Abstract
With the development of capacitive deionization technology, charge efficiency and electrosorption capacity have become some of the biggest technical bottlenecks. Asymmetric activated carbon electrodes with ion-selective functional groups inspired by membrane capacitive deionization were developed to conquer these issues. The deionization capacity increased from 11.0 mg g−1 to 23.2 mg g−1, and the charge efficiency increased from 0.54 to 0.84, due to ion-selective functional groups minimizing the co-ion effect. The charge efficiency and electrosorption capacity resulting from better wettability of these electrodes are effectively enhanced by grafting ion-selective functional groups, which are propitious to ion movement. In addition, asymmetric deionization capacitors show better cycling stability and higher desalination rates. These experimental results have demonstrated that the modification of the ion-selective (oxygen-containing) functional groups on the surfaces of activated carbon could greatly minimize the co-ion effects and increase the salt removal from the solution. These results have indicated that the ion-selective asymmetric carbon electrodes can promote well the development of deionization capacitors for practical desalination.
Highlights
The water crisis is one of the most threatening issues in the foreseeable future due to the decrease of available fresh water caused by the growing population and environmental pollution.[1,2,3,4] Deionization of brackish water can provide abundant fresh water for humans
Asymmetric deionization capacitors show better cycling stability and higher desalination rates. These experimental results have demonstrated that the modification of the ion-selective functional groups on the surfaces of activated carbon could greatly minimize the co-ion effects and increase the salt removal from the solution. These results have indicated that the ion-selective asymmetric carbon electrodes can promote well the development of deionization capacitors for practical desalination
The BET speci c area decreased from 2759 m2 gÀ1 for activated carbon (AC) to 1090 m2 gÀ1 for S-AC and 696 m2 gÀ1 for N-AC, especially, the speci c area of N-AC is the lowest because the gra ed groups may increase the total weight of the samples and decrease the speci c surface area correspondingly
Summary
The water crisis is one of the most threatening issues in the foreseeable future due to the decrease of available fresh water caused by the growing population and environmental pollution.[1,2,3,4] Deionization of brackish water can provide abundant fresh water for humans. The charge efficiency of most carbon electrodes in the CDI process is lower than 0.6, which is far less than 1 and limits its large-scale industrial application.[2,4,10] To promote the practical application of CDI technology, it is quite urgent to improve the charge efficiency and reducing energy consumption of the electrodes These limitations may be overcome effectively by introducing ion-exchange membranes (IEM) into the CDI.[7,32] The ion-exchange membranes capacitive deionization (MCDI) have ion selectivity which prevents reverse adsorption and prohibits the mobility of co-ions.[33] The movement of counter-ions is free and the co-ions are prohibited in the IEM.[34] It will minimize the co-ions expulsion effect and increase CE and salt removal efficiency.
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