Cobalt-porphyrin catalyzed electrochemical reduction of carbon dioxide in water. 1. A density functional study of intermediates.

The reduction of carbon dioxide by cobalt porphyrins is thought to be a multistep reaction with several possible intermediates and reaction pathways. We here investigate a number of possible intermediates in this reaction using density functional theory, including both hybrid (B3LYP) and pure (PBE and BP86) functionals. Optimum structures are located, and harmonic vibrational frequencies and thermal corrections are computed for the low-lying electronic states for all intermediates. Free energies of solvation are predicted for all species, providing a reaction profile in the aqueous phase, which enables identification of likely pathways. Finally, the reaction energy for the binding of carbon dioxide to the cobalt porphine cation is determined in the gas phase and in solution.