To evaluate the effect of individual functional groups on the energy of each intermediate reaction step in the ORR catalytic cycle, we generated an enumerative library of catalysts with hydrogen replaced by functional groups. The full set of functional groups used to replace hydrogens atoms is shown in Figure . For catalysts A, B, and C, we generated all possible catalysts with a single functional group substitution, producing to 33 derivatives of catalyst A, 88 derivatives of catalyst B, and 77 derivatives of catalyst C. For catalysts B and C, we additionally generated a number of possible catalysts with two functional group substitutions, producing 126 derivatives of catalyst B and 338 derivatives of catalyst C. We used RDKit's python library to produce these functional group substitutions and generate initial geometries. We used DFT to optimize all functionalized catalysts. We subsequently used these DFT optimized geometries as inputs to a python script we wrote to produce initial guesses for the geometry of the catalytic cycle intermediates O2, O2H, O, and OH. We then optimized all these intermediates with DFT and computed the free energy of each reaction step (SI section 1). We also computed the difference between the intermediate reaction energies of the derivatized catalyst and its corresponding underivatized catalyst, which directly measures the effect of each functional group on the catalytic cycle energetics.