Construction of fully coated polypyrrole oxygen-barrier film based on MXene nanosheets for high reliability capacitive deionization

Abstract

MXene has emerged as a promising capacitive deionization (CDI) faradic material for the advantages of excellent hydrophilicity, outstanding specific capacitance, and highly reversible ions intercalation/de-intercalation. However, its practical applications are severely restricted by the bottleneck problems of severe self-stacking and susceptibility to be oxidized by dissolved oxygen in aqueous solution. Herein, polypyrrole (PPy) oxygen-barrier film was fabricated and fully coated on the surface of MXene by the in-situ polymerization method to construct the composite electrode of PPy@MXene. In this unique architecture, the PPy oxygen-barrier film both enhances the antioxidant properties of MXene and weakens the strong interfacial interactions between MXene nanosheets to reduce the self-aggregation. Meanwhile, by doping different ions (Cl– and dodecyl benzene sulfonate, DBS–), PPy films were provided with excellent conductivity, abundant hole sites, and good ion exchange properties, which significantly promoted the charge priority adsorption capability of PPy-Cl@MXene and PPy-DBS@MXene electrodes. Consequently, compared with MXene//MXene cell, the PPy-Cl@MXene//PPy-DBS@MXene CDI cell presents dominant deionization capacity (55 mg g−1) and outstanding cycling stability (3 % degradation after 40 cycles). Most importantly, the morphology, structure and surface charge characteristics of the electrodes after long-term desalination confirmed that the MXene with fully coated PPy film was not destroyed by dissolved oxygen and maintained good structural integrity, which is conducive to improving the reliability of the MXene-based electrodes in CDI. Additionally, ion doped PPy@MXene electrodes highlight preferential adsorption to divalent cations. The work proposes a new strategy to advance the practical application of MXene by simultaneously solving its self-stacking and oxidative degradation issues.