Efficient utilization of the active sites of MXene: MXene/PSSNa films with a 3D-stabilized porous structure as high-capacitance and high-rate electrodes for flexible supercapacitors

Abstract

The self-stacking between MXene nanosheets and their fragile mechanical properties are the main reasons for their limited performance during application. This study propounds a surface-initiated strategy to in situ grow flexible polymers on the surface of MXene through covalent interactions to expose more active sites. 3D-stable, porous and self-supported Ti₃C₂T_x@MPS film electrodes are obtained after assembly. The grown polymer chains successfully enlarge the interlayer size of the MXene nanosheets and enable better participation of the active sites on the surface in the charging and discharging processes. Meanwhile, the –SO₃⁻ on the chains could effectively channel electrolyte ions. With the combined effects of stability and porosity, this film electrode demonstrates significant and superior rate properties (1876 F cm⁻², 5 mV s⁻¹; 1069 F cm⁻², 1000 mV s⁻¹) and remarkable stability in cycling (retaining 93% capacitance after 10 000 cycles). The chemical valence state and atomic structure of the membrane electrode were investigated using synchrotron radiation XAFS technology, while DFT was developed to calculate the evolution of the band structure during composite material synthesis. Furthermore, the mechanism by which Ti₃C₂T_x@MPS composites enhance active sites utilization was elucidated. In addition, symmetric supercapacitors based on Ti₃C₂T_x@MPS films achieve a maximum energy density of 80 μW h cm⁻² and a maximum power density of 180.4 mW cm⁻². This study provides an effective strategy for constructing high specific capacitance MXene-based film electrodes for supercapacitors.