The standard reduction voltage for this reaction is 𝐸 𝑂 2 𝑂 2 •- ⁄ 0 = -0.33 V vs. SHE. However, this voltage corresponds to a superoxide activity of 1. In contrast, its formal reduction voltage, E 0 ', can be calculated as follows, where R is the ideal gas constant, T is the absolute temperature, 𝑝 𝑂 2 is the partial pressure of O2, and a is the activity of species in the aqueous solution: