Hydrogen separation by dual functional cermet membranes with self-repairing capability against the damage by H2S

A Pd-YSZ cermet is synthesized to fabricate a hydrogen separation membrane that performs coupled operations of the separation of hydrogen from a mixed-gas stream containing H2S and the simultaneous production of hydrogen by water-splitting. The reason for the loss of hydrogen permeation function of Pd-based membranes in H2S environment has been the formation of Pd4S by the reaction of H2S with Pd. In the present study, the high thermal and chemical stability of YSZ in H2S environment helps operation at higher temperature to attain a high hydrogen permeation flux and, also, the Pd-YSZ membrane shows better tolerance against H2S because of its self-repairing capacity against the damage by H2S. The self-repairing capacity of Pd-YSZ membrane originates mainly from the conversion of Pd4S back into metallic Pd and SO2 by ambipolar-diffused oxygen obtained from water-splitting. Also, the operation at higher temperatures helps in reducing the effective concentration of H2S in the mixed-gas stream by converting a part of H2S into SO2 and H2 by ambipolar-diffused oxygen assisted reactions. The Pd-YSZ cermet membrane devised in the present work gives a comprehensive solution to many issues related with the hydrogen separation membranes.

► Simultaneous diffusion of oxygen and hydrogen was confirmed.
► High sulfur tolerance was proved.
► Oxygen diffusion assisted Pd4S oxidation.