Sulfurized NiFe 2 O 4 Electrocatalyst with In Situ Formed Fe-NiOOH Nanoparticles to Realize Industrial-Level Oxygen Evolution.

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 NiFe 2 O 4 into crystalline NiFe 2 O 4 @amorphous S-NiFe 2 O 4 with core-shell structure (C-NiFe 2 O 4 @A-S-NiFe 2 O 4 ), and Fe-NiOOH nanoparticles are subsequently in situ generated on its surface during the process of electrocatalytic OER. The C-NiFe 2 O 4 @A-S-NiFe 2 O 4 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-NiFe 2 O 4 @A-S-NiFe 2 O 4 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-NiFe 2 O 4 in C-NiFe 2 O 4 @A-S-NiFe 2 O 4 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.