Mixed protonic-electronic

MIXED PROTON/ELECTRONIC CONDUCTORS 8.8.1 Proton Mixed Conductors... 

The use of a mixed oxygen ion-electronic conductor membrane for oxygen separation with direct reforming of methane, followed by the use of a mixed protonic-electronic membrane conductor for hydrogen extraction has also been proposed in the literature [34]. The products are thus pure hydrogen and synthesis gas with reduced hydrogen content, the latter suitable, for example, in the Fish-er-Tropsch synthesis of methanol [34]. 

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... 

Mixed Protonic-Electronic Conducting Membrane for Hydrogen Production from Solid Fuels... 

Mixed Protonic-Electronic Conducting (MPEC) Membrane... 

Qi X, Lin YS. Electrical conduction and hydrogen permeation through mixed proton-electron conducting strontium cerate membranes. Solid State Ionics. 2000 130 149. 

Li L, Iglesia E. Modeling and analysis of hydrogen permeation in mixed proton-electronic conductors. Chem Eng Sd. 2003 58 1977-88. 

Figure 1.1a shows schematically the operation of a membrane that is permeable to hydrogen molecules (corresponding to a porous membrane or a dense material in which molecules dissolve and diffuse) or to neutral hydrogen atoms (corresponding to a material in which hydrogen dissolves dissociatively, as in a metal). Figure 1.1b shows schematically how a mixed proton-electron conductor performs the same process by so-caUed ambipolar diffusion of both protons and electrons in the same direction to maintain electroneutrality and zero net current. 

Defect-structure-wise there are two main routes to a mixed proton-electron conducting oxide. The simplest would be to dissolve protons compensated by electrons originating directly from hydrogen gas ... 

Surface Kinetics of Hydrogen Permeation in Mixed Proton-Electron Conductors 21... 

Figure 2.1 Hydrogen transport through a dense mixed protonic-electronic membrane.

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... 

Tab. 2.2 S ummary of transport numbers of various mixed protonic-electronic conductors in various gas concentration cells. 

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