Abstract
Pd membranes act in an important role in H2 purification and H2 production in membrane reactors. Pd-Ag alloy membranes fabricated by consecutive electroless- and electroplating process on alumina tubes exhibited good stability under stringent heating/cooling cycles at a ramp rate of 10 K/min, imitating practical fast initiation or emergency shutdown conditions. Bilayer Pd-Ag membranes can form dense and uniform alloy after thermal treatment for 24 h at 823 K under H2 atmosphere, despite a porous structure due to the development of liquid-like properties above Tamman temperature to enforce the migrativity. On the contrary, alloying under N2 atmosphere resulted in a Pd-enriched layer. This led to a lower H2 flux but superior thermal stability compared to that alloying under H2 atmosphere. The trilayer approach of electroless-plated Pd, electro-polated Ag and electroless-plated Pd is not suitable to achieve homogeneous Pd-Ag alloys, which, on the other hand, presented the occurrence of a small gap between top Pd layer and middle Ag layer, probably due to insufficient wetting during plating process. An on-site repair treatment in analogous to MOCVD (Metal-organic Chemical Vapor Deposition) process was first proposed to extend the lifetime of Pd-Ag membrane, i.e., by vaporizing, and subsequent decomposition of Ag(OOCC2F5) powders to “preferentially” block the pinholes under vacuum and at working temperature of ca. 473–673 K, which effectively reduced the N2 flux by 57.4% compared to the initial value. The H2 flux, however, declined by 16.7% due to carbon deposition on the membrane surface, which requires further investigation. This approach shows some potential for on-site repair without disassembly or cooling to room temperature.
Highlights
Pd and its alloy membranes have attracted extensive attention for their application in hydrogen purification and hydrogen production in membrane reactors, owing to their extraordinary hydrogen permeability and selectivity [1,2,3,4]
Pd-Ag alloy membranes investigated in this study are depicted in Table 1, denoted as PA-1, 6.14 ±
This study investigates the microstructure, thermal stability and onsite repair of bilayer and trilayer study investigates the microstructure, thermal stability and onsite repair ofonbilayer
Summary
Pd and its alloy membranes have attracted extensive attention for their application in hydrogen purification and hydrogen production in membrane reactors, owing to their extraordinary hydrogen permeability and selectivity [1,2,3,4]. There is a method to achieve high and stable hydrogen permeability of palladium-silver films at low temperatures by coating the surface [13]. The content of silver determines the critical temperature of the α-β transition, as well as the hydrogen permeability of supported Pd-Ag alloy membranes [2,19], whereas it is not easy to control the Ag content, microstructure and morphology during the fabrication process. The electroless co-deposition method was developed to obtain a uniform distribution of Pd-Ag alloy membranes [22], but much exploration is required to determine the appropriate preparation conditions. Liquid–liquid displacement porometry (MLLDP) to characterize the defect size, followed by the repair of defects in the palladium composite film by filling with high-temperature-resistant silicate gel (HTRSG). An onsite repair treatment was first proposed by vaporizing and the subsequent decomposition of Ag(OOCC2 F5 ) powders at working temperatures to “preferentially” block the pinholes under vacuum conditions without membrane disassembly
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
