In a combined experiment-theory study, some of us recently proposed that the mechanism for forming Ac on Cu is very much in line with the "desorption-re-adsorption-reaction" mechanism. The case of Ac is just slightly more complicated by the fact that it is not directly acetate, but ketene, that desorbs from the surface. This earlier intermediate is then attacked by OH -ions in the electrolyte to finally form Ac via a solution reaction step.