Tetramethylammonium bisulfate is primarily used in organic synthesis as a phase-transfer catalyst. It facilitates the transfer of reactants between immiscible phases, enhancing reaction rates and yields. This compound is particularly effective in nucleophilic substitution reactions, where it helps in the alkylation of various substrates. Additionally, it is employed in the preparation of quaternary ammonium compounds, which are widely used in surfactants, disinfectants, and fabric softeners. In the field of electrochemistry, it serves as an electrolyte additive to improve the performance of batteries and capacitors. Its role in these applications underscores its versatility in both industrial and research settings.