A positive-negative alternate adsorption effect for capacitive deionization in nano-porous carbon aerogel electrodes to enhance desalination capacity

Abstract

Carbon aerogels (CAs) with different microstructure were prepared via ambient pressure drying for capacitive deionization (CDI) of NaCl solution. The activated CAs exhibit a hierarchical porous structure, whose micro-, meso- and macropore size distribution can be varied with the molar ratio of resorcinol to catalyst (R/C). Desalination experiments illustrate that CA electrode with R/C of 200 shows the maximum salt adsorption capacity (SAC) of 10.34 mg/g at a working voltage of 1.5 V. It is found that electrosorption capacity of CA electrodes dose not only depend on the micro-porosity for large surface area but also the mesopores who provide transport channels. A positive-negative alternate adsorption (PNAA) method by alternating the polarity of voltage applied on the electrodes was developed to enhance the desalination capacity. The ultimate SAC of CA electrode with R/C of 200 is 25.45 mg/g, which is more than twice of the adsorption amount for the single adsorption. This method makes full use of the pores of the CAs and provides a further enhancing capacity for CA CDI.