Modeling CO2 reduction on Pt(111)

Density functional theory was used to model the electrochemical reduction of CO2 on Pt(111) with an explicit solvation layer and the presence of extra hydrogen atoms to represent a negatively charged electrode. We focused on the electronic energy barriers for the first four lowest energy proton-electron transfer steps for reducing CO2 on Pt(111) beginning with adsorbed *CO2 and continuing with *COOH, *CO + H2O, *COH, and ending with *C + H2O.

We find that simple elementary steps in which a proton is transferred to an adsorbate (such as the protonation of *CO to *COH) have small barriers on the order of 0.1 eV. Elementary steps in which a proton is transferred and a C-O bond is simultaneously cleaved show barriers on the order of 0.5 eV. All barriers calculated for these steps show no sign of being insurmountable at room temperature.

To explain why these barriers are so small, we analyze the charge density and the density of states plots to see that first, the electron transfer is decoupled from the proton transfer so that in the initial state, the surface and adsorbate are already charged up and can easily accept the proton from solution.

Also, we see that in the cases where barriers are on the order of 0.1 eV, electron density in the initial state localizes on the oxygen end of the adsorbate, while electron density is more spread out on the surface for initial states of the C-O bond cleaving elementary steps.