High‐Performance Ultrathin Flexible Solid‐State Supercapacitors Based on Solution Processable Mo1.33C MXene and PEDOT:PSS

MXenes, a young family of 2D transition metal carbides/nitrides, show great potential in electrochemical energy storage applications. Herein, a high performance ultrathin flexible solid‐state supercapacitor is demonstrated based on a Mo1.33C MXene with vacancy ordering in an aligned layer structure MXene/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) composite film posttreated with concentrated H2SO4. The flexible solid‐state supercapacitor delivers a maximum capacitance of 568 F cm−3, an ultrahigh energy density of 33.2 mWh cm−3 and a power density of 19 470 mW cm−3. The Mo1.33C MXene/PEDOT:PSS composite film shows a reduction in resistance upon H2SO4 treatment, a higher capacitance (1310 F cm−3) and improved rate capabilities than both pristine Mo1.33C MXene and the nontreated Mo1.33C/PEDOT:PSS composite films. The enhanced capacitance and stability are attributed to the synergistic effect of increased interlayer spacing between Mo1.33C MXene layers due to insertion of conductive PEDOT, and surface redox processes of the PEDOT and the MXene. A MXene‐based solution processable flexible solid‐state supercapacitor with high performance is developed from a MXene/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) composite film. After posttreatment with concentrated H2SO4, the PEDOT nanofiber network is aligned between the MXene sheets, leading to highly improved flexibility and, most importantly, improved capacitances (1310 F cm−3), rate‐capabilities, and stability.