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Hydrogen storage by spillover in porous carbon material (PCM) has achieved great success in experiments. During the past 20 years, a large number of theoretical works have been performed to explore the hydrogen spillover mechanism, look for high-performance hydrogen storage materials and high-efficiency catalysts. In this paper, we summarize and analyze the results of the past researches, and draw the following conclusions: (1) In PCM surface, the stability of chemisorbed H can be reached through phase nucleation process, which can be initiated in the vicinity of surface impurities or defects. (2) To achieve the 2020 U.S. Department of Energy (DOE) target, the PCM material used for hydrogen storage by spillover should have a sp2 carbon ratio greater than 0.43 and a surface area less than 3500 m2/g, which gives us an inspiration for exploring hydrogen spillover materials. (3) Due to a high barrier, the hydrogen spillover almost can not be initiated on pure PCM substrate at room temperature. By introducing the defects or impurities (e.g. holes, carbon bridges, oxygen functional groups, boron atoms and fluorine atoms), the spillover barriers can be reduced to a reasonable range. In addition, hydrogen atoms may also migrate in a gas phase. (4) According to our previous results of kinetic Monte Carlo simulations, there is a linear relationship between the reaction temperature and the migration barrier. The optimal barrier for the hydrogen spillover should be in the range of 0.60–0.88 eV. (5) Once the hydrogen atoms are chemically adsorbed on the carbon substrate, it is difficult to diffuse again due to the strong strength of C–H bond. Several theoretical diffusion mechanisms have been proposed. For example, the H atoms in physisorption state can diffuse freely on carbon surfaces with high mobility, using the shuttle gases (e.g. BH−4, H2O, HF and NH3) to make the migration thermodynamically possible and decrease the migration barrier, the H atoms diffuse inside the interlayer space of the bi- and tetralayer graphene, and introducing the impurities on the surface to facilitate the hydrogen diffusion. (6) The H desorption through the directly recombination or the reverse spillover is unlikely to occur at normal temperature. The Eley-Rideal reaction may be the only possible mechanism for desorption of the adsorbed H atoms in carbon substrate. Finally, we have made a prospect for further research works on hydrogen storage by spillover.

Nanodevices based on two-dimensional materials hold great promise for DNA sequencing. Owing to some unique properties, silicene has become a potential alternative to the well-known graphene as a se...

How to reduce the H migration barrier in hydrogen spillover is one of the crucial points for hydrogen storage. In this study, we use COF-8 as a representative to study the effect of F decoration fo...

With the aid of computer simulation, we have designed four covalent-organic frameworks based on tetrakis(4-aminophenyl)silsesquioxane (taps-COFs) and their hydrogen storage properties were predicted with grand canonical Monte Carlo (GCMC) simulation. The structural parameters and physical properties were investigated after the geometrical optimization. The accessible surface for H2 molecule (5564.68–6754.78 m2/g) were estimated using the numerical Monte Carlo integration and the pore volume (4.06–10.74 cm3/g) was evaluated by the amounts of the containable nonadsorbing helium molecules at low pressures and room temperature. GCMC simulation reveals that at 77 K, taps COF 1 has the highest gravimetric H2 adsorption capacity of 51.43 wt% and taps COF 3 possesses the highest volumetric H2 adsorption capacity of 58.51 g/L. Excitedly, at room temperature of 298 K, the gravimetric hydrogen adsorption capacities of taps COF 1 (8.58 wt%) and taps COF 2 (8.20 wt%) have exceeded the target (5.5 wt%) of onboard hydrogen storage system for 2025 set by the U.S Department of Energy.

In this work, combining first-principles calculations with kinetic Monte Carlo (KMC) simulations, we constructed an irregular carbon bridge on the graphene surface and explored the process of H migration from the Pt catalyst to carbon bridge, and further migration to the graphene surface. The calculated reaction diagrams show that the hydrogen atoms can easily migrate from the Pt cluster to the carbon bridge with a low barrier of 0.22-0.86 eV, and KMC simulations indicate that the migration reactions can take place at intermediate temperatures (91.9-329.5 K). Our research clarified the role of the carbon bridge: (1) the close combination of Pt clusters and carbon bridges reduces H2 adsorption enthalpy, which facilitates the spillover of H atoms from the Pt cluster to the carbon bridges and (2) the unsaturated carbon atoms on the carbon bridges have radical character and tend to bind radical H atoms. The subsequent study shows that the F atoms decorated on graphene can greatly reduce the migration barrier of H atoms from the carbon bridge to graphene. With F atoms decorated, the carbon atoms are in an electron-deficient state, which have a strong ability to bind the hydrogen atoms, and it promotes the migration of H atoms to the graphene surface. The migration barrier and reaction temperature are reduced to 0.72 eV and 279 K, respectively.

In previous study, we reported that kaempferol ameliorates significantly lung ischemia-reperfusion injury (LIRI), and may be achieved by targeting the SIRT 1 pathway. This study further explored the anti-LIRI mechanism of kaempferol. In vitro, the rat alveolar epithelial cells L2 was cultured and subjected to anoxia/reoxygenation (A/R) insult. In vivo, SD rats were operated to establish LIRI model. The related indicators of oxidative stress and apoptosis in L2 cells and rats lung tissues were detected. Results showed that kaempferol pre-treatment significantly increased the cell viability, improved mitochondrial membrane potential, inhibited the opening of mitochondrial permeability transition pores, reduced the levels of oxidative stress and apoptosis, increased the expressions of Bcl-2 and mitochondrial cytochrome c, and decreased the expressions of Bax and cytoplasmic cytochrome c in L2 cells after A/R insult. In vivo, kaempferol improved the pathological injury, inhibited the levels of oxidative stress and apoptosis, increased the expressions of Bcl-2 and mitochondrial cytochrome c, and decreased the expressions of Bax and cytoplasmic cytochrome c in rats lung tissues after I/R. However, the aforementioned effects of kaempferol were significantly attenuated by the SIRT 1 inhibitor EX527 or the PGC-1α inhibitor SR-18292. What’s more, SR-18292 has not reversed the effect of kaempferol on increasing the protein activity of SIRT 1. Above results suggest that kaempferol ameliorates LIRI by improving mitochondrial function, reducing oxidative stress and inhibiting cell apoptosis. Its molecular mechanism of action includes the SIRT 1/PGC-1α/mitochondria signaling pathway.

In this paper, we designed a good hydrogen storage material of Li-doped ILCOF-1 in theory. The first-principles studies show that the Li-doped ILCOF-1 has a high hydrogen storage capacity (the gravimetric and volumetric uptake are 7.26 wt% and 27.2 g/L, respectively). The 2020 U.S. Department of Energy (DOE) gravimetric target can be achieved. The kinetic Monte Carlo simulations are performed to predict the optimal condition for hydrogen storage and release. Based on the DOE limits, the optimal condition for hydrogen storage is at 250 K and 12 bar, and for hydrogen release is at 350 K and 0.5 bar.

Penta-graphene is a new 2D allotrope of carbon exclusively consists of pentagons in a planar sheet geometry. In this work, we explored that if it can be a substrate for hydrogen spillover. The density-functional theory (DFT) studies show that the H atom can stably adsorb on sp2 carbons. The saturation hydrogen storage density of penta-graphene is estimated to be 5.3 wt%. The Pt4, Pd4 Ni4, and Ti4 clusters are used as the catalyst for hydrogen spillover, and the migration barriers are 1.25, 1.07, 1.03 and 1.35 eV, respectively. The kinetic Monte Carlo simulations are performed to study the migration process for massive H atoms. The results show that the optimal reaction temperatures are 467, 405, 390, and 504 K for Pt4, Pd4, Ni4, and Ti4 catalyst, respectively. For Pd4 and Ni4 catalysts, the spillover reaction can occur at the appropriate temperature (355 and 340 K, respectively) for onboard hydrogen storage systems applied to light-duty vehicles.

It is recognized that “the bridge-building technique remains an art”, due to unclear microscopic nature of the bridging-spillover mechanism. In this paper, a theoretical model of a carbon bridge is designed to reveal the bridging-spillover mechanism in covalent organic frameworks (COFs) by the first-principles calculations and kinetic Monte Carlo (KMC) simulations. It is found that the activation barrier of H migration from a Pt cluster to carbon bridge ranges from 0.23 to 1.05 eV, which is much lower than the direct migration from the Pt6 cluster to COF-8 (activation barrier of 2.1 eV). The bare carbon atoms on carbon bridges are mainly responsible for facilitating hydrogen spillover. KMC simulations display that H would not directly migrate from the Pt6 cluster to COF-8 unless elevating the temperature to 700 K, in contrast to that of lower temperature (88–360 K) for H migration from the Pt6 cluster to carbon bridges. In addition, the introduction of oxygen impurities can reduce the H migration barrier ...

The inhibition mechanism and the inhibition performance of four typical kinetic hydrate inhibitors (KHIs), poly(N-vinyl pyrrolidone) (PVP), poly(N-vinyl piperidone) (PVPip), poly(N-vinyl caprolactam) (PVCap) and poly(N-vinyl azacyclooctanone) (PVAco), have been studied using first-principle calculations and simulations. The results show that the inhibitors can disturb the local water structure, but also can adsorb onto the open hydrate cage, exhibiting the features of both the perturbation-inhibition and the adsorption-inhibition. By analyzing the molecular reactivity, KHI-water interactions, and adsorption ability of KHIs, it is found that the inhibition performance of the inhibitor increases with the increase of the lactam ring size, that is, PVP

Based on spin-polarized first-principles density functional theory in conjunction with the nonequilibrium Green's function method, the spin transport properties of transition metal (TM)–dibenzotetraaza[14]annulene (DBTAA) complexes (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) sandwiched between two Au electrodes are investigated. The results show that Fe– and Co–DBTAA can display perfect spin filtering behavior in a wide bias voltage region. Moreover, it is found that the connected position of anchoring groups on the complexes affect significantly the spin filtering efficiency. The observed spin filtering behavior is explained by the spin-resolved transmission spectrum and molecular projected self-consistent Hamiltonian state analyses.

A new type of 1,3,5,7-tetraphenyladamantane-based covalent organic framework (adm-COF) was designed under the ctn and bor net topology with the method of molecular mechanics. The computed results reveal that all four designed adm-COFs exhibit extremely high porosity (86–95%) and large H2 accessible surface area (5967–6709 m2 g−1). The grand canonical Monte Carlo method was employed to simulate the adsorption isotherms of H2 gas in these adm-COFs at 77 K and 298 K. The simulated results indicate that, at 77 K and 100 bar, adm-COF-4 has the highest gravimetric H2 adsorption capacity of 38.36 wt%, while adm-COF-1 has the highest volumetric H2 adsorption capacity of 60.71 g L−1. Impressively, the gravimetric H2 adsorption capacity of adm-COF-1 can reach up to 5.81 wt% under 100 bar at room temperature, which is very close to the criterion of 6 wt% for the practical application of hydrogen at room temperature set by the U.S. Department of Energy. In addition, possible schemes for synthesizing these adm-COFs have been proposed.

A novel ionic liquid 1,1,3,3-tetramethylguanidinium lactate (TMGL) has been prepared. And the stability of ionic liquid was determined at different temperatures and pressures, which shows extremely low vapor pressure and high thermal stability. TMGL was immobilized by adjusting the feed ratio (TMGL/SiO2) and particle size, the concentration of 0.90% sulfur dioxide gas passed into a certain amount of the loaded ionic liquid TMGL-SiO2, quickly reduced to less than 0.05%, the concentration was measured by a BRUKER Infra-red Spectrometer. This ionic liquid has potential applications in flue gas desulphuration (FGD).

A multiscale theoretical investigation has been performed to study the hydrogen and acetylene storage in Ca2+- and Mg2+-doped COFs (COF-105 and COF-108). The first-principles calculations show that the Ca2+ and Mg2+ can be immobilized at the COFs surfaces, and the doped Ca and Mg cations can adsorb five H2 molecules and three C2H2 molecules with ideal binding energies. The Grand Canonical Monte Carlo (GCMC) simulations were carried out to obtain the hydrogen and acetylene uptakes of Ca2+- and Mg2+-doped COFs at room temperature in the different pressure ranges. Our results demonstrate that, at T = 298 K and p = 100 bar, the total gravimetric uptakes of H2 in Ca2+-doped COF-105 and COF-108 reach 6.78 and 6.54 wt%, respectively, and a higher uptakes of 7.14 and 7.27 wt% have been reached for Mg2+-doped COF-105 and COF-108, respectively. At T = 298 K and p = 1 bar, the acetylene uptakes of Ca2+-doped COF-105, Ca2+-doped COF-108, Mg2+-doped COF-105, and Mg2+-doped COF-108 are 406.42, 366.24, 308.07, and 319.88 cm3/g (corresponding to the excess uptakes of 358.37, 316.38, 236.7109, and 245.42 cm3/g), respectively. The Ca2+-doped COF-105 displays a highest acetylene storage capacity among all materials reported. The Ca2+- and Mg2+-doped COFs can be very practical hydrogen or acetylene storage medium in the future.

In this paper, we performed a multiscale study on the hydrogen storage capacity of Li-doped phthalocyanine covalent organic frameworks (Li-doped Pc-PBBA COF). We combine the first-principles studies of hydrogen adsorption and migration energies with the kinetic Monte Carlo simulations of hydrogen adsorption, diffusion, and desorption processes in Li-doped Pc-PBBA COF. The first-principles calculations revealed that the Li atoms can be doped on the surface of the channel of Pc-PBBA COF with a binding energy of 1.08 eV. Each Li cation can bind three H2 molecules with an average adsorption energy of 0.11 eV. At most, 24 H2 molecules can be adsorbed in one formula unit, corresponding to a maximum of gravimetric density of 5.3 wt % and volumetric uptake of 45.2 g/L. The diffusion barriers of H2 between different Li-adsorption sites are in the range 0.027–0.053 eV. The KMC simulations have predicted that the optimum conditions of hydrogen storage for Li-doped Pc-PBBA COF are at T = 250 K and P = 100 bar, with a...

Using first-principles calculations, we investigate the adsorption behaviors of H2 in B/C/N sheets (including BCN, BC2N, and BC3N) and discuss the effect of external electric fields on H2 adsorbed for BCN and BC2N sheets. For a single H2 adsorbed on BCN and BC2N sheets, the adsorption energy increases dramatically with the electric field intensity increasing, and the maximum adsorption energy can reach 0.55 eV in the electric field of F = 0.050 a.u. and one layer H2 can adsorb on BCN and BC2N sheets, corresponding to the maximum hydrogen storage capacity of 5.1 wt%. The average adsorption energy calculated larger than that of in the field-free case.

Maximum capacities of the hydrogen storage in organometallic compounds consisting of Co and Ni atoms bound to CmHm ring (m = 4, 5; capped type) were, respectively, found as 3.48 and 3.49 wt % (Guo et al., Struct Chem, 2009, 20, 1107). Here, we extend this study to structures having a transition metal (TM) inserted in CmHm ring (inserted type), having TM located on either a C4H or a C5H molecule, and the CH3 ligand bound to the organometallic compounds. We find that for the CoC4H4 and NiC4H4 complexes, the capped types are 1.39 eV and 1.41 eV higher in energy than the inserted types, respectively, while the ground states for CoC5H5 and NiC5H5 complexes are found to be the capped type, which are lower than the inserted types, respectively, by 1.27 eV and 1.31 eV. The maximum capacity of hydrogen storage reached 5.13 wt % for both of CoC4H(H2)3 complex and the inserted-type CoC4H4(H2)3 complex with a reasonable binding energy (0.3–1.0 eV per H2). The positively charged C4H4 and C5H5 molecules do not only improve the capacity of hydrogen storage but also make all H2 adsorbing in molecular form and keep the adsorption energy in an ideal range. After adding the CH3 ligand to the compounds, the average adsorption energy of H2 decreased to an ideal range 0.61–0.94 eV per H2 and the stability of the compounds is also improved. Finally, we analyze the HOMO–LUMO gaps and display the kinetic stability when H2 was added to organometallic compounds. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

The binding property of hydrogen on organometallic compounds consisting of Co, and Ni transition metal atoms bound to C m H m rings (m = 4, 5) is studied through density functional theory calculation. CoC m H m and NiC m H m complexes can store up to 3.49 wt% hydrogen with an average binding energy of about 1.3 eV. The adsorption characteristics of hydrogen to organometallic compounds are investigated by analyzing vibrational spectra of CoC4H4(H2) n and NiC4H4(H2) n (n = 0, 1, 2). The kinetic stability of these hydrogen-covered organometallic complexes is assured by analyzing the energy gap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals. It is also discussed the application of 18-electron rule in predicting maximum number of hydrogen molecules that could be adsorbed by these organometallic compounds.

Applying density functional theory (DFT) calculations, we have designed fullerenes (C20, C24, C26, C28, C30, C36, C60 and C70) intercalated phthalocyanine covalent organic frameworks (Cn-Pc-PBBA COFs). First principles molecular dynamics (MD) simulations showed that the structures of Cn-Pc-PBBA COFs are stable at room temperature and even at higher temperature (500 K). The interlayer distance of Pc-PBBA COF has been expanded to 7.48-13.25 Å by the intercalated fullerenes, and the pore volume and surface area were enlarged by 2.3-3.1 and 2.0-2.6 times, respectively. The grand canonical Monte Carlo (GCMC) simulations show that our designed Cn-Pc-PBBA COFs exhibit a superior hydrogen storage capability: at 77 K and P = 100 bar, the hydrogen gravimetric and volumetric uptakes reach 9.4-12 wt% and 48.1-52.2 g L(-1), respectively. To meet the requirement for practical application in hydrogen storage, we use the Li-doping method to modify the hydrogen storage performance of Cn-Pc-PBBA COFs. Our results show that the Li atoms can stably locate on the surface of C30-, C36, C60 and C70-Pc-PBBA COFs. At T = 298 K and P = 100 bar, for these four Li-doped Cn-Pc-PBBA COFs, the gravimetric and volumetric uptakes of H2 reach 4.2 wt% and 18.2 g L(-1), respectively.

The hydrogen spillover mechanism, including the H chemisorption, diffusion, and H(2) associative desorption on the surface of COFs and H atoms migration from metal catalyst to COFs, have been studied via density functional theory (DFT) calculation. The results described herein show that each sp(2) C atom on COFs' surface can adsorb one H atom with the bond length d(C-H) between 1.11 and 1.14 Å, and the up-down arrangement of the adsorbed H atoms is the most stable configuration. By counting the chemisorption binding sites for these COFs, we can predict the saturation storage densities. High hydrogen storage densities show that the gravimetric uptakes of COFs are in the range of 5.13-6.06 wt%. The CI-NEB calculations reveal that one H atom diffusing along the C-C path on HHTP surface should overcome the 1.41-2.16 eV energy barrier. We chose tetrahedral Pt(4) cluster and HHTP as the representative catalyst and substrate, respectively, to study the H migration from metal cluster to COFs. At most, two H atoms can migrate from Pt(4) cluster to HHTP substrate. The migration reaction is an endothermic process, undergoing an activation barrier of 1.87 eV and 0.57 eV for the first and second H migration process, respectively. Three types of H(2) associative desorption from hydrogenated COFs were studied: (I) the two H adatoms recombining to one H(2) molecule with a recombination barrier of 4.28 eV, (II) the abstraction of adsorbed H atoms by gas-phase hydrogen atoms through ER type recombination reactions with a recombination barrier of 1.05 eV, (III) the H(2) desorption through the reverse spillover mechanism with an energy barrier of 2.90 eV.