Dehydrogenation characteristics of Ti- and Ni/Ti-catalyzed Mg hydrides

doi:10.1016/j.jallcom.2009.02.125

Journal of Alloys and Compounds

Volume 481, Issues 1–2, 29 July 2009, Pages 152-155

https://doi.org/10.1016/j.jallcom.2009.02.125 Get rights and content

Abstract

The desorption capacity, thermodynamics, and kinetics of Ti- and Ni/Ti-catalyzed Mg hydrides were investigated using Sievert-type apparatus and differential scanning calorimetry. Based on analysis of the van’t Hoff equation and the Kissinger equation, the addition of Ti and Ni as catalysts has been found to play a key role in improving the thermodynamic and kinetic properties of MgH₂ by decreasing the desorption temperature and the activation energy. A combination of Ti and Ni is a more effective catalyst than either Ti or Ni alone, suggesting the existence of a synergetic effect.

Introduction

The increasing demand for “clean” energy sources has drawn attention to the prospects for a “Hydrogen Economy”, in which hydrogen is used as the main energy carrier to provide a long-term solution to a sustainable future as well as energy security [1]. Being a gas, however, hydrogen faces great challenges in terms of practical storage, especially in on-board storage systems for hydrogen-powered vehicles. A suitable material for hydrogen storage is one of the key requirements for any future hydrogen economy. The MgH₂ system is one of the most promising metal hydrides because it can store hydrogen reversibly up to 7.6 wt.% and has a high volumetric hydrogen density of 106 kg H₂/m³. Furthermore, magnesium is abundant and inexpensive.

However, the use of magnesium as a practical storage material is hindered by its slow sorption kinetics. It has been previously demonstrated that additives can significantly improve the reaction kinetics, which enables hydrogen to be desorbed at temperatures far below 300 °C [2], [3], [4], [5]. Among the additives used in different studies, the catalytic effect of Ti and Ni alone [3] and the transition-metal compounds show high potential [6], [7]. However, in the ball-milled Ti-catalyzed MgH₂ system, the addition of Ti does not change the thermodynamic properties of MgH₂, despite a significant reduction in the activation energy of hydrogen desorption [3]. Catalysts consisting of mixed transition metals were found to have synergetic catalytic effects which significantly improved the hydrogen dissociation and diffusion characteristics in nanostructured magnesium [8], [9]. Moreover, Ni element is effective in promoting the hydrogenation kinetics of Mg-based alloys [3] and often plays a vital catalytic role in Ti-based alloy electrodes during electrochemical reactions [10]. The Mg–Ni–Ti ternary alloys have also been studied as hydrogen storage electrodes using electrochemical method [11]. However, only few studies have been carried out about synergetic catalytic effects of Ni and Ti elements on Mg hydride, especially using van’t Hoff equation and the Kissinger equation. Furthermore, the storage capacity, kinetics, and desorption temperature are the most important parameters for the application of hydrides as hydrogen storage materials [12]. The desorption behavior is more important than the absorption behavior because a material can only be regarded as a suitable hydrogen storage material if it has favorable hydrogen desorption characteristics [12].

In this work, the storage capacity, thermodynamics, and kinetics of the hydrogen desorption performance of nanocrystalline Mg hydrides catalyzed by Ti element alone and the combination of Ni and Ti elements have been studied using Sievert-type apparatus and differential scanning calorimetry (DSC).

Section snippets

Experimental

The elemental powders with high purity (>99 wt.%) from Sigma–Aldrich were used for the experiments. The following ratios were used for the catalyzed Mg hydrides: MgH₂–x at.% Ti (x = 1 and 5) and MgH₂–Ni/Ti (Ni:Ti = 1:1 in molar ratio, with 16.7 at.% Ni, and Ni:Ti = 4:1, with 26.7 at.% Ni). The samples were prepared by ball milling under hydrogen atmosphere at an initial pressure of about 7 atm for 35 h. The ball-milling equipment was a magnetically controlled Uni-Ball-Mill with a rotational speed of 60 rpm.

Results and discussion

The grain size after ball milling is important for an understanding of hydrogen sorption behavior. As shown previously [2], [13], the catalyst in the nanoscale is very essential for improving the kinetics of hydrogen sorption. The nanostructured alloys reveal improved hydrogen storage properties, mainly due to the large volume fraction of the grain-boundary regions. The mean grain size of the as-received magnesium particles was found to be about 10 μm, and it was reduced to 15 nm after the

Conclusion

In summary, the Ti and Ni/Ti additives significantly improved the desorption performance of MgH₂ in terms of desorption temperature and activation energy, i.e. being able to release 80% of its hydrogen content within 30 s. The sample with Ni:Ti (4:1 ratio) had the best hydrogen desorption performance. Work based on first-principle calculations is currently underway to study the Ni–Ti catalysis system in view of its importance and the seemingly intriguing synergetic effect.

Acknowledgements

Dr. H.B. Lu and C.K. Poh have made equal contributions to this work. We are grateful to Dr. David Wexler for his technical assistance and to Dr. Tania Silver for her proof reading of the manuscript. The research was financially supported by the Commonwealth Scientific & Industrial Research Organisation (CSIRO) National Hydrogen Materials Alliance and an Australian Research Council (ARC) Discovery project (DP0771193).

Reference (18)

A. Zaluska et al.
J. Alloys Compd.
(1999)
G. Liang et al.
J. Alloys Compd.
(1999)
G. Barkhordarian et al.
J. Alloys Compd.
(2004)
N. Hanada et al.
J. Alloys Compd.
(2004)
G. Barkhordarian et al.
Scripta Mater.
(2003)
X.L. Wang et al.
J. Power Sources
(2006)
H.L. Chu et al.
Int. J. Hydrogen Energy
(2007)
S. Ruggeri et al.
J. Power Sources
(2002)
T. Czujko et al.
J. Alloys Compd.
(2006)

There are more references available in the full text version of this article.

Cited by (59)

Progress and prospects of Mg-based amorphous alloys in azo dye wastewater treatment
2024, Journal of Magnesium and Alloys
Mg-based amorphous alloys exhibit efficient catalytic performance and excellent biocompatibility with a promising application probability, specifically in the field of azo dye wastewater degradation. However, the problems like difficulty in preparation and poor cycling stability need to be solved. At present, Mg-based amorphous alloys applied in wastewater degradation are available in powder and ribbon. The amorphous alloy powder fabricated by ball milling has a high specific surface area, and its reactivity is thousands of times better than that of gas atomized alloy powder. But the development is limited due to the high energy consumption, difficult and costly process of powder recycling. The single roller melt-spinning method is a new manufacturing process of amorphous alloy ribbon. Compared to amorphous powder, the specific surface area of amorphous ribbon is relatively lower, therefore, it is necessary to carry out surface modification to enhance it. Dealloying is a way that can form a pore structure on the surface of the amorphous alloys, increasing the specific surface area and providing more reactive sites, which all contribute to the catalytic performance. Exploring the optimal conditions for Mg-based amorphous alloys in wastewater degradation by adjusting amorphous alloy composition, choosing suitable method to preparation and surface modification, reducing cost, expanding the pH range will advance the steps to put Mg-based amorphous alloys in industrial environments into practice.
Processing, production and anticorrosion behavior of metallic glasses: A critical review
2023, Journal of Non-Crystalline Solids
Metallic glass (MG), a new type of multi-component alloy with unique disordered atomic stacking structure, has gradually been recognized as a promising anticorrosive material for engineering applications. The present review focuses on the current studies and developments concerning corrosion resistant MGs, and puts forward valuable suggestions for subsequent researches. The review discusses the commonly used processing approaches of MG products in different forms (glassy bulk materials or ribbons and coatings) with their respective characteristics, exemplifies the applications of anticorrosive MGs with different protection mechanisms, and summarizes the influencing factors on their anticorrosion performance such as amorphous structure, partial crystallization and composition. Although MGs have made great progress in the field of corrosion protection presently, there exist challenges in terms of using them, which mainly lies in the issues that how to ensure service stability, optimize structure and improve the relation between cost and benefit. Herein, future prospects and possible enhancement in the performance of MGs for corrosion protection are explored at the end of this paper. We expect that this review provides new ideas for the future development of MGs, and can exert viable strengths for actual corrosion protection applications in different situations.
The rare earth doped Mg<inf>2</inf>Ni (0 1 0) surface enhances hydrogen storage
2023, Applied Surface Science
Rare earth doping has been proved to be an effective method to improve hydrogen storage properties of Mg-based alloys. In this work, the effect of rare earth (Y, Ce, La, Sc) doping on the thermal stability, electronic property and hydrogen adsorption/desorption behavior of Mg₂Ni (0 1 0) surface are systematically investigated by first principles calculation. The results show that rare earth doping in Mg₂Ni (0 1 0) surface are thermodynamic feasible. The calculated electronic structures shown that rare earth atoms weaken the binding strength between H and Mg₂Ni (0 1 0) substrate, thus reduce the hydrogen diffusion and desorption energies barriers, and improve the hydrogen storage properties of Mg₂Ni. Among the four rare earth elements, Ce shows the best potential. Notably, the substitution doping of Ce to Mg atom significantly reduces the H diffusion barrier by 0.32 eV and H₂ desorption barrier by 1.0 eV. This discovery provides a direction for the preparation of rare earth doped Mg₂Ni hydrogen storage materials.
Effects of transition metal Ti and its compounds on hydrogen adsorption performance of Mg17Al12
2022, International Journal of Hydrogen Energy
Catalytic effects of Ti, Ti_n (n = 2–4), TiC, and TiO₂ clusters on hydrogenation of the Mg17Al12(110) surface were investigated by using density functional theory. The geometry structure, adsorption energy, dissociation barrier, density of state, electron density, and electron density difference were calculated. As a result, the adsorption energy and dissociation barrier of hydrogen on the Ti-containing Mg17Al12(110) surfaces were effectively improved as compared with the clean Mg17Al12(110) surface. Such as the adsorption energy of H(H2) on the Mg17Al12(110) surface was −0.18 (−0.13) eV, while the related energy of H(H2) on the Mg17Al12(110)/TiO2 system was −1.50 (−1.22) eV. In addition, H2 molecules could be spontaneously dissociated to H atoms on the Mg15Ti2Al12(110), Mg17Al12(110)/Ti3, and Mg17Al12(110)/TiO2 surfaces. The results of electronic structures indicated that the H s states principally hybridized with the Ti s and d states. The mechanism of Ti, Ti_n (n = 2–4), TiC, and TiO2 clusters on the promoted hydrogenation of Mg17Al12 was explained.
Enhancing hydrogen storage performance via optimizing Y and Ni element in magnesium alloy
2022, Journal of Magnesium and Alloys
Magnesium-based hydrogen storage materials are considered as one of the most promising candidates for solid state hydrogen storage due to their advantages of high hydrogen capacity, excellent reversibility and low cost. In this paper, Mg_91.4Ni₇Y_1.6 and Mg_92.8Ni_2.4Y_4.8 alloys were prepared by melting and ball milling. Their microstructures and phases were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope, and hydrogen absorbing and desorbing properties were tested by the high pressure gas adsorption apparatus and differential scanning calorimetry (DSC). In order to estimate the activation energy and growth mechanism of alloy hydride, the JMAK, Arrhenius and Kissinger methods were applied for calculation. The hydrogen absorption content of Mg_92.8Ni_2.4Y_4.8 alloy reaches 3.84 wt.% within 5 min under 350 ℃, 3 MPa, and the maximum hydrogen capacity of the alloy is 4.89 wt.% in same condition. However, the hydrogen absorption of Mg_91.4Ni₇Y_1.6 alloy reaches 5.78 wt.% within 5 min, and the maximum hydrogen absorption of the alloy is 6.44 wt.% at 350 ℃ and 3 MPa. The hydrogenation activation energy of Mg_91.4Ni₇Y_1.6 alloy is 25.4 kJ/mol H₂, and the enthalpy and entropy of hydrogen absorption are -60.6 kJ/mol H₂ and 105.5 J/K/mol H₂, separately. The alloy begins to dehydrogenate at 210 ℃, with the dehydrogenation activation energy of 87.7 kJ/mol H₂. By altering the addition amount of Ni and Y elements, the 14H-LPSO phase with smaller size and ternary eutectic areas with high volume fraction are obtained, which provides more phase boundaries and catalysts with better dispersion, and there are a lot of fine particles in the alloy, these structures are beneficial to enhance the hydrogen storage performance of the alloys.
Effects of adding Nd on the microstructure and dehydrogenation performance of Mg<inf>90</inf>Al<inf>10</inf> alloy
2021, Materials Characterization
Citation Excerpt :
It can be seen from Table 2 that the dehydrogenation platform pressure of the lower platform is 0.2395, 0.1857, 0.2278 and 0.2552 MPa at 613 K and the calculated dehydrogenation enthalpy by means of Van't Hoff equation is 74.44, 82.59, 74.58 and 73.72 kJ/mol H2 for the NdxMg90-xAl10 (x = 2, 5, 8 and 10) alloys, respectively. The ΔHde value of the Nd-2 alloy is slightly smaller than that of pure Mg (76.00–78.00 kJ/mol H2) [18,21,28]. One reason is that Al atoms with smaller atomic radius dissolve into Mg unit cell, which causes the lattice volume of Mg to decrease and the platform pressure of forming MgH2 to rise [22].
In order to reduce the thermodynamic stability and improve the dehydrogenation kinetics of Mg hydride, a certain quantity of Nd was introduced into Mg₉₀Al₁₀ alloy to prepare the Nd_xMg_90-xAl₁₀ (x = 2, 5, 8 and 10) alloys. The phase composition and distribution of the alloys identified by X-ray diffraction and scanning electron microscopy showed that there generated hydrogenation phases of Mg(Nd), Mg₁₂Nd and Mg₃Nd with increasing Nd content, which formed MgH₂ and NdH₃ phases during the hydrogenation through disproportionation reactions. The crystalline structure characterized by transmission electron microscopy showed that the grain size of the alloys decreases gradually with increasing Nd content after repeated hydrogenation cycles. The changes of phase composition and microstructure have significant improvement effect on the activation performance and dehydrogenation kinetics. However, Mg hydride in the alloys exhibited different thermodynamic stability. The dehydrogenation enthalpy (ΔH_de) was 74.44, 82.59, 74.58 and 73.72 kJ/mol H₂ for the Nd_xMg_90-xAl₁₀ (x = 2, 5, 8 and 10) alloys, respectively. Mechanism analysis showed that the existence of Mg(Nd) phase was the root cause of the increase of ΔH_de for the Nd-5 alloy. For the Nd-8 and Nd-10 alloys, the formed Nd₂H₅ phase lowered the thermodynamic stability of MgH₂ through causing the lattice deformation of Mg phase.

View all citing articles on Scopus

View full text

Dehydrogenation characteristics of Ti- and Ni/Ti-catalyzed Mg hydrides

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgements

J. Alloys Compd.

J. Alloys Compd.

J. Alloys Compd.

J. Alloys Compd.

Scripta Mater.

J. Power Sources

Int. J. Hydrogen Energy

J. Power Sources

J. Alloys Compd.