Determining Diffusion Coefficients in Polymer Electrolyte Membranes With Lab Based Micro X‐Ray Fluorescence Analysis: A Proof of Concept

ABSTRACT The diffusion of metal ions in polymer electrolyte membranes is an important parameter for aging and capacity loss in electrochemical cells. Here, the diffusion coefficients of vanadium ions in Nafion membranes are studied. These are important to describe transportation of the ions through the membrane separator in vanadium redox flow batteries. Commonly, the concentration change in dialysis cells is used for this purpose. They yield an average value on all influencing factors. For a better understanding of ion mobility in these membranes, a direct study of ion transport in the membranes is a highly valuable addition. This can be done by obtaining concentration profiles. Here, we have applied laboratory based mXRF, as it is excellently suited to probe vanadium in hydrated membranes. Two processing methods were compared. It was determined that the diffusion coefficients decrease from > > , with values of , , and m 2 /s.