Engineering of electrolyte ion channels in MXene/holey graphene electrodes for superior supercapacitive performances

MXene has given great promises to supercapacitor electrode material due to its high conductivity and redox properties. However, the self-agglomeration of the MXene lamella will reduce its contact area with the electrolyte and generate a tortuous transportation pathway of the electrolyte ions, thereby reducing its capacitive performance and rate capability. In this work, we engineered the electrolyte ion channels by adjusting the MXene lamella size and inserting holey graphene (HG) nanosheets into the interlayer of the MXene flakes. The developed MXene/HG electrode can not only avoid the self-restacking of MXene but also provide unimpeded ion transport channels. As a result, the supercapacitive and rate performances of the small MXene lamella-based MXene/HG (S-MXene/HG) supercapacitor are prominently ameliorated. By adjusting the content of HG, the S-MXene/HG_0.05 electrode exhibits excellent gravimetric capacitance of 446 F·g⁻¹ and a rate capability of 77.5%. The S-MXene/HG_0.05-based symmetric supercapacitor provides an impressive energy density of 14.84 Wh·kg⁻¹ with excellent cyclic stability of 96% capacitance retention after 10,000 cycles. This demonstration of the engineering of the ion channels shows great potential in two-dimensional material-based supercapacitor electrodes.