temperature,and the gas constant. Thus, the activation energy, Ea, can beobtained from the slope in a plot of ln[β/Tp

2] versus 1000/Tp.Figures 6 and 7 show the DSC traces for the FeCl3-dopedsample and the FeCl3 and CNT co-doped sample at differentheating rates. From a Kissinger plot of the DSC data, as shownin Figure 8, the apparent activation energy, Ea, for H2 releasefrom the MgH2 in the FeCl3-doped sample was found to be 130kJ/mol. This value was lowered by 18 kJ/mol after being co-doped with CNT and FeCl3 (Ea ≈ 112 kJ/mol). This resultshows that a synergistic catalysis between the FeCl3 and CNTexisted for the MgH2.In order to determine the phase structures of the MgH2 + 10

wt % FeCl3 + 5 wt % CNT sample after milling, after

Figure 3. Isothermal rehydrogenation kinetics at 300 °C under 3.0MPa of hydrogen pressure of the as-milled MgH2, MgH2 + 10 wt %FeCl3, and MgH2 + 10 wt % FeCl3 + 5 wt % CNT.

Figure 4. SEM micrographs of (a) pure MgH2, (b) MgH2 + 10 wt %FeCl3, and (c) MgH2 + 10 wt % FeCl3 + 5 wt % CNT after ballmilling.

Figure 5. DSC traces of the as-received and as-milled MgH2, MgH2 +10 wt % FeCl3, and MgH2 + 10 wt % FeCl3 + 5 wt % CNT (heatingrate: 10 °C/min; argon flow: 30 mL/min).

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dehydrogenation at 450 °C, and after rehydrogenation at 300°C under 3.0 MPa of hydrogen pressure, XRD was used, withthe results as shown in Figure 9. After milling, as well as withthe MgH2 phases, the results show that there was a peakcorresponding to the CNT. This result is in accordance withWu et al.’s report on single-walled carbon nanotube (SWNT)-doped MgH2.

30 In their report, after milling for 1 h, MgH2doped with 5 wt % SWNT also showed an XRD peak for theSWNT. In addition, neither FeCl3 nor any secondary FeCl-containing phase was detected after milling, which was probablydue to the fact that the FeCl3 grains were too small to bedetectable in the MgH2 matrix by XRD or because the FeCl-containing phases may have existed in an amorphous statedirectly after ball milling. In the dehydrogenation spectra, there

were distinct peaks of Mg, which indicates that thedehydrogenation of MgH2 was completed. A small amount ofMgO was also detected in the dehydrogenation spectra, whichis likely due to the slight oxygen contamination. In addition,some peaks of the MgCl2 and Fe appeared after dehydrogen-ation, suggesting that the reactions of MgH2−FeCl3 may haveoccurred, as discussed in our previous paper.35 The peakcorresponding to the CNT still existed after the dehydrogen-ation process. For the rehydrogenated sample, it can be seenthat the Mg was largely transformed into MgH2. The peaks ofthe MgCl2 and Fe remained unchanged alongside the CNT,together with a small peak of MgO.The cycling performance of the MgH2 co-doped with FeCl3

and CNT mixture was further characterized, as shown in Figure10. Temperatures of 300 and 320 °C were applied in the

cycling study of the MgH2 + 10 wt % FeCl3 + 5 wt % CNTsample. The sorption kinetics persisted well, even after the 10thcycle, indicating that CNTs combined with FeCl3 is a goodcatalyst for the cycle life of MgH2. The hydrogen storagecapacity after 10 min of desorption shows almost no decreasewith cycling, being maintained at about 5.5 wt %. In order toexamine the phases of the sample after cycling, XRD scans wereperformed on the MgH2 + 10 wt % FeCl3 + 5 wt % CNTsample, as shown in Figure 11. As seen in Figure 9b and c,CNT, Fe, and MgCl2 were also detected in re/dehydrogenationstates after cycling. Besides, MgH2 and Mg were observed inthe pattern of the hydrogenated and dehydrogenation states,with a small amount of MgO.

Figure 6. DSC traces of the MgH2 + 10 wt % FeCl3 at differentheating rates.

Figure 7. DSC traces of the MgH2 + 10 wt % FeCl3 + 5 wt % CNT atdifferent heating rates.

Figure 8. Kissinger plot for (a) MgH2 + 10 wt % FeCl3 and (b) MgH2+ 10 wt % FeCl3 + 5 wt % CNT composites.

Figure 9. XRD patterns of the MgH2 + 10 wt % FeCl3 + 5 wt % CNT(a) after milling, (b) after dehydrogenation, and (c) afterrehydrogenation.

Figure 10. Isothermal re/dehydrogenation kinetics of the MgH2 + 10wt % FeCl3 + 5 wt % CNT mixture in the 1st and 10th cycles.

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On the basis of the above results, it is clearly shown that theonset decomposition temperature and de/rehydrogenationkinetics of MgH2 were improved by introducing a co-dopant,namely, FeCl3 and a CNT. As discussed in our previouspaper,35 the formation of the Fe particle resulting from thereaction of the MgH2 and FeCl3 during the dehydrogenationprocess may play an important role in the enhancement ofMgH2 storage properties because it is well-known that Fe is agood catalyst for MgH2.

18,39 The Fe metal may interact withhydrogen molecules, which may lead to the dissociation of thehydrogen molecules and the enhancement of the sorptionkinetics.40 Apart from the speculated catalytic effects of the Fespecies, the function of Cl− may also introduce an extracatalytic effect on MgH2 sorption properties. The chlorine-based product, MgCl2, may contribute to the enhancement ofthe de/rehydrogenation kinetics by serving as the active site fornucleation and creation of the dehydrogenated product byshortening the diffusion distance of the reaction ions.41 Thecatalytic effect of MgCl2 may further combine with the catalyticfunction of the Fe species to generate a synergetic effect.In addition, a combination of active metal nanoparticles and

nanostructured carbon materials as mixed dopants is aneffective catalyst for enhancement of the hydrogen storageproperties of metal hydrides and complex hydrides, as reportedin the literatures.31−34,42,43 The unique nanostructure of theCNT is expected to form a net-like architecture after beingmilled together with the host materials and acting as a diffusionchannel for hydrogen, while the metal nanoparticles have highcatalytic activity.44,45 In this study, the enhancement of theCNT-added MgH2−FeCl3 sample may also have been due tothe hardness of the CNT. The presence of the CNT in theMgH2−FeCl3 composite prevented particle agglomeration, asshown above in Figure 4c. It is well-known that the hydrogenstorage properties of light metal hydride are improved withreduced particle agglomeration.37 Therefore, in this study, it isbelieved that the enhancement of the hydrogenation process ofMgH2 co-doped with FeCl3 and CNT is due to thecombination of the active Fe-species and the function of Clanions with the catalytic effect of the CNT.

4. CONCLUSIONIn this study, CNTs showed good effect as a cocatalyst, givingthe MgH2−FeCl3 composite both a decreased onset desorptiontemperature and improved sorption kinetics. The addition of 5wt % CNT led to the release of hydrogen at about 230 °C,

decreasing the desorption temperature by 45 °C compared tothe undoped MgH2−FeCl3 composite. In terms of the sorptionkinetics, the 5 wt % CNT-added MgH2−FeCl3 compositesample released about 4.3 wt % hydrogen at 320 °C after 4 minof dehydrogenation, while the MgH2−FeCl3 composite samplereleased about 3.1 wt % hydrogen under the same conditions.Meanwhile, for absorption kinetics, the 5 wt % CNT-addedsample absorbed about 5.21 wt % hydrogen at 300 C after 1min of rehydrogenation, but the undoped MgH2−FeCl3composite sample only absorbed about 4.8 wt % hydrogenunder the same conditions. The apparent activation energy, Ea,for dehydrogenation was reduced from 130 to 112 kJ/mol forthe MgH2−FeCl3 composite by the addition of 5 wt % CNT. Itis believed that the in situ formation of the Fe and MgCl2species as well as the presence of the unique structure of theCNTs plays a critical role in the improvement of hydrogenstorage properties in the MgH2/FeCl3/CNTs composite.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: [email protected]. Tel: +609-6683487.Fax: +609- 6683991.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThe authors are grateful to the Universiti Malaysia Terengganufor providing the facilities to carry out this project. The authorsalso acknowledge the Ministry of Education Malaysia forfinancial support through the Fundamental Research GrantScheme (FRGS 59295). N. Juahir and N.S. Mustafa are gratefulto the Ministry of Education Malaysia for a MyBrain15scholarship.

■ REFERENCES(1) Dantzer, P. Properties of Intermetallic Compounds Suitable forHydrogen Storage Applications. Mater. Sci. Eng., A 2002, 329−331,313−320.(2) Ismail, M.; Zhao, Y.; Yu, X. B.; Dou, S. X. Effects of NbF5Addition on the Hydrogen Storage Properties of LiAlH4. Int. J.Hydrogen Energy 2010, 35, 2361−2367.(3) Ismail, M.; Zhao, Y.; Yu, X. B.; Nevirkovets, I. P.; Dou, S. X.Significantly Improved Dehydrogenation of LiAlH4 Catalysed withTiO2 Nanopowder. Int. J. Hydrogen Energy 2011, 36, 8327−8334.(4) Zaluska, A.; Zaluski, L.; Strom-Olsen, J. O. NanocrystallineMagnesium for Hydrogen Storage. J. Alloys Compd. 1999, 288, 217−225.(5) Huot, J.; Liang, G.; Boily, S.; Van Neste, A.; Schulz, R. StructuralStudy and Hydrogen Sorption Kinetics of Ball-Milled MagnesiumHydride. J. Alloys Compd. 1999, 293−295, 495−500.(6) Yu, X. B.; Guo, Y. H.; Yang, Z. X.; Guo, Z. P.; Liu, H. K.; Dou, S.X. Synthesis of Catalyzed Magnesium Hydride with Low Absorption/Desorption Temperature. Scripta Mater. 2009, 61, 469−472.(7) Ma, L.-P.; Wang, P.; Cheng, H.-M. Hydrogen Sorption Kineticsof MgH2 Catalyzed with Titanium Compounds. Int. J. Hydrogen Energy2010, 35, 3046−3050.(8) Ranjbar, A.; Ismail, M.; Guo, Z. P.; Yu, X. B.; Liu, H. K. Effects ofCNTs on the Hydrogen Storage Properties of MgH2 and MgH2−BCCComposite. Int. J. Hydrogen Energy 2010, 35, 7821−7826.(9) Walker, G. S.; Abbas, M.; Grant, D. M.; Udeh, C. Destabilisationof Magnesium Hydride by Germanium as a New PotentialMulticomponent Hydrogen Storage System. Chem. Commun. 2011,47, 8001−8003.(10) Ismail, M.; Zhao, Y.; Yu, X. B.; Mao, J. F.; Dou, S. X. TheHydrogen Storage Properties and Reaction Mechanism of the MgH2−

Figure 11. XRD patterns of the MgH2 + 10 wt % FeCl3 + 5 wt %CNT sample (a) after the 10th dehydrogenation and (b) after the 10threhydrogenation.

The Journal of Physical Chemistry C Article

dx.doi.org/10.1021/jp5046436 | J. Phys. Chem. C 2014, 118, 18878−1888318882

NaAlH4 Composite System. Int. J. Hydrogen Energy 2011, 36, 9045−9050.(11) Zhang, Y.; Tian, Q.-F.; Liu, S.-S.; Sun, L.-X. The DestabilizationMechanism and De/Re-Hydrogenation Kinetics of MgH2−LiAlH4

Hydrogen Storage System. J. Power Sources 2008, 185, 1514−1518.(12) Ismail, M.; Zhao, Y.; Yu, X. B.; Dou, S. X. Effect of DifferentAdditives on the Hydrogen Storage Properties of the MgH2−LiAlH4

Destabilized System. RSC Adv. 2011, 1, 408−414.(13) Chen, R.; Wang, X.; Xu, L.; Chen, L.; Li, S.; Chen, C. AnInvestigation on the Reaction Mechanism of LiAlH4−MgH2 HydrogenStorage System. Mater. Chem. Phys. 2010, 124, 83−87.(14) Ismail, M.; Zhao, Y.; Dou, S. X. An Investigation on theHydrogen Storage Properties and Reaction Mechanism of theDestabilized MgH2−Na3AlH6 (4:1) System. Int. J. Hydrogen Energy2013, 38, 1478−1483.(15) Mustafa, N. S.; Ismail, M. Enhanced Hydrogen StorageProperties of 4MgH2 + LiAlH4 Composite System by Doping withFe2O3 Nanopowder. Int. J. Hydrogen Energy 2014, 39, 7834−7841.(16) Ismail, M. Study on the Hydrogen Storage Properties andReaction Mechanism of NaAlH4−MgH2−LiBH4 Ternary-HydrideSystem. Int. J. Hydrogen Energy 2014, 39, 8340−8346.(17) Mao, J.; Guo, Z.; Yu, X.; Ismail, M.; Liu, H. Enhanced HydrogenStorage Performance of LiAlH4−MgH2−TiF3 Composite. Int. J.Hydrogen Energy 2011, 36, 5369−5374.(18) Hanada, N.; Ichikawa, T.; Fujii, H. Catalytic Effect ofNanoparticle 3d-Transition Metals on Hydrogen Storage Propertiesin Magnesium Hydride MgH2 Prepared by Mechanical Milling. J. Phys.Chem. B 2005, 109, 7188−7194.(19) Shevlin, S. A.; Guo, Z. X. MgH2 DehydrogenationThermodynamics: Nanostructuring and Transition Metal Doping. J.Phys. Chem. C 2013, 117, 10883−10891.(20) Li, P.; Wan, Q.; Li, Z.; Zhai, F.; Li, Y.; Cui, L.; Qu, X.; Volinsky,A. A. MgH2 Dehydrogenation Properties Improved by MnFe2O4

Nanoparticles. J. Power Sources 2013, 239, 201−206.(21) Ma, T.; Isobe, S.; Wang, Y.; Hashimoto, N.; Ohnuki, S. Nb-Gateway for Hydrogen Desorption in Nb2O5 Catalyzed MgH2

Nanocomposite. J. Phys. Chem. C 2013, 117, 10302−10307.(22) Hanada, N.; Ichikawa, T.; Isobe, S.; Nakagawa, T.; Tokoyoda,K.; Honma, T.; Fujii, H.; Kojima, Y. X-ray Absorption SpectroscopicStudy on Valence State and Local Atomic Structure of TransitionMetal Oxides Doped in MgH2. J. Phys. Chem. C 2009, 113, 13450−13455.(23) Malka, I. E.; Czujko, T.; Bystrzycki, J. Catalytic Effect of HalideAdditives Ball Milled with Magnesium Hydride. Int. J. Hydrogen Energy2010, 35, 1706−1712.(24) Ismail, M.; Zhao, Y.; Yu, X. B.; Dou, S. X. Improved HydrogenStorage Properties of MgH2 Doped with Chlorides of TransitionMetals Hf and Fe. Energy Educ. Sci. Technol., Part A 2012, 30(SpecialIssue 1), 107−122.(25) Shang, C. X.; Guo, Z. X. Effect of Carbon on HydrogenDesorption and Absorption of Mechanically Milled MgH2. J. PowerSources 2004, 129, 73−80.(26) Wu, C. Z.; Wang, P.; Yao, X.; Liu, C.; Chen, D. M.; Lu, G. Q.;Cheng, H. M. Effect of Carbon/Noncarbon Addition on HydrogenStorage Behaviors of Magnesium Hydride. J. Alloys Compd. 2006, 414,259−264.(27) Huang, Z. G.; Guo, Z. P.; Calka, A.; Wexler, D.; Liu, H. K.Effects of Carbon Black, Graphite and Carbon Nanotube Additives onHydrogen Storage Properties of Magnesium. J. Alloys Compd. 2007,427, 94−100.(28) Zhou, S.; Chen, H.; Ran, W.; Wang, N.; Han, Z.; Zhang, Q.;Zhang, X.; Niu, H.; Yu, H.; Liu, D. Effect of Carbon from AnthraciteCoal on Decomposition Kinetics of Magnesium Hydride. J. AlloysCompd. 2014, 592, 231−237.(29) Amirkhiz, B. S.; Danaie, M.; Barnes, M.; Simard, B.; Mitlin, D.Hydrogen Sorption Cycling Kinetic Stability and Microstructure ofSingle-Walled Carbon Nanotube (SWCNT) Magnesium Hydride(MgH2) Nanocomposites. J. Phys. Chem. C 2010, 114, 3265−3275.

(30) Wu, C. Z.; Wang, P.; Yao, X.; Liu, C.; Chen, D. M.; Lu, G. Q.;Cheng, H. M. Hydrogen Storage Properties of MgH2/SWNTComposite Prepared by Ball Milling. J. Alloys Compd. 2006, 420,278−282.(31) Babak Shalchi, A.; Danaie, M.; Mitlin, D. The Influence ofSWCNT−Metallic Nanoparticle Mixtures on the Desorption Proper-ties of Milled MgH2 Powders. Nanotechnology 2009, 20, 204016.(32) Yao, X.; Wu, C.; Du, A.; Zou, J.; Zhu, Z.; Wang, P.; Cheng, H.;Smith, S.; Lu, G. Metallic and Carbon Nanotube-Catalyzed Couplingof Hydrogenation in Magnesium. J. Am. Chem. Soc. 2007, 129, 15650−15654.(33) Wu, C.; Wang, P.; Yao, X.; Liu, C.; Chen, D.; Lu, G. Q.; Cheng,H. Effects of SWNT and Metallic Catalyst on Hydrogen Absorption/Desorption Performance of MgH2. J. Phys. Chem. B 2005, 109,22217−22221.(34) Luo, Y.; Wang, P.; Ma, L.-P.; Cheng, H.-M. Enhanced HydrogenStorage Properties of MgH2 Co-Catalyzed with NbF5 and Single-Walled Carbon Nanotubes. Scripta Mater. 2007, 56, 765−768.(35) Ismail, M. Influence of Different Amounts of FeCl3 onDecomposition and Hydrogen Sorption Kinetics of MgH2. Int. J.Hydrogen Energy 2014, 39, 2567−2574.(36) Kukovecz, A.; Kanyo, T.; Konya, Z.; Kiricsi, I. Long-Time Low-Impact Ball Milling of Multi-Wall Carbon Nanotubes. Carbon 2005,43, 994−1000.(37) Adelhelm, P.; de Jongh, P. E. The Impact of Carbon Materialson the Hydrogen Storage Properties of Light Metal Hydrides. J. Mater.Chem. 2011, 21, 2417−2427.(38) Kissinger, H. E. Reaction Kinetics in Differential ThermalAnalysis. Anal. Chem. 1957, 29, 1702−1706.(39) Liang, G.; Huot, J.; Boily, S.; Van Neste, A.; Schulz, R. CatalyticEffect of Transition Metals on Hydrogen Sorption in NanocrystallineBall Milled MgH2−Tm (Tm = Ti, V, Mn, Fe and Ni) Systems. J. AlloysCompd. 1999, 292, 247−252.(40) Malka, I. E.; Pisarek, M.; Czujko, T.; Bystrzycki, J. A Study ofthe ZrF4, NbF5, TaF5, and TiCl3 Influences on the MgH2 SorptionProperties. Int. J. Hydrogen Energy 2011, 36, 12909−12917.(41) Zhai, F.; Li, P.; Sun, A.; Wu, S.; Wan, Q.; Zhang, W.; Li, Y.; Cui,L.; Qu, X. Significantly Improved Dehydrogenation of LiAlH4Destabilized by MnFe2O4 Nanoparticles. J. Phys. Chem. C 2012, 116,11939−11945.(42) Ismail, M.; Zhao, Y.; Yu, X. B.; Ranjbar, A.; Dou, S. X. ImprovedHydrogen Desorption in Lithium Alanate by Addition of SWCNT−Metallic Catalyst Composite. Int. J. Hydrogen Energy 2011, 36, 3593−3599.(43) Ismail, M.; Zhao, Y.; Yu, X. B.; Dou, S. X. Improved HydrogenStorage Property of LiAlH4 by Milling with Carbon Based Additives.Int. J. Electroactive Mater. 2013, 1, 13−22.(44) Fang, Z. Z.; Kang, X. D.; Dai, H. B.; Zhang, M. J.; Wang, P.;Cheng, H. M. Reversible Dehydrogenation of LiBH4 Catalyzed by As-Prepared Single-Walled Carbon Nanotubes. Scripta Mater. 2008, 58,922−925.(45) Mao, J.; Guo, Z.; Liu, H. Enhanced Hydrogen StorageProperties of NaAlH4 Co-Catalysed with Niobium Fluoride andSingle-Walled Carbon Nanotubes. RSC Adv. 2012, 2, 1569−1576.

The Journal of Physical Chemistry C Article

dx.doi.org/10.1021/jp5046436 | J. Phys. Chem. C 2014, 118, 18878−1888318883