MoS2–MoO2/Ni3S2/Nickel Foam Electrocatalysts Decorated with NiFeOxHy for Energy-Saving Hydrogen Evolution via Urea Oxidation Reaction-Assisted Water Splitting

Clean hydrogen extracted from water splitting is a sustainable energy source, but it remains challenging because it requires a low-cost and high-efficient electrocatalyst. Herein, a two-step chemical vapor deposition (CVD) method is applied to fabricate a dual-functional electrocatalyst consisting of Mo (oxy)sulfide alongside Ni3S2, from a single-source precursor, self-supported on Ni foam (NF), providing effective control on competitive sulfurization of Ni and Mo. The MoS2–MoO2/Ni3S2/NF allows not only the suitable exposure of highly active heterointerfaces but also the facilitated charge transport along both the metallic Ni3S2 and MoO2 anchored on the conducting Ni foam, resulting in kinetics and activity improvement for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under alkaline conditions. In the next step, benefitting from a simple immersing method, a NiFeOxHy nanolayer decorates the surface of the prepared MoS2–MoO2/Ni3S2/NF. The NiFeOxHy/MoS2–MoO2/Ni3S2/NF exhibits low overpotentials of 220 and 147 mV (@±10 mA/cm2) and small Tafel slope values of 33 and 89 mV/dec in 1.0 M KOH for OER and HER, respectively. Replacing the OER with a urea oxidation reaction (UOR) leads to energy-efficient hydrogen generation. Assembling a two-electrode electrolyzer, the designed electrocatalyst achieves a low cell voltage of 1.47 V @10 mA/cm2 for the UOR.