Journal of Alloys and Compounds 645 (2015) S454–S459

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Journal of Alloys and Compounds

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Magnesium-based hydrogen storage nanomaterials preparedby high energy reactive ball milling in hydrogen at the presenceof mixed titanium–iron oxide

http://dx.doi.org/10.1016/j.jallcom.2014.12.0840925-8388/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author.E-mail address: mlototskyy@uwc.ac.za (M. Lototskyy).

M. Lototskyy ⇑, M.W. Davids, J.M. Sibanyoni, J. Goh, B.G. PolletHySA Systems Competence Centre, South African Institute for Advanced Materials Chemistry, Faculty of Natural Sciences, University of the Western Cape, Private Bag X17,Bellville 7535, South Africa

a r t i c l e i n f o a b s t r a c t

Article history:Available online 20 December 2014

Keywords:Magnesium hydrideBall milling in hydrogenOxide additivesCarbon additives

An experimental study was undertaken on the preparation, by High Energy Reactive Ball Milling inHydrogen (HRBM), of hydrogen storage materials on the basis of Mg mixed with FeTiO3, and their furthercharacterisation (SEM, TEM, XRD, volumetric H2 absorption studies, TDS). It was shown that the additionof P5 wt.% of FeTiO3 dramatically improves H absorption in Mg and reduces the temperature of further Hdesorption. Subsequent addition of carbon, including Graphite (G), Activated Carbon (AC) and Multi-WallCarbon Nanotubes (MWCNT) results in some slowing of the H absorption down but significantlyimproves re-hydrogenation performances of the material, which in time is able to re-absorb about5 wt.% H in less than 5–7 min (15 bar H2/250 �C). These improvements were associated with thereduction of FeTiO3 to yield nanoparticles of Fe and TiFe(Hx).

� 2014 Elsevier B.V. All rights reserved.

1. Introduction

High Energy Reactive Ball Milling in Hydrogen (HRBM) is a veryefficient route for the preparation of hydrogen storage materials onthe basis of nanostructured magnesium hydride (n-MgH2) [1].When combined with catalysts, including easily hydrogenatedalloys [2], HRBM of Mg has been shown to be a good method forthe production of the hydride materials suitable for large-scaleweight efficient hydrogen storage [3]. Further improvement onperformances of the n-MgH2 can be achieved with the additionof carbon which apart from intensification of heat transfer in theMH bed [3], also improves the H2 absorption/desorption kineticsand operation lifetime, even when the carbon additive loading isbelow 5 wt.% [4].

There are several solutions to improve the HRBM preparation ofMgH2 and to facilitate dehydrogenation–re-hydrogenation pro-cesses. Some of these solutions suggest addition of various metaloxides. Apart from the binary ones, including Al2O3, Fe2O3, Cr2O3,CeO2, Yb2O3, TiO2, Nb2O5 [5–13], the catalytic effect was alsoobserved for the mixed oxide, NiCo2O4; the improvements wereassociated with the formation of metallic nanoparticles formed inthe course of the oxide reduction [14]. The catalytic effect of thereduced oxide nanoparticles formed during HRBM was also dis-

cussed by Ma et al. [15]. The improvement of hydrogenation/dehydrogenation of Mg by the oxides was also observed for Mgor MgH2 ball milled with the additives in an inert (argon) atmo-sphere [14,16–23]. The catalytic effect of oxides was found to beespecially pronounced in the presence of transition metal[10,13,18,21], nanoscale carbon [11,13], or organic solvents [22].

The use of the mixed iron–titanium oxide, FeTiO3 (ilmenite), asan additive for HRBM of Mg, seems to be quite promising. FeTiO3is cheap and easily available, and can be reduced (at least, partially)under moderate conditions. Its hardness (5–6 Mohs [24]) is suffi-cient to facilitate ‘nanostructuring’ of the softer magnesium(2.5 Mohs [25]) and, at the same time, not too high to cause damageto the milling tools which can be made even of low-grade steels.

This work presents the results of an experimental study of thepreparation and characterisation of Mg-based hydrogen storagematerials prepared by HRBM of Mg and TiFeO3 with and withoutcarbon additives [26].

2. Experimental

The charge for the preparation of Mg-based hydrogen storage materials byHRBM included:

� �8 g of Mg powder (Alfa Aesar; �20. . .+100 mesh, 99.8%);� 0.16–1.6 g (2–20 wt.% as respect to Mg) of TiFeO3 (natural ilmenite ore,

Saldanha Steel, Western Cape, South Africa; 50.78 wt.% FeO, 44.48 wt.% TiO2,4.74 wt.% impurities/B, Mn, Al, Mg, Na, Ni, Ca, V/).

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0 20 40 60 80 100 120

0

1

2

3

4

5

6

7

8A

Mg-10FeTiO3-5MWCNT

Mg-10FeTiO3-5AC

Mg-15FeTiO3

Mg-20FeTiO3

Mg-10FeTiO3

Mg-5FeTiO3

Mg-10FeTiO3-5G

Mg-2FeTiO3

Mg

wt.%

H

Milling time [minutes]

2

3

4

5

6 B Mg-10FeTiO3-5MWCNT Mg-10FeTiO

3-5G

Mg-10FeTiO3-5AC Mg-2FeTiO3

Mg-5FeTiO3

Mg

wt.%

H

M. Lototskyy et al. / Journal of Alloys and Compounds 645 (2015) S454–S459 S455

For the composition Mg �10 wt.% TiFeO3 additional carbon-containing sampleswere prepared, by further addition of 0.4 g (5 wt.% as respect to Mg) of carbon, inthe form of Graphite (G) powder (Fluka; 620 lm, 99+%); YP-50F Activated Carbon(AC; Kuraray Chemical Co.); and Multi-Wall Carbon Nanotubes (MWCNT; CarbonNano-Material Technology Co., Ltd.).

HRBM was carried out in Retsch PM100 planetary ball mill using 220 mL hard-ened steel vial equipped with pressure–temperature monitoring system (EvicoMagnetics GmbH), at ball-to-powder ratio, BPR = 40:1, and 500 rpm rotation speed.Milling was started at room temperature and H2 pressure of 30 bar. Both pressureand temperature in the vial were monitored to yield the data on hydrogenationkinetics during HRBM. The milling was interrupted every time when the tempera-ture approached 65 �C, or hydrogen pressure dropped below 20 bar; the vial wasthen cooled down to the room temperature and refilled with H2 before resumingHRBM.

The characterisation of HRBM and re-hydrogenation products included SEM(Zeiss Auriga Field Emission Gun; InLens (working distance 5 mm) and secondaryelectron (10 mm) detectors at 5 kV), TEM (FEI Tecnai 30, 120 kV; the sample holderwas cooled to liquid nitrogen temperature), and XRD (Bruker AXS D8 Advance, CuKa, k1 = 1.5406 Å, k2 = 1.5444 Å, 2h = 10–85�; the data were further processed byRietveld full-profile analysis using GSAS software, the characteristics of the constit-uent phases were taken from CRYSTMET database [27,28]). TDS (dynamic vacuum;T = 25–470 �C, ramp rate 5 �C/min) and re-hydrogenation (15 bar H2/250 �C) werecarried out using a Sieverts-type volumetric installation; sample weight was of200 mg.

The re-hydrogenation data were fitted using a modified Avrami–Erofeevequation:

C ¼ Cmax 1� exp �tt0

� �n� �� �; ð1Þ

where C and Cmax are the actual and maximum hydrogen concentrations, respec-tively; t is time; t0 is a characteristic reaction time; and n is a parameter (‘‘Avramiexponent’’) indirectly related to the reaction mechanism.

Further details on the experimental procedure and data processing can be foundin [4].

0 5 10 15 20 25 100 200 300

0

1 Mg-10FeTiO3

Time [minutes]

Fig. 1. Hydrogen absorption in Mg and Mg–x FeTiO3–(5C) during HRBM (A) and re-hydrogenation (B).

3. Results and discussion

Fig. 1 shows hydrogen absorption kinetics in the studied sam-ples Mg–x FeTiO3–(5C)1 during HRBM (A) and re-hydrogenationafter TDS (B). The corresponding curves for magnesium withoutadditives (Mg) taken at the same conditions are presented for thereference.

Quite distinct from individual Mg (whose hydrogenation duringHRBM is very slow and requires more than 5 h milling to achievemaximum H storage capacity), the samples containing TiFeO3require 1–2 h to achieve complete hydrogenation (Fig. 1A). Thehydrogenation rates gradually increase with the increase of TiFeO3content and at P5 wt.% TiFeO3 the amount of H absorbed during1 h long HRBM is 5.8–6.7 wt.%. With carbon additives, hydrogena-tion proceeds slower and is characterised by an incubation periodwhose duration depends on the type of the additive. Nevertheless,about 7 wt.% H is absorbed during 1 h of HRBM for AC and MWCNT,and during 2 h for graphite.

The presence of FeTiO3 also improves re-hydrogenation kineticsas compared to HRBM Mg (Table 1). The time (t0) required toabsorb (1 � 1/e) � 63.2% of the total amount of hydrogen (Cmax)in the modified samples gradually decreases from �25 min forthe unmodified HRBM Mg to �6.5 min for Mg–5 FeTiO3. Furtherincrease of FeTiO3 content to 10 wt.% results in slowing the re-hydrogenation down (t0 � 14 min), but the reaction is still fasterthan for the individual HRBM Mg. However, the introduction ofFeTiO3 significantly reduces the total amount of the re-absorbedhydrogen, from �5 wt.% for HRBM Mg alone to 3.8 wt.% for Mg–2FeTiO3 and further to 2.7 wt.% for Mg–10 FeTiO3. The fitted n valuesare significantly lower in the Mg–x FeTiO3 samples (0.32–0.54)than the one for HRBM Mg (0.73) testifying about change of thereaction mechanism.

1 Here and below the notation corresponds to the samples containing x wt.% oFeTiO3 and, if present, 5 wt.% of carbon (C = G, AC or MWCNT).

f

The samples additionally modified with carbon additives exhibithigher hydrogen absorption capacities during re-hydrogenation,>5 wt.%, and the kinetics are further improved (Fig. 1B, Table 1).The n values (0.75–1) for the carbon-containing samples are quiteclose to the one for HRBM Mg, similarly to our earlier observationsfor HRBM Mg + C [4].

As can be seen from Fig. 2, the introduction of FeTiO3 signifi-cantly lowers the temperatures of the onset and peak of hydrogendesorption. The lowest peak temperature (316 �C, or almost 60�lower than for the HRBM Mg alone) was observed for Mg–10FeTiO3. Further introduction of MWCNT does not significantlyaffect the MgH2 decomposition temperature. For graphite andactivated carbon the peak temperatures were �20 �C higher, butstill significantly lower than that of HRBM Mg.

The as-milled samples exhibit typical morphology for HRBM Mg(porous agglomerates of submicron particles) on SEM images [4];the morphology is similar for the samples with and without carbonadditives (compare Fig. 3A and B). As can be observed from theTEM images (Fig. 3C and D), small,

Table 1Fitted kinetic parameters (Eq. (1)) of the re-hydrogenation of HRBM Mg and Mg–xFeTiO3–(5C).

FeTiO3/carbon(type) (wt.%)

Cmax t0 n Pearson correlationcoefficient, R2

Mg (no additives) 4.976(1) 23.47(5) 0.731(2) 0.99312 3.781(7) 11.5(1) 0.397(2) 0.98795 2.857(1) 6.43(7) 0.535(4) 0.991510 2.71(2) 14.2(5) 0.321(4) 0.984410/5 (G) 5.454(2) 4.87(2) 1.031(5) 0.992310/5 (AC) 5.231(2) 6.52(3) 0.746(4) 0.986010/5 (MWCNT) 5.217(3) 3.20(2) 0.809(7) 0.9665

200 300 400-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Mg-10FeTiO3-5G

(332)

Mg-10FeTiO3-5MWCNT

(317)

Mg-10FeTiO3-5AC

(336)Mg-10FeTiO3(316)

Mg(375)

Rat

e [w

t.% H

/min

]

T [°C]

Fig. 2. Hydrogen Thermal Desorption Spectra (TDS) for the re-hydrogenated HRBMMg and Mg–10 FeTiO3–(5C). The peak temperatures are specified in brackets.

Fig. 3. SEM (A and B) and bright-field TEM (C and D) images of as milled Mg–10

S456 M. Lototskyy et al. / Journal of Alloys and Compounds 645 (2015) S454–S459

observed (points) and calculated (lines) intensities, as well as thedifference (observed–calculated; bottom line). The bottom labels(Fig. 4A, C, D) correspond to the diffraction angles for the peaks cal-culated for the identified phases (labelled from the left). In all casesthe goodness of fit corresponded to Rp � 0.02.

All as-milled samples (Table 2) contain tetragonal a- (P42/mnm,#36; a = 4.52 Å, c = 3.02 Å; [27], record AL2897) and orthorhombicc- (Pbcn, #60; a = 4.48 Å, b = 5.40 Å, c = 4.90 Å; [27], record506717) modifications of MgH2 as major phases. For Mg–x FeTiO3,both phases exhibit calculated crystallite size between 13 and17 nm; and the total abundance of MgH2 gradually decreases from97.4 to 86 wt.% following the increase of FeTiO3 content in thecharge. The samples without carbon additives contain a singleimpurity phase of FeTiO3 (R-3, #148; a = 5.09 Å, c = 14.09 Å; [27],record 503413) with lattice periods close to the reference dataand crystallite size between 16 and 70 nm. The abundance of FeTi-O3 approximately corresponds to the content of the oxide in thecharge only at x 6 5 wt.% and exhibits underestimations by2.8 wt.% for x = 10 wt.%, and by about 6 wt.% for x P 15 wt.%.

The introduction of carbon significantly changes phase-structural properties of the as-milled Mg–10 FeTiO3. First, theabundance of FeTiO3 decreases twofold for C = G. The samples alsoexhibit significant amounts of nanocrystalline (�5 nm) MgO (Fm-3m, #225; a = 4.21 Å; [27], record 31985). For C = AC, the FeTiO3phase disappears, and the abundance of MgO increases in 2.3 timesas compared to C = G; this sample also exhibits the highestabundance of c-MgH2.

For the patterns of as-milled Mg–10 FeTiO3–5C, better refine-ment was obtained assuming appearance of microcrystalline TiF-eH�1 (P2221, #17; a = 3.09 Å, b = 4.52 Å, c = 4.39 Å; [27], record133245) for C = G and nanocrystalline Fe (hexagonal high-pressuremodification, hcp-Fe; P63/mmc, #194, a = 2.47 Å, c = 3.96 Å; [27],record 27813) for C = AC. The difference of impurity phases in

FeTiO3 (A and C), as milled (B) and re-hydrogenated (D) Mg–10 FeTiO3–5AC.

10 20 30 40 50 60 70 80 90

A

hcp-FeMgO

-MgH2

α-MgH2

2 θ [°]20 30 40 50 60 70 80 90

C

TiFeHMgO

-FeMg

-MgH2

41 42 43 44 45 46 47 48 49

B

TiFe

(H) (

002)

hcp-

Fe (0

02)

hcp-

Fe (1

00)

MgO

(2 0

0)

hcp-

Fe (1

01)

FeTi

O3 (

20-4

) Mg-10FeTiO

3Mg-10FeTiO

3-5G

Mg-10FeTiO3-5AC

20 30 40 50 60 70 80 90

D

FeTiO3

-FeTiFeH

MgOα-MgH

2

γα

α

2 [°]θ

2 [°]θ2 [°]θ

α

Fig. 4. Typical XRD patterns: (A) as milled Mg–10 FeTiO3–5AC; (B) combined data (observed) for as milled Mg–10 FeTiO3–(5C) in the range 2h = 41–50�; (C) re-hydrogenatedMg–10 FeTiO3; (D) re-hydrogenated Mg–10 FeTiO3–5MWCNT.

M. Lototskyy et al. / Journal of Alloys and Compounds 645 (2015) S454–S459 S457

Mg–10 FeTiO3 and Mg–10 FeTiO3–5C (C = G, AC) can be clearlyseen in Fig. 4B where all three patterns are presented together inthe range 2h = 49–51�.

TDS followed by re-hydrogenation dramatically changesphase-structural properties of the as-milled materials (Table 3).In all samples Mg–x FeTiO3 the FeTiO3 phase disappears accom-panied by the appearance of rather high amount of nanocrystal-line MgO whose abundance correlates with the initial content ofFeTiO3. All the samples exhibit nanocrystalline a-Fe (Im-3m,#229, a = 2.87 Å; [27], record 29057) and (except for Mg–2 FeTi-O3 and Mg–10 FeTiO3–5G) TiFeH. For the re-hydrogenated sam-ples Mg–10 FeTiO3–5C, the abundance of MgO decreases, ascompared to Mg–10 FeTiO3, in 1.8, 2.6 and 3.7 times for C = G,AC and MWCNT, respectively. All carbon-containing re-hydroge-nated samples are characterised by the reduction of crystallitesize of a-MgH2 in 1.5–1.8 times (similar to our earlier observa-tion for HRBM-Mg–C [4]), and significantly lower abundance(or disappearance) of the non-hydrogenated Mg which, if pres-ent, has significantly bigger crystallite size than in the sampleswithout carbon. Interestingly, for all re-hydrogenated Mg–10FeTiO3–5C samples, TiFeO3 was found in the amount of�3 wt.% while for the as-milled Mg–10 FeTiO3–5AC (Table 1) itwas absent.

Analysis of the presented data allows the authors to assumethat during dehydrogenation and re-hydrogenation TiFeO3 reactswith magnesium (or magnesium hydride) according to thereactions:

FeTiO3 þ 3MgðH2Þ ! TiFeþ 3MgO ðþ3H2Þ; ð2Þ

FeTiO3 þMgðH2Þ ! FeþMgOþ TiO2 ðþH2Þ: ð3Þ

Since neither TiO2, nor possible product of its interaction withMgO (Mg2TiO4), were detected by XRD, it was assumed that theseproducts of Reaction (3) are amorphous (indirectly confirmed byTEM results; see Fig. S2C in the Supplementary Information).Nevertheless, both reactions resulted in:

(i) generation of metallic nanoparticles which (especially, TiFe)are known to catalyse hydrogen dissociation/recombinationand thus improve re-hydrogenation and dehydrogenationkinetics;

(ii) consumption of magnesium to form MgO.

Most probably, Reactions (2) and (3) take place at the end of thedehydrogenation process. At high contents of FeTiO3 (x P 5 wt.%)they may begin already on the HRBM stage to yield amorphousproducts. It can be testified by (i) significant increase of the hydro-genation rate during HRBM when FeTiO3 content approaches thethreshold value and (ii) underestimation of XRD abundances forFeTiO3 in the as-milled samples. In the presence of carbon, XRDof the as-milled samples (Table 2) directly indicate that the inter-action takes place already during HRBM.

In Mg–x FeTiO3, MgO formed by Reactions (2) or (3) covers theMg particles as a dense film inhibiting their re-hydrogenation,

Table 2Summary of the XRD data on the as milled samples Mg–FeTiO3–(C).

Phase Characteristics FeTiO3/carbon (type) (wt.%)

2 5 10 10/5 (G) 10/5 (AC) 15 20

a-MgH2 Abundance 0.841(–) 0.829(–) 0.871(–) 0.621(–) 0.53(–) 0.773(–) 0.779(–)Crystallite size (nm) 13 13 17 11 11 13 14a (A) 4.520(1) 4.516(1) 0.058(1) 4.5135(7) 4.5144(4) 4.519(1) 4.519(1)c (A) 3.016(1) 3.0149(8) 3.0208(7) 3.0227(6) 3.0259(5) 3.016(1) 3.023(1)

c-MgH2 Abundance 0.133(4) 0.121(3) 0.058(1) 0.124(4) 0.23(2) 0.139(1) 0.081(4)Crystallite size (nm) 13 13 17 7 10 13 14a (A) 4.453(7) 4.489(6) 4.505(5) 4.517(8) 4.528(6) 4.472(7) 4.259(6)b (A) 5.620(8) 5.468(6) 5.468(6) 5.46(1) 5.429(7) 5.491(7) 5.75(2)c (A) 4.945(5) 4.957(4) 4.963(4) 4.96(1) 4.957(6) 4.973(5) 5.076(8)

FeTiO3 Abundance 0.026(2) 0.05(2) 0.072(2) 0.036(1) – 0.088(3) 0.140(5)Crystallite size (nm) 24 16 71 31 – 32 25a (A) 5.128(5) 5.094(4) 5.101(3) 5.093(2) – 5.095(3) 5.087(2)c (A) 14.07(3) 14.11(2) 14.10(1) 14.035(9) – 14.07(1) 14.07(1)

MgO Abundance – – – 0.159(3) 0.37(2) – –Crystallite size (nm) – – – 5 7 – –a (A) – – – 4.220(2) 4.242(1) – –

TiFeH Abundance – – – 0.06(8) – – –Crystallite size (nm) – – – 160 – – –a (A) – – – 3.09(–) – – –b (A) – – – 4.52(–) – – –c (A) – – – 4.39(–) – – –

HCP-Fe Abundance – – – – 0.014(5) – –Crystallite size (nm) – – – – 8 – –a (A) – – – – 2.474(2) – –c (A) – – – – 3.937(8) – –

Table 3Summary of the XRD data on the re-hydrogenated samples Mg–FeTiO3–(C).

Phase Characteristics FeTiO3/carbon (type) (wt.%)

2 10 10/5 (G) 10/5 (AC) 10/5 (MWCNT)

a-MgH2 Abundance 0.641(–) 0.433(–) 0.698(–) 0.767(–) 0.69756Crystallite size (nm) 86 65 44 36 41a (A) 4.5087(1) 4.5108(2) 4.5134(2) 4.5164(3) 4.5107(2)c (A) 3.0154(1) 3.0170(2) 3.0183(1) 3.0206(2) 3.0164(2)

Mg Abundance 0.158(2) 0.077(2) 0.008(1) 0.006(1) –Crystallite size (nm) 102 79 250 400 –a (A) 3.2066(2) 3.2053(4) 3.209(1) 3.212(2) –c (A) 5.2067(5) 5.204(1) 5.219(4) 5.225(6) –

MgO Abundance 0.178(5) 0.435(3) 0.245(3) 0.167(4) 0.118(4)Crystallite size (nm) 7 7 5 6 47a (A) 4.218(2) 4.233(1) 4.238(2) 4.240(2) 4.239(2)

FeTiO3 Abundance – – 0.026(2) 0.031(3) 0.031(3)Crystallite size (nm) – – 15 28 15a (A) – – 5.080(8) 5.088(9) 5.049(6)c (A) – – 14.13(4) 14.00(3) 14.21(3)

TiFeH Abundance – 0.008(2) – 0.009(2) 0.011(1)Crystallite size (nm) – 38 – 11 19a (A) – 3.104(8) – 3.21(2) 3.27(1)b (A) – 4.52(2) – 4.07(4) 4.04(2)c (A) – 4.24(1) – 4.24(3) 4.30(1)

a-Fe Abundance 0.022(2) 0.048(1) 0.023(1) 0.020(1) 0.144(2)Crystallite size (nm) 6 18 9 18 5a (A) 2.858(5) 2.8681(5) 2.856(2) 2.857(2) 2.861(3)

S458 M. Lototskyy et al. / Journal of Alloys and Compounds 645 (2015) S454–S459

especially when the formed layer of MgH2 creates an additionaldiffusion barrier for hydrogen atoms. HRBM in the presence ofcarbon was shown to result in the formation of graphene layersencapsulating the MgH2 nanoparticles [4]. Apart from creating aninterface for the migration of active hydrogen species and prevent-ing grain growth of MgH2, carbon may also alter Reactions (2) and(3) thus maintaining some kind of ‘‘equilibrium’’ between TiFeO3from one side and MgO, TiFe and/or TiO2 + Fe from the other. Thisresults in the less pronounced lowering of the H amount absorbed

in the course of re-hydrogenation of the carbon-containingmaterials.

4. Conclusions

� Addition of FeTiO3 to Mg results in shorter hydrogenation timesduring HRBM, improved dehydrogenation and re-hydrogena-tion kinetics, but reduced reversible H storage capacity of thematerial.

M. Lototskyy et al. / Journal of Alloys and Compounds 645 (2015) S454–S459 S459

� During HRBM, dehydrogenation and re-hydrogenation, FeTiO3reacts with Mg (or MgH2) to yield MgO and nanoparticles ofFe and TiFe(Hx) which are known to catalyse H2 dissociation/recombination and thus improve dehydrogenation and hydro-genation kinetics.� Further addition of carbon, including graphite, activated carbon

and multi-walled carbon nanotubes results in some slowingdown of H absorption during HRBM but significantly increasesreversible hydrogen storage capacity of the material.

Acknowledgements

This work was supported by the Department of Science andTechnology (DST) in South Africa within the HySA Programme(project KP3-S02 – On-Board Use of Metal Hydrides for UtilityVehicles), and Human Resources for Industry Programme, jointlymanaged by the South African National Research Foundation andthe Department of Trade and Industry (NRF/DTI; THRIP projectTP1207254249). It is also supported by ERAfrica FP7 program, pro-ject RE-037 ‘‘HENERGY’’. Finally, ML acknowledges NRF support viaincentive funding grant 76735.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.jallcom.2014.12.084.

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Magnesium-based hydrogen storage nanomaterials prepared by high energy reactive ball milling in hydrogen at the presence of mixed titanium–iron oxide1 Introduction2 Experimental3 Results and discussion4 ConclusionsAcknowledgementsAppendix A Supplementary materialReferences