Direct growth of 2D nickel hydroxide nanosheets intercalated with polyoxovanadate anions as a binder-free supercapacitor electrode

A mesoporous nanoplate network of two-dimensional (2D) layered nickel hydroxide Ni(OH)₂ intercalated with polyoxovanadate anions (Ni(OH)₂-POV) was built using a chemical solution deposition method. This approach will provide high flexibility for controlling the chemical composition and the pore structure of the resulting Ni(OH)₂-POV nanohybrids. The layer-by-layer ordered growth of the Ni(OH)₂-POV is demonstrated by powder X-ray diffraction and cross-sectional high-resolution transmission electron microscopy. The random growth of the intercalated Ni(OH)₂-POV nanohybrids leads to the formation of an interconnected network morphology with a highly porous stacking structure whose porosity is controlled by changing the ratio of Ni(OH)₂ and POV. The lateral size and thickness of the Ni(OH)₂-POV nanoplates are ∼400 nm and from ∼5 nm to 7 nm, respectively. The obtained thin films are highly active electrochemical capacitor electrodes with a maximum specific capacity of 1440 F g^-1 at a current density of 1 A g^-1, and they withstand up to 2000 cycles with a capacity retention of 85%. The superior electrochemical performance of the Ni(OH)₂-POV nanohybrids is attributed to the expanded mesoporous surface area and the intercalation of the POV anions. The experimental findings highlight the outstanding electrochemical functionality of the 2D Ni(OH)₂-POV nanoplate network that will provide a facile route for the synthesis of low-dimensional hybrid nanomaterials for a highly active supercapacitor electrode.