Multi-species ion exchange model with competitive adsorption for iron removal in PEM water electrolysis

To mitigate chemical membrane degradation in PEM water electrolyzers, ion exchange systems are typically implemented to remove iron ions from water. Predicting iron ion removal efficiency over time requires a model that captures interactions between the ion exchanger and electrolyzer, including the competitive adsorption of

and

ions. Building on the single-species model by Thomas (1944), we developed a multi-species ion exchange model by integrating a multi-species Langmuir model and introducing a competitive adsorption factor. Additionally, we coupled the model with an iron ion concentration source term accounting for ion production within the PEM electrolyzer. The model was fitted to new laboratory data by adjusting surface diffusivities. It successfully captures competitive adsorption dynamics, revealing transient peaks in

outlet concentrations compared to inlet concentrations due to displacement by

. For a specific case study, the model predicts that the ion exchange bed reaches exhaustion after approximately 10 000 h.