Hydrogen Binding Strength Research Articles

High-Capacity Room-Temperature Hydrogen Storage in Carbon Nanotubes via Defect-Modulated Titanium Doping

Carbon materials have been at the forefront of hydrogen storage research. However, without improvements in the hydrogen binding strength, as provided by transition-metal dopants, they will not meet practical targets. We performed ab initio density functional theory simulations on titanium-atom dopants adsorbed on the native defects of an (8,0) nanotube. Adsorption on a vacancy strongly binds titanium, preventing nanoparticle coalescence (a major issue for atomic dopants). The defect-modulated Ti adsorbs five H2 molecules with H2 binding energies in the range from −0.2 to −0.7 eV/H2, desirable for practical applications. Molecular dynamics simulations indicate that this complex is stable at room temperature, and simulation of a C112Ti16H160 unit cell finds that a structure with 7.1 wt % hydrogen storage is stable.

Charged Fullerenes as High-Capacity Hydrogen Storage Media

Using first-principles calculations within density functional theory, we explore systematically the capacity of charged carbon fullerenes Cn (20 <or= n <or= 82) as hydrogen storage media. We find that the binding strength of molecular hydrogen on either positively or negatively charged fullerenes can be dramatically enhanced to 0.18-0.32 eV, a desirable range for potential room-temperature, near ambient applications. The enhanced binding is delocalized in nature, surrounding the whole surface of a charged fullerene, and is attributed to the polarization of the hydrogen molecules by the high electric field generated near the surface of the charged fullerene. At full hydrogen coverage, these charged fullerenes can gain storage capacities of up to approximately 8.0 wt %. We also find that, contrary to intuitive expectation, fullerenes containing encapsulated metal atoms only exhibit negligible enhancement in the hydrogen binding strength, because the charge donated by the metal atoms is primarily confined inside the fullerene cages. These predictions may prove to be instrumental in searching for a new class of high-capacity hydrogen storage media.

QUANTIFICATION OF NON-COVALENT INTERACTIONS ON THE BASIS OF THE THERMODYNAMIC HYDROGEN BOND PARAMETERS

This paper describes how empirical free energy and/or enthalpy values for hydrogen binding strength are derived from thousands of corresponding measurements between H-bond donors and acceptors, mostly in carbon tetrachloride, and how they can be used to construct common scales or factor values (increments) also for other reactions involving electron donor and acceptor ability of functions. The corresponding databases and programs (HYBOT) allow one to predict thermodynamic values for experimentally unknown equilibria, including also ionophore complexes with crown ethers or cryptands. Applications in QSAR involve the prediction of lipophilicity from any structure on the basis of only two variables, e.g. 234 systems are described this way with a correlation coefficient r=0·96. Similarly, permeabilities and some biological properties such as narcotic activities of chemicals and anti-HIV-1 activity of some porphyrins are evaluated. © 1997 John Wiley & Sons, Ltd.

QUANTIFICATION OF NON‐COVALENT INTERACTIONS ON THE BASIS OF THE THERMODYNAMIC HYDROGEN BOND PARAMETERS

This paper describes how empirical free energy and/or enthalpy values for hydrogen binding strength are derived from thousands of corresponding measurements between H-bond donors and acceptors, mostly in carbon tetrachloride, and how they can be used to construct common scales or factor values (increments) also for other reactions involving electron donor and acceptor ability of functions. The corresponding databases and programs (HYBOT) allow one to predict thermodynamic values for experimentally unknown equilibria, including also ionophore complexes with crown ethers or cryptands. Applications in QSAR involve the prediction of lipophilicity from any structure on the basis of only two variables, e.g. 234 systems are described this way with a correlation coefficient r=0·96. Similarly, permeabilities and some biological properties such as narcotic activities of chemicals and anti-HIV-1 activity of some porphyrins are evaluated. © 1997 John Wiley & Sons, Ltd.