To shed further light on the different NO3R selectivities towards NH2OH, NH3 and N2 observed with the Cu, Zn and Zn93Cu7 electrocatalysts, we performed a mechanistic investigation by means of periodic density functional theory (DFT) calculations (see Supplementary Information for details). To avoid the well-documented issues associated with the modelling of charged species through the introduction of a background charge in the unit cell, and since the reduction from NO3 -to nitric oxide (NO) is widely understood. we set the zero of energies in our calculations to be the neutral NO molecule instead of NO3 - (see Supplementary Information for further details).