Effect of air bubbling on electroless Pd plating for the practical application of hydrogen selective membranes

In this study, an air bubbling electroless plating (ELP) method was newly developed for the production of Pd composite membranes. The air bubble ELP alleviated the concentration polarization of Pd ions, making it possible to achieve a plating yield of 99.9% in 1 h and form very fine Pd grains with a uniform layer of ∼4.7 μm. A membrane with a diameter of 25.4 mm and a length of 450 mm was produced by the air bubbling ELP, achieving a hydrogen permeation flux of 4.0 × 10^-1 mol m^-2 s^-1 and selectivity of ∼10 000 at 723 K with a pressure difference of 100 kPa. To confirm the reproducibility, six membranes were produced by the same method and assembled in a membrane reactor module to produce high-purity hydrogen by ammonia decomposition. Hydrogen permeation flux and selectivity of the six membranes at 723 K with a pressure difference of 100 kPa were 3.6 × 10^-1 mol m^-2 s^-1 and ∼8900, respectively. An ammonia decomposition test with an ammonia feed rate of 12 000 mL min^-1 showed that the membrane reactor produced hydrogen with >99.999% purity and a production rate of 1.01 Nm³ h^-1 at 748 K with a retentate stream gauge pressure of 150 kPa and a permeation stream vacuum of -10 kPa. The ammonia decomposition tests confirmed that the newly developed air bubbling ELP method affords several advantages, such as rapid production, high ELP efficiency, reproducibility, and practical applicability.