Spontaneous Activation of CO₂and Possible Corrosion Pathways on the Low-Index Iron Surface Fe(100)

Spin-polarized density functional theory (DFT) calculations and periodic slab models were used to study the reactive pathways leading to corrosion products on the low-index (100) surface of iron. We determined the binding energies of CO2 and the barrier to decomposition of adsorbed CO2 to O + CO, as well as to the formation of adsorbed CO32− and H2CO3 on the Fe(100) surface. The barriers of these pathways were determined with nudged elastic band (NEB) calculations. Short trajectories with DFT-based dynamics were employed to identify the most important species. These simulations (up to 0.5 ML coverage) show that CO2 is spontaneously activated and can bind with two or all three atoms assuming bent configurations strongly reminiscent of the radical CO2−. This spontaneous activation of CO2 is possible through charge rearrangement of the slab density. The CO2 decomposition to O + CO has a barrier of 5.0 kcal/mol. The subsequent formation of CO32− by reaction with an incoming CO2 is strongly favored thermodynamically. Interaction of H2O with the adsorbed CO2 forms a loosely bound complex that leads to the formation of surface-bound carbonic acid, with a barrier of approximately 35.0 kcal/mol.