Predicting capacitive deionization processes using an electrolytic-capacitor (ELC) model: 2D dynamics, leakages, and multi-ion solutions

Clean water and affordable energy are critical worldwide challenges for which electrolytic capacitors are increasingly considered as viable alternatives. The upcoming technology of capacitive deionization (CDI) uses similar electrolytic capacitors for the desalination of water. The current work presents a new method that leverages existing support for supercapacitors in the form of current-distribution models, which enables detailed and separated descriptions of the rate-limiting resistances. Crucially, the new model blends this basis with a novel formulation centered on the adsorption of chemical species in CDI. Put together, it is adaptable to solving a wide range of problems related to chemical species in electrochemical cells. The resulting electrolytic-capacitor (ELC) model has enhanced stability and ease-of-implementation for simulations in 2D. The results demonstrate that the model accurately simulates dynamics CDI performance under a variety of operational conditions. The enhanced stability together with the adaptability further allows tractable simulations of leakage reactions and even handling multi-ion deionization in 2D. Moreover, the model naturally blends with existing interfaces in COMSOL Multiphysics, which automatically generalizes, stabilizes, and simplifies the implementation. In conclusion, the ELC model is user-friendly and tractable for standard simulations while also being especially powerful when simulating complex structures, leakage reactions, and multi-ion solutions.