Novel three dimensional (3D) porous carbon nanosheets with few layers are successfully prepared using intrinsically porous cellulose as carbon matrix only by means of calcination and KOH activation. Further, the N-doped 3D carbon nanosheets show high density of pyridinic N and extremely high specific surface area (1756 m(2) g(-1)). As oxygen reduction catalyst, they possess an outperformed onset (E-0 =-0.03 V) and half-wave (E-1/2 = 0.17 V) potential compared with the platinum (Pt) electrocatalyst (E-0=-0.05 V, E-1/2 = -0.2 V) in an alkaline system. In addition, excellent electrochemical stability as well as improved CO poisoning resistance and suppressed methanol crossover relative to Pt is also obtained. In an acid system, the catalyst also exhibits good activity and higher durability than Pt/C. Significantly, when used as a catalyst of the air electrode for Zn-air batteries, it demonstrates a higher peak power density of 208 mW cm(-2) and a voltage plateau at the controlled discharge current density compared to the commercial Pt/C electrode. This simple and scalable approach provides a direct route to synthesize low cost and highly efficient electrocatalysts from biomass without addition of extra metal catalysts. (C) 2017 Elsevier B.V. All rights reserved.