Photoactive Manganese Ferrite-Modified Bacterial Anode to Simultaneously Boost Both Mediated and Direct Electron Transfer Processes in Microbial Fuel Cells

Photomicrobial fuel cells can efficiently improve the power density of microbial fuel cells (MFCs), but bimetallic spinel ferrite photoactive material-based microbial devices have not been investigated yet. Herein, a dissimilatory iron-reducing bacterium, Shewanella putrefaciens CN32 (S. putrefaciens CN32), is selected as a model bacterium due to its possible enhanced affinity with iron-containing photoactive materials. Three bimetallic spinel ferrite nanoparticles, cobalt ferrite (CoFe₂O₄), nickel ferrite (NiFe₂O₄), and manganese ferrite (MnFe₂O₄), were used to modify the surface of S. putrefaciens CN32 for photo-MFCs, showing that MnFe₂O₄ has the best catalytic effect. Results reveal that these nanoparticle coatings on bacteria not only enhance direct electron transfer mediated by outer membrane c-type cytochromes (OMCs) while serving as conductive paths for charge transport between bacteria and the electrode surface but also significantly promote bacterial growth for increased flavin production from S. putrefaciens CN32. In addition, the extracellular electron transfer can be greatly accelerated with the assistance of photosensitive MnFe₂O₄ nanoparticles under visible light. This work demonstrates that the photomicrobial anode can simultaneously enhance both mediated and direct electron transfer processes and offers universal significance for photo-bio-electrocatalysis.