Proton mobility in liquid and frozen HClO4•5.5H2O: NMR and conductivity measurements

Abstract : In recent studies it has been shown that the investigation of processes at the metal - aqueous electrolyte interface can be extended to temperatures below the freezing point of the electrolyte, and it has been demonstrated for reactions as well as double layer properties. The electrolyte that has been used in these investigations wes aqueous perchloric acid of the composition HC104*5.5H2O. In the phase diagram of H2O-HC104 this composition represents an acid hydrate of a stoichiometric composition with the highest water content possible. Since this perchloric acid hydrate is a suitable electrolyte also in the frozen state it was assumed that the protons are relatively mobile even in the solid phase. In order to clarify this point, NMR and conductivity measurements were performed to obtain some insight into the proton mobility of HC104*5H2O at various temperatures in the liquid and frozen state of the electrolyte.