The Missing Link for Electrochemical CO2 Reduction: Classification of CO vs. HCOOH Selectivity via PCA, Reaction Pathways and Coverage Analysis

For the electrochemical CO2 reduction reaction, different metal catalysts produce different products preferentially. However, the differences between the metals' reaction pathways that lead to these different products is still not fully understood. In this work, we analyze CO vs. HCOOH formation from CO2 using statistical analysis and DFT calculations. This is carried out by considering multiple descriptors, along with the competing reaction pathways, reaction barriers, and high coverage of mixed adsorbates on the surface. This method is capable of explaining the discrepancy between simulations and experiments regarding Ag and Au selectivity, and of properly classifying elements according to their product distribution. We find that, when considering water-assisted protonation for the disproportionation to CO, Ag and Au have a lower barrier for CO production in agreement with experimental results. We also find that, when considering high coverage of mixed adsorbates on the Ag/Au surface, the most stable adsorbate configuration contains adsorbates capable of forming CO preferentially. These findings help to bridge the gap between simulations and experiments and provide a missing link for our understanding of the CO2 reduction reaction.