For both environmental and economic reasons, hydrogen becomes an important alternative energy feedstock. If combined with fuel-cell technology, very efficient energy conversion system can be built on hydrogen. However, the mature and low temperature hydrogen fuel-cells require high purity hydrogen because the catalyst used in fuel cell is easily deactivated by ppm level CO and NH3, and ppb level sulfur. Making high purity hydrogen with a low cost is a key for the successful application of hydrogen fuel-cell technologies. Palladium based membranes, which has 100% permeation selectivity for H2, has been a focus for developing membrane reactors for producing high purity hydrogen in short and easy processes. Pd-Cu alloy composite membrane has a comparable hydrogen permeation flux with, and is superior to pure Pd membrane in several aspects, i.e., better thermostability, lower cost, better resistance to hydrogen embrittlement and poisoning by gaseous impurities, e.g. H2S, CO and H2O, etc. In this work, Pd-Cu alloy membrane was prepared by an electroless plating method on a porous stainless steel support.

It was found that the intermediate layer between the support and the Pd membrane plays a decisive role for the performance of the composite membrane system in application, because this layer prevents intermetallic diffusion, controls the overall diffusion barrier and enhances affinity between the support and the membrane. CeO2 has a stable fluorite structure and a close coefficient of linear thermal expansion to that of the Pd-Cu alloy membrane, and therefore was recommended as a suitable material. Here, the introduction and modification techniques for using CeO2 as the intermediate layer were examined. It was found that CeO2 can moderate the pore size and porosity of PSS support effectively to meet the needs of the system. High temperature permeation and stability tests showed that the CeO2 intermediate layer was effective as the diffusion barrier for Pd-Cu alloy membranes on PSS support in a temperature range of 573 to 773 K, which is suitable for water-gas shift reaction. A 48 h stable performance was observed with CeO2 as the intermediate layer at 773 K. The performance of the membranes in this work is also compared with that in our previous work in which pure Pd membrane and yttrium stabilized zirconia intermediate layer were investigated [1,2].

Keywords: Palladium-copper alloy membrane; intermediate layer; hydrogen permeation; electroless plating; CeO2, sol-gel.

References

1. Zhang et al., High-temperature stability of palladium membranes on porous metal supports with different intermediate layers, Ind. Eng. Chem. Res., DOI: 10.1021/ie801417w

2. Zhang et al., Effect of metal-support interface on hydrogen permeation through palladium membranes, AIChEJ, DOI: 10.1002/aic.11760