To improve the power generation of the microbial fuel cell, activated carbon is modified by the CO3O4/NiCO2O4 double-shelled nanocage, which prepared via a metal-organic framework method. When tested as cathodic material, the mesoporous CO3O4/NiCO2O4 double-shelled nanocage with a large surface (112.9m(2)g(-1)) exhibits higher open circuit potential (0.252 V) and higher exchange current density (19.70 x 10(-4) A cm(-2)). Moreover, the maximum power density of the air-cathode microbial fuel cell equipped with the 5% as-prepared catalyst is 1810mWm(-2), 104% higher than the control. The morphology and crystal structure of CO3O4/NiCO2O4 are investigated by the Transmission electron microscope and X-ray diffraction. X-ray photoelectron spectroscopy analysis indicates that there exists Co3+/Co2+ and Ni3+/Ni2+ redox couples in the catalyst, and divalence trivalence - divalence redox cycles contribute to the improved oxygen reduction reaction performance and enhanced power output. Owing to the structural merits and improved electrochemical activity, the synthesized CO3O4/NiCO2O4 double-shelled nanocage would be considered as a replacement of the new material for Pt in microbial fuel cell.