An Li-Mg-N-H system has been synthesized from Mg(NH2)2 and LiH in the ratio 3:8 by a ball-milling process and its dehydrogenation/rehydrogenation properties at around 190°C were investigated. XRD, FTIR and TG res...An Li-Mg-N-H system has been synthesized from Mg(NH2)2 and LiH in the ratio 3:8 by a ball-milling process and its dehydrogenation/rehydrogenation properties at around 190°C were investigated. XRD, FTIR and TG results showed that the system was composed of an LiH phase and an amorphous Mg(NH2)2 phase with a purity of 90%. A reversible hydrogen storage capacity of 4.7% was observed during the first cycle and more than 90% of the stored hydrogen was desorbed within 100 min for each cycle. However, only 4.2% and 2.9%, respectively, of hydrogen was observed during two subsequent dehydrogenation cycles. In situ GC results showed that no NH3 could be observed during the dehydrogenation process. On the basis of the SEM and XRD results, the loss in hydrogen storage capacity can be mainly attributed to agglomeration, oxidation and crystallization of the materials.展开更多
The mutual destabilization between complex hydrides and lithium amide has been comprehensively reported. In this paper, CeH2 doped Li-Mg-N-H/NaAlH4 composite was successfully synthesized by ball milling Li-Mg-N-H mixt...The mutual destabilization between complex hydrides and lithium amide has been comprehensively reported. In this paper, CeH2 doped Li-Mg-N-H/NaAlH4 composite was successfully synthesized by ball milling Li-Mg-N-H mixture and NaAlH4 in a molar ratio of 1：2. It was found that a total of 5 wt.% of hydrogen could be desorbed from the newly synthesized composite with a three-step reaction. Temperature-programmed-desorption （TPD） measurements showed that the composite ball milled for 10 min began to desorb hydrogen below 100 °C, which was about 75 °C lower than the pristine materials. XRD analysis revealed that NaAlH4 firstly reacted with LiH to yield Na2LiAlH6 and Al below 150 °C, then the newly developed Na2LiAlH6 reacted with Mg（NH2）2 to form NaH, Al, and Li2MgN2H2 in the temperature range of 180–250 °C. From 200 to 300 °C, the newly formed Al and Li2MgN2H2 reacted further to form Li2NH and some stable phase （AlN and Mg3N2）. The H-cycling properties of the composite were further investigated by a standard Sievert’s type apparatus at 150, 200 and 250 °C, respectively. Finally, the reversibility of the newly synthesized composite was discussed.展开更多
Hydrogen storage MgH2-xNbH （x = 0 and 0.05） properties of 2LiNH2- composites and the catalysis of NbH on hydrogen sorption reaction of the Li-Mg- N-H system were investigated. Hydrogen sorption properties of 2LiNH2-...Hydrogen storage MgH2-xNbH （x = 0 and 0.05） properties of 2LiNH2- composites and the catalysis of NbH on hydrogen sorption reaction of the Li-Mg- N-H system were investigated. Hydrogen sorption properties of 2LiNH2-MgH2 system are effectively improved by adding NbH. Temperature programmed desorption results show the addition of NbH reduces the dehydriding onset temperature of 2LiNH2-MgH2 system by 21 K. Approximate 3.62 wt% hydrogen in 2LiNH2-MgHz- 0.05NbH composite is released following a 500 min at 433 K, whereas the amount of hydrogen desorption is only -3.16 wt% for the pristine system under the same condition. The sample with NbH exhibits higher dehydriding rate compared with the pristine one. Moreover, hydrogen absorption rate increases by adding NbH into the 2LiNH2- MgH2 system. Hydrogen absorption capacity of the samples with NbH is 3.23 wt% within 400 rain, which is higher than that of pristine sample. Fine NbH particles homogeneously distribute in the 2LiNH2-MgH2-0.05NbH composite, and catalyze the hydrogen sorption reaction rather than reacts as a reactant into new compound.展开更多
Hydrogen storage properties of 2LiNH2-MgH2 system were improved by adding lanthanum hydride （LaH3）, and the role of LaH3 in hydrogen sorption process of Li-Mg-N-H system was investigated. Temperature programmed sorp...Hydrogen storage properties of 2LiNH2-MgH2 system were improved by adding lanthanum hydride （LaH3）, and the role of LaH3 in hydrogen sorption process of Li-Mg-N-H system was investigated. Temperature programmed sorption results showed that the addition of lanthanum hydride reduced the dehydriding/hydriding onset temperature of 2LiNH2-MgH2 system by at least 15 K. Moreover, A 0.053 wt.%/min average rate was determined for the hydrogen desorption of 2LiNH2-MgH2-0.05LaH3 composite, while it was only 0.035 wt.%/min for 2LiNH2-MgH2 system. Hydrogen absorption capacity increased from 1.62 wt.% to 2.12 wt.% within 200 min by adding LaH3 into 2LiNH2-MgH2 system at 383 K. In the dehydrogenation of 2LiNH2-MgH2-0.05LaH3 composite, LaH2 transferred to LaN phase, which reversed to LaH2 in the following hydrogen adsorption process. The reversible reaction of LaH2 ef- fectively promoted the hydrogen sorption of Li-Mg-N-H system. Moreover, the homogenous distribution of fine La hydride was fa- vorable to improving effect of lanthanum hydride.展开更多
The Li-Mg-N-H hydrogen storage system is a promising hydrogen storage material due to its moderate operation temperature,good reversibility,and relatively high capacity.In this work,the Li-Mg-N-H composite was directl...The Li-Mg-N-H hydrogen storage system is a promising hydrogen storage material due to its moderate operation temperature,good reversibility,and relatively high capacity.In this work,the Li-Mg-N-H composite was directly synthesized by reactive ball milling(RBM) of Li3N and Mg powder mixture with a molar ratio of 2:1 under hydrogen pressure of 9 MPa.More than 8.8 wt%hydrogen was absorbed during the RBM process.The phases and structural evolution during the in situ hydrogenation process were analyzed by means of in situ solidgas absorption and ex situ X-ray diffraction(XRD) measurements.It is determined that the hydrogenation can be divided into two steps,leading to mainly the formation of a lithium magnesium imide phase and a poorly crystallized amide phase,respectively.The H-cycling properties of the as-milled composite were determined by temperature-programmed dehydrogenation(TPD) method in a closed system.The onset dehydrogenation temperature was detected at 125℃,and it can reversibly desorb 3.1 wt% hydrogen under a hydrogen back pressure of 0.2 MPa.The structural evolution during dehydrogenation was further investigated by in situ XRD measurement.It is found that Mg(NH_(2))_(2)phase disappears at about 200 ℃,and Li_(2)Mg_(2)N_(3)H_(3),LiNH_(2),and Li_(2)MgN_(2)H_(2)phases coexist at even 300 ℃,revealing that the dehydrogenation process is step-wised and only partial hydrogen can be desorbed.展开更多
基金Supported by the 863 Program of China (Grant No. 2007AA05Z149)the Natural Science Foundation of Tianjin, China (Grant No. 07JCZDJC02700)
文摘An Li-Mg-N-H system has been synthesized from Mg(NH2)2 and LiH in the ratio 3:8 by a ball-milling process and its dehydrogenation/rehydrogenation properties at around 190°C were investigated. XRD, FTIR and TG results showed that the system was composed of an LiH phase and an amorphous Mg(NH2)2 phase with a purity of 90%. A reversible hydrogen storage capacity of 4.7% was observed during the first cycle and more than 90% of the stored hydrogen was desorbed within 100 min for each cycle. However, only 4.2% and 2.9%, respectively, of hydrogen was observed during two subsequent dehydrogenation cycles. In situ GC results showed that no NH3 could be observed during the dehydrogenation process. On the basis of the SEM and XRD results, the loss in hydrogen storage capacity can be mainly attributed to agglomeration, oxidation and crystallization of the materials.
基金Project supported by the Hi-Tech Research and Development Program of China (2009AA034400)the National Basic Research Program of China (2010CB631305) under the Ministry of Science and Technology of China
文摘The mutual destabilization between complex hydrides and lithium amide has been comprehensively reported. In this paper, CeH2 doped Li-Mg-N-H/NaAlH4 composite was successfully synthesized by ball milling Li-Mg-N-H mixture and NaAlH4 in a molar ratio of 1：2. It was found that a total of 5 wt.% of hydrogen could be desorbed from the newly synthesized composite with a three-step reaction. Temperature-programmed-desorption （TPD） measurements showed that the composite ball milled for 10 min began to desorb hydrogen below 100 °C, which was about 75 °C lower than the pristine materials. XRD analysis revealed that NaAlH4 firstly reacted with LiH to yield Na2LiAlH6 and Al below 150 °C, then the newly developed Na2LiAlH6 reacted with Mg（NH2）2 to form NaH, Al, and Li2MgN2H2 in the temperature range of 180–250 °C. From 200 to 300 °C, the newly formed Al and Li2MgN2H2 reacted further to form Li2NH and some stable phase （AlN and Mg3N2）. The H-cycling properties of the composite were further investigated by a standard Sievert’s type apparatus at 150, 200 and 250 °C, respectively. Finally, the reversibility of the newly synthesized composite was discussed.
基金supported by the National Natural Science Foundation of China(Nos.51001043 and 50971112)Program for New Century Excellent Talents in University(No.NCET-11-0943)+2 种基金China Postdoctoral Science Special Foun-dation(No.201104390)Foundation for University Key Teacher in the University of Henan Province(No.2011GGJS-052)Program for Innovative Research Team(in Science and Technology)in the University of Henan Province(No.2012IRTSTHN007)
文摘Hydrogen storage MgH2-xNbH （x = 0 and 0.05） properties of 2LiNH2- composites and the catalysis of NbH on hydrogen sorption reaction of the Li-Mg- N-H system were investigated. Hydrogen sorption properties of 2LiNH2-MgH2 system are effectively improved by adding NbH. Temperature programmed desorption results show the addition of NbH reduces the dehydriding onset temperature of 2LiNH2-MgH2 system by 21 K. Approximate 3.62 wt% hydrogen in 2LiNH2-MgHz- 0.05NbH composite is released following a 500 min at 433 K, whereas the amount of hydrogen desorption is only -3.16 wt% for the pristine system under the same condition. The sample with NbH exhibits higher dehydriding rate compared with the pristine one. Moreover, hydrogen absorption rate increases by adding NbH into the 2LiNH2- MgH2 system. Hydrogen absorption capacity of the samples with NbH is 3.23 wt% within 400 rain, which is higher than that of pristine sample. Fine NbH particles homogeneously distribute in the 2LiNH2-MgH2-0.05NbH composite, and catalyze the hydrogen sorption reaction rather than reacts as a reactant into new compound.
基金Project supported by National Natural Science Foundation of China(51001043,50971112)Program for New Century Excellent Talents in University(NCET-11-0943)+2 种基金China Postdoctoral Science Special Foundation(201104390)Foundation for University Key Teacher in the University of Henan Province(2011GGJS-052)Program for Innovative Research Team(in Science and Technology)in the University of Henan Province(2012IRTSTHN007)
文摘Hydrogen storage properties of 2LiNH2-MgH2 system were improved by adding lanthanum hydride （LaH3）, and the role of LaH3 in hydrogen sorption process of Li-Mg-N-H system was investigated. Temperature programmed sorption results showed that the addition of lanthanum hydride reduced the dehydriding/hydriding onset temperature of 2LiNH2-MgH2 system by at least 15 K. Moreover, A 0.053 wt.%/min average rate was determined for the hydrogen desorption of 2LiNH2-MgH2-0.05LaH3 composite, while it was only 0.035 wt.%/min for 2LiNH2-MgH2 system. Hydrogen absorption capacity increased from 1.62 wt.% to 2.12 wt.% within 200 min by adding LaH3 into 2LiNH2-MgH2 system at 383 K. In the dehydrogenation of 2LiNH2-MgH2-0.05LaH3 composite, LaH2 transferred to LaN phase, which reversed to LaH2 in the following hydrogen adsorption process. The reversible reaction of LaH2 ef- fectively promoted the hydrogen sorption of Li-Mg-N-H system. Moreover, the homogenous distribution of fine La hydride was fa- vorable to improving effect of lanthanum hydride.
基金financially supported by the Beijing Science and Technology Program(No.D141100002014002)the European COST Action(No.MP1103)
文摘The Li-Mg-N-H hydrogen storage system is a promising hydrogen storage material due to its moderate operation temperature,good reversibility,and relatively high capacity.In this work,the Li-Mg-N-H composite was directly synthesized by reactive ball milling(RBM) of Li3N and Mg powder mixture with a molar ratio of 2:1 under hydrogen pressure of 9 MPa.More than 8.8 wt%hydrogen was absorbed during the RBM process.The phases and structural evolution during the in situ hydrogenation process were analyzed by means of in situ solidgas absorption and ex situ X-ray diffraction(XRD) measurements.It is determined that the hydrogenation can be divided into two steps,leading to mainly the formation of a lithium magnesium imide phase and a poorly crystallized amide phase,respectively.The H-cycling properties of the as-milled composite were determined by temperature-programmed dehydrogenation(TPD) method in a closed system.The onset dehydrogenation temperature was detected at 125℃,and it can reversibly desorb 3.1 wt% hydrogen under a hydrogen back pressure of 0.2 MPa.The structural evolution during dehydrogenation was further investigated by in situ XRD measurement.It is found that Mg(NH_(2))_(2)phase disappears at about 200 ℃,and Li_(2)Mg_(2)N_(3)H_(3),LiNH_(2),and Li_(2)MgN_(2)H_(2)phases coexist at even 300 ℃,revealing that the dehydrogenation process is step-wised and only partial hydrogen can be desorbed.
