Novel method for producing high H 2 permeability Pd membranes with a thin layer of the sulfur tolerant Pd/Cu fcc phase

Abstract

A novel method for producing high permeance, Pd/Cu alloy membranes in the fcc phase is presented. The deposition of sub-micron layers of Cu by electroless plating and Pd by the galvanic displacement of Cu on top of an already dense Pd membrane enabled an fcc Pd/Cu alloy to be present on just the surface of the membrane. The result was a Pd/Cu/Pd tri-layer that when annealed formed the sulfur resistant fcc phase without the hydrogen permeance decrease associated with fcc Pd/Cu alloys. Atomic absorption spectroscopy (AAS) was used to study the effect of stirring on the kinetics of both the plating and displacement baths. Bath agitation rates of 400 rpm were found sufficient to deposit uniform sub-micron layers at high deposition rates by minimizing the diffusional mass transfer resistance within the solutions. XRD studies showed that the tri-layer formed the sulfur tolerant fcc phase within 36 h of annealing at 450 °C in H 2. A tri-layer Pd/Cu/Pd alloy membrane was fabricated by depositing 0.4 μm of Cu with a bath agitation speed of 400 rpm on an already dense Pd membrane and depositing 0.15 μm of Pd through the displacement of Cu with a bath agitation speed of 400 rpm. The total membrane thickness was 19.0 μm. The permeance at 450 °C was 22.9 m 3/m 2 bar 0.5 h which was 93% of the permeance of a pure Pd foil of the same thickness. Previous Pd/Cu fcc alloy membranes resulted in permeances with roughly 50–60% of the permeance of pure Pd foils of the same thicknesses. The membrane tested in this work performed similarly to pure Pd membranes due to thin layer of the fcc Pd/Cu alloy.