The improvement of high-performance and low cost hydrogen purification membranes tailored to large-scale industries is critical in order to expand fuel cells and other hydrogen based technologies. Subsequently, strong efforts have been invested in the development of alternative multilayer membrane architecture using a palladium thin layer deposited onto a metallic substrate. Unfortunately, interdiffusion phenomena occur between the Pd and the Ni based substrate alloy and promptly destroy the membrane performance at working (or purification) temperatures close to 600°C.
Several diffusion barriers were investigated in order to avoid these devastating diffusion effect, and among them, TiN emerges as the most promising one.
We have developed an original and fast method to analyze the diffusion mechanisms in order to validate the efficiency of the TiN diffusion barrier. The designed samples consisted of a stack of TiN/Ni (1µm) layers deposited by DC sputtering on a Pd alloy substrate. A laboratory-made device allows to heat locally the stack at high temperatures (up to 1200°C) directly inside the scanning electron microscope chamber. In-situ Energy Dispersive X-ray analysis (EDX) enables us to follow the evolution of the chemical composition of the surface layer upon heating. The fluxes of Ni and Pd across the TiN barrier were derived from the EDX measurements. The thickness dependence of the TiN efficiency was interpreted in the frame of the solid state diffusion theory. Preliminary results show that a 450 nm thick TiN film drastically reduces the Pd/Ni interdiffusion with respect to a barrier-free stack.