Quantum chemical study of the dissociative adsorption of OH and H ₂O on pristine and defective graphite (0001) surfaces: Reaction mechanisms and kinetics

Quantum chemical studies of the dissociative adsorption mechanisms and kinetics of OH_x (x = 1, 2) on graphite (0001) surface models were carried out with emphasis on the influence of surface defects. Finite-size model systems for Stone-Wales type (SW), mono- (1V), and divacancy (2V) defects are studied in addition to the defect-free (0D) surface models. Horizontal and vertical bulk effects have been considered by variation of the model system size and number of graphene layers. Potential energy surfaces for dissocative adsorption of one and two OH radicals on pristine graphite and for H ₂O adsorption on 1V, 2V, and SW defects are presented at the dispersion-augmented density functional tight binding (DFTB-D), integrated ONIOM(B3LYP/6-31+G(d):DFTB-D), and density functional theory B3LYP/6-31+G(d) levels of theory. OH is found to oxidatively erode the graphite surface by producing gaseous CO and hydrogenated vacancy defects (L1H1V), while water is found to react only with monovacancy defects. The rate constants for the dissociative adsorption have been predicted by RRKM theory. Quantum chemical molecular dynamical (QM/MD) simulations at high temperatures of adsorption products of OH and H₂O on graphite surface models have been carried out using the DFTB-D method.