Chenggang Li

High catalytic activity for CO oxidation on single Fe atom stabilized in graphene vacancies

Inspired by the recently discovered dynamics of single Fe atoms in graphene vacancies, we systemically examined the stable configurations, electronic structures, and catalytic activities of Fe-atom-embedded graphene substrates (including monovacancy graphene (MG) and divacancy graphene (DG)) by using first-principles calculations. We found that the doped Fe on the MG sheet (Fe/MG) is more stable than that on the DG sheet (Fe/DG). Doping with Fe atoms provides more transferred electrons to fill the vacancy defects of graphene and allows it to exhibit a more positive charge, which effectively regulates O2 and CO adsorption. Also, the degree of interactions between the reactants and substrates are connected to the reaction pathways and energy barriers. For the Fe/MG sheet, the low coadsorption energy of gas molecules can promote the catalytic reaction through the Langmuir–Hinshelwood (LH) mechanism. In comparison, the initial step for CO oxidation on the Fe/DG sheet is through the Eley–Rideal (ER) mechanism, which is an energetically more favorable process. Moreover, the more stable Fe/MG sheet is a much more efficient catalyst for CO oxidation at low temperature, because the sequential reaction processes (LH and ER) have low enough energy barriers. These results provide valuable guidance on selecting the metal dopant in graphene materials to design effective atomic-scale catalysts.

Insights into the structures and electronic properties of Cu n+1 μ and Cu n S μ (n = 1–12; μ = 0, ±1) clusters

AbstarctThe stability and reactivity of clusters are closely related to their valence electronic configuration. Doping is a most efficient method to modify the electronic configuration and properties of a cluster. Considering that Cu and S posses one and six valence electrons, respectively, the S doped Cu clusters with even number of valence electrons are expected to be more stable than those with odd number of electrons. By using the swarm intelligence based CALYPSO method on crystal structural prediction, we have explored the structures of neutral and charged Cun+1 and CunS (n = 1–12) clusters. The electronic properties of the lowest energy structures have been investigated systemically by first-principles calculations with density functional theory. The results showed that the clusters with a valence count of 2, 8 and 12 appear to be magic numbers with enhanced stability. In addition, several geometry-related-properties have been discussed and compared with those results available in the literature.

Geometric stability, electronic structure, and intercalation mechanism of Co adatom anchors on graphene sheets.

We perform a systematic study of the adsorption of Co adatom on monolayer and bilayer graphene sheets, and the calculated results are compared through the van der Waals density functional (vdW-DF) and the generalized gradient approximation of Perdew, Burke and Ernzernhof (GGA + PBE) methods. For the single Co adatom, its adsorption energy at vacancy site was found to be larger than at the high-symmetry adsorption sites. For the different vdW corrections, the calculated adsorption energies of Co adatom on grapheme substrates are slightly changed to some extent, but they do not affect the most preferable adsorption configurations. NEB calculations prove that the Co adatom has smaller energy barrier within pristine bilayer graphene (PBG) than that on the upper layer, indicating the high mobility of Co atom anchors at overlayer and easily aggregates. For the PBG substrate, the Co adatom intercalates into graphene sheets with a large energy barrier (9.29 eV). On the bilayer graphene with a single-vacancy (SV), the Co adatom can easily be trapped at the SV site and intercalates into graphene sheets with a much lower energy barrier (2.88 eV). These results provide valuable information on the intercalation reaction and the formation mechanism of metal impurity in graphene sheets.

Systematic theoretical investigation of structure and electronic properties of pure copper and lithium doped copper clusters

ABSTRACT The pure copper and lithium-doped copper clusters are studied using the unbiased CALYPSO structure searching method and density function theory to understand the evolution of various structure and electronic properties. Theoretical results show the growth behaviours of doped clusters are organised as follows: Li capped Cun clusters or Li substituted Cun+1 clusters as well as Cu capped Cun-1Li clusters. Moreover, the lowest energy structures of CunLi favour planar structures for n ≤ 3 and three-dimensional structures for n = 4–12. In addition, the calculated averaged binding energies, fragmentation energies and second-order difference of energies exhibit obvious odd–even alternations as cluster size increasing. At last, the highest occupied-lowest unoccupied molecular orbital gaps, molecular orbital energy, magnetic property, natural population analysis, natural electron configurations, electrostatic potential, electron density difference, Infrared and Raman spectra and density of states are also, respectively, operative for characterising and rationalising the electronic properties of doped clusters. GRAPHICAL ABSTRACT

Geometric Stability, Electronic Structure and Reactivity of Pt4 Cluster Supported on Defective Graphene

The geometric stability, electronic structure and magnetic properties of the Pt4 clusters on graphene substrates are investigated using the first-principles methods. It is found that the Pt4 clusters on the defective graphene with a single vacancy defect (SV-graphene) have larger binding energies than that on the pristine graphene. The different position of SV sites can modulate the geometric stability of Pt4 clusters. The Pt4 clusters provide more transferred electrons to the SV-graphene and exhibit the positively charged, which helps to weaken the CO adsorption. The results would be important for understanding that the adsorption behavior of metal clusters on graphene.

The formation of H2S on metal-modified graphene under hydrogen environments

Abstract The adsorption behaviors of H2S, SH, and S on Co-embedded graphene surface (Co-graphene) are investigated using the first-principles calculations. It is found that the adsorbed SH and S species on Co-graphene are strongly stabilized than that of the H2S molecule. Besides, the chemisorbed SH and S can lead to dramatic changes in the electronic structure and magnetic property of Co-graphene system by the transferred electrons, and the electronic transport behavior of Co-graphene exhibits high sensitivity for detecting SH and S. Moreover, the deposited S-based species would be converted into H2S molecule by the hydrogenation reaction. Compared to the hydrogen molecule, the presence of hydrogen atoms can more easily inhibit the formation of sulfur deposition on Co-graphene surface, which provides valuable guidance on designing graphene-based catalysis as electrode in fuel cells.

Structures, stabilities and electronic properties of boron-doped silicon clusters B3Sin (n=1–17) and their anions

The structures, stabilities and electronic properties of neutral and anionic B3Sin (n = 1–17) clusters have been systemically investigated on the basis of density functional theory at the B3LYP/6-311 + G(d) level and CALYPSO structure prediction method. The structural searches show that three boron atoms tend to form B3 triangle encapsulated into Sin cages with the increasing number of silicon atoms. Most of the lowest energy structures can be derived by using the squashed pentagonal bipyramid structure of B3Si4 and B3Si4− as the major building unit. The relative stabilities are studied based on the calculated binding energies, second-order difference of energies and HOMO–LUMO gaps of the lowest energy structures. In addition, Hirshfeld, natural population analysis, Bader approaches and natural electronic configuration are performed to explore the charge transfer. At last, molecular orbital, magnetic properties, IR, Raman and UV–vis spectra are also, respectively, analysed for providing strong support for essential theoretical and experimental research. GRAPHICAL ABSTRACT

First-principle study of structural, electronic and magnetic properties of (FeC) n (n = 1–8) and (FeC) 8 TM (TM = V, Cr, Mn and Co) clusters

The structural, electronic and magnetic properties of the (FeC)n (n = 1–8) clusters are studied using the unbiased CALYPSO structure search method and density functional theory. A combination of the PBE functional and 6–311 + G* basis set is used for determining global minima on potential energy surfaces of (FeC)n clusters. Relatively stabilities are analyzed via computing their binding energies, second order difference and HOMO-LUMO gaps. In addition, the origin of magnetic properties, spin density and density of states are discussed in detail, respectively. At last, based on the same computational method, the structures, magnetic properties and density of states are systemically investigated for the 3d (V, Cr, Mn and Co) atom doped (FeC)8 cluster.

Correlations between the Oxygen Ionic Conductivity of Sr- and Mg-doped LaGaO3 and Its Crystal Structure

Oxygen vacancy formation and migration in La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) with various crystal symmetries (cubic, orthorhombic and monoclinic) are studied by employing first-principles calculations based on density functional theory (DFT). The calculated vacancy formation energy of the cubic LSGM is 3.96 eV, much lower than those of orthorhombic and monoclinic LSGM. The calculated averaged migration energies increase in the order of

Effect of Laser Rapid Sintering on the Electrical Properties of Sr- and Mg-doped LaGaO3

Materials La0.9Sr0.1Ga0.8Mg0.2O3−δ and La0.8Sr0.2Ga0.83Mg0.17-xCoxO3−δ with x=0, 0.05, 0.085, 0.10 and 0.15 are synthesized by laser rapid sintering (LRS). It is found that the total conductivities of La0.8Sr0.2Ga0.83Mg0.17-xCoxO3−δ by LRS are obviously improved by Co doping, showing a general increase with the content Co except that for x=0.15. The conductivities of the La0.9Sr0.1Ga0.8Mg0.2O3−δ and La0.8Sr0.2Ga0.83Mg0.085Co0.085O3−δ samples synthesized by LRS are superior to those of both samples for the same compositions by solid state reaction (SSR) at any temperatures. The conductivities of La0.9Sr0.1Ga0.8Mg0.2O3−δ and La0.8Sr0.2Ga0.83Mg0.085Co0.085O3−δ samples synthesized by LRS are about twice and thrice as much as those of the samples for the same compositions synthesized by SSR, respectively. The improved conductivities of La0.9Sr0.1Ga0.8Mg0.2O3−δ and La0.8Sr0.2Ga0.83Mg0.085Co0.085O3−δ prepared by laser rapid sintering with respect to that by solid state reactions for the same composition is attributed to the unique microstructures of the samples generated during laser rapid sintering. La0.9Sr0.1Ga0.8Mg0.2O3−δ and La0.8Sr0.2Ga0.83Mg0.17-xCoxO3−δ (x=0, 0.05, 0.085, 0.10, 0.15) samples were prepared with starting materials of La2O3 (99.99%), Ga2O3 (99.99%), SrCO3 (99%), MgO (98%) and and Co2O3 (99.9%). Two series of La 0.9Sr0.1Ga0.8Mg0.2O3−δ samples were prepared by high-temperature solid state reactions and laser rapid sintering, respectively. Five series of La0.8Sr0.2Ga0.83Mg0.17-xCoxO3−δ (x=0, 0.05, 0.085, 0.10, 0.15) samples were prepared by laser rapid sintering, for comparison the La0.8Sr0.2Ga0.83Mg0.085Co0.085O3−δ sample was synthesized by