Electronic Modulation via Introducing Polyoxometalate to Fe-Ni₃S₂ Nanosheet for Enhanced Water Electrolysis

Modulating electronic structure and local coordination environment of electrocatalysts is a promising strategy to facilitate water adsorption and dissociation. Herein, we prepare polyoxometalate (POM) modulated Fe-doped Ni₃S₂ nanosheets (PMo₁₂-Fe-Ni₃S₂) on a nickel foam (NF) substrate by a one-step hydrothermal method. The PMo₁₂ clusters are homogeneously dispersed, preventing nanosheets from agglomerating, while rich electrons in PMo₁₂ are conducive to promoting electron transfer, thereby tuning electronic configuration effectively. PMo₁₂-Fe-Ni₃S₂ on NF exhibits superior electrocatalytic performance for water splitting in an alkaline medium, delivering an overpotential of 221 mV at 10 mA cm^-2, a small Tafel slope of 37.7 mV dec^-1, and long-term stability over 100 h for oxygen evolution reaction (OER). Further applying to an anion exchange membrane water electrolysis (AEMWE) electrolyzer, PMo₁₂-Fe-Ni₃S₂ achieves a current density of 10 mA cm^-2 at a cell voltage below 1.69 V. Physical characterizations and density functional theory (DFT) calculations prove that PMo₁₂ is sacrificed while newly formed MoFe-doped NiOOH is the real active species after OER, thus accelerating electron transfer and optimizing adsorption energy of intermediates. This work provides an insightful POM engineering strategy for electronic modulation of POM-based electrocatalysts, possessing great potentials for water electrolysis applications.