TY - JOUR
T1 - Exploratory Direct Dynamics Simulations of 3O2 Reaction with Graphene at High Temperatures
AU - Hariharan, Seenivasan
AU - Majumder, Moumita
AU - Edel, Ross
AU - Grabnic, Tim
AU - Sibener, S. J.
AU - Hase, William L.
N1 - Funding Information:
The research reported here is based upon work supported by the Air Force Office of Scientific Research (AFOSR) Grant FA9550-16-1-0133 and the Robert A. Welch Foundation Grant D-0005. Theoretical calculations were performed on the high-performance computer clusters, Hrothgar and Quanah, maintained by High Performance Computing Center (HPCC) at Texas Tech University, under the direction of Alan Sill. Some parts of the computational calculations were also performed on the Chemdynm cluster of the Hase Research Group. S.J.S. acknowledges support by the Air Force Office of Scientific Research, Grant No. FA9550-15-1-0428, with focus on graphite erosion and ablation, and the NSF, Grant No. CHE-1566364, with focus on spatiotemporal reaction kinetics. Support from the NSF-Materials Research Science and Engineering Center at the University of Chicago, Grant No. NSF-DMR-14-20709, is also gratefully acknowledged.
Publisher Copyright:
© Copyright 2018 American Chemical Society.
PY - 2018/12/27
Y1 - 2018/12/27
N2 - Direct chemical dynamics simulations at high temperatures of reaction between 3O2 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 3O2 collision energies Ei 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, 3O2 dissociative chemisorption was observed for collisions on four- (with a different morphology), five- and 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 Ei = 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 O2 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/CO2 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/CO2 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 3O2 dissociative chemisorption dynamical mechanism on defective-graphene/graphite surfaces at high temperatures.
AB - Direct chemical dynamics simulations at high temperatures of reaction between 3O2 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 3O2 collision energies Ei 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, 3O2 dissociative chemisorption was observed for collisions on four- (with a different morphology), five- and 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 Ei = 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 O2 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/CO2 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/CO2 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 3O2 dissociative chemisorption dynamical mechanism on defective-graphene/graphite surfaces at high temperatures.
UR - http://www.scopus.com/inward/record.url?scp=85058888606&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.8b10146
DO - 10.1021/acs.jpcc.8b10146
M3 - Article
AN - SCOPUS:85058888606
VL - 122
SP - 29368
EP - 29379
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
SN - 1932-7447
IS - 51
ER -