Hierarchical NiO/TiO2 composite structures for enhanced electrochromic durability

Abstract This study presents the fabrication of nickel oxide (NiO) thin films with enhanced electrochromic durability by combining titanium dioxide (TiO2) honeycomb structure. The final structure possesses an hierarchical architecture with a substructure of honeycomb structured TiO2 prepared by liquid phase deposition through polystyrene sphere monolayer template with diameter of 800 nm and a superstructure of porous NiO nanoflake array prepared by chemical bath deposition. Compared to the pure NiO nanoflake film, the composite NiO/TiO2 films exhibits noticeable electrochromic cycling durability (only 25% decrease after 5000 cycles) at 550 nm and fast coloration and bleaching response rate (13.4 and 6.7 s). This improvement in electrochromic properties is due to the rapid dissociation of electrons and photons through the composite structure of the n-type TiO2 core/p-type NiO shell and rapid electrolyte penetration through ordered array geometry with increased surface area.