Hierarchical N/Se dual-doped porous carbon drives four-electron oxygen reduction for superior efficiency and durability of microbial fuel cells

Microbial fuel cells (MFCs) are eco-friendly energy conversion systems that simultaneously degrade organic matter and convert its chemical energy into electricity. However, a formidable challenge in MFC development is designing efficient and stable catalysts to enhance cathodic oxygen reduction reaction (ORR). Herein, we propose a hierarchical nitrogen and selenium dual-doped porous carbon (NSeC-800) for MFC applications. The NSeC-800 exhibits superior ORR activity and durability, with initial potential of 0.99 V, limiting current density of 6.25 mA cm⁻² and 90.1 % retention in neutral electrolyte, surpassing commercial Pt/C (0.95 V, 5.69 mA cm⁻² and 70.8 %). The high performance is attributed to the synergism of N/Se doping, creating abundant active sites such as combined pyridinic N and C-Se (p-N/C-Se) within a hierarchical porous structure (1571.3 m² g⁻¹). Density functional theory calculations reveal the strong adsorption energies of O₂ and ∗OOH (−2.34 and −3.62 eV) on p-N/C-Se sites, facilitating O-O bond cleavage and boosting the four-electron oxygen reduction. In MFCs, NSeC-800 outperforms commercial Pt/C, demonstrating 2.6 times higher maximum power density (1018.7 ± 4.3 mW m⁻²) and 4.5 times longer running time (450 h/period). This work provides a dual-heteroatom doping strategy to construct an efficient and stable electrocatalyst with dominated 4e⁻ pathway for high-performance MFCs.