Modelling of pseudocapacitive ion adsorption of electrochemically switched ion exchange based on electroactive site concentration

Electrochemically switched ion exchange (ESIX) technology has been proved as a promising valid method for separation of valued-added ions in diluted solutions. Herein, to promote industrial application of the ESIX technology, a general theoretical framework based on the electroactive site concentration (ESC) is proposed to describe the rigorous mechanism of ESIX process with electroactive ion exchange material (EIXM) coated electrodes. In particular, the pseudocapacitive ion adsorption process is modeled by modifying the electrochemical potential of the electroactive sites of EIXM. The proposed ESIX model reveals that the constant current density operation should be more suitable than the constant cell voltage operation for the ESIX process. It is found that the increasing of operating current density and the initial ion concentration can improve the average ion adsorption rate. For the ESIX process with the electroactive bismuth oxybromide (BiOBr) film coated electrode for bromine ions (Br-) separation, the simulation results are in good agreement with the dynamic experiment data. It is confirmed that the modeling of ESIX process based on the ESC provides an effective way to elucidate the ion separation mechanism in pseudocapacitive adsorption process and to predict the effect of various operating parameters on the ESIX process performance conveniently.