•Quantum dots SnO2/nitrogen-doped graphene oxide composite were synthesized for Li-ion battery.•SnO2@NRGO electrode show superior electrochemical performance to SnO2@RGO electrode and SnO2 electrode.•SnO2@NRGO electrode exhibits excellent reversible capacity of 1333.5 mAh g−1 over 450 cycles.SnO2 is considered as one of the anode material for Li-ion batteries in terms of its superiority in high theoretical capacity (1494 mAh g−1), low cost and environmental friendly. However, it is suffered from several issues such as rapid capacity deterioration, undesirable aggregation of tin particles and pesky expansion of volume. To conquer these shortcomings, a novel composite of ultrasmall SnO2 quantum dots with an average particle size of 4–5 nm anchored on nitrogen-doped reduced graphene oxide (SnO2@NRGO) was first in situ synthesized By means of hydrothermal method. The results show that as-prepared SnO2@NRGO electrode exhibits a greater enhancement in its initial discharge capacity (1678.4 mAh g−1) and reversible capacity (1333.5 mAh g−1 after 450 cycles) at a current density of 500 mA g−1, implying a long cycle life. Furthermore, the high rate capability of SnO2@NRGO is superior to SnO2@RGO and SnO2 electrodes. The excellent electrochemical reversibility of SnO2@NRGO electrode can be ascribed to the great conductivity, ultrahigh specific surface area and the synergetic effect between ultrasmall SnO2 quantum dots and NRGO.

•The effects of Mn substitution for Co in the ZrCo1−xMnx were investigated.•The initial activation behavior of ZrCo1−xMnx is improved with increasing Mn.•Co substituted with Mn results in the disproportionation during the activation.ZrCo1−xMnx (x = 0–0.1) alloys for tritium storage were prepared by induction levitation melting under an argon atmosphere. The effect of Mn substitution for Co on the alloy microstructure, initial activation behavior, hydrogen storage kinetics and thermodynamics was investigated. The results show that the ZrCo1−xMnx (x = 0, 0.025, 0.05) alloys have a single phase of ZrCo, while ZrCo1−xMnx (x = 0.075, 0.1) alloys consist of a main phase of ZrCo and a secondary phase of ZrMn2. It is observed that the initial activation time (uptake to 95% of saturated hydrogen capacity) decreases from 63.73 h to 0.24 h as the Mn content increases from x = 0 to x = 0.1. However, Mn substituted for Co is determined to result in disproportionation during activation and a loss in hydrogen capacity. For increasing Mn content in the alloy, the plateau width for Pressure-Composition-Temperature (P-C-T) curve is shortened, while the plateau pressure remains mostly unchanged. DSC measurements were also performed to investigate the thermal stability of the ZrCo1−xMnx system.

•A new strategy to improve hydrogen desorption properties of LiBH4 is achieved by compositing with fluorographene.•LiBH4–50FG composite can release hydrogen at low temperature of 148.1 °C with a capacity of 8.2 wt.% H2.•A remarkably enhanced reversible hydrogen desorption capacity of 7.1 wt.% is obtained in LiBH4–40FG composite.LiBH4 is a promising hydrogen storage material for its large capacity. However, high desorption temperature, sluggish kinetics and demanding rehydrogenation severely hinder its practical use. Surface functional groups of graphene in many cases are treated as effective approaches to obtain some kinds of excellent properties of energy storage materials. In the current work, a new facile and effective strategy to improve the reversible hydrogen desorption properties of LiBH4 is proposed by composing with functionalized graphene to form the LiBH4–fluorographene composite. The fluorographene (FG) nanosheets are successfully exfoliated from fluorographite (FGi) and composed with LiBH4. It is demonstrated that the FG can remarkably improve the hydrogen desorption thermodynamics, kinetics and reversibility of LiBH4 via reactant destabilization method. An extremely fast hydrogen desorption process with a high capacity of 8.2 wt.% at 148.1 °C is achieved in the LiBH4–50FG composite. Further research reveals that the enhancement actually roots in the strengthened interfacial interaction between LiBH4 and exfoliated FG. Moreover, it is confirmed that the LiBH4–40FG composite exhibits a significantly enhanced reversible hydrogen desorption capacity of 7.2 wt.% and LiBH4 is regenerated. Such enhanced reversible hydrogen desorption properties are ascribed to the strengthened interfacial interactions between LiBH4 and FG with large surface, as well as the formation of LiHxF1−x phase.

•Carbon coated Na2Ti3O7 nanotubes (NTs) were synthesized for Na-ion battery.•Na2Ti3O7@C show better electrochemical performance than bare Na2Ti3O7 NTs.•Na2Ti3O7@C NTs deliver high reversible capacity of 142.2 mA h g−1 for over 100 cycles.•Na2Ti3O7@C NTs show relatively stable capacities at high rate current.Na2Ti3O7 is a promising intercalation anode material for sodium ion batteries. However, low electronic conductivity and structural instability restrict its practical applications. Herein, a novel carbon coated sodium-titanate nanotube was successfully synthesized via a facile solvothermal method. The carbon combines all individual Na2Ti3O7 nanotubes into a stable union, which is characterized and confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The carbon encapsulation together with the unique nanotube structure of the Na2Ti3O7 endows the favorable high conductivity and improves the structural stability during cycling. Therefore, Na2Ti3O7@C electrode shows a much higher specific capacity and good cycling stability (142.2 mAh g−1 at 311 mA g−1 after 100 cycles), whereas the bare Na2Ti3O7 only shows a capacity of 84.9 mAh g−1 at 311 mA g−1 after 100 cycles. Furthermore, Na2Ti3O7@C composite electrode has relatively stable capacities at high rate current (84 mAh g−1 at 3.11 A g−1). The present study provides a facile and scalable method to escalate the electrochemical performance of the intercalation anode materials for sodium ion batteries.Download high-res image (306KB)Download full-size image

In this paper, we present a new method to synthesize a dual-cation (Li+, Mg2+) borohydride. It is found that Li–Mg–B–H is formed by mechanical milling a mixture of LiBH4 and MgCl2 with a molar ratio of 3 : 1 in diethyl ether (Et2O) and a subsequent heating process. The morphology and structure of the as-prepared Li–Mg–B–H compound are studied by SEM, XRD, FTIR and NMR measurements. Further experiments testify that Li–Mg–B–H can release approximately 12.3 wt% of hydrogen under 4 bar initial hydrogen pressure from room temperature to 500 °C and reach a maximum desorption rate of 13.80 wt% per h at 375 °C, which is 30 times faster than that of pristine LiBH4. Thermal analysis indicates that the decomposition process of the new compound involves three steps: (1) Li–Mg–B–H first decomposes into LiBH4 and MgH2 and synchronously releases a number of H2 molecules; (2) MgH2 decomposes to Mg and H2; (3) LiBH4 reacts with Mg, generating H2, MgB2 and LiH. Moreover, Li–Mg–B–H is proved to be partially reversible, which can release 5.3 wt% hydrogen in the second dehydrogenation process. The strategy of altering the χp of metal ions in borohydrides may shed light on designing dual-cation borohydrides with better hydrogen storage performance.

Magnesium hydride (MgH2) exhibits long-term stability and has recently been developed as a safe alternative to store hydrogen in the solid state, due to its high capacity of 7.6 wt% H2 and low cost compared to other metal hydrides. However, the high activation energy and poor kinetics of MgH2 lead to inadequate hydrogen storage properties, resulting in low energy efficiency. Nano-catalysis is deemed to be the most effective strategy in improving the kinetics performance of hydrogen storage materials. In this work, robust and efficient architectures of carbon-wrapped transition metal (Co/C, Ni/C) nanoparticles (8–16 nm) were prepared and used as catalysts in the MgH2 system via ball milling to improve its de/rehydrogenation kinetics. Between the two kinds of nano-catalysts, the Ni/C nanoparticles exhibit a better catalytic efficiency. MgH2 doped with 6% Ni/C (MgH2-6%Ni/C) exhibits a peak dehydrogenation temperature of 275.7 °C, which is 142.7, 54.2 and 32.5 °C lower than that of commercial MgH2, milled MgH2 and MgH2 doped with 6% Co/C (MgH2-6%Co/C), respectively. MgH2 doped with 6% Ni/C can release about 6.1 wt% H2 at 250 °C. More importantly, the dehydrogenated MgH2-6%Ni/C is even able to uptake 5.0 wt% H2 at 100 °C within 20 s. Moreover, a cycling test of MgH2 doped with 8% Ni/C demonstrates its excellent hydrogen absorption/desorption stability with respect to both capacity (up to 6.5 wt%) and kinetics (within 8 min at 275 °C for dehydrogenation and within 10 s at 200 °C for rehydrogenation). Mechanistic research reveals that the in situ formed Mg2Ni and Mg2NiH4 nanoparticles can be regarded as advanced catalytically active species in the MgH2-Ni/C system. Meanwhile, the carbon attached around the surface of transition metal nanoparticles can successfully inhibit the aggregation of the catalysts and achieve the steadily, prompting de/rehydrogenation during the subsequent cycling process. The intrinsic catalytic effects and the uniform distributions of Mg2Ni and Mg2NiH4 result in a favorable catalytic efficiency and cycling stability. Nano-catalysts with this kind of morphology can also be applied to other metal hydrides to improve their kinetics performance and cycling stability.

A remarkable improvement in the hydrogen desorption performance of Mg(BH4)2–NaBH4 eutectic composite is achieved by simply ball-milling with fluorographene (FG). It is found that the desorption temperature of Mg(BH4)2–NaBH4 (∼200 °C) is still too high and liquid phase appears during dehydrogenation. Particularly, the novel bowl-like 3D Mg(BH4)2–NaBH4–FG composite can be formed after ball-milling. The novel Mg(BH4)2–NaBH4–FG exhibits a low dehydrogenation temperature of 114.9 °C with 6.9 wt% of pure hydrogen in seconds. In-depth investigations show that such greatly improved hydrogen desorption properties of the Mg(BH4)2–NaBH4–FG composite could be ascribed to both the “novel bowl-like 3D structure” with large specific surface area and the “reactant destabilized modification” owing to the decrease of the reaction enthalpy caused by the formation of NaMgF3. This finding provides a facile preparation of complex borohydride composites with low dehydrogenation temperature and fast rate, which accelerates its practical application in fuel cells.

•CoTiO3/graphene composite were firstly synthesized for anode of Li-ion battery.•CoTiO3/graphene composite shows better electrochemical performances than bare CoTiO3.•CoTiO3 nanoparticles could uniformly distribute on the surface of graphene.A novel perovskite CoTiO3/graphene composite with a particle size of 100 nm was synthesized by ball-milling and high temperature solid method and utilized as anode materials for lithium-ion batteries. The structure morphology and electrochemical performance of CoTiO3/graphene nanocomposite were investigated by X-ray diffraction (XRD), Raman spectroscopy measurements, scanning electron microscopy (SEM), galvanostatic charge-discharge tests and electrochemical impedance spectroscopy (EIS) tests. The CoTiO3/graphene nanocomposite delivers a higher stable discharge capacity (∼500 mAh g−1) and better cycling stability (86.2%), as well as improved rate capability over 80 cycles, compared with those of bare CoTiO3. Moreover, this CoTiO3/graphene nanocomposite exhibits stable discharge capacity (∼350 mAh g−1) after 3000 cycles at high current density (1 A g−1). The improved electrochemical properties of CoTiO3/graphene can be attributed to the good conductivity and large surface of graphene and the combination novel nanostructure of CoTiO3 and graphene.Download high-res image (210KB)Download full-size image

•Firstly synthesized and investigated Mg(BH4)2AlH3 complex hydride.•Mg(BH4)2AlH3 composite starts to decompose from 130.8 °C.•Mechanism of AlH3 improving dehydrogenation of Mg(BH4)2 was studied.•Altering dehydrogenation temperature can control Mg(BH4)2AlH3 reversibility.Mg(BH4)2 has been considered as one of the promising light metal complex hydrides due to its high hydrogen capacity and low cost. But its higher thermal stability (dehydrogenation at above 300 °C) needs to be improved for the practical application. In this study, the aluminum hydride AlH3 was introduced into complex borohydride Mg(BH4)2 to synthesize a new Mg(BH4)2AlH3 composite by ball milling method. It is found that the active Al∗ formed from the self-decomposition of AlH3 can effectively improve the dehydrogenation properties of Mg(BH4)2, the Mg(BH4)2AlH3 composite starts to release hydrogen at 130.8 °C with a total hydrogen capacity of 11.9 wt.%. The dehydrogenated products of the composite is composed of Mg2Al3 and B at 350 °C, resulting in the improved hydrogen desorption properties of Mg(BH4)2AlH3 composite. The Mg2Al3 and B products would be further transformed into MgAlB4 and Al at 500 °C. Moreover, the Mg2Al3 and B dehydrogenated products show better reversible hydrogen storage property than that of the MgAlB4 and Al products. This research shows a way to alter hydrogen de/hydrogenation route and reversibility of Mg(BH4)2 complex hydride by compositing with AlH3 and controlling the dehydrogenation temperature.

Nanoscale catalyst doping is regarded as one of the most effective strategies to improve the kinetics performance of hydrogen storage materials, but the agglomeration of nanoparticles is usually unavoidable during the repeated de/rehydrogenation processes. Herein, hierarchically structured catalysts (Fe/C, Co/C and Ni/C) were designed and fabricated to overcome the agglomeration issue of nanocatalysts applied to the 2LiBH4-MgH2 system for the first time. Uniform transition metal (TM) nanoparticles (∼10 nm) wrapped by few layers of carbon are synthesized by pyrolysis of the corresponding metal–organic frameworks (MOFs), and introduced into the 2LiBH4-MgH2 reactive hydride composites (RHCs) by ball milling. The particular features of the carbon-wrapped architecture effectively avoid the agglomeration of the TM nanoparticles during hydrogen storage cycling, and high catalysis is maintained during the subsequent de/rehydrogenation processes. After de/rehydrogenation cycling, FeB, CoB and MgNi3B2 can be formed as the catalytically active components with a particle size of 5–15 nm, which show a homogeneous distribution in the hydride matrix. Among the three catalysts, in situ-formed MgNi3B2 shows the best catalytic efficiency. The incubation period of the Fe/C, Co/C and Ni/C-doped 2LiBH4-MgH2 system between the two dehydrogenation steps was reduced to about 8 h, 4 h and 2 h, respectively, which is about 8 h, 12 h and 14 h shorter than that of the undoped 2LiBH4-MgH2 sample. In addition, the two-step dehydrogenation peak temperatures of the Ni/C-doped 2LiBH4-MgH2 system drop to 323.4 °C and 410.6 °C, meanwhile, the apparent activation energies of dehydrogenated MgH2 and LiBH4 decrease by 58 kJ mol−1 and 71 kJ mol−1, respectively. In particular, the cycling hydrogen desorption of the Ni/C-doped 2LiBH4-MgH2 sample exhibits very good stability compared with the undoped sample. The present approach, which ideally addresses the agglomeration of nanoparticles with efficient catalysis on the RHCs, provides a new inspiration to practical hydrogen storage application for high performance complex hydrides.

As anode materials, TiO2 exhibits a suitable potential, fast kinetics and excellent cycling performance, while other transition metal oxides (such as NiO) deliver a much higher theoretical capacity with a moderate kinetics and limited cycling performance. Herein, a novel perovskite NiTiO3/reduced graphene oxide (RGO) composite with a particle size of 40–50 nm was first synthesized by solvothermal method and introduced as anode materials for lithium-ion batteries. The structure morphology and electrochemical performance of NiTiO3/RGO nanocomposite were investigated by X-ray diffraction (XRD), Raman spectroscopy measurements, scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests. The NiTiO3/RGO nanocomposite delivers a higher discharge capacity (1110.7 mA h g−1) and better cycling stability (65.3%), as well as improved rate capability over 50 cycles, compared with those of bare NiTiO3. The improved electrochemical properties of NiTiO3/RGO can be attributed to the good conductivity and large surface of RGO and the combination nanostructure of NiTiO3 and RGO.

•The hydrogen desorption properties of LiBH4–Ca(BH4)2–NbF5@CMK-3 were investigated.•The modified sample releases H2 at 120 °C, lower by 80 °C than primitive sample.•13.3 wt% H2 is released within 250 min for LiBH4–Ca(BH4)2–NbF5@CMK-3.NbF5 and eutectic 0.68LiBH4–0.32Ca(BH4)2 were successively infiltrated into highly ordered mesoporous carbon (CMK-3) to obtain a LiBH4–Ca(BH4)2–NbF5@CMK-3 composite. A synergetic effect of nanoconfinement and catalysis on hydrogen desorption properties of the composite was achieved. The onset desorption temperature of LiBH4–Ca(BH4)2–NbF5@CMK-3 is dramatically lower than 120 °C compared with that of as-milled LiBH4–Ca(BH4)2 or LiBH4–Ca(BH4)2@CMK-3. A hydrogen amount as high as 13.3 wt% can be released within 250 min for LiBH4–Ca(BH4)2–NbF5@CMK-3, compared with only 10.4 wt% for pure LiBH4–Ca(BH4)2, in which nanoconfinement and catalysis both make some contribution. The cycling hydrogen desorption performance of the composite becomes better likewise due to the addition of NbF5. Further microstructure analysis reveals that F− tended to bind with Ca2+ to form CaF2, whereas Nb compound is believed to catalyze the whole system in the form of Nb-based boride (NbB2).

Mg2FeH6 doped with and without Ti and its alloys (TiMn2, TiAl) were prepared combing ball milling and heat treatment. The effects of these additives on the dehydrogenation performance of Mg2FeH6 were studied systematically. The results show that all additives have favor influence on improving the hydrogen desorption property of Mg2FeH6. Especially, TiMn2 exhibits prominent effect on enhancing the dehydrogenation kinetics of Mg2FeH6. Moreover, the activation energy of TiMn2-doped Mg2FeH6 calculated by Kissinger equation is 94.87 kJ/mol, which is 28 kJ/mol lower than that of the undoped Mg2FeH6. The cycling tests suggest that the improved dehydrogenation kinetics of Mg2FeH6 doped by TiMn2 can maintain in the second cycle.

•Novel synergistic effects of NbCl5 and h-BN on improving the dehydrogenation kinetics properties of LiBH4.•Dehydrogenation of NbCl5/h-BN co-doped LiBH4 is two-dimensional diffusion controlled kinetics mechanism.•The in situ formed nano-NbH@BN probably acts as the active species during the dehydrogenation.LiBH4 is an attractive material for hydrogen storage owing to its high hydrogen capacity of 13.8 wt% capacities. However, its high thermodynamic stability and sluggish kinetics limit its practical application as an onboard hydrogen storage medium. In this work, a synergetic effect of NbCl5 and hexagonal BN (h-BN) on notably improving the dehydrogenation properties of LiBH4 was investigated. It is found that the addition of NbCl5 and h-BN co-dopants can significantly enhance the dehydrogenation kinetics of LiBH4, and the catalytic effect of co-dopant is better than that of NbCl5 or h-BN dopant separately. The NbCl5/h-BN co-doped LiBH4 can release 10.78 wt% hydrogen, which is about 13 times and 5 times more than that of the NbCl5 doped LiBH4 and h-BN doped LiBH4 within 10 min at 400 °C, respectively. The major dehydrogenation temperature of NbCl5/h-BN co-doped LiBH4 is reduced to 377 °C, much lower than that of ball-milled LiBH4 (464 °C). The apparent activation energy (Ea) of hydrogen desorption is reduced from 195.81 kJ/mol of LiBH4 to 122.75 kJ/mol of NbCl5/h-BN co-doped LiBH4. The microstructural results reveal that the catalytic effect of NbCl5/h-BN co-dopant on improving the dehydrogenation kinetics of LiBH4 could be ascribed to the in situ formed nano NbH@h-BN, which serves as the heterogeneous nucleation site to reduce the decomposition activation energy barrier of LiBH4 and shortens the distance of the solid–liquid phase boundary movement of LiBH4 decomposition.

•6 Mg(BH4)2-4FGi composite decompose below 170 °C.•Numerous nanoscale spots formed in 3 Mg(BH4)2–3LiBH4-4FGi composite.•Synergetic modification of FGi and LiBH4 could suppress the B2H6 released from Mg(BH4)2.•Synergetic effect of FGi and LiBH4 can significantly improve the dehydrogenation kinetics of Mg(BH4)2.Mg(BH4)2 is considered as one of the most promising light metal complex hydrides because of its high volumetric and gravimetric hydrogen capacities and world-wide abundance. However, its higher major desorption temperatures (above 300 °C) and poor reaction kinetics have to be improved for the practical application. Herein, Mg(BH4)2 was successfully synthesized via wet-chemical technique and a significant enhancement in dehydrogenation performance of Mg(BH4)2 is achieved by the synergetic effect of fluorographite (FGi) and LiBH4. Under the effect of FGi, the hydrogen desorption of 6 Mg(BH4)2-4FGi composite could be completed below 170 °C in seconds. However, the hydrogen released from 6 Mg(BH4)2-4FGi suffers from impurities of B2H6 and HF. More importantly, it is demonstrated that almost all the B2H6 and HF impurities can be suppressed by synergetic modifying Mg(BH4)2 with FGi and LiBH4. The 3 Mg(BH4)2–3LiBH4-4FGi composite exhibits a capacity over 8.0 wt% H2 and starts to release hydrogen at 125.7 °C, which is 143.8 °C and 254.3 °C lower than that of pure Mg(BH4)2 and LiBH4, respectively. These significant improvements could be attributed to both the novel morphology that numerous nano-scale borohydride spots formed on the surface of FGi, and the formations of stable fluorides (MgF2 and LiF) from the interaction between borohydrides and FGi.

Magnesium hydride is widely investigated because of its high hydrogen storage capacity. However, the unfavorable thermodynamic and kinetic barriers hinder its practical application. To ease these problems, three kinds of NbHx nanoparticles were prepared by wet-chemical methods and then introduced into MgH2 for catalytically enhancing its hydrogen storage properties in this work. The results show that all the NbHx nanoparticles are effective in promoting the de-/rehydrogenation kinetics of MgH2, and the three NbHx doped MgH2 composites can desorb 7.0 wt % H2 within 9 min at 300 °C while ball milled MgH2 only releases 0.2 wt % H2 in 9 min and 4.1 wt % H2 even in 200 min. Interestingly, the significant hydrogen absorption by NbHx doped MgH2 under lower temperature ranging from 50 to 100 °C was observed; thus, MgH2/c-NbHx sample can uptake about 4.0 wt % H2 at 100 °C. It is found that the more disordered the structure and smaller the size of the NbHx particles, the better is the catalytic effect on hydrogen storage performances of MgH2. Analyses of XRD, XPS, and TEM results indicate that the NbHx remains stable in the ball milling and following de-/rehydrogenation process and act as active catalytic species in improving hydrogen storage performance of MgH2. Moreover, a mechanism is proposed to understand how the nanosized NbHx acted as charge transfer between Mg2+ and H–, which contributes to the significantly improved hydrogen storage performances of MgH2. It is believed that the use of Nb-based nanoparticles as catalysts would greatly promote the development of the practical applications of MgH2 for hydrogen storage.

A simple approach to dramatically enhance the dehydrogenation properties of sodium borohydride is achieved by ball milling NaBH4 with fluorographite (FGi). It was found that the ball-milled NaBH4–FGi composite starts to release hydrogen without impurity gas at a lower temperature of 125 °C, and obtains a hydrogen desorption capacity of ca. 4.8 wt% below 130 °C in seconds, which is improved markedly compared to the ball-milled pristine NaBH4. The significant thermodynamic and kinetic improvement of the NaBH4–FGi composite can be ascribed to the reaction between NaBH4 and FGi as well as the formation of micro-scale NaBH4. Moreover, since the dehydrogenation process of NaBH4–FGi composite is exothermal, the fully reverse reaction is not feasible. In-depth investigations show that the partial rehydrogenation is due to the formation of Na2B12H12 and another new borohydride.

•Superior dehydrogenation property is achieved for nano-sized LiBH4 adsorbed on surface of FGi.•The LiBH4–FGi composite starts to release hydrogen without impurity gas at around 180 °C.•About 7.4 wt% hydrogen is released within seconds below 200 °C for the LiBH4–FGi composite.•Partial reversibility of the LiBH4–FGi composite has been demonstrated.A significant enhancement in the dehydrogenation performance of LiBH4 is achieved by modifying with fluorographite (FGi). In-depth investigations show that the dehydrogenation thermodynamics and kinetics of LiBH4 are strongly improved by ball milling LiBH4 with FGi. The ball-milled LiBH4–FGi (mass ratio of 1:1) composite starts to release hydrogen without impurity gas at around 180 °C, and obtains a hydrogen desorption capacity of 7.2 wt% below 200 °C in seconds, which is improved dramatically compared with pristine ball-milled LiBH4. Microscopic morphology indicates that numerous ∼90 nm spots formed on the surface of FGi. Based on the microstructure analyses combined with hydrogen storage performances, the prominent effect of FGi is largely attributed to the nano-modifying effect and the exothermic reaction between LiBH4 and FGi during the dehydrogenation process. Furthermore, partial reversibility of the LiBH4–FGi composite has been demonstrated and the mechanism underlying the cycling capacity loss is discussed. The use of FGi may shed light on future study on searching for new strategies to improve both the thermodynamics and kinetics of light-metal complex hydrides.Superior hydrogenation performance is achieved for the nano-sized LiBH4 adsorbed on the surface of FGi, in which a capacity close to 7.4 wt% is realized within seconds. Furthermore, hydrogen can be released at a temperature as low as 180 °C, which can fulfill the operation temperature range of PEM fuel cells. This method is highly promising for monitoring of dehydrogenation properties of metal complex borohydrides and could lead new solid-state hydrogen storage materials to higher performances.

NaAlH4 complex hydrides doped with lanthanon hydrides were prepared by hydrogenation of the ball-milled NaH/Al+ xmol.% RE-H composites (RE=La, Ce; x=2, 4, 6) using NaH and Al powder as raw materials. The influence of lanthanon hydride catalysts on the hydriding and dehydriding behaviors of the as-synthesized composites were investigated. It was found that the composite doped with 2 mol.% LaH3.01 displayed the highest hydrogen absorption capacity of 4.78 wt.% and desorption capacity of 4.66 wt.%, respectively. Moreover, the composite doped with 6 mol% CeH2.51 showed the best hydriding/dehydriding reaction kinetics. The proposed catalytic mechanism for reversible hydrogen storage properties of the composite was attributed to the presence of active LaH3.01 and CeH2.51 particles, which were scattering on the surface of NaH and Al particles, acting as the catalytic active sites for hydrogen diffusion and playing an important catalytic role in the improved hydriding/dehydriding reaction.Hydriding (a) and dehydriding (b) curves of NaH/Al+x mol.% LaH3.01 (x=2, 4, 6) composites in the 3rd cycle and pure NaAlH4

The synthesis and hydrogen-storage properties of the mixed alkali metal and alkaline-earth metal borohydride are systematically investigated. It is found that mechanical milling a mixture of LiBH4 and CaCl2 with molar ratio of 3:1 in tetrahydrofuran (THF) forms a new LiBH4·Ca(BH4)2·2THF compound. Thermal analysis indicates that the decomposition process of the new compound involves four steps: (1) LiBH4·Ca(BH4)2·2THF decomposes first into high temperature phase of LiBH4, CaB6, and an intermediate phase Ca–B–H–Cl hydride and synchronously releases a large number of H2 and THF gas together with less B2H6; (2) the eutectic melting of LiBH4 and Ca–B–H–Cl hydride; (3) Ca–B–H–Cl hydride decomposes into CaHCl, CaB6, and a little H2; (4) LiBH4 reacts with CaHCl, generating H2, CaH2, CaB6, LiH, and LiCl. The first dehydrogenation step starts at ca. 70 °C, which is much lower than that of the pristine LiBH4 and Ca(BH4)2. According to Kissenger’s equation, the activation energies of the different dehydrogenation steps are respectively 291.95, 132.06, and 117.13 kJ/mol, except the second decomposition step. Moreover, this new compound LiBH4·Ca(BH4)2·2THF is proved to be partially reversible, which can release 5.63 wt % hydrogen in the second rehydrogenation/dehydrogenation cycle.

A remarkable improvement in the hydrogen desorption performance of Mg(BH4)2–NaBH4 eutectic composite is achieved by simply ball-milling with fluorographene (FG). It is found that the desorption temperature of Mg(BH4)2–NaBH4 (∼200 °C) is still too high and liquid phase appears during dehydrogenation. Particularly, the novel bowl-like 3D Mg(BH4)2–NaBH4–FG composite can be formed after ball-milling. The novel Mg(BH4)2–NaBH4–FG exhibits a low dehydrogenation temperature of 114.9 °C with 6.9 wt% of pure hydrogen in seconds. In-depth investigations show that such greatly improved hydrogen desorption properties of the Mg(BH4)2–NaBH4–FG composite could be ascribed to both the “novel bowl-like 3D structure” with large specific surface area and the “reactant destabilized modification” owing to the decrease of the reaction enthalpy caused by the formation of NaMgF3. This finding provides a facile preparation of complex borohydride composites with low dehydrogenation temperature and fast rate, which accelerates its practical application in fuel cells.

Magnesium hydride (MgH2) exhibits long-term stability and has recently been developed as a safe alternative to store hydrogen in the solid state, due to its high capacity of 7.6 wt% H2 and low cost compared to other metal hydrides. However, the high activation energy and poor kinetics of MgH2 lead to inadequate hydrogen storage properties, resulting in low energy efficiency. Nano-catalysis is deemed to be the most effective strategy in improving the kinetics performance of hydrogen storage materials. In this work, robust and efficient architectures of carbon-wrapped transition metal (Co/C, Ni/C) nanoparticles (8–16 nm) were prepared and used as catalysts in the MgH2 system via ball milling to improve its de/rehydrogenation kinetics. Between the two kinds of nano-catalysts, the Ni/C nanoparticles exhibit a better catalytic efficiency. MgH2 doped with 6% Ni/C (MgH2-6%Ni/C) exhibits a peak dehydrogenation temperature of 275.7 °C, which is 142.7, 54.2 and 32.5 °C lower than that of commercial MgH2, milled MgH2 and MgH2 doped with 6% Co/C (MgH2-6%Co/C), respectively. MgH2 doped with 6% Ni/C can release about 6.1 wt% H2 at 250 °C. More importantly, the dehydrogenated MgH2-6%Ni/C is even able to uptake 5.0 wt% H2 at 100 °C within 20 s. Moreover, a cycling test of MgH2 doped with 8% Ni/C demonstrates its excellent hydrogen absorption/desorption stability with respect to both capacity (up to 6.5 wt%) and kinetics (within 8 min at 275 °C for dehydrogenation and within 10 s at 200 °C for rehydrogenation). Mechanistic research reveals that the in situ formed Mg2Ni and Mg2NiH4 nanoparticles can be regarded as advanced catalytically active species in the MgH2-Ni/C system. Meanwhile, the carbon attached around the surface of transition metal nanoparticles can successfully inhibit the aggregation of the catalysts and achieve the steadily, prompting de/rehydrogenation during the subsequent cycling process. The intrinsic catalytic effects and the uniform distributions of Mg2Ni and Mg2NiH4 result in a favorable catalytic efficiency and cycling stability. Nano-catalysts with this kind of morphology can also be applied to other metal hydrides to improve their kinetics performance and cycling stability.