Manganese-Doped Fe3S4/Mo3S4 Nanoparticles on Nickel Foam as Durable Electrocatalysts for Water Electrolysis

Developing highly efficient, durable, and low-cost non-precious-metal bifunctional electrocatalysts is essential for sustainable water electrolysis. Herein, Mn-incorporated Fe3S4/Mo3S4 heterostructured nanoparticles were constructed in situ on nickel foam (NF) through a three-step hydrothermal sulfurization strategy. The resulting catalyst features a hierarchical nanoscale architecture consisting of interconnected nanosheets and nanoparticles, with intimate Fe3S4/Mo3S4 nanoscale interfaces and a homogeneous distribution of Mn. X-ray photoelectron spectroscopy (XPS) analysis reveals that Mn incorporation markedly modulates the local electronic environments of Fe, Mo, and S, promoting electronic redistribution within the Fe3S4/Mo3S4 heterostructure. In situ Raman spectroscopy further reveals potential-dependent structural evolution of the catalyst under operating conditions. During hydrogen evolution reaction (HER), the Mo−S vibrational signals progressively weaken with increasing cathodic polarization, indicating pronounced changes in the local Mo−S coordination environment. During oxygen evolution reaction (OER), the Fe−S-related signals remain comparatively stable, while the Mo−S-related region exhibits distinct potential-dependent evolution, demonstrating a dynamically responsive surface structure under anodic polarization. In 1.0 M KOH, the optimized Mn−Fe3S4/Mo3S4/NF-0.2 electrode requires overpotentials of only 29 and 212 mV to deliver 10 mA cm−2 for HER and OER, respectively, with corresponding Tafel slopes of 75.99 and 24.93 mV dec−1. When employed as both the cathode and anode, the resulting electrolyzer requires only 1.53 V to achieve 10 mA cm−2 and maintains stable operation for 200 h. These results highlight the integration of hierarchical nanoscale architecture, nanoscale heterointerfaces, Mn-induced electronic modulation, and potential-dependent structural evolution for developing durable bifunctional electrocatalysts for alkaline water electrolysis.