The Co2P@NiCo2O4 bi-functional electrocatalyst was fabricated for hydrogen evolution reaction and oxygen evolution reaction in acidic, neutral and alkaline media. The Co2P@NiCo2O4 in alkaline media exhibites an extremely low overpotential of 170 mV in oxygen evolution to achieve a current density of 10 mA cm(-2) and produces stable water splitting nearly 30 h. The anchored-Co2P can enhance the electrochemical performance of pristine NiCo2O4 as well as increase the tolerance in acidic media of NiCo2O4. Additional, the Co2P is oxidized to oxides/hydroxides species during the electrocatalytic reaction, which acts as the active centers of the electrocatalysis. The Co2P@NiCo2O4 catalyst can be used as an effective bifunctional synergistic center in a wide range of pH values (from 0 to 14). (C) 2018 Elsevier Inc. All rights reserved.