Theoretical study of NH3 , H2 S, and HCN adsorption enhancement on defective graphene-supported Cu19 clusters.

Recent studies have shown that graphene-supported metal clusters can enhance catalytic reactivity compared with corresponding metal clusters. In this study, the adsorptions of NH3 , H2 S, and HCN on Cu19 and defective graphene-supported Cu19 clusters are investigated using plane-wave density functional theory. The results reveal the three gas molecules can be adsorbed on three types of top sites of Cu atoms, respectively. The adsorption energies of the corresponding adsorption sites on the defective graphene-supported Cu19 clusters are all increased compared with those on the Cu19 clusters. The orbital-resolved, crystal orbital Hamilton population analysis demonstrates that the larger the integrated crystal orbital Hamilton population, the stronger the adsorption between the gas molecule and the bonded Cu atom. The center of antibonding states on the defective graphene-supported Cu19 is shifted upward relative to Fermi level compared to the corresponding one on pure Cu19 , which explains the enhanced adsorption energy on defective graphene-supported Cu19. In addition, the closer d-band center to the Fermi level on the defective graphene-supported Cu19 indicates a stronger adsorption capacity than on pure Cu19 .

Chemical Bonding Tuned Lattice Anharmonicity Leads to a High Thermoelectric Performance in Cubic AgSnSbTe3.

Comprehension of chemical bonding and its intertwined relation with charge carriers and heat propagation through a crystal lattice is imperative to design compounds for thermoelectric energy conversion. Here, we report the synthesis of large single crystal of new p-type cubic AgSnSbTe3 which shows an innately ultra-low lattice thermal conductivity (κlat ) of 0.47-0.27 Wm-1  K-1 and a high electrical conductivity (1238 - 800 S cm-1 ) in the temperature range 294-723 K. We investigated the origin of the low κlat by analysing the nature of the chemical bonding and its crystal structure. The interaction between Sn(5 s)/Ag(4d) and Te(5p) orbitals was found to generate antibonding states just below the Fermi level in the electronic band structure, resulting in a softening of the lattice in AgSnSbTe3 . Furthermore, the compound exhibits metavalent bonding which provides highly polarizable bonds with a strong lattice anharmonicity while maintaining the superior electrical conductivity. The electronic band structure exhibits nearly degenerate valence-band maxima that help to achieve a high Seebeck coefficient throughout the measured temperature range and, as a result, the maximum thermoelectric figure of merit reaches to ≈1.2 at 661 K in pristine single crystal of AgSnSbTe3 .

Hydrogen Atom Transfer from Water or Alcohols Activated by Presolvated Electrons.

High-energy irradiation of protic solvents can transiently introduce excess electrons that are implicated in a diverse range of reductive processes. Here we report the evolution of electron solvation in water and in alcohols following photodetachment from aqueous hydroxide or the corresponding alkoxides studied by two- and three-pulse femtosecond spectroscopy and ab initio molecular dynamic simulations. The experiments reveal an ultrafast recombination channel of the excess electrons. Through the calculations this channel emerges as an H-atom transfer process to the hydroxyl or alkoxy radical species from neighboring solvent molecules, which are activated as the presolvated electron occupies their antibonding orbitals. The initially low activation barrier in the early stages of electron solvation was found to increase (from 12 to 44 kJ/mol in water) as full solvation proceeded.