We used Φmax to study trends in activity across 23 d-block monometallic metal surfaces for flat and stepped facets (i.e. ( ), (110), (211)) at three applied potentials: 0.0, -0.25, and -0.5 V vs. SHE. The geometries of bare metal surfaces and their corresponding adsorbate-surfaces (i.e., the metal surface with an adsorbate bound to an active site) were optimized using GC-DFT under implicit solvation at each bias (see Methods). The calculated grand free energies, Φ, include both enthalpic and entropic contributions at 298 K. Reaction free energy diagrams (see section 2.4 in the SI) were generated from ΔΦ's of intermediate states, from which Φmax was calculated for each surface at each potential using the steps that define the energetic span. Φmax for each material is calculated for both the associative alternating and associative distal pathways in the composite mechanism (see section 2.2 in the SI for all energetic spans). However, only the pathway with the more endergonic Φmax was used to assess activity. For many materials, the energetic span encompasses steps shared by both pathways in the composite mechanism (e.g., orange, yellow, and green lines in Figure ).