Bogdan Kuchta

Nanospace engineering of KOH activated carbon

This paper demonstrates that nanospace engineering of KOH activated carbon is possible by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. High specific surface areas, porosities, sub-nanometer (<1 nm) and supra-nanometer (1-5 nm) pore volumes are quantitatively controlled by a combination of KOH concentration and activation temperature. The process typically leads to a bimodal pore size distribution, with a large, approximately constant number of sub-nanometer pores and a variable number of supra-nanometer pores. We show how to control the number of supra-nanometer pores in a manner not achieved previously by chemical activation. The chemical mechanism underlying this control is studied by following the evolution of elemental composition, specific surface area, porosity, and pore size distribution during KOH activation and preceding H(3)PO(4) activation. The oxygen, nitrogen, and hydrogen contents decrease during successive activation steps, creating a nanoporous carbon network with a porosity and surface area controllable for various applications, including gas storage. The formation of tunable sub-nanometer and supra-nanometer pores is validated by sub-critical nitrogen adsorption. Surface functional groups of KOH activated carbon are studied by microscopic infrared spectroscopy.

Hypothetical High-Surface-Area Carbons with Exceptional Hydrogen Storage Capacities: Open Carbon Frameworks

A class of high-surface-area carbon hypothetical structures has been investigated that goes beyond the traditional model of parallel graphene sheets hosting layers of physisorbed hydrogen in slit-shaped pores of variable width. The investigation focuses on structures with locally planar units (unbounded or bounded fragments of graphene sheets), and variable ratios of in-plane to edge atoms. Adsorption of molecular hydrogen on these structures was studied by performing grand canonical Monte Carlo simulations with appropriately chosen adsorbent-adsorbate interaction potentials. The interaction models were tested by comparing simulated adsorption isotherms with experimental isotherms on a high-performance activated carbon with well-defined pore structure (approximately bimodal pore-size distribution), and remarkable agreement between computed and experimental isotherms was obtained, both for gravimetric excess adsorption and for gravimetric storage capacity. From this analysis and the simulations performed on the new structures, a rich spectrum of relationships between structural characteristics of carbons and ensuing hydrogen adsorption (structure-function relationships) emerges: (i) Storage capacities higher than in slit-shaped pores can be obtained by fragmentation/truncation of graphene sheets, which creates surface areas exceeding of 2600 m(2)/g, the maximum surface area for infinite graphene sheets, carried mainly by edge sites; we call the resulting structures open carbon frameworks (OCF). (ii) For OCFs with a ratio of in-plane to edge sites ≈1 and surface areas 3800-6500 m(2)/g, we found record maximum excess adsorption of 75-85 g of H(2)/kg of C at 77 K and record storage capacity of 100-260 g of H(2)/kg of C at 77 K and 100 bar. (iii) The adsorption in structures having large specific surface area built from small polycyclic aromatic hydrocarbons cannot be further increased because their energy of adsorption is low. (iv) Additional increase of hydrogen uptake could potentially be achieved by chemical substitution and/or intercalation of OCF structures, in order to increase the energy of adsorption. We conclude that OCF structures, if synthesized, will give hydrogen uptake at the level required for mobile applications. The conclusions define the physical limits of hydrogen adsorption in carbon-based porous structures.

Enhanced hydrogen adsorption in boron substituted carbon nanospaces

Activated carbons are one of promising groups of materials for reversible storage of hydrogen by physisorption. However, the heat of hydrogen adsorption in such materials is relatively low, in the range of about 4-8 kJ/mol, which limits the total amount of hydrogen adsorbed at P=100 bar to approximately 2 wt % at room temperature and approximately 8 wt % at 77 K. To improve the sorption characteristics the adsorbing surfaces must be modified either by substitution of some atoms in the all-carbon skeleton by other elements, or by doping/intercalation with other species. In this letter we present ab initio calculations and Monte Carlo simulations showing that substitution of 5%-10% of atoms in a nanoporous carbon by boron atoms results in significant increases in the adsorption energy (up to 10-13.5 kJ/mol) and storage capacity ( approximately 5 wt % at 298 K, 100 bar) with a 97% delivery rate.

Electrical and related properties of organic solids

Some Applications of Organic Conductors M. Kryszewski. Hole Transport in Triphenylmethane Doped Polymers P.M. Borsenberger. Photoconductivity of Polymers: Influence of the Photoinduced Charge Transfer S. Nespurek, M. Mensik. Intermediate Excited States in Photoconductivity and Luminescence of PPV: Study by Spin-Dependent Techniques E.L. Frankevich. Electroluminescence in Polymeric Systems with Defined Chemical and Morphological Structure D. Neher, et al. Theoretical Characterization of Electroluminescence in Semiconducting Conjugated Polymers and Oligomers J.-L. Bredas. Calculation of Charge-Transfer States in Molecular Crystals R.W. Munn. Charge Carriers as Electronic and Molecular Polarons in Organic Crystals: Formation and Transfer Processes E.A. Silinsh. Molecular Electronic Relaxation in Organic Solids N. Sato. Electron Processes in Organic Electroluminescence J. Kalinowski. Time-Resolved Fluorescence Quenching and Carrier Generation in Titanyl Phthalocyanine (TiOPc) Z.D. Popovic, et al. Gallium Phthalocyanine Thin Films Studied by Electroabsorption K. Yamasaki, M. Kotani. Three Component Organic Semiconductors, Conductors and Superconductors H. Inkokuchi, K. Imaeda. Conductivity of the ET Polyiodiles Crystalline Networks Transformed Into Superconducting Phase J. Ulanski, et al. Electron Donor-Acceptor Interactions of C60 with Tetraphenylphosphonium and Tetraphenylarsonium Halides A. Graja, et al. Novel Organic Crystals for Nonlinear and Electro-Optics C. Bosshard, et al. Heterocyclic Squaraines: Second-Harmonic Generation from Langmuir-Blodgett Films of a Centrosymmetric Donor-Acceptor-Donor Molecule G.J. Ashwell, P. Leeson. Photorefractive Polymers for Digital Holographic Optical Storage D.M. Burland. Dye-Doped Liquid Crystal for Real-Time Holograph A. Miniewicz, et al. Nonlinear Spectroscopy in Conjugated Molecules S. Delysse, et al. Fluorescence Microscopy of Single Molecules: Temperature Dependence of Linewidths T. Irngartner, et al. Proton Tunnelling in Molecular Crystals: Translational Tunnelling Along Hydrogen Bonds and Rotational Tunnelling of Methyl Groups as Studied by Optical Spectroscopy, NMR, and Neutron Scattering H.P. Trommsdorff, et al. Ab Initio Molecular Dynamics Simulation of Condensed Molecular Systems M. Sprik. Electron-Proton Co-Operation in 1-D Metallic States T. Mitani, H. Kitagawa. The Influence of Electronic Changes on Structural Phase Transformations in Solid Iodine Under Pressure B. Kuchta, et al. Theory of Optical Switching in a Model Based on Electron Transfer in H2+ E. Canel. Langmuir-Blodgett Films of Archaeal Lipids: Properties and Perspectives S. Dante, et al.

Static and dynamic properties of solid CO2 at various temperatures and pressures

A constant pressure Monte Carlo formalism, lattice dynamics, and classical perturbation theory are used to calculate the thermal expansion, pressure–volume relation at room temperature, the temperature dependence of the zone center libron frequencies, and the pressure dependence of the three vibron modes of vibration, in solid CO2 at pressures 0≤p≤16 GPa and temperatures 0≤T≤300 K. The agreement with experiment is good. At room temperature the observed Pa3 phase is predicted for P≤11 GPa, above which a transition occurs into an orthorhombic Cmca structure, with a volume change upon transition of ΔV=0.4 cm3 /mol. Calculated physical quantities in this phase are consistent with experiment.

Dielectric properties of single crystals of the substituted diacetylene pTS: effect of the solid-state polymerization and phase transitions

Abstract Dielectric permittivities of the polymerizable organic solid, p TS diacetylene have been measured between 115 and 330 K in the directions parallel and perpendicular to the direction of polymer chain growth. The upper phase transition in monomer, polymer and mixed crystals at various stages of the solid-state polymerization manifests itself as a maximum in the temperature dependence of e measured in the direction parallel to the molecular stacks, being particularly well pronounced in fully polymerized crystals. The transition was identified as an antiferroelectric one, the sublattice polarization being most probably the order parameter. The lower phase transition could be observed only in monomer and monomer-rich crystals as a shoulder on the e( T ) dependence. This transition could be detected only in the crystals containing less than ≈ 10–15% of polymer. The dielectric permittivity was found to be independent of frequency up to 3 GHz. The polymerization results in changes of the dielectric permittivity. In samples where the direction of measurements coincides with the b axis, these changes follow the monomer-polymer conversion curve.

A Monte Carlo study of the α–β order–disorder transition in solid nitrogen

The α–β phase transition in solid N2 has been investigated using the constant pressure Monte Carlo method. This is accomplished by examining both phases in the temperature range 25≤T≤50 K, where they are everywhere at least metastable. It is found that the cubic α phase undergoes an orientational order–disorder transition into a disordered cubic phase as the temperature is increased to T=41 K, and remains in this state until melting. Similarly the orientationally disordered hexagonal phase persists from melting down to 33 K, where it undergoes a transition into a hexagonal structure with short‐range orientational order.

Mean field approach to orientational transitions in charge–transfer molecular crystals

The mean field approach to orientational transitions in two‐component molecular crystals has been formulated and illustrated by numerical calculations for two model systems: complexes of tetracyanobenzene (TCNB) with naphthalene (N–TCNB) and anthracene (A–TCNB). The study had addressed the characterization of the orientational disorder and mechanism of phase transitions in the crystals by calculating single particle and coupled rotational susceptibilities. It is concluded that the orientational instability in A–TCNB crystal is of the displacive type and a soft librational phonon mode at the M point of the Brillouin zone is predicted. In the N–TCNB crystal, an order–disorder type of the instability is predicted. For both systems the orientational phase transitions are found to be predominantly two dimensional.

Lattice dynamics of solid nitrogen with an ab initio intermolecular potential. II. Anharmonic librations in the α phase

Using an intermolecular N2–N2 potential from ab initio calculations, we have performed calculations of frequencies for anharmonic librational modes at zero wave vector in the α phase of solid nitrogen. In the first step, the librations (Eg, Tg, Tg) were considered as uncoupled oscillators with frequencies calculated from an effective one‐dimensional anharmonic potential being a section of the crystal potential surface along a direction specified by harmonic eigenvectors of a given mode. Within the approximation, very good agreement with the experimental frequency for the Eg mode has been found. Finally, the coupling between two Tg librational modes has been introduced and the calculated frequencies were found to be almost identical to the experimental ones.

Understanding universal adsorption limits for hydrogen storage in nano porous systems.

Despite of more than 15 years of research, no materials possess the adsorbing properties required for mobile storage. At this time of state-of-the-art technology, the essential question should be asked: why is it so difficult to prepare a material with the desired properties? Here, we discuss the sources of physical limitations of existing materials and indicate the directions for further material research.