The results indicate that all systems show significant overbinding; in no case does the ORR reaction occur spontaneously at 1.23, indicating that higher overpotentials are needed. The last three (H + + e -) transfer steps are still endothermic (uphill). The only exception is the second (H + + e -) transfer step (Equation ) in Pt10/silicene, Pt10/SmSI and Pt5Ge5/SmSI. Nonetheless, even though this step is downhill, the reaction still has to climb two consecutive uphill steps. OOH* formation is always downhill regardless of the support and cluster composition.