Hierarchical Ni3N/Ni0.2Mo0.8N heterostructure nanorods arrays as efficient electrocatalysts for overall water and urea electrolysis

In this work, we grew hierarchical Ni3N/Ni0.2Mo0.8N heterostructure microspheres on 3D NF, Ni3N/Ni0.2Mo0.8N/NF, which displays robust and high-performance catalytic activities for both water and urea electrolysis. [Display omitted] •The hierarchical Ni3N/Ni0.2Mo0.8N heterostructure nanorods arrays were prepared.•The obtained material shows great trifunctional catalytic performances.•For both water and urea electrolysis, lower cell voltages are required.•Metallic states, synergistic effect and hierarchical structure work together. The energy-saving urea electrolysis integrating the HER and smart urea oxidation reaction (UOR) can supplant the kinetics-restricted oxygen evolution reaction (OER) for hydrogen generation, but is still severely thwarted by poor electrocatalysts. Herein, a tractable hydrothermal protocol coupled with subsequent nitridation is found to enable uniform growth of the Ni3N/Ni0.2Mo0.8N heterostructure microspheres assembled by the uniform nanorod arrays on the nickel foam framework (Ni3N/Ni0.2Mo0.8N/NF). The as-obtained Ni3N/Ni0.2Mo0.8N/NF catalyst exhibits multifunctional superior performance for both overall water and urea electrolysis. For HER, the low overpotentials of 55 and 65 mV can be only required to deliver 10 mA cm−2 in alkaline and neutral electrolytes, respectively. Furthermore, for UOR a ultrasmall potential of 1.328 V (vs. RHE) at 10 mA cm−2 occurs, which is much lower than that required for OER process. When applying the Ni3N/Ni0.2Mo0.8N/NF as anode for OER and cathode for HER, the water electrolyzer requires low cell voltages of 1.487 and 1.724 V to achieve 10 and 200 mA cm−2, respectively. More significantly, the urea electrolyser presents ultralow cell voltages of 1.348 and 1.514 V at 10 and 200 mA cm−2 and remarkable longevity for over 500 h. Such impressive performances exceed most reported noble-metal-free catalysts and even vie for the benchmarking noble metal catalysts, heralding its tremendous utilitarian prospects for the cost-effective and energy-saving hydrogen generation.