The reaction

2NH3 + 3O- NOx + 3H2O + 3e-

does not make any sense. What are O- and NOx?

In water engineering NOx is the sum of NO2- and NO3- and few works include N2O.

To make a balanced reaction and to consider the energetic feasibility of a reaction you must select one species.

Agree with Yurii V Geletii the reaction doesn't make sense as it is written. Nitrogen, oxygen and charge must be balanced and it cannot be so with any of the species in the NO definition.

Dear all, the question as it is written is ambigous, you should clarify more. The following documents may be helpfull. My Regards

https://doi.org/10.1016/0302-4598(93)86114-G

https://doi.org/10.1021/ja01037a007

In addition, Mr. Senapati, you mean "electrode potential", because "redox potential" is ambiguous (please look up the difference between an reduction potential and an oxidation potential, and the IUPAC recommendation for naming potentials). The value of the O2/O2dot- electrode potential is -0.35 V (pO2 = 100 kPa) vs NHE at any pH, not -0.28 V at pH 7, see: D. A. Armstrong et al., Standard electrode potentials involving radicals in aqueous solution: Inorganic radicals. Pure Appl.Chem. 87 (11-12):1139-1150, 2015, attached.

Willem H Koppenol : thank you for sharing very useful paper!