Porous N-Doped Carbon Nanospheres Modified with Fe/Zr Sulfide-Based Heterostructures for Enhancing Bioelectrocatalytic Activity and Sustainable Energy Conversion Efficiency of Microbial Fuel Cells

Microbial fuel cells (MFCs) represent a green and sustainable energy technology capable of generating electricity through biomass conversion. However, their widespread application is hindered by the relatively low energy conversion efficiency and electricity generation activity of biofilms. The selection of appropriate bioelectrocatalysts emerges as a promising strategy to enhance extracellular electron transfer (EET) efficiency and substrate utilization rates. This study introduces a novel biofunctional anode material composed of Zr3S4/FeS heterogeneous nanostructures embedded in hierarchical porous N-doped carbon spheres (HPNC/Zr3S4/FeS), designed to optimize EET efficiency and interfacial charge transfer kinetics. Compared to HPNC/ZrO2 MFC, the maximum power density of HPNC/Zr3S4/FeS MFC increased by 51.11% (from 4.05 to 6.12 W/m2) and the Coulombic efficiency improved from 24.33% to 30.76%. The bioelectrocatalytic activity of the HPNC/Zr3S4/FeS bioanode was significantly enhanced, as evidenced by increased exchange current density (from 0.76 to 1.74 mA/cm2) and reduced charge transfer resistance (from 3.16 to 1.24 Ω). Fourier-Transformed alternating current voltammetry (FTACV) and distribution of relaxation time (DRT) analyses jointly confirmed that the Zr3S4/FeS heterogeneous interface mediates and promotes the c-type cytochrome-mediated direct EET process, enhancing charge transfer rates at the biofilm-electrode interface. Density Functional Theory (DFT) calculations indicated that the Zr3S4/FeS interface facilitates the adsorption of c-type cytochrome proteins with heme prosthetic groups. High-throughput sequencing demonstrated that HPNC/Zr3S4/FeS selectively enriches electrogenic bacteria (Desulfurivibrio and Geoalkalibacter), a process that further enhances the electrogenic functional traits of the biofilm. This study not only validates the superior bioelectrocatalytic activity of HPNC/Zr3S4/FeS but also highlights the mechanistic role of heterogeneous structures in regulating the sustainable energy conversion efficiency.