Effects of the Spacer Obstacles on the Capacitive Deionization Performance

Abstract

The capacitive deionization (CDI) process uses porous electrodes to adsorb electrostatic ions, offering the possibility of efficient desalination of salty water. The purpose of this study is to investigate the effects of obstacles in CDI spacers on charge transfer and adsorption. The results reveal that the adsorption rate of the CDI cells increases remarkably for the obstacle height ratios of h = 0.8 and 0.9 in comparison with the original channel. In contrast, the performance deteriorates for the cells with height ratios of h = 0.3 and 0.6. For desalination operations that end at half the equilibrium salt adsorption capacity (SAC), the CDI channel containing rectangular obstacles covering 80% of the channel, improves the ASAR (0.13 mg g−1 min−1) by 8% compared to the same situation with the original spacer (0.12 mg g−1 min−1). This gain increases to 25% for the barriers covering 90% of the channel height. The results show that as the barrier height is modest, it prevents salt from entering the electrodes, allowing a low concentration zone to be identified adjacent to the barrier inside the electrode. Interestingly, if the barrier height ratio is as high as h = 0.8 and 0.9, the strong vortices facilitate the ions transfer towards the electrode and consequently, more adsorption occurs.