Simultaneous analysis of electrosorption capacity and kinetics for CDI desalination using different electrode configurations

Abstract

Capacitive deionization (CDI) offers an affordable technology for the reduction of salt concentrations in brackish water. However, there are still drawbacks concerning electrode capacity and energy consumption, compared to other well-established technologies such as reverse osmosis or electrodialysis. This study investigates high-adsorption electrodes based on polyaniline-activated carbon, applying different configurations (symmetric and asymmetric electrodes, and membrane CDI) to optimize electrosorption capacity and energy consumption. A new approach called OSR (optimized salt removal) is proposed, based on simultaneous analysis of the electrosorption capacity and the adsorption/desorption kinetics. This technique was used to evaluate different electrode configurations. The best performance was obtained using MCDI, which improved the electrode capacity from 14.9 to 20.0mgg−1, while reducing the specific energy consumption by 21%. It was demonstrated that the performance of the electrode depended on both the specific adsorption capacity (SAC) and the electrosorption/desorption kinetics. Fitting the electrosorption and desorption curves using a pseudo-first order kinetic model and applying the OSR method showed that the best desalination was achieved using MCDI at 1.2V. This configuration did not present the highest SAC or the fastest electrosorption/desorption kinetics, but a good balance was obtained between these two variables.