Incorporating Manganese Dioxide in Carbon Nanotube–Chitosan as a Pseudocapacitive Composite Electrode for High-Performance Desalination

This is the authors' abstract. We don't add key points for this paper.

Pseudocapacitive electrode materials that involve a Faradaic process are being used in capacitive deionization (CDI). In the present work, manganese dioxide was electrodeposited onto a carbon nanotube-chitosan composite to create a pseudocapacitive electrode (denoted MnO 2 /CNT–CS) for an enhanced desalination performance. The benefits of coupling MnO 2 with the CNT–CS matrix are attributed to the mesoporosity to facilitate ion transport, hydrophilicity to increase the electrochemical contact, and good electrical conductivity to improve the Faradaic charge-transfer of MnO 2 . The electrochemical properties were investigated by electrochemical impedance, galvanostatic charge–discharge and cyclic voltammetry studies. Considering its low specific surface area (89.8 m 2 g –1 ), the MnO 2 /CNT–CS composite electrode exhibited pseudocapacitive-like behaviors with a high specific capacitance (42.3 F g –1 at 5 mV s –1 ) and good rate capability. Furthermore, when the MnO 2 /CNT–CS electrode served as a cathode in batch-mode CDI at 1.2 V, the salt adsorption capacity was 6.01 mg g –1 for 1 mM NaCl, which is higher than that of most MnO 2 -coated carbon electrodes. The improved sorption capacity was ascribed to the intercalation of Na + ions via the Mn redox reaction between +4 and +3 oxidation states. The cycling performance was further tested over 15 charge–discharge cycles. Consequently, the pseudocapacitive MnO 2 /CNT–CS electrode is a promising cathode material for high-performance desalination. These results also suggest a promising approach for using redox-active MnO 2 in CDI.