Selective reduction of CO2

CO₂ can be reduced to several C₁ products like CO or HCOOH, HCHO, CH₃OH and CH₄ which vary in the number of electrons and protons transferred to CO₂. The thermodynamic driving forces for all these nH⁺/ne^- reductions fall within a narrow range with the 2e^-/2H⁺ reduction being most energy demanding. This, along with a similar reduction potential for H⁺ reduction, makes attaining selectivity for a single product difficult to attain under electrocatalytic conditions. Factors like hydrogen bonding, electrostatic interactions and spin states have been proposed to affect the selectivity of 2e^-/2H⁺ reduction and will be briefly discussed. The lecture will detail the newest developments from this laboratory in obtaining selective reduction of CO₂ to HCHO, CH₃OH and CH₄. It will focus on the mechanism of these reaction via identifying the intermediates using in-situ spectro-electrochemistry and parallel chemical preparation of these species followed by their spectroscopic characterization. The mechanism discovered thus far reveals that the product of CO₂ reduction can be generally controlled by regioselective protonation of these CO₂ derived intermediates involved. In fact, these intermediates can also be used to methylate organic molecules and even form C-C bonds to result in C₂ products like ethane selectively.