Hierarchically porous carbon with pentagon defects as highly efficient catalyst for oxygen reduction and oxygen evolution reactions

Highly dispersed electrocatalysts and single-atom catalysts receive extensive attention in the field of multiple reactions involving water spitting, oxygen reduction, and CO2 reduction. Herein, we develop a Fe/N co-doped hierarchically structured porous carbon (Fe/N/C-DT) by the dual-templating approach, involving the incorporation of ferrocenecarboxaldehyde (Fc–CHO) into the polyimide, followed by carbonization at 900 °C and etching. A steric hindrance offered by the ferrocene and the porosity of the obtained nanostructure prevent the aggregation of Fe atoms, resulting in the maximization of catalytic efficiency of iron-based sites. FeCl2/N/C-DT and FeSO4/N/C-DT using FeCl2 and FeSO4 as iron sources, respectively, are prepared for comparison, to further confirm the potential positive effect of Fc–CHO and explore the synergistic effect of the pentagon defects and Fe–N4 on the catalytic performance in oxygen reduction reaction (ORR). The prepared Fe/N/C-DT exhibits outstanding electrochemical activity toward ORR (E1/2 = 0.902 V vs RHE) and impressive OER activity (Ej=10 = 1.66 V) in alkaline conditions. The rechargeable Zn–air battery using Fe/N/C-DT as a cathode catalyst shows a peak power density of 220 mW cm−2 and a high open–circuit voltage of 1.451 V in the all-solid-state Zn–air battery.