Electronic Conductivity and Its Improvement

As discussed in the previous section, one effective way to improve the H2 permeability of SrCe03-based proton-conducting ceramic membranes is to improve their electronic conductivity. Different ahovalent dopants have been studied for their effect on the electronic conductivity. Qi and Lin [66] found that the electronic conductivity is inversely related to the ionization potentials of 6 + and dopants. Table 2.3 lists experimentally determined electronic conductivities of SrCe03-based materials in pure O2 with the ionization potentials [67] of their dopant ions. 

As shown, the electronic conductivity increases with decreasing ionization potential of the dopants. Among SrCe03-based materials, Tm-doped SrCe03 has the 

Material Charge transfer equation Ionization potential of the doping ions (eV) Electronic conductivity (S cm- ) 

The other approach to increase the electronic conductivity of these perovskite-based membranes is to add a metal phase (10-40 vol%). The metal phases studied include palladium, niobium, tantalum, vanadium and zirconium or their binary mixtures [69-72]. In order to nrmirtiize the stress at internal interfaces that can lead to the formation of dislocations and initiation of cracks, the ceramic support materials were chosen so as to be lattice matched to the metals and metal alloys [73]. 

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