Tetraethylammonium iodide is commonly used in organic synthesis as a phase-transfer catalyst, facilitating the transfer of reactants between immiscible phases, such as aqueous and organic layers. It is also employed in electrochemistry as an electrolyte additive to enhance ionic conductivity in various electrochemical systems. In pharmacology, it serves as a potassium channel blocker, aiding in the study of ion channels and their role in cellular processes. Additionally, it is utilized in the preparation of ionic liquids and as a reagent in the synthesis of quaternary ammonium compounds. Its applications extend to material science, where it is used in the development of conductive polymers and other advanced materials.