Synthesis and Application of Zirconium Metal–Organic Framework in Microbial Fuel Cells as a Cost-Effective Oxygen Reduction Catalyst with Competitive Performance

Porous catalysts with a higher activated surface area are strategic materials to enhance the oxygen reduction reaction (ORR) and improve the performance of the microbial fuel cells (MFCs). In this investigation, a highly porous cagelike zirconium metal–organic framework (Zr-MOF) was synthesized by the solvothermal method and used as the ORR catalyst in an air-cathode MFC. Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy revealed the successful synthesis of Zr-MOF having a high specific surface area of 858 m2/g. Cyclic voltammetry analysis demonstrated a sharp ORR peak current at −0.38 V having a current value of 11 mA compared to the negligible amount of peak current observed for cathode having no catalyst. The MFC having Zr-MOF-catalyzed cathode could translate a power density of 131.2 ± 3.5 mW/m2 at a coulombic efficiency of 29.04 ± 1.54% from the organic matter present in wastewater; these values were comparable with the MFC having 10% Pt/C on cathode (128.7 ± 4.9 mW/m2 and 29.03 ± 2.76%, respectively). The cost of energy production by the Zr-MOF cathode was estimated to be ca. 4.4 times lower than that by the 10% Pt/C cathode. The performance of MFC indicates that Zr-MOF could be an excellent alternative cathode catalyst, to the costly Pt/C, upon ambitious scale-up of MFCs.