NiCo2O4 porous nanotubes as the earth abundant and efficient bifunctional electrocatalyst were successfully synthesized via the template-free method involving the hydrothermal process and subsequent heat treatment Benefiting from the porous nanotube structure and the template-free method, they show a superior low charge transfer resistance and more exposed active sites. With those advantages, the NiCo2O4 porous nanotubes show an outstanding electrocatalytic performance with an overpotential of 264 mV at j = 20 mA cm(-2) for oxygen evolution reaction and 106.5 mV at j = 10 mA cm(-2) for hydrogen evolution reaction, respectively. More significantly, the NiCo2O4 porous nanotubes show a potential of 1.63 V at j = 20 mA cm(-2) for overall water-splitting, and there is no obvious change after running for 12 h. In a word, this work offers a novel routine for fabricating NiCo2O4 porous nanotubes with excellent electrocatalytic performance and durability for overall water-splitting. (C) 2019 Elsevier Ltd. All rights reserved.