DALTON TRANSACTIONS
·
2015
·Vol. 44
·期 41
·18012-18018
·
IF 4.197
Yongfeng Liu,Yaxiong Yang,Xin Zhang,You Li,Mingxia Gao,Hongge Pan
The thermal dehydrogenation process of the KOH-containing Mg(NH2)2–2LiH system was systematically investigated by identifying changes in the structure and composition of its components by XRD and FTIR. During ball milling, the added KOH reacts with Mg(NH2)2 and LiH to produce MgO, KH and Li2K(NH2)3. During the initial heating process (<120 °C), the newly formed KH and Li2K(NH2)3 react with Mg(NH2)2 and LiH to yield MgNH, LiNH2 and Li3K(NH2)4 along with hydrogen release. Raising the temperature to 185 °C results in a reaction between Mg(NH2)2, MgNH and LiH that gives Li2Mg2N3H3 as the product and further releases hydrogen. As the temperature is increased to 220 °C, Li2Mg2N3H3 reacts with LiNH2 and LiH to produce Li2MgN2H2 and H2. Meanwhile, two parallel reactions between Li2Mg2N3H3, Li3K(NH2)4 and LiH also generate additional hydrogen. Specifically, the KH and Li2K(NH2)3, formed in situ during ball milling, serve as reactants in the dehydrogenation reaction of the Mg(NH2)2–2LiH system, which is responsible for the significantly improved thermodynamics and kinetics of hydrogen storage.
研究领域:
材料科学
·
化学工程
✓ 已验证
DOI
高影响因子
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY
·
2024
·
IF 11.2
Haoyuan Zheng,Yuxiao Jia,Chen Jin,Hang Che,Chia-TseLee,Guang Liu,Li Wang,Yuyuan Zhao,Shixuan He,Haizhen Liu,Xinhua Wang,Yifeng Yu,Mi Yan
The magnesium based metal hydrogen storage composite system Mg(NH 2 ) 2 -2LiH has a theoretical hydrogen storage capacity of 5.6 wt.% and is a promising hydrogen storage material for vehicles. However, its application is limited due to serious thermodynamic and kinetic barriers. Introducing efficient catalysts is an effective method to improve the hydrogen storage performance of Mg(NH 2 ) 2 -2LiH. This article investigates for the first time the use of nano rare earth oxide CeO 2 (∼44.5 nm) as an efficient modifier, achieving comprehensive regulation of the hydrogen storage performance of Mg(NH 2 ) 2 -2LiH composite system through oxygen vacancy driven catalysis. The modification mechanism of nano CeO 2 is also systematically studied using density functional theory (DFT) calculations and experimental results. Research has shown that the comprehensive hydrogen storage performance of the Mg(NH 2 ) 2 -2LiH-5 wt.% CeO 2 composite system is optimal, with high hydrogen absorption and desorption kinetics and reversible performance. The initial hydrogen absorption and desorption temperatures of the composite system were significantly reduced from 110/130°C to 65/80°C, and the release of by-product ammonia was significantly inhibited. Under the conditions of 170°C/50 min and 180°C/100 min, 4.37 wt.% of hydrogen can be rapidly absorbed and released. After 10 cycles of hydrogen release, the hydrogen cycle retention rate increased from 85% to nearly 100%. Further mechanistic studies have shown that the nano CeO 2− x generated in situ during hydrogen evolution can effectively weaken the Mg–N and N–H bonds of Mg(NH 2 ) 2 , exhibiting good catalytic effects. Meanwhile, oxygen vacancies provide a fast pathway for the diffusion of hydrogen atoms in the composite system. In addition, nano CeO 2− x can effectively inhibit the polycrystalline transformation of the hydrogen evolving product Li 2 MgN 2 H 2 in the system at high temperatures, reducing the difficulty of re-hydrogenation of the system. This study provides an innovative perspective for the efficient modification of magnesium based metal hydrogen storage composite materials using rare earth based catalysts, and also provides a reference for regulating the comprehensive hydrogen storage performance of hydrogen storage materials using rare earth catalysts with oxygen vacancies.
研究领域:
材料科学
·
催化
·
氢气存储
·
纳米技术
✓ 已验证
DOI
高影响因子
JOURNAL OF RARE EARTHS
·
2024
·
IF 5.2
Haoyuan Zheng,Yuxiao Jia,Chen Jin,Hang Che,Chia-Tse Lee,Zhenke Chen,Guang Liu,Li Wang,Shixuan He,Xinhua Wang,Haizhen Liu,Mi Yan
The Mg(NH 2 ) 2 -2LiH composite system is a promising vehicle-mounted hydrogen storage material, but its application is limited due to serious thermodynamic and kinetic barriers. Adding additives can effectively optimize their hydrogen absorption and desorption kinetics and thermodynamic performance. In this work the comprehensive hydrogen storage performance of Mg(NH 2 ) 2 -2LiH with extremely small nano rare earth borides is improved, and a series of characterization methods and density functional theory (DFT) calculation systems was combined to study its hydrogen storage improvement mechanism. The research results show that the method of adding 5 wt% molten salt to prepare nano CeB 6 (24.5 nm) can significantly reduce the initial hydrogen absorption/release temperature of Mg(NH 2 ) 2 -2LiH from 110/130 to 45/90 °C, inhibit the generation of ammonia by-products, and improve hydrogen purity. Under low-temperature hydrogen absorption conditions at 120 °C, the improved sample can absorb 2.81 wt% hydrogen gas, with a hydrogen absorption capacity more than 3.5 times of the unmodified sample. The amount of hydrogen released at 150 °C reaches 3.35 wt%, which is more than twice that of the pristine sample, demonstrating excellent hydrogen absorption and release kinetics performance. After 10 consecutive hydrogen cycles, 4.64 wt% hydrogen can still be released, and the cycle retention rate can be increased from 85% before improvement to nearly 100%, demonstrating good reversibility. Mechanism studies show that nano CeB 6 can effectively weaken the Mg–N and N–H bonds of Mg(NH 2 ) 2 and inhibit the polycrystalline transformation of the hydrogen evolution product Li 2 MgN 2 H 2 at high temperatures. It can also provide nucleation active sites for hydrogen absorption and desorption in the material, making the system possess superior hydrogen absorption and desorption performance and cycling stability. This study provides new insights into the role of rare earth borides in Mg(NH 2 ) 2 -2LiH hydrogen storage materials, both experimentally and theoretically.
研究领域:
材料科学
·
化学工程
·
物理化学
·
理论化学
✓ 已验证
DOI
高影响因子
Journal of Physical Chemistry C
·
2013
·
IF 4.814
Yongfeng Liu,Chao Li,Bo Li,Mingxia Gao,Hongge Pan
The hydrogen storage properties and mechanisms of the Mg(NH2)2–2LiH system with potassium halides (KF, KCl, KBr, and KI) were investigated and discussed. The results show that the KF-added sample exhibits superior hydrogen storage properties as ∼5.0 wt % of hydrogen can be reversibly stored in the 0.08KF-added sample via a two-stage reaction with an onset dehydrogenation temperature of 80 °C. However, hydrogen storage behaviors of the samples with KCl, KBr, and KI remain almost unchanged. The fact that KF can readily react with LiH to convert to KH and LiF due to the favorable thermodynamics during ball milling should be the primary reason for its significant effects, as the presence of KH provides a synergetic thermodynamic and kinetic destabilization in the hydrogen storage reaction of the Mg(NH2)2–2LiH system by declining the activation energy of the first-step dehydrogenation as a catalyst and reducing the desorption enthalpy change of the second step as a reactant. The understanding on the role played by KF sheds light on how to further decrease the operating temperature and enhance the hydrogen storage kinetics of the metal–N–H system.
研究领域:
材料科学
·
化学工程
✓ 已验证
产品关联
DOI
高影响因子
危险品化学品经营许可证（带存储）