Core-shell nanoparticles of Prussian blue analogues as efficient capacitive deionization electrodes for brackish water desalination

Abstract

Capacitive deionization (CDI) has recently drawn much attention, which is considered as an effective electrochemical technology for brackish water desalination. Sodium iron hexacyanoferrate (NaFeHCF) as a novel kind of electrode based on reversibly electrochemical redox reactions to store ions is proposed lately to make an application in CDI. However, the inevitable disadvantages of NaFeHCF are low deionization capacity and poor cycling stability due to the structural collapse during the process of Na+ intercalation/deintercalation. Herein, we made an attemption to encapsulate NaFeHCF with sodium nickel hexacyanoferrate (NaNiHCF) by a facile method in which the highly stable NaNiHCF at shell portion could protect the core from irreversible structural change to improve desalination capacity and cycling stability. Electrochemical analysis was carried out to investigate the electrochemical performance of the composite in-depth and the established CDI units displayed a specific capacitance as high as 138.15 F g−1 at 0.5 mA cm−2, low charge-transfer resistance and superior electrochemical stability. Moreover, high adsorption amount of 59.38 mg g−1 and energy consumption of 2.34 kg NaCl/kWh in 50 mM NaCl were observed during the deionization tests, and it remained 87% of initial desalination capacity after 50 cycles. These results indicate that NaNiHCF @ NaFeHCF with core–shell heterostructure is a promising electrode for brackish water desalination.