As such, we believe this Tafel mechanism to be the pathway for HCOOH formation, as opposed to the Heyrovsky mechanism for CO formation, as also hypothesized by Morrison et al. In short, if we assume that *COOH makes CO (and possibly HCOOH) via the water-assisted shuttling mechanism, but that HCOO** makes HCOOH via the Tafel mechanism, then CO formation has the lowest activation barrier on Au and Ag. Even if we assume that HCOO** to HCOOH also occurs via water shuttling, that still makes *COOH more likely to make CO than HCOOH.