Overall Conductivity and Electromotive Force of SrZr sub(0.9)Yb sub(0.1)O sub(3-a) Cell System Supplied with Moist CH sub(4)

A proton-conducting ceramic cell for recovering tritium from process streams was investigated for its application to a fusion reactor system. The ceramic cell tested here was composed of a SrZr sub(0.9)Yb sub(0.1)O sub(3-a) tube, one end of which was closed, and Ni/SiO sub(2) and NiO/SiO sub(2) porous electrodes. Its anode was supplied with moist CH sub(4) or H sub(2) and its cathode with moist O sub(2). All of the j-V curves obtained by a direct-current method were correlated to the relation V=E sub(0)-jd/[sigma] at 600-700 degree C regardless of the two different conditions of the CH sub(4) + H sub(2)O and H sub(2) + H sub(2)O supply. The rate-controlling step of charged hydrogen ion transfer was determined from the dependences of the overall conductivity [sigma] and the electromotive force E sub(0) on the anode H sub(2)O partial pressure and temperature. The E sub(0) value under the condition of the CH sub(4) + H sub(2)O supply was affected by the diffusion of reaction products of CH sub(4) + H sub(2)O = CO + 3H sub(2) through the porous anode. On the other hand, the [sigma] value was limited by the oxygen reduction rate at the cathode interface between the ceramic and the Ni electrode regardless of the different conditions between CH sub(4) + H sub(2)O and H sub(2) + H sub(2)O. These results were consistent with our results obtained by an alternating-current method. The activation energy of the overall conductivity was 60 kJ/mol.