Self‐Driven Ni‐Based Electrochromic Devices for Energy‐Efficient Smart Windows

Abstract Electrochromic devices (ECDs) with adjustable transmittance have opened new opportunities to the development of smart windows for energy‐efficiency building. However, the switching between colored and bleached state of conventional ECD will bring extra energy consumption, the design of high‐performance ECD with low consumption is still an elusive goal. To address this issue, a self‐driven and energy‐saving Ni anode‐based ECD using Prussian blue as electrochromic material is developed. During the day, it can be colored by solar energy. By contrast, it can spontaneously bleach when the ECD's anode and cathode are short‐circuiting using the internal redox potential during the night. It is worth noting that no extra energy is inputted in the coloring‐bleaching cycle. In comparison with the ECD using electrolyte with high Ni²⁺ (K⁺:Ni²⁺ = 1:9) or high K⁺ (K⁺:Ni²⁺ = 9:1) concentration with poor optical contrast and cyclic stability (failed <100 cycles), the Ni‐based ECD with the electrolyte containing equal amount of K⁺ and Ni²⁺ exhibits a high optical contrast (39.45%), good coloration response time (6 s), and excellent stability (1000 cycles). These properties suggest that the Ni‐based electrochromic configuration is expected to be a catalyst for the development of energy‐storage EC smart window in the future.