Construction of hierarchical FeNi3@(Fe,Ni)S2 core-shell heterojunctions for advanced oxygen evolution

The investigation of earth-abundant electrocatalysts for efficient water electrolysis is of central importance in renewable energy system, which is currently impeded by the large overpotential of oxygen evolution reaction (OER). NiFe sulfides show promising OER activity but are troubled by their low intrinsic conductivities. Herein, we demonstrate the construction of the porous core-shell heterojunctions of FeNi3@(Fe,Ni)S-2 with tunable shell thickness via the reduction of hierarchical NiFe(OH)(x) nanosheets followed by a partial sulfidization. The conductive FeNi3 core provides the highway for electron transport, and the (Fe,Ni)S-2 shell offers the exposed surface for in situ generation of S-doped NiFe-oxyhydroxides with high intrinsic OER activity, which is supported by the combined experimental and theoretical studies. In addition, the porous hierarchical morphology favors the electrolyte access and O-2 liberation. Consequently, the optimized catalyst achieves an excellent OER performance with a low overpotential of 288 mV at 100 mA.cm(-2), a small Tafel slope of 48 mV.dec(-1), and a high OER durability for at least 1,200 h at 200 mA.cm(-2). This study provides an effective way to explore the advanced earth-abundant OER electrocatalysts by constructing the heterojunctions between metal and corresponding metal-compounds via the convenient post treatment, such as nitridation and sulfidization.

Automated summary

In this study, a porous core-shell heterojunction NiFe sulfide catalyst was demonstrated for efficient water electrolysis, showing excellent performance with low overpotential, small Tafel slope, and high durability. The construction of advanced earth-abundant OER electrocatalysts through heterojunctions between metal and corresponding metal-compounds via post treatments provides an effective way for further exploration in this field.