In Situ Construction of Nickel Sulfide Nano-Heterostructures for Highly Efficient Overall Urea Electrolysis

Constructing high-performance bifunctional catalysts for urea oxidation (UOR) and hydrogen evolution reactions (HER) is beneficial to improving the hydrogen production efficiency and reducing the cost of electrolyzers. Currently, nickel sulfides are of wide concern due to their theoretically high catalytic activity and the characteristic that their activity is very sensitive to the phase structure. Integrating the respective advantages of different phases to form heterojunctions can effectively enhance the bifunctionality of nickel sulfides; however, their performance is still far lower than that of an electrolyzer assembled with noble-metal catalysts. Herein, with NiMoO4 as the parent material, rod-like Ni3S2/NiS heterojunctions were controllably prepared on nickel foam (NF) via sulfurization and Mo leaching. Thanks to the abundant Ni2+ active sites in NiS, the metallic conductivity of Ni3S2, and the favorable three-dimensional mass transfer channels, the Ni3S2-NiS/NF exhibits an excellent bifunctionality with 1.273 V for UOR and -0.146 V for HER at 10 mA cm-2. Furthermore, the urea electrolyzer with Ni3S2-NiS/NF as both the anode and cathode only requires 1.54 V to drive 50 mA cm-2, outperforming the most advanced urea electrolyzers. This work provides a useful strategy for synthesizing efficient bifunctional or multifunctional catalysts by combining the advantages of different phases of the same composition material to design nano-heterostructures.