Fig. 9. (a) ORR polarization curves of Ni–N/C_3_H₂O catalyst before and after SCN⁻ poisoning. (b) Determination of C_CN⁻ using a UV-vis spectrophotometer before and after CN⁻ poisoning on Ni–N/C_3_H₂O catalyst surface. (Inset) the SD value of Ni–N/C_3_H₂O catalyst. (c) TOF for H₂O₂ production of Ni–N/C_3_H₂O catalyst per Ni single site.