Crystal reconstructed cubic nickel oxide with energetic reactive interfaces for exceptional electrochromic smart windows.

Electrochromic smart windows can realize intelligent photothermal regulation by applying a low potential, which is of great significance for energy-saving buildings and achieving low carbon emission. However, the dense structure of conventional metal oxide electrochromic materials limits ion transport efficiency, resulting in poor electrochromic properties. Here, we propose a surface crystal reconstruction strategy for cubic NiO through phosphorylation (P-NiO) to build energetic reactive interfaces and enhance the electrochromic performance. Theoretical simulations and experiments reveal that the introduction of PO₄ tetrahedra tailored the crystal structure of cubic NiO, which endows it with a large number of contiguous intracrystal cavities and unsaturated P-O bonds on the surface. The energetic reactive interface optimizes the transport path of OH^- and gets rid of the dependence on K⁺ in the adsorption process, thus improving the reaction kinetics of NiO. The P-NiO film delivers a large optical modulation (90.3%, at 500 nm), a high coloration efficiency (81.1 cm² C^-1, at 500 nm), and a fast switching speed (6 s and 7.2 s for coloring and bleaching processes). Furthermore, a model of an electrochromic smart window was fabricated based on the P-NiO film, using which a potential energy saving of 60.81 MJ m^-2 and CO₂ emission reduction of 11.98 kg m^-2 can be achieved in hot climate zones according to energy simulations. The in-depth insights gained into the fundamental mechanism of this surface crystal reconstruction strategy will facilitate the rational design of high-performance electrochromic and electrochemical materials.