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

Abstract

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 chargetransfer 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 highperformance desalination. These results also suggest a promising approach for using redox-active MnO 2 in CDI.

Synthesis and characterisation of amorphous MnO 2 /CNT via solid‐state microwave for high‐performance supercapacitors

“…Figure C shows the O 1s orbital spectrum, three different fitting peaks located at 531.3, 532.2, and 532.9 eV pertain to Mn–O–Mn, Mn–O–H, and H–O–H, respectively. The Mn 2p spectra (Figure D) possess two main peaks located at 641.2 and 653.3 eV, which can be vested in Mn 2p 3/2 and Mn 2p 1/2 of Mn 4+ in MnO 2 , respectively. The TG curve is shown in Figure S1.…”

Faradaic Electrodes Open a New Era for Capacitive Deionization

“…Apart from manganese oxides with unique crystalline structures, various amorphous manganese oxides have been applied as Faradaic electrodes for CDI as well. [76,108,[159][160][161][162] For instance, Wu et al [76] employed an amorphous MnO 2 as a Faradaic electrode for a HCDI cell, which exhibited an ion removal capacity of 14.9 mg g −1 in 500 mg L −1 NaCl solution and maintained 95.4% of the initial capacity after 350 cycles. Moreover, considering that the electronic conductivity of carbon materials (about 50 S cm −1 ) [163] is much higher than that of manganese oxides (10 −7 -10 −3 S cm −1 ), [164,152] carbon materials have been incorporated into manganese oxides to further improve their Faradaic charge-transfer.…”

“…Moreover, considering that the electronic conductivity of carbon materials (about 50 S cm −1 ) [163] is much higher than that of manganese oxides (10 −7 -10 −3 S cm −1 ), [164,152] carbon materials have been incorporated into manganese oxides to further improve their Faradaic charge-transfer. [108,159,160,162] For example, Liu et al successively developed a manganese dioxide/activated carbon (MnO 2 /AC) composite [159] and manganese dioxide/carbon nanotube-chitosan composite (MnO 2 /CNT-CS) [160] as Na + insertion Faradaic electrodes for CDI. Compared to either the pure carbon or MnO 2 electrode, the use of these two composites exhibited enhanced desalination performances of 9.3 mg g −1 at 1.0 V in a 10 × 10 −3 m NaCl solution, and 6.01 mg g −1 at 1.0 V in 1 × 10 −3 m NaCl solution, respectively.…”

“…Apart from manganese oxides with unique crystalline structures, various amorphous manganese oxides have been applied as Faradaic electrodes for CDI as well. [ 76,108,159–162 ] For instance, Wu et al. [ 76 ] employed an amorphous MnO 2 as a Faradaic electrode for a HCDI cell, which exhibited an ion removal capacity of 14.9 mg g −1 in 500 mg L −1 NaCl solution and maintained 95.4% of the initial capacity after 350 cycles.…”

Electrochemical supercapacitors: Operation, components and materials

“…Манган-оксид се често користи уместо рутенијум-оксида, због релативно ниске цене, мале токсичности, прихватљивости за становишта животне средине, уз одлична капацитивна својства -теоријска капацитивност је око 1200 F g -1 [161][162][163][164][165][166][167][168][169][170][171]. Као и код свих металних оксида, механизам складиштења енергије код оксида мангана је сачињен од низа реверзибилних редокс прелаза који укључују размену протона и/или катјона са електролитом.…”