Defect-Engineered 3D hierarchical NiMo₃S₄ nanoflowers as bifunctional electrocatalyst for overall water splitting

The design and construction of bifunctional electrocatalysts with high activity and durability is essential for overall water splitting. Herein, a unique 3D hierarchical NiMo₃S₄ nanoflowers with abundant defects and reactive sites were grown directly on carbon textiles (NiMo₃S₄/CTs) using a facile hydrothermal synthesis method. The defect-rich NiMo₃S₄ nanoflakes, prepared by doping Ni²⁺ in the lattice of Mo-S, displays extended d-spacing of (002) crystal plane, resulting in the electrocatalytic activity of hydrogen evolution and oxygen evolution reaction (HER and OER) was improved under alkaline conditions. The self-supported NiMo₃S₄/CTs electrode delivers a small overpotential of 149.5 mV for HER and 126.2 mV for OER at 10 mA cm^-2, respectively. Based on detailed structure analysis and density functional theory (DFT) calculations, the excellent HER and OER activities can be attributed to the unique structure of the nanoflowers, where the metallic characteristics for Ni-doped Mo-S lead to the enhancement of intrinsic conductivity and the rich abundance of Ni³⁺ active sites. As a result, the NiMo₃S₄/CTs as efficient bifunctional electrocatalysts for overall water-splitting was performed in alkaline electrolyte, where the system required only 1.55, 1.66 and 1.76 V to deliver current densities of 10, 50 and 100 mA cm^-2, respectively. This study provides a new method for improving the electrocatalysis properties of transition metal sulfides by metal-ion doping to generate more active defect sites, thus promoting the development of non-noble-metal electrocatalysts for overall water splitting.