Noble metals significantly outperformed base metals beyond what can be explained by adsorption thermodynamics alone (see Figure ). In the volcano-type plot developed in this work, the HER activity for all experiments involving at least one noble metal was on average about an order of magnitude higher Compositions where a bimetallic material is predicted to be the most active are hatched. Combinations predicted to have surfaces with favorable HER thermodynamics are shown in blue, demonstrating approximately a 50% reduction in search space across all combinations or a 30% reduction in combinations where a bimetallic material was expected to form (hatched). Pure aluminum was not predicted to form a metastable metal.