Tetraethylammonium hydrogen sulfate is commonly used as a phase-transfer catalyst in organic synthesis. It facilitates the transfer of reactants between immiscible phases, enhancing reaction rates and yields. This compound is particularly useful in nucleophilic substitution reactions, where it helps in the transfer of anions from the aqueous phase to the organic phase. Additionally, it is employed in the preparation of quaternary ammonium compounds, which are widely used in surfactants, disinfectants, and fabric softeners. Its role in electrochemical applications is also notable, where it serves as an electrolyte additive to improve conductivity and stability in various electrochemical systems.