Figure : Volcano plots constructed by plotting the surface low-coverage hydrogen adsorption energy closest to the optimum (i.e. the surface minimum hydrogen adsorption energy closest to -0.24 eV) across all stable materials in for each metal combination against the highest experimental HER rate observed over all metal salt concentrations for that combination. A grey trend is drawn on as a guide for the eye. The four points to the right that lie above the trend contain Au and Ag, which are known to have improved hydrogen adsorption energies in nanoparticle form due to surface strain ; the adsorption energies used in this work do not account for that effect. Note that the y-axis is not normalized by surface area, meaning that differences in absolute rates are affected by variations in the area of the total reactive interface. Materials with binding energies above 0.2 (pure In and Pb) were removed for clarity; neither was experimentally active in any solvent condition. (a) This plot is colored by the metal in each bimetallic composition that had the highest pure activity: Pt (grey), Au (orange), Pd (green), Ni (pink), or Cu (orange). (b) This plot is colored by the presence (gold) or absence (black) of a noble metal. Across all solvent conditions, experiments containing at least one noble metal (shown in gold) tend to fall above the rest (black) at similar points on the x-axis. thermodynamic neutrality (-0.41eV < ∆E(H * ) < -0.23eV , see Fig. ), whereas systems containing only thermodynamically unfavorable surfaces are less active, with the upper envelope of experimental activities relative to binding energies forming a volcano shape. This relationship is not perfect: a large number of chemical systems are predicted to express surfaces with favorable binding energies but are not very active experimentally. This observation is consistent with a physical picture in which aggregate reactivity is dominated by the most active surface present, but in some experiments this surface is deactivated or not present. One important caveat is that unlike in a Sabatier plot, plotted experimental activity is not normalized by surface area, meaning that data may underperform the Sabatier trend due to reduced surface area relative to the most active points. Additionally, this relationship is mediated by a substantial amount of noise in both the x-and y-axis (see Figures ). The full set of predictions generated using this method for all metal combinations can be seen in Figure .