JDFTx optimization was implemented in the Atomic Simulation Environment (ASE). All structure optimization scripts used here are available at . The GGA PBE functional with D3 dispersion corrections were used for all calculations using an energy cutoff of 20 Hartrees and a charge density cutoff of 100 Hartrees. All calculations were converged with spin polarization and initialized with a magnetic moment of zero with the exception of cobalt, which was initialized in a high-spin state. The coulomb interaction was truncated in the z-direction for surface calculations to prevent self-interaction. Aqueous electrolyte was modeled using H2O as the solvent with ion concentrations of 0.5 M for F -and Na + ions. The absolute potential of 4.66 eV for the standard hydrogen electrode was previously calibrated for the CANDLE solvent model by fitting experimental work functions to calculated chemical potentials. To model the composite mechanism on each surface, 11 NRR intermediates were studied: N2*, N2H*, NNH2*, NNH3*, N*, NH*, NHNH*, NHNH2*, NH2NH2*, NH2*, and NH3*. Adsorbates were bound to each surface in three different binding configurations: atop, bridge, and 3 atom hollow sites. The lowest energy binding configuration for each intermediate was taken as the ground state and used in the Φmax analysis. A hydrogen adatom was also bound at the atop, bridge, and hollow sites for each surface to model HER. Each clean surface and set of adsorbed structures were modeled at three biases: 0, -0.25, and -0.5 V vs. SHE. In total, more than 2500 surface and adsorbate optimizations were run.