Co-reporter:Yun Cao;Yaxiong Yang;Zhuanghe Ren;Ni Jian;Mingxia Gao;Yongjun Wu;Min Zhu;Feng Pan;Hongge Pan
Advanced Functional Materials 2017 Volume 27(Issue 16) pp:
Publication Date(Web):2017/04/01
DOI:10.1002/adfm.201700342
In this work, a new facile and scalable strategy to effectively suppress the initial capacity fading of iron oxides is demonstrated by reacting with lithium borohydride (LiBH4) to form a B-containing nanocomposite. Multielement, multiphase B-containing iron oxide nanocomposites are successfully prepared by ball-milling Fe2O3 with LiBH4, followed by a thermochemical reaction at 25–350 °C. The resulting products exhibit a remarkably superior electrochemical performance as anode materials for Li-ion batteries (LIBs), including a high reversible capacity, good rate capability, and long cycling durability. When cycling is conducted at 100 mA g−1, the sample prepared from Fe2O3–0.2LiBH4 delivers an initial discharge capacity of 1387 mAh g−1. After 200 cycles, the reversible capacity remains at 1148 mAh g−1, which is significantly higher than that of pristine Fe2O3 (525 mAh g−1) and Fe3O4 (552 mAh g−1). At 2000 mA g−1, a reversible capacity as high as 660 mAh g−1 is obtained for the B-containing nanocomposite. The remarkably improved electrochemical lithium storage performance can mainly be attributed to the enhanced surface reactivity, increased Li+ ion diffusivity, stabilized solid-electrolyte interphase (SEI) film, and depressed particle pulverization and fracture, as measured by a series of compositional, structural, and electrochemical techniques.
Co-reporter:You Li, Yi Zhang, Mingxia Gao, Hongge Pan, Yongfeng Liu
Progress in Natural Science: Materials International 2017 Volume 27, Issue 1(Volume 27, Issue 1) pp:
Publication Date(Web):1 February 2017
DOI:10.1016/j.pnsc.2016.12.010
A porous Co3O4 with a particle size of 1–3 µm was successfully prepared by heating Co-based metal organic frameworks MOF-74(Co) up to 500 °C in air atmospheric conditions. The as-prepared porous Co3O4 significantly reduced the dehydrogenation temperatures of the LiBH4-2LiNH2 system and improved the purity of the released hydrogen. The LiBH4-2LiNH2-0.05/3Co3O4 sample started to release hydrogen at 140 °C and released hydrogen levels of approximately 9.7 wt% at 225 °C. The end temperature for hydrogen release was lowered by 125 °C relative to that of the pristine sample. Structural analyses revealed that the as-prepared porous Co3O4 is in-situ reduced to metallic Co, which functions as an active catalyst, reducing the kinetic barriers and lowering the dehydrogenation temperatures of the LiBH4-2LiNH2 system. More importantly, the porous Co3O4-containing sample exhibited partially improved reversibility for hydrogen storage in the LiBH4-2LiNH2 system.
Co-reporter:Tao Huang;Yaxiong Yang;Kaichao Pu;Jiaxun Zhang;Mingxia Gao;Hongge Pan
RSC Advances (2011-Present) 2017 vol. 7(Issue 4) pp:2273-2280
Publication Date(Web):2017/01/04
DOI:10.1039/C6RA25714C
We demonstrate a first attempt to understand the particle size-dependence of electrochemical Li storage properties of silicon monoxide (SiO). SiO powder particles of different sizes are obtained by planetary ball milling at 300 rpm for 0–12 h. The 10 h-milled SiO sample exhibits relatively uniform particle morphology with significantly reduced particle size, which induces optimal electrochemical Li storage properties. The specific surface area of the 10 h-milled SiO sample is determined to be approximately 20.1 m2 g−1, which is more than 22 times that of pristine SiO (∼0.9 m2 g−1). The first discharge and charge capacities of the 10 h-milled SiO sample are 2684 and 2091 mA h g−1, respectively, at 100 mA g−1. After 150 cycles, the discharge capacity of the 10 h-milled sample remains at 1159 mA h g−1, while the discharge capacity is only 777 mA h g−1 for the pristine SiO sample. The mechanism of the capacity loss upon cycling is also analysed and discussed.
Co-reporter:Jiaxun Zhang;Yiqi Wang;Min Zhang;Zihan Leng;Mingxia Gao;Jianjiang Hu;Hongge Pan
RSC Advances (2011-Present) 2017 vol. 7(Issue 48) pp:30357-30364
Publication Date(Web):2017/06/08
DOI:10.1039/C7RA05166B
A CsH and KH co-doped Mg(NH2)2/2LiH composite was prepared with a composition of Mg(NH2)2/2LiH–(0.08 − x)CsH–xKH, and the hydrogen storage characteristics was systematically investigated. The results showed that the presence of KH further improved the reaction thermodynamics and kinetics of hydrogen storage in a CsH-containing Mg(NH2)2/2LiH system. A sample with 0.04 mol CsH and 0.04 mol KH had optimal hydrogen storage performance; its dehydrogenation could proceed at 130 °C and hydrogenation at 120 °C with 4.89 wt% of hydrogen storage capacity. At 130 °C, a 25-fold increase in the dehydrogenation rate was achieved for the CsH and KH co-doped sample. More importantly, the CsH and KH co-doped sample also had good cycling stability because more than 97% of the hydrogen storage capacity (4.34 wt%) remained for the Mg(NH2)2/2LiH–0.04CsH–0.04KH sample after 30 cycles. A structural characterization revealed that added CsH and KH participated in the dehydrogenation and hydrogenation reactions by reversibly forming mixed amides of Li–K and Cs–Mg, which caused the improved hydrogen storage thermodynamics and kinetics.
Co-reporter:You Li, Yongfeng Liu, Xin Zhang, Di Zhou, Yunhao Lu, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2016 vol. 4(Issue 21) pp:8366-8373
Publication Date(Web):27 Apr 2016
DOI:10.1039/C6TA02944B
Metal borohydride ammoniates are a novel family of high-capacity hydrogen storage materials. However, high dehydrogenation temperature and low hydrogen purity retard their practical applications. Reducing the particle size to the nanometre range is an effective approach to improve the hydrogen storage properties of hydrides. In this work, we demonstrate a novel ultrasound-assisted wet-chemistry approach to synthesize Mg(BH4)2·6NH3 nanoparticles measuring 20–40 nm in diameter with uniform morphologies. The prepared Mg(BH4)2·6NH3 nanoparticles exhibit dehydrogenation thermodynamics and kinetics much superior to their bulk counterparts because they start releasing hydrogen below 30 °C and peak at 135 °C. More importantly, hydrogen, instead of ammonia, is observed to be the major decomposition product upon heating, thereby representing a substantial advantage. Further investigation revealed that Mg(BH4)2·6NH3 nanoparticles decompose to produce BN and a new Mg–B–N compound instead of Mg. The underlying mechanism of the changed dehydrogenation behaviour of nano-Mg(BH4)2·6NH3 is understood with first-principle calculations.
Co-reporter:Yongfeng Liu, Hufei Du, Xin Zhang, Yaxiong Yang, Mingxia Gao and Hongge Pan
Chemical Communications 2016 vol. 52(Issue 4) pp:705-708
Publication Date(Web):03 Nov 2015
DOI:10.1039/C5CC08801A
The superior catalytic effects derived from a 2D Ti3C2 (MXene), synthesized by the exfoliation of Ti3AlC2 powders, towards the hydrogen storage reaction of MgH2 were demonstrated. The 5 wt% Ti3C2-containing MgH2 releases 6.2 wt% H2 within 1 min at 300 °C and absorbs 6.1 wt% H2 within 30 s at 150 °C, exhibiting excellent dehydrogenation/hydrogenation kinetics.
Co-reporter:Ruyan Wu, Hufei Du, Zeyi Wang, Mingxia Gao, Hongge Pan, Yongfeng Liu
Journal of Power Sources 2016 Volume 327() pp:519-525
Publication Date(Web):30 September 2016
DOI:10.1016/j.jpowsour.2016.07.095
•A 2D Ti3C2 is introduced into NaAlH4 to improve its hydrogen storage properties.•The NaAlH4-7 wt% Ti3C2 sample exhibits optimal hydrogen storage properties.•The NaAlH4-7 wt% Ti3C2 reversibly stores 4.9 wt% hydrogen below 140 °C.•The Ti3C2-containing samples have good cycling stabilities.•The Ti3C2 reacts with NaAlH4 to form metallic Ti and Ti3+ species during BM.A 2D Ti3C2 MXene is introduced into NaAlH4 to improve its hydrogen storage properties for the first time. In the presence of Ti3C2, the operating temperatures for hydrogen storage in NaAlH4 are remarkably reduced, and the hydrogenation/dehydrogenation kinetics are significantly enhanced. The onset dehydrogenation temperature of the 7 wt% Ti3C2-containing NaAlH4 sample is reduced to 100 °C, and hydrogen recharging starts at 50 °C. Approximately 4.7 wt% hydrogen is released from the NaAlH4-7 wt% Ti3C2 sample within 100 min at 140 °C, and the dehydrogenated sample absorbs 4.6 wt% hydrogen within 60 min at 120 °C. However, pristine NaAlH4 only absorbs 0.4 wt% hydrogen under identical conditions. Further cycling measurements show significantly improved cycling stability for the Ti3C2-containing NaAlH4; the hydrogenation/dehydrogenation behaviour remains nearly constant after 10 cycles. XRD and XPS analyses reveal that the Ti3C2 reacts with NaAlH4 and is reduced to metallic Ti and Ti3+ species, which are responsible for the lowered operating temperatures and improved dehydrogenation/hydrogenation kinetics.
Co-reporter:You Li, Yongfeng Liu, Xin Zhang, Yaxiong Yang, Mingxia Gao, Hongge Pan
International Journal of Hydrogen Energy 2016 Volume 41(Issue 4) pp:2788-2796
Publication Date(Web):30 January 2016
DOI:10.1016/j.ijhydene.2015.12.036
•A novel Mg(BH4)2·2NH3–xNaAlH4 combination system is studied.•Combining NaAlH4 with Mg(BH4)2·2NH3 reduces the dehydrogenation temperatures.•11.3 wt% hydrogen is released from the Mg(BH4)2·2NH3–2NaAlH4 system.•Hydrogen storage in Mg(BH4)2·2NH3–2NaAlH4 is partially reversible.The Mg(BH4)2·2NH3–xNaAlH4 (x = 0–4) combination systems were prepared by ball milling, and the reversible hydrogen storage behavior and its mechanisms were investigated and discussed. Combining NaAlH4 with Mg(BH4)2·2NH3 significantly reduces the operating dehydrogenation temperatures and effectively suppresses the emission of NH3 by-products. The dehydrogenation onset temperature of the Mg(BH4)2·2NH3–2NaAlH4 system is lowered to ca. 70 °C, which is much lower than the onset temperatures of either Mg(BH4)2·2NH3 or NaAlH4. In addition, ammonia emission from Mg(BH4)2·2NH3 is thoroughly suppressed by the addition of NaAlH4, leading to approximately 11.3 wt% hydrogen released upon heating to 570 °C. Further investigations revealed that at the initial heating stage, Mg(BH4)2·2NH3 first reacts with NaAlH4 to produce NaBH4, Al3Mg2, Mg, Al0.95Mg0.05, BN, Na and AlN along with the release of hydrogen. Further increasing the operation temperature gives rise to a chemical reaction between NaBH4, AlN and Mg that liberates all of the hydrogen and yields the resultant products of MgAlB4, BN, Na and Al3Mg2. The dehydrogenated products can take up ∼3.5 wt% of hydrogen at 450 °C and 100 bar of hydrogen pressure, exhibiting a partial reversibility for hydrogen storage.
Co-reporter:Jiaxun Zhang, Yongfeng Liu, Xin Zhang, Yaxiong Yang, Qihang Zhang, Ting Jin, Yuxuan Wang, Mingxia Gao, Lixian Sun, Hongge Pan
International Journal of Hydrogen Energy 2016 Volume 41(Issue 26) pp:11264-11274
Publication Date(Web):13 July 2016
DOI:10.1016/j.ijhydene.2016.04.057
•CsH is synthesized by a molten ball milling technique within H2 atmosphere.•Adding CsH significantly improves hydrogen storage properties of Mg(NH2)2-2LiH.•The 0.08CsH-added sample reversibly stores 4.62 wt% hydrogen starting at 70 °C.•A good cycling stability is achieved for the 0.08CsH-added sample.•CsH first remains unchanged and then participates in the reaction upon heating.Cesium hydride (CsH) was successfully synthesized by ball milling Cs under a hydrogen atmosphere of 50 bar at 50 °C. The effect of the prepared CsH on the hydrogen storage properties of the Mg(NH2)2-2LiH system was systematically investigated. The Mg(NH2)2-2LiH-0.08CsH composite exhibited optimal hydrogen storage properties because it reversibly stores approximately 4.62 wt% hydrogen with a dehydrogenation onset temperature of 70 °C via a two-stage reaction. At 150 °C, approximately 80% of the reversible capacity was quickly released from the Mg(NH2)2-2LiH-0.08CsH composite within 100 min. The fully dehydrogenated CsH-containing sample began to absorb hydrogen at 55 °C and took up approximately 4.58 wt% hydrogen at 130 °C. A cycling analysis indicated that the CsH-containing Mg(NH2)2-2LiH system exhibited good reversible hydrogen storage abilities. Detailed mechanistic studies revealed that during the initial heating process, CsH gradually reacted with Mg(NH2)2 to afford CsMg(NH)(NH2), and CsH acted as a catalyst to reduce the activation energy barrier of the first dehydrogenation step. As the operating temperature increased, CsMg(NH)(NH2) as a reactant participated in a second dehydrogenation step to decrease the desorption enthalpy change. This behavior reasonably explains the significantly improved hydrogen storage properties of the CsH-containing Mg(NH2)2-2LiH system.
Co-reporter:Yongfeng Liu;Yaxiong Yang;Mingxia Gao;Hongge Pan
The Chemical Record 2016 Volume 16( Issue 1) pp:189-204
Publication Date(Web):
DOI:10.1002/tcr.201500224
Co-reporter:Yanjing Yang, Yongfeng Liu, You Li, Xin Zhang, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2015 vol. 3(Issue 20) pp:11057-11065
Publication Date(Web):17 Apr 2015
DOI:10.1039/C5TA00697J
The utilization of metal borohydride ammoniates as practical hydrogen storage materials is hindered by their unfavorable exothermic dehydrogenation thermodynamics. Here, we report a first successful attempt to tailor the dehydrogenation thermodynamics of magnesium borohydride hexaammoniate (Mg(BH4)2·6NH3) through nanoconfinement into microporous activated carbon (AC). The onset temperature for hydrogen release from the nanoconfined Mg(BH4)2·6NH3 is dramatically decreased to approximately 40 °C, and more encouragingly, hydrogen desorption is endothermic in nature. The relationship between pore size and dehydrogenation behavior is established, and the critical pore size for the endothermic dehydrogenation of the nanoconfined Mg(BH4)2·6NH3 is found to be less than 4 nm. The nanoconfinement effect of carbon scaffolds is believed to be the primary reason for the change in the dehydrogenation pathway caused by incorporating Mg(BH4)2·6NH3 into microporous activated carbon. This finding opens up the possibility to achieve reversible hydrogen storage in metal borohydride ammoniates.
Co-reporter:Yanjing Yang, Yongfeng Liu, You Li, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2015 vol. 3(Issue 2) pp:570-578
Publication Date(Web):06 Nov 2014
DOI:10.1039/C4TA04765F
The F-substituted Mg(BH4)2·2NH3 was successfully prepared for the first time by mechanochemically reacting Mg(BH4)2·2NH3 and LiBF4 based on the structural and chemical similarity of [BH4]− and [BF4]− anions. The results indicate that the dehydrogenation properties of Mg(BH4)2·2NH3 are significantly improved by the partial substitution of fluorine for hydrogen. Hydrogen release from the F-substituted Mg(BH4)2·2NH3 is initiated at approximately 70 °C, which is an 80 °C decrease in comparison with the pristine sample. At 150 °C, the 15 mol% F-substituted sample releases ∼5.2 wt% of hydrogen within 40 min. However, only 1.2 wt% of hydrogen could be desorbed from the pristine Mg(BH4)2·2NH3 under identical conditions. Mechanistic investigations reveal that the B–H bonds in Mg(BH4)2·2NH3 are strengthened after F-substitution, which induces more ionised Hδ− in the ammoniate and consequently facilitates the local Hδ+–Hδ− combinations within the Mg(BH4)2·2NH3 molecule. In addition, the F-substitution weakens the Mg–B bonds in Mg(BH4)2·2NH3, which favours the generation of B–N bonds during dehydrogenation. These factors are the most important reasons for the improved dehydrogenation properties of F-substituted Mg(BH4)2·2NH3.
Co-reporter:Ruijun Ma, Yongfeng Liu, Yaxiong Yang, Kaichao Pu, Mingxia Gao, Hongge Pan
Acta Materialia 2015 Volume 98() pp:128-134
Publication Date(Web):1 October 2015
DOI:10.1016/j.actamat.2015.07.033
Abstract
Low Coulombic efficiency and fast capacity fading are still the key bottlenecks for practical applications of Mg2Si as an anode material for Li-ion batteries. Herein, we report a first attempt to alleviate these problems by combining the Mg2Si anode with Li12Si7. A novel 7Mg2Si–xLi12Si7 composite with x = 0, 0.25, 0.5, 0.8, 1.0, 1.5 and 2 is designed and prepared. The results show that the presence of Li12Si7 changes the lithiation/delithiation reaction process and significantly improves the cycling stability of the Mg2Si anode. The 7Mg2Si–Li12Si7 (molar ratio: 7:1) composite shows the best cycling stability because it maintains 72.6% of the maximum Li-extraction capacity (814 mAh g−1) after 50 cycles, which is more than a 3-fold increase compared with that of pristine Mg2Si (19.5%), and also quite superior to those of any presently known bulk Mg2Si systems. The significantly improved cyclability is primarily attributed to the successful avoidance of Mg dissociation during the lithiation process because the added Li12Si7 reacts with Mg2Si to convert it into Li2MgSi. This conversion effectively increases the Coulombic efficiency of 7Mg2Si–xLi12Si7 upon cycling and improves the reversibility of Li-storage, consequently inducing a significant improvement in the cycling stability. The finding of this study provides new, valuable information to further improve the cycling life of bulk Si-based anode materials for next-generation Li-ion batteries.
Co-reporter:Yi Zhang, Yongfeng Liu, Xin Zhang, You Li, Mingxia Gao and Hongge Pan
Dalton Transactions 2015 vol. 44(Issue 32) pp:14514-14522
Publication Date(Web):13 Jul 2015
DOI:10.1039/C5DT02148K
Addition of a minor quantity of CoO significantly reduces the dehydrogenation temperature, accelerates the dehydrogenation rate and increases the hydrogen purity of the LiBH4·NH3–3LiH system. The LiBH4·NH3–3LiH–0.1CoO sample exhibits optimal dehydrogenation properties because it releases 8.5 wt% of hydrogen below 250 °C, which is approximately 90 °C lower than that of the pristine sample. At 200 °C, approximately 8.0 wt% of hydrogen is released from the LiBH4·NH3–3LiH–0.1CoO sample within 100 min, whereas only 4.1 wt% is released from the pristine sample under identical conditions. The EXAFS analyses reveal that upon heating, CoO is first reduced to metallic Co at 130 °C and then partially combines with B to form a Co–B species. The in situ formed Co and Co–B are finely dispersed in the dehydrogenated intermediates, and they play critical roles as active catalysts in favour of breaking the B–H bonds of the Li–B–N–H species. This effectively decreases the thermodynamic and kinetic barriers of the dehydrogenation reaction of the LiBH4·NH3–3LiH system.
Co-reporter:Yuepeng Pang, Yongfeng Liu, Xin Zhang, You Li, Mingxia Gao and Hongge Pan
RSC Advances 2015 vol. 5(Issue 16) pp:12144-12151
Publication Date(Web):09 Jan 2015
DOI:10.1039/C4RA15187A
The effects of the NaCl and LiCl by-products generated during the synthesis of Mg(AlH4)2 on the hydrogen storage properties of a 6LiBH4–Mg(AlH4)2 composite are investigated and clarified for the first time. The results indicate that the presence of NaCl and LiCl changes the dehydrogenation/hydrogenation kinetics of the 6LiBH4–Mg(AlH4)2 composite in addition to producing a distinct reduction in the hydrogen capacity. For the NaCl-containing sample, the chemical composition is changed due to the metathesis reaction between NaCl and LiBH4 during ball milling, which converts the NaCl and LiBH4 to LiCl and NaBH4. However, for the LiCl-containing system, the kinetic barriers of the dehydrogenation reaction were changed by the presence of LiCl, which is responsible for the change in the dehydrogenation temperature. These findings elucidate the effects of NaCl and LiCl, which are produced during the synthesis of Mg(AlH4)2, on the hydrogen storage behaviours of the 6LiBH4–Mg(AlH4)2 composite.
Co-reporter:Yanping He;Ruijun Ma;Mingxia Gao;Hongge Pan
Ionics 2015 Volume 21( Issue 9) pp:2439-2445
Publication Date(Web):2015 September
DOI:10.1007/s11581-015-1457-4
To obtain the optimal hydrogen-driven chemical reaction process for the preparation of Mg2Si as an anodic material of Li-ion batteries, the effects of the dehydrogenation temperatures on the structure and electrochemical properties are systematically investigated. The results indicate that Mg2Si prepared by isothermal dehydrogenation at 310 and 330 °C exhibit better cycling stability than the samples prepared at 290 and 350 °C due to the joint effects of the product purity and the particle size, especially for the 330 °C-prepared sample. In particular, the initial discharge capacity of the Mg2Si prepared at 330 °C is 1010 mAh/g with a coulombic efficiency of 92 %. After 50 cycles, the discharge capacity is approximately 416 mAh/g and the corresponding capacity retention is calculated to be approximately 41 %.
Co-reporter:Xin Zhang;Ke Wang;Mingxia Gao;Hongge Pan
Nano Research 2015 Volume 8( Issue 2) pp:533-545
Publication Date(Web):2015 February
DOI:10.1007/s12274-014-0667-9
Adding a small amount of nanocrystalline TiO2@C (TiO2 supported on nanoporous carbon) composite dramatically decreases the operating temperatures and improves the reaction kinetics for hydrogen storage in NaAlH4. The nanocrystalline TiO2@C composite synthesized at 900 °C (referred as TiO2@C-900) exhibits superior catalytic activity to other catalyst-containing samples. The onset dehydrogenation temperature of the TiO2@C-900-containing sample is lowered to 90 °C; this is 65 °C lower than that of the pristine sample. The dehydrogenated sample is completely hydrogenated at 115 °C and 100 bar of hydrogen pressure with a hydrogen capacity of 4.5 wt.%. Structural analyses reveal that the Ti undergoes a reduction process of Ti4+→Ti3+→Ti2+→Ti during the ball milling and heating processes, and further converts to Ti hydrides or forms Ti-Al species after rehydrogenation. The catalytic activities of Ti-based catalytic species decrease in the order Al-Ti-species > TiH0.71 > TiH2 > TiO2. This understanding guides further improvement in hydrogen storage properties of metal alanates using nanocrystalline transition metal-based additives.
Co-reporter:Yi Zhang
The Journal of Physical Chemistry C 2015 Volume 119(Issue 44) pp:24760-24768
Publication Date(Web):October 14, 2015
DOI:10.1021/acs.jpcc.5b09256
A nanosized Ni@C composite (Ni particles: < 10 nm) was successfully synthesized by casting a Ni-based metal–organic framework MOF-74(Ni) filled with furfuryl alcohol at 700 °C. The resulting Ni@C composite exhibits remarkable catalytic activity for reducing the operating temperature of hydrogen release from the LiBH4–2LiNH2 system. The LiBH4–2LiNH2–10 wt % Ni@C sample releases approximately 10 wt % of hydrogen at 135–250 °C, and the end temperature for hydrogen release is reduced by 110 °C in comparison to that of the pristine sample. During dehydrogenation, nanosized Ni remains almost unchanged and only works as a catalyst to reduce kinetic barriers of hydrogen release from the LiBH4–2LiNH2 system, which is responsible for lowered dehydrogenation temperatures of the Ni@C-containing sample. More importantly, the dehydrogenated Ni@C-containing sample presents a loose porous morphology that slightly improves its rehydrogenation properties.
Co-reporter:Xin Zhang; Yongfeng Liu;Ke Wang;You Li; Mingxia Gao; Hongge Pan
ChemSusChem 2015 Volume 8( Issue 24) pp:4180-4188
Publication Date(Web):
DOI:10.1002/cssc.201501266
Abstract
A nanocrystalline CeO2@C-containing NaAlH4 composite is successfully synthesized in situ by hydrogenating a NaH-Al mixture doped with CeO2@C. Compared with NaAlH4, the as-prepared CeO2@C-containing NaAlH4 composite, with a minor amount of excess Al, exhibits significantly improved hydrogen storage properties. The dehydrogenation onset temperature of the hydrogenated [NaH-Al-7 wt % CeO2@C]-0.04Al sample is 77 °C lower than that of the pristine sample because of a reduced kinetic barrier. More importantly, the dehydrogenated sample absorbs ∼4.7 wt % hydrogen within 35 min at 100 °C and 10 MPa of hydrogen. Compositional and structural analyses reveal that CeO2 is converted to CeH2 during ball milling and that the newly formed CeH2 works with the excess of Al to synergistically improve the hydrogen storage properties of NaAlH4. Our findings will aid in the rational design of novel catalyst-doped complex hydride systems with low operating temperatures, fast kinetics, and long-term cyclability.
Co-reporter:Dr. Yuepeng Pang; Yongfeng Liu;Xin Zhang; Qian Li;Dr. Mingxia Gao; Hongge Pan
Chemistry – An Asian Journal 2015 Volume 10( Issue 11) pp:2452-2459
Publication Date(Web):
DOI:10.1002/asia.201500334
Abstract
Herein, an initial attempt to understand the relationships between hydrogen storage properties, reaction pathways, and material compositions in LiBH4–x Mg(AlH4)2 composites is demonstrated. The hydrogen storage properties and the reaction pathways for hydrogen release from LiBH4–x Mg(AlH4)2 composites with x=1/6, 1/4, and 1/2 were systematically investigated. All of the composites exhibit a four-step dehydrogenation event upon heating, but the pathways for hydrogen desorption/absorption are varied with decreasing LiBH4/Mg(AlH4)2 molar ratios. Thermodynamic and kinetic investigations reveal that different x values lead to different enthalpy changes for the third and fourth dehydrogenation steps and varied apparent activation energies for the first, second, and third dehydrogenation steps. Thermodynamic and kinetic destabilization caused by the presence of Mg(AlH4)2 is likely to be responsible for the different hydrogen desorption/absorption performances of the LiBH4–x Mg(AlH4)2 composites.
Co-reporter:Yu Zhang, Yongfeng Liu, Yuepeng Pang, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2014 vol. 2(Issue 29) pp:11155-11161
Publication Date(Web):10 Jun 2014
DOI:10.1039/C4TA01422G
Adding a small amount of Co3O4 significantly reduces the operating temperatures of dehydrogenation and improves the hydrogen storage reversibility of the LiBH4–2LiNH2 system. The LiBH4–2LiNH2–0.05/3Co3O4 composite desorbs ∼9.9 wt% hydrogen by a four-step reaction with a 96 °C reduction in the midpoint temperature with respect to the pristine sample. The first and third steps of the dehydrogenation of the 0.05/3Co3O4-added sample are endothermic in nature, which is different from the pristine sample. Upon thermal dehydrogenation, the Co3O4 additive undergoes a series of chemical transformations and finally converts to the metallic Co, which is responsible for the improved thermodynamics and kinetics of the Co3O4-added sample. More importantly, 1.7 wt% of hydrogen is recharged into the 0.05/3Co3O4-added system under 110 bar hydrogen at 220 °C, which is superior to the pristine system.
Co-reporter:Chao Li, Yongfeng Liu, Yanjing Yang, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2014 vol. 2(Issue 20) pp:7345-7353
Publication Date(Web):08 Apr 2014
DOI:10.1039/C4TA00025K
We report the high-temperature failure behaviours and mechanisms of K-based additives in the Mg(NH2)2–2LiH hydrogen storage system. The onset of hydrogen release from a Mg(NH2)2–2LiH–0.08KF sample is approximately 80 °C; this is a 50 °C reduction in comparison with the pristine Mg(NH2)2–2LiH. However, the positive effects of K-based additives disappear when the hydrogen release and uptake of the KF-added Mg(NH2)2–2LiH samples are performed at higher temperatures (>200 °C). The change in the crystal structure of the dehydrogenation product, the enlargement in the grain and particle sizes of the dehydrogenation/hydrogenation products, and the increase in the inhomogeneous degree of mixing and distribution of K-based additives should be the three most important reasons for the increased operating temperature during the follow-up cycles. In particular, the ability of K-based additives to lower the operating temperature for hydrogen storage in the Mg(NH2)2–2LiH system can be sufficiently recovered after ball milling. Therefore, the failure of K-based additives after high-temperature treatment is only phenomenological instead of being natural. Strictly limiting the dehydrogenation/hydrogenation of the K-added Mg(NH2)2–2LiH system at lower temperatures is critical for maintaining the superior effect of K-based additives.
Co-reporter:Bo Li, Yongfeng Liu, Chao Li, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2014 vol. 2(Issue 9) pp:3155-3162
Publication Date(Web):21 Jan 2014
DOI:10.1039/C3TA14331G
Lithium halides were introduced into the LiNH2–MgH2 system by ball milling the corresponding chemicals under 50 bar of H2 to decrease the dehydrogenation temperature and enhance the dehydrogenation kinetics. The results show that the LiNH2–MgH2–0.05LiBr sample exhibited optimal hydrogen storage performance. The onset dehydrogenation temperature of the LiNH2–MgH2–0.05LiBr sample was only 120 °C, which represents a 55 °C reduction with respect to that of the pristine LiNH2–MgH2 sample. The dehydrogenation rate of the LiNH2–MgH2 sample at 210 °C was increased threefold upon addition of LiBr, which is attributed to the reduction in the dehydrogenation activation energy. Moreover, the addition of LiBr could significantly suppress ammonia emission during the dehydrogenation process of the LiNH2–MgH2 sample. Structural examinations reveal that the added LiBr could react with LiNH2 to form Li7(NH2)6Br during the dehydrogenation process. The in situ-formed Li7(NH2)6Br not only weakens the N–H bond but also promotes the migration of Li+, consequently improving the dehydrogenation kinetics of the LiNH2–MgH2 sample.
Co-reporter:Xin Zhang, Yongfeng Liu, Yuepeng Pang, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2014 vol. 2(Issue 6) pp:1847-1854
Publication Date(Web):17 Dec 2013
DOI:10.1039/C3TA14202G
A well-crystallized Ti-incorporated metal organic framework, MIL-125(Ti), synthesized using a solvothermal method, was introduced into NaAlH4 as the catalyst precursor to improve the dehydrogenation–hydrogenation kinetics. Adding 5 wt% MIL-125(Ti) dramatically decreased the operating temperatures and improved the reaction kinetics for hydrogen storage in NaAlH4. The starting temperature for hydrogen desorption from the sample containing MIL-125(Ti) was lowered by 50 °C relative to that of the pristine sample. The apparent activation energies of the first two dehydrogenation steps of the 5 wt% MIL-125(Ti)-added NaAlH4 were ca. 98.9 and 96.3 kJ mol−1, respectively; both these values are lower than those of the pristine sample. Mechanistic studies revealed that the catalytic function of the Ti-based active species and the nanopore effects of the dehydrogenation decreased the operating temperatures and increased the rate of the dehydrogenation–hydrogenation process in the MIL-125(Ti)-added sample. This understanding will facilitate further improvements in the hydrogen storage properties of metal alanates using optimized MOF-based additives.
Co-reporter:Chao Li, Yongfeng Liu, Ruijun Ma, Xin Zhang, You Li, Mingxia Gao, and Hongge Pan
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 19) pp:17024
Publication Date(Web):September 17, 2014
DOI:10.1021/am504592x
The coaddition of KH and RbH significantly improves the hydrogen storage properties of the Mg(NH2)2-2LiH system. An Mg(NH2)2-2LiH-0.04KH-0.04RbH composite was able to reversibly store 5.2 wt % H2 when the dehydrogenation operates at 130 °C and the hydrogenation operates at 120 °C. The isothermal dehydrogenation rate at 130 °C was approximately 43 times that of a pristine sample. During ball-milling, KH reacts with RbH to form a K(Rb)H solid solution. Upon heating, RbH first separates from the K(Rb)H solid solution and participates in the first step of dehydrogenation reaction, and then the remaining KH participates in the second dehydrogenation reaction. The presence of RbH and KH provide synergetic effects, which improve the thermodynamics and kinetics of hydrogen storage in the Mg(NH2)2-2LiH system. In particular, more than 93% of the hydrogen storage capacity (4.4 wt %) remains after cycling a sample with 0.04 mol of KH and RbH for 50 cycles, indicating notably better cycling stability compared with any presently known Li–Mg–N–H systems.Keywords: amides; cycling stability; hydrogen storage materials; potassium hydride; rubidium hydride
Co-reporter:Yanjing Yang, Yongfeng Liu, Hui Wu, Wei Zhou, Mingxia Gao and Hongge Pan
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 1) pp:135-143
Publication Date(Web):14 Nov 2013
DOI:10.1039/C3CP54099E
We demonstrate the synthesis, crystal structure and thermal decomposition behavior of a novel ammonia-stabilized mixed-cation borohydride where the NH3 groups enable the coexistence of Li and Mg cations as an “assistant”. Li2Mg(BH4)4·6NH3, which is comprised of orderly arranged Mg[NH3]62+ ammine complexes and Li2[BH4]42− complex anions, was synthesized by the mechanochemical reaction between Mg(BH4)2·6NH3 and LiBH4. This novel compound crystallizes in a tetragonal P43212 (No. 96) structure with lattice parameters a = b = 10.7656(8) Å and c = 13.843(1) Å with very short dihydrogen bonds, which determine a very low onset temperature of 80 °C for hydrogen release and are also responsible for the nucleation of Li2Mg(BH4)4·3NH3 as a decomposition intermediate. Mechanistic investigations on the thermal decomposition showed that the Hδ+–Hδ− combination in the ammonia-stabilized mixed-cation borohydride was significantly enhanced due to the strengthened Mg–N bonds. Upon heating, 11.02 moles of H2 (equivalent to 11.1 wt%) and 3.07 moles of NH3 are evolved from one mole of Li2Mg(BH4)4·6NH3 with a three-step reaction. The insights into the formation mechanism of ammonia-stabilized mixed-cation borohydride and the role played by NH3 group are very useful as a guideline for the design and synthesis of novel B–N-based materials with high hydrogen content.
Co-reporter:Chao Li, Yongfeng Liu, Yuepeng Pang, Yingjie Gu, Mingxia Gao and Hongge Pan
Dalton Transactions 2014 vol. 43(Issue 6) pp:2369-2377
Publication Date(Web):16 Oct 2013
DOI:10.1039/C3DT52296B
Potassium hydride (KH) was directly added to a Mg(NH2)2–2LiH system to improve the hydrogen storage properties; the corresponding mechanisms were elucidated. The Mg(NH2)2–2LiH–0.08KH composite displays optimized hydrogen-storage properties, reversibly storing approximately 5.2 wt% hydrogen through a two-stage reaction and a dehydrogenation onset at 70 °C. The 0.08KH-added sample fully dehydrogenated at 130 °C begins to absorb hydrogen at 50 °C, and takes up approximately 5.1 wt% of hydrogen at 140 °C. Adding KH significantly enhances the de-/hydrogenation kinetic properties; however, an overly rapid hydrogenation rate enlarges the particle size and raises the dehydrogenation temperature. A cycling evaluation reveals that the KH-added Mg(NH2)2–2LiH system possesses good reversible hydrogen storage abilities, although the operational temperatures for de-/hydrogenation increase during cycling. Detailed mechanistic investigations indicate that adding KH catalytically decreases the activation energy of the first dehydrogenation step and reduces the enthalpy of desorption during the second dehydrogenation step as a reactant, significantly improving the hydrogen storage properties of Mg(NH2)2–2LiH.
Co-reporter:You Li, Yongfeng Liu, Yanjing Yang, Mingxia Gao, Hongge Pan
International Journal of Hydrogen Energy 2014 Volume 39(Issue 23) pp:11999-12006
Publication Date(Web):4 August 2014
DOI:10.1016/j.ijhydene.2014.05.191
•A novel Mg(BH4)2⋅6NH3-xLiH combination system is prepared.•The onset dehydrogenation temperature of the LiH-contained samples is only 80 °C.•The Mg(BH4)2⋅6NH3-6LiH composite releases 14.3 wt% hydrogen below 340 °C.•The dehydrogenated Mg(BH4)2⋅6NH3-6LiH sample at 210 °C absorbs 2.2 wt% hydrogen.A reactive composite of Mg(BH4)2⋅6NH3-xLiH is prepared, and the effects of the LiH content on the dehydrogenation/hydrogenation properties of the material are investigated. The results show that the presence of LiH with x = 3 reduces the onset dehydrogenation temperature of Mg(BH4)2⋅6NH3 from 130 °C to 80 °C in TPD mode. Approximately 14.3 wt% hydrogen is released from the Mg(BH4)2⋅6NH3-6LiH composite with distinctly reduced ammonia evolution while heating to 340 °C. Upon heating, Mg(BH4)2⋅6NH3 first reacts with LiH to form Mg(NH2)2, Li3BN2H8 and LiBH4 with the release of H2 and the evolution of a minor amount of NH3. The newly formed Mg(NH2)2 then reacts with LiH to produce H2 and Li2Mg(NH)2. Further elevating the operating temperature induces chemical reactions between Li2Mg(NH)2, LiBH4 and Li3BN2H8, causing the release of additional H2 and production of Li3BN2, LiMgBN2 and LiH. The dehydrogenated sample at 210 °C absorbs 2.2 wt% of hydrogen, exhibiting partial reversibility for hydrogen storage.
Co-reporter:Chu Liang, Yongfeng Liu, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2013 vol. 1(Issue 16) pp:5031-5036
Publication Date(Web):11 Mar 2013
DOI:10.1039/C3TA01071F
In this paper, we report a KOH-doped Mg(NH2)2–2LiH system with low operating temperatures and good cycling stability. The Mg(NH2)2–2LiH–0.07KOH sample can reversibly desorb/absorb ∼4.92 wt% hydrogen with a starting and peak dehydrogenation temperature of ∼75 °C and ∼120 °C, respectively, the lowest in the current Mg(NH2)2–2LiH system studied. Moreover, the cycling stability of de-/hydrogenation is also remarkably improved by KOH doping as the average capacity degradation of the Mg(NH2)2–2LiH–0.07KOH system is of only 0.002 wt% per cycle within 30 cycles. Detailed structural investigations reveal that during ball milling, the doped KOH can react with Mg(NH2)2 and LiH to convert to MgO, KH and Li2K(NH2)3, which work together to provide the synergistic effects of thermodynamics and kinetics on hydrogen desorption and absorption of the Mg(NH2)2–2LiH system upon heating, consequently inducing a significant improvement in hydrogen storage properties.
Co-reporter:Hongge Pan, Songbo Shi, Yongfeng Liu, Bo Li, Yanjing Yang and Mingxia Gao
Dalton Transactions 2013 vol. 42(Issue 11) pp:3802-3811
Publication Date(Web):23 Nov 2012
DOI:10.1039/C2DT32266H
A Mg(BH4)2-added Mg(NH2)2–2LiH system was prepared by ball milling the corresponding chemicals. The hydrogen storage properties of the Mg(NH2)2–2LiH–xMg(BH4)2 (x = 0, 0.1, 0.2, 0.3) samples and the role played by Mg(BH4)2 were systematically investigated. The results show that the onset and peak temperatures for hydrogen desorption from the Mg(BH4)2-added Mg(NH2)2–2LiH sample shifted to lower temperatures. In particular, the Mg(NH2)2–2LiH–0.1Mg(BH4)2 sample could reversibly absorb ∼4.5 wt% of hydrogen in the temperature range of 120–150 °C, which is superior to the pristine sample. During ball milling, a metathesis reaction between Mg(BH4)2 and LiH readily occurred to form LiBH4 and MgH2 and subsequently, the newly formed MgH2 reacted with Mg(NH2)2 to generate MgNH. Upon heating, the presence of LiBH4 not only decreased the recrystallization temperature of Mg(NH2)2 but also reacted with LiNH2 to form the Li4(BH4)(NH2)3 intermediate, which weakens the N–H bonding and enhances the ion conductivity. Meanwhile, MgNH may act as the nucleation center for the dehydrogenation product of Li2MgN2H2 due to the structural similarity. Thus, the in situ formed LiBH4 and MgNH provide a synergetic effect to improve the hydrogen storage performances of the Mg(NH2)2–2LiH system.
Co-reporter:Yuepeng Pang, Yongfeng Liu, Xin Zhang, Mingxia Gao, Hongge Pan
International Journal of Hydrogen Energy 2013 Volume 38(Issue 3) pp:1460-1468
Publication Date(Web):6 February 2013
DOI:10.1016/j.ijhydene.2012.11.006
The decreased dehydrogenation temperature and improved dehydrogenation kinetics were achieved by high-energy ball milling Mg(AlH4)2. The particle size, grain size, microstrain and lattice distortion of the post-milled samples, i.e., from macro- to micro-scale, were systematically characterized by means of SEM and XRD measurements. The results indicated that the high-energy ball milling process led to not only a decrease in the particle size and grain size but also an increase in the microstrain and lattice distortion, which provides a synergetic effect of the thermodynamics and kinetics on lowering the dehydrogenation temperatures of the post-milled Mg(AlH4)2 samples. From the kinetic point of view, the refinement of the particles and grains shortens the diffusion distance, and the increase of the microstrain and lattice distortion enhances the diffusivity, which work together to decrease the apparent activation energy for hydrogen desorption. Besides, the presence of microstrain and lattice distortion increased the free energy of the post-milled samples, which was released by recovery and recrystallization processes upon heating. This offers more heat release during the first-step dehydrogenation, consequently leading to thermodynamically decline in dehydrogenation temperatures of the post-milled samples. Such a finding provides insights into the mechanistic understanding on decreased dehydrogenation temperature and improved dehydrogenation kinetics of the post-milled metal hydrides as hydrogen storage materials.Highlights► Improved dehydrogenation properties were achieved by ball milling Mg(AlH4)2. ► Synergetic thermodynamic and kinetic effects were found. ► Decreased particle and grain size reduced dehydrogenation activation energy. ► Increased microstrain and lattice distortion enhanced the exothermic effect.
Co-reporter:Yu Zhang, Yongfeng Liu, Tao Liu, Mingxia Gao, Hongge Pan
International Journal of Hydrogen Energy 2013 Volume 38(Issue 30) pp:13318-13327
Publication Date(Web):8 October 2013
DOI:10.1016/j.ijhydene.2013.07.084
•CoO was first introduced into the Li–B–N–H system as a catalyst precursor.•The onset dehydrogenation temperature decreased by 120 °C after adding CoO.•Metallic Co was identified to be the active catalytic species.•CoO-added samples exhibited partial reversibility for hydrogen storage.Cobalt monoxide (CoO) was introduced into the Li–B–N–H system as a catalyst precursor, and the hydrogen desorption behavior of the LiBH4–2LiNH2–xCoO (x = 0–0.20) composites was investigated. It was observed that the majority of hydrogen desorption from the CoO-added sample occurred simultaneously with the melting of α-Li4BN3H10. Moreover, the 0.05CoO-added sample exhibited optimized dehydrogenation properties, desorbing 9.9 wt% hydrogen completely with an onset temperature of 100 °C and exhibiting a decrease of more than 120 °C in the onset dehydrogenation temperature with respect to that of the additive-free sample. The activation energy of hydrogen desorption for the 0.05CoO-added sample was reduced by 30%. XAFS measurements showed that the CoO additive was first reduced chemically to metallic Co during the initial stage of thermal dehydrogenation, and the newly produced metallic Co acted as the catalytic active species in favor of the creation of B–N bonding. More importantly, approximately 1.1 wt% of hydrogen could be recharged into the fully dehydrogenated 0.05CoO-added sample at 350 °C and a hydrogen pressure of 110 atm, which represents much better performance than that exhibited by the pristine sample.
Co-reporter:Yuepeng Pang, Yongfeng Liu, Xin Zhang, Mingxia Gao, Hongge Pan
International Journal of Hydrogen Energy 2013 Volume 38(Issue 30) pp:13343-13351
Publication Date(Web):8 October 2013
DOI:10.1016/j.ijhydene.2013.07.099
•TiF4-doped Mg(AlH4)2 exhibits improved dehydrogenation properties.•TiF4 participates in the dehydrogenation reaction upon heating.•TiF4 changes the type of nucleation and growth of dehydrogenation products.•The presence of Ti species is also beneficial for hydrogen uptake.A significant decrease in the dehydrogenation temperature of Mg(AlH4)2 was achieved by low-energy ball milling with TiF4. Approximately 8.0 wt% of hydrogen was released from the Mg(AlH4)2-0.025TiF4 sample with an on-set temperature of 40 °C, which represents a decrease of 75 °C relative to pristine Mg(AlH4)2. In contrast to the three-step reaction for pristine Mg(AlH4)2, hydrogen desorption from the TiF4-doped sample involves a two-step process because the Ti-based species participates in the dehydrogenation reaction. The presence of TiF4 alters the nucleation and growth of the dehydrogenation product, significantly decreasing the activation energy barrier of the first step in the dehydrogenation of Mg(AlH4)2. Further hydrogenation measurements revealed that the presence of the Ti-based species was also advantageous for hydrogen uptake, as the on-set hydrogenation temperature was only 100 °C for the dehydrogenated TiF4-doped sample, compared with 130 °C for the additive-free sample.
Co-reporter:Bo Li, Yongfeng Liu, Jian Gu, Yingjie Gu, Mingxia Gao, Hongge Pan
International Journal of Hydrogen Energy 2013 Volume 38(Issue 12) pp:5030-5038
Publication Date(Web):22 April 2013
DOI:10.1016/j.ijhydene.2013.02.011
The hydrogen storage properties and mechanisms of the Ca(BH4)2-added 2LiNH2–MgH2 system were systematically investigated. The results showed that the addition of Ca(BH4)2 pronouncedly improved hydrogen storage properties of the 2LiNH2–MgH2 system. The onset temperature for dehydrogenation of the 2LiNH2–MgH2–0.3Ca(BH4)2 sample is only 80 °C, a ca. 40 °C decline with respect to the pristine sample. Further hydrogenation examination indicated that the dehydrogenated 2LiNH2–MgH2–0.1Ca(BH4)2 sample could absorb ca. 4.7 wt% of hydrogen at 160 °C and 100 atm while only 0.8 wt% of hydrogen was recharged into the dehydrogenated pristine sample under the same conditions. Structural analyses revealed that during ball milling, a metathesis reaction between Ca(BH4)2 and LiNH2 firstly occurred to convert to Ca(NH2)2 and LiBH4, and then, the newly developed LiBH4 reacted with LiNH2 to form Li4(BH4)(NH2)3. Upon heating, the in situ formed Ca(NH2)2 and Li4(BH4)(NH2)3 work together to significantly decrease the operating temperatures for hydrogen storage in the Ca(BH4)2-added 2LiNH2–MgH2 system.Highlights► Hydrogen storage properties of 2LiNH2–MgH2 are improved by doping Ca(BH4)2. ► Hydrogen desorption from the 0.3Ca(BH4)2-doped sample starts at 80 °C. ► Ca(BH4)2 reacts with LiNH2 to form Ca(NH2)2 and LiBH4 during ball milling. ► The newly formed Ca(NH2)2 and LiBH4 provide the synergetic effects.
Co-reporter:Yanjing Yang, Yongfeng Liu, You Li, Mingxia Gao, and Hongge Pan
The Journal of Physical Chemistry C 2013 Volume 117(Issue 32) pp:16326-16335
Publication Date(Web):August 6, 2013
DOI:10.1021/jp404424m
The detailed mechanism of thermal decomposition of Mg(BH4)2·6NH3 synthesized via a mechanochemical reaction between Mg(BH4)2 and NH3 at room temperature was investigated for the first time. A six-step decomposition process, which involves several parallel and interrelated reactions, was elucidated through a series of structural examinations and property evaluations. First, the thermal decomposition of Mg(BH4)2·6NH3 evolves 3 equiv of NH3 and forms Mg(BH4)2·3NH3. Subsequently, Mg(BH4)2·3NH3 decomposes to release an additional 1 equiv of NH3 and 3 equiv of H2 to produce the [MgNBHNH3][BH4] polymer. And then, [MgNBHNH3][BH4] further desorbs 3 equiv of H2 through a three-step reaction to give rise to the formation of the polymer intermediates of [MgNBHNH2][BH4], MgNBHNH2BH2, and MgNBNHBH, respectively. Finally, an additional 1 equiv of H2 is liberated from MgNBNHBH to yield Mg and BN as the resultant solid products. In total, about 7 equiv of H2 and 4 equiv of NH3 are released together from Mg(BH4)2·6NH3 upon heating. Moreover, there is a strong dependence of the gas compositions released from Mg(BH4)2·6NH3 on the heating rate because the decomposition reaction of Mg(BH4)2·3NH3 is sensitive to the heating rate, as the faster heating rate induces a lower ammonia evolution. The finding in this work provides us with insights into the dehydrogenation mechanisms of the metal borohydride ammoniates as hydrogen storage media.
Co-reporter:Yanjing Yang;Dr. Yongfeng Liu;You Li;Dr. Mingxia Gao ;Dr. Hongge Pan
Chemistry – An Asian Journal 2013 Volume 8( Issue 2) pp:476-481
Publication Date(Web):
DOI:10.1002/asia.201200970
Abstract
An ammonia-redistribution strategy for synthesizing metal borohydride ammoniates with controllable coordination number of NH3 was proposed, and a series of magnesium borohydride ammoniates were easily synthesized by a mechanochemical reaction between Mg(BH4)2 and its hexaammoniate. A strong dependence of the dehydrogenation temperature and purity of the released hydrogen upon heating on the coordination number of NH3 was elaborated for Mg(BH4)2⋅x NH3 owing to the change in the molar ratio of Hδ+ and Hδ−, the charge distribution on Hδ+ and Hδ−, and the strength of the coordinate bond N:Mg2+. The monoammoniate of magnesium borohydride (Mg(BH4)2⋅NH3) was obtained for the first time. It can release 6.5 % pure hydrogen within 50 minutes at 180 °C.
Co-reporter:Bo Li;Dr. Yongfeng Liu;Jian Gu;Dr. Mingxia Gao ;Dr. Hongge Pan
Chemistry – An Asian Journal 2013 Volume 8( Issue 2) pp:374-384
Publication Date(Web):
DOI:10.1002/asia.201200938
Abstract
Hydrogen storage properties and mechanisms of the Ca(BH4)2-doped Mg(NH2)2–2 LiH system are systematically investigated. It is found that a metathesis reaction between Ca(BH4)2 and LiH readily occurs to yield CaH2 and LiBH4 during ball milling. The Mg(NH2)2–2 LiH–0.1 Ca(BH4)2 composite exhibits optimal hydrogen storage properties as it can reversibly store more than 4.5 wt % of H2 with an onset temperature of about 90 °C for dehydrogenation and 60 °C for rehydrogenation. Isothermal measurements show that approximately 4.0 wt % of H2 is rapidly desorbed from the Mg(NH2)2–2 LiH–0.1 Ca(BH4)2 composite within 100 minutes at 140 °C, and rehydrogenation can be completed within 140 minutes at 105 °C and 100 bar H2. In comparison with the pristine sample, the apparent activation energy and the reaction enthalpy change for dehydrogenation of the Mg(NH2)2–2 LiH–0.1 Ca(BH4)2 composite are decreased by about 16.5 % and 28.1 %, respectively, and thus are responsible for the lower operating temperature and the faster dehydrogenation/hydrogenation kinetics. The fact that the hydrogen storage performances of the Ca(BH4)2-doped sample are superior to the individually CaH2- or LiBH4-doped samples suggests that the in situ formed CaH2 and LiBH4 provide a synergetic effect on improving the hydrogen storage properties of the Mg(NH2)2–2 LiH system.
Co-reporter:Chao Li;Dr. Yongfeng Liu;Yingjie Gu;Mingxia Gao ;Dr. Hongge Pan
Chemistry – An Asian Journal 2013 Volume 8( Issue 9) pp:2136-2143
Publication Date(Web):
DOI:10.1002/asia.201300323
Abstract
The introduction of RbF into the Mg(NH2)2–2 LiH system significantly decreased its (de-)hydrogenation temperatures and enhanced its hydrogen-storage kinetics. The Mg(NH2)2–2 LiH–0.08 RbF composite exhibits the optimal hydrogen-storage properties as it could reversibly store approximately 4.76 wt % hydrogen through a two-stage reaction with the onset temperatures of 80 °C for dehydrogenation and 55 °C for hydrogenation. At 130 °C, approximately 70 % of hydrogen was rapidly released from the 0.08 RbF-doped sample within 180 min, and the fully dehydrogenated sample could absorb approximately 4.8 wt % of hydrogen at 120 °C. Structural analyses revealed that RbF reacted readily with LiH to convert to RbH and LiF owing to the favorable thermodynamics during ball-milling. The newly generated RbH participated in the following dehydrogenation reaction, consequently resulting in a decrease in the reaction enthalpy change and activation energy.
Co-reporter:Yifan Zhou, Yongfeng Liu, Yu Zhang, Mingxia Gao and Hongge Pan
Dalton Transactions 2012 vol. 41(Issue 36) pp:10980-10987
Publication Date(Web):30 Jul 2012
DOI:10.1039/C2DT30945A
A significant improvement of hydrogen storage properties was achieved by introducing MgH2 into the 6LiBH4–CaH2 system. It was found that ∼8.0 wt% of hydrogen could be reversibly stored in a 6LiBH4–CaH2–3MgH2 composite below 400 °C and 100 bar of hydrogen pressure with a stepwise reaction, which is superior to the pristine 6LiBH4–CaH2 and LiBH4 samples. Upon dehydriding, MgH2 first decomposed to convert to Mg and liberate hydrogen with an on-set temperature of ∼290 °C. Subsequently, LiBH4 reacted with CaH2 to form CaB6 and LiH in addition to further hydrogen release. Hydrogen desorption from the 6LiBH4–CaH2–3MgH2 composite finished at ∼430 °C in non-isothermal model, a 160 °C reduction relative to the 6LiBH4–CaH2 sample. JMA analyses revealed that hydrogen desorption was a diffusion-controlled reaction rather than an interface reaction-controlled process. The newly produced Mg of the first-step dehydrogenation possibly acts as the heterogeneous nucleation center of the resultant products of the second-step dehydrogenation, which diminishes the energy barrier and facilitates nucleation and growth, consequently reducing the operating temperature and improving the kinetics of hydrogen storage.
Co-reporter:Bo Li, Yongfeng Liu, Yu Zhang, Mingxia Gao, and Hongge Pan
The Journal of Physical Chemistry C 2012 Volume 116(Issue 25) pp:13551-13558
Publication Date(Web):June 15, 2012
DOI:10.1021/jp3027308
Hydrogen storage properties and mechanisms of the Li3N–xMg3N2 (x = 0, 0.25, 0.5, 1.0) composites were investigated in this paper. It was found that the Li3N–0.25Mg3N2 composite exhibited optimal hydrogen storage performances as it can store reversibly ∼8.4 wt % hydrogen with an onset temperature of 125 °C for dehydrogenation. Upon absorbing hydrogen, Li3N converted to Li2NH and LiH first and was further hydrogenated to generate LiNH2. The newly developed LiNH2 then reacted with Mg3N2 under hydrogen pressure to produce Li2Mg2N3H3 and MgNH. Finally, Li2Mg2N3H3 and MgNH along with LiNH2 further reacted with hydrogen to form the resultant products of Mg(NH2)2 and LiH. More Mg3N2 in the Li3N–xMg3N2 composites retarded Li3N to react with H2 at the beginning of hydrogenation due to the baffle effect but facilitated the hydrogenation of Mg3N2 at the second-stage hydrogenation because of the decreased particle size and the frequent contact of the constituent species.
Co-reporter:Ruijun Ma, Yongfeng Liu, Yanping He, Mingxia Gao, and Hongge Pan
The Journal of Physical Chemistry Letters 2012 Volume 3(Issue 23) pp:3555-3558
Publication Date(Web):November 21, 2012
DOI:10.1021/jz301762x
Silicon represents one of the most promising anodes for next-generation Li-ion batteries due to its very high capacity and low electrochemical potential. However, the extremely poor cycling stability caused by the huge volume change during charge/discharge prevents it from the commercial use. In this work, we propose a strategy to decrease the intrinsic volume change of bulk Si-based anodes by preinsertion Li into Si with a chemical reaction. Amorphous Li12Si7 was successfully synthesized by a hydrogen-driven reaction between LiH and Si associated with subsequent energetic ball milling. The as-prepared amorphous Li12Si7 anode exhibits significantly improved lithium storage ability as ∼70.7% of the initial charge capacity is retained after 20 cycles. This finding opens up the possibility to develop bulk Si-based anodes with high capacity, long cycling life and low fabrication cost for Li-ion batteries.Keywords: cycling stability; hydrogen-driven reaction; Li-ion batteries; Si; volume change;
Co-reporter:Yifan Zhou ; Yongfeng Liu ; Wei Wu ; Yu Zhang ; Mingxia Gao ;Hongge Pan
The Journal of Physical Chemistry C 2012 Volume 116(Issue 1) pp:1588-1595
Publication Date(Web):December 19, 2011
DOI:10.1021/jp2101573
A reactive composite of LiBH4–xLa2Mg17 was successfully prepared by means of mechanochemical reaction under 40 bar of H2. It was found that MgH2 and LaH3 were readily formed in situ during high-pressure ball milling, and a strong dependency of hydrogen storage performance of the LiBH4–xLa2Mg17 composites on the content of La2Mg17 was observed. The as-prepared LiBH4–0.083La2Mg17 composite under 40 bar of H2 exhibits superior hydrogen storage properties as ∼6.8 wt % of hydrogen can be reversibly desorbed and absorbed below 400 °C. It was also purposed that the self-decomposition of MgH2 first occurred to convert into Mg with hydrogen release upon dehydrogenation and subsequently catalyzed the reaction of LiBH4 and LaH3 to liberate additional hydrogen along with the formation of LaB6 and LiH. The in situ formed MgH2 and LaH3 provide a synergetic thermodynamic and kinetic destabilization on the de/hydrogenation of LiBH4, which is responsible for the distinct reduction in the operating temperatures of the as-prepared LiBH4–xLa2Mg17 composites.
Co-reporter:Chu Liang, Yongfeng Liu, Ying Jiang, Zhijun Wei, Mingxia Gao, Hongge Pan and Qidong Wang
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 1) pp:314-321
Publication Date(Web):28 Oct 2010
DOI:10.1039/C0CP00340A
A mechanistic understanding on the enhanced kinetics of hydrogen storage in the NaBH4-added Mg(NH2)2-2LiH system is provided by carrying out experimental investigations associated with first-principles calculations. It is found that the operating temperatures for hydrogen desorption of the Mg(NH2)2-2LiH system are reduced by introducing NaBH4, and the NaBH4 species seems almost unchanged during dehydrogenation/hydrogenation process. First-principles calculations reveal that the presence of NaBH4 in the Mg(NH2)2-2LiH system facilitates the formation of Mg vacancies in Mg(NH2)2. The appearance of Mg vacancies not only weakens the N–H bonds but also promotes the diffusion of atoms and/or ions, consequently resulting in the improvement of the reaction kinetics of hydrogen desorption/absorption of the NaBH4-added Mg(NH2)2-2LiH system. This finding provides us with a deep insight into the role played by NaBH4 in the Li–Mg–N–H system, as well as ideas for designing high-performance catalysts for metal–N–H-based hydrogen storage media.
Co-reporter:Chu Liang, Yongfeng Liu, Zhijun Wei, Ying Jiang, Fan Wu, Mingxia Gao, Hongge Pan
International Journal of Hydrogen Energy 2011 Volume 36(Issue 3) pp:2137-2144
Publication Date(Web):February 2011
DOI:10.1016/j.ijhydene.2010.11.068
The effects of NaOH addition on hydrogen absorption/desorption properties of the Mg(NH2)2–2LiH system were investigated systematically by means of dehydrogenation/hydrogenation measurements and structural analyses. It is found that the NaOH-added Mg(NH2)2–2LiH samples exhibit an enhanced dehydrogenation/hydrogenation kinetics. In particular, a ∼36 °C reduction in the peak temperature for dehydrogenation is achieved for the Mg(NH2)2–2LiH–0.5NaOH sample with respect to the pristine sample. Structural examinations reveal that NaOH reacts with Mg(NH2)2 and LiH to convert to NaH, LiNH2 and MgO during ball milling. Then, their co-catalytic effects result in a significant improvement in the dehydrogenation/hydrogenation kinetics of the Mg(NH2)2–2LiH system. This finding will help in designing and optimizing the novel high-performance catalysts to further improve hydrogen storage in the amide-hydride combined systems.
Co-reporter:Chu Liang, Dr.;Kun Luo;Bo Li;Mingxia Gao Dr.;Hongge Pan Dr. ;Qidong Wang Dr.
Chemistry - A European Journal 2010 Volume 16( Issue 2) pp:693-702
Publication Date(Web):
DOI:10.1002/chem.200901967
Abstract
The dehydrogenation/hydrogenation processes of the LiNH2/MgH2 (1:1) system were systematically investigated with respect to balller milling and the subsequent heating process. The reaction pathways for hydrogen desorption/absorption of the LiNH2/MgH2 (1:1) system were found to depend strongly on the milling duration due to the presence of two competing reactions in different stages (i.e., the reaction between Mg(NH2)2 and MgH2 and that between Mg(NH2)2 and LiH), caused by a metathesis reaction between LiNH2 and MgH2, which exhibits more the nature of solid–solid reactions. The study provides us with a new approach for the design of novel hydrogen storage systems and the improvement of hydrogen-storage performance of the amide/hydride systems.
Co-reporter:Fenghuai Wang, Yongfeng Liu, Mingxia Gao, Kun Luo, Hongge Pan and Qidong Wang
The Journal of Physical Chemistry C 2009 Volume 113(Issue 18) pp:7978-7984
Publication Date(Web):2017-2-22
DOI:10.1021/jp9011697
Na2LiAlH6 was synthesized by ball-milling a mixture of NaH and LiAlH4 at a molar ratio of 2:1. NaH and LiAlH4 were readily converted in the initial ball-milling process to LiH and NaAlH4, which subsequently reacted with the remaining excessive NaH to form Na2LiAlH6. The thermodynamic and kinetic mechanisms of dehydrogenation of Na2LiAlH6 were systematically elucidated. Approximately 6.7 wt % of hydrogen was found stored reversibly in Na2LiAlH6 through a few sequential reactions. An enthalpy change of 63.8 kJ/mol-H2 and an apparent activation energy of about 173 kJ/mol were determined for the first-step hydrogen storage reaction, indicating the reaction was thermodynamically relatively stable with a high kinetic barrier for the decomposition of Na2LiAlH6. In depth kinetic investigations showed that the first-step dehydrogenation reaction of Na2LiAlH6 could be well interpreted with a nucleation and growth model, and its reaction rate was controlled by the diffusion of substance. The dehydrogenation mechanism developed in this work can be helpful for further efforts on the improvement of the hydrogenation/dehydrogenation performances of Na2LiAlH6.
Co-reporter:Yongfeng Liu, Hongge Pan, Mingxia Gao, He Miao, Yongquan Lei, Qidong Wang
International Journal of Hydrogen Energy 2008 Volume 33(Issue 1) pp:124-133
Publication Date(Web):January 2008
DOI:10.1016/j.ijhydene.2007.09.016
The cycling behavior of the La0.7Mg0.3Ni2.65-xCo0.75Mn0.1AlxLa0.7Mg0.3Ni2.65-xCo0.75Mn0.1Alx(x=0,0.3)(x=0,0.3) alloy electrodes was systematically investigated by XRD, SEM, EIS, XPS and AES measurements, and the function of Al in the La–Mg–Ni-based alloys and the reasons for the improvement of the cycling stability of the alloy electrode with Al were discussed. Results show that the cycling behavior of the La0.7Mg0.3Ni2.35Co0.75Mn0.1Al0.3La0.7Mg0.3Ni2.35Co0.75Mn0.1Al0.3 alloy electrode can be divided into three stages, i.e., the pulverization and Mg oxidation stage, the Mg oxidation and La and/or Al oxidation stage, and the La and Al oxidation and Al oxide film protection stage. The improvement of the cycling stability of the alloy electrode with Al can be ascribed to two factors. One is the decrease in the pulverization of the alloy particles during charge/discharge cycling due to the alloy with Al undergoes a smaller cell volume expansion and contraction. The other is the increase in the anti-oxidation/corrosion due to the formation of a dense Al oxide film during cycling, which is believed to be the most important reason for the improvement of the cycling stability of the La–Mg–Ni–Co–Mn–Al-type alloy electrodes.
Co-reporter:Ke Wang, Hufei Du, Zeyi Wang, Mingxia Gao, Hongge Pan, Yongfeng Liu
International Journal of Hydrogen Energy (16 February 2017) Volume 42(Issue 7) pp:
Publication Date(Web):16 February 2017
DOI:10.1016/j.ijhydene.2016.10.073
•MAX-phase Ti3AlC2 is used to improve the hydrogen storage properties of MgH2.•The MgH2-7 wt% Ti3AlC2 sample exhibited optimal hydrogen storage properties.•The presence of Ti3AlC2 reduced the dehydrogenation onset temperature by 70 °C.•The dehydrogenated MgH2-7 wt% Ti3AlC2 sample absorbed 5.8 wt% H2 in 60 s at 150 °C.•Ti3AlC2 functions as a catalyst in improving hydrogen storage properties of MgH2.A MAX-phase carbide (Ti3AlC2) with purity 99% was synthesized by first ball milling a mixture of Ti, Al and C and subsequently sintering at 1500 °C. The catalytic effects of the as-prepared Ti3AlC2 on the hydrogen storage reaction of MgH2 were evaluated for the first time. The results indicated that the MgH2-7 wt% Ti3AlC2 sample had optimal hydrogen storage properties. The dehydrogenation onset temperature of the MgH2-7 wt% Ti3AlC2 sample decreased to 205 °C, which is 70 °C lower than that of the as-milled pristine MgH2. While heating to 340 °C, the hydrogen desorption reached 6.9 wt%. The dehydrogenated MgH2-7 wt% Ti3AlC2 sample absorbed 5.8 wt% hydrogen within 60 s at 150 °C, while the hydrogen uptake amount in dehydrogenated pristine MgH2 was only 2.7 wt%, even after 2000 s. The apparent activation energy was calculated to be 104.7 kJ/mol for the MgH2-7 wt% Ti3AlC2 sample, which is 50.4 kJ/mol lower than that of the pristine MgH2. The existence state of Ti3AlC2 during dehydrogenation was also analyzed and discussed.
Co-reporter:Bo Li, Yongfeng Liu, Chao Li, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2014 - vol. 2(Issue 9) pp:NaN3162-3162
Publication Date(Web):2014/01/21
DOI:10.1039/C3TA14331G
Lithium halides were introduced into the LiNH2–MgH2 system by ball milling the corresponding chemicals under 50 bar of H2 to decrease the dehydrogenation temperature and enhance the dehydrogenation kinetics. The results show that the LiNH2–MgH2–0.05LiBr sample exhibited optimal hydrogen storage performance. The onset dehydrogenation temperature of the LiNH2–MgH2–0.05LiBr sample was only 120 °C, which represents a 55 °C reduction with respect to that of the pristine LiNH2–MgH2 sample. The dehydrogenation rate of the LiNH2–MgH2 sample at 210 °C was increased threefold upon addition of LiBr, which is attributed to the reduction in the dehydrogenation activation energy. Moreover, the addition of LiBr could significantly suppress ammonia emission during the dehydrogenation process of the LiNH2–MgH2 sample. Structural examinations reveal that the added LiBr could react with LiNH2 to form Li7(NH2)6Br during the dehydrogenation process. The in situ-formed Li7(NH2)6Br not only weakens the N–H bond but also promotes the migration of Li+, consequently improving the dehydrogenation kinetics of the LiNH2–MgH2 sample.
Co-reporter:Chu Liang, Yongfeng Liu, Ying Jiang, Zhijun Wei, Mingxia Gao, Hongge Pan and Qidong Wang
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 1) pp:NaN321-321
Publication Date(Web):2010/10/28
DOI:10.1039/C0CP00340A
A mechanistic understanding on the enhanced kinetics of hydrogen storage in the NaBH4-added Mg(NH2)2-2LiH system is provided by carrying out experimental investigations associated with first-principles calculations. It is found that the operating temperatures for hydrogen desorption of the Mg(NH2)2-2LiH system are reduced by introducing NaBH4, and the NaBH4 species seems almost unchanged during dehydrogenation/hydrogenation process. First-principles calculations reveal that the presence of NaBH4 in the Mg(NH2)2-2LiH system facilitates the formation of Mg vacancies in Mg(NH2)2. The appearance of Mg vacancies not only weakens the N–H bonds but also promotes the diffusion of atoms and/or ions, consequently resulting in the improvement of the reaction kinetics of hydrogen desorption/absorption of the NaBH4-added Mg(NH2)2-2LiH system. This finding provides us with a deep insight into the role played by NaBH4 in the Li–Mg–N–H system, as well as ideas for designing high-performance catalysts for metal–N–H-based hydrogen storage media.
Co-reporter:Yanjing Yang, Yongfeng Liu, Hui Wu, Wei Zhou, Mingxia Gao and Hongge Pan
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 1) pp:NaN143-143
Publication Date(Web):2013/11/14
DOI:10.1039/C3CP54099E
We demonstrate the synthesis, crystal structure and thermal decomposition behavior of a novel ammonia-stabilized mixed-cation borohydride where the NH3 groups enable the coexistence of Li and Mg cations as an “assistant”. Li2Mg(BH4)4·6NH3, which is comprised of orderly arranged Mg[NH3]62+ ammine complexes and Li2[BH4]42− complex anions, was synthesized by the mechanochemical reaction between Mg(BH4)2·6NH3 and LiBH4. This novel compound crystallizes in a tetragonal P43212 (No. 96) structure with lattice parameters a = b = 10.7656(8) Å and c = 13.843(1) Å with very short dihydrogen bonds, which determine a very low onset temperature of 80 °C for hydrogen release and are also responsible for the nucleation of Li2Mg(BH4)4·3NH3 as a decomposition intermediate. Mechanistic investigations on the thermal decomposition showed that the Hδ+–Hδ− combination in the ammonia-stabilized mixed-cation borohydride was significantly enhanced due to the strengthened Mg–N bonds. Upon heating, 11.02 moles of H2 (equivalent to 11.1 wt%) and 3.07 moles of NH3 are evolved from one mole of Li2Mg(BH4)4·6NH3 with a three-step reaction. The insights into the formation mechanism of ammonia-stabilized mixed-cation borohydride and the role played by NH3 group are very useful as a guideline for the design and synthesis of novel B–N-based materials with high hydrogen content.
Co-reporter:Chu Liang, Yongfeng Liu, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2013 - vol. 1(Issue 16) pp:NaN5036-5036
Publication Date(Web):2013/03/11
DOI:10.1039/C3TA01071F
In this paper, we report a KOH-doped Mg(NH2)2–2LiH system with low operating temperatures and good cycling stability. The Mg(NH2)2–2LiH–0.07KOH sample can reversibly desorb/absorb ∼4.92 wt% hydrogen with a starting and peak dehydrogenation temperature of ∼75 °C and ∼120 °C, respectively, the lowest in the current Mg(NH2)2–2LiH system studied. Moreover, the cycling stability of de-/hydrogenation is also remarkably improved by KOH doping as the average capacity degradation of the Mg(NH2)2–2LiH–0.07KOH system is of only 0.002 wt% per cycle within 30 cycles. Detailed structural investigations reveal that during ball milling, the doped KOH can react with Mg(NH2)2 and LiH to convert to MgO, KH and Li2K(NH2)3, which work together to provide the synergistic effects of thermodynamics and kinetics on hydrogen desorption and absorption of the Mg(NH2)2–2LiH system upon heating, consequently inducing a significant improvement in hydrogen storage properties.
Co-reporter:Yu Zhang, Yongfeng Liu, Yuepeng Pang, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2014 - vol. 2(Issue 29) pp:NaN11161-11161
Publication Date(Web):2014/06/10
DOI:10.1039/C4TA01422G
Adding a small amount of Co3O4 significantly reduces the operating temperatures of dehydrogenation and improves the hydrogen storage reversibility of the LiBH4–2LiNH2 system. The LiBH4–2LiNH2–0.05/3Co3O4 composite desorbs ∼9.9 wt% hydrogen by a four-step reaction with a 96 °C reduction in the midpoint temperature with respect to the pristine sample. The first and third steps of the dehydrogenation of the 0.05/3Co3O4-added sample are endothermic in nature, which is different from the pristine sample. Upon thermal dehydrogenation, the Co3O4 additive undergoes a series of chemical transformations and finally converts to the metallic Co, which is responsible for the improved thermodynamics and kinetics of the Co3O4-added sample. More importantly, 1.7 wt% of hydrogen is recharged into the 0.05/3Co3O4-added system under 110 bar hydrogen at 220 °C, which is superior to the pristine system.
Co-reporter:Chao Li, Yongfeng Liu, Yanjing Yang, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2014 - vol. 2(Issue 20) pp:NaN7353-7353
Publication Date(Web):2014/04/08
DOI:10.1039/C4TA00025K
We report the high-temperature failure behaviours and mechanisms of K-based additives in the Mg(NH2)2–2LiH hydrogen storage system. The onset of hydrogen release from a Mg(NH2)2–2LiH–0.08KF sample is approximately 80 °C; this is a 50 °C reduction in comparison with the pristine Mg(NH2)2–2LiH. However, the positive effects of K-based additives disappear when the hydrogen release and uptake of the KF-added Mg(NH2)2–2LiH samples are performed at higher temperatures (>200 °C). The change in the crystal structure of the dehydrogenation product, the enlargement in the grain and particle sizes of the dehydrogenation/hydrogenation products, and the increase in the inhomogeneous degree of mixing and distribution of K-based additives should be the three most important reasons for the increased operating temperature during the follow-up cycles. In particular, the ability of K-based additives to lower the operating temperature for hydrogen storage in the Mg(NH2)2–2LiH system can be sufficiently recovered after ball milling. Therefore, the failure of K-based additives after high-temperature treatment is only phenomenological instead of being natural. Strictly limiting the dehydrogenation/hydrogenation of the K-added Mg(NH2)2–2LiH system at lower temperatures is critical for maintaining the superior effect of K-based additives.
Co-reporter:Xin Zhang, Yongfeng Liu, Yuepeng Pang, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2014 - vol. 2(Issue 6) pp:NaN1854-1854
Publication Date(Web):2013/12/17
DOI:10.1039/C3TA14202G
A well-crystallized Ti-incorporated metal organic framework, MIL-125(Ti), synthesized using a solvothermal method, was introduced into NaAlH4 as the catalyst precursor to improve the dehydrogenation–hydrogenation kinetics. Adding 5 wt% MIL-125(Ti) dramatically decreased the operating temperatures and improved the reaction kinetics for hydrogen storage in NaAlH4. The starting temperature for hydrogen desorption from the sample containing MIL-125(Ti) was lowered by 50 °C relative to that of the pristine sample. The apparent activation energies of the first two dehydrogenation steps of the 5 wt% MIL-125(Ti)-added NaAlH4 were ca. 98.9 and 96.3 kJ mol−1, respectively; both these values are lower than those of the pristine sample. Mechanistic studies revealed that the catalytic function of the Ti-based active species and the nanopore effects of the dehydrogenation decreased the operating temperatures and increased the rate of the dehydrogenation–hydrogenation process in the MIL-125(Ti)-added sample. This understanding will facilitate further improvements in the hydrogen storage properties of metal alanates using optimized MOF-based additives.
Co-reporter:Yanjing Yang, Yongfeng Liu, You Li, Xin Zhang, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2015 - vol. 3(Issue 20) pp:NaN11065-11065
Publication Date(Web):2015/04/17
DOI:10.1039/C5TA00697J
The utilization of metal borohydride ammoniates as practical hydrogen storage materials is hindered by their unfavorable exothermic dehydrogenation thermodynamics. Here, we report a first successful attempt to tailor the dehydrogenation thermodynamics of magnesium borohydride hexaammoniate (Mg(BH4)2·6NH3) through nanoconfinement into microporous activated carbon (AC). The onset temperature for hydrogen release from the nanoconfined Mg(BH4)2·6NH3 is dramatically decreased to approximately 40 °C, and more encouragingly, hydrogen desorption is endothermic in nature. The relationship between pore size and dehydrogenation behavior is established, and the critical pore size for the endothermic dehydrogenation of the nanoconfined Mg(BH4)2·6NH3 is found to be less than 4 nm. The nanoconfinement effect of carbon scaffolds is believed to be the primary reason for the change in the dehydrogenation pathway caused by incorporating Mg(BH4)2·6NH3 into microporous activated carbon. This finding opens up the possibility to achieve reversible hydrogen storage in metal borohydride ammoniates.
Co-reporter:Yanjing Yang, Yongfeng Liu, You Li, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2015 - vol. 3(Issue 2) pp:NaN578-578
Publication Date(Web):2014/11/06
DOI:10.1039/C4TA04765F
The F-substituted Mg(BH4)2·2NH3 was successfully prepared for the first time by mechanochemically reacting Mg(BH4)2·2NH3 and LiBF4 based on the structural and chemical similarity of [BH4]− and [BF4]− anions. The results indicate that the dehydrogenation properties of Mg(BH4)2·2NH3 are significantly improved by the partial substitution of fluorine for hydrogen. Hydrogen release from the F-substituted Mg(BH4)2·2NH3 is initiated at approximately 70 °C, which is an 80 °C decrease in comparison with the pristine sample. At 150 °C, the 15 mol% F-substituted sample releases ∼5.2 wt% of hydrogen within 40 min. However, only 1.2 wt% of hydrogen could be desorbed from the pristine Mg(BH4)2·2NH3 under identical conditions. Mechanistic investigations reveal that the B–H bonds in Mg(BH4)2·2NH3 are strengthened after F-substitution, which induces more ionised Hδ− in the ammoniate and consequently facilitates the local Hδ+–Hδ− combinations within the Mg(BH4)2·2NH3 molecule. In addition, the F-substitution weakens the Mg–B bonds in Mg(BH4)2·2NH3, which favours the generation of B–N bonds during dehydrogenation. These factors are the most important reasons for the improved dehydrogenation properties of F-substituted Mg(BH4)2·2NH3.
Co-reporter:You Li, Yongfeng Liu, Xin Zhang, Di Zhou, Yunhao Lu, Mingxia Gao and Hongge Pan
Journal of Materials Chemistry A 2016 - vol. 4(Issue 21) pp:NaN8373-8373
Publication Date(Web):2016/04/27
DOI:10.1039/C6TA02944B
Metal borohydride ammoniates are a novel family of high-capacity hydrogen storage materials. However, high dehydrogenation temperature and low hydrogen purity retard their practical applications. Reducing the particle size to the nanometre range is an effective approach to improve the hydrogen storage properties of hydrides. In this work, we demonstrate a novel ultrasound-assisted wet-chemistry approach to synthesize Mg(BH4)2·6NH3 nanoparticles measuring 20–40 nm in diameter with uniform morphologies. The prepared Mg(BH4)2·6NH3 nanoparticles exhibit dehydrogenation thermodynamics and kinetics much superior to their bulk counterparts because they start releasing hydrogen below 30 °C and peak at 135 °C. More importantly, hydrogen, instead of ammonia, is observed to be the major decomposition product upon heating, thereby representing a substantial advantage. Further investigation revealed that Mg(BH4)2·6NH3 nanoparticles decompose to produce BN and a new Mg–B–N compound instead of Mg. The underlying mechanism of the changed dehydrogenation behaviour of nano-Mg(BH4)2·6NH3 is understood with first-principle calculations.
Co-reporter:Yifan Zhou, Yongfeng Liu, Yu Zhang, Mingxia Gao and Hongge Pan
Dalton Transactions 2012 - vol. 41(Issue 36) pp:NaN10987-10987
Publication Date(Web):2012/07/30
DOI:10.1039/C2DT30945A
A significant improvement of hydrogen storage properties was achieved by introducing MgH2 into the 6LiBH4–CaH2 system. It was found that ∼8.0 wt% of hydrogen could be reversibly stored in a 6LiBH4–CaH2–3MgH2 composite below 400 °C and 100 bar of hydrogen pressure with a stepwise reaction, which is superior to the pristine 6LiBH4–CaH2 and LiBH4 samples. Upon dehydriding, MgH2 first decomposed to convert to Mg and liberate hydrogen with an on-set temperature of ∼290 °C. Subsequently, LiBH4 reacted with CaH2 to form CaB6 and LiH in addition to further hydrogen release. Hydrogen desorption from the 6LiBH4–CaH2–3MgH2 composite finished at ∼430 °C in non-isothermal model, a 160 °C reduction relative to the 6LiBH4–CaH2 sample. JMA analyses revealed that hydrogen desorption was a diffusion-controlled reaction rather than an interface reaction-controlled process. The newly produced Mg of the first-step dehydrogenation possibly acts as the heterogeneous nucleation center of the resultant products of the second-step dehydrogenation, which diminishes the energy barrier and facilitates nucleation and growth, consequently reducing the operating temperature and improving the kinetics of hydrogen storage.
Co-reporter:Hongge Pan, Songbo Shi, Yongfeng Liu, Bo Li, Yanjing Yang and Mingxia Gao
Dalton Transactions 2013 - vol. 42(Issue 11) pp:NaN3811-3811
Publication Date(Web):2012/11/23
DOI:10.1039/C2DT32266H
A Mg(BH4)2-added Mg(NH2)2–2LiH system was prepared by ball milling the corresponding chemicals. The hydrogen storage properties of the Mg(NH2)2–2LiH–xMg(BH4)2 (x = 0, 0.1, 0.2, 0.3) samples and the role played by Mg(BH4)2 were systematically investigated. The results show that the onset and peak temperatures for hydrogen desorption from the Mg(BH4)2-added Mg(NH2)2–2LiH sample shifted to lower temperatures. In particular, the Mg(NH2)2–2LiH–0.1Mg(BH4)2 sample could reversibly absorb ∼4.5 wt% of hydrogen in the temperature range of 120–150 °C, which is superior to the pristine sample. During ball milling, a metathesis reaction between Mg(BH4)2 and LiH readily occurred to form LiBH4 and MgH2 and subsequently, the newly formed MgH2 reacted with Mg(NH2)2 to generate MgNH. Upon heating, the presence of LiBH4 not only decreased the recrystallization temperature of Mg(NH2)2 but also reacted with LiNH2 to form the Li4(BH4)(NH2)3 intermediate, which weakens the N–H bonding and enhances the ion conductivity. Meanwhile, MgNH may act as the nucleation center for the dehydrogenation product of Li2MgN2H2 due to the structural similarity. Thus, the in situ formed LiBH4 and MgNH provide a synergetic effect to improve the hydrogen storage performances of the Mg(NH2)2–2LiH system.
Co-reporter:Chao Li, Yongfeng Liu, Yuepeng Pang, Yingjie Gu, Mingxia Gao and Hongge Pan
Dalton Transactions 2014 - vol. 43(Issue 6) pp:NaN2377-2377
Publication Date(Web):2013/10/16
DOI:10.1039/C3DT52296B
Potassium hydride (KH) was directly added to a Mg(NH2)2–2LiH system to improve the hydrogen storage properties; the corresponding mechanisms were elucidated. The Mg(NH2)2–2LiH–0.08KH composite displays optimized hydrogen-storage properties, reversibly storing approximately 5.2 wt% hydrogen through a two-stage reaction and a dehydrogenation onset at 70 °C. The 0.08KH-added sample fully dehydrogenated at 130 °C begins to absorb hydrogen at 50 °C, and takes up approximately 5.1 wt% of hydrogen at 140 °C. Adding KH significantly enhances the de-/hydrogenation kinetic properties; however, an overly rapid hydrogenation rate enlarges the particle size and raises the dehydrogenation temperature. A cycling evaluation reveals that the KH-added Mg(NH2)2–2LiH system possesses good reversible hydrogen storage abilities, although the operational temperatures for de-/hydrogenation increase during cycling. Detailed mechanistic investigations indicate that adding KH catalytically decreases the activation energy of the first dehydrogenation step and reduces the enthalpy of desorption during the second dehydrogenation step as a reactant, significantly improving the hydrogen storage properties of Mg(NH2)2–2LiH.
Co-reporter:Yi Zhang, Yongfeng Liu, Xin Zhang, You Li, Mingxia Gao and Hongge Pan
Dalton Transactions 2015 - vol. 44(Issue 32) pp:NaN14522-14522
Publication Date(Web):2015/07/13
DOI:10.1039/C5DT02148K
Addition of a minor quantity of CoO significantly reduces the dehydrogenation temperature, accelerates the dehydrogenation rate and increases the hydrogen purity of the LiBH4·NH3–3LiH system. The LiBH4·NH3–3LiH–0.1CoO sample exhibits optimal dehydrogenation properties because it releases 8.5 wt% of hydrogen below 250 °C, which is approximately 90 °C lower than that of the pristine sample. At 200 °C, approximately 8.0 wt% of hydrogen is released from the LiBH4·NH3–3LiH–0.1CoO sample within 100 min, whereas only 4.1 wt% is released from the pristine sample under identical conditions. The EXAFS analyses reveal that upon heating, CoO is first reduced to metallic Co at 130 °C and then partially combines with B to form a Co–B species. The in situ formed Co and Co–B are finely dispersed in the dehydrogenated intermediates, and they play critical roles as active catalysts in favour of breaking the B–H bonds of the Li–B–N–H species. This effectively decreases the thermodynamic and kinetic barriers of the dehydrogenation reaction of the LiBH4·NH3–3LiH system.
Co-reporter:Yongfeng Liu, Hufei Du, Xin Zhang, Yaxiong Yang, Mingxia Gao and Hongge Pan
Chemical Communications 2016 - vol. 52(Issue 4) pp:NaN708-708
Publication Date(Web):2015/11/03
DOI:10.1039/C5CC08801A
The superior catalytic effects derived from a 2D Ti3C2 (MXene), synthesized by the exfoliation of Ti3AlC2 powders, towards the hydrogen storage reaction of MgH2 were demonstrated. The 5 wt% Ti3C2-containing MgH2 releases 6.2 wt% H2 within 1 min at 300 °C and absorbs 6.1 wt% H2 within 30 s at 150 °C, exhibiting excellent dehydrogenation/hydrogenation kinetics.
