While this last step introduces an additional pH dependence (through the involvement of OH -), the selectivity towards Ac is still driven by the competition between surface kinetics and diffusion. The resulting ∝ 1/ρ dependence on catalyst morphology thus provides a reasonable explanation for lower Ac yields measured on more roughened Cu electrodes. Our present model thus suggests the inverse effect from Pd-or Ag-based alloying. This trend is well reproduced by the kinetic model when only varying the ρ parameter and keeping all other parameters fixed (solid red line in Fig. ). The emerging mechanistic picture is thus very simple as it reduces the effect of alloying to merely lowering ρ within the "desorption-re-adsorption-reaction" model. One may therefore even think of alloying as changing the atomic-scale roughness. Lower ρ ultimately means that more Ac will escape as an intermediate species when measured against later, further-reduced C 2+ products. We therefore suggest that high Ac selectivity is not necessarily unique to Cu-based alloys, but may be expected also on pure Cu electrodes if the surface morphology remains smooth enough under reaction conditions. There exists some experimental evidence to support this hypothesis. Finally, generalizing this alloying effect, we note that similar observations have been made by the group of Koper for the volatile CO product during the eCO 2 RR on Cu-Zn alloys.