Ultra-thin (<1 μm) internally-coated Pd–Ag alloy hollow fiber membrane with superior thermal stability and durability for high temperature H2 separation

Ultrathin (<1 μm) Pd–Ag alloy membranes have been successfully coated on the internal surface of YSZ-mixed Al2O3 hollow fibers by sequential electroless plating. The H2 permeance and selectivity of internally-coated (0.8 μm thick) Pd–Ag alloy membrane is more than 5 μmol m−2 s−1 Pa−1 and well over 1200, respectively, at 450 °C and the pressure difference of 100 kPa. The internally-coated Pd–Ag alloy membranes exhibit the significantly improved thermal stability and durability of membranes. This is due to the support layer constrains the thermal expansion of Pd–Ag alloy during the annealing as well as the permeation tests, preventing the delaminating of Pd–Ag alloy membrane, and hence allowing the membranes to tolerate the repeated cyclic permeation tests over at least 5 cycles (10 h/cycle) without the significant loss of H2 selectivity. Moreover, mechanical damages (e.g., scratching) of Pd–Ag membrane can also be prevented as the Pd–Ag membrane is not exposed directly to the external surface.