Due to the low thickness of Pd membrane (1.0 mm) and low
sintering temperature (1300 C) of the hollow fibre substrate,
Pd-1.0/HF-1300 shows the highest hydrogen permeation flux.
In contrast, when a thicker Pd membrane (3.3 mm) is used,
namely Pd-3.3/HF-1300, there is a reduction in hydrogen
permeation flux by approximately 3 times, for example from
0.87 to 0.29 mol s1m2 at 450 C and 165 KPa. The relationship observed between H2 permeation flux and membrane thickness suggests that diffusion of H2 in the Pd layer is the ratelimiting step for hydrogen permeation, as the intermediate
layer formed is still porous and provided negligible resistance.