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Facile Synthesis of Carbon Supported Nano-Ni Particles with Superior Catalytic Effect on Hydrogen Storage Kinetics of MgH2 Zhongliang Ma, Jiguang Zhang, Yunfeng Zhu, Huaijun Lin, Yana Liu, Yao Zhang, Delong Zhu, and Liquan Li ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.7b00266 • Publication Date (Web): 28 Feb 2018 Downloaded from http://pubs.acs.org on March 1, 2018
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ACS Applied Energy Materials
Facile Synthesis of Carbon Supported Nano-Ni Particles with Superior Catalytic Effect on Hydrogen Storage Kinetics of MgH2 Zhongliang Maa,b, Jiguang Zhanga,b, Yunfeng Zhua,b*, Huaijun Linc, Yana Liua,b, Yao Zhangb,d, Delong Zhua,b, Liquan Lia,b*
a
College of Materials Science and Engineering, Nanjing Tech University, 5 Xinmofan Road,
Nanjing 210009, PR China b
Jiangsu Collaborative Innovation Centre for Advanced Inorganic Function Composites,
Nanjing Tech University, Nanjing 210009, PR China c
Institute of Advanced Wear & Corrosion Resistant and Functional Materials, Jinan University,
Guangzhou 510632, PR China d
School of Materials Science and Engineering, Southeast University, Nanjing 211189, PR China
KEYWORDS: Mg hydride; carbon supported nano-Ni; hydrogen storage kinetics; mechanical milling; catalysis.
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ABSTRACT
Metal nano-catalysis is an effective method to enhance the hydrogen storage properties of magnesium hydride (MgH2), and the catalytic effect can be further improved by a matrix materials supported nano-metal. In this work, carbon supported nano-Ni (Ni@C) was synthesized by calcination of dimethylglyoxime dinickel chelate, and then it was doped into MgH2 to improve the de/re-hydrogenation kinetics. It shows that the homogeneously distributed Ni with refined particle size in carbon base leads to superior catalytic effects on hydrogen absorption/desorption of MgH2-5 wt.% Ni@C. The MgH2-5 wt.% Ni@C starts to desorb hydrogen at 187 °C, which is 113 °C lower than that of as-milled MgH2. Moreover, it takes only 500 s to thoroughly desorb hydrogen at 300 °C, which is 3000 s faster than as-milled MgH2 under the same dehydrogenation conditions. According to the Kissinger’s method, the apparent activation energy for desorption of the MgH2-5 wt.% Ni@C is 66.5±1.8 kJ·mol-1, which is about 79.9 kJ·mol-1 lower than that of as-milled MgH2. Cycling experiments show that the capacity retentions of hydrogen absorption and desorption after 10 cycles at 275 °C are 91 % and 93 %, respectively. Transmission electron microscope analysis shows part of Ni transformed to Mg2NiH4/Mg2Ni during hydrogen absorption/desorption cycles.
1. INTRODUCTION Mg-based hydride is widely considered as a promising material to store hydrogen, which is an ideal clean energy to deal with energy crisis, global warming and environmental pollution issues.1-4 MgH2 has been extensively studied due to a high gravimetric hydrogen storage capacity (7.6 wt.%) with excellent reversibility, and abundance of Mg-mineral resources on the earth.5
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ACS Applied Energy Materials
Unfortunately, MgH2 is hardly applied currently because of the sluggish hydrogen absorption and desorption kinetics, and too high hydrogen desorption temperature.6-8 Up to now, several methods, such as alloying,9-14 nanoscaling,15-18 mixing with other components19-24 and catalyzing,25-27 have been used to overcome these drawbacks. Among these strategies, catalyzing is proved to be an effective way to improve the reaction kinetics of MgH2.26-31 Both theoretical calculation and experimental observation have proved that hydrogen desorption kinetics of MgH2 can be remarkably improved by introducing catalysts such as oxides, hydrides and transition metals, etc.25, 32-39 In particular, Ni has been prepared by various strategies and doped into MgH2 to enhance the hydrogen storage properties. Yao et al.40 developed a one-step method to capitalize on the in situ bottom-up reduction of a Ni-MOF-74 precursor in the presence of MgH2 as a reducing and sacrificial agent via mechanic chemical ball milling, and the MgH2-5 wt.% (Ni-MOF-74) composite can absorb 2.7 wt.% hydrogen at room temperatures within 10 h. El-Eskandarany et al.41 proposed a new approach to gradually dope MgH2 powders with Ni particles upon Ni-balls milling media under 5 MPa hydrogen gas atmosphere. The results show that the onset decomposition temperature and dehydrogenation activation energy of MgH2 can be reduced to 218 °C and 75 kJ⋅mol-1. More recent studies indicate that the catalytic effect can be further improved by supporting nano-Ni particles on matrix materials. Lillo-Ródenas et al.42,
43
reported that carbon supported Ni catalysts have
superior catalytic effects on the desorption kinetics of MgH2 than Ni or carbon alone, and discussed the effect of milling time, Ni particles size and temperature on desorption performance of MgH2, respectively. Chen et al.44 studied the role of the carbon in the MgH2-Ni@C composites and discussed the effect of Mg2Ni and Mg2NiH4 during the cycling process, which
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were regarded as the catalytically active species, leading to H dissociation and nucleation of MgH2 easily. In summary, compared with bare nano-Ni, carbon supported nano-Ni catalysts show a better catalytic effect on improving the hydrogen storage properties of MgH2. Therefore, preparing uniformly dispersed and extra-fine Ni-based catalyst with high catalytic activity is of significant value to the application of MgH2. However, it still remains a challenge to synthesize such a kind of catalyst via facile ways. Moreover, it is also necessary to enrich the study of MgH2 catalyzed by different kinds of carbon supported Ni catalysts. In this work, Ni@C was synthesized successfully by a facile method via calcination of dimethylglyoxime dinickel chelate, and then it was doped into MgH2 to improve the de/re-hydrogenation kinetics. The enhanced hydrogen storage performances of the MgH2 catalyzed by Ni@C together with the corresponding mechanism have been investigated in detail.
2. EXPERIMENTAL METHODS 2.1 Syntheses of Ni@C and MgH2-Ni@C composite Chemicals were all obtained commercially and used without any purification. Mg powder (99.7 wt% in purity and
