Development of Redox-Active Ionic Liquids and Their Electrochemical Properties

Redox-active ionic liquids (RAILs) exhibit high redox density and non-volatility. A low-melting RAIL, [C4VC7][TFSI]2, was developed using asymmetric design and anion selection. Charge-transfer interactions were introduced by mixing with a carbazole-based RAIL, tuning viscosity and redox behavior. A semi-empirical method based on the Nernst–Planck equation was applied to evaluate the apparent diffusion coefficient without supporting electrolytes. An all-in-one electrochromic device using viologen and ferrocene-based RAILs showed clear color change, cycling stability, and oxygen resistance. These results demonstrate the promise of RAILs as functional electrolytes for electrochemical applications.