Pd-YSZ cermet membranes with self-repairing capability in extreme H2S conditions

Abstract

A Pd-YSZ cermet membrane that performs coupled operations of hydrogen separation from a mixed-gas stream and simultaneous hydrogen production by non-galvanic water-splitting, and have high sulfur tolerance is fabricated. It is proved that in H2S containing atmosphere the Pd-YSZ membrane has self-repairing capability, originating mainly from the conversion of Pd4S back to metallic Pd and SO2 by ambipolar-diffused oxygen obtained from water-splitting. The performance of membrane was analyzed at different temperatures in high H2S containing (0-4000 ppm H2S) mixed gas feed during the operation as a hydrogen separation membrane as well as during the coupled operation of hydrogen separation and hydrogen production. At 900 degrees C with the feed stream having >= 2000 ppm H2S, the hydrogen flux was severely affected due to the formation of some liquid phase of Pd4S, resulting in the segregation of hydrogen permeating Pd-phase at the membrane surface. But at 800 degrees C, though the membrane was affected by the Pd4S formation in high H2S environment (up to 1200 ppm H2S), its self-repairing capability and additional hydrogen production by water-splitting is capable of maintaining the hydrogen flux around similar to 1.24 cm(3) (STP)/min.cm(2), a value expected by the same membrane while performing only the hydrogen separation function in H2S-free environment.