Synergistic engineering of Fe−N4−S active sites and pore architecture for high-performance oxygen reduction reaction

The sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode severely limits the electricity generation and pollutant degradation of microbial fuel cells (MFCs). Herein, we report a facile one-pot pyrolysis strategy for fabricating a highly dispersed iron-embedded N/S co-doped hierarchical porous carbon catalyst (FeSNC) with accessible Fe−N 4 −S active sites using tetramethylammonium hydroxide (TMAH)-optimized Fe-ZIF-8-N-H precursors. TMAH enables rapid synthesis (16 min), 3.6-fold yield enhancement, mesopore engineering for efficient Fe 2+ capture and dense Fe−N 4 −S site formation, and hierarchical pore construction for accelerated mass/electron transport. The Fe source (NH 4 ) 2 Fe(SO 4 ) 2 ·6 H₂O synchronously introduces N and S to optimize pyridinic N and Fe−N x coordination. Theoretical calculations reveal that S-doping modulates the electronic structure of the central Fe, while mesopore-induced defects act as a secondary modulator, collectively establishing a dual-modulation mechanism to optimize the adsorption/desorption of ORR intermediates. The 6 %FeSNC-N-H catalyst outperforms commercial Pt/C in ORR across neutral/alkaline/acidic media and, as an MFC cathode, delivers a peak power density of 987.0 ± 5.3 mW cm⁻², 96.75 % COD removal, and high degradation efficiency for phenol (93.4 %) and methylene blue (95.6 %). This work underscores the critical synergy between of metal centers electronic microenvironment and nanostructural pore engineering for advanced electrocatalysts.