Starting from activation energies of all elementary steps, we then constructed a mean-field micro-kinetic model (MKM) for the reaction mechanism presented in Eq. 1, which was solved in the steady-state approximation using the CatMAP program package. 11 Fig. shows the activity volcano plot of the turnover frequency (TOF) of CO formation obtained from the MKM model as a function of the two descriptors, CO adsorption energy and PZC, at -1.0 V vs. SHE, the voltage at which CO is primarily formed on most CO forming metals. By looking at the figure, the first notable point is the strong curvature of the high activity ridge resulting from the PZC dependence of the CO activity. This distinguishes the volcano substantially from the conventionally considered CO activity volcano that is given as a mere function of the CO adsorption energy and does not consider surface charging nor the *CO 2 intermediate (right panel in Fig. ). The PZC dependence effectively breaks the scaling relations and introduces a further dimension in the figure, which opens up a new area of even higher CO conversion rate which is located at lower CO adsorption energy compared to the traditional volcano.