ELECTROCHEMICAL HYDROGEN PERMEATION IN A PROTON-HOLE MIXED CONDUCTOR AND ITS APPLICATION TO A MEMBRANE REACTOR

A proton-hole mixed conduction in SrCe0.95Yb0.05O3-alpha ceramic has been studied under an asymmetrical atmosphere with respect to hydrogen species. The following electrochemical cell was constructed; (I) 1% hydrogen, Pt I specimen ceramic I Pt, O2-Ar mixture (II) and electrochemical hydrogen permeation through this sample was examined under open- and closed-circuit conditions. When the circuit was closed, the hydrogen or water vapor evolution rates at the cathode decreased with increasing partial pressure of oxygen in the cathode. From the conductivity measurement under various p(O2), it was confirmed that the main charge carrier except protons was a positive hole, and that this ceramic behaved as a proton-hole mixed conductor under the asymmetrical condition. When the circuit was open, water vapor evolved spontaneously, and its formation rates were enhanced with increasing p(O2) in compartment (II). These phenomena indicate that this cell is a self-short-circuited via hole conduction in the bulk, and that hydrogen permeates electrochemically from compartment (I) to (II). Further, based on the principle of hydrogen permeation due to the proton-hole mixed conduction, CH4 dimerization was carried out at 1173 K using SrCe0.95Yb0.05O3-alpha ceramic as a membrane reactor. Formation rates of C2-hydrocarbons were enhanced markedly by self-short-circuiting the electrochemical reactor due to the mixed conduction. Th clarify the mechanism for the acceleration of CH4 dimerization, the electrolytic synthesis of ethane from CH, was carried out at 948 K using SrCe0.95Yb0.05O3-alpha ceramic as a membrane reactor.