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.