Hydrogen transport through V85Ni10M5 alloy membranes

Despite their inherent high permeability, unalloyed body-centred cubic (BCC) metals are prone to brittle failure due to their excessive hydrogen solubility. The primary challenge for BCC metal membrane development is therefore to control the solubility to a point where embrittlement is inhibited, while increasing the rate of hydrogen diffusion through the alloy. This can be potentially achieved through alloying, with several V-based BCC alloys exhibiting much improved resistance to embrittlement compared to pure vanadium, while maintaining higher hydrogen permeabilities than palladium alloys. While several binary and ternary V-based alloys have been investigated, a systematic approach is needed to properly evaluate potential alloying elements. In response, alloys of the general formula V85Ni10M5 (atom%), where M is Si, Mn, Fe, Co, Ni, Cu, Pd, Ag, or Al have been fabricated, coated with 500 nm of Pd, and their microstructure, hydrogen permeability and hydrogen solubility evaluated. The results obtained showed small compositional variations can lead to large changes in permeability, whereas diffusivity is less-dependent on composition. Formation of multi-phase microstructures can enhance the permeability by increasing the vanadium content and hydrogen solubility of the BCC primary phase. The multiphase V85Ni10Ti5 alloy exhibited a hydrogen permeability of 9.3 × 10−8 mol m−1 s−1 Pa−0.5 at 400 °C.

► Small changes in alloy composition lead to large changes in hydrogen solubility.
► Corresponding changes in the hydrogen diffusion coefficient are much smaller.
► Formation of a dual-phase microstructure increases the V content of the BCC solid solution which increases H solubility and permeability.
► The permeability of V85Ni10Ti5 was 9.3 × 10−8 mol m−1 s−1 Pa−0.5 at 400 °C, 3.5 times greater than V85Ni15 at the same temperature.