Abstract: Microbial fuel cells (MFCs), a sustainable green energy technology, have emerged as promising alternatives to conventional fossil fuels because of their safety and environmental compatibility. However, their power generation efficiency remains notably constrained by the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode. In this study, a kind of bead-like porous carbon nanofibers (CNFs)-AgFe alloys ORR catalyst with abundant macroporous structures was successfully synthesised by embedding zeolitic imidazolate framework-8 (ZIF-8) nanocubes doped with Ag+ and Fe3 + into electrospun CNFs. The decomposition characteristics of ZIF-8—namely, framework collapse and Zn2 + volatilisation—were exploited to realise this hierarchical structure. The hierarchical porous architecture of the catalyst substantially enhances the exposure of metallic active sites, thereby facilitating interfacial contact between ORR intermediates and catalytic surfaces. The synergistic interaction between Ag and Fe within the alloy structure generates highly efficient catalytic centres, resulting in exceptional performance metrics, including a remarkable limiting diffusion current density of 0.424 mA cm^-2 and exchange current density of 0.828 A m^-2, as well as outstanding MFC operational parameters: chemical oxygen demand removal efficiency of 74.07 % ± 2.77 %, coulombic efficiency of 39.35 % ± 3.04 %, stable output voltage of 0.62 V and a record-high power density of 1282.05 mW m^-2. These findings collectively address critical challenges in cathode catalysis while establishing new benchmarks for bio-electrochemical system performance.

Key words: Microbial fuel cells, Oxygen reduction reaction, Electrospinning, Metal organic frameworks, Porous catalyst, cathodes