NiFeS2/NiFe2O4 composites constructed by etching modified Fe foam as an efficient bifunctional catalysts for overall water splitting

The construction of NiFe-based composites on foam metal is an advanced strategy to design high-performance catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we chose Fe foam (FF) as the substrate, which was first modified by anodic electrodeposition to form a porous and loose FeS x / FeO x layer. This modified layer facilitates the construction of nanoflower-structured NiFeS 2 /NiFe 2 O 4 composites with large electrochemical active surface area, higher Ni content and enhanced ratio of Ni 3 + to Ni 2+ , compared with the sample fabricated by direct etching FF. The prepared NiFeS 2 /NiFe 2 O 4 /FF electrode only requires overpotentials of 242 and 273 mV to achieve current densities of 100 and 500 mA cm⁻ 2 for OER, respectively. It also possesses faster reaction kinetics with a low Tafel slope of 31.12 mV dec −1 and superior durability without potential reduction for 200 h at a large current density of 500 mA cm⁻ 2 . Meanwhile, the performance of overall water splitting cell assembled with NiFeS 2 /NiFe 2 O 4 /FF is better than that of cell based on the noble metal Pt/C/FF- |RuO 2 /FF. This work provides a simple and cost-effective strategy for constructing efficient electrocatalysts, making it promising for large-scale industrial applications in alkaline water electrolysis.