•The palladium at Pd/Al2O3 membranes can be recycled by HCl–H2O2 treatment.•Both the recycled palladium and Al2O3 substrate can be reused.•The prepared new membranes are as permeable and selective as the originals.•It reduces the membrane cost and solves the problem of limited membrane life.The increasing applications of hydrogen energy greatly promote the development of composite palladium membranes, which are ideal for hydrogen purification because of their high permeability, excellent permselectivity and easy modulation. However, these membranes are still associated with problems such as high cost and limited operating life. This work investigates membrane recycling and reuse as a solution to these problems. Pd/Al2O3 membranes were prepared by electroless plating. The recycling of palladium was achieved by treating it with HNO3 and HCl–H2O2 agents. Adequate results were achieved using an agent composed of 2 mol/L HCl and 1 mol/L H2O2. The recycled palladium can be utilized in a new plating bath, while the Al2O3 substrate remaining after palladium recycling can be reused as the substrate material for the preparation of new membranes. The surface morphology, thickness and permeation performances of the recycled membranes, as characterized by scanning electron microscopy, metallographic microscopy and permeation tests, are similar to those of the original palladium membranes. It can be concluded that the recycling and reuse of the Pd/Al2O3 membranes are successful and may provide a solution to the current key problems associated with the application of composite palladium membranes.

•H2-permeable Pd membranes were deposited on porous stainless steel (PSS) tubes.•Aluminizing and oxidation treatments improved PSS surface and membrane integrity.•Effects of these treatments on membrane performance were investigated.•Intermetallic diffusion was not observed after treated at 500 °C in H2 for 200 h.Composite palladium membranes based on porous stainless steel (PSS) substrate are idea hydrogen separators and purifiers for hydrogen energy systems, and the surface modification of the PSS is of key importance. In this work, the macroporous PSS tubes were aluminized through pack cementation at 850 °C in argon, followed by an oxidation with air at 600 °C. Palladium membranes were prepared by electroless plating. Their permeation performances were tested, and the hydrogen permeation kinetics was discussed. The substrate materials and the palladium membranes were characterized by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD). An Al2O3-enriched surface layer with small pore size was created through aluminizing and oxidation treatments, which greatly improves the membrane integrity. The intermetallic diffusion between the palladium membranes and the PSS substrate material was not observed after a heat-treatment at 500 °C under hydrogen for 200 h. However, the aluminizing and oxidation treatments still need to be further optimized in order to improve the membrane permeability and selectivity, and particularly, the high diffusion resistance of the substrate materials greatly limited the hydrogen flux.

The stability of composite palladium membranes is of key importance for their application in hydrogen energy systems. Most of these membranes are prepared by electroless plating, and beforehand the substrate surface is activated by a SnCl2–PdCl2 process, but this process leads to a residue of Sn, which has been reported to be harmful to the membrane stability. In this work, the Pd/Al2O3 membranes were prepared by electroless plating after the SnCl2–PdCl2 process. The amount of Sn residue was adjusted by the SnCl2 concentration, activation times and additional Sn(OH)2 coating. The surface morphology, cross-sectional structure and elemental composition were analyzed by scanning electron microscopy (SEM), metallography and energy dispersive spectroscopy (EDS), respectively. Hydrogen permeation stability of the prepared palladium membranes were tested at 450–600 °C for 400 h. It was found that the higher SnCl2 concentration and activation times enlarged the Sn residue amount and led to a lower initial selectivity but a better membrane stability. Moreover, the additional Sn(OH)2 coating on the Al2O3 substrate surface also greatly improved the membrane selectivity and stability. Therefore, it can be concluded that the Sn residue from the SnCl2–PdCl2 process cannot be a main factor for the stability of the composite palladium membranes at high temperatures.The Sn residue on the substrate surface from SnCl2–PdCl2 process is not the main factor influencing the stability (or more precisely, the stability of selectivity) of the palladium membranes at high temperatures.Download full-size image