The cathodic behavior of tetraalkylammonium iodides was studied at a polished palladium cathode in aprotic dimethylformamide (DMF). Coulometric and electrochemical quartz crystal microbalance analyses allowed to show the formation of phases, the stoichiometry of which was fully determined. The reversible insertion of tetraalkylammonium cations as well as the electrolyte into palladium was demonstrated.