Hydrogen-Bonded\nOrganic Framework-Polyoxometalate-Based\nSystem for Electrochromic Devices

Abstract

A porous\nhydrogen-bonded organic framework (HOF) structure was\nexplored for the first time in the design of high-performance electrochromic\ndevices (ECDs) using polyoxometalate (POM)-based charge-balancing\nlayers as counter electrodes (CEs). The novelty of this work lies\nin the facile construction of films using small molecule-based EC\nmaterials to form a porous HOF structure. A full-cell model of an\nECD was constructed by utilizing a POM-based CE to optimize the voltage\ndistribution on the HOF-coated working electrode (WE). The addition\nof PW₁₂O₄₀^3– (PW₁₂) on CE significantly enhanced the voltage distribution on EC electrodes\nand decreased the overvoltage on the WE, further preventing the formation\nof non-EC species and resulting in a 3.3-fold increase in the lifetime\nof the ECD. The optical contrast was enhanced from 47% (TiO₂ only) to 68%, and the coloration efficiency was enhanced from 185\n(TiO₂ only) to 373 cm² C^–1. The optimized voltage distribution on the WE, leading to the fast\nresponse time and high optical EC contrast, could be explained by\nthe charge-balancing effect. Overall, this new finding provides a\nrobust framework for designing high-performance ECDs, taking advantage\nof the porous morphology and potential matching of the HOF and PW₁₂.