Sulfurized NiFe2O4 Electrocatalyst with In Situ Formed Fe‐NiOOH Nanoparticles to Realize Industrial‐Level Oxygen Evolution

Abstract Constructing composite catalysts with refined geometric control and optimal electronic structure provides a promising route to enhance electrocatalytic performance toward the oxygen evolution reaction (OER). Herein, a composite catalyst is prepared with multiple components using chemical vapour deposition method to transform crystalline NiFe2O4 into crystalline NiFe2O4@amorphous S‐NiFe2O4 with core‐shell structure (C‐NiFe2O4@A‐S‐NiFe2O4), and Fe‐NiOOH nanoparticles are subsequently in situ generated on its surface during the process of electrocatalytic OER. The C‐NiFe2O4@A‐S‐NiFe2O4 catalyst exhibits a low overpotential of 275 mV while possessing an excellent stability for 500 h at 10 mA cm−2. The anion exchange membrane water electrolyzer with C‐NiFe2O4@A‐S‐NiFe2O4 anode catalyst obtains a current density of 4270 mA cm−2 at 2.0 V. Further, in situ Raman spectroscopy result demonstrates that in situ generated Fe‐NiOOH nanoparticles are revealed to act as the catalytic active phase for catalyzing the OER. Besides, introducing A‐S‐NiFe2O4 in C‐NiFe2O4@A‐S‐NiFe2O4 facilitates the formation of Fe‐NiOOH nanoparticles with high‐valency Ni, thus increasing the proportion of lattice oxygen‐participated OER. This work not only provides an alternative strategy for the design of high‐performance catalysts, but also lays a foundation for the exploration of catalytic mechanisms.