Effects of thin film Pd deposition on the hydrogen permeability of Pd 60 Cu 40 wt% alloy membranes

Abstract

Effects of thin film Pd deposition on the Hydrogen permeability of Pd 60 Cu 40 wt% alloy membranes, Journal of Membrane Science, http://dx. AbstractPd 60 Cu 40 wt% (Pd 47.3 Cu 52.7 at%) membranes were surface modified by depositing Pd thin films of three different thicknesses (~100, 800 and 1,400 nm) on to one side of a range of as-received Pd 60 Cu 40 wt% cold-rolled foils via magnetron sputtering. The hydrogen permeability of the membranes was then measured and compared to uncoated material. The Pd 60 Cu 40 wt% membrane coated with a 1,400 nm thick Pd thin film positioned on the feed side (445 kPa of hydrogen pressure) during hydrogen permeability measurements and cycled between 50 and 450 °C achieved the highest hydrogen permeability of 1.09  10 -8 mol m -1 s -1 Pa -0.5 at 450 °C in the third cycle. This is a 58% increase on the value measured for the as-received Pd 60 Cu 40 wt% under the same conditions. This improvement can be attributed to a Pd-rich Pd-Cu face centred cubic (FCC) phase forming through interdiffusion between the Pd thin film and bulk Pd-Cu membrane as a result of the test conditions used during hydrogen permeability measurements. This introduces a larger concentration gradient across the membrane due to the relatively high hydrogen solubility of the Pd-rich Pd-Cu FCC phase resulting in the observed increase in permeability.The Pd 60 Cu 40 wt% membranes coated with a ~1,400 nm and ~800 nm thick Pd thin film retained an almost pure Pd surface throughout cycling between 50 and 450 °C with a feed and permeate hydrogen pressure of 445 and 100 kPa, respectively. This is possibly due to the clamping effect of the Pd-Cu membrane substrate applied on the Pd thin film which would prevent embrittlement caused by cycling across the critical temperature of 295 °C. 2

Hydrogen solubility and diffusivity at Σ3 grain boundary of PdCu

“…A lot of researches have shown that the hydrogen solubility of FCC PdCu phase is much higher than that of BCC counterpart, which is due to the stronger binding of hydrogen at FCC PdCu phase. 20,34,38,55 As to the effect of grain boundary (GB) on hydrogen solubility at PdCu phases, however, there is not any report so far in the literature. The present rst principles calculation is therefore executed to have a comparative study of fundamental inuence of GB on hydrogen solubility of PdCu phases.…”

“…Interestingly, some experimental studies reveal that hydrogen diffusion in GB of nickel is much faster than that in bulks due to a lower activation energy, 3,6 whereas the hydrogen diffusivity in GB of aluminum and nickel with ne grains is smaller than that in the bulks. 7,10,11,13 As to hydrogen diffusion in PdCu membranes, the reported experimental results are mainly concentrated on the polycrystalline phases, [19][20][21][22][24][25][26][27][28][29][30][31][32][33][34][35]37,39 while the theoretical investigations are all related to single crystals. 17,23,36,38,[40][41][42] It is therefore of importance to nd out the effect of GB on hydrogen diffusion of PdCu by means of rst principles calculation.…”

“…14 It is well known that the PdCu membrane is a kind of excellent candidates for hydrogen separation and purication, and compared with pure Pd and other Pd alloys, PdCu possesses excellent hydrogen selectivity, high thermal stability, superior resistance against poisoning, moderate mechanical properties, relatively low price, and wide operating temperature range. [17][18][19][20] Regarding hydrogen solubility and hydrogen diffusivity of various PdCu phases, there are already a lot of experimental and theoretical investigations in the literature. 17, These experimental studies are mainly concentrated on polycrystalline phases of PdCu, [19][20][21][22][24][25][26][27][28][29][30][31][32][33][34][35]37,39 while the reported theoretical calculations are all related to single crystals of PdCu.…”

X-ray diffraction study on the effects of hydrogen on Pd60Cu40 wt% foil membranes

“…Eq. 1 has been derived from data presented in an earlier article with a greater degree of accuracy than previously reported [27] VTXRD experiments were performed on Foils 1 and 2 in the as-received state. Initially, Foil 1 was cycled under flowing helium at a pressure of 445 kPa throughout the VTXRD experiment for the purpose of determining the phase transition temperature in a hydrogen-free inert atmosphere.…”

Influence of temperature and pressure on surface modified Pd-Cu alloy foils for hydrogen purification applications

“…It was previously reported [26] that depositing a Pd thin film onto one side of an FCC Pd 60 Cu 40 wt% alloy foil membrane had the effect of increasing hydrogen permeability when the coated surface was positioned on the relatively high hydrogen pressure feed side during rig testing. This improvement in hydrogen permeability has been attributed to the presence of the Pd-rich Pd-Cu FCC phase which is formed as a result of Cu interdiffusing out of the bulk Pd 60 Cu 40 wt% foil membrane and into the Pd thin film.…”