Pyridine-Based Extended Viologen Coupled with Poly(5-cyanoindole)/CoMn₂O₄ for an Electrochromic Hybrid...

An electrochromic hybrid supercapacitor-battery (EHSB) is developed using a poly(5-cyanoindole)/CoMn₂O₄ (P5CIn/CMO) composite as the anode and an extended viologen, dipyridyl dibutylpyridine (DPDBPy), embedded in a gel-film matrix as the cathode. The P5CIn/CMO/DPDBPy EHSB operates over a 1.5 V potential window and exhibits reversible deep purple-to-yellow switching via a diffusion-controlled two-electron transfer process, enabled by the extended π-conjugation of the viologen's central pyridine ring. This leads the EHSB to deliver a coloration efficiency of 153.8 cm² C^-1, an integrated visible transmission modulation of 50%, and switching times of the order of seconds. Simultaneously, the EHSB delivers an areal specific capacitance (ASC) of 33.3 mF cm^-2 (0.3 mA cm^-2) and a discharge capacity of 89.9 mAh g^-1 (0.18 A g^-1), validating its classification as a hybrid storage device. The cell retains 94% of its ASC over 10,000 cycles in capacitive mode (26.5 mF cm^-2 at 1.2 mA cm^-2), shows a 14.4% decline in diffusive-battery-mode capacity after 100 cycles (80.3 mAh g^-1 at 0.3 A g^-1), and maintains 92% of its optical modulation after 1000 color-switching cycles. The chromatic transition enables real-time visual assessment of the state of charge, positioning the EHSB as a promising platform for scalable integrated energy storage and smart window applications.