Based on experimental results in which VH0.81/MgH2 interface was found during the process of mechanically milling MgH2+5at%V nanocomposite, a VH/MgH2 in- terface is designed and constituted in this work. A first-princ...Based on experimental results in which VH0.81/MgH2 interface was found during the process of mechanically milling MgH2+5at%V nanocomposite, a VH/MgH2 in- terface is designed and constituted in this work. A first-principles plane-wave pseudopo- tential method based on Density Functional Theory (DFT) has been used to investigate the vanadium alloying effects on the dehydrogenating properties of magnesium hydride, i.e., MgH2. A low absolute value of the negative heat of formation of VH/MgH2 interface compared with that of MgH2 indicates that vanadium hydrides befit to improve the dehydrogenating properties of MgH2. Based on the analysis of the density of states (DOS) and the total valence electron density distribution of MgH2 before and after V alloying, it was found that the improvement of the dehydrogenating properties of MgH2 caused by V alloying originates from the increasing of the valence electrons at Fermi level (EF) and the decreasing of the HOMO-LUMO gap ( Δ E H ?L) after V alloying. The catalysis effect of V on dehydrogenating kinetics of MgH2 may attribute to a stronger bonding between V and H atoms than that between Mg and H atoms, which leads to nucleation of the α-Mg at the VH/MgH2 interface in the MgH2-V systems easier than that in pure MgH2 phase.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 new approach was developed to successfully load Mg into the nanometre-sized pores of an anodic aluminium oxide（AAO） template for realizing the nano-confinement of Mg. Structural characterization shows that Mg nano...A new approach was developed to successfully load Mg into the nanometre-sized pores of an anodic aluminium oxide（AAO） template for realizing the nano-confinement of Mg. Structural characterization shows that Mg nano-particles are nucleated along the AAO pipe wall together with the formation of MgO and Mg17Al12 as byproducts. The flow rate of argon gas, the temperature of the AAO template and the transporting distance between the Mg vapour source and the AAO template were optimized to achieve the confinement of Mg nano-particles with larger loading rate. Under optimized deposition conditions, the particle size of the loaded Mg is less than 100 nm and the effective filling factor is about 35 wt%. The confined Mg/MgH2 even after 10 de-/hydrogenation cycles still shows favourable kinetics. Furthermore, the slight reduction in hydrogen desorption enthalpy and entropy of MgH2 from（74.42 ± 0.12） to（73.21 ± 0.04） k J·mol^-1 and（130.98 ±0.05） to（130.11 ± 0.24） Jámol^-1·K^-1 is also found in the present nano-confinement.展开更多
Nanocrystalline MgH2 and MgH2-based composites with 25%（mass fraction） of Al, Ca, or CaH2 as an individual additive respectively were prepared by ball milling. The crystallite size and morphology of the as-milled po...Nanocrystalline MgH2 and MgH2-based composites with 25%（mass fraction） of Al, Ca, or CaH2 as an individual additive respectively were prepared by ball milling. The crystallite size and morphology of the as-milled powders were characterized and their hydrolysis behaviours were investigated in comparison with commercial polycrystalline MgH2. The results show that the crystallite size of both MgH2 and MgH2-based composites is reduced to less than 13nm after milling for 15h. Due to its enhanced specific surface area and unique nanocrystalline structure, the as-milled MgH2 shows much better hydrolysis kinetics than the commercial polycrystalline MgH2, with the hydrolysed fraction upon hydrolysing for 70min enhances from 7.5% to about 25%. As compared with the as-milled MgH2, the MgH2-based composites with either CaH2 or Ca as an additive present further greatly improved hydrolysis kinetics, with the hydrolysed fraction for 80min achieving about 76% and 62% respectively. However, the addition of Al doesn’t show any positive effect on the improvement of the hydrolysis kinetics of MgH2.展开更多
The Ni−25%X(X=Fe,Co,Cu,molar fraction)solid solutions were prepared and then doped into MgH_(2) through high-energy ball milling.The initial dehydrogenation temperatures of MgH_(2)/Ni−25%X composites are all decreased...The Ni−25%X(X=Fe,Co,Cu,molar fraction)solid solutions were prepared and then doped into MgH_(2) through high-energy ball milling.The initial dehydrogenation temperatures of MgH_(2)/Ni−25%X composites are all decreased by about 90℃relative to the as-milled pristine MgH_(2).The Ni−25%Co solid solution exhibits the most excellent catalytic effect,and the milled MgH_(2)/Ni−25%Co composite can release 5.19 wt.%hydrogen within 10 min at 300℃,while the as-milled pristine MgH_(2) can only release 1.78 wt.%hydrogen.More importantly,the dehydrogenated MgH_(2)/Ni−25%Co composite can absorb 5.39 wt.%hydrogen at 275℃within 3 min.The superior hydrogen sorption kinetics of MgH_(2)/Ni−25%Co can be ascribed to the actual catalytic effect of in-situ formed Mg_(2)Ni(Co)compounds.First-principles calculations show that the hydrogen absorption/desorption energy barriers of Mg/MgH_(2) systems decrease significantly after doping with transition metal atoms,which interprets well the improved hydrogen sorption properties of MgH_(2) catalyzed by Ni-based solid solutions.展开更多
文摘Based on experimental results in which VH0.81/MgH2 interface was found during the process of mechanically milling MgH2+5at%V nanocomposite, a VH/MgH2 in- terface is designed and constituted in this work. A first-principles plane-wave pseudopo- tential method based on Density Functional Theory (DFT) has been used to investigate the vanadium alloying effects on the dehydrogenating properties of magnesium hydride, i.e., MgH2. A low absolute value of the negative heat of formation of VH/MgH2 interface compared with that of MgH2 indicates that vanadium hydrides befit to improve the dehydrogenating properties of MgH2. Based on the analysis of the density of states (DOS) and the total valence electron density distribution of MgH2 before and after V alloying, it was found that the improvement of the dehydrogenating properties of MgH2 caused by V alloying originates from the increasing of the valence electrons at Fermi level (EF) and the decreasing of the HOMO-LUMO gap ( Δ E H ?L) after V alloying. The catalysis effect of V on dehydrogenating kinetics of MgH2 may attribute to a stronger bonding between V and H atoms than that between Mg and H atoms, which leads to nucleation of the α-Mg at the VH/MgH2 interface in the MgH2-V systems easier than that in pure MgH2 phase.
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financially supported by the Ministry of Science and Technology under Project of ‘‘Key Fundamental Research on Novel High-Capacity Hydrogen Storage Materials’’ (No. 2010CB631302)the National Natural Science Foundation of China (No. 50971061)
文摘A new approach was developed to successfully load Mg into the nanometre-sized pores of an anodic aluminium oxide（AAO） template for realizing the nano-confinement of Mg. Structural characterization shows that Mg nano-particles are nucleated along the AAO pipe wall together with the formation of MgO and Mg17Al12 as byproducts. The flow rate of argon gas, the temperature of the AAO template and the transporting distance between the Mg vapour source and the AAO template were optimized to achieve the confinement of Mg nano-particles with larger loading rate. Under optimized deposition conditions, the particle size of the loaded Mg is less than 100 nm and the effective filling factor is about 35 wt%. The confined Mg/MgH2 even after 10 de-/hydrogenation cycles still shows favourable kinetics. Furthermore, the slight reduction in hydrogen desorption enthalpy and entropy of MgH2 from（74.42 ± 0.12） to（73.21 ± 0.04） k J·mol^-1 and（130.98 ±0.05） to（130.11 ± 0.24） Jámol^-1·K^-1 is also found in the present nano-confinement.
文摘Nanocrystalline MgH2 and MgH2-based composites with 25%（mass fraction） of Al, Ca, or CaH2 as an individual additive respectively were prepared by ball milling. The crystallite size and morphology of the as-milled powders were characterized and their hydrolysis behaviours were investigated in comparison with commercial polycrystalline MgH2. The results show that the crystallite size of both MgH2 and MgH2-based composites is reduced to less than 13nm after milling for 15h. Due to its enhanced specific surface area and unique nanocrystalline structure, the as-milled MgH2 shows much better hydrolysis kinetics than the commercial polycrystalline MgH2, with the hydrolysed fraction upon hydrolysing for 70min enhances from 7.5% to about 25%. As compared with the as-milled MgH2, the MgH2-based composites with either CaH2 or Ca as an additive present further greatly improved hydrolysis kinetics, with the hydrolysed fraction for 80min achieving about 76% and 62% respectively. However, the addition of Al doesn’t show any positive effect on the improvement of the hydrolysis kinetics of MgH2.
基金the National Natural Science Foundation of China(Nos.51874049,51904036)the Science Research Project of Hunan Province Office of Education,China(No.20A024)+2 种基金the Changsha Science and Technology Program Project(No.kq1907092)the Hunan Provincial Key Laboratory of Materials Protection for Electric Power and Transportation,China(No.2019CL03)the Research and Innovation Project of Graduate Students in Changsha University of Science and Technology,China(No.CX2020SS35).
文摘The Ni−25%X(X=Fe,Co,Cu,molar fraction)solid solutions were prepared and then doped into MgH_(2) through high-energy ball milling.The initial dehydrogenation temperatures of MgH_(2)/Ni−25%X composites are all decreased by about 90℃relative to the as-milled pristine MgH_(2).The Ni−25%Co solid solution exhibits the most excellent catalytic effect,and the milled MgH_(2)/Ni−25%Co composite can release 5.19 wt.%hydrogen within 10 min at 300℃,while the as-milled pristine MgH_(2) can only release 1.78 wt.%hydrogen.More importantly,the dehydrogenated MgH_(2)/Ni−25%Co composite can absorb 5.39 wt.%hydrogen at 275℃within 3 min.The superior hydrogen sorption kinetics of MgH_(2)/Ni−25%Co can be ascribed to the actual catalytic effect of in-situ formed Mg_(2)Ni(Co)compounds.First-principles calculations show that the hydrogen absorption/desorption energy barriers of Mg/MgH_(2) systems decrease significantly after doping with transition metal atoms,which interprets well the improved hydrogen sorption properties of MgH_(2) catalyzed by Ni-based solid solutions.
