H2 permeation increase of electroless pore-plated Pd/PSS membranes with CeO2 intermediate barriers

Abstract This work presents the improvement of hydrogen permeance on electroless pore-plated Pd-composite membranes by the incorporation of ceria as intermediate barrier. This modification, in case of preparing a thick barrier, reduces both average pore size and external roughness of an oxidized Porous Stainless Steel (PSS) tube used as support. However, it also provokes a marked reduction of its permeance, turning more difficult the pass of the hydrazine through the modified support and, therefore, the palladium incorporation by electroless pore-plating. An optimization of this process leads to a Pd/CeO 2 /PSS composite membrane in which the initial roughness is halved, achieving a stable and selective Pd layer of around 15 μm. This composite membrane exhibits a hydrogen permeance of 5.37 · 10 −4  mol m −2  s −1  Pa −0.5 at 400 °C, an ideal H 2 /N 2 perm-selectivity ≥10,000 and an activation energy of 8.9 kJ mol −1 . Moreover, the hydrogen flux increases around 400% with regard to previous results, in which no ceria was used as intermediate layer (measured range: 0.03–0.12 mol m −2  s −1 versus 0.01–0.03 mol m −2  s −1 ). This increase is derived from a high reduction, of around 30%, in the resistance to the permeation process when using electroless pore-plated membranes due to a lower penetration grade of the Pd external film into the support. In addition, it has been confirmed the successfully stability of the Pd membrane under thermal cycles and different operating conditions, including the variation of permeate flux direction from the inner to the outer of the membrane, where the Pd-layer is placed, or vice versa .