Spectroscopically unraveling high-valence Ni-Fe catalytic synergism in NiSe2/FeSe2 heterostructure

Heterostructured compounds with rationally engineered interfaces are widely reported as efficient oxygen evolution reaction (OER) electrocatalysts, but the mechanism of the intrinsic activities still unclear. Herein, a typical model catalyst of NiSe2/FeSe2 heterostructure with a low overpotential of 230 mV at 10 mA cm−2 and long-term durability is fabricated by selenizing Ni-Fe Prussian-blue analog (PBA) templates. In-situ/operando Raman spectroscopy and synchrotron-based X-ray absorption spectroscopy (XAS) are employed to reveal the real catalytic process. It is attested that the dynamic surface reconstruction into Ni-O-Fe configurations, and the high-valence NiIII-O-FeIII moieties in Ni–FeOOH is responsible for the high oxygen evolution. Density functional theory (DFT) simulations further confirm that the electron transfer driven by strong Ni-Fe synergistic effect in NiSe2/FeSe2 heterostructure not only improves the density of Ni/Fe active sites, but also modulates the nature active sites. This works may deepen our understanding of intrinsic activities of metal compound heterostructures and the correlation between dynamic surface structural evolution and catalytic activity.