Performance of tunable Fe-N-C-based oxygen reduction reaction catalysts prepared based on ZIF-8

Developing highly active, durable, and cost-effective oxygen reduction reaction (ORR) catalysts is crucial for fuel cell commercialization through the use of non-precious metal alternatives to platinum. In this study, the tunable dodecahedral Fe-N-C catalysts were synthesized through controlled pyrolysis of Fe-doped zeolite imidazolate framework-8 (ZIF-8) precursors. The optimized 5% Fe@NC-8 catalyst demonstrates excellent ORR performance with an onset potential of 0.92 V vs. RHE, a half-wave potential (E_1/2) of 0.83 V vs. RHE, and a limiting diffusion current density (j_d) of 6.06 mA cm⁻², surpassing commercial 20% Pt/C catalysts (onset potential 0.89 V vs. RHE; E_1/2 0.81 V vs. RHE; j_d 4.27 mA cm⁻²). It also shows strong durability, retaining 86.16% of its current after prolonged polarization (@0.80 V vs. RHE for 10,000 s) and minimal negative shift in half-wave potential after extensive cycling(@200 mV s⁻¹ for 5000 CV cycles). The enhanced catalytic performance is attributed to (i) possessing a high specific surface area (319 m² g⁻¹) and favorable porosity to maximize active site accessibility; (ii) having abundant active sites of Fe-N_x, graphitic N, and pyridinic N as active catalytic centers; and (iii) forming N-doped carbon matrices to provide a conductive framework. These advantages boost the density of accessible active sites and thus remarkably improve the ORR catalytic activity.