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1.
The hydrogen storage (H-storage) capacity of alkali (Li+, Na+ and K+) and alkaline earth metal ion (Mg2+ and Ca2+) doped cubane, cyclohexane and adamantane has been investigated using Density Functional Theory (DFT) based M05-2X functional employing 6-31+G∗∗ basis set. The adsorption of number of H2 molecules on the metal ion doped complexes depends on ionic radii and charge of the metal ions. Among the 15 complexes investigated in this study, Mg2+ ion doped cubane, cyclohexane and adamantane complexes have higher H-storage capacity when compared to other complexes. The calculated binding energy (BE) of 5H2@Cub-Mg2+ complex is 46.85 kcal/mol with binding energy per H2 molecule (BE/nH2) of 9.37 kcal/mol. The corresponding gravimetric density of the complexes is 7.3 wt%. In the case of 4H2@Cyc-Mg2+ complex, the BE is 32.19 kcal/mol (BE/nH2 is 8.05 kcal/mol with 6.9 wt% in gravimetric density). The Adm-Mg2+ complexes adsorb 4H2 molecules with BE of 33.33 kcal/mol, the BE of per H2 molecule is 8.33 kcal/mol. The corresponding gravimetric density of the complex is around 4.8 wt%, respectively. A new linker modified MOP-9 has been constructed based on the results and their H-storage capacity has also estimated.  相似文献   

2.
The strong metal-support interactions between metal and its support have been considered as an effective way to improve the electrocatalytic activity in heterogeneous catalysis, which can modulate metal d-band's energy level and, consequently, affect the adsorption/desorption of the intermediates on the metal nanoparticle's surface. In this paper, we use a self-assembly strategy for construction nano-sized Ru nanoparticles (NPs) anchored on B, N co-doping carbon nanorod carrier (Ru/BCN) as HER catalyst by using unique boron cluster-organic framework as precursor and self-sacrificing templates. This supramolecular framework forming with cucurbit [6]uril as the host and closo-[B12H12]2- as the guest can feature unique hexagonal nanorod morphology to confine the Ru NPs into framework through weak reductivity of closo-[B12H12]2-. After pyrolysis, the strong metal-support interactions between B, N co-doping carbon support (BCN) and Ru NPs have been found due to the synergistic coupling effect of co-dopants B and N, which can increase electron transfer between the metal nanoparticle and support. The overpotentials of 33 mV and 40 mV are required for as-prepared catalyst Ru/BCN to achieve a current density of 10 mA cm?2 in alkaline and acidic conditions, respectively, which are approximately one third of those of Ru/CN. These findings demonstrate that our synthetic way offers a potential route for fabricating co-doping carbon with B and N atoms to support Ru NPs with enhanced HER performance in pH-independent conditions.  相似文献   

3.
The H2 storage properties of isoreticular metal-organic framework materials (IRMOFs), MOF-5 and IRMOF-10, impregnated with different numbers and types of heterogeneous C48B12 molecules were investigated using density functional theory and grand canonical Monte Carlo (GCMC) calculations. The excess hydrogen adsorption isotherms of IRMOFs at 77 K within 20 bar indicate that suitable number and type of C48B12 molecules play a crucial role in improving the H2 storage properties of IRMOFs. Among the studied pure and nC48B12 (n = 1, 2, 4, 8) in Ci symmetry impregnating into MOF-5, at 77 K under 6 bar, MOF-5-4C48B12 with a 3.5 wt% and 29.9 g/L hydrogen storage density, and at 77 K under 12 bar, the pure MOF-5 with a 4.9 wt% and 31.0 g/L hydrogen storage density has the best hydrogen storage properties. Whereas, among the studied pure and nC48B12 (n = 1, 2, 4, 8) in S6 symmetry impregnating into IRMOF-10, IRMOF-10-8C48B12 always shows the best hydrogen storage properties among the pure and C48B12-impregnated IRMOF-10 at 77 K within 20 bar. IRMOF-10-8C48B12 has a 6.0 wt% and 34.6 g/L hydrogen storage density at 77 K under 6 bar, and has a 7.1 wt% and 41.4 g/L hydrogen storage density at 77 K under 12 bar. The confinement effect of IRMOFs on C48B12 molecules, and steric hindrance effect of C48B12 molecules on IRMOFs mainly affects the H2 uptake capacity by comparing the absolute H2 molecules in individual IRMOFs units, C48B12 molecules, and IRMOFs-nC48B12 compounds. The absolute hydrogen adsorption profiles show that eight C48B12 molecules impregnating into MOF-5 can exert obvious steric effects for H2 adsorption. The saturated gravimetric and volumetric H2 densities of IRMOF-10-8C48B12 higher than those of MOF-5-8C48B12 due to with larger free volume.  相似文献   

4.
Density Functional Theory (DFT) with B3LYP/6-311++g** level has been performed to investigate the electronic structures of cage B12Hn for up to n ≤ 12 and AlB12Hn for up to n ≤ 13. Moreover, the computations has been extended to the charged clusters of [B12H12]q, [AlB12H12]q and [AlB12H13]q where (q = ±1 and ±2). Their energetics are calculated and structural analysis have been carried out. Cage form of the B12 remains stable against to hydrogen adsorptions.  相似文献   

5.
In this present study, novel aqueous-phase catalytic systems, namely spherical Au and Pd nanoparticles (NPs) capped with Cs2 [closo-B12H12], were used to produce ethanol and methanol via direct oxidation of methane in the presence of H2O2 and O2 under mild conditions. The ethanol selectivity surpassed 52.96% and 86.33% at 50 °C, and the productivity reached 8.86 and 25.18 mol·kgcat1·h1, respectively. Plausible methane–ethane–ethanol pathway involving free radial •OH radicals was proposed based on the electron paramagnetic resonance (EPR) result. According to the theoretical calculations, the surfaces of {111} plane of Au NPs and {100} plane of Pd NPs were capped with Cs2 [closo-B12H12], and Au–B and Pd–B bonds were consequently formed, respectively. Moreover, the binding energies of Au NPs and Pd NPs capped with Cs2 [closo-B12H12] were calculated to be −128.9 and −230.1 kcal mol−1, respectively. Based on the theoretical calculations, higher binding energy indicates a larger amount of charge on the surfaces of the planes of NPs. A lower peak intensity can lead to the formation of a more stable catalyst with enhanced catalytic activity. Thus, the ethanol selectivity of the as-prepared catalyst was considerably higher than that for methanol.  相似文献   

6.
We report on an easy synthesis method for the preparation of a hybrid composite of Pt-loaded MWCNTs@MOF-5 [Zn4O(benzene-1,4-dicarboxylate)3] that greatly enhanced hydrogen storage capacity at room temperature. To prepare the composite, we first prepared Pt-loaded MWCNTs, which were then incorporated in-situ into the MOF-5 crystals. The obtained composite was characterized by various techniques such as powder X-ray diffractometry, optical microscopy, porosimetry by nitrogen adsorption, and hydrogen adsorption. The analyses confirmed that the product has a highly crystalline structure with a Langmuir specific surface area of over 2000 m2/g. The hybrid composite was shown to have a hydrogen storage capacity of 1.25 wt% at room temperature and 100 bar, and 1.89 wt% at cryogenic temperature and 1 bar. These H2 storage capacities represent significant increases over those of virgin MOF-5s and Pt-loaded MWCNTs.  相似文献   

7.
Metal-organic frameworks (MOFs) exhibiting high surface area and tunable pore size own broad application prospects. Compared with existing MOFs, MOF-5 [Zn4O(bdc)3] is a promising hydrogen storage material due to high H2 uptake capacity and thermostability. However, further wider applications of MOF-5 have been limited because atmospheric moisture levels cause MOF-5 instability. MOF-5 and multi-walled carbon nanotubes (MWCNTs) hybrid composite (denoted MOFMC) can enhance stability toward ambient moisture and improve hydrogen storage capacity. In this paper, the MOFMC, which has an interpenetrated structure with high mesoporosity, was synthesized. The MOFMC is denoted as Int-MOFMC-meso. It stored 2.02 wt% H2 at 77 K under 1 bar, which is higher than the MOF-5 with similar structure and the earlier reported MOFMC material. Moreover, the Int-MOFMC-meso can also show more excellent performance of thermostability and moisture stability than the MOF-5 with similar structure.  相似文献   

8.
The effect of light metal ion decoration of the organic linker in metal-organic framework MOF-5 on its hydrogen adsorption with respect to its hydrogen binding energy (ΔB.E.) and gravimetric storage capacity is examined theoretically by employing models of the form MC6H6:nH2 where M = Li+, Na+, Be2+, Mg2+, and Al3+. A systematic investigation of the suitability of DFT functionals for studying such systems is also carried out. Our results show that the interaction energy (ΔE) of the metal ion M with the benzene ring, ΔB.E., and charge transfer (Qtrans) from the metal to benzene ring exhibit the same increasing order: Na+ < Li+ < Mg2+ < Be2+ < Al3+. Organic linker decoration with the above metal ions strengthened H2-MOF-5 interactions relative to its pure state. However, amongst these ions only Mg2+ ion resulted in ΔB.E. magnitudes that were optimal for allowing room temperature hydrogen storage applications of MOF-5. A much higher gravimetric storage capacity (6.15 wt.% H2) is also predicted for Mg2+-decorated MOF-5 as compared to both pure MOF-5 and Li+-decorated MOF-5.  相似文献   

9.
Alkaline or alkaline earth octahydrotriborate M(B3H8)x and dodecahydro-closo-dodecaborate MxB12H12 (M = Li, Na, Mg or Ca with x = 1 or 2) have recently attracted a lot of interest for hydrogen storage and solid electrolyte applications. Nevertheless, their syntheses are still a roadblock for large scale applications. In this paper we propose a novel approach for their syntheses starting from the cheapest borohydride NaBH4. The process involves first the solvothermal synthesis of tetrabutylammonium octahydrotriborate (C4H9)4NB3H8 (TBAB3H8) being the basis for the syntheses of the others boranes. Starting from TBAB3H8, we have synthesized pure and unsolvated NaB3H8 by salt metathesis reaction with sodium tetraphenylborate. Then, we have successfully obtained Na2B12H12 by solvothermal decomposition of NaB3H8. This approach has shown to be quantitative and reproducible, which could lead to the development of these boranes in real life applications.  相似文献   

10.
The Mg(BH4)2-xLiH (0.1 ≤ x ≤ 0.8) composites which exhibit favorable dehydrogenation and encouraging reversibility are experimentally investigated. LiH additive reduces the onset temperature for dehydrogenation to 150 °C. And hydrogen release exceeds 10 wt.% from the new binary material below 250 °C. Furthermore, rehydrogenation results show that 3.6 wt.% hydrogen can still be recharged after twenty cycles at 180 °C. It should be emphasized that the long-term reversibility of borohydride under 200 °C is long overdue. TPD, PCT, and high-pressure DSC measurements are used to characterize the improvements in thermodynamic and kinetic ways. In addition, FT-IR and NMR studies indicate that the composite has a significant synergistic effect during (de)hydrogenation processes. This work suggests that controlled cation stoichiometry combined with doping by metal Li+ subvalent to Mg2+ facilitate the formation of polyborane intermediates [B3H8] and [B2H6]2−. They improve the dehydrogenation properties and make the material reversible under mild conditions.  相似文献   

11.
The metal-organic framework Zn4O (BDC)3 (BDC = 1,4-bezene dicarboxlate), also known as MOF-5, has demonstrated considerable adsorption of hydrogen, up to 7 excess wt.% at 77 K. Consequently, it has attracted significant attention for vehicular hydrogen storage applications. To improve the volumetric hydrogen density and thermal conductivity of MOF-5, prior studies have examined the hydrogen storage capacities of dense MOF-5 pellets and the impact of thermally conductive additives such as expanded natural graphite (ENG). However, the performance of a storage system based on densified MOF-5 powders will also hinge upon the rate of hydrogen mass transport through the storage medium. In this study, we further characterize MOF-5 compacts by measuring their hydrogen transport properties as a function of pellet density (ρ = 0.3–0.5 g cm−3) and the presence/absence of ENG additions. More specifically, the Darcy permeability and diffusivity of hydrogen in pellets of neat MOF-5, and composite pellets consisting of MOF-5 with 5 and 10 wt.% ENG additions, have been measured at ambient (296 K) and liquid nitrogen (77 K) temperatures. The experimental data suggest that the H2 transport in densified MOF-5 is strongly related to the MOF-5 pellet density ρ.  相似文献   

12.
Metal-organic frameworks are new kinds of porous crystalline materials. The Zr-based metal-organic framework (MOF-801) is consists of [Zr6(u3-O)4(u3-OH)4]12+ clusters and fumaric acid connectors. MOF-801 has excellent mechanical properties, high chemical stability and high water absorption capacity. There are a large number of hydrophilic functional groups inside MOF-801, which is effective to promote interfacial compatibility between MOF-801 and polymer matrixes. In this work, the MOF-801 with structural defects was synthesized through the solvothermal method by adding excess formic acids as the regulator. These structural defects could confer MOF-801 high surface area (2476.34 m2 g?1) and promote the water absorption capacity. Moreover, structural defects could also expose more open metal sites of MOF-801, thereby increasing the Lewis acidity of MOF-801. Then, the hybrid membranes were synthesized by combining the MOF-801 with structural defects and C-SPAEKS. Dense hydrogen-bond networks formed between the MOF-801 and C-SPAEKS further promote enhance proton conductivity. At the condition of 90 °C and 100% relative humidity, the highest proton conductivity of hybrid membranes reached 0.100 S cm?1, which is similar to that of Nafion 117. Meanwhile, these hybrid membranes showed outstanding chemical and thermal stabilities. These results indicate that these hybrid membranes have potential as proton exchange membranes.  相似文献   

13.
The metal-organic framework MOF-5 has attracted significant attention due to its ability to store large quantities of H2 by mass, up to 10 wt.% absolute at 70 bar and 77 K. On the other hand, since MOF-5 is typically obtained as a bulk powder, it exhibits a low volumetric density and poor thermal conductivity—both of which are undesirable characteristics for a hydrogen storage material. Here we explore the extent to which powder densification can overcome these deficiencies, as well as characterize the impact of densification on crystallinity, pore volume, surface area, and crush strength. MOF-5 powder was processed into cylindrical tablets with densities up to 1.6 g/cm3 by mechanical compaction. We find that optimal hydrogen storage properties are achieved for ρ ∼ 0.5 g/cm3, yielding a 350% increase in volumetric H2 density with only a modest 15% reduction in gravimetric H2 excess in comparison to the powder. Higher densities result in larger reductions in gravimetric excess. Total pore volume and surface area decrease commensurately with the gravimetric capacity, and are linked to an incipient amorphization transformation. Nevertheless, a large fraction of MOF-5 crystallinity remains intact in densities up to 0.75 g/cm3, as confirmed from powder XRD. Predictably, the radial crush strength of the pellets is enhanced by densification, increasing by a factor of 4.3 between a density of 0.4 g/cm3 and 0.6 g/cm3. Thermal conductivity increases slightly with tablet density, but remains below the single crystal value.  相似文献   

14.
AB5 compounds (A = rare earth, B = transition metal) have been widely studied as anodes for Ni-MH applications. However, they have reached their technical limitations and the search for new promising materials with high capacity is foreseen. ABy compounds (2 < y < 5) are good candidates. They are made by stacking [AB5] and [A2B4] units along the c crystallographic axis. The latter unit allows a large increase in capacity, while the [AB5] unit provides good cycling stability. Consequently, the AB3.8 composition (i.e. A5B19 with three [AB5] for one [A2B4]) is expected to exhibit better cycling stability than the AB3.5 (i.e. A2B7 with two [AB5] for one [A2B4]). Furthermore, substitution of rare earth by light magnesium improves both the capacity and cycling stability. In this paper, we compare the hydrogenation and corrosion properties of two binary compounds, SmNi3.5 and SmNi3.8, and two pseudo-binary ones, (Sm, Mg)Ni3.5 and (Sm, Mg)Ni3.8. A better solid-gas cycling stability is highlighted for the binary SmNi3.8. The pseudo-binary compounds also exhibit higher cycling stability than the binary ones. Furthermore, their resistance to corrosion was investigated.  相似文献   

15.
The hydrogen storage capacity of alkali metal ion decorated boric acid (BA) based bowl, sheet and ball structures have been investigated using B3LYP method employing 6-31+G∗∗ basis set. The maximum gravimetric density has been observed for the bowl shaped clusters. These values for Li+, Na+ and K+ decorated clusters are 8.3, 8.8 and 7.8 wt.%, respectively. The range of the calculated binding energy per H2 molecule (BE/H2) for Li+, Na+ and K+ decorated bowl shaped clusters are 2.57-3.59, 1.88-2.11 and 0.76-1.00 kcal/mol, respectively. The same for the sheet clusters are 3.18-3.73, 1.68-2.40 and 0.73-0.97 kcal/mol, respectively. Similarly, BE/H2 of Na+ decorated ball clusters ranges from 1.88 kcal/mol to 2.62 kcal/mol. It has been shown in earlier studies that the BE/H2 should be in between the physisorption and chemisorption limits for realizing the practical applications of different class of materials. In this context, both BE/H2 and gravimetric density of Na+ decorated clusters indicate that these systems have appropriate properties. Hence Na+ decorated (BA)n structures are suitable for hydrogen storage applications.  相似文献   

16.
A series of salts of the B12H122− anion has been prepared: a solvent-free (N2H5)2B12H12, its solvates – (N2H5)2B12H12·H2O, (N2H5)2B12H12·2(CH3CN), (N2H5)2B12H12·(CH3OH), and the salt of a protonated azine – [(CH3)2CNNHC(CH3)2]2B12H12. These compounds have been synthesized from the commercially available precursors via one- or two-step procedures and fully identified on the basis of single-crystal and powder X-ray diffraction. At room temperature (N2H5)2B12H12 crystallizes in C2/c space group, with a = 18.480(5) Å, b = 6.5344(19) Å, c = 13.106(4) Å and β = 131.911(16)o, V = 1177.8(7) Å3, Z = 4. While this compound nominally contains ca. 10.7 wt% of hydrogen, it thermally decomposes above 200 °C releasing mainly N2 and NH3, with H2 being only the minor gaseous product. Contrary to the recently reported case of hydrazinates of borohydrides, doping with 5 mol% of FeCl3 does not increase the relative amount of hydrogen significantly, however, it alters the ratio of N2 and NH3.  相似文献   

17.
Using ab initio based quantum chemical calculations, we have studied the structure, stability and hydrogen adsorption properties of different boron hydrides decorated with lithium, examples of the corresponding anions being dihydrodiborate dianion, B2H22− and tetrahydrodiborate dianion, B2H42− which can be considered to be analogues and isoelectronic to acetylene (C2H2) and ethelene (C2H4) respectively. It is shown that there exists a B-B double bond in B2H4Li2 and a B-B triple bond in B2H2Li2. In both the complexes, the lithium sites are found to be cationic in nature and the calculated lithium ion binding energies are found to be very high. The cationic sites in these complexes are found to interact with molecular hydrogen through ion-quadrupole and ion-induced dipole interactions. In both the complexes, each lithium site is found to bind a maximum of three hydrogen molecules which corresponds to a gravimetric density of ∼23 wt% in B2H4Li2 and ∼24 wt% in B2H2Li2. We have also studied the hydrogen adsorption in a model one-dimensional nanowire with C6H4B2Li2 as the repeating unit and found that it can adsorb hydrogen to the extent 9.68 wt% and the adsorption energy is found to be −2.34 kcal/mol per molecular hydrogen.  相似文献   

18.
Here, we describe the preparation of four structurally modified MOF-5s and carried out a systematic study of the effects of the structural modifications on the evolution of the crystal structure, pore characteristics, and H2 capacities of MOF-5s. The structural modifications were found to significantly influence the pore characteristics, and the specific surface areas of the MOF-5s decreased with the evolution of an ultrafine porosity. These changes were correlated with an increase in the H2 storage capacity of the MOF-5 (from 1.2 to 2.0 wt% at −196 °C and 1 bar). The structural modifications also enhanced the thermal stability of the MOF-5s (the decomposition temperature increased from 438 °C to 510 °C). These results are particularly useful for the design of favorable MOF-based adsorbents with a high H2 uptake coupled with a high thermal stability.  相似文献   

19.
A heterometallic metal–organic framework, {[Ce(oda)3Zn1.5(H2O)3]·0.75H2O}n (1, H2oda = oxydiacetic acid), has been synthesized under hydrothermal condition. The single-crystal X-ray diffraction analysis reveals that compound 1 belongs to hexagonal crystal system with space group P6/mcc and exhibits 3D porous framework. The hydrogen adsorption experiments suggest that 1 possesses reversible hydrogen storage capacity, up to 1.34 wt.% at 77 K and 0.86 wt.% at 298 K, respectively.  相似文献   

20.
This study aims to present the hydro-catalytic treatment of organoamine boranes for efficient thermal dehydrogenation for hydrogen production. Organoamine boranes, methylamine borane (MeAB), and ethane 1,2 diamine borane (EDAB), known as ammonia borane (AB) carbon derivatives, are synthesized to be used as a solid-state hydrogen storage medium. Thermal dehydrogenation of MeAB and EDAB is performed at 80 °C, 100 °C, and 120 °C under different conditions (self, catalytic, and hydro-catalytic) for hydrogen production and compared with AB. For this purpose, a cobalt-doped activated carbon (Co-AC) catalyst is fabricated. The physicochemical properties of Co-AC catalyst is investigated by well-known techniques such as ATR/FT-IR, XRD, XPS, ICP-MS, BET, and TEM. The synthesized Co-AC catalyst obtained in nano CoOOH structure (20 nm, 12% Co wt) is formed and well-dispersed on the activated carbon support. It has indicated that Co-AC exhibits efficient catalytic activity towards organoamine boranes thermal dehydrogenation. Hydrogen release tests show that hydro-catalytic treatment improves the thermal dehydrogenation kinetics of neat MeAB, EDAB, and AB. Co-AC catalyzed hydro-treatment for thermal dehydrogenation of MeAB and EDAB acceleras the hydrogen release from 0.13 mL H2/min to 46.12 mL H2/min, from 0.16 mL H2/min to 38.06 mL H2/min, respectively at 80 °C. Moreover, hydro-catalytic treatment significantly lowers the H2 release barrier of organoamine boranes thermal dehydrogenation, from 110 kJ/mol to 19 kJ/mol for MeAB and 130 kJ/mol to 21 kJ/mol for EDAB. In conclusion, hydro and catalytic treatment presents remarkable synergistic effect in thermal dehydrogenation and improves the hydrogen release kinetics.  相似文献   

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