Thermal stability study of Pd-composite membrane fabricated by surfactant induced electroless plating (SIEP)

Abstract

ABSTRACTOver the years, several different methods have been developed by modifying the conventional electroless plating (CEP) technique to fabricate dense thin Pd composite membranes with high H2 permselectivity. In this study, Pd composite membranes on macroporous stainless steel substrate (MPSS) were fabricated using CEP and novel surfactant induced electroless plating (SIEP) methods. The structural characteristics of CEP and SIEP fabricated Pd membranes were investigated before and after the heat treatment using SEM, XRD, EDS, and AFM techniques. The H2 permselectivity performance of the SIEP membranes was compared with that of CEP at different temperatures and trans-membrane pressures in the range of 523-823 K and 20-100 psi, respectively. The long-term thermal stability test of SIEP fabricated membranes was carried out on two different membranes, fabricated on MPSS substrates with and without oxide layer at 15 psi trans-membrane pressure and thermal cycling of 573-723-573 K. The microstructure analysis revealed that SIEP membranes have finer grains and diffused grain boundaries resulting in uniform, smooth, continuous, and pinhole free Pd-film. The SIEP membrane showed eight-fold higher H2 flux (1.7172 mol/m2/s) and four-fold higher H2 selectivity (~148) at 823 K and 100 psi trans-membrane pressure, compared to CEP membrane. Pd/MPSS membrane subjected to test for long-term performance and thermal cycling showed stable performance up to 1200 h while maintaining infinite H2 selectivity. Interestingly, although the thickness of Pd/oxi-MPSS (13.49 µm) membrane was higher than that of Pd/MPSS (11.6 µm) membrane, the H2 flux of Pd/oxi-MPSS membrane was two times higher than that of Pd/MPSS, attributed to the effective action of oxide layer as diffusion barrier.