Developing carbazole-based redox ionic liquids for enhanced charge retention and stability in porous carbon electrode

Ionic liquids (ILs) are promising electrolytes for energy storage due to their wide electrochemical windows and tunable molecular structures, yet challenges such as limited electron‐transfer efficiency and high self‐discharge still hinder their performance in porous carbon electrodes. This work aims to design and evaluate novel carbazole‐based redox ionic liquids (RILs) to enhance charge retention and minimize leakage current in such systems. Two RILs, 3‐(2‐(9H‐carbazol‐9‐yl)ethyl)‐1‐methyl‐1H‐imidazol‐3‐ium bis((trifluoromethyl)sulfonyl)amide ([CazIm][NTf2]) and 3‐ethyl‐1‐methyl‐1H‐imidazol‐3‐ium((3‐(9H‐carbazol‐9 yl)propyl)sulfonyl)((trifluoromethyl)sulfonyl)amide ([CazNTf2][EMlm]), along with a neutral analogue, were synthesized and tested using a gold cavity ultramicroelectrode with porous activated carbon. [CazIm][NTf2] demonstrated ~ 90% redox peak current retention after 5 h in open‐circuit conditions, outperforming [CazNTf2][EMlm] (~ 50% retention), and selected combinations with anthraquinone‐based RILs further improved charge stability. These results indicate that molecular design integrating carbazole’s π‐electron‐rich framework with imidazolium‐based ionic liquids can effectively confine redox species within electrode pores, providing a promising approach to suppress self‐discharge and enhance the stability of high‐performance electrochemical energy storage devices.