Solid acids as electrolyte materials for proton exchange membrane (PEM) electrolysis: Review

Superionic conductors are materials which exhibit exceptionally high ionic conductivity whilst in the solid state. The manner in which certain structures accommodate superionic conduction has preoccupied many scientists throughout the latter part of the last century, beginning with the early debate about the disordered structure of the superionic α-phase of silver iodide. In this review, the key methods that have been used to deduce structural disorder in superionic conductors are described, and the important results summarized. The review focuses on simple archetypal systems, since these have dominated the literature, concentrating on more recent work and including emerging methodologies for deducing structural disorder. In most cases, the interpretation of diffuse scattering, as observed in scattering measurements, has played a crucial role in the understanding of these highly disordered systems and this is considered in some detail.

https://iopscience.iop.org/article/10.1088/0953-8984/14/32/201/pdf

Disordering phenomena in superionic conductors

The complex 18Crown[6]·[NH4][HSO4]·2H2O has been prepared by co-grinding of solid 18Crown[6] ether and solid [NH4][HSO4], while the complex (15Crown[5])3·[NH4]2[H3O][HSO4]3·H2O has been obtained by kneading liquid 15Crown[5] together with solid [NH4][HSO4]. Structural characterization has been achieved on single crystals obtained by recrystallization of the solid products from water.

Unprecedented mechanochemical preparation of 18Crown[6] and 15Crown[5] adducts of ammonium hydrogen sulfate by grinding or kneading

High-temperature phase behavior in the Rb3H(SO4)2–RbHSO4 pseudo-binary system and the new compound Rb5H3(SO4)4

Impedance spectroscopy study on the phase transition in Cs1 − x(NH4)xHSO4

Electric and dielectric measurements have been used to study the superionic conductivity and the ferroelectricity respectively in Rb0.8(NH4)0.2HSO4 single crystal. This material presents a high level of conductivity at high temperature. Activation energies were determined from the temperature dependence of the alternating-current conductivity in the regions 440-560 K and beyond 560 K; they are respectively 0.15 and 0.10 eV. The dielectric measurements show an intense anomaly at 285 K indicating a ferroelectric-paraelectric phase transition. This phase transition is accompanied by a significant dispersion of the real part of the dielectric constant in the frequency region investigated, in accordance with the high level of conductivity of this material.

https://iopscience.iop.org/article/10.1088/0953-8984/13/37/308/pdf

H Feki

Papers

H+-ion conductivity and ferroelectric properties of rubidium ammonium hydrogen sulphate