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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...

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.

The catalytic property of the bimetallic Ni/Pd, Ni/Pt and Pt/Pd particles for hydrogen spillover on penta-graphene (PG) are studied by using the first-principles and kinetic Monte Carlo (KMC) calculations. The bimetallic Ni/Pd, Ni/Pt and Pt/Pd particles can be stably decorated on PG surface with binding energies in the range of 4.15–5.52 eV. The adsorption enthalpies of H2 molecules on bimetallic particles are in the range of −11.56–−15.35 kcal/mol. The H atom can migrate from the bimetallic particles to PG with the migration barriers range from 0.67 to 0.95 eV. The KMC simulations show that the hydrogen spillover reactions can occur at a suitable temperature (260–361 K), which meet DOE target for onboard hydrogen storage systems applied to light-duty vehicles. In the study, the highest occupied molecular orbital and electric field analysis shows that the bimetal mixing can reduce the hydrogen adsorption enthalpy, and thereby reduce the H migration barrier, which displays a synergistic effect for hydrogen spillover.

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.

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

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 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.