The role of supported dual-atom on graphitic carbon nitride for selective and efficient CO2electrochemical reduction.

The electrochemical reduction of CO2into value-added fuels and chemicals using single atom (SACs) or dual-atom catalysts (DACs) has been extensively studied, but the reaction mechanism and design rules are still unclear. Here, we studied the role of dual-metal atoms on graphite carbon nitride (M1M2@g-CN, M1M2 = CuCu, FeFe, RuRu, RuCu, RuFe, CuFe) for selective and efficient CO2electrochemical reduction based on density functional theory. Our results show that CO2RR on RuRu@g-CN catalyst prefers the *COOH pathway, while for CuCu@g-CN, FeFe@g-CN, RuCu@g-CN, RuFe@g-CN, CuFe@g-CN catalysts, the *OCHO pathway is more suitable. Among all the DACs combinations, we found that RuCu@g-CN and RuFe@g-CN are the most promising electrocatalysts for CO2RR with a lower limiting potential, which is attributed to the synergistic effect of different O- and C-affinity of the heterocenters in DACs. The selectivity of RuCu@g-CN and RuFe@g-CN to the production of CH4is better than that of H2evolution. In addition, we also found that the adsorption free energy of intermediate on heteroatomic DACs can be predicted by those on homoatomic DACs, which can be used to further predict the limiting potential.

Photocatalytic Reduction of CO2 over Heterostructure Semiconductors into Value-Added Chemicals.

Photoreduction of CO2 , which utilizes solar energy to convert CO2 into hydrocarbons, can be an effective means to overcome the increasing energy crisis and mitigate the rising emissions of greenhouse gas. This article covers recent advances in the CO2 photoreduction over heterostructure-based photocatalysts. The fundamentals of CO2 photoreduction and classification of the heterostructured photocatalysts are discussed first, followed by the latest work on the CO2 photoreduction over heterostructured photocatalysts in terms of the classification of the coupling semiconductors. Finally, a brief summary and a perspective on the challenges in this area are presented.

From 1D chain to 3D network: A theoretical study on TiO2 low dimensional structures.

We have performed a systematic study on a series of low dimensional TiO2 nanostructures under density functional theory methods. The geometries, stabilities, growth mechanism, and electronic structures of 1D chain, 2D ring, 2D ring array, and 3D network of TiO2 nanostructures are analyzed. Based on the Ti2O4 building unit, a series of 1D TiO2 nano chains and rings can be built. Furthermore, 2D ring array and 3D network nanostructures can be constructed from 1D chains and rings. Among non-periodic TiO2 chain and ring structures, one series of ring structures is found to be more stable. The geometry model of the 2D ring arrays and 3D network structures in this work has provided a theoretical understanding on the structure information in experiments. Based on these semiconductive low dimensional structures, moreover, it can help to understand and design new hierarchical TiO2 nanostructure in the future.

Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains.

The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ∼10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.

The structural and electronic properties of Ag-adsorbed (SiO2)n (n=1-7) clusters.

Equilibrium geometries, charge distributions, stabilities, and electronic properties of the Ag-adsorbed (SiO(2))(n) (n=1-7) clusters have been investigated using density functional theory with generalized gradient approximation for exchange-correlation functional. The results show that the Ag atom preferably binds to silicon atom with dangling bond in nearly a fixed direction, and the incoming Ag atoms tend to cluster on the existing Ag cluster leading to the formation of Ag islands. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of the silica clusters is minor, attributing to the tendency of stability order of Ag(SiO(2))(n) (n=1-7) clusters in consistent with silica clusters. In addition, the energy gaps between the highest occupied and lowest unoccupied molecular orbitals remarkably decrease compared with the pure (SiO(2))(n) (n=1-7) clusters, eventually approaching the near infrared radiation region. This suggests that these small clusters may be an alternative material which has a similar functionality in treating cancer to the large gold-coated silica nanoshells and the small Au(3)(SiO(2))(3) cluster.

Computational investigation of TiSin (n=2-15) clusters by the density-functional theory.

The geometries, stabilities, and electronic properties of TiSin (n=2-15) clusters with different spin configurations have been systematically investigated by using density-functional theory approach at B3LYP/LanL2DZ level. According to the optimum TiSin clusters, the equilibrium site of Ti atom gradually moves from convex to surface, and to a concave site as the number of Si atom increases from 2 to 15. When n=12, the Ti atom in TiSi12 completely falls into the center of the Si outer frame, forming metal-encapsulated Si cages, which can be explained by using 16-electron rule. On the basis of the optimized geometries, various energetic properties are calculated for the most stable isomers of TiSin clusters, including the average binding energy, the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gap, fragmentation energy, and the second-order difference of energy. It is found that at size n=6,8,12 the clusters are more stable than neighboring ones. According to the Mulliken charge population analysis, charges always transfer from Si atoms to Ti atom. Furthermore, the HOMO-LUMO gaps of the most stable TiSin clusters are usually smaller than those of Sin clusters.