A simple approach to uniform PdAg alloy membranes: Comparative study of conventional and silver concentration-controlled co-plating

• A method to make ultrathin PdAg membranes with uniform Ag composition ∼25%.
• Improved membrane microstructure.
• Improved metal utilization rate.
• Short alloying time.

An Ag-controlled co-plating method was developed for the preparation of palladium/silver alloy membranes on porous tubular alumina supports. By controlling the feed rate of Ag to the Pd bath, the concentration of the silver in the plating bath was restricted during the course of plating. As a result, preferential deposition of silver at the beginning was suppressed and uniform dispersion of silver inside the membrane with silver composition in the desired range was achieved. Ultrathin (∼2.5 μm) PdAg alloy membranes with uniform silver composition of ∼25% were successfully obtained. The membrane showed a hydrogen permeance of 0.88 mol m−2 s−1 and pure-gas H2/N2 selectivity of 2140 at 823 K with ΔP   = 100 kPa. Only one hydride phase existed in the studied temperature range from 373 to 823 K with ΔPH2=100kPa. Direct comparisons with the conventional simply-mixed co-plating method showed that membranes made by the novel Ag-controlled co-plating method had much more uniform silver distribution, smoother surface, denser membrane structure, higher utilization rate of metal sources, and shorter alloying time.

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