A popular assumption in the field of electrochemical CO 2 reduction is that the monodentate intermediate *COOH produces CO, while the bidentate intermediate HCOO** produces HCOOH (see Fig. for illustration of adsorbates). The reasoning then goes, if one can show the existence or stability of the given intermediate, one has proven product formation of its assumed corresponding product. Unfortunately, there are problems with this thinking. Several studies have tried to give an explanation regarding CO vs. HCOOH selectivity. Many hypotheses have been made as to what critical factor is needed to consider in order for theoretical calculations to explain this part of CO 2 R product selectivity, such as pH, cations, the surface structure, the amount of water molecules in solution, the binding energy and coverage of protons on the surface, steric constraints, and adsorbate-adsorbate interactions. So far, however, a comprehensive, data-based explanation, reproducing the experimental trends with DFT calculations and explaining CO vs. HCOOH selectivity, has to our knowledge not been made.