Herein, an advanced technique of plasma-enhanced atomic layer deposition is applied to in-situ adjust the intrinsic crystal structure and chemical composition of cobalt oxides by nitrogen-doping. The homogeneous N-CoOx thinfilm is conformally deposited on high-surface-area carbon nanotubes which maintains the one-dimensional structures. The N-CoOx/carbon nanotubes electrocatalyst displays remarkable bifunctional electrocatalytic activity and stability towards the oxygen reduction reaction and oxygen evolution reaction. The onset potential for oxygen reduction reaction is 0.9 V, which is about 80 mV positively shifted compared to the undoped sample while the oxygen evolution reaction performance is also improved by reducing the overpotential of 35 mV after nitrogen doping. Moreover, the limiting current density of N-CoOx/carbon nanotubes electrocatalyst is comparable to the benchmarking Pt/C while the former one exhibits better stability which is only 5% loss of current after operation for 10000 s and for the latter one is 11%. The improved electrochemical performance is affected by the introduction of N-dopant and the results provide a direction for designing and constructing other metal oxides as bifunctional electrocatalysts for air batteries and water splitting reactions. (C) 2018 Elsevier Ltd. All rights reserved.