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Microbial fuel cells (MFCs) are a promising biotechnology that realizes the transformation of wastewater treatment from an energy consumption to an electricity generation process. However, the tedious process and the large resources consuming in preparing powder ORR catalysts are still non-negligible limiting factors for application. This study aims at proposing an energy-efficient method for preparing three-dimensional binder-free air cathode for MFCs: non-noble composite catalysts based on graphene and MnO 2 are synthesized directly on stainless steel fiber felt (SSFF) by pre-fixing and electro-reducing graphene oxide on SSFF (rGO-SSFF), and then in-situ depositing MnO 2 nanocatalysts on rGO-SSFF (rGO@MnO 2 -SSFF). The experimental results show that the ORR ability of rGO@MnO 2 -SSFF cathode is greater than that of Pt/C-CC cathode, even if the performance of rGO@MnO 2 powder catalyst is slightly lower than that of the traditional Pt/C catalyst. The excellent performance is found to be due to the three-dimensional framework-pore structure of SSFF which helps the prepared cathode possess larger electrochemical active area (8415.18 m2 m−3) than Pt/C-CC cathode (7518.13 m2 m−3). The proposed method provides a new way to reduce the cost (labor, materials and energy) of air cathode while ensuring the high electricity output of MFCs. [Display omitted] • The non-noble composite catalysts are synthesized on SSFF for preparing air cathode. • This catalyst loading method is low-consumption and eco-friendly. • The proposed cathode exhibits higher ORR activity than Pt/C-CC cathode. • The 3D framework-pore structure of SSFF helps achieve the high electric output. [ABSTRACT FROM AUTHOR]