Search

Lithium borohydride (LiBH4) with a theoretical hydrogen storage capacity of 18.5 wt % has attracted intense interest as a high-density hydrogen storage material. However, high dehydrogenation temperatures and limited kinetics restrict its practical applications. In this study, mesoporous nickel- and cobalt-based oxide nanorods (NiCo2O4, Co3O4 and NiO) were synthesized in a controlled manner by using a hydrothermal method and then mixed with LiBH4 by ball milling. It is found that the dehydrogenation properties of LiBH4 are remarkably enhanced by doping the as-synthesized metal oxide nanorods. When the mass ratio of LiBH4 and oxides is 1:1, the NiCo2O4 nanorods display the best catalytic performance owing to the mesoporous rod-like structure and synergistic effect of nickel and cobalt active species. The initial hydrogen desorption temperature of the LiBH4-NiCo2O4 composite decreases to 80 °C, which is 220 °C lower than that of pure LiBH4, and 16.1 wt % H2 is released at 500 °C for the LiBH4-NiCo2O4 composite. Meanwhile, the composite also exhibits superior dehydrogenation kinetics, which liberates 5.7 wt % H2 within 60 s and a total of 12 wt % H2 after 5 h at 400 °C. In comparison, pure LiBH4 releases only 5.3 wt % H2 under the same conditions. [ABSTRACT FROM AUTHOR]

Abstract: A bi-component catalyst TiB2/GNSs (GNSs is the abbreviation of graphene nanosheets) is synthesized by a solid-state method. Microstructural characterizations based on SEM (scanning electron microscopy), TEM (transmission electron microscopy) and N2 physisorption show that the size of TiB2/GNSs catalyst is at nanoscale (20–30 nm) with a surface area of 84.69 m2 g−1. The TiB2/GNSs nanoparticles ball milled with MgH2 and exhibit enhanced catalytic effects on the dehydrogenation properties of MgH2 compares to TiB2 and GNSs individually. DSC (differential scanning calorimetry) measurements confirm that the peak desorption temperature of MgH2-5 wt%TiB2/GNSs composites can be lowered more than 44 °C than the pure as-milled MgH2. And the dehydrogenation kinetics of TiB2/GNSs-doped MgH2 is severalfold acceleration compares to the pure as-milled MgH2. It is proposed that the TiB2/GNSs nanoparticles could significantly enhance the intimate interface between TiB2/GNSs and hydride, therefore, provide more active “catalytic sites” and H “diffusion channels” to reduce the dehydrogenation temperature and improve the dehydrogenation kinetics of MgH2. The synergistic effect of nano-GNSs and TiB2 nanoparticles contributes to the highly efficient for dehydrogenation of MgH2-5wt%TiB2/GNSs composites. [Copyright &y& Elsevier]

The catalytic effects of Co@C additive on hydrogen storage properties of LiAlH 4 prepared by ball milling have been systematically investigated. The onset desorption temperature of Co@C–LiAlH 4 sample is 100.0 °C, which is 51 °C lower than that of as-received LiAlH 4 . Isothermal desorption results show that for Co@C–LiAlH 4 dehydrogenated at 130 °C, 4.58 wt% of hydrogen can be released with 180 min, which is 3.56 wt% higher than that of as-received LiAlH 4 under the same conditions. Approximately 7.05 wt% of hydrogen is released at 150 °C. Through the Kissinger desorption kinetics analyses, the apparent activation energy, E a , of Co@C–LiAlH 4 is calculated as 95.36 kJ mol −1 H 2 and 115.6 kJ mol −1 H 2 for the first two decomposition processes, respectively. It indicates that dehydrogenation kinetics of LiAlH 4 matrix considerably improves by doping the Co@C catalyst. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogen storage properties of LiAlH4 doped efficient TiN catalyst were systematically investigated. We observe that TiN catalyst enhances the dehydrogenation kinetics and decreases the dehydrogenation temperature of LiAlH4. The dehydrogenation behaviors of 2%TiN–LiAlH4 are investigated using temperature programmed desorption (TPD), differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy (FTIR). Interestingly, the onset hydrogen desorption temperature of 2%TiN–LiAlH4 sample gets lowered from 151.0 °C to 90.0 °C with a faster kinetics, and the dehydrogenation rate reached a maximum value at 137.2 °C. By adding a small amount of as-prepared TiN, approximately 7.1 wt% of hydrogen can be released from the LiAlH4 at 130 °C. Interestingly, the result of the FTIR indicates that the 2%TiN–LiAlH4 maybe restore hydrogen under 5.5 MPa hydrogen. Moreover, 2%TiN–LiAlH4 displayed a substantially reduced activation energy for LiAlH4 dehydrogenation. [Copyright &y& Elsevier]

Abstract: Co–B doped NaAlH4 is successfully synthesized by two-step synthesis process. The first activation step is milling NaH/Al powder and Co–B mixtures under Ar atmosphere. The second step is milling in a lower hydrogen pressure atmosphere. XRD patterns and FTIR spectrum demonstrate that NaAlH4 is completely formed after 15 h milling in Ar atmosphere following by 40 h milling in 2 MPa H2 atmosphere. PCT curves of as-prepared NaAlH4 show that it can release hydrogen at a low temperature of 90 °C. The activation energy value calculated by Arrhenius equation is only 67.95 kJ mol−1. Moreover, the formation mechanism of NaAlH4 is also discussed. [Copyright &y& Elsevier]

NaAlH 4 is one of the most promising hydrogen storage materials due to its high energy density. However, the sluggish kinetic hindered it stepping into practical application. In this work, a bottom-up strategy was employed to confine NaAlH 4 between graphene nanosheets with a millefeuille-liked multi-layer morphology. The NaAlH 4 particles were uniformly arranged between graphene layers, with a high loading up to 90%, and performed improved dehydrogenation kinetic. The dehydrogenation peak temperature 55.7 °C decreased comparing with commercial NaAlH 4. The generality of this nano-structuring strategy were confirmed by the successful synthesis of TiO 2 –NaAlH 4 co-confined composites as well as the further enhanced kinetic. An evaporation induced packing strategy is developed to confine NaAlH 4 particles between graphene nanosheets. The picture demonstrates the morphology changing before and after construction. Image 1 • The sodium alanate was successfully confined between graphene layers through a bottom-up strategy. • The confined sodium alanate arranged on graphene layers uniformly even loading up to 90 wt%. • Nano-confinement and catalytic effects improved dehydrogenation kinetic of sodium alanate. [ABSTRACT FROM AUTHOR]

The dehydrogenation behavior of LiBH 4 has been investigated when confined into porous NiMnO 3 microsphere via a wet chemical impregnation method. The confinement of LiBH 4 in the pores of NiMnO 3 nanoparticles leads to a significant decrease of the onset and the maximum desorption temperatures. The composites begin to release hydrogen at 150 °C and the maximum desorption temperature is 300 °C, which are much lower compared to the raw LiBH 4 . Also, the hydrogen release amount is found to be increased. Moreover, the LiBH 4 @NiMnO 3 composites exhibit excellent dehydrogenation kinetics, with 2.8 wt% hydrogen released in 1 h at 300 °C. X-ray diffraction and Fourier transform infrared spectroscopy are used to deduce the desorption mechanism of NiMnO 3 . [ABSTRACT FROM AUTHOR]

The nanoscaled Ni-based compounds (Ni 3 C, Ni 3 N, NiO and Ni 2 P) are synthesized by chemical methods. The MgH 2 -X (X = Ni 3 C, Ni 3 N, NiO and Ni 2 P) composites are prepared by mechanical ball-milling. The dehydrogenation properties of Mg-based composites are systematically studied using isothermal dehydrogenation apparatus, temperature-programmed desorption system and differential scanning calorimetry. It is experimentally confirmed that the dehydrogenation performance of the Mg-based materials ranks as following: MgH 2 Ni 3 C, MgH 2 Ni 3 N, MgH 2 NiO and MgH 2 Ni 2 P. The onset dehydrogenation temperatures of MgH 2 Ni 3 C, MgH 2 Ni 3 N, MgH 2 NiO and MgH 2 Ni 2 P are 160 °C, 180 °C, 205 °C and 248 °C, respectively. The four Mg-based composites respectively release 6.2, 4.9, 4.1 and 3.5 wt% H 2 within 20 min at 300 °C. The activation energies of MgH 2 Ni 3 C, MgH 2 Ni 3 N, MgH 2 NiO and MgH 2 Ni 2 P are 97.8, 100.0, 119.7 and 132.5 kJ mol −1 , respectively. It' found that the MgH 2 Ni 3 C composites exhibit the best hydrogen storage properties. Moreover, the catalytic mechanism of the Ni-based compounds is also discussed. It is found that Ni binding with low electron-negativity element is favorable for the dehydrogenation of the Mg-based composites. [ABSTRACT FROM AUTHOR]

In this report, Ni and TiO 2 are successfully embedded into porous carbon aerogel (CA) (donated as Ni TiO 2 @CA). Meanwhile, the synergistic effect of Ni, TiO 2 and CA on the dehydrogenation properties of LiBH 4 is systematically studied. Ni@CA, TiO 2 @CA and CA are also investigated for comparisons. Compared to other three materials, Ni TiO 2 @CA exhibits better performance when used as a carrier to support LiBH 4 . More than 6.75 wt% H 2 is released from LiBH 4 Ni TiO 2 @CA system in nearly 120 min at 350 °C, exhibiting a higher dehydrogenation capacity than that of LiBH 4 Ni@CA (3.15 wt %), LiBH 4 TiO 2 @CA (5.15 wt%) and LiBH 4 -CA (2.05 wt %), respectively. Furthermore, the apparent energy (Ea) calculated with Kissinger method is 118.8 kJ/mol, much lower than that of pure LiBH 4 . Dehydrogenation performance of LiBH 4 Ni TiO 2 @CA may be due to the synergetic effect of destabilization of TiO 2 , catalysis of Ni, as well as the nanoconfinement of CA. [ABSTRACT FROM AUTHOR]

Nitrogen-doped hierarchically porous carbon (NHPC) materials have been synthesized by using a zeolitic imidazolate framework, ZIF-8, as self-sacrificing template. The initial derived carbon (D-carbon) contains a 3-dimensional (3D) hierarchically porous carbon framework with rich nitrogen doping (11.22%). Chemical activation by KOH, the further activated carbon (Ac-carbon) shows a specific high surface area (2477 m 2 g −1 ), but lower N content (1.99%). LiBH 4 -(D-carbon)/(Ac-carbon) is prepared by ball-milling method and the dehydrogenation performance of LiBH 4 is significantly improved. More than 6.13 wt% H 2 can be released from either of the two mixtures within 100 min at 320 °C, respectively, showing better dehydrogenation performance than that of pure LiBH 4 . Additionally, the controlled experiments reveal that those improved dehydrogenation properties of LiBH 4 might be attributed to the synergetic contributions of high N heteroatom loading, large surface area and catalysis of carbon materials. We provided a simple method to prepare solely MOF-derived nitrogen-doped carbon materials, which might be a promising catalyst for the hydrogen storage materials. [ABSTRACT FROM AUTHOR]

A new hybrid nanocatalyst Ni-CeO x /GNS (graphene nanosheets supported nanoscale Ni and CeO x , x = 1.69) of high surface area and porosity is synthesized by impregnation-reduction method. It is demonstrated that the Ni-CeO x /GNS nanocatalyst exhibits improved catalytic effect on the dehydrogenation performances of MgH 2 compares to individual Ni/GNS, CeO x /GNS, or GNS. Differential scanning calorimetry (DSC) measurement proved that both the onset and peak desorption temperature of MgH 2 -5 wt% Ni-CeO x /GNS (abbreviated as MgNCG) nanocomposites can be decreased by 90.2 and 60.1 °C, respectively. Isothermal desorption kinetic test confirmed that the dehydrogenation kinetics of MgNCG nanocomposites is dozens of times higher than the pure milled MgH 2 , e.g. MgNCG nanocomposites can release 6.50 wt% H 2 within 10 min at 300 °C with an initial hydrogen pressure of 5 KPa, superior to 0.16 wt% H 2 desorbed by MgH 2 under the same condition. Additionally, the activation energy (Ea) of MgNCG decreases significantly contrast with pure milled MgH 2 , it is proposed that the tri-component of Ni-CeO x /GNS nanocatalyst has a synergistic effect on the highly efficient dehydrogenation of MgH 2 . [ABSTRACT FROM AUTHOR]

In this work, 3D hierarchical flower-like MoS 2 spheres are successfully fabricated via a hydrothermal method followed by a heat treatment. The obtained product is composed of few-layered MoS 2 nanosheets with enlarged interlayer distance (ca. 0.66 nm) of the (002) plane. Meanwhile, the hydrogen storage properties of the as-prepared MoS 2 ball milled with LiBH 4 are systematically investigated. The results of temperature programmed desorption (TPD) and isothermal measurement suggest that the LiBH 4 –MoS 2 (as-prepared) mixture exhibits favorable dehydrogenation properties in both lowering the hydrogen release temperature and improving kinetics of hydrogen release rate. LiBH 4 –MoS 2 (as-prepared) sample (the preparation mass ratio is 1:1) starts to release hydrogen at 171 °C, and roughly 5.6 wt% hydrogen is released within 1 h when isothermally heated to 320 °C, which presents superior dehydrogenation performance compared to that of the bulk LiBH 4 . The excellent dehydrogenation performance of the LiBH 4 –MoS 2 (as-prepared) mixture may be attributed to the high active site density and enlarged interlayer distance of the MoS 2 nanosheets, 3D architectures and hierarchical structures. [ABSTRACT FROM AUTHOR]

Different Ti-based materials are added to MgH 2 and their catalytic effects are systematically investigated. The results suggested that all these Ti-based additives could effectively improve the dehydrogenation performances of MgH 2 . And the ionic TiF 3 shows the best catalytic effects, followed by elemental Ti, oxide TiO 2 and covalent TiN sequentially. Onset desorption temperature decreases from 308 °C for pure MgH 2 to 280 °C for MgH 2 –TiN, further lowers to 257 and 216 °C for the MgH 2 –Ti and MgH 2 –TiO 2 composites, finally reduces to 173 °C for the MgH 2 –TiF 3 sample. Kissinger analysis indicated that apparent activation energy ( E a ) of MgH 2 was reduced to various degrees with the addition of different Ti-based materials. A fundamental understanding about the catalytic mechanism of these Ti-based materials on MgH 2 is proposed, regarding to their different reaction processes and the formation of different active species. [ABSTRACT FROM AUTHOR]

Dehydrogenation behavior of LiAlH 4 (lithium alanate) admixed with TiF 3 is investigated by pressure-composition-temperature (PCT), fourier transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), differential scanning calorimetry (DSC) and temperature programmed desorption (TPD). The TiF 3 addition enhances kinetics of LiAlH 4 and decreases the decomposition temperature. The LiAlH 4 -2 mol % TiF 3 sample starts to release hydrogen at about 35 °C and the dehydrogenation rate reaches a maximum value at 108.4 °C, compared with 145 °C and 179.9 °C for the as-received LiAlH 4 . As for the dehydrogenation kinetics, the LiAlH 4 -2 mol % TiF 3 sample releases about 7.0 wt % H 2 at 140 °C within 80 min. In comparison, the as-received LiAlH 4 sample releases only 0.8 wt % hydrogen under the same conditions. The existence of proposed catalyst, Al 3 Ti formed in-situ in the process of dehydrogenation, has been confirmed experimentally by XRD measurements. The activation energy of LiAlH 4 -2 mol % TiF 3 composite is deduced to be 66.76 kJ mol −1 and 88.21 kJ mol −1 for the first and second reaction stages of LiAlH 4 dehydrogenation. [ABSTRACT FROM AUTHOR]

Lithium aluminum hydride (LiAlH4) is considered as an attractive candidate for hydrogen storage owing to its favorable thermodynamics and high hydrogen storage capacity. However, its reaction kinetics and thermodynamics have to be improved for the practical application. In our present work, we have systematically investigated the effect of NiCo2O4 (NCO) additive on the dehydrogenation properties and microstructure refinement in LiAlH4. The dehydrogenation kinetics of LiAlH4 can be significantly increased with the increase of NiCo2O4 content and dehydrogenation temperature. The 2 mol% NiCo2O4-doped LiAlH4 (2% NCO–LiAlH4) exhibits the superior dehydrogenation performances, which releases 4.95 wt% H2 at 130 °C and 6.47 wt% H2 at 150 °C within 150 min. In contrast, the undoped LiAlH4 sample just releases <1 wt% H2 after 150 min. About 3.7 wt.% of hydrogen can be released from 2% NCO–LiAlH4 at 90 °C, where total 7.10 wt% of hydrogen is released at 150 °C. Moreover, 2% NCO–LiAlH4 displayed remarkably reduced activation energy for the dehydrogenation of LiAlH4. [ABSTRACT FROM AUTHOR]

A synergistic effect of nanoconfinement and catalyzing is a new strategy to enhance the dehydrogenation properties of complex hydrides. Herein, LiBH4 has been infiltrated into a CoNiB-loaded carbon aerogels system (donated as LiBH4@CA@CoNiB). It is found that the desorption performances of LiBH4 are significantly strengthened. The onset desorption temperature of LiBH4@CA@CoNiB is decreased to 192 °C, and majority of the liberation occurs at about 320 °C, much lower than that of pure LiBH4. Also, about 15.9 wt% H2 could be released below 600 °C. Furthermore, LiBH4 doped with CA@CoNiB exhibits an excellent desorption kinetics, with a capacity of 9.33 wt% H2 released in 30 min at 350 °C, while only 2.13 wt% H2 is gained for bulk LiBH4. In addition, the apparent activation energy (Ea) is reduced sharply from 59.00 kJ/mol (pure LiBH4) to 46.39 kJ/mol. [ABSTRACT FROM AUTHOR]

Highlights: • The dehydrogenation properties of NaAlH4 are enhanced significantly by adding TiN. • The onset dehydrogenation temperature of 2%TiN–NaAlH4 is lowered to 130.0°C. • Approximately 5.44wt.% of hydrogen can be released from 2%TiN–NaAlH4 at 190.0°C. • TiN–NaAlH4 system indicates an excellent reversibility according to HP-DSC. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen is a promising energy carrier in future energy systems. However, hydrogen storage is facing increasing challenges within the development of more environmentally friendly energy systems with high capacity, fast kinetics, favorable thermodynamics, controllable reversibility, especially for applications in vehicles with fuel cells that use proton–exchange membranes (PEMs). In this report, we present a critical review on catalyst modified and nanoconfined NaAlH4, focusing on their thermodynamics and kinetics behaviors. Catalyst is of increasing interest and may lead to significantly enhanced kinetics, higher degree of stability and/or more favorable thermodynamic properties. Thus, catalyst–doped NaAlH4 is expected to strongly contribute by the development of novel catalysts and synthesis methods. Additionally, nanoconfined NaAlH4 may also have a wide range of applications in the PEM fuel cells. Selected catalyst materials, porous scaffold materials, methods for preparation of NaAlH4 systems and their hydrogen storage properties are reviewed. This is the first review report on catalyst modified and nanoconfined NaAlH4. [Copyright &y& Elsevier]

Abstract: Nanosized cobalt sulfide and cobalt boride were synthesized and doped into LiBH4 to improve the dehydrogenation properties of this important candidate for hydrogen storage. With respect to CoS x doping, the dehydrogenation temperature (peak temperature observed by mass spectrometry) of pristine LiBH4 can be reduced from 440 °C to 175 °C with a maximum capacity of 6.7 wt% at 50% doping. Unfortunately, B2H6 is liberated and the process is not reversible because the CoS x dopant reacts with LiBH4 to form more stable compounds. By changing CoS x to CoB x , a reversible dehydrogenation was realized with greatly improved reversibility. The dehydrogenation temperature was reduced to 350 °C with a maximum capacity of 8.4 wt% at 50% doping amount. It is very significant that CoB x is stable and the release of B2H6 is eliminated. A reversible hydrogen desorption of about 5.3 wt% can be achieved with a LiBH4 + 50% CoB x mixture under a mild rehydrogenation condition of 400 °C at 10 MPa H2. It is obvious that CoS x acts as a reactant even though the dehydrogenation is greatly enhanced, while CoB x behaves as a catalyst significantly promoting the dehydrogenation and reversibility of LiBH4. [Copyright &y& Elsevier]