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 (E_1/2 = 0.902 V vs RHE) and impressive OER activity (E_j=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.