Electrochemical Capacitive Desalination Behavior of Activated Carbon Fibers

Introduction Capacitive deionization (CDI), which is ion electrosorption onto the surface of porous materials to remove ions from aqueous solutions, may serve as an energy-efficient alternative for the desalination of brackish water comparing with conventional desalination methods such as membrane separation and thermal distillation [1]. The CDI process operates at low direct voltages. Ions adsorbed are hold in the electrical double layers (EDL) near charged surface of an electrode and could be released back into bulk solution by canceling the potential difference between the electrodes [1]. No additional chemicals are required for regeneration. The part of discharging energy is able to be restored for the energy recycling. A prerequisite for the high deionization efficiency of CDI method is the demand for the high electrosorptive capacity endowed by the electrode materials. To obtain the objective, it is important that a large surface area is created and thus typical materials such as high specific surface area (SSA) materials are used. High SSA, a key factor of electrosorptive capacity, is determined mainly by the contribution of the surface area of mesopores and micropores present in carbon materials. SSA is explicitly related to pore size, thus it is especially important to understand its effect on electrosorptive capacity. The latest research in the related field of electric double layer capacitors (EDLC) has shown an anomalous increase in carbon capacitance at pore sizes less than 1 nm [2]. In CDI, the pore openings of activated carbons were controllably tuned to exhibit excellent electrochemical selectivity for ions [3]. Electrosorptive performance with modified activated carbon cloth as CDI electrodes was also investigated [4]. Up to now, more emphasis is focused on high SSA of porous carbon materials with the order of 10 m/g. Activated carbon fibers (ACFs) are typical microporous materials with large surface areas and good conductivity along fiber axis. Thus they can serve as candidate for active component of CDI electrodes. The aim in present work is to identify effect of SSA on capacitive electrosorptive capacity using activated carbon materials electrodes.