The heat maps in Figures show the formation energies of the different spinel oxide compositions. The higher density of formation energies below 0.030 eV/atom demonstrates that the AB2O4 spinel composition is generally the most stable composition type, followed by A0.5B2.5O4 and then A1.5B1.5O4. This is probably because in the latter two compositions, at least one of the cations should occupy both tetrahedral and octahedral sites in the spinel oxide structure. This cation should be able to assume both +2 and +3 oxidation states and should not have any strong preference for tetrahedral or octahedral coordination geometry. This constraint would limit the number of possible stable compositions for both A0.5B2.5O4 and A1.5B1.5O4 compositions relative to AB2O4. It can be observed that spinel oxides containing 3d metal cations are typically more stable than spinel oxides containing 4d and 5d metal cations. Mn, Co and Fe-containing spinels, in particular, are more likely than other metal cations to have formation energies that are within 0.030 eV of their convex hulls. This makes Mn, Co and Fe-containing spinels more likely to exist in nature . This observation can first be partly rationalized by the fact that Mn, Co and Fe are stable in the +2 and +3 oxidation states 26 . Furthermore, according to Kocevski and coworkers, Mn, Co and Fe ions do not have a strong preference for either tetrahedral or octahedral sites in spinels and are frequently seen in either of them . Therefore, Co, Mn and Fe containing spinel structures have a greater amount of flexibility in accommodating a wider variety of other cations as a result, making them more ubiquitous than other elements; an observation that was further corroborated by the calculations performed in this work . Spinels containing metals of higher oxidation states can be stabilized through the engineering of oxygen vacancies into the structure . This study, however, did not consider defects such as oxygen vacancies in order to keep computational costs reasonable. After this step had been performed, 290 materials were identified as being potentially thermodynamically stable. They were selected for the final step of this highthroughput computational screen, where their OER activity was estimated.