The diffusivity and solubility of hydrogen in metallized polymer membranes measured by the non-equilibrium stripping potentiostatic method

Abstract

The diffusion and permeation rates of hydrogen through a metallized polymer membrane were measured by a non-equilibrium stripping potentiostatic method. A description of the gas membrane electrolyte permeation cell is given. The membrane was made of commercial polyethylene terephthalate (PET) (thickness, 7.3 × 10 −3cm) coated on the detection side with a thin palladium film (thickness, 800 – 1400 Å). The membrane was first charged with hydrogen under a constant pressure at the entrance side until a linear concentration gradient was established across its thickness. Meanwhile, currents (stationary anodic current) were recorded corresponding to anodic removal of hydrogen from the detection side, while a constant anodic potential E a was applied to the detection side. The E a value corresponded to the potential of the palladium film free of hydrogen and was in the range 880–890 mV versus the reference hydrogen electrode in the same solution. Subsequently, hydrogen charging was ceased by replacing hydrogen with argon or air at the entrance side and the current corresponding to the stripping of hydrogen held within the membrane was recorded. The diffusion coefficient B was estimated from the stripping current-time curves, while the permeation coefficient P was estimated from the stationary anodic current within the range 283–333 K. The solubility coefficient S was calculated from the relation P = DS. Data on similar measurements carried out when hydrogen was electrolytically generated on Pd/PET/Pd membranes are also reported.