(764a) Effects of Electrolyte Ions on Electrochemical CO2 Reduction

The identity of both metal cations and anionic species in the electrolyte is known to influence the electrochemical reduction of CO₂; however, detailed understanding of these effects is still lacking. Here we present a combination of experimental and theoretical studies of the effects of electrolyte cation size on the activity and selectivity of metal catalysts for the reduction of CO₂. Further, we explore how the identity of anionic and buffering species in the electrolyte influence catalytic activity. Experiments were conducted under conditions where the influence of electrolyte concentration polarization is minimal in order to separate intrinsic kinetic and mass transport effects. Interpretation of the findings for CO₂ reduction was aided by studies of the reduction of gyloxal and CO, key intermediates along the reaction pathway to final products. Density functional theory calculations show that the effect of the presence of alkali metal cations can be understood in terms of electrostatic interactions between solvated cations and adsorbed species with large dipole moments, while trends in activity with cation size arise from additional chemical interactions for larger cations. The effect of anions on CO2 reduction rates can be understood in terms of the hydrogen donation ability of the most willing donor in solution.