Efficient electricity generation and wastewater degradation simultaneously in microbial fuel cell: Synergistic effect of amplifying localized charge density of carbon shell and confinement of hollow structures for oxygen reduction reaction

The sluggish oxygen reduction reaction (ORR) in neutral microbial fuel cell (MFC) significantly limits the electricity generation and degradation of wastewater. Confinement effects of carbon-encapsulated alloy and hollow structure facilitate electrons transfer and O₂ transport in ORR, but unrevealing their collaborative interaction and the mechanism of alloy cores on the superficial N-doped carbon sites remains a great challenge. Here, a ligand exchange-induced dual metal–organic-frameworks (MOFs, ZIF-8@CoFe PBA) precursor is proposed to synthesize a rambutan-like electrocatalyst (CoFe@NC-HCS) of N-doped carbon nanotubes (CNT)-encapsulated CoFe particles rooting on hollow nanocages. The abundant micro/mesopores contribute to electrolyte penetration and mass transfer, and density functional theory (DFT) calculations indicate that CoFe improves the localized charge density of N-doped carbon shell for O-intermediates. Consequently, CoFe@NC-HCS exhibits a higher half-wave potential of 0.128 V than that of Pt/C in PBS solution. The maximum power density of MFC with CoFe@NC-HCS cathode reaches up to 2627 ± 53 mW·m⁻² and COD removal efficiency is 91.54 %. MFCs can drive a digital watch successfully and also power electroadsoption of phenol with a removal ratio of 92.3 %. Our study offers a new insight into engineering coupled confinement structures and the effect of encapsulated metal on carbon shell for ORR catalysis.