ORR is a multielectron reaction characterized by several elementary steps involving different reaction intermediates, as shown in Table and. In acidic solutions, ORR occurs through two pathways: the direct four-electron transfer pathway from O 2 to H 2 O and a two-electron transfer pathway from O 2 to hydrogen peroxide (H 2 O 2 ). Alternately, there is also a two-electron pathway that transfers H 2 O 2 to water . Different reaction processes will result in a different potential under different reaction conditions.