Lin, Wei-YouWei-YouLinSilori, Gaurav KumarGaurav KumarSiloriYu, Hsin-FuHsin-FuYuKUO-CHUAN HO2025-06-172025-06-172025-08-15https://www.scopus.com/record/display.uri?eid=2-s2.0-105003991663&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/730093Ionic liquids (ILs) are increasingly used in electrochromic devices (ECDs) due to their unique properties that make them well-suited for enhancing the performance and longevity of these devices. In this regard, 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) has widely been utilized in ECDs due to its high ionic conductivity, wide electrochemical stability window, and low volatility. However, studies have revealed that ECDs suffer from the adsorption of the BMIMBF4's cations on the electrode surface, causing increased charge transfer resistance, thus leading to poor electrochemical surface reaction and optical properties. In this study, we provide a recipe to address this issue by incorporating a poly(ionic liquid) (PIL, poly(vinylidene fluoride-co-difluorovinylidene aminooxoethyl-1-butylimidazolium-co-vinylidene aminooxoethyl-1-butylimidazolium tetrafluoroborate) as an electrolyte in an alkyl viologen-based ECD. The PIL-based ECD exhibited impressive performance due to the immobilized IL's cations (BMIM+) on the polymer (PVdF-HFP) backbone, thus preventing their accumulation on the electrode's active area and facilitating better redox kinetics. In compare to pristine viologen-based ECD (BrBzV/Fc) which showed ionic conductivity (σ) of ∼4.7 mS/cm, transmittance change (ΔT, 605 nm) of ∼71 %, and long-term stability (ΔT-retention after 10,000 cycles) of ∼89 %, flagship improvement in a PIL-based ECD (5PIL-BrBzV/Fc) was realized through high σ (∼13.1 mS/cm), increased ΔT (∼74 % at 605 nm) and remarkable long-term stability (∼98 % ΔT-retention after 20,000 cycles). The electrochemical quartz crystal microbalance (EQCM) analysis revealed that PIL-based ECD greatly diminished the cation's ion-accumulation issue. Our findings demonstrate that the adoption of PIL as a substitute for conventional ILs may result in substantial advancements in the electrochemical and optical characteristics of gel electrolyte-based ECDs.Electrochromic devicesEQCMGel polymer electrolyteIon-accumulationpoly(ionic liquid)Viologensjournal article10.1016/j.solmat.2025.113676