For the development of metal-air batteries and fuel cells, highly efficient and inexpensive electrocatalysts are one of the main issues for scalable applications of these advanced energy devices. Herein, based on the in situ conversion of FeS to gamma-FeOOH with a two-dimensional (2D) layered structure, a special nanohybrid, N, S co-doped porous carbon nanosheets loaded with gamma-FeOOH, is fabricated by carbonization of Fe3+-coordinated polydopamine, which uniformly coats the surface of bacterial cellulose. The nanocomposites exhibit high activity towards the cathodic oxygen reduction reaction (ORR), characterized by a more positive half-wave potential (10 mV) than the commercial Pt/C (20 wt%) electrocatalyst in alkaline medium. Additionally, the nanohybrid has excellent stability and a high methanol tolerance towards the ORR. Further experiments and density functional theory (DFT) calculations demonstrate that the doped N, S in the carbon matrix and the (01 0) plane of gamma-FeOOH are the ORR active sites. A zinc-air battery equipped with this nanohybrid presents better a power density (92 mW cm(-2)) and specific capacity (740 mA h g(-1)) than the Pt/C electrocatalyst, demonstrating its promising potential for application in energy conversion devices. (C) 2019 Elsevier Inc. All rights reserved.