Membrane separations are a key enabling technology for energy conversion devices. Ionic transport membranes must have both proton and electronic conductivity to function as hydrogen separation membranes without an external power supply. A technical obstacle to material modification by compositional changes is that the hydrogen flux through a dense membrane is a function of both the proton ionic conductivity and the electronic conductivity.
In addition, the materials electronic conductivity or material crystal structure stability should not be greatly affected by the presence of contaminant gases such as CO2, CO, CH4 and H2O which are commonly associated with from steam reforming/water gas shift reactions. Perovskite materials of the general formula SrCeO3 and BaCeO3 form the basis of most ceramic compositions with proton conductivities in the range of 2×10−2 S/cm at 600° C., showing good stability under the extremely low oxygen partial pressure where many Perovskites decompose to their primary oxides, “A”-site doping of the ABO3 Perovskite structure and stoichiometry modifications have been explored to increase the stability in the presence of contaminated gases while maintaining acceptable proton conductivity levels.
There remains room for variation and improvements in the art of conductive membrane and hydrogen flux through a membrane.