Dense metal membranes are a well-developed technology for the production of high-purity hydrogen. The physical mechanism of hydrogen transport across metal films—dissociation of molecular hydrogen, diffusion of interstitial atomic hydrogen, and subsequent recombinative desorption of molecular hydrogen—means that metal membranes can have extremely high selectivities for hydrogen transport relative to other gases. We describe current experimental and theoretical trends in the development of metal alloy membranes for hydrogen purification in practical, chemically robust processes.

Ag–Pd alloy nanoparticles have been generated from silver and palladium nitrate precursors using a high temperature aerosol method, the liquid flame spray (LFS) process. In the LFS process, a spray aerosol of precursor liquid is introduced into a high-temperature H2–O2 flame. The primary micron-sized spray droplets evaporatein the flame, and the final particulate product is a result of the nucleation of the pure metal vapors shortly after the flame. In the study, three Ag–Pd molar ratios—10:90, 50:50, and 90:10—were used in the precursor. As a result of the synthesis, metalalloy nanoparticles with practically the same concentration ratios, correspondingly, were produced with the method. In the experiments, metal mass flow rates of 0.01–0.8 g/min were covered. The size of the particles was determined to be in the rangeof 10–50 nm by aerosol instrumentation. The particles were spherical and slightly agglomerated. It was concluded that the particle size can be controlled via the total precursor mass flow rate, and the composition can be controlled by the molar ratio of Ag and Pd compounds in the precursor liquid.