We next measure nitrate rate order experimentally (Supplementary Figures and) and develop a microkinetic model demonstrating the impact of competition between nitrate and H * on NO3RR activity (Figure ). This model describes how thermodynamic and kinetic parameters drive the rate-limiting steps of the HER and NO3RR. Here we highlight modelling results of three TMs along the weak H chemisorption arm of Figure (e.g. Cu, Ni, and Ni0.68Cu0.32, see SI for model details and experimental nitrate rate order for additional TMs, Supplementary Figure ).