First-principles study of hydrogen storage on Si atoms decorated C60

Hydrogen storage capacity of Si_nC₆₀ is studied via first-principles theory based on DFT and Canonical Monte Carlo Simulation (CMCS). It is shown that Si atoms strongly prefer D-site rather than other sites and in these structures maximum number of hydrogen molecule onto any Si atom is one. Each Si atom adsorbs one hydrogen molecule in molecular form and with proper binding energies when Si atom is placed in any D-site of C₆₀. Si atoms enhance remarkably hydrogen storage capability in fullerene.     

Modeling and comparison to literature data of composite solid oxide fuel cell electrode-electrolyte interface conductivity

A Monte Carlo percolation model previously used to characterize Triple Phase Boundary (TPB) formation in composite SOFC electrode-electrolyte interfaces has been augmented to allow for investigation of the effects of composition, gas-phase percolation, and surface exchange and transport phenomena on the overall conductivity of these electrode-electrolyte interfaces. The model has been utilized to replicate the results of a previous modeling effort, with similar assumptions and application to an SOFC electrode electrolyte interface. Although the models are similar in many aspects, their key differences allow equivalent predictions of the behavior of overall electrode conductivity as a function of electrode composition, thereby verifying the assumptions and overall approach of the current model. The validity of omitting charge-transfer and activation resistances when comparing overall interfacial conductivity trends is confirmed. The current model is then used to simulate several experimental results. The comparisons among these results show the importance of including gas-phase percolation physics and surface exchange and transport phenomena features in the model. Including gas-phase percolation and these surface phenomena can significantly alter the predictions of conductivity behavior and better predicts experimental observations, particularly at low and high electronic conductor volume fractions.     

Changes of hydrogen storage properties of MgH2 induced by heavy ion irradiation

In order to understand the influence of defect zones on desorption behavior of _MgH2${\mathrm{MgH}}_2$, Xe 120 keV ion irradiation of this material has been performed. DSC, SEM measurements, and SRIM calculations have been used to characterize induced modifications and its influence on the hydrogen desorption behavior of _MgH2${\mathrm{MgH}}_2$. We have demonstrated that the near-surface area of _MgH2${\mathrm{MgH}}_2$ plays the crucial role in hydrogen desorption kinetics. DSC analysis provides clear picture of vacancies influence on H diffusion and desorption in _MgH2${\mathrm{MgH}}_2$, and points out that there is possibility to control the thermodynamic parameters by controlled ion bombardment.     

Hydrogen storage comparison of M doped vanadium oxide nanotubes (M = Mo,Zr and W): A molecular simulation study

Zr, Mo and W doped Vanadium oxide nanotube were considered as remarkable materials for hydrogen storage applications. Monte Carlo molecular simulation was performed to study the adsorption behavior of hydrogen molecules on Vanadium oxide nanotubes (VONTs). The effects of temperature, pressure and mole percent of hydrogen on adsorption capacity of VONTs were investigated to provide deep insight of adsorption behavior. The results represented that hydrogen adsorption is an increasing function of pressure and at about 50 MPa all three metal doped VONT has maximum hydrogen capacity. At 5 MPa and room temperature, the hydrogen capacities of Mo, W and Zr doped VONTs were 1.39, 0.88 and 1.43 w% respectively. With temperature increment up to room temperature, more reduction in initial hydrogen capacity were observed in Mo and Zr doped VONTs.Evaluating hydrogen adsorption of Zr doped VONT from pure and hydrogen /nitrogen mixtures at 300 K indicated that under 2 Mpa, modifications in adsorption capacities were insignificant after N2 addition to the environment. Therefore, Zr doped VONT in hydrogen /nitrogen mixture environment can act as a capable adsorbent for Hydrogen storage system in comparison with Mo and W doped VONTs.     

Hydrogen adsorption on graphene,hexagonal boron nitride,and graphene-like boron nitride-carbon heterostructures: A comparative theoretical study

The results of DFT and ab initio calculations of the hydrogen physisorption on graphene, hexagonal boron nitride (h-BN), and a graphene-like boron nitride-carbon heterostructure (GBNCH) are discussed. PBE-D3, B3LYP-D3 as well as MP2 methods were employed in calculating the adsorption energies (Ea) of a hydrogen molecule to the appropriate structure and the optimal distances between them. Six adsorption sites were examined, and it is demonstrated that the ‘hollow’ sites are favorable for hydrogen adsorption. It was established that GBNCH exhibits increased Ea values in comparison with graphene and h-BN. Hydrogen adsorption isotherms at different temperatures were obtained using grand canonical Monte-Carlo simulations, and it was shown that GBNCH reveals advanced adsorption properties in comparison with its counterparts. The usage of GBNCHs for hydrogen storage is also discussed.     

Hydrogen storage in magnesium decorated boron clusters (Mg2Bn,n = 4–14): A density functional theory study

The capacity of hydrogen adsorption of magnesium (Mg) decorated small boron (B) clusters (Mg₂B_n; n = 4–14) was studied using density functional theory (DFT). The calculated results indicate that H₂ adsorbed in the molecular form. The Bader's topological analysis indicates the presence of closed shell type interaction between clusters and H₂ molecules. The clusters are stable even after the adsorption of H₂ molecules. The average energy of H₂ adsorption is calculated to be in the range of 0.13–0.22 eV/H₂. The Mg₂B₆ cluster shows maximum H₂ adsorption (8.10 wt%) at ambient temperature and pressure. Further, we have performed molecular dynamic (MD) simulation at room temperature for each cluster to understand adsorption and desorption of H₂ molecules with time. The MD simulation revealed that most of the adsorbed H₂ molecules moved away from the clusters within 200 fs. However, one H₂ molecule remains attached with the Mg₂B₁₁ cluster even after 200 fs.     

Grand canonical Monte Carlo simulation of hydrogen physisorption in single-walled boron nitride nanotubes

The properties of hydrogen physisorption in single-walled boron nitride nanotubes (SWBNNTs) and single-walled carbon nanotubes (SWCNTs) are investigated in detail by the grand canonical Monte Carlo simulations. A great deal of our computational results show that the hydrogen storage capacity of SWBNNTs is slightly larger than the capacity of SWCNTs at any time when their diameters were equal and in the same conditions, and indicate that the hydrogen storage capacity of SWBNNTs at 293 K and 10 MPa with a diameter of more than 30 nm or at 293 K and 15 MPa with a diameter of more than 25 nm could exceed the 2010 goal of 6 wt%, which is presented by the U.S. Department of Energy. In addition, these results are discussed in theory.     

The influence of pre-adsorbed Pt on hydrogen adsorption on B2 FeTi(111)

The hydrogen adsorption properties on a Pt covered Fe-terminated B2-FeTi (111) surface are studied using the Density Functional Theory (DFT). The calculations are employed to trace relevant orbital interactions and to discuss the geometric and electronic consequences of incorporating one Pt atom or a Pt monolayer on top of the FeTi surface. The most stable adsorption site is a distorted FCC hollow for one Pt atom and from this location we build the Pt monolayer (ML). The H-adsorption energy is very close among BRIDGE, HCP and FCC hollow sites (∼−0.45 eV) being lower for the TOP site (−0.34 eV) in the case of a Pt(111) fcc surface. In the case of a Pt ML/FeTi, the H more stabilized on a BRIDGE site (∼−1.13 eV) interacting with both a Pt and Fe atom. We also computed the density of states (DOS) and the overlap population density of states (OPDOS) in order to study the evolution of the chemical bonding after adsorption.     

Reconnoitring the nature of interaction and effect of electric field on Pd/Pt/Ni decorated 5-8-5/55–77 defected graphene sheet for hydrogen storage

There is plenty of graphene based Hydrogen storage technologies and studies still few questions like ‘what kind of interaction present between Metal-Metal, Metal-Graphene, Metal-Hydrogen and Graphene-Metal and a possible way of controlling it to enhance H₂ adsorption’ are not revealed properly. Similarly, the chosen metal atoms Pd, Pt and Ni are widely reported as a promising catalyst yet there is no conclusive evidence to show the best among three atoms. Thus, in this present work 5-8-5 and 55–77 defected graphene is decorated with the Pd, Pt and Ni metal atoms to adsorb Hydrogen molecules. The obtained results have shown that the better adsorption of H₂ molecule depends on Metal-Metal and Metal-Graphene interaction. Similarly, the adhesive force between Pt and 5-8-5/55–77 sheets are slightly higher than the Pd and Ni atoms. Pd–Pd (−0.47 eV) and Pt–Pt (−1.99 eV) interaction values on the surface of 5-8-5 sheets are slightly lesser in magnitude than the Pd–C (−1.14 eV, −1.19 eV) and Pt–C (−2.42 eV, −2.55 eV) interactions. The topological analysis results exhibit the partially covalent nature of interaction and it confirms that the adhesive force between Metal-Graphene is higher than the cohesive force between Metal-Metal on 5-8-5 and 55–77 sheets. The electrophilicity results of Pd, Pt and Ni decorated sheets show that the two Pt decorated 5-8-5 sheet has higher electrophilicity value of 16.782 eV which is considerably higher than other sheets and this particular 5-8-5-Pt₂ system has higher H₂ adsorption energy value of −1.696 eV. The overall pattern of H₂ adsorption on chosen three metals are Pt > Ni > Pd and our results show that both strong Metal-Metal and Metal-Graphene interactions lead to poor adsorption activity. The metals are strongly polarizing the H₂ molecules which lead to good adsorption. Further, the results confirm that the π orbitals of Metal and Graphene play a major role in the adsorption of excessive H₂ molecules. In order to enhance and control the H₂ adsorption energy, a positive electric field is applied to the system. This applied electric field enhances the polarization which leads to H–H bond elongation and strong adsorption. From the obtained results, it is conclusive that the 5-8-5-Pt system has shown good response for the supplied electric field with the maximum adsorption energy value of −5.23 eV. Comparatively, the 5-8-5 systems are responding well for the applied electric field by increasing the adsorption energy than 55–77 systems.