Bifunctional palladium composite membrane for hydrogen separation and catalytic CO methanation

Abstract

NiO was introduced into the porous Al 2 O 3 substrate by impregnation, and the resulting NiO/Al 2 O 3 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/Al 2 O 3 substrate, and a Pd/Pencil/Ni/Al 2 O 3 membrane was obtained after reduction with hydrogen. For reference, a Ni-free Pd/Pencil/Al 2 O 3 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/Al 2 O 3 and Pd/Pencil/NiO/Al 2 O 3 membranes were tested with a hydrogen feed composed of H 2 77.8%, CO 5.2%, CO 2 13.5%, and CH 4 3.5%. The Ni-free Pd/Pencil/Al 2 O 3 membrane only shows function of hydrogen separation, while the Pd/Pencil/Ni/Al 2 O 3 is also catalytically effective for methanation of CO and CO 2 in hydrogen, forming a bifunctional palladium membrane concept. Since the amount of CO and CO 2 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. Aiming at the hydrogen purification for proton exchange membrane fuel cells, a bifunctional Pd/Pencil/Ni/Al 2 O 3 membrane that is capable of hydrogen separation and catalytic CO methanation was developed. It was compared with the Pd/Pencil/Al 2 O 3 membrane without the nickel methanation catalyst.