Insights into C-C Coupling in CO2 Electroreduction on Copper Electrodes

We present a first-principles theoretical study of carbon– carbon coupling in CO2 electroreduction on the copper 211 surface. Using DFT, we have determined kinetic barriers to the formation of a CC bond between adsorbates derived from CO. The results of our nudged elastic band calculations dem- onstrate that kinetic barriers to CC coupling decrease signifi- cantly with the degree of hydrogenation of reacting adsor- bates. We also show that this trend is not affected by the elec- trical fields present at the solid-electrolyte interface during electrocatalysis. Our results explain how copper can catalyze the production of higher hydrocarbons and oxygenates in theelectrochemical environment, despite producing only single carbon atom products in gas-phase catalysis, and how CC bonds can be formed at room temperature in the electro- chemical environment, whereas substantially higher tempera- tures are needed in the Fischer–Tropsch catalysis. The unique feature of the electrochemical environment is that the chemi- cal potential of hydrogen (electrons and protons) can be varied through the applied potential. This allows a variation of the degree of hydrogenation of the reactants and thus the activation barrier for CC coupling.