Enhanced Desalination Efficiency of Activated Carbon Electrode Coated with Ion-exchange Layer for Membrane Capacitive Deionization

Membrane capacitive deionization (MCDI) is an alternative desalination technology, which combined with the ion-exchange membrane (IEM) in front of electrodes. Based on the principle of capacitive deionization (CDI), the ions are removed by applying electric field and ions, which stored in the surface of porous carbon electrodes from aqueous solution. During the process of electrosorption, the IEM plays an important role to exclude the co-ion effect due to the characteristic of permselective. A membrane that completely blocks transport of co-ions while allowing transport of counter-ions simultaneously. However, the IEM is expensive, requires strong physical pressure between membrane and electrodes. In order to solve the problems of contact resistance and thickness of electrodes, the heterogeneous membrane/activated carbon electrode (RMCDI) was developed by adhering the powder of ion-exchange resin (IER) on the surface of electrodes directly. The electrodes were characterized by electrochemical analysis, contact angle and surface structure analysis. The results show IER layer can not only reduce the resistance between electrode and IEM but also improve the hydrophilic properties. In addition, the results also show the functional groups of IER will not be destroyed during product process. For the cyclic voltammetry, the specific capacitance still keeps up after coating IER layer. From the electrosorption experiments of 5 mM NaCl at applied potential of 1.2 V over 30 min period in RMCDI system, the electrosorption capacity (6.21 mg/g-carbon) is 40 % higher than the un-coating electrode and also have good performance of charge efficiency (71.4%) and lower energy consumption (0.0434 kWh/mole). Furthermore, a cyclic test was performance for continuous operation of RMCDI including electrosorption and desorption process for 5 cycles. The electrosorption capacity was measured between 5.91 and 6.23 mg/g-carbon over the repeat operations. This implies that the RMCDI system would have stable performance and good generation of electrodes over the repeated operation