The Synergistic Impact of Lanthanide-Doped Nickel Iron Sulphides (NiFeSs) Synthesized by a Hydrothermal Method for Effective Water and Urea Electrolysis in Anion Exchange Membranes
来源：ACS Publications
One of the major barriers to sustainable hydrogen production is the development of highly efficient, economically viable electrocatalysts for alkaline and urea water splitting. In this work, we report the synthesis of lanthanum-modified nickel–iron–sulfide (Ni–Fe–S) nanostructures via the hydrothermal method. X-ray diffraction analysis reveals the formation of a multiphase heterostructure consisting of NiFeS2, NiS, FeS2, and lanthanum-based sulfide phases. Surface and compositional analyses confirm the uniform distribution of Ni, Fe, S, and La, while morphological studies demonstrate the formation of highly aggregated nanostructures with abundantly exposed active sites, favorable for catalytic reactions. In three-electrode electrochemical assessments, the optimized (7.5% La-doped nickel iron sulfide) catalyst exhibits superior HER performance, with a low overpotential of 65 mV at 10 mA cm–2 and a reduced Tafel slope of 144 mV dec–1. For the OER, the 7.5% La-doped nickel iron sulfide catalyst delivers a decreased overpotential of 337 mV at 10 mA cm–2 with a favorable Tafel slope of 101 mV dec–1. For the UOR, the 7.5% La-doped nickel iron sulfide catalyst remarkably reduced the overpotential by 177 mV and significantly decreased the Tafel slope to 68 mV dec–1. Furthermore, the NFS3∥SS configuration in an actual two-electrode AEM water and urea electrolyzer had low cell voltages of 1.90 and 1.45 V, respectively, at 10 mA cm–2, both with improved Tafel slopes (0.22 V dec–1). The long-term stability test shows little degradation over 100 h. The results of this study suggest that lanthanum-doped nickel iron sulfide is a viable, Pt-free, low-cost electrocatalyst for the eco-friendly, efficient production of hydrogen in an AEM water- and urea-based electrolytic system.