Facile self-repair of ultrathin palladium membranes

Abstract

Pd membranes can play an important role in H2 separation and purification for the development of sustainable and renewable energies. By supporting on porous substrates, Pd layer thickness can be reduced to several micrometers, thus improving the H2 permeance by several orders of magnitude. However, the supported thin Pd membranes are concomitant with pinhole formation due to either fabrication (e.g., electroless-plating) or thermal treatment, which exist as a remarkable challenge for its widespread applications. This study presents a novel and facile approach for self-repair of Pd membrane defects by immersing the stainless-steel supported Pd membranes in PdCl2 solution. Three membranes were deliberately selected with a low selectivity of 152–1687 (400 ​°C, 0.1Mpa), for which disproportionation reactions between Pd2+ and Fe/Cr/Ni at the defect sites spontaneously occur leading to the formation of Pd particles at the exact point of defects. This self-repair process can be enhanced when applying a high pressure of 30–50 ​bar in the PdCl2 solution for 30 ​min, by overcoming the capillary resistance and penetrating through the pinholes. Interestingly, densely distributed hillocks were observed on the membrane surface probably due to reduction of PdCl2 under following H2 treatment, thus increasing the H2 permeance with a higher effective surface area. The H2/N2 selectivity can be improved by more than one order of magnitude (in the best case from 1687 to 8768) and a long-term stability test of 300 ​h was achieved for the repaired membranes, corroborating the application potential of this approach.

Keywords

• Palladium composite membrane
• PdCl2
• Hydrogen separation
• Defect repair
• Selectivity