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Improved hydrogen storage properties of MgH2 with Ni-based compounds
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Improved hydrogen storage properties of MgH2 with Ni-based compounds Qiuyu Zhang a, Lei Zang a, Yike Huang a, Panyu Gao c, Lifang Jiao a, Huatang Yuan a, Yijing Wang a,b,* a
Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071, China b Collaborative Innovation Center of Chemical Science and Engineering, Nankai University, Tianjin 300071, China c School of Material Science and Engineering, Hebei University of Technology, Tianjin 300071, China
article info
abstract
Article history:
The nanoscaled Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) are synthesized by
Received 13 June 2017
chemical methods. The MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites are prepared by
Received in revised form
mechanical ball-milling. The dehydrogenation properties of Mg-based composites are
27 July 2017
systematically studied using isothermal dehydrogenation apparatus, temperature-
Accepted 29 July 2017
programmed desorption system and differential scanning calorimetry. It is experimen-
Available online xxx
tally confirmed that the dehydrogenation performance of the Mg-based materials ranks as following: MgH2eNi3C, MgH2eNi3N, MgH2eNiO and MgH2eNi2P. The onset dehydrogena-
Keywords:
tion temperatures of MgH2eNi3C, MgH2eNi3N, MgH2eNiO and MgH2eNi2P are 160 C,
Hydrogen storage
180 C, 205 C and 248 C, respectively. The four Mg-based composites respectively release
MgH2
6.2, 4.9, 4.1 and 3.5 wt% H2 within 20 min at 300 C. The activation energies of MgH2eNi3C,
Ni-based compounds
MgH2eNi3N, MgH2eNiO and MgH2eNi2P are 97.8, 100.0, 119.7 and 132.5 kJ mol1, respec-
Hydrogen storage mechanism
tively. It' found that the MgH2eNi3C composites exhibit the best hydrogen storage properties. Moreover, the catalytic mechanism of the Ni-based compounds is also discussed. It is found that Ni binding with low electron-negativity element is favorable for the dehydrogenation of the Mg-based composites. © 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.
Introduction Hydrogen, as abundant and clean energy carrier, is considered as a prospective candidate to substitute the traditional fossil fuels [1e4]. However, efficient and safe hydrogen storage is the technology barrier for the hydrogen utilization. MgH2 is one of the most promising hydrogen storage materials due to its low cost and high gravimetric hydrogen storage density [5e7]. But, the high desorption temperature and slow
desorption kinetics seriously restrict practical applications of MgH2. In recent decades, numerous researches focused on the improvement of dehydrogenation properties of MgH2. The efficient approaches contain nano-confinement [8e15], adding catalyst [16e20] and reacting with other metal hydrides or complex hydrides [21e28]. Nano-confining Mg/MgH2 into carbon materials is an attractive method to enhance desorption kinetics by efficiently reducing the particle size. However, the total hydrogen capacity dramatically decreases due to the
* Corresponding author. Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071, China. E-mail address: [email protected] (Y. Wang). http://dx.doi.org/10.1016/j.ijhydene.2017.07.220 0360-3199/© 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. Please cite this article in press as: Zhang Q, et al., Improved hydrogen storage properties of MgH2 with Ni-based compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.220
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extensive adding of carbon materials. Adding catalyst is another promising way to improve the hydrogen storage performance of MgH2. In particular, recent investigations focus on efficient catalyst for MgH2 system [29e32]. Notably, Ni-based compounds exhibit efficient catalyzing effect on the dehydrogenation of MgH2. Cabo et al. [33] reported that the desorption rate of MgH2eNiO sample was seven times faster than that of pure MgH2. Mao et al. [34] found that the MgH2e NiCl2 sample started to release hydrogen at 300 C, which was 30 C lower than that of pure MgH2. The MgH2eNiCl2 sample released 4.58 wt% hydrogen in 60 min at 300 C. Xie et al. [35] found that MgeNiS composites could uptake 3.5 wt % H2 within 10 min at 250 C and release 3.1 wt % H2 within 10 min at 300 C. Particularly, Liu et al. [36] reported that NiB even reduced the dissociation temperature of MgH2 by 120 C. The activation energy of MgH2-10 wt%NiB decreased to 59.7 kJ mol1. Moreover, in our previous work, it is interesting to find that Ni-based compounds (Ni2P and Ni3N) with different anions exert different catalytic activity towards the dehydrogenation of MgH2 [37,38]. These findings motivate our interest in investigating the effect of anions on the catalytic ability of Ni-based compounds for dehydrogenation of MgH2. The Ni-based compounds containing Ni3C, Ni3N and Ni2P possess highly catalytic activity due to the non-compensated electronic structure [39e41]. The electrons transfer from anion-forming element to Ni, which makes nickel electron enriched. Recently, these Ni-based compounds are widely studied to catalyze the organic synthesis and water splitting [42e45]. Meanwhile, NiO is a commonly catalytic material in the field of hydrogen storage. Furthermore, it is found that the anion-forming elements of the Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) are in the same period or diagonal location. Therefore, Ni3C, Ni3N, NiO and Ni2P are chosen to investigate the effect of anion on the catalytic ability for the dehydrogenation of MgH2. Herein, the dehydrogenation properties of MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) are investigated using isothermal dehydrogenation apparatus, temperatureprogrammed desorption system and differential scanning calorimetry. Moreover, the catalytic mechanism of the Nibased compounds with different anion-forming elements for dehydrogenation of the Mg-based material is also discussed. Further, the MgH2-xwt%Ni3C (x ¼ 1, 3, 5, 7 and 10) composites are systematically explored.
Experimental Preparation of Ni-based compounds The commercial chemical reagents were used without further purification. Ni3C nanoparticles were synthesized by thermal decomposition method [46]. 0.708 g nickel acetate and 28 mL oleylamine were mixed in three-necked flask. The mixture was heated at 250 C for 2 h under Ar flow. Then, the suspension was centrifuged and washed with ethanol. The Ni3C nanoparticles were obtained by drying 80 C for 12 h Ni3N nanoparticles were synthesized by sol-gel method. 0.25 g nickel acetate tetrahydrate and 0.24 g solid urea were mixed with 6 mL alcohol. The mixture was stirred for 3 h until the gel
was completely formed. The Ni3N nanoparticles was finally obtained by heating at 325 C for 3 h. NiO nanoparticles were synthesized by the method proposed by Fouladgar [47]. 2.908 g Ni(NO3)2$6H2O and 0.6 g sodium hydroxide was respectively dissolved in 50 mL distilled water. The NaOH solution was heated to 70 C. Then, Ni(NO3)2 solution was added dropwise to the NaOH solution under stirring. The Ni(OH)2 precipitates were heated at 350 C for 2 h to obtain the NiO nanoparticles. Ni2P nanoparticles were prepared by a facile hydrothermal technique. 0.95 g NiCl6$6H2O, 1.25 g CH3COONa$3H2O, 0.20 g CTAB and 0.64 g red phosphorus were dispersed in 40 mL deionized water. After magnetically stirring for 1 h at room temperature, the slurry-like mixture was gained and subsequently poured into a 50 mL Teflon-lined autoclave. Next, the autoclave was heated at 160 C for 10 h. Then, the precipitates were washed with distilled water. Finally, the Ni2P nanoparticles were obtained after vacuum drying.
Preparation of Mg-based hydrogen storage materials Commercial MgH2 powders (Alfa Aesar, 98%) were used without further purification. The MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) were synthesized by ball-milling MgH2 with different Ni-based compounds with the ratio of 95:5. The mixture was poured into a 100 mL steel vessel loaded with steel balls; and the ball-to-powder mass ratio was 40:1. Then, the mixture was ball-milled under 0.5 MPa H2. Planetary ball mill model was employed as followed: ball milling the mixture for 5 h with a rotational speed of 450 rpm at room temperature. For comparison, the pure MgH2 was also prepared under the same condition. All of the operating and transportation was performed in glove box filled with purified argon (99.999%) to prevent samples from oxidation.
Characteristics The structures and morphologies of as-synthesized samples were characterized by powder X-ray diffraction (XRD, Rigaku Mini FlexII, Cu Ka radiation), scanning electron microscopy (SEM, JEOL JSM7500) and transmission electron microscopy (TEM, JEOL JEM-2010FEF). The decomposition performances of the Mg-based materials were measured by a temperatureprogrammed desorption system (TPD, PX200). Typically, the sample was loaded into the sample chamber and heated to 500 C by a 2 C min1 heating rate. The isothermal desorption kinetics of the different materials were determined by volumetric method using a homemade Sievert's apparatus. The isothermal desorption curves were undertaken in vacuum at different temperatures. The thermal properties were characterized by differential scanning calorimetry (DSC, Q20P, TA Instruments).
Results and discussion Characterization of Ni-based complexes The XRD patterns of the as-prepared Ni-based compounds are shown in Fig. 1. The diffraction peaks are respectively indexed as Ni3C (PDF:72-1467), Ni3N (PDF:89-5144), NiO (PDF:73-1519)
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Table 1 e The refined crystal parameters and average crystal sizes of the Ni-based compounds. Phase Crystal parameters ( A) Crystal size (nm)
Ni3C Ni3N NiO Ni2P
Fig. 1 e The XRD patterns of the as-prepared Ni-based compounds, (a) Ni3C, (b) Ni3N, (c) NiO, (d) Ni2P.
and Ni2P (PDF:89-4864). The refined crystal parameters are listed in Table 1, which are in agreement with standard values. Besides, the average crystal sizes of the Ni-based compounds are 7e22 nm, calculated from the Scherrer equation [48]. The microstructures of as-prepared Ni-based compounds were explored by SEM examination. As shown in Fig. S1, the Ni3C, Ni3N and NiO are all composed of the particles, and Ni2P displays a plate-like structure with the aggregation of numerous nanoparticles. Meanwhile, it is observed that the average diameters of Ni3C, Ni3N, NiO and Ni2P are 31.0, 17.8, 18.4 and 20.8 nm, respectively (Fig. S2). Moreover, the size of particles is in the range of 10e50 nm.
a
b
c
4.569 4.606 4.174 5.854
4.569 4.606 4.174 5.854
12.92 4.332 4.174 3.382
22.0 14.1 7.2 13.5
performance compared to the other Mg-based materials. Meanwhile, the hydrogen capacity of the Mg-based materials was displayed at Fig. 2. Compared with the pure MgH2, hydrogen capacities of the MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites decrease. The MgH2eNi3C and MgH2eNi3N composites possess the highest hydrogen capacity (6.5 wt%) among the Mg-based composites. Meanwhile, the hydrogen capacity of the MgH2eNi2P composites is lowest (6.1 wt%). The hydrogen desorption kinetics of the MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites were also evaluated. Fig. 3 shows the isothermal hydrogen desorption curves of the Mgbased composites at 275, 300 and 325 C. It is obvious that the MgH2eNi3C composites exhibit the fastest desorption kinetics among all the composites. The MgH2-5wt%Ni3C composites can release 6.3, 6.2 and 3.3 wt% hydrogen in 20 min at 325, 300 and 275 C, respectively. Ni3N and NiO exhibit the less positive effect on improving the desorption kinetics of MgH2. At 325 C, the MgH2eNi3N and MgH2eNiO composites desorb about 6.0 wt% hydrogen in 20 min. It is found that the hydrogen desorption rate of the MgH2eNi3N composites is faster than that of the MgH2eNiO composites at lower desorption temperatures. The MgH2eNi3N composites release 4.9 and 2.9 wt% hydrogen in 20 min at 300 and 275 C, respectively. For MgH2eNiO composites, 4.1 and 1.3 wt% hydrogen is released in 20 min at 300 and 275 C. Besides, the MgH2eNi2P composites show the slowest hydrogen desorption rate. The composites only decrease 0.4 wt% hydrogen in 20 min at 275 C. The isothermal hydrogen desorption results
Dehydrogenation performance of the MgH2-X composites The hydrogen decomposition properties of MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites and the pure MgH2 were investigated by temperature programmed desorption (TPD). As shown in Fig. S3, the onset decomposition temperatures of MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites significantly reduce compared with the pure MgH2. In particular, MgH2eNi3C composites have the lowest onset temperature among all the composites. The MgH2eNi3C composites start to release hydrogen at 160 C, which is even 175 C lower than that of pure MgH2 (335 C). The downward trends are less impressive with adding other Ni-based compounds. The onset dehydrogenation temperatures of MgH2eNi3N, MgH2eNiO and MgH2eNi2P are 180 C, 205 C and 248 C, respectively. The comparison of onset temperature reveals that the MgH2eNi3C composites have a more superior dehydrogenation
Fig. 2 e The corresponding thermally programmed H2 desorption capacity curves of MgH2 and MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites.
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Fig. 3 e Isothermal dehydrogenation curves of Mg-based materials at 275, 300 and 325 C, (a) MgH2eNi3C, (b) MgH2eNi3N, (c) MgH2eNiO and (d) MgH2eNi2P.
obviously indicate that the MgH2eNi3C composites possess the best dehydrogenation performance, followed by MgH2e Ni3N, MgH2eNiO and MgH2eNi2P. The thermal properties of the MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites were further investigated by DSC, and the results are shown in Fig. 4a. There is an exothermic peak for the Mg-based composites, which is attributed to the dehydrogenation reaction. Clearly, among all the Mg-based materials, the MgH2eNi3C composites exhibit the most excellent performance. The endothermic peak temperature of MgH2eNi3C is 310.7 C, which is even 43 C lower than that of pure MgH2. Other Mg-based composites also exhibit better properties than the pure MgH2. To further understand the improvement of the dehydrogenation kinetics, the Kissinger method was used to calculate the apparent activation energy (Ea) of the Mg-based composites. The resultant Kissinger plots are shown in Fig. 4b. The values of Ea for the Mg-based composites are much lower compared with the pure MgH2. The activation energies of MgH2eNi3C, MgH2eNi3N, MgH2eNiO and MgH2eNi2P are calculated as 97.8, 100.0, 119.7 and 132.5 kJ mol1, respectively. By contrast, the Ea of the pure MgH2 was 161.9 kJ mol1. It is worthy to mention that the apparent activation energy of the MgH2eNi3C is even 64 kJ mol1 lower than that of the pure MgH2. The reduction in the desorption activation energy is believed to contribute to the improvement on the hydrogen desorption kinetics. In addition, the enthalpy change of MgH2-
X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites was measured by integrating the DSC peaks. As shown in Fig. S4, the enthalpy change of Mg-based composites in dehydrogenation significantly reduces compared with the pure MgH2. It implies that the Mg-based composites exhibit an improved thermodynamics property compared with the pure MgH2. In order to study the dehydrogenation mechanism of the Mg-based composites, the XRD measurements of the Mgbased composites and the composites after dehydrogenation were carried out. It is found that the diffraction peaks for asprepared Mg-based composites are indexed as b-MgH2 together with weak peaks of the corresponding Ni-based compounds. As shown in Fig. 5, the as-prepared MgH2eNi3C mainly contains MgH2 and a small amount of Ni3C. Other Mgbased composites show the similar results. After dehydrogenation, the main diffraction peaks are identified as Mg, which indicates that b-MgH2 transforms into Mg. Meanwhile, it is observed that the Ni3C, Ni3N and NiO peaks still remains in the composites after dehydrogenation. However, for the MgH2e Ni2P composites after dehydrogenation, the Mg2Ni and Mg3P2 phases are detected [34,49]. The dehydrogenation process of the MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites is a gas-solid reaction, whose reaction rate is affected significantly by the gas-solid interface [50,51]. The schematic diagram displays the effect of Ni-based compounds on the dehydrogenation of MgH2 (Fig. 6). Nix/y stands for the multivalences of the Ni-based compound, in
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which x/y refers to the valence state of Ni. Notably, the Nix/y can gain electrons more easily than Mg2þ, and thus act as an electron transfer medium during dehydrogenation process [51]. The dehydrogenation of Mg-based composites proceeds as the following steps: (1) H between the Mg2þ and Nix/y tends to diffuse to Nix/y and form the NieH bonds; (2) H diffuses across the Nix/y layer and arrives on the surfaces; (3) the NieH bonds breaks. Based on dehydrogenation process, the hydrogen desorption relates to the formation of NieH bonds, transformation of H and the break of NieH bonds. Moreover, the breaking of NieH bonds is the control step. It is reported that the break of bond between the metal and H ion is more easily as the metal has lower electron-negativity [51]. As the Ni binds with the low electron-negativity element, the stability of NieH bond decreases. The electron-negativity of C, N, O and P is 2.55, 3.04, 3.44 and 1.64, respectively. Therefore, the dehydrogenation performance of the Mg-based composites ranks as MgH2eNi3C, MgH2eNi3N and MgH2eNiO. Besides, the dehydrogenation mechanism of MgH2eNi2P composites is an exception due to the formation of Mg2Ni and Mg3P2.
Dehydrogenation performance of the MgH2eNi3C composites
Fig. 4 e (a) DSC curves and (b) the Kissinger plots of MgH2 and MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites.
Among all the Mg-based composites, it is found that the MgH2eNi3C composites possess the best dehydrogenation properties. Therefore, the hydrogen storage properties of MgH2-xwt%Ni3C (x ¼ 1, 3, 5, 7 and 10) composites are further explored. The hydrogen decomposition properties of MgH2-xwt% Ni3C (x ¼ 1, 3, 5, 7 and 10) composites were depicted in Fig. S5. The onset dehydrogenation temperature of all the MgH2eNi3C composites is around 160 C. However, the peak temperature shows a downward shift with the increasing addition of Ni3C.
Fig. 5 e XRD patterns of the (A) as-milled composites and (B) composites after dehydrogenation. (a) MgH2eNi3C, (b) MgH2e Ni3N, (c) MgH2eNiO and (d) MgH2eNi2P. Please cite this article in press as: Zhang Q, et al., Improved hydrogen storage properties of MgH2 with Ni-based compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.220
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Fig. 6 e The schematic diagram of the dehydrogenation of MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites.
Fig. 7 e The corresponding thermally programmed H2 desorption capacity curves of MgH2-xwt%Ni3C (x ¼ 1, 3, 5, 7 and 10) composites.
Fig. 8 e Isothermal dehydrogenation curves of MgH2-xwt% Ni3C (x ¼ 1, 3, 5, 7 and 10) composites at 300 C.
Fig. 9 e (a) Hydrogen desorption kinetic curves of the MgH2-5wt%Ni3C composites at different temperatures; (b) JMA fitting plots for the isothermal dehydrogenation of MgH2-5wt%Ni3C composites at different temperatures.
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The MgH2-xwt%Ni3C (x ¼ 5, 7 and 10) composites possess the lowest desorption hydrogen peak temperature (about 260 C). Meanwhile, the amount of desorbed hydrogen is also displayed in Fig. 7. A hydrogen desorption capacity of 5.7 wt% can be reached on heating the MgH2-5wt%Ni3C composites to 300 C. In contrast, the MgH2-xwt%Ni3C (x ¼ 3, 7 and 10) and MgH2-1wt%Ni3C composites respectively desorb 5.4 wt% and 4.8 wt% hydrogen under the same heating temperature. The comparison results reveal that the MgH2-5wt%Ni3C composites exhibit the best decomposition property. The isothermal hydrogen desorption curves of MgH2-xwt% Ni3C (x ¼ 1, 3, 5, 7 and 10) composites are shown in Fig. 8. The MgH2-5wt%Ni3C composites exhibit the fastest desorption rate. The MgH2-5wt%Ni3C composites desorb about 6.2 wt% hydrogen within 20 min at 300 C. By contrast, the MgH2-1wt% Ni3C composites only desorb 2.7 wt% hydrogen under the same condition. The MgH2-3wt%Ni3C, MgH2-7wt%Ni3C and MgH2-10 wt%Ni3C composites release 6.1, 6.0 and 5.9 wt% hydrogen in 20 min, respectively. The isothermal dehydrogenation curves of the MgH2-5wt% Ni3C composites at different temperatures are showed in Fig. 9a. The desorption kinetics becomes sluggish as the temperature decreases. However, the MgH2-5wt%Ni3C composites still release 4.8 wt% hydrogen within 120 min at 250 C.
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Additionally, in order to realize the dehydrogenation mechanism of MgH2-5wt%Ni3C composites, the data of isothermal desorption at different temperatures were fitted by JMA equation described as below [7]: 1=n
½ lnð1 aÞ
¼ kt
(1)
where t is the reaction time, a is the reacted fraction at time t, k is the rate constant, n is the Avrami exponent that is relevant to the transformation mechanism. As displayed in Fig. 9b, ln[ln(1a)] vs. lnt exhibits a good linearity. When the isothermal desorption hydrogen temperature varies from 250 C to 300 C, the Avrami exponent n is 1.26, 1.52 and 1.34, respectively. It is interesting to observe that the Avrami exponent n is around 1.5 for desorption data with different temperatures, indicating that the hydrogen desorption of MgH2-5wt%Ni3C is a diffusion-controlled reaction. In addition, the isothermal dehydrogenation curves of the MgH2-5wt% Ni3C composites with four cycles are shown in Fig. S6. After successive four cycles, the hydrogen desorption kinetics of MgH2-5wt%Ni3C does not degrade and amount of desorbed hydrogen still remains at 5.9 wt% H2. Thus, we conclude that the MgH2-5wt%Ni3C composite has good cycle stability and reversibility. Additionally, the microstructures of the MgH2-5wt% Ni3N@NC composites after ball milling, dehydrogenation and cycling processes were also characterized. The relevant SEM and TEM images are displayed in Fig. 10. As exhibited in Fig. 10, the sample of the as-milled MgH2-5wt%Ni3N@NC consists of large irregular-shaped particles with the size of 200e500 nm. There is no obvious agglomeration of particles even after four cycles. It is favorable for the improvement on reversibility of MgH2-5wt%Ni3N@NC composites.
Conclusions A series of Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) was synthesized by chemical method. The particle sizes of Nibased compounds are in the range of 10e50 nm. The MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites were prepared by mechanical ball-milling method. The Mg-based composites show enhanced hydrogen storage properties compared with pure MgH2. Moreover, the dehydrogenation performance of the Mg-based composites ranks as MgH2eNi3C, MgH2eNi3N, MgH2eNiO and MgH2eNi2P. The MgH2eNi3C composites start to release hydrogen at 160 C, and release 6.2 wt% hydrogen within 20 min at 300 C.
Acknowledgement This work was financially supported by NSFC (51471089, 51501072, 51571124), MOE (IRT13R30), 111 Project (B12015).
Appendix A. Supplementary data Fig. 10 e The SEM and TEM images of the MgH2-5wt%Ni3C composites after (aeb) ball milling, (ced) dehydrogenation and (eef) cycling.
Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ijhydene.2017.07.220.
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references
[1] Grochala W, Edwards PP. Thermal decomposition of the noninterstitial hydrides for the storage and production of hydrogen. Chem Rev 2004;104:1283e315. [2] Li PZ, Aijaz A, Xu Q. Highly dispersed surfactant-free nickel nanoparticles and their remarkable catalytic activity in the hydrolysis of ammonia borane for hydrogen generation. Angew Chem Int Ed 2012;51:6753e6. [3] Javadian P, Sheppard DA, Buckley CE, Jensen TR. Hydrogen storage properties of nanoconfined LiBH4-Ca(BH4)2. Nano Energy 2015;11:96e103. [4] Huang Z, Eagles M, Porter S, Sorte EG, Billet B, Corey RL, et al. Thermolysis and solid state NMR studies of NaB3H8, NH3B3H7, and NH4B3H8. Dalton T 2013;42:701e8. [5] Lu J, Choi YJ, Fang ZZ, Sohn HY, Ronnebro E. Hydrogen storage properties of nanosized MgH2-0.1TiH2 prepared by ultrahigh-energy-high-pressure milling. J Am Chem Soc 2009;131:15843e52. [6] Wang JC, Du Y, Sun LX, Li XH. Effects of F and Cl on the stability of MgH2. Int J Hydrogen Energy 2014;39:877e83. [7] Aguey-Zinsou KF, Ares-Fernandez JR. Hydrogen in magnesium: new perspectives toward functional stores. Energy Environ Sci 2010;3:526e43. [8] Jeon KJ, Moon HR, Ruminski AM, Jiang B, Kisielowski C, Bardhan R, et al. Air-stable magnesium nanocomposites provide rapid and high-capacity hydrogen storage without using heavy-metal catalysts. Nat Mater 2011;10:286e90. [9] Konarova M, Tanksale A, Beltramini JN, Lu GQ. Effects of nano-confinement on the hydrogen desorption properties of MgH2. Nano Energy 2013;2:98e104. [10] Liu W, Aguey-Zinsou KF. Size effects and hydrogen storage properties of Mg nanoparticles synthesised by an electroless reduction method. J Mater Chem A 2014;2:9718e26. [11] Liu Y, Zou J, Zeng X, Ding W. Study on hydrogen storage properties of Mg-X (X¼Fe, V, Co) nano-composites coprecipitated from solution. RSC Adv 2014;5:7687e96. [12] Liu Y, Zou J, Zeng X, Wu X, Li D, Ding W. Hydrogen storage properties of a Mg-Ni nanocomposite coprecipitated from solution. J Phys Chem C 2014;118:18401e11. [13] Norberg NS, Arthur TS, Fredrick SJ, Prieto AL. Size-dependent hydrogen storage properties of Mg nanocrystals prepared from solution. J Am Chem Soc 2011;133:10679e81. [14] Xia G, Tan Y, Chen X, Sun D, Guo Z, Liu H, et al. Monodisperse magnesium hydride nanoparticles uniformly self-assembled on graphene. Adv Mater 2015;27:5981e8. [15] Zhang S, Gross AF, Van Atta SL, Lopez M, Liu P, Ahn CC, et al. The synthesis and hydrogen storage properties of a MgH2 incorporated carbon aerogel scaffold. Nanotechnology 2009;20. [16] Bhatnagar A, Pandey SK, Vishwakarma AK, Singh S, Shukla V, Soni PK, et al. Fe3O4@graphene as a superior catalyst for hydrogen de/absorption from/in MgH2/Mg. J Mater Chem A 2016;4:14761e72. [17] Halim Yap FA, Mustafa NS, Ismail M. A study on the effects of K2ZrF6 as an additive on the microstructure and hydrogen storage properties of MgH2. RSC Adv 2015;5:9255e60. [18] House SD, Vajo JJ, Ren C, Rockett AA, Robertson IM. Effect of ball-milling duration and dehydrogenation on the morphology, microstructure and catalyst dispersion in Nicatalyzed MgH2 hydrogen storage materials. Acta Mater 2015;86:55e68. [19] Shahi RR, Bhatnagar A, Pandey SK, Dixit V, Srivastava ON. Effects of Ti-based catalysts and synergistic effect of SWCNTs-TiF3 on hydrogen uptake and release from MgH2. Int J Hydrogen Energy 2014;39:14255e61.
[20] Zhang LT, Xiao XZ, Xu CC, Zheng JG, Fan XL, Shao J, et al. Remarkably improved hydrogen storage performance of MgH2 catalyzed by multivalence NbHx nanoparticles. J Phys Chem C 2015;119:8554e62. [21] Wang K, Kang X, Zhong Y, Hu C, Wang P. Improved reversible dehydrogenation properties of 2LiBH4-MgH2 composite by milling with graphitic carbon nitride. Int J Hydrogen Energy 2014;39:13369e74. [22] Mustafa NS, Ismail M. Enhanced hydrogen storage properties of 4MgH2þLiAlH4 composite system by doping with Fe2O3 nanopowder. Int J Hydrogen Energy 2014;39:7834e41. [23] Xueping Z, Guo X, Qiuhua M, Shenglin L, Tao L, Xin F, et al. Hydrogen release capacity of the LiAlH4-MgH2 system. J Power Sources 2013;231:173e6. [24] Ismail M. The hydrogen storage properties of destabilized MgH2-AlH3(2:1) system. Mater Today Proc 2016;3:S80e7. [25] Liu HZ, Wang XH, Liu YG, Dong ZH, Li SQ, Ge HW, et al. Microstructures and hydrogen desorption properties of the MgH2-AlH3 composite with NbF5 addition. J Phys Chem C 2014;118:18908e16. [26] Sirsch P, Che FN, Titah JT, McGrady GS. Hydride-hydride bonding interactions in the hydrogen storage materials AlH3, MgH2, and NaAlH4. Chem Eur J 2012;18:9476e80. [27] Puszkiel JA, Arneodo Larochette P, Gennari FC. Thermodynamic-kinetic characterization of the synthesized Mg2FeH6-MgH2 hydrides mixture. Int J Hydrogen Energy 2008;33:3555e60. [28] Wang J, Han S, Wang Z, Ke D, Liu J, Ma M. Enhanced hydrogen storage properties of the 2LiBH4-MgH2 composite with BaTiO3 as an additive. Dalton T 2016;45:7042e8. [29] Kwak YJ, Park HR, Song MY. Changes in microstructure, phases, and hydrogen storage characteristics of metal hydroborate and nickel-added magnesium hydride with hydrogen absorption and release reactions. Int J Hydrogen Energy 2017;42:1018e26. [30] Liu G, Wang KF, Li JP, Wang YJ, Yuan HT. Enhancement of hydrogen desorption in magnesium hydride catalyzed by graphene nanosheets supported Ni-CeOx hybrid nanocatalyst. Int J Hydrogen Energy 2016;41:10786e94. [31] Mustafa NS, Ismail M. Hydrogen sorption improvement of MgH2 catalyzed by CeO2 nanopowder. J Alloy Compd 2017;695:2532e8. [32] Sulaiman NN, Ismail M. Enhanced hydrogen storage properties of MgH2 co-catalyzed with K2NiF6 and CNTs. Dalton T 2016;45:19380e8. [33] Cabo M, Garroni S, Pellicer E, Milanese C, Girella A, Marini A, et al. Hydrogen sorption performance of MgH2 doped with mesoporous nickel- and cobalt-based oxides. Int J Hydrogen Energy 2011;36:5400e10. [34] Mao J, Guo Z, Yu X, Liu H, Wu Z, Ni J. Enhanced hydrogen sorption properties of Ni and Co-catalyzed MgH2. Int J Hydrogen Energy 2010;35:4569e75. [35] Xie XB, Ma XJ, Liu P, Shang JX, Li XG, Liu T. Formation of multiple-phase catalysts for the hydrogen storage of Mg nanoparticles by adding flowerlike NiS. ACS Appl Mater Interfaces 2017;9:5937e46. [36] Liu G, Qiu FY, Li J, Wang YJ, Li L, Yan C, et al. NiB nanoparticles: a new nickel-based catalyst for hydrogen storage properties of MgH2. Int J Hydrogen Energy 2012;37:17111e7. [37] Zhang QY, Xu YN, Wang Y, Zhang H, Wang YJ, Jiao LF, et al. Enhanced hydrogen storage performance of MgH2-Ni2P/ graphene nanosheets. Int J Hydrogen Energy 2016;41:17000e7. [38] Zhang QY, Wang Y, Zang L, Chang X, Jiao L, Yuan H, et al. Core-shell Ni3N@nitrogen-doped carbon: synthesis and application in MgH2. J Alloy Compd 2017;703:381e8.
Please cite this article in press as: Zhang Q, et al., Improved hydrogen storage properties of MgH2 with Ni-based compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.220
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[39] Chen JG. Carbide and nitride overlayers on early transition metal surfaces: preparation, characterization, and reactivities. Chem Rev 1996;96:1477e98. [40] Oyama ST. Crystal structure and chemical reactivity of transition metal carbides and nitrides. J Solid State Chem 1992;96:442e5. [41] Schaefer ZL, Weeber KM, Misra R, Schiffer P, Schaak RE. Bridging hcp-Ni and Ni3C via a Ni3C1-x solid solution: tunable composition and magnetism in colloidal nickel carbide nanoparticles. Chem Mater 2011;23:2475e80. [42] Kucernak ARJ, Sundaram VNN. Nickel phosphide: the effect of phosphorus content on hydrogen evolution activity and corrosion resistance in acidic medium. J Mater Chem A 2014;2:17435e45. [43] Pan Y, Liu Y, Zhao J, Yang K, Liang J, Liu D, et al. Monodispersed nickel phosphide nanocrystals with different phases: synthesis, characterization and electrocatalytic properties for hydrogen evolution. J Mater Chem A 2015;3:1656e65. [44] Shalom M, Ressnig D, Yang XF, Clavel G, Fellinger TP, Antonietti M. Nickel nitride as an efficient electrocatalyst for water splitting. J Mater Chem A 2015;3:8171e7. [45] Shalom M, Molinari V, Esposito D, Clavel G, Ressnig D, Giordano C, et al. Sponge-like nickel and nickel nitride
[46]
[47]
[48] [49]
[50]
[51]
9
structures for catalytic applications. Adv Mater 2014;26:1272e6. Chiang RT, Chiang RK, Shieu FS. Emergence of interstitialatom-free HCP nickel phase during the thermal decomposition of Ni3C nanoparticles. RSC Adv 2014;4:19488e94. Fouladgar M, Karimi-Maleh H, Gupta VK. Highly sensitive voltammetric sensor based on NiO nanoparticle room temperature ionic liquid modified carbon paste electrode for levodopa analysis. J Mol Liq 2015;208:78e83. Patterson AL. The Scherrer formula for X-ray particle size determination. Phys Rev 1939;56:978e87. Sulaiman NN, Juahir N, Mustafa NS, Halim Yap FA, Ismail M. Improved hydrogen storage properties of MgH2 catalyzed with K2NiF6. J Energy Chem 2016;5:832e9. Lototskyy M, Sibanyoni JM, Denys RV, Williams M, Pollet BG, Yartys VA. Magnesium-carbon hydrogen storage hybrid materials produced by reactive ball milling in hydrogen. Carbon 2013;57:146e60. Cui J, Liu JW, Wang H, Ouyang LZ, Sun DL, Zhu M, et al. MgTM (TM: Ti, Nb, V, Co, Mo or Ni) core-shell like nanostructures: synthesis, hydrogen storage performance and catalytic mechanism. J Mater Chem A 2014;2:9645e55.
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Improved hydrogen storage properties of MgH2 with Ni-based compounds Qiuyu Zhang a, Lei Zang a, Yike Huang a, Panyu Gao c, Lifang Jiao a, Huatang Yuan a, Yijing Wang a,b,* a
Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071, China b Collaborative Innovation Center of Chemical Science and Engineering, Nankai University, Tianjin 300071, China c School of Material Science and Engineering, Hebei University of Technology, Tianjin 300071, China
article info
abstract
Article history:
The nanoscaled Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) are synthesized by
Received 13 June 2017
chemical methods. The MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites are prepared by
Received in revised form
mechanical ball-milling. The dehydrogenation properties of Mg-based composites are
27 July 2017
systematically studied using isothermal dehydrogenation apparatus, temperature-
Accepted 29 July 2017
programmed desorption system and differential scanning calorimetry. It is experimen-
Available online xxx
tally confirmed that the dehydrogenation performance of the Mg-based materials ranks as following: MgH2eNi3C, MgH2eNi3N, MgH2eNiO and MgH2eNi2P. The onset dehydrogena-
Keywords:
tion temperatures of MgH2eNi3C, MgH2eNi3N, MgH2eNiO and MgH2eNi2P are 160 C,
Hydrogen storage
180 C, 205 C and 248 C, respectively. The four Mg-based composites respectively release
MgH2
6.2, 4.9, 4.1 and 3.5 wt% H2 within 20 min at 300 C. The activation energies of MgH2eNi3C,
Ni-based compounds
MgH2eNi3N, MgH2eNiO and MgH2eNi2P are 97.8, 100.0, 119.7 and 132.5 kJ mol1, respec-
Hydrogen storage mechanism
tively. It' found that the MgH2eNi3C composites exhibit the best hydrogen storage properties. Moreover, the catalytic mechanism of the Ni-based compounds is also discussed. It is found that Ni binding with low electron-negativity element is favorable for the dehydrogenation of the Mg-based composites. © 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.
Introduction Hydrogen, as abundant and clean energy carrier, is considered as a prospective candidate to substitute the traditional fossil fuels [1e4]. However, efficient and safe hydrogen storage is the technology barrier for the hydrogen utilization. MgH2 is one of the most promising hydrogen storage materials due to its low cost and high gravimetric hydrogen storage density [5e7]. But, the high desorption temperature and slow
desorption kinetics seriously restrict practical applications of MgH2. In recent decades, numerous researches focused on the improvement of dehydrogenation properties of MgH2. The efficient approaches contain nano-confinement [8e15], adding catalyst [16e20] and reacting with other metal hydrides or complex hydrides [21e28]. Nano-confining Mg/MgH2 into carbon materials is an attractive method to enhance desorption kinetics by efficiently reducing the particle size. However, the total hydrogen capacity dramatically decreases due to the
* Corresponding author. Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071, China. E-mail address: [email protected] (Y. Wang). http://dx.doi.org/10.1016/j.ijhydene.2017.07.220 0360-3199/© 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. Please cite this article in press as: Zhang Q, et al., Improved hydrogen storage properties of MgH2 with Ni-based compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.220
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extensive adding of carbon materials. Adding catalyst is another promising way to improve the hydrogen storage performance of MgH2. In particular, recent investigations focus on efficient catalyst for MgH2 system [29e32]. Notably, Ni-based compounds exhibit efficient catalyzing effect on the dehydrogenation of MgH2. Cabo et al. [33] reported that the desorption rate of MgH2eNiO sample was seven times faster than that of pure MgH2. Mao et al. [34] found that the MgH2e NiCl2 sample started to release hydrogen at 300 C, which was 30 C lower than that of pure MgH2. The MgH2eNiCl2 sample released 4.58 wt% hydrogen in 60 min at 300 C. Xie et al. [35] found that MgeNiS composites could uptake 3.5 wt % H2 within 10 min at 250 C and release 3.1 wt % H2 within 10 min at 300 C. Particularly, Liu et al. [36] reported that NiB even reduced the dissociation temperature of MgH2 by 120 C. The activation energy of MgH2-10 wt%NiB decreased to 59.7 kJ mol1. Moreover, in our previous work, it is interesting to find that Ni-based compounds (Ni2P and Ni3N) with different anions exert different catalytic activity towards the dehydrogenation of MgH2 [37,38]. These findings motivate our interest in investigating the effect of anions on the catalytic ability of Ni-based compounds for dehydrogenation of MgH2. The Ni-based compounds containing Ni3C, Ni3N and Ni2P possess highly catalytic activity due to the non-compensated electronic structure [39e41]. The electrons transfer from anion-forming element to Ni, which makes nickel electron enriched. Recently, these Ni-based compounds are widely studied to catalyze the organic synthesis and water splitting [42e45]. Meanwhile, NiO is a commonly catalytic material in the field of hydrogen storage. Furthermore, it is found that the anion-forming elements of the Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) are in the same period or diagonal location. Therefore, Ni3C, Ni3N, NiO and Ni2P are chosen to investigate the effect of anion on the catalytic ability for the dehydrogenation of MgH2. Herein, the dehydrogenation properties of MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) are investigated using isothermal dehydrogenation apparatus, temperatureprogrammed desorption system and differential scanning calorimetry. Moreover, the catalytic mechanism of the Nibased compounds with different anion-forming elements for dehydrogenation of the Mg-based material is also discussed. Further, the MgH2-xwt%Ni3C (x ¼ 1, 3, 5, 7 and 10) composites are systematically explored.
Experimental Preparation of Ni-based compounds The commercial chemical reagents were used without further purification. Ni3C nanoparticles were synthesized by thermal decomposition method [46]. 0.708 g nickel acetate and 28 mL oleylamine were mixed in three-necked flask. The mixture was heated at 250 C for 2 h under Ar flow. Then, the suspension was centrifuged and washed with ethanol. The Ni3C nanoparticles were obtained by drying 80 C for 12 h Ni3N nanoparticles were synthesized by sol-gel method. 0.25 g nickel acetate tetrahydrate and 0.24 g solid urea were mixed with 6 mL alcohol. The mixture was stirred for 3 h until the gel
was completely formed. The Ni3N nanoparticles was finally obtained by heating at 325 C for 3 h. NiO nanoparticles were synthesized by the method proposed by Fouladgar [47]. 2.908 g Ni(NO3)2$6H2O and 0.6 g sodium hydroxide was respectively dissolved in 50 mL distilled water. The NaOH solution was heated to 70 C. Then, Ni(NO3)2 solution was added dropwise to the NaOH solution under stirring. The Ni(OH)2 precipitates were heated at 350 C for 2 h to obtain the NiO nanoparticles. Ni2P nanoparticles were prepared by a facile hydrothermal technique. 0.95 g NiCl6$6H2O, 1.25 g CH3COONa$3H2O, 0.20 g CTAB and 0.64 g red phosphorus were dispersed in 40 mL deionized water. After magnetically stirring for 1 h at room temperature, the slurry-like mixture was gained and subsequently poured into a 50 mL Teflon-lined autoclave. Next, the autoclave was heated at 160 C for 10 h. Then, the precipitates were washed with distilled water. Finally, the Ni2P nanoparticles were obtained after vacuum drying.
Preparation of Mg-based hydrogen storage materials Commercial MgH2 powders (Alfa Aesar, 98%) were used without further purification. The MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) were synthesized by ball-milling MgH2 with different Ni-based compounds with the ratio of 95:5. The mixture was poured into a 100 mL steel vessel loaded with steel balls; and the ball-to-powder mass ratio was 40:1. Then, the mixture was ball-milled under 0.5 MPa H2. Planetary ball mill model was employed as followed: ball milling the mixture for 5 h with a rotational speed of 450 rpm at room temperature. For comparison, the pure MgH2 was also prepared under the same condition. All of the operating and transportation was performed in glove box filled with purified argon (99.999%) to prevent samples from oxidation.
Characteristics The structures and morphologies of as-synthesized samples were characterized by powder X-ray diffraction (XRD, Rigaku Mini FlexII, Cu Ka radiation), scanning electron microscopy (SEM, JEOL JSM7500) and transmission electron microscopy (TEM, JEOL JEM-2010FEF). The decomposition performances of the Mg-based materials were measured by a temperatureprogrammed desorption system (TPD, PX200). Typically, the sample was loaded into the sample chamber and heated to 500 C by a 2 C min1 heating rate. The isothermal desorption kinetics of the different materials were determined by volumetric method using a homemade Sievert's apparatus. The isothermal desorption curves were undertaken in vacuum at different temperatures. The thermal properties were characterized by differential scanning calorimetry (DSC, Q20P, TA Instruments).
Results and discussion Characterization of Ni-based complexes The XRD patterns of the as-prepared Ni-based compounds are shown in Fig. 1. The diffraction peaks are respectively indexed as Ni3C (PDF:72-1467), Ni3N (PDF:89-5144), NiO (PDF:73-1519)
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Table 1 e The refined crystal parameters and average crystal sizes of the Ni-based compounds. Phase Crystal parameters ( A) Crystal size (nm)
Ni3C Ni3N NiO Ni2P
Fig. 1 e The XRD patterns of the as-prepared Ni-based compounds, (a) Ni3C, (b) Ni3N, (c) NiO, (d) Ni2P.
and Ni2P (PDF:89-4864). The refined crystal parameters are listed in Table 1, which are in agreement with standard values. Besides, the average crystal sizes of the Ni-based compounds are 7e22 nm, calculated from the Scherrer equation [48]. The microstructures of as-prepared Ni-based compounds were explored by SEM examination. As shown in Fig. S1, the Ni3C, Ni3N and NiO are all composed of the particles, and Ni2P displays a plate-like structure with the aggregation of numerous nanoparticles. Meanwhile, it is observed that the average diameters of Ni3C, Ni3N, NiO and Ni2P are 31.0, 17.8, 18.4 and 20.8 nm, respectively (Fig. S2). Moreover, the size of particles is in the range of 10e50 nm.
a
b
c
4.569 4.606 4.174 5.854
4.569 4.606 4.174 5.854
12.92 4.332 4.174 3.382
22.0 14.1 7.2 13.5
performance compared to the other Mg-based materials. Meanwhile, the hydrogen capacity of the Mg-based materials was displayed at Fig. 2. Compared with the pure MgH2, hydrogen capacities of the MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites decrease. The MgH2eNi3C and MgH2eNi3N composites possess the highest hydrogen capacity (6.5 wt%) among the Mg-based composites. Meanwhile, the hydrogen capacity of the MgH2eNi2P composites is lowest (6.1 wt%). The hydrogen desorption kinetics of the MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites were also evaluated. Fig. 3 shows the isothermal hydrogen desorption curves of the Mgbased composites at 275, 300 and 325 C. It is obvious that the MgH2eNi3C composites exhibit the fastest desorption kinetics among all the composites. The MgH2-5wt%Ni3C composites can release 6.3, 6.2 and 3.3 wt% hydrogen in 20 min at 325, 300 and 275 C, respectively. Ni3N and NiO exhibit the less positive effect on improving the desorption kinetics of MgH2. At 325 C, the MgH2eNi3N and MgH2eNiO composites desorb about 6.0 wt% hydrogen in 20 min. It is found that the hydrogen desorption rate of the MgH2eNi3N composites is faster than that of the MgH2eNiO composites at lower desorption temperatures. The MgH2eNi3N composites release 4.9 and 2.9 wt% hydrogen in 20 min at 300 and 275 C, respectively. For MgH2eNiO composites, 4.1 and 1.3 wt% hydrogen is released in 20 min at 300 and 275 C. Besides, the MgH2eNi2P composites show the slowest hydrogen desorption rate. The composites only decrease 0.4 wt% hydrogen in 20 min at 275 C. The isothermal hydrogen desorption results
Dehydrogenation performance of the MgH2-X composites The hydrogen decomposition properties of MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites and the pure MgH2 were investigated by temperature programmed desorption (TPD). As shown in Fig. S3, the onset decomposition temperatures of MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites significantly reduce compared with the pure MgH2. In particular, MgH2eNi3C composites have the lowest onset temperature among all the composites. The MgH2eNi3C composites start to release hydrogen at 160 C, which is even 175 C lower than that of pure MgH2 (335 C). The downward trends are less impressive with adding other Ni-based compounds. The onset dehydrogenation temperatures of MgH2eNi3N, MgH2eNiO and MgH2eNi2P are 180 C, 205 C and 248 C, respectively. The comparison of onset temperature reveals that the MgH2eNi3C composites have a more superior dehydrogenation
Fig. 2 e The corresponding thermally programmed H2 desorption capacity curves of MgH2 and MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites.
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Fig. 3 e Isothermal dehydrogenation curves of Mg-based materials at 275, 300 and 325 C, (a) MgH2eNi3C, (b) MgH2eNi3N, (c) MgH2eNiO and (d) MgH2eNi2P.
obviously indicate that the MgH2eNi3C composites possess the best dehydrogenation performance, followed by MgH2e Ni3N, MgH2eNiO and MgH2eNi2P. The thermal properties of the MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites were further investigated by DSC, and the results are shown in Fig. 4a. There is an exothermic peak for the Mg-based composites, which is attributed to the dehydrogenation reaction. Clearly, among all the Mg-based materials, the MgH2eNi3C composites exhibit the most excellent performance. The endothermic peak temperature of MgH2eNi3C is 310.7 C, which is even 43 C lower than that of pure MgH2. Other Mg-based composites also exhibit better properties than the pure MgH2. To further understand the improvement of the dehydrogenation kinetics, the Kissinger method was used to calculate the apparent activation energy (Ea) of the Mg-based composites. The resultant Kissinger plots are shown in Fig. 4b. The values of Ea for the Mg-based composites are much lower compared with the pure MgH2. The activation energies of MgH2eNi3C, MgH2eNi3N, MgH2eNiO and MgH2eNi2P are calculated as 97.8, 100.0, 119.7 and 132.5 kJ mol1, respectively. By contrast, the Ea of the pure MgH2 was 161.9 kJ mol1. It is worthy to mention that the apparent activation energy of the MgH2eNi3C is even 64 kJ mol1 lower than that of the pure MgH2. The reduction in the desorption activation energy is believed to contribute to the improvement on the hydrogen desorption kinetics. In addition, the enthalpy change of MgH2-
X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites was measured by integrating the DSC peaks. As shown in Fig. S4, the enthalpy change of Mg-based composites in dehydrogenation significantly reduces compared with the pure MgH2. It implies that the Mg-based composites exhibit an improved thermodynamics property compared with the pure MgH2. In order to study the dehydrogenation mechanism of the Mg-based composites, the XRD measurements of the Mgbased composites and the composites after dehydrogenation were carried out. It is found that the diffraction peaks for asprepared Mg-based composites are indexed as b-MgH2 together with weak peaks of the corresponding Ni-based compounds. As shown in Fig. 5, the as-prepared MgH2eNi3C mainly contains MgH2 and a small amount of Ni3C. Other Mgbased composites show the similar results. After dehydrogenation, the main diffraction peaks are identified as Mg, which indicates that b-MgH2 transforms into Mg. Meanwhile, it is observed that the Ni3C, Ni3N and NiO peaks still remains in the composites after dehydrogenation. However, for the MgH2e Ni2P composites after dehydrogenation, the Mg2Ni and Mg3P2 phases are detected [34,49]. The dehydrogenation process of the MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites is a gas-solid reaction, whose reaction rate is affected significantly by the gas-solid interface [50,51]. The schematic diagram displays the effect of Ni-based compounds on the dehydrogenation of MgH2 (Fig. 6). Nix/y stands for the multivalences of the Ni-based compound, in
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which x/y refers to the valence state of Ni. Notably, the Nix/y can gain electrons more easily than Mg2þ, and thus act as an electron transfer medium during dehydrogenation process [51]. The dehydrogenation of Mg-based composites proceeds as the following steps: (1) H between the Mg2þ and Nix/y tends to diffuse to Nix/y and form the NieH bonds; (2) H diffuses across the Nix/y layer and arrives on the surfaces; (3) the NieH bonds breaks. Based on dehydrogenation process, the hydrogen desorption relates to the formation of NieH bonds, transformation of H and the break of NieH bonds. Moreover, the breaking of NieH bonds is the control step. It is reported that the break of bond between the metal and H ion is more easily as the metal has lower electron-negativity [51]. As the Ni binds with the low electron-negativity element, the stability of NieH bond decreases. The electron-negativity of C, N, O and P is 2.55, 3.04, 3.44 and 1.64, respectively. Therefore, the dehydrogenation performance of the Mg-based composites ranks as MgH2eNi3C, MgH2eNi3N and MgH2eNiO. Besides, the dehydrogenation mechanism of MgH2eNi2P composites is an exception due to the formation of Mg2Ni and Mg3P2.
Dehydrogenation performance of the MgH2eNi3C composites
Fig. 4 e (a) DSC curves and (b) the Kissinger plots of MgH2 and MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites.
Among all the Mg-based composites, it is found that the MgH2eNi3C composites possess the best dehydrogenation properties. Therefore, the hydrogen storage properties of MgH2-xwt%Ni3C (x ¼ 1, 3, 5, 7 and 10) composites are further explored. The hydrogen decomposition properties of MgH2-xwt% Ni3C (x ¼ 1, 3, 5, 7 and 10) composites were depicted in Fig. S5. The onset dehydrogenation temperature of all the MgH2eNi3C composites is around 160 C. However, the peak temperature shows a downward shift with the increasing addition of Ni3C.
Fig. 5 e XRD patterns of the (A) as-milled composites and (B) composites after dehydrogenation. (a) MgH2eNi3C, (b) MgH2e Ni3N, (c) MgH2eNiO and (d) MgH2eNi2P. Please cite this article in press as: Zhang Q, et al., Improved hydrogen storage properties of MgH2 with Ni-based compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.220
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Fig. 6 e The schematic diagram of the dehydrogenation of MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites.
Fig. 7 e The corresponding thermally programmed H2 desorption capacity curves of MgH2-xwt%Ni3C (x ¼ 1, 3, 5, 7 and 10) composites.
Fig. 8 e Isothermal dehydrogenation curves of MgH2-xwt% Ni3C (x ¼ 1, 3, 5, 7 and 10) composites at 300 C.
Fig. 9 e (a) Hydrogen desorption kinetic curves of the MgH2-5wt%Ni3C composites at different temperatures; (b) JMA fitting plots for the isothermal dehydrogenation of MgH2-5wt%Ni3C composites at different temperatures.
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The MgH2-xwt%Ni3C (x ¼ 5, 7 and 10) composites possess the lowest desorption hydrogen peak temperature (about 260 C). Meanwhile, the amount of desorbed hydrogen is also displayed in Fig. 7. A hydrogen desorption capacity of 5.7 wt% can be reached on heating the MgH2-5wt%Ni3C composites to 300 C. In contrast, the MgH2-xwt%Ni3C (x ¼ 3, 7 and 10) and MgH2-1wt%Ni3C composites respectively desorb 5.4 wt% and 4.8 wt% hydrogen under the same heating temperature. The comparison results reveal that the MgH2-5wt%Ni3C composites exhibit the best decomposition property. The isothermal hydrogen desorption curves of MgH2-xwt% Ni3C (x ¼ 1, 3, 5, 7 and 10) composites are shown in Fig. 8. The MgH2-5wt%Ni3C composites exhibit the fastest desorption rate. The MgH2-5wt%Ni3C composites desorb about 6.2 wt% hydrogen within 20 min at 300 C. By contrast, the MgH2-1wt% Ni3C composites only desorb 2.7 wt% hydrogen under the same condition. The MgH2-3wt%Ni3C, MgH2-7wt%Ni3C and MgH2-10 wt%Ni3C composites release 6.1, 6.0 and 5.9 wt% hydrogen in 20 min, respectively. The isothermal dehydrogenation curves of the MgH2-5wt% Ni3C composites at different temperatures are showed in Fig. 9a. The desorption kinetics becomes sluggish as the temperature decreases. However, the MgH2-5wt%Ni3C composites still release 4.8 wt% hydrogen within 120 min at 250 C.
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Additionally, in order to realize the dehydrogenation mechanism of MgH2-5wt%Ni3C composites, the data of isothermal desorption at different temperatures were fitted by JMA equation described as below [7]: 1=n
½ lnð1 aÞ
¼ kt
(1)
where t is the reaction time, a is the reacted fraction at time t, k is the rate constant, n is the Avrami exponent that is relevant to the transformation mechanism. As displayed in Fig. 9b, ln[ln(1a)] vs. lnt exhibits a good linearity. When the isothermal desorption hydrogen temperature varies from 250 C to 300 C, the Avrami exponent n is 1.26, 1.52 and 1.34, respectively. It is interesting to observe that the Avrami exponent n is around 1.5 for desorption data with different temperatures, indicating that the hydrogen desorption of MgH2-5wt%Ni3C is a diffusion-controlled reaction. In addition, the isothermal dehydrogenation curves of the MgH2-5wt% Ni3C composites with four cycles are shown in Fig. S6. After successive four cycles, the hydrogen desorption kinetics of MgH2-5wt%Ni3C does not degrade and amount of desorbed hydrogen still remains at 5.9 wt% H2. Thus, we conclude that the MgH2-5wt%Ni3C composite has good cycle stability and reversibility. Additionally, the microstructures of the MgH2-5wt% Ni3N@NC composites after ball milling, dehydrogenation and cycling processes were also characterized. The relevant SEM and TEM images are displayed in Fig. 10. As exhibited in Fig. 10, the sample of the as-milled MgH2-5wt%Ni3N@NC consists of large irregular-shaped particles with the size of 200e500 nm. There is no obvious agglomeration of particles even after four cycles. It is favorable for the improvement on reversibility of MgH2-5wt%Ni3N@NC composites.
Conclusions A series of Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) was synthesized by chemical method. The particle sizes of Nibased compounds are in the range of 10e50 nm. The MgH2-X (X ¼ Ni3C, Ni3N, NiO and Ni2P) composites were prepared by mechanical ball-milling method. The Mg-based composites show enhanced hydrogen storage properties compared with pure MgH2. Moreover, the dehydrogenation performance of the Mg-based composites ranks as MgH2eNi3C, MgH2eNi3N, MgH2eNiO and MgH2eNi2P. The MgH2eNi3C composites start to release hydrogen at 160 C, and release 6.2 wt% hydrogen within 20 min at 300 C.
Acknowledgement This work was financially supported by NSFC (51471089, 51501072, 51571124), MOE (IRT13R30), 111 Project (B12015).
Appendix A. Supplementary data Fig. 10 e The SEM and TEM images of the MgH2-5wt%Ni3C composites after (aeb) ball milling, (ced) dehydrogenation and (eef) cycling.
Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ijhydene.2017.07.220.
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references
[1] Grochala W, Edwards PP. Thermal decomposition of the noninterstitial hydrides for the storage and production of hydrogen. Chem Rev 2004;104:1283e315. [2] Li PZ, Aijaz A, Xu Q. Highly dispersed surfactant-free nickel nanoparticles and their remarkable catalytic activity in the hydrolysis of ammonia borane for hydrogen generation. Angew Chem Int Ed 2012;51:6753e6. [3] Javadian P, Sheppard DA, Buckley CE, Jensen TR. Hydrogen storage properties of nanoconfined LiBH4-Ca(BH4)2. Nano Energy 2015;11:96e103. [4] Huang Z, Eagles M, Porter S, Sorte EG, Billet B, Corey RL, et al. Thermolysis and solid state NMR studies of NaB3H8, NH3B3H7, and NH4B3H8. Dalton T 2013;42:701e8. [5] Lu J, Choi YJ, Fang ZZ, Sohn HY, Ronnebro E. Hydrogen storage properties of nanosized MgH2-0.1TiH2 prepared by ultrahigh-energy-high-pressure milling. J Am Chem Soc 2009;131:15843e52. [6] Wang JC, Du Y, Sun LX, Li XH. Effects of F and Cl on the stability of MgH2. Int J Hydrogen Energy 2014;39:877e83. [7] Aguey-Zinsou KF, Ares-Fernandez JR. Hydrogen in magnesium: new perspectives toward functional stores. Energy Environ Sci 2010;3:526e43. [8] Jeon KJ, Moon HR, Ruminski AM, Jiang B, Kisielowski C, Bardhan R, et al. Air-stable magnesium nanocomposites provide rapid and high-capacity hydrogen storage without using heavy-metal catalysts. Nat Mater 2011;10:286e90. [9] Konarova M, Tanksale A, Beltramini JN, Lu GQ. Effects of nano-confinement on the hydrogen desorption properties of MgH2. Nano Energy 2013;2:98e104. [10] Liu W, Aguey-Zinsou KF. Size effects and hydrogen storage properties of Mg nanoparticles synthesised by an electroless reduction method. J Mater Chem A 2014;2:9718e26. [11] Liu Y, Zou J, Zeng X, Ding W. Study on hydrogen storage properties of Mg-X (X¼Fe, V, Co) nano-composites coprecipitated from solution. RSC Adv 2014;5:7687e96. [12] Liu Y, Zou J, Zeng X, Wu X, Li D, Ding W. Hydrogen storage properties of a Mg-Ni nanocomposite coprecipitated from solution. J Phys Chem C 2014;118:18401e11. [13] Norberg NS, Arthur TS, Fredrick SJ, Prieto AL. Size-dependent hydrogen storage properties of Mg nanocrystals prepared from solution. J Am Chem Soc 2011;133:10679e81. [14] Xia G, Tan Y, Chen X, Sun D, Guo Z, Liu H, et al. Monodisperse magnesium hydride nanoparticles uniformly self-assembled on graphene. Adv Mater 2015;27:5981e8. [15] Zhang S, Gross AF, Van Atta SL, Lopez M, Liu P, Ahn CC, et al. The synthesis and hydrogen storage properties of a MgH2 incorporated carbon aerogel scaffold. Nanotechnology 2009;20. [16] Bhatnagar A, Pandey SK, Vishwakarma AK, Singh S, Shukla V, Soni PK, et al. Fe3O4@graphene as a superior catalyst for hydrogen de/absorption from/in MgH2/Mg. J Mater Chem A 2016;4:14761e72. [17] Halim Yap FA, Mustafa NS, Ismail M. A study on the effects of K2ZrF6 as an additive on the microstructure and hydrogen storage properties of MgH2. RSC Adv 2015;5:9255e60. [18] House SD, Vajo JJ, Ren C, Rockett AA, Robertson IM. Effect of ball-milling duration and dehydrogenation on the morphology, microstructure and catalyst dispersion in Nicatalyzed MgH2 hydrogen storage materials. Acta Mater 2015;86:55e68. [19] Shahi RR, Bhatnagar A, Pandey SK, Dixit V, Srivastava ON. Effects of Ti-based catalysts and synergistic effect of SWCNTs-TiF3 on hydrogen uptake and release from MgH2. Int J Hydrogen Energy 2014;39:14255e61.
[20] Zhang LT, Xiao XZ, Xu CC, Zheng JG, Fan XL, Shao J, et al. Remarkably improved hydrogen storage performance of MgH2 catalyzed by multivalence NbHx nanoparticles. J Phys Chem C 2015;119:8554e62. [21] Wang K, Kang X, Zhong Y, Hu C, Wang P. Improved reversible dehydrogenation properties of 2LiBH4-MgH2 composite by milling with graphitic carbon nitride. Int J Hydrogen Energy 2014;39:13369e74. [22] Mustafa NS, Ismail M. Enhanced hydrogen storage properties of 4MgH2þLiAlH4 composite system by doping with Fe2O3 nanopowder. Int J Hydrogen Energy 2014;39:7834e41. [23] Xueping Z, Guo X, Qiuhua M, Shenglin L, Tao L, Xin F, et al. Hydrogen release capacity of the LiAlH4-MgH2 system. J Power Sources 2013;231:173e6. [24] Ismail M. The hydrogen storage properties of destabilized MgH2-AlH3(2:1) system. Mater Today Proc 2016;3:S80e7. [25] Liu HZ, Wang XH, Liu YG, Dong ZH, Li SQ, Ge HW, et al. Microstructures and hydrogen desorption properties of the MgH2-AlH3 composite with NbF5 addition. J Phys Chem C 2014;118:18908e16. [26] Sirsch P, Che FN, Titah JT, McGrady GS. Hydride-hydride bonding interactions in the hydrogen storage materials AlH3, MgH2, and NaAlH4. Chem Eur J 2012;18:9476e80. [27] Puszkiel JA, Arneodo Larochette P, Gennari FC. Thermodynamic-kinetic characterization of the synthesized Mg2FeH6-MgH2 hydrides mixture. Int J Hydrogen Energy 2008;33:3555e60. [28] Wang J, Han S, Wang Z, Ke D, Liu J, Ma M. Enhanced hydrogen storage properties of the 2LiBH4-MgH2 composite with BaTiO3 as an additive. Dalton T 2016;45:7042e8. [29] Kwak YJ, Park HR, Song MY. Changes in microstructure, phases, and hydrogen storage characteristics of metal hydroborate and nickel-added magnesium hydride with hydrogen absorption and release reactions. Int J Hydrogen Energy 2017;42:1018e26. [30] Liu G, Wang KF, Li JP, Wang YJ, Yuan HT. Enhancement of hydrogen desorption in magnesium hydride catalyzed by graphene nanosheets supported Ni-CeOx hybrid nanocatalyst. Int J Hydrogen Energy 2016;41:10786e94. [31] Mustafa NS, Ismail M. Hydrogen sorption improvement of MgH2 catalyzed by CeO2 nanopowder. J Alloy Compd 2017;695:2532e8. [32] Sulaiman NN, Ismail M. Enhanced hydrogen storage properties of MgH2 co-catalyzed with K2NiF6 and CNTs. Dalton T 2016;45:19380e8. [33] Cabo M, Garroni S, Pellicer E, Milanese C, Girella A, Marini A, et al. Hydrogen sorption performance of MgH2 doped with mesoporous nickel- and cobalt-based oxides. Int J Hydrogen Energy 2011;36:5400e10. [34] Mao J, Guo Z, Yu X, Liu H, Wu Z, Ni J. Enhanced hydrogen sorption properties of Ni and Co-catalyzed MgH2. Int J Hydrogen Energy 2010;35:4569e75. [35] Xie XB, Ma XJ, Liu P, Shang JX, Li XG, Liu T. Formation of multiple-phase catalysts for the hydrogen storage of Mg nanoparticles by adding flowerlike NiS. ACS Appl Mater Interfaces 2017;9:5937e46. [36] Liu G, Qiu FY, Li J, Wang YJ, Li L, Yan C, et al. NiB nanoparticles: a new nickel-based catalyst for hydrogen storage properties of MgH2. Int J Hydrogen Energy 2012;37:17111e7. [37] Zhang QY, Xu YN, Wang Y, Zhang H, Wang YJ, Jiao LF, et al. Enhanced hydrogen storage performance of MgH2-Ni2P/ graphene nanosheets. Int J Hydrogen Energy 2016;41:17000e7. [38] Zhang QY, Wang Y, Zang L, Chang X, Jiao L, Yuan H, et al. Core-shell Ni3N@nitrogen-doped carbon: synthesis and application in MgH2. J Alloy Compd 2017;703:381e8.
Please cite this article in press as: Zhang Q, et al., Improved hydrogen storage properties of MgH2 with Ni-based compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.220
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e9
[39] Chen JG. Carbide and nitride overlayers on early transition metal surfaces: preparation, characterization, and reactivities. Chem Rev 1996;96:1477e98. [40] Oyama ST. Crystal structure and chemical reactivity of transition metal carbides and nitrides. J Solid State Chem 1992;96:442e5. [41] Schaefer ZL, Weeber KM, Misra R, Schiffer P, Schaak RE. Bridging hcp-Ni and Ni3C via a Ni3C1-x solid solution: tunable composition and magnetism in colloidal nickel carbide nanoparticles. Chem Mater 2011;23:2475e80. [42] Kucernak ARJ, Sundaram VNN. Nickel phosphide: the effect of phosphorus content on hydrogen evolution activity and corrosion resistance in acidic medium. J Mater Chem A 2014;2:17435e45. [43] Pan Y, Liu Y, Zhao J, Yang K, Liang J, Liu D, et al. Monodispersed nickel phosphide nanocrystals with different phases: synthesis, characterization and electrocatalytic properties for hydrogen evolution. J Mater Chem A 2015;3:1656e65. [44] Shalom M, Ressnig D, Yang XF, Clavel G, Fellinger TP, Antonietti M. Nickel nitride as an efficient electrocatalyst for water splitting. J Mater Chem A 2015;3:8171e7. [45] Shalom M, Molinari V, Esposito D, Clavel G, Ressnig D, Giordano C, et al. Sponge-like nickel and nickel nitride
[46]
[47]
[48] [49]
[50]
[51]
9
structures for catalytic applications. Adv Mater 2014;26:1272e6. Chiang RT, Chiang RK, Shieu FS. Emergence of interstitialatom-free HCP nickel phase during the thermal decomposition of Ni3C nanoparticles. RSC Adv 2014;4:19488e94. Fouladgar M, Karimi-Maleh H, Gupta VK. Highly sensitive voltammetric sensor based on NiO nanoparticle room temperature ionic liquid modified carbon paste electrode for levodopa analysis. J Mol Liq 2015;208:78e83. Patterson AL. The Scherrer formula for X-ray particle size determination. Phys Rev 1939;56:978e87. Sulaiman NN, Juahir N, Mustafa NS, Halim Yap FA, Ismail M. Improved hydrogen storage properties of MgH2 catalyzed with K2NiF6. J Energy Chem 2016;5:832e9. Lototskyy M, Sibanyoni JM, Denys RV, Williams M, Pollet BG, Yartys VA. Magnesium-carbon hydrogen storage hybrid materials produced by reactive ball milling in hydrogen. Carbon 2013;57:146e60. Cui J, Liu JW, Wang H, Ouyang LZ, Sun DL, Zhu M, et al. MgTM (TM: Ti, Nb, V, Co, Mo or Ni) core-shell like nanostructures: synthesis, hydrogen storage performance and catalytic mechanism. J Mater Chem A 2014;2:9645e55.
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