Enhanced cation storage capacity in MXene electrode through the incorporation of polypyrrole for hybrid capacitive deionization

Abstract

Enhanced chemical stability of two-dimensional (2D) MXene materials is essential for their application as electrode material in capacitive deionization (CDI). In this study, we present an in situ electrodeposition method to fabricate a Ti₃C₂T_x@PPy electrode by incorporating conductive polymer polypyrrole (PPy) between layers of Ti₃C₂T_x. The introduction of PPy not only mitigates the self-restacking of Ti₃C₂T_x by expanding its lattice spacing but also forms a protective layer to prevent self-oxidation. The abundant functional groups and high conductivity of PPy effectively enhance the exposure of ion adsorption sites and accelerate the ion migration towards Ti₃C₂T_x. The synergistic effect between these two components results in excellent desalination performance for Ti₃C₂T_x@PPy, with a high salt adsorption capacity of 201.9 mg/g, salt removal efficiency of 73.48 %, low molar energy consumption of 121.89 KJ/mol, and exceptional cycling stability when used as an HCDI electrode. Notably, the superior desalination performance is preserved even in the presence of higher-valence-state heavy metal ions commonly found in real wastewater samples. Overall, the novel Ti₃C₂T_x@PPy electrode exhibits a stable microstructure and excellent ion adsorption properties, making it a promising candidate for highly efficient desalination applications. This study presents a viable strategy for the construction of MXene-based heterostructures, aiming to enhance the practicality and application potential of 2D MXene nanosheets in CDI systems.