Enhanced Electrosorption Ability of Carbon Nanocages as an Advanced Electrode Material for Capacitive Deionization

The structure of an electrode material has an important impact on the performance of a capacitive deionization (CDI) device. However, it is still a challenge to design and synthesize electrode materials with a rational structure based on deep understanding of their structure-dependent CDI performance. Herein, we report the preparation of carbon nanocages (CNCs) with regulated shell thickness and a rich pore structure as an advanced material for high-performance CDI electrodes. The as-prepared CNC has a considerable specific capacitance of 149 F g^-1 at a scan rate of 5 mV s^-1. When used as CDI electrodes, the CNC shows an outstanding electrosorption ability of 17.5 mg g^-1 at 1.4 V at an initial concentration of 250 mg L^-1 NaCl solution. Furthermore, the CNC electrode displays high salt adsorption rate and good cyclic stability. Finite element simulations reveal that the superior structure of the CNC substantially promotes the ion transfer rate by shortening ion diffusion paths in the cavity of the electrode material. Also, both inner and outer walls of the CNC provide sufficient active sites for fast adsorption and desorption of salty ions. This work not only demonstrates that the CNC is a potential electrode material for CDI applications but also paves a way to design and prepare high-performance electrode materials based on a new perspective on their structure-performance relationship.