Exploratory Direct Dynamics Simulations of ³O₂ Reaction with Graphene at High Temperatures

Abstract

Direct chemical dynamics simulations at high temperatures of reaction between 3 O 2 and graphene containing varied number of defects were performed using the VENUS-MOPAC code. Graphene was modeled using (5a,6z)-periacene, a poly aromatic hydrocarbon with 5 and 6 benzene rings in the armchair and zigzag directions, respectively. Up to six defects were introduced by removing carbon atoms from the basal plane. Usage of the PM7/ unrestricted Hartree−Fock (UHF) method, for the simulations, was validated by benchmarking singlet-triplet gaps of n-acenes and (5a,nz) periacenes with high-level theoretical calculations. PM7/UHF calculations showed that graphene with different number of vacancies has different ground electronic states. Dynamics simulations were performed for two 3 O 2 collision energies E i of 0.4 and 0.7 eV, with the incident angle normal to the graphene plane at 1375 K. Collisions on graphene with one, two, three, and four vacancies (1C-, 2C-, 3C-, and 4C-vacant graphene) showed no reactive trajectories, mainly due to the nonavailability of reactive sites resulting from nascent site deactivation, a dynamical phenomenon. On the other hand, 3 O 2 dissociative chemisorption was observed for collisions on four-(with a different morphology), fiveand six-vacant graphene (4C-2-, 5C-and 6C-vacant graphene). A strong morphology dependence was observed for the reaction conditions. On all reactive surfaces, larger reaction probabilities were observed for collisions at E i = 0.7 eV. This is in agreement with the nucleation time measured by supersonic molecular beam experiments wherein about 2.5 times longer nucleation time for O 2 impinging at 0.4 eV compared with 0.7 eV was observed. Reactivity at both collision energies, viz., 0.4 and 0.7 eV, showed the following trend: 5C-< 6C-< 4C-vacant graphene. Formation of carboxyl/semiquinone (CO)-and ether (−C−O−C−)-type dissociation products was observed on all reactive surfaces, whereas a higher probability of formation of the ether (−C−O−C−) group was found on 4C-vacant graphene on which dangling carbon atoms are present in close proximity. However, no gaseous CO/CO 2 formation was observed on any of the graphene vacancies even for simulations that were run up to 10 ps. This is apparently the result of the absence of excess oxygen atoms that can aid the formation of larger groups, the precursors for CO/CO 2 formation. Although the results of this study do not provide a conclusive understanding of the mechanism of graphene/graphite oxidation, this work serves as an initial study attempting to understand the 3 O 2 dissociative chemisorption dynamical mechanism on defective-graphene/graphite surfaces at high temperatures.

The Role of Oxygenic Groups and sp3 Carbon Hybridization in Activated Graphite Electrodes for Vanadium Redox Flow Batteries

“…10–15 h), Such processing creates defects at the surfaces and edges, [10,26,27] which are likely covered with functional groups upon further oxidation [6,16,29,30,31] . At high temperature and longer duration, the defect of six‐carbon (6C) ring is the most stable defect in the basal surface of graphite [32] . The purpose of this study is to investigate the interaction of the VO 2+ /VO 2 + with the epoxy, OH, C=O, and COOH groups; and to establish possible correlations between structural changes, sp 2 /sp 3 hybridization, oxygenic groups, and the VO 2+ /VO 2 + affinity to the electrode.…”

Self-assembled graphene-based microfibers with eclectic optical properties

“…All the same, in the case of NOG, high-temperature etching along with oxidation of most of the other C=C bonds to oxygencontaining functional groups accounts for the significant diminution of C=C percentage from 79.2 to 26.7% 33 . Additionally, depletion of C-O species coupled with the remarkable escalation of carbonyl percentage within 51.93% and increment of carboxyl content up to 7.79% in thermal oxidation process are most likely attributed to the fact that at the elevated temperatures, oxygen is prone to incorporate itself into graphene lattice both to form epoxides on the basal plane (energy barrier ~ 0.3 eV) and semiquinones, carbonyls, lactones, carboxylic acids, and ethers at defects [34][35][36] . Moreover, while the thermal reduction gives rise to the recovery of conjugated sp 2 network along with the diminution of sp 3 carbons in OGOS-450 37,38 , the introduction of numerous defects by means of thermal oxidation process accounts for the recreation of sp 3 -hybridized carbons in NOG [39][40][41][42] .…”

The Role of Oxygenic Groups and Sp3 Carbon Hybridization in Activated Graphite Electrodes for Vanadium Redox Flow Batteries

“…[6,16,32]. At high temperature and longer duration, the defect of six-carbon (6C) ring is the most stable defect in the basal surface of graphite [33]. The purpose of this study is to investigate the interaction of the VO 2+ /VO2 + with the epoxy, OH, C=O, and COOH groups; and to establish possible correlations between structural changes, sp 2 /sp 3 hybridization, oxygenic groups, and the VO 2+ /VO2 + affinity to the electrode.…”