From a physical point of view, the charge sensitivity parameter ∆ i a should depend on the amount of transferred charge during adsorption. Charge is transferred from the Fermi level of the metallic slab to the adsorbate. We thus concluded that the Fermi level might be an intuitive choice for predicting the qualitative trends of this property across metals. Indeed, the work function which correlates with the PZC trends across metals, has been already been discussed as an important parameter for CO 2 RR to CO and the Hydrogen evolution reaction (HER). Intriguingly, we found the inclusion of this descriptor in a two-dimensional multi-regression model to increase all R 2 values of adsorption energies and charge sensitivity parameters significantly to 0.9-1.0, with only the charge sensitivity parameter of *CO 2 being not perfectly scalable at R 2 = 0.76 (Supplementary Fig. ). We think that this larger uncertainty is related to the instability of the * CO 2 state on many surfaces which required us to extrapolate the energy to smaller charges using a fixed high charge geometry. This extrapolation procedure bears some numerical error which might actually be canceled out to some degree by the linear scaling model. In sum, the two-dimensional descriptor space spanned by CO adsorption energy and Fermi level gives an almost perfect approximation to the exact free energy landscape for all considered metal surfaces. Note that this includes both planar surface facets, but also stepped once, highlighting the generality of this approach.