The surface properties of TiC(001) and TiC(111) surfaces

Bulk and surface properties of metal carbides: implications for catalysis

We present a comprehensive study of the bulk and surface properties of transition metal carbides with rock salt structures and discuss their formation energies, electronic structure and potential catalytic activity.

Titania Composites with 2 D Transition Metal Carbides as Photocatalysts for Hydrogen Production under Visible-Light Irradiation

MXenes, a family of two-dimensional transition-metal carbides, were successfully demonstrated as co-catalysts with rutile TiO2 for visible-light-induced solar hydrogen production from water splitting. The physicochemical properties of Ti3 C2 Tx MXene coupled with TiO2 were investigated by a variety of characterization techniques. The effect of the Ti3 C2 Tx loading on the photocatalytic performance of the TiO2 /Ti3 C2 Tx composites was elucidated. With an optimized Ti3 C2 Tx content of 5 wt %, the TiO2 /Ti3 C2 Tx composite shows a 400 % enhancement in the photocatalytic hydrogen evolution reaction compared with that of pure rutile TiO2 . We also expanded our exploration to other MXenes (Nb2 CTx and Ti2 CTx ) as co-catalysts coupled with TiO2 , and these materials also exhibited enhanced hydrogen production. These results manifest the generality of MXenes as effective co-catalysts for solar hydrogen production.

Ab initio structure modelling of complex thin-film oxides: thermodynamical stability of TiC/thin-film alumina

We present a strategy to identify energetically favourable oxide structures in thin-film geometries. Thin-film candidate configurations are constructed from a pool of sublattices of stable and metastable oxide bulk phases. Favourable stoichiometric compositions and atomic geometries are identified by comparing total and Gibbs free energies of the relaxed configurations. This strategy is illustrated for thin-film alumina on TiC, materials which are commonly fabricated by chemical vapour deposition (CVD) and used as wear-resistant multilayer coatings. Based on the standard implementation of ab initio thermodynamics, with an assumption of equilibrium between molecular O(2) and the oxide, we predict a stability preference of TiC/alumina configurations that show no binding across the interface. This result is seemingly in conflict with the wear-resistant character of the material and points towards a need for extending standard ab initio thermodynamics to account for relevant growth environments.

A systematic density functional theory study of the electronic structure of bulk and (001) surface of transition-metals carbides

A systematic study of the bulk and surface geometrical and electronic properties of a series of transition-metal carbides (TMC with TM = Ti, V, Zr, Nb, Mo, Hf, Ta, and W) by first-principles methods is presented. It is shown that in these materials the chemical bonding is strongly covalent, the cohesive energies being directly related to the bonding-antibonding gap although the shift of the center of the C(2s) band related peak in the density of states with respect to diamond indicates that some metal to carbon charge transfer does also take place. The (001) face of these metal carbides exhibits a noticeable surface rumpling which grows along the series. It is shown that neglecting surface relaxation results in very large errors on the surface energy and work function. The surface formation induces a significant shift of electronic energy levels with respect to the corresponding values in the bulk. The extent and nature of the shift can be understood from simple bonding-antibonding arguments and is enhanced by the structural rippling of this surface.