Figure 2.

Example of a Bayesian ORR composition optimization for the quinary Ag‐Ir‐Pd‐Pt‐Ru system. a) Pseudo‐ternary plots (with Ir, Pt, and Ru collected into a single concentration) of the surrogate function after sampling of 15, 28, 54, and 150 compositions. Yellow colors signify regions with high absolute values of modeled current density, and blue colors signify regions with correspondingly low values. Previously sampled compositions are shown as black circles, and the best composition found so far is marked with a star. When projecting current densities from the quinary to the pseudo‐ternary composition space, more compositions will inevitably occupy the same points in the diagram. In the shown plots the maximal absolute value of the current density for overlapping compositions has therefore been depicted. b) Current densities sampled during the Bayesian optimization (black solid line) and the emergence of the three most active locally optimal compositions (blue dashed lines). c,d) Variation of the GP squared exponential kernels’ [Eq. (4)] constant term (c) and length scale (d) hyper‐parameters.