Abstract:

NiO was introduced into the porous Al₂O₃ substrate by impregnation, and the resulting NiO/Al₂O₃ was coated with the lead of a 2B pencil to modify its surface. A palladium layer with a thickness of 5 μm was deposited by electroless plating on the Pencil/NiO/Al₂O₃ substrate, and a Pd/Pencil/Ni/ Al₂O₃ membrane was obtained after reduction with hydrogen. For reference, a Ni-free Pd/Pencil/ Al₂O₃ membrane was also fabricated. The surface and cross-sectional morphologies of the membranes were studied by scanning electron microscopy and metallographic microscopy. The hydrogen permeation kinetics was investigated by single gas tests, and the hydrogen separation performances of the Pd/Pencil/Al₂O₃ and Pd/Pencil/NiO/Al₂O₃ membranes were tested with a hydrogen feed composed of H₂ 77.8%, CO 5.2%, CO₂ 13.5%, and CH₄ 3.5%. The Ni-free Pd/Pencil/Al₂O₃ membrane only shows function of hydrogen separation, while the Pd/Pencil/Ni/Al₂O₃ is also catalytically effective for methanation of CO and CO₂ in hydrogen, forming a bifunctional palladium membrane concept. Since the amount of CO and CO₂ in the hydrogen after membrane separation is very low, the consumption of hydrogen by the methanation reactions is negligible. The bifunctional membrane is promising for proton exchange membrane fuel cells because the catalytic methanation treatment solves the CO poisoning problem of the fuel cell electrodes and consequently allows the palladium membrane to tolerate more membrane defects and to achieve longer life.

Key words: Palladium membrane, Hydrogen separation, Carbon monoxide methanation, Bifunction, Nickel catalyst, Proton exchange membrane fuel cell