Bimetallic nickel iron sulfide directly grown on defect-rich Ti3C2 MXene as an efficient bifunctional electrocatalyst for water electrolysis

Water electrolysis has been regarded as ideal method for producing high-purity hydrogen without the generation of environmental pollutants. Accordingly, the development of precious metal-free electrocatalysts that demonstrate high activity for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is essential for practical water electrolysis. Herein, porosity-engineered Ti3C2 MXene is employed as an efficient substrate for a bimetallic Ni-Fe-S electrocatalyst. The porous and defect-rich Ti3C2 (D-Ti3C2) flakes provide metal-like electrical conductivity and large surface area for direct growth of active species. Simultaneously, the Ni-Fe-S nanoparticles, constructed through a strong coupling between NiS2 and (Ni,Fe)S2 solid solution, not only serve as active sites with rich redox properties, but also generate charge transfer channels for electrochemical reactions. Leveraging these advantageous properties, the resulting Ni-Fe-S/D-Ti3C2 electrocatalyst exhibits excellent bifunctional electrocatalytic performance toward both OER and HER. As a result, the symmetric water electrolysis cell using the Ni-Fe-S/D-Ti3C2 requires a low cell voltage of 1.621 V to deliver current density of 10 mA cm−2, and shows stable electrocatalytic performance over 100 h of continuous operation.