Nickel oxide electrochromic films: mechanisms, preparation methods, and modification strategies–a review

Abstract

Intelligent energy-saving technologies have received widespread global attention amidst the continuous intensification of energy issues. Electrochromic technology provides dynamically adjustable optical properties aimed at reducing building energy consumption. NiO is one of the most widely studied and applied anode electrochromic materials due to its excellent high optical modulation capability, fast response, and electrochemical stability. In this review, after briefly introducing the research background of electrochromic devices, we focus on the electrochromic mechanism in different electrolytes, preparation methods, and modification strategies of NiO films. The widely accepted electrochromic mechanism of NiO is the reversible conversion between colorless Ni²⁺ and colored Ni³⁺ and Ni⁴⁺. By optimizing the preparation parameters, the morphology, crystal structure, and chemical state of the NiO film can be adjusted to improve its electrochromic performance. Meanwhile, finding a preparation method with a large area and cost-effectiveness has become an urgent task. The electrochromic performance of NiO can be further enhanced by using appropriate modification strategies, such as surface modification, nanomaterialization, material compounding, doping, and electrolyte design. Finally, the future development prospects of NiO electrochromic films and electrochromic devices are explored.