Synergetic effects of different ion-doped polypyrrole layer coupled with β-cyclodextrin-derived hollow bottle-like carbon supporting framework for enhanced capacitive deionization performance

The structural characteristics of electrode material greatly affect desalination performance of capacitive deionization (CDI) process. Currently, there appears a new trend to develop novel materials with improved salt adsorption ability by designing reasonable hollow and robust spatial supporting structure. Herein, we report a novel hollow porous bottle-like carbon supporting framework (HPBC) derived from β-cyclodextrin for enhancing the CDI performance. The superior framework endows HPBC with large surface area, robust spatial supporting structure, optimized ion diffusion pathway, and ample ion storage space. By coupling ion-doped polypyrrole layer with HPBC, two types of composite materials (PPy-Cl/HPBC and PPy-DBS/HPBC) are developed with the integrated advantage of electrical-double layer ion storage process and ion-exchange pseudo-capacitive behavior. Electrochemical tests results indicate that both composite electrodes present considerable specific capacitances of 241.6 and 210.2 F g −1, fast charge transfer rate, and stable cycling performance. When PPy-Cl/HPBC and PPy-DBS/HPBC electrodes are assembled into the CDI cell (named cell Cl/C-DBS/C), the cell demonstrates the superior desalination ability of 34.5 mg g −1. Furthermore, the CDI cell Cl/C-DBS/C exhibits fast salt adsorption rate (4.0 mg g −1 min −1 ), prominent charge efficiency (77.6%), and excellent deionization stability after multi-regeneration cycles owing to the synergetic effect of ion-exchange ability of the PPy layer and the unique structural characteristics of HPBC. The CDI cell Cl/C-DBS/C also shows preferable adsorption of monovalent ions to divalent ions in the multi-salt solutions.