Non-Pd BCC alloy membranes for industrial hydrogen separation

▶ BCC alloy membranes have higher hydrogen permeability than FCC alloys. ▶ BCC alloys are susceptible to hydrogen embrittlement because of high H solubility. ▶ Hydrogen solubility can be tailored through selective alloying. ▶ These membranes can meet future cost and flux targets. ▶ Achieving sufficient durability remains the greatest challenge. With low cost raw materials and high hydrogen permeabilities, body-centred-cubic (BCC) alloys comprising Group IV and V metals are of considerable interest for high-temperature hydrogen separation applications. Until recently, their tendency to embrittle severely has tempered the enthusiasm for these materials in the membrane research community, but efforts to develop BCC alloy membranes suitable for industrial H 2 separation processes have increased recently and significant gains have been made in overcoming the inherent instability of these materials in hydrogen. Compared to competing face-centred-cubic alloys, BCC alloys have much higher solubilities that provide them with a high driving force for hydrogen permeation. This high solubility, however, exacerbates the problem of hydrogen embrittlement. Given their low cost components and high permeabilities, the development of membranes with sufficient durability and embrittlement resistance remains the greatest barrier to the widespread uptake of BCC membrane technology. This review discusses the key scientific issues pertaining to the development of BCC alloy membranes in high-temperature industrial processes, including hydrogen solubility and diffusivity, embrittlement and manufacturing. Compositional modification to tailor the hydrogen solubility, maximize the rate of hydrogen diffusion and inhibit the onset of embrittlement is discussed.