Theoretical study of electrochemical reduction of CO2 to CO using a nickel-N4-Schiff base complex

The electrochemical reduction (ECR) of CO2 to CO by nickel-N4-Schiff base complexes as catalysts was investigated using density functional theory (DFT). Three nickel complexes, 1-Ni, 2-Ni, and [2-Ni]Me were considered. Two CO2 reduction pathways, i.e., external and internal proton transfer, were proposed and their reaction energy profiles were computed. The external proton transfer pathway which includes three steps has no transition state. The reaction energies for all steps are exothermic and the reaction catalyzed by 1-Ni has the lowest overall reaction energy (-5.72 eV) followed by those by 2-Ni (-5.56 eV) and [2-Ni]Me (-5.54 eV). The internal proton transfer pathway is composed of four steps. The internal proton transfer step (carboxylic formation) includes a transition state. The CO2 reduction by [2-Ni]Me could not proceed via this mechanism, since [2-Ni]Me does not have an NH group in the ligand and 1-Ni has a lower activation energy (0.83 eV), which is in agreement with the experiment. The charge of the pre-adsorption nickel complex seems to be related to the activity of the catalysts. The catalyst with a less positive nickel charge is more active.

Open-Bandgap Graphene-Based Field-Effect Transistor Using Oligo(phenylene-ethynylene) Interfacial Chemistry

Organic interfacial compounds (OICs) are required as linkers for the highly stable and efficient immobilization of bioprobes in nanobiosensors using 2D nanomaterials such as graphene. Herein, we first demonstrated the fabrication of a field-effect transistor (FET) via a microelectromechanical system process after covalent functionalization on large-scale graphene by introducing oligo(phenylene-ethynylene)amine (OPE). OPE was compared to various OICs by density functional theory simulations and was confirmed to have a higher binding energy with graphene and a lower band gap than other OICs. OPE can improve the immobilization efficiency of a bioprobe by forming a self-assembly monolayer via anion-based reaction. Using this technology, Magainin I-conjugated OGMFET (MOGMFET) showed a high sensitivity, high selectivity, with a limit of detection of 100  cfu mL-1 . These results indicate that the OPE OIC can be applied for stable and comfortable interfacing technology for biosensor fabrication.

The adsorption behaviors of N2O on penta-graphene and Ni-doped penta-graphene

In order to develop the adsorption application of penta-graphene (PG) to N₂O gas molecule, we calculated the sensing properties of PG and Ni-doped PG to N₂O molecule via first-principles calculations. Based on the calculated adsorption energy, charge transfer, band gap, density of states and partial density of states, we observed that this gas molecule was weakly physically adsorbed on the surface of intrinsic PG, while the adsorption behaviors on the surface of Ni-doped PG were greatly influenced by the doping sites and adsorption orientations. With the Ni atom doped at the sp² hybridized carbon site, strong chemical adsorption between the gas molecule and the substrate was induced. The adsorption structure of the N₂O molecule with its N atom close to the substrate exhibited better stability. Moreover, an external perpendicular electric field could enhance the adsorption performance of the N₂O molecule and adjust the charge transfer between the molecule and substrate. Our results broaden the adsorption applications of PG and indicate that Ni-doped PG is a potential candidate for N₂O gas sensors.

N₂O molecule is chemically adsorbed on the surface of Ni-doped penta-graphene only when the Ni atom is doped at the sp² hybridized carbon site. External perpendicular electric field can enhance the adsorption performance.

Activation of the methane C–H bond by Al- and Ga-doped graphenes: a DFT investigation

The potential of Al- and Ge-embedded graphene to activate the C–H bond of CH4 in the presence of a N2O molecule was studied using DFT calculations.

Density Functional Theory Investigation on the Catalytic Reduction of NO by CO on the Char Surface: the Effect of Iron

The catalytic reduction of NO in the presence of CO was investigated by density functional theory calculations with consideration of the iron involved in char (Fe-adsorbed char). The quantitative information of reaction kinetics was also evaluated using canonical variational transition-state theory in the temperature range of 500-1800 K. The analysis of the associated adsorption energies indicates that the affinity of the carbon active site toward NO and CO is stronger than that at the Fe site, and the NO adsorption on the carbon site in the N-down mode is the most energetically favorable. Following the chemisorption step, the reactions proceed for N₂O, N₂, and CO₂ desorption by different reduction mechanisms, depending on whether CO exists. The FeO group formed and transformed during the NO reduction is of significant importance for the whole catalytic process. The results show that the heterogeneous reduction of NO is promoted much more dramatically with the help of CO, which brings about a decrease in the activation energies accompanied by an increase in the reaction rate constants. The effectiveness of the Fe-adsorbed model derives from its prominent effect on NO-CO reaction and becomes more realistic than the original metal-free structure.

A DFT study on NO reduction to N2O using Al- and P-doped hexagonal boron nitride nanosheets

Using the dispersion-corrected DFT calculations, the catalytic reduction of NO molecules to N₂O is investigated over Al- and P-doped hexagonal boron nitride nanosheets (h-BNNS). It is found that NO dissociation over both these surfaces needs a very large energy barrier, which indicates it cannot proceed at normal temperature. In contrast, the results show that NO molecules can be easily reduced into N₂O via a dimer mechanism. The obtained activation energies reveal that the catalytic activity of Al-doped h-BNNS is better than that of P-doped one, mainly due to the moderate coadsorption energies of NO molecules over this surface.

Enhanced hydrogen storage performance of graphene nanoflakes doped with Cr atoms: a DFT study

The hydrogen storage performances of novel graphene nanoflakes doped with Cr atoms were systematically investigated using first-principles density functional theory. The calculated results showed that one Cr atom could be successfully doped into the graphene nanoflake with a binding energy of −4.402 eV. Different from the H₂ molecule moving away from the pristine graphene nanoflake surface, the built Cr-doped graphene nanoflake exhibited a high affinity to the H₂ molecule with a chemical adsorption energy of −0.574 eV. Moreover, the adsorptions of two to five H₂ molecules on the Cr-doped graphene nanoflake were studied as well. It was found that there were a maximum of three H₂ molecules stored on the graphene nanoflake doped with one Cr atom. Also, the further calculations showed that the numbers of the stored H₂ molecules were effectively improved to be six (or nine) when the graphene nanoflakes were doped with two (or three) Cr atoms. This research reveals that the graphene nanoflake doped with Cr atom could be a promising material to store H₂ molecules and its H₂ storage performance could be effectively enhanced through modifying the number of doped Cr atoms.

Our study reveals that the H₂ storage performance of a graphene nanoflake based material could be significantly enhanced through doping with Cr atoms.

Regioselectivity in hexagonal boron nitride co-doped graphene

The active electron transfer (ET) sites on the graphene surface can be controlled by hexagonal boron nitride (h-BN) doping.