Trace Iron-Doped Nickel-Cobalt selenide with rich heterointerfaces for efficient overall water splitting at high current densities.

Developing bifunctional electrocatalysts based on non-precious metals for overall water splitting, while maintaining high catalytic activity and stability under high current densities, remains challenging. Herein, we successfully constructred trace iron-doped nickel-cobalt selenide with abundant CoSe (210)-NiSe (202) heterointerfaces via a simple one-step selenization reaction. The synthesized Fe-NiCoSe/NCFF (NCFF stands for nickel-cobalt-iron foam) exhibits outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity with low overpotentials of 328 mV for HER and 345 mV for OER at a high current density of 1000 mA cm, while maintaining stability for over 20 h. Additionally, the Fe-NiCoSe/NCFF exhibits the lowest Tafel slope values for both HER (33.7 mV dec) and OER (55.92 mV dec), indicating the fastest kinetics on its surface. The Fe-NiCoSe/NCFF features uniformly distributed micrometer-sized selenide particles with dense nanowires on their surface, providing a large reactive surface area and abundant active sites. Moreover, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses reveal that the catalyst is composed of nickel, cobalt, and iron, forming micrometer-sized particles with both crystalline and amorphous phases, thereby enhancing HER and OER performance under high current density. Density functional theory (DFT) calculations demonstrate that the heterostructure CoSe (210)-NiSe (202), with high electron density and suitable adsorption capacity for reaction intermediates, and low energy barriers for HER (-0.384 eV) and OER (ΔG: 0.243 eV, ΔG: 0.376 eV), serves as an active center for both HER and OER.