BROMIDE ANION CONDUCTIVITIES OF QUATERNARY PHOSPHONIUM BROMIDES POSSESSING LONG ALKYL CHAINS

Ionic conductive solids have attracted much attention in recent years, because they may give high energy density of battery free from the leakage of the electrolyte solution. In this work halide anion conductivities of several quaternary alkylphosphonium bromides and tetrabutylphosphonium chlorides were measured by a complex impedance method. Tetrahexylphosphonium bromide (C6PBr) showed the highest bromide anion conductivity. The bromide anion conductivities decreased as the alkyl lengths of quaternary phosphonium bromides become both longer and shorter than C6PBr. Bromide anion conductivities of quaternary alkylphosphonium bromides were higher than those of quaternary alkylammonium bromides reported. The mixture of tetrabutylphosphonium bromide, tetrahexylphosphonium bromide, and tetraoctylphosphonium bromide was found to be a new kind of a room temperature molten salt.