High‐Performance Ultrathin Flexible Solid‐State Supercapacitors Based on Solution Processable Mo 1.33 C MXene and PEDOT:PSS

Abstract 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 Mo 1.33 C MXene with vacancy ordering in an aligned layer structure MXene/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) composite film posttreated with concentrated H 2 SO 4 . 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 Mo 1.33 C MXene/PEDOT:PSS composite film shows a reduction in resistance upon H 2 SO 4 treatment, a higher capacitance (1310 F cm −3 ) and improved rate capabilities than both pristine Mo 1.33 C MXene and the nontreated Mo 1.33 C/PEDOT:PSS composite films. The enhanced capacitance and stability are attributed to the synergistic effect of increased interlayer spacing between Mo 1.33 C MXene layers due to insertion of conductive PEDOT, and surface redox processes of the PEDOT and the MXene.