Online measurements of fluoride ions in proton exchange membrane water electrolysis through ion chromatography

This work investigates the online monitoring of fluoride ion concentration in proton exchange membrane water electrolysers (PEMWE) effluent water using an automated ion chromatography (IC) setup. Prototype catalyst coated membranes (CCMs) with different thicknesses have been tested and fluoride measurements under different operating conditions at both single cell and stack level have been carried out. The study reports the impact of both current density and temperature on the cathodic fluoride concentrations showing a maximum at low current densities, at around 0.4 A/cm2 for the single cells, and at 0.2–0.4 A/cm2 for the short stack. It is also reported that higher PEMWE working temperature has an adverse effect on the membrane stability, resulting in a significant increase of the fluoride release at the cathode outlet. Noticeably, CCMs with reduced membrane thickness exhibited lower values of area-specific fluoride release rates with respect to thicker CCMs. Finally, the study also reports that fluoride concentrations and water conductivity are very well correlated, displaying a linear correlation. This new finding could represent a low cost and straightforward method to obtain quantitative information about membrane degradation rates in larger commercial PEMWE systems.