Spherical Ni₃S₂/Fe‐NiP<i>_x</i> Magic Cube with Ultrahigh Water/Seawater Oxidation Efficiency

Abstract

The rational construction of earth-abundant and advanced electrocatalysts for oxygen evolution reaction (OER) is extremely desired and significant to seawater electrolysis. Herein, by directly etching Ni₃ S₂ nanosheets through potassium ferricyanide, a novel self-sacrificing template strategy is proposed to realize the in situ growth of NiFe-based Prussian blue analogs (NiFe PBA) on Ni₃ S₂ in an interfacial redox reaction. The well-designed Ni₃ S₂ @NiFe PBA composite as precursor displays a unique spherical magic cube architecture composed of nanocubes, which even maintains after a phosphating treatment to obtain the derived Ni₃ S₂ /Fe-NiP_x on nickel foam. Specifically, in alkaline seawater, the Ni₃ S₂ /Fe-NiP_x as OER precatalyst marvelously realizes the ultralow overpotentials of 336 and 351 mV at large current densities of 500 and 1000 mA cm^-2 , respectively, with remarkable durability for over 225 h, outperforming most reported advanced OER electrocatalysts. Experimentally, a series of characterization results confirm the reconstruction behavior in the Ni₃ S₂ /Fe-NiP_x surface, leading to the in situ formation of Ni(OH)₂ /Ni(Fe)OOH with abundant oxygen vacancies and grain boundaries, which constructs the Ni₃ S₂ /Fe-NiP_x reconstruction system responsible for the remarkable OER catalytic activity. Theoretical calculation results further verify the enhanced OER activity for Ni₃ S₂ /Fe-NiP_x reconstruction system, and unveil that the Fe-Ni₂ P/FeOOH as active origin contributes to the central OER activity.