Sustainable Mn-doped ZnO Nanoparticles as an Efficient Cathode Catalyst for Enhanced ORR and Photocatalytic Dye Degradation in Microbial Fuel Cells

In this study, Crocus sativus plant extract was employed in the synthesis of manganese-doped ZnO (Mn-doped ZnO) nanoparticles, which served as cathode catalysts in a Microbial Fuel Cell (MFC) for enhanced oxygen reduction reaction (ORR) and photocatalytic dye degradation. X-ray diffraction (XRD) confirmed the wurtzite hexagonal structure of ZnO, with minor peak shifts confirming successful Mn doping. UV–Vis spectroscopy revealed narrowed bandgap, enhancing visible light absorption. Fourier Transform Infrared (FTIR) spectroscopy confirmed Zn–O and Mn–O bonding. High-Resolution Transmission Electron Microscopy (HRTEM) analysis revealed well-defined nanoparticles though with slight agglomeration at higher Mn concentrations. Photocatalytic testing achieved 96.10% crystal violet degradation with 6% Mn-doped ZnO. MFC performance evaluated via polarization study, Electrochemical Impedance Spectroscopy (EIS), Linear Sweep Voltammetry (LSV), and biofouling study. MFC performance analysis showed that Mn-doped ZnO at 2 mg/cm² achieved a maximum volumetric power density of 12.51 W/m³. Mn-doped ZnO exhibited Pt-comparable cost-effective performance, highlighting its potential as an efficient and eco-friendly cathode catalyst for MFCs and photocatalysis.