Functionally graded Pd/γ-alumina composite membrane fabricated by electroless plating with emulsion of supercritical CO₂

This paper proposes a functionally graded Pd/γ-alumina composite membrane fabricated by a novel method for electroless plating by combining supercritical fluid technology and Pd electroless plating in a hybrid technique. The electroless plating reactions on catalyzed nanoporous γ-alumina surfaces were carried out in an emulsion of supercritical carbon dioxide (sc-CO₂) and an electroless plating solution with fluorinated surfactant F(CF(CH₃)CF₂O)₃CF(CF₃)COO(CH₂CH₂O)CH₃. Pd/γ-alumina graded membrane produced by electroless plating with sc-CO₂ had thicker Pd/γ-alumina graded layer and smoother surface than conventional electroless plating. In electroless plating with sc-CO₂, the penetration into the nanoporous γ-alumina pores was dominant reaction because the deposited Pd particles were smaller and, moreover, the electroless plating media with dispersed CO₂ has lower viscosity than conventional electroless plating. The Pd membrane formed in the emulsion of sc-CO₂ was about 1 μm thickness and composed of a composite membrane of 0.45 mol m^-2 min^-1 as hydrogen flux, while 0.30 mol m^-2 min^-1 of the Pd membrane formed by conventional electroless plating.