Enhancing electrochromic performance and stability: A novel ionic complex based on carbon dots

초록

Electrolytes are crucial in electrochemical applications such as rechargeable batteries, supercapacitors, fuel cells, and electrochromic devices (ECDs). Therefore, developing new electrolytes with high ionic conductivity, electrochemical stability, and environmental friendliness is essential for advancing next-generation electrochemical systems. Herein, we developed a novel type of ionic complexes composed of multivalent carbon dot polyanions (C dot) and equivalent alkali cations such as Li+ (Li-C dot), Na+ (Na-C dot), and K+ (K-C dot). As an electrolyte, the K-C dot demonstrated superior electrochromic behavior of Prussian blue (PB)-a promising electrochromic material for ECDs-compared to commercially available KCl. The PB thin films exhibit high coloration efficiency (eta) of 103.5 cm(2) C-1, good optical density (OD) of 0.90, and fast color switching time (1.5 and 2.6 s for the bleaching and coloring processes, respectively). Furthermore, the PB thin films exhibit long-term stability, retaining 97 % of the initial optical contrast (Delta T) even after 1,000 color switching cycles. The electrochromic performance of PB is influenced by counter cations such as Li+, Na+, and K+, which occupy the interstitial cavities in the lattice of PB during the electrochromic process. These results suggest that to improve the electrochromic performance of PB thin films in ECDs, it is essential to balance the migration of counter cations into and out of the lattice channels of the PB structure with the electron transfer between the PB thin film and the electrode substrate to maintain the charge neutrality of PB. We anticipate that our study will enhance the understanding of the electrochromic process in ECDs and provide new insights into the design of electrolytes for electrochemical systems.

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