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Developing efficient, stable and ideal urea oxide (UOR) electrocatalyst is key to produce green hydrogen in an economical way. Herein, Ru doped three dimensional (3D) porous Ni 3 N spheres, with tannic acid (TA) and urea as the carbon and nitrogen resources, is synthesized via hydrothermal and low-temperature treated process (Ru–Ni 3 N@NC). The porous nanostructure of Ni 3 N and the nickel foam provide abundant active sites and channel during catalytic process. Moreover, Ru doping and rich defects favor to boost the reaction kinetics by optimizing the adsorption/desorption or dissociation of intermediates and reactants. The above advantages enable Ru–Ni 3 N@NC to have good bifunctional catalytic performance in alkaline media. Only 43 and 270 mV overpotentials are required for hydrogen evolution (HER) and oxygen evolution (OER) reactions to drive a current of 10 mA cm−2. Moreover, it also showed good electrocatalytic performance in neutral and alkaline seawater electrolytes for HER with 134 mV to drive 10 mA cm−2 and 83 mV to drive 100 mA cm−2, respectively. Remarkably, the as-designed Ru–Ni 3 N@NC also owns extraordinary catalytic activity and stability toward UOR. Moreover, using the synthesized Ru–Ni 3 N@NC nanomaterial as the anode and cathode of urea assisted water decomposition, a small potential of 1.41 V was required to reach 10 mA cm−2. It can also be powered by sustainable energy sources such as wind, solar and thermal energies. In order to make better use of the earth's abundant resources, this work provides a new way to develop multi-functional green electrocatalysts. [Display omitted] • The synthesized electrocatalyst exhibits porous specific sphere morphology to exposed abundant active sites. • The prepared electrocatalyst presents excellent electrocatalytic performances toward HER, OER and UOR. • Small overpotential is required to drive overall water-splitting under the urea assistance with remarkable stability. • Sustainable energies are investigated to power the electrolyzer for hydrogen generation. [ABSTRACT FROM AUTHOR]