One-step hydrothermal synthesis of a Ni₃S₂-FeMoO₄ nanowire-nanosheet heterostructure array for synergistically...

A key factor for boosting oxygen evolution reaction (OER) is the design of heterostructures with steerable defects and interfaces, which can optimize the surface electronic structures and achieve efficient water splitting to produce hydrogen fuel. Herein, we propose a novel one-step hydrothermal approach to fabricate hierarchical Ni₃S₂ nanowires with an S-doped FeMoO₄ nanosheet heterostructure array in situ on Ni-Fe foam (NFF) as a self-standing electrode for synergistically boosted OER. The metalloid Ni₃S₂ nanowires with good conductivity support the FeMoO₄ nanosheets and act as high-speed paths for the charge transfer. Numerous ultrathin S-doped FeMoO₄ nanosheets are uniformly distributed on each Ni₃S₂ nanowire to form heterostructures with larger specific surface area and more revealable active sites, and a strong synergistic effect is created at the heterostructure interfaces to further promote the OER dynamics. Additionally, the NFF serves as the conductive support substrate and simultaneously provides the Ni and Fe sources for the self-growing Ni₃S₂-FeMoO₄, leading to a structurally-integrated electrode with low contact resistance, fast mass transfer, and good stability. Therefore, the Ni₃S₂-FeMoO₄/NFF electrode offers a low overpotential of 331 mV to achieve 500 mA cm^-2 and long-term stability at 100 mA cm^-2 level for more than 40 h. This work provides insight into the heterostructure of molybdate and sulfide, and a deep understanding of the significance of the synergism in OER operation.