Mg2FeH6 doped with and without Ti and its alloys (TiMn2, TiAl) were prepared combing ball milling and heat treatment. The effects of these additives on the dehydrogenation performance of Mg2FeH6 were studied systemati...Mg2FeH6 doped with and without Ti and its alloys (TiMn2, TiAl) were prepared combing ball milling and heat treatment. The effects of these additives on the dehydrogenation performance of Mg2FeH6 were studied systematically. The results show that all additives have favor influence on improving the hydrogen desorption property of Mg2FeH6. Especially, TiMn2 exhibits prominent effect on enhancing the dehydrogenation kinetics of Mg2FeH6. Moreover, the activation energy of TiMn2-doped Mg2FeH6 calculated by Kissinger equation is 94.87 kJ/mol, which is 28 kJ/mol lower than that of the undoped Mg2FeH6. The cycling tests suggest that the improved dehydrogenation kinetics of Mg2FeH6 doped by TiMn2 can maintain in the second cycle.展开更多
Using the plane wave ultrasoft pseudopotential method based on the first-principles density functional theory(DFT),the influence on the electronic structure and dehydrogenation properties of VH2 doped with Zr,Cu and Z...Using the plane wave ultrasoft pseudopotential method based on the first-principles density functional theory(DFT),the influence on the electronic structure and dehydrogenation properties of VH2 doped with Zr,Cu and Zn has been studied.The results show that the negative heat of formation increases and the valence electron number at the Fermi level EF,N(EF) decreases in the Zr-doped model,indicating the higher stability of VH2 after Zr alloying.On the other hand,the negative heat of formation of VH2 decreases and the N(EF) increases in Cu-or Zn-doped systems,suggesting the lower stability of VH2 after Cu or Zn alloying.The calculated overlap populations and electron densities of the V-H bond demonstrate that the bonding is strengthened by Zr doping and weakened by Cu or Zn doping.The results predict that the maximum capacity to absorb and desorb hydrogen can be raised by the introduction of Zr and reduced by the introduction of Cu or Zn,while the dehydrogenation properties will be poorer in Zr-doped systems and enhanced in Cu-or Zn-doped systems.These predictions are consistent with the experimental results.Mulliken populations were also calculated and it was found that the Mulliken population of the V 3d orbitals decreased as a result of Zr doping,and increased after Cu or Zn doping.展开更多
The catalytic hydrogenation of magnesium under atmospheric pressure has been optimized so that the reaction can be completed within seven hours.The resulted magnesium hydride is in the form of superfine powder with an...The catalytic hydrogenation of magnesium under atmospheric pressure has been optimized so that the reaction can be completed within seven hours.The resulted magnesium hydride is in the form of superfine powder with an average primary particle size of 15 nm.This magnesium hydride exhibits higher dehydrogenation/hydrogenation rates than that obtained under pressure with the same catalyst system.展开更多
Uniform-uispersed Ni nanoparticics(NPs)anchored on reduced graphene oxide(Ni@rGO)catalyzed MgH2(MH-Ni@rGO)has been fabricated by mechanical milling.The effects of milling time and Ni loading amount on the hydrogen sto...Uniform-uispersed Ni nanoparticics(NPs)anchored on reduced graphene oxide(Ni@rGO)catalyzed MgH2(MH-Ni@rGO)has been fabricated by mechanical milling.The effects of milling time and Ni loading amount on the hydrogen storage properties of MgH2 have been investigated.The initial hydrogen desorption temperature of MgH2 catalyzed by 10 wt.%Ni4@rGO6 for milling 5 h is significantly decreased from 251℃ to 190℃.The composite can absorb 5.0 wt.%hydrogen in 20 min at 100℃,while it can desorb 6.1 wt.%within 15 min at 300℃.Through the investigation of the phase transformation and dehydrogenation kinetics during hydrogen ab/desorption cycles,we found that the in-situ formed Mg2Ni/Mg2NiH4 exhibited better catalytic effect than Ni.When Ni loading amount is 45 wt.%,the rGO in Ni@rGO catalysts can prevent the reaction of Ni and Mg due to the strong interaction between rGO and Ni NPs.展开更多
A first-principles study was reported based on density functional theory of hydrogen vacancy,metal dopants,metal dopant-vacancy complex in LiBH4,a promising material for hydrogen storage.The formation of H vacancy and...A first-principles study was reported based on density functional theory of hydrogen vacancy,metal dopants,metal dopant-vacancy complex in LiBH4,a promising material for hydrogen storage.The formation of H vacancy and metal doping in LiBH4 is difficult,and their concentrations are low.The presence of one kind of defect is helpful to the formation of other kind of defect.Based on the analysis of electronic structure,the improvement of the dehydrogenating kinetics of LiBH4 by metal catalysts is due to the weaker bonding of B—H and the new metal-like system,which makes H atom diffuse easily;H vacancy accounts for a trace amount of BH3 release during the decomposing process of LiBH4;metal dopant weakens the strength of B—H bonds,which reduces the dehydriding temperature of LiBH4.The roles of metal and vacancy in the metal dopant-vacancy complex can be added in LiBH4 system.展开更多
The effects of NaA1H4, TiF3 and NaA1H4-TiF3 co-additive on dehydriding reaction of Mg（A1H4）2 are systematically investigated. The on- set dehydrogenation temperature of the co-doped Mg（A1H4）2 composites decreased ...The effects of NaA1H4, TiF3 and NaA1H4-TiF3 co-additive on dehydriding reaction of Mg（A1H4）2 are systematically investigated. The on- set dehydrogenation temperature of the co-doped Mg（A1H4）2 composites decreased to 74 ℃, which is about 59 ℃ lower than that of pure Mg（A1H4）2. The dehydrogenation kinetics of NaA1H4-TiF3 co-doped Mg（A1H4）2 sample was also improved, which released about 94% hydrogen within 48 min, but no visible hydrogen was released from pure Mg（A1H4）2 under the same conditions. The activation energy of co-doped Mg（A1H4）2 was 85.6 kJ.mol-t, which was significantly lower than that of additive-free Mg（A1H4）2 sample. The synergetic effects of NaA1H4 and TiF3 on the dehydrogenation performance of Mg（A1H4）2 were confirmed. In addition, a possible catalytic mechanism is discussed, regarding the different roles of NaA1H4 and TiF3 on Mg（A1H4）2.展开更多
First-principles calculations were used to study the energetics and electronic structures of Ni and Sc co-doped MgH<sub>2</sub> system. The preferential positions for dopants were determined by the minimal...First-principles calculations were used to study the energetics and electronic structures of Ni and Sc co-doped MgH<sub>2</sub> system. The preferential positions for dopants were determined by the minimal total electronic energy. The results of formation enthalpy indicate that Ni and Sc co-doped MgH<sub>2</sub> system is more stable than Ni single-doped system. The hydrogen desorption enthalpies of these two hydrides are investigated. Ni and Sc co-doping can improve the dehydrogenation properties of MgH<sub>2</sub>. The lowest hydrogen desorption enthalpy of 0.30 eV appears in co-doped system, which is significantly lower than that of Ni doping. The electronic structure analysis illustrates that the hybridization of dopants with Mg and H atom together weakens the Mg-H interaction. And the Mg-H bonds are more susceptible to dissociate by Ni and Sc co-doping because of the reduced magnitude of Mg-H hybridization peaks. These behaviors effectively improve the dehydrogenation properties of Ni and Sc co-doped cases.展开更多
This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity vacancy complex in LiNH2, a promising material for hydrogen storage. It f...This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity vacancy complex in LiNH2, a promising material for hydrogen storage. It finds easy formation of H vacancy in the form of impurity-vacancy complex, and the rate-limiting step to the H diffusion. Based on the analysis of the density of states, it finds that the improvement of the dehydrogenating kinetics of LiNH2 by Ti catalysts and Mg substitution is due to the weak bonding of N-H and the new system metal-like, which makes H atom diffuse easily. The mulliken overlap population analysis shows that H vacancy leads to the H local diffusion, whereas impurity-vacancy complexes result from H nonlocal diffusion, which plays a dominant role in the process of dehydrogenation reaction of LiNH2.展开更多
Experiments on a ball milled mixture with a 1：1 molar ratio of LiNH2 and LiH with a small amount （1 mol %） of Ti^nano, TICl3 and TiO2^nano have revealed a superior catalytic effect on Li N H hydrogen storage materi...Experiments on a ball milled mixture with a 1：1 molar ratio of LiNH2 and LiH with a small amount （1 mol %） of Ti^nano, TICl3 and TiO2^nano have revealed a superior catalytic effect on Li N H hydrogen storage materials. In the x-ray diffraction profiles, no trace of Ti^nano, TICl3 and TiO2^nano was found in these doped composites, by which we deduced that Ti atoms enter LiNH2 by partial element substitution. A first-principles plane-wave pseudopotential method based on density functional theory has been used to investigate the catalytic effects of Ti catalysts on the dehydrogenating properties of LiNH2 system. The results show that Ti substitution can reduce the dehydrogenation reaction activation energy of LiNH2 and improve the dehydrogenating properties of LiNH2. Based on the analysis of the density of states and overlap populations for LiNH2 before and after Ti substitution, it was found that the stability of the system of LiNH2 is reduced, which originates from the increase of the valence electrons at the Fermi level （EF） and the decrease of the highest occupied molecular orbital （HOMO） lowest unoccupied molecular orbital （LUMO） gap （△EH-L） near EF. The catalytic effect of Ti on the dehydrogenating kinetics of LiNH2 may be attributed to the reduction of average populations between N-H per unit bond length （nm-1）, which leads to the reduction of the chemical bond strength of NH.展开更多
基金Project(2010CB631300)supported by the National Basic Research Program of ChinaProject(2012AA051503)supported by the National High Technology Research&Development Program of China+1 种基金Projects(51001090,51171173)supported by the National Natural Science Foundation of ChinaProject(IRT13037)supported by the Program for Innovative Research Team in University of Ministry of Education of China
文摘Mg2FeH6 doped with and without Ti and its alloys (TiMn2, TiAl) were prepared combing ball milling and heat treatment. The effects of these additives on the dehydrogenation performance of Mg2FeH6 were studied systematically. The results show that all additives have favor influence on improving the hydrogen desorption property of Mg2FeH6. Especially, TiMn2 exhibits prominent effect on enhancing the dehydrogenation kinetics of Mg2FeH6. Moreover, the activation energy of TiMn2-doped Mg2FeH6 calculated by Kissinger equation is 94.87 kJ/mol, which is 28 kJ/mol lower than that of the undoped Mg2FeH6. The cycling tests suggest that the improved dehydrogenation kinetics of Mg2FeH6 doped by TiMn2 can maintain in the second cycle.
基金supported by the National Natural Science Foundation of China (20971132)the Natural Science Foundation of Chongqing City (CSTC2009BB4243)the Foundation of Chongqing Municipal Education Commission (KJ090810,KJ070809)
文摘Using the plane wave ultrasoft pseudopotential method based on the first-principles density functional theory(DFT),the influence on the electronic structure and dehydrogenation properties of VH2 doped with Zr,Cu and Zn has been studied.The results show that the negative heat of formation increases and the valence electron number at the Fermi level EF,N(EF) decreases in the Zr-doped model,indicating the higher stability of VH2 after Zr alloying.On the other hand,the negative heat of formation of VH2 decreases and the N(EF) increases in Cu-or Zn-doped systems,suggesting the lower stability of VH2 after Cu or Zn alloying.The calculated overlap populations and electron densities of the V-H bond demonstrate that the bonding is strengthened by Zr doping and weakened by Cu or Zn doping.The results predict that the maximum capacity to absorb and desorb hydrogen can be raised by the introduction of Zr and reduced by the introduction of Cu or Zn,while the dehydrogenation properties will be poorer in Zr-doped systems and enhanced in Cu-or Zn-doped systems.These predictions are consistent with the experimental results.Mulliken populations were also calculated and it was found that the Mulliken population of the V 3d orbitals decreased as a result of Zr doping,and increased after Cu or Zn doping.
文摘The catalytic hydrogenation of magnesium under atmospheric pressure has been optimized so that the reaction can be completed within seven hours.The resulted magnesium hydride is in the form of superfine powder with an average primary particle size of 15 nm.This magnesium hydride exhibits higher dehydrogenation/hydrogenation rates than that obtained under pressure with the same catalyst system.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51671118)the research grant(No.16520721800 and No.19ZR1418400)from Science and Technology Commission of Shanghai Municipality.The authors gratefully acknowledge support for materials analysis and research from Instrumental Analysis and Research Center of Shanghai University.
文摘Uniform-uispersed Ni nanoparticics(NPs)anchored on reduced graphene oxide(Ni@rGO)catalyzed MgH2(MH-Ni@rGO)has been fabricated by mechanical milling.The effects of milling time and Ni loading amount on the hydrogen storage properties of MgH2 have been investigated.The initial hydrogen desorption temperature of MgH2 catalyzed by 10 wt.%Ni4@rGO6 for milling 5 h is significantly decreased from 251℃ to 190℃.The composite can absorb 5.0 wt.%hydrogen in 20 min at 100℃,while it can desorb 6.1 wt.%within 15 min at 300℃.Through the investigation of the phase transformation and dehydrogenation kinetics during hydrogen ab/desorption cycles,we found that the in-situ formed Mg2Ni/Mg2NiH4 exhibited better catalytic effect than Ni.When Ni loading amount is 45 wt.%,the rGO in Ni@rGO catalysts can prevent the reaction of Ni and Mg due to the strong interaction between rGO and Ni NPs.
基金Project (2009AA05Z105) supported by the High-tech Research and Development Program of ChinaProject (20102173) supported by the Natural Science Foundation of Liaoning Province,China
文摘A first-principles study was reported based on density functional theory of hydrogen vacancy,metal dopants,metal dopant-vacancy complex in LiBH4,a promising material for hydrogen storage.The formation of H vacancy and metal doping in LiBH4 is difficult,and their concentrations are low.The presence of one kind of defect is helpful to the formation of other kind of defect.Based on the analysis of electronic structure,the improvement of the dehydrogenating kinetics of LiBH4 by metal catalysts is due to the weaker bonding of B—H and the new metal-like system,which makes H atom diffuse easily;H vacancy accounts for a trace amount of BH3 release during the decomposing process of LiBH4;metal dopant weakens the strength of B—H bonds,which reduces the dehydriding temperature of LiBH4.The roles of metal and vacancy in the metal dopant-vacancy complex can be added in LiBH4 system.
基金supported by the MOST Project(2010CB631303,2012AA051901)NSFC(5117108)+1 种基金111 Project(B12015)MOE(IRT-13R30)
文摘The effects of NaA1H4, TiF3 and NaA1H4-TiF3 co-additive on dehydriding reaction of Mg（A1H4）2 are systematically investigated. The on- set dehydrogenation temperature of the co-doped Mg（A1H4）2 composites decreased to 74 ℃, which is about 59 ℃ lower than that of pure Mg（A1H4）2. The dehydrogenation kinetics of NaA1H4-TiF3 co-doped Mg（A1H4）2 sample was also improved, which released about 94% hydrogen within 48 min, but no visible hydrogen was released from pure Mg（A1H4）2 under the same conditions. The activation energy of co-doped Mg（A1H4）2 was 85.6 kJ.mol-t, which was significantly lower than that of additive-free Mg（A1H4）2 sample. The synergetic effects of NaA1H4 and TiF3 on the dehydrogenation performance of Mg（A1H4）2 were confirmed. In addition, a possible catalytic mechanism is discussed, regarding the different roles of NaA1H4 and TiF3 on Mg（A1H4）2.
文摘First-principles calculations were used to study the energetics and electronic structures of Ni and Sc co-doped MgH<sub>2</sub> system. The preferential positions for dopants were determined by the minimal total electronic energy. The results of formation enthalpy indicate that Ni and Sc co-doped MgH<sub>2</sub> system is more stable than Ni single-doped system. The hydrogen desorption enthalpies of these two hydrides are investigated. Ni and Sc co-doping can improve the dehydrogenation properties of MgH<sub>2</sub>. The lowest hydrogen desorption enthalpy of 0.30 eV appears in co-doped system, which is significantly lower than that of Ni doping. The electronic structure analysis illustrates that the hybridization of dopants with Mg and H atom together weakens the Mg-H interaction. And the Mg-H bonds are more susceptible to dissociate by Ni and Sc co-doping because of the reduced magnitude of Mg-H hybridization peaks. These behaviors effectively improve the dehydrogenation properties of Ni and Sc co-doped cases.
基金supported by the National High Technology Research and Development Program of China (Grant No. 2009AA05Z105)the Natural Science Foundation of Liaoning Province of China (Grant No. 20102173)
文摘This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity vacancy complex in LiNH2, a promising material for hydrogen storage. It finds easy formation of H vacancy in the form of impurity-vacancy complex, and the rate-limiting step to the H diffusion. Based on the analysis of the density of states, it finds that the improvement of the dehydrogenating kinetics of LiNH2 by Ti catalysts and Mg substitution is due to the weak bonding of N-H and the new system metal-like, which makes H atom diffuse easily. The mulliken overlap population analysis shows that H vacancy leads to the H local diffusion, whereas impurity-vacancy complexes result from H nonlocal diffusion, which plays a dominant role in the process of dehydrogenation reaction of LiNH2.
基金Project supported by the National High Technology Research & Development of China (Grant No. 2009AA05Z105)the National Natural Science Foundation of China (Grant No. 50671069)+1 种基金the Science Research Program of the Education Bureau of Liaoning Province of China (Grant Nos. 2008S345,2008511 and 2007T165)the Financial Support from Shenyang Normal University
文摘Experiments on a ball milled mixture with a 1：1 molar ratio of LiNH2 and LiH with a small amount （1 mol %） of Ti^nano, TICl3 and TiO2^nano have revealed a superior catalytic effect on Li N H hydrogen storage materials. In the x-ray diffraction profiles, no trace of Ti^nano, TICl3 and TiO2^nano was found in these doped composites, by which we deduced that Ti atoms enter LiNH2 by partial element substitution. A first-principles plane-wave pseudopotential method based on density functional theory has been used to investigate the catalytic effects of Ti catalysts on the dehydrogenating properties of LiNH2 system. The results show that Ti substitution can reduce the dehydrogenation reaction activation energy of LiNH2 and improve the dehydrogenating properties of LiNH2. Based on the analysis of the density of states and overlap populations for LiNH2 before and after Ti substitution, it was found that the stability of the system of LiNH2 is reduced, which originates from the increase of the valence electrons at the Fermi level （EF） and the decrease of the highest occupied molecular orbital （HOMO） lowest unoccupied molecular orbital （LUMO） gap （△EH-L） near EF. The catalytic effect of Ti on the dehydrogenating kinetics of LiNH2 may be attributed to the reduction of average populations between N-H per unit bond length （nm-1）, which leads to the reduction of the chemical bond strength of NH.
