Yue-jie Liu

Silicon-Doped Graphene: An Effective and Metal-Free Catalyst for NO Reduction to N2O?

Density functional theory (DFT) calculations were performed on the NO reduction on the silicon (Si)-doped graphene. The results showed that monomeric NO dissociation is subject to a high barrier and large endothermicity and thus is unlikely to occur. In contrast, it was found that NO can easily be converted into N2O through a dimer mechanism. In this process, a two-step mechanism was identified: (i) the coupling of two NO molecules into a (NO)2 dimer, followed by (ii) the dissociation of (NO)2 dimer into N2O + O(ad). In the energetically most favorable pathway, the trans-(NO)2 dimer was shown to be a necessary intermediate with a total energy barrier of 0.464 eV. The catalytic reactivity of Si-doped graphene to NO reduction was interpreted on the basis of the projected density of states and charge transfer.

Can Si-doped graphene activate or dissociate O2 molecule?

Recently, the adsorption and dissociation of oxygen molecule on a metal-free catalyst has attracted considerable attention due to the fundamental and industrial importance. In the present work, we have investigated the adsorption and dissociation of O(2) molecule on pristine and silicon-doped graphene, using density functional theory calculations. We found that O(2) is firstly adsorbed on Si-doped graphene by [2+1] or [2+2] cycloaddition, with adsorption energies of -1.439 and -0.856eV, respectively. Following this, the molecularly adsorbed O(2) can be dissociated in different pathways. In the most favorable reaction path, the dissociation barrier of adsorbed O(2) is significantly reduced from 3.180 to 0.206eV due to the doping of silicon into graphene. Our results may be useful to further develop effective metal-free catalysts for the oxygen reduction reactions (ORRs), thus greatly widening the potential applications of graphene.

Boosting sensitivity of boron nitride nanotube (BNNT) to nitrogen dioxide by Fe encapsulation

The pristine boron nitride nanotube (BNNT) exhibits a poor chemical reactivity to some adsorbates, thus greatly limiting its application for the gas sensor. In the present work, using density functional theory (DFT) methods, we put forward a novel strategy to enhance the sensitivity of BNNT to nitrogen dioxide (NO2) by the encapsulation of a single Fe atom inside its cavity. The results suggest that the NO2 molecule can be only physically adsorbed on the pristine BNNT with a small adsorption energy (-0.10 eV). After the inclusion of the Fe atom inside BNNT (Fe@BNNT), the interaction of NO2 molecules with this tube is significantly enhanced, leading to a transformation from the physisorption of on pristine BNNT to the current chemisorption. Interestingly, up to five NO2 molecules can be adsorbed on this encapsulated BNNT along its circumference with the average adsorption energy of -0.52 eV, corresponding to a short recovery time (6 ms). Moreover, 0.38 electrons are transferred from the Fe@BNNT to the adsorbed NO2 molecules, which is enough to induce the obvious change of its electrical conductance. Thus, we predict that the encapsulation of Fe atom inside BNNT would greatly boosts its sensitivity to NO2 molecules, indicating its potential application as NO2 sensors.

High stability and superior catalytic reactivity of nitrogen-doped graphene supporting Pt nanoparticles as a catalyst for the oxygen reduction reaction: a density functional theory study

We investigated the structural and electronic properties of Pt13 nanoparticles on various nitrogen (N)-doped graphene and their interaction with O by density functional theory (DFT) calculations. The results revealed that the N-doping can greatly enhance the binding strength of Pt13 nanoparticles on the graphene surface, thus ensuring their high stability. For NC doping (N atoms directly substituting for C atoms), the enhanced binding strength of the Pt13 cluster is attributed to the activation of the carbon atoms around the N-dopant, while the strong hybridization of the d states of the Pt13 cluster with the sp2 dangling bonds of the N atoms in defective N-doped graphenes contributes to the strong adsorption. Moreover, a certain amount of electrons are transferred from Pt13 to the substrate accompanied by a substantial downshift of the Pt13 d-band center, thus greatly weakening the interaction of O on these composites: the adsorption energy of O is reduced from −3.700 eV on freestanding Pt13 nanoparticles to −1.762, −1.723, and −1.507 eV on deposited Pt13 ones on NC, 3NV, and 4ND structures, respectively. Hence, it is expected that N-doped graphene supported Pt nanoparticles exhibit super catalytic reactivity in the ORR.

Catalyst-free achieving of controllable carbon doping of boron nitride nanosheets by CO molecules: a theoretical prediction

Controllable carbon (C) doping in a boron nitride (BN) nanostructure can render it exciting magnetic and conductive properties, which would be very valuable for its potential applications in optoelectronics and spintronics. Thus, searching for an efficient method to achieve C-doped BN nanostructure is of vital importance. Here, using density functional theory (DFT) calculations, we propose a mechanism to obtain C-doping of BN nanosheet by the interactions of two CO molecules with three kinds of defective BN nanosheets, including B or N vacancy and BN divacancy. The results show that the proposed mechanism in the present work has the following advantages: (i) the activation energies are only 0.30 and 0.37 eV for BN sheet with B and N vacancy, respectively, suggesting that this reaction can easily occur. For BN sheet divacancy configuration, because the released energy of CO-coadsorption (−5.49 eV) can completely offset the subsequent barrier (1.72 eV), C-doped BN nanosheet can also be achieved using BN nanosheet with divacancy as a reactant. (ii) No catalyst is needed, thus no extra step is needed to remove the catalyst. (3) The harmful CO molecule can be used as a reactant and transformed into CO2 or O2 molecule. (4) The selectivity of CO for vacancy defect sites is high. The present results provide an effective theoretical method to synthesize C-doped BN nanosheets, which would be useful for the development of BN nanosheet-based devices.

DFT-based study on the mechanisms of the oxygen reduction reaction on Co(acetylacetonate)2 supported by N-doped graphene nanoribbon

Development of low-cost and highly efficient electrocatalysts for oxygen reduction reaction (ORR) is still a great challenge for the large-scale application of fuel cells and metal–air batteries. In this work, by means of density functional theory (DFT) computations, we have systemically explored the anchoring of Co(acac)2 (acac = acetylacetonate) on N-doped graphene nanoribbon and its potential as the ORR electrocatalyst. Our DFT computations revealed that N-doped graphene nanoribbon can be used as the anchoring material of the Co(acac)2 complex due to the formation of a Co–O4–N moiety, thus ensuring its high stability. Especially, an O2 molecule can be moderately activated on the surface of the anchored Co(acac)2 complex, and the subsequent ORR steps prefer to proceed though a more efficient 4e pathway with a small overpotential (0.67 V). Therefore, the hybridization of Co(acac)2 with N-doped graphene can give rise to outstanding catalytic performance for ORR in fuel cells.