Electrochemical modulation methods for investigating hydrogen diffusion in metallic membranes are well-established due to the simplicity of their experimental procedures and since they do not need to measure the absolute flow. We adapted the electrochemical impedance method to measure hydrogen permeation through membranes by adding a modulating dead-volume device to an existing membrane permeation setup, using a simplified volumetric method originally proposed by Altunoglu et al. We demonstrate that this volumetric impedance spectroscopy is superior to steady-state methods, particularly for distinguishing diffusion from non-diffusional properties. We derive a simple relation for the hydrogen diffusion coefficient from gas impedance using the theoretical framework of electrochemical impedance, and provide a quality parameter based on the frequency dependence (the Montella condition), which is not available in steady-state methods. Setup and measurement errors of gas-impedance measurements are described. Experiments on hydrogen permeation in archetypal Pd membranes corroborate the feasibility and advantages of the modulation method. • A simplified volumetric impedance method provides model-independent diffusion in membranes. • Quality parameter (Montella condition) is derived. • Method is tested along hydrogen permeation in Pd membranes. • Hydrogen diffusion as function of pressure and temperature. • Method applicable to non-metallic membranes.
Borgschulte et al. (Wed,) studied this question.