Incorporation of ammonium ions in Cs2(HSO4)(H2PO4) confirmed by solid-state NMR

Abstract

Inorganic solid acid salt Cs2(HSO4)(H2PO4) showed high proton conductivity in the superprotonic phase, and the phase was retained on cooling even at room temperature for a long period. In the present work, we attempt partial replacement of Cs ions by ammonium ions. Incorporation of ammonium ions up to 2.3% of the total cations is succeeded. Successful incorporation of ammonium ions is confirmed by the crystal structure measured by X-ray powder diffraction, the phase transition measured by thermal analyses and phosphorus environments measured by 31P magic-angle-spinning (MAS) NMR. Furthermore, we present 1H and 133Cs MAS NMR spectra and the result of 1H{31P} rotational-echo double resonance (REDOR) experiments. The 1H and 133Cs MAS NMR spectra show that incorporation of ammonium ions leads to increase of disordered structures.