Pd–V–Pd composite membranes: Hydrogen transport in a wide pressure range and mechanical stability

The composite membranes based on group 5 metals are capable of H2 separation with high speed and infinite selectivity. Hydrogen transport through Pd–V–Pd composite membranes of planar and tubular shape was investigated in the pressure range of (1×10−8–6×10−1) MPa at 400 °C. Due to the wide pressure range both the diffusion rate limited regime of hydrogen permeation and the regime limited by the H2 molecule dissociation were observed in one experiment. The density of flux permeating through the 100 µm-membrane reached 2.4 scc/(cm2 s) that seems to be one of highest ever achieved in the membranes based on group 5 metals as well as in any other unsupported metallic membranes. The concentration of dissolved hydrogen image reached 0.42 but no noticeable reduction in hydrogen diffusivity was found. The constant value of sticking probability of H2 molecules (4×10−4) that was observed over full range of pressures used in this study indicates that the surface saturation has insignificant influence on the kinetics of boundary processes. The 100-fold cycling of hydrogen pressure from 0 to 0.6 MPa did not result in any loss of tubular membrane integrity and change of its shape despite the fact that the ductile-to-brittle transition occurred in each cycle. The operation with samples of planar and tubular shape demonstrated that V-based composite membranes can be used at least for laboratory studies. Further work to improve the long-term stability is necessary for their practical applications.