多孔碳材與嵌入型材料於電容去離子技術之研析

Abstract

Rapid urbanization and population growth have resulted in severe demand on water and energy resources. In order to keep the sustainability of the urban resources and environmental, new energy-efficient desalination technology play a key role to decrease the demand of water and energy. Capacitive deionization (CDI) is a promising water desalination technology with lower energy consumption. Porous materials such as activated carbons can be used to electroadsorb ions from the water by the formation of electrical double layer (EDL). At the current stage, activated carbons are widely used as electrode materials for CDI applications due to the high surface area and good conductivity. Most recently, there are some studies propose the intercalation-based battery-type electrodes for CDI. It is found that higher salt adsorption capacity (SAC) of intercalation-based electrodes can be achieved as compared to porous carbon electrodes. However, there are still many unknowns about the CDI performances by using intercalation-based battery-like electrode. The objective of this research is to improve the fundamental understanding of using the EDL-based electrode and intercalation-based electrode in CDI. It is found that the AC//AC cell (EDL-based electrode) has higher means deionization rate but with lower salt adsorption capacity (~9 mg g−1). In comparison with AC//AC cell, NiHCF//AC cell (intercalation-based electrode) has lower means deionization rate but with higher salt adsorption capacity (~15 mg g−1). However, the means deionization rate and salt adsorption capacity of AC//AC cell is largely decreased with increasing the salt concentration (~5 mg g−1). It is because the excessive ions that exist in water has a significant influence on the electric fields. In addition, the performance of NiHCF//AC cell has less dependence on the salt concentration. From the aspect of energy consumption, AC//AC cell has lower charging efficiency (~60%) and higher energy consumption (~0.17 kMh m−3). On the other hand, NiHCF//AC cell has higher charging efficiency (~75%) and lower energy consumption (0.06 kMh m−3). The larger energy loss in AC//AC cell is due to the co-ions effect, which results from the movement of unwanted ions (co-ions) in EDL that consume additional energy. For the selectivity experiments of cations, the selectivity of AC//AC is determined by the ion charge and hydrated radius, whereas NiHCF//AC cell prefers small hydrated radius ions. In addition, a competitive adsorption experiment was conducted by using equimolar concentrations of ammonium ions and sodium ions. The results showed that 1.15 mM of NH4+ and 0.425 mM of Na+ were removed by AC//AC cell. For NiHCF//AC cell, 2.3 mM of NH4+ and 0.2 mM of Na+ were removed. The removal ratio of NH4+ to Na+ is higher in NiHCF//AC cell.