Decoupling the above processes and identifying the relevant transition states is thus crucial to the resulting ORR selectivity. and 2e -ORR are colored in blue and red, respectively. The competing PCET (solid arrows) and non-PCET (dashed arrows) elementary steps directly following OOH* define the four investigated mechanisms discussed in the text: (i) aquoxyl, (ii) dissociative, (iii) peroxide, and (iv) desorption.