Permselectivity of a nickel/ceramic composite membrane at elevated temperatures: A new prospect in hydrogen separation?

The objective of this study was to develop a metal/ceramic membrane with high permeability and selectivity to hydrogen at elevated temperatures, able to replace the high cost conventional palladium-based membranes. The intent was to use the effect of the interaction between hydrogen and a metal surface existing for the metals from group VIII of the Periodic Table, such as Pd, Ni and Pt. Thus, a composite membrane consisting of a thin and pure nickel layer (thickness ≈1–1.5 μm) deposited on an asymmetric tubular alumina support was prepared by electroless plating using hydrazine as reducing agent. In comparison to a Ni–P amorphous alloy membrane, this composite membrane showed unique permeability characteristics for both separate (H2 or N2) and mixed (H2 + N2) gases. Indeed, despite not being dense, the nickel layer was selective to hydrogen and its permselectivity increased with temperature. Moreover, both the microstructure and the permselectivity of the Ni/ceramic membrane were stable up to 600 °C. The use of a sweep gas provides an optimal H2/N2 (mixture) separation factor of 28 at 600 °C, the main diffusion mechanism of hydrogen being surface diffusion through the pores.