In this review the phenomenon of proton conductivity in materials and the elements of proton conduction mechanismsproton transfer, structural reorganization and diffusional motion of extended moietiesare discussed with special emphasis on proton chemistry. This is characterized by a strong proton localization within the valence electron density of electronegative species (e.g., oxygen, nitrogen) and self-localization effects due to solvent interactions which allows for significant proton diffusivities only when assisted by the dynamics of the proton environment in Grotthuss and vehicle type mechanisms. In systems with high proton density, proton/proton interactions lead to proton ordering below first-order phase transition rather than to coherent proton transfers along extended hydrogen-bond chains as is frequently suggested in textbooks of physical chemistry. There is no indication for significant proton tunneling in fast proton conduction phenomena for which almost barrierless proton transfer is suggest...

Proton Conductivity: Materials and Applications

The principal features of the thermodynamics and kinetics of ion-exchange processes in inorganic ion exchangers are discussed. The literature data on the ion-exchange properties of oxide systems, globular hydrates, and salts of polyvalent cations are surveyed. The methods for carrying out ion-exchange processes and the characteristic features of their occurrence on typical inorganic ion-exchange materials are examined. The bibliography includes 306 references.

https://iopscience.iop.org/article/10.1070/RC1997v066n07ABEH000348/pdf

Ion exchange on inorganic sorbents

The β′′-alumina structure is examined in detail and an analysis is presented of the three-dimensional integrity of the lattice. The layer structure that is responsible for the very high sodium conduction rate is the specific focus. Rigid layers that are derived from the cubic spinel structure are interleaved by more open honeycomb pathways where rapid ion diffusion takes place. The three-dimensional rigidity of the spinel block in this structure makes it possible to accurately quantify the conduction layer thickness based only on the hexagonal unit-cell dimensions, as suggested originally by Harbach [(1983), J. Mater. Sci. 18, 2437–2452]. His calculation is tested rigorously against the many single-crystal structure determinations that have been made on the β′′-alumina family compounds and excellent correlation is found.

On the structural integrity of the spinel block in the β"-alumina structure.

Solid oxides that show proton conduction at elevated temperatures may be useful materials for many applications, such as hydrogen sensors, fuel cells etc. These materials contain no structural protons and only become proton conductors if some cations are ion exchanged with H3O+ or NH
 4
 +
 or hydrogen and/or water vapour is dissolved in the oxides according to the relationships derived by Wagner. The several basic mechanisms whereby mobile protons can be introduced into oxides, and the properties of a number of examples are discussed.

J. O. Thomas

Papers

Protonic solid electrolytes: a single-crystal neutron diffraction study of ammonium–hydronium β''-alumina