Applicability range of potential step chronoamperometry for determining reliable diffusion coefficients of hydrogen and lithium in host materials

Potential step chronoamperometry is often used to study the electrochemical unloading process and to determine the diffusion coefficient D of an intercalating atom species in a host material, as it is seemingly easily applicable. The present work emphasises the importance of ensuring a diffusion-controlled unloading process during the potential step chronoamperometry measurement, if determination of the diffusion coefficient is targeted. As an example, diffusion-controlled and non-diffusion-controlled hydrogen unloading series from palladium samples and the resulting diffusion coefficients are presented, for comparison. A literature review summarising the diffusion coefficients of different intercalating species determined for several different systems by this method reveals a systematic error in the results. It turned out that insufficient diffusion control is a common issue in the application of the chronoamperometry method. Based on this finding, it is suggested to verify measurements in the diffusion-controlled regime when chronoamperometry is applied. A suitable verification technique is provided.