Considering the experiments by Hori on single crystalline Cu electrodes of defined facets, we also find that the PZC acts as an effective parameter to describe the transition from C 1 to C 2 selectivity. Although single crystalline electrode experiments have to be taken with care, since minority active sites like defects can always determine the overall activity, the trends are quite convincingly predicted by the PZC descriptor as seen from Fig. a. Motivated from this, we also applied the PZC descriptor to predict the C 1 vs. C 2 selectivity on metal doped Cu catalysts from recent experimental data 85 (Fig. ). Interestingly, the descriptor correlates almost perfectly with the selectivity data with the exception of the experimental data on Sn which has been also noted as a special case in the original paper. The enhancement of C 2 product formation with increased PZC can be explained by increased electric double layer field facilitating the rate-limiting coupling of two *CO intermediates. The strong field-dependence and correspondingly large ∆ i a-coefficients of this step has been previously pointed out. Due to this, a more positive PZC usually increases the C 2 over C 1 selectivity.