Increasing capacitive desalination stability of active carbon by forming methanol layer on its surface

[Display omitted] •Methanol layer hinders oxidization of carbon and improves cycle stability.•Methanol increased desalination capacity retention of active carbon by 64%.•The method is applicable in flowing-electrode capacitive deionization. Capacitive deionization (CDI) based on active carbon is a promising technology for desalinating brackish water, but its desalination performance usually decreases after multiple adsorption/desorption cycles, which seriously hinders its practical application. To explore a solution method, study was conducted on regulating cyclic stability of active carbon electrode by utilizing methanol in NaCl solution. When the methanol content of the solution was 2 vol%, the active carbon electrode displayed 82% desalination capacity retention after the 12th cycle, which was 64% higher than the value reached when the methanol content was 0 vol%. This enhancement in stability was due to the formation of protective methanol layer on electrode surface, which retarded contact of carbon with water and thus oxidation of positive electrode. To put this finding into use, methanol was employed to improve stability of flowing electrode of a flowing CDI (FCDI) device, which does not need continuous addition of methanol into NaCl solution. The capacity retention of the flowing electrode after the 9th cycle was also markedly increased (94%＞80%) by methanol. This study provided a new route for improving cyclic stability of active carbons, which was suitable for application in FCDI.