The synthesis of W-Ni₃S₂/NiS nanosheets with heterostructure as a high-efficiency catalyst for urea oxidation

The development of efficient and stable non-precious-metal-based electrocatalysts is essential for practical water splitting applications. The electrolysis of water for hydrogen production is a green and efficient method, while urea electrolysis can improve energy conversion efficiency. In this paper, W-Ni₃S₂/NiS catalysts with heterogeneous structures were synthesized via a one-step hydrothermal method using a W-doping-induced phase transition strategy. The doping of W modulates the morphology of the catalyst, which can form uniform nanorod arrays and improve the activity of the electrocatalyst. In an alkaline solution of 1 M KOH and 0.5 M urea, W-Ni₃S₂/NiS requires a potential of only 1.309 V to achieve a current density of 10 mA cm^-2. An electrolyzer containing urea with W-Ni₃S₂/NiS as both the cathode and anode can drive a current density of 10 mA cm^-2 with a potential of only 1.569 V and has relatively good stability after testing for 20 h. Experimental results show that the improvement in the catalytic activity is due to the rapid charge transfer, exposure of more active sites and better conductivity. Density functional theory calculations show that the W-Ni₃S₂ material exhibits higher urea adsorption energy, indicating that urea is preferentially adsorbed on its surface. The NiS material shows more state density near the Fermi level, indicating that the introduction of this material enhances the conductivity of the W-Ni₃S₂/NiS material. The synergistic catalysis of the two materials promoted the improvement of the catalytic activity. This work provides new ideas for the development of highly efficient and stable catalysts by means of doping and interface construction.