Mixed proton—electron conducting materials

In general the charge carriers in mixed proton-electron conducting materials could be protons, oxygen ions (or oxygen vacancies), hydroxyl ions, electronic-holes and electrons. To determine the nature of the charge carriers and their transport numbers, various defect structure models have been presented [36-38]. These defect models were fitted to the total electrical conductivity data measured... [Pg.52]

Proton-conducting materials [38-47], analogous to oxygen conductors but with stationary oxygen anions, can show mixed protonic-electronic conductivity, without considerable oxygen transport in hydrogen or water atmospheres [40,41], These materials have not been widely studied in comparison... [Pg.471]

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... [Pg.91]

With the requirement of electronic conductivity, oxides containing cations with mixed valence and, in particular, reducible cations are preferable. Oxides containing transition metals are therefore appropriate alternatives. There are indications based on conductivity measurements that Ti02 could be a possible candidate [83], but no direct measurements of hydrogen permeability have been reported. Tita-nates, in general, however, are interesting because there are a number of materials classes that accommodate oxygen vacancies and may dissolve protons. [Pg.41]