Intrinsic Catalytic Properties of ZEZ N₈^- for Oxygen Reduction Reactions in Both Alkaline and Acidic Media

ZEZ N₈^- polynitrogen (PN) was successfully synthesized under ambient conditions with the cyclic voltammetry (CV) method. The PN material showed excellent oxygen reduction reaction (ORR) activity that surpassed a Pt/C commercial catalyst in both acidic and alkaline media. Moreover, its ORR activity is higher in alkaline than in an acidic medium. Through density functional theory (DFT) calculations, Cs (the cyclic point group of a single in-plane reflection) is found to be the ORR active species, and a unique dissociative ORR mechanism on Cs N₈^- occurs in both media. Molecular oxygen binds to the two N atoms at the end of the Cs N₈^- chain through a side-on chemisorption mode, causing an N₈ configuration change. The bonded O₂ splits, which is consistent with the experimental 4-electron dissociative pathway for the ORR. On N₈, the sequential elementary steps are: *O*O + H → *O*OH is spontaneous; *O*OH + H → 2*OH is exergonic; and the desorption of the chemisorbed OH group (2*OH → 2OH + 2*) is spontaneous. However, on Pt, the binding of *OH is too strong for ideal activity. Thus, while OH coverage is a problem on Pt, it does not hinder the ORR activity on N₈, and it explains the higher current density on N₈. Additionally, the external potential shows the ease with which the PN can reach the operating potential, 0.6 V for PN in alkaline media, compared to 0.9 V for Pt. The remarkable unique property of PN is its structural flexibility, as the configuration cycles from zigzag to Cs, to staircase, and original configuration, replenishing the active sites. These new insights of the ORR explicate the excellent electrocatalytic performance of ZEZ N₈^- PN as a nonmetallic green catalyst for fuel cells and other practical applications.