Copper-Incorporated heterostructures of amorphous NiSe_x/Crystalline NiSe₂ as an efficient electrocatalyst for overall water splitting

In this research, we designed a novel heterostructure of porous amorphous-crystalline nickel selenide incorporated with copper (Cu-(a-NiSe_x/c-NiSe₂)) and shelled over one-dimensional TiO₂ nanorods (NRs) to simultaneously accelerate both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics in alkaline environment. The Cu-(a-NiSe_x/c-NiSe₂)/TiO₂ NRs supported by carbon cloth displayed as an effective bifunctional catalyst, which required low overpotentials of 156.9 mV for HER and 339 mV for OER to achieve a current response of 10 mA cm⁻² in 1.0 M KOH medium. An electrolyzer derived from the Cu-(a-NiSe_x/c-NiSe₂)/TiO₂ NRs material allowed an operation voltage of 1.62 V at 10 mA cm⁻² along with good long-term stability after 21.5 h operation towards water splitting in alkaline medium. This achievement was resulted from the fine-tuned 3D porous architecture of the amorphous NiSe_x-crystalline NiSe₂ heterostructures doped by copper, which led to significant modulation of electronic properties as well as large surface of exposed electroactive site/types, thereby effectively promoting the catalytic performance. This study suggested a rational approach of structure and shape engineering to design a potential catalyst for producing green hydrogen via water spitting.