Fig. 2. (a) Illustration of the composition plotting schema for compositions containing 1, 2, 3 and 4 cation elements, with example compositions noted for the placeholder element names A, B, C and D. (b) The 2121 OER overpotentials in dataset A for the 6, 15, 20 and 15 compositions spaces containing 1, 2, 3 and 4 cations, respectively. The 21 compositions outlined in black comprise the top percentile in catalyst activity. The overpotential color scale is noted at bottom left.