1H NMR study of proton dynamics in (NH4)3H(SO4)2

Proton dynamics in (NH4)3H(SO4)2 has been studied by means of 1H solid-state NMR. The 1H magic-angle-spinning (MAS) NMR spectra were traced at room temperature (RT) and at Larmor frequency of 400.13 MHz. 1H static NMR spectra were measured at 200.13 MHz in the range of 135–490 K. 1H spin-lattice relaxation times, T1, were measured at 200.13 and 19.65 MHz in the ranges of 135–490 and 153–456 K, respectively. The 1H chemical shift for the acidic proton (14.7 ppm) indicates strong hydrogen bonds. In phase III, NH4+ reorientation takes place; one type of NH4+ ions reorients with an activation energy (Ea) of 14 kJ mol− 1 and the inverse of a frequency factor (τ0) of 0.85 × 10− 14 s. In phase II, a very fast local and anisotropic motion of the acidic protons takes place. NH4+ ions start to diffuse translationally, and no proton exchange is observed between NH4+ ions and the acidic protons. In phase I, both NH4+ ions and the acidic protons diffuse translationally. The acidic protons diffuse with parameters of Ea = 27 kJ mol− 1 and τ0 = 4.2 × 10− 13 s. The translational diffusion of the acidic protons is responsible for the macroscopic proton conductivity, as the NH4+ translational diffusion is slow and proton exchange between NH4+ ions and the acidic protons is negligible.