Cobalt ferrite microspheres as a biocompatible anode for higher power generation in microbial fuel cells

In the present study, spinel cobalt ferrite hierarchical flower-like microspheres (CoFe₂O₄-MS) are fabricated using a hydrothermal method and utilized as a biocompatible anode in microbial fuel cells (MFCs) for power generation. A maximum power density of 1964 mW m⁻² is achieved with CoFe₂O₄-MS in a mediator-less MFC using Escherichia coli as a biocatalyst and glucose as a fuel. The unprecedented power generation by CoFe₂O₄-MS can be attributed to (i) the morphology of the flower-like CoFe₂O₄-MS, with a rough surface and large surface area suitable for biofilm formation, (ii) the rapid immobilization of negatively charged E. coli cells on the positively charged CoFe₂O₄-MS, facilitating stronger bacterial adhesion between the bacterial cells and CoFe₂O₄-MS, which leads to lower contact resistance and advantageous interfacial properties with rapid electron transfer, and, more importantly, (iii) enhanced interfacial charge transfer due to the presence of multi-valent cations and multiple valence states in the highly electrocapacitive CoFe₂O₄-MS. Thus, the enrichment of electroactive E. coli on CoFe₂O₄-MS produces a large number of electron-shuttling endogenous redox mediators, which promotes efficient extracellular electron transfer between E. coli and the electrocapacitive CoFe₂O₄-MS during the oxidation of the substrate, thus generating higher power output.