A modular and programmable electrolyte platform: Covalently anchored thermochromic hydrogels for on‐demand electrochromic devices

Electrochromic (EC) devices have garnered growing interest due to their adaptability for diverse applications and cost‐effectiveness. Enhancing their multifunctionality through the incorporation of thermochromic feature significantly broadens their applicability in various scenarios. Here, we introduce a paradigm‐shifting, modular electrolyte platform that transcends conventional material‐by‐material optimization. By covalently tethering thermosensitive poly(N‐isopropylacrylamide) (PNIPAM) blocks into a polyampholyte network via atom transfer radical polymerization, we create a foundational hydrogel powder resistant to phase separation. The key innovation lies in on‐demand reconstituability: the gel powder can be seamlessly reconfigured into custom electrolytes by simply mixing with different salt solutions, accommodating diverse EC materials and application requirements. We demonstrate that the choice and concentration of salt programmatically tune the lower critical solution temperature from 33.8 to 2.3°C, and compatibility with diverse EC materials (WO 3 , Prussian blue or viologen). Consequently, this single platform enables the rapid fabrication of high‐performance devices for disparate applications: low‐temperature (2°C) information encryption, energy‐saving smart windows with a ∼7°C indoor cooling benefit, and ultra‐stable organic EC displays with exceptional cycling (>1000 cycles) and fast switching (1.6–5.6 s). This work establishes a designer electrolyte toolkit that offers unprecedented flexibility, stability, and performance‐by‐design for next‐generation adaptive multifunctional devices.