NH₄F-induced morphology-dependent NiSe₂/CoSe electrocatalysts on Ni foam for enhanced overall water splitting

Morphological control is a highly effective strategy to enhance the intrinsic activity for overall water splitting. However, designing and synthesizing persistent morphological changes still present significant challenges. In this study, a series of NiSe₂/CoSe/nickel foam (NF) self-supported bifunctional electrocatalysts with tunable morphologies from flower-like microstructures, and microflowers to nanosheets are prepared by adjusting the molar ratios of NH₄F/Ni(NO₃)₂·6H₂O during the precursor preparation stage. Electrocatalytic performance tests indicate that the NiSe₂/CoSe/NF-3.0 electrode exhibits remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity, along with excellent cycling stability. This is attributed to the exposure of more active sites, shortened ionic diffusion paths, and an enhanced synergistic effect of metallic site. Furthermore, the NiSe₂/CoSe/NF-3.0 (+, -) electrodes achieve a current density of 20 mA cm^-2 at a low voltage of 1.54 V in an alkaline electrolyte. Density functional theory (DFT) calculations reveal that the synergistic effect of NiSe₂ and CoSe improves the electron transfer characteristics of the electrocatalysts. Overall, this work not only verifies the feasibility of morphological control but also provides novel insights into designing affordable, high-performance bifunctional electrocatalysts for water electrolysis.