Oxygen-rich 3D hierarchical porous MXene prepared by Zn powder reduction for flexible supercapacitors

Abstract

TiCT MXene is highly compelling as an energy storage material, but 2D MXene sheets experience significant stacking due to hydrogen bonding and van der Waals forces. This blocks active sites and impedes fast electrolyte ion transport. The pseudocapacitance of MXene materials is highly reliant on their terminal groups. Therefore, an effective strategy was designed herein to prepare an oxygen-rich 3D hierarchical porous MXene (P-OR-TiCT). First, Zn powder was used as a template to construct three-dimensional hierarchical porous structures that spanned the microporous, mesoporous, and macroporous scales. Second, Zn powder was used as a metal reducing agent in a reaction at 500 °C to eliminate most −F terminal groups on the MXene. Then, a subsequent acid washing step was used to introduce numerous −O terminal groups. The energy storage process of the prepared MXene was investigated by in situ Raman. More redox active sites (−O terminal groups) are exposed by the constructed oxygen-rich 3D hierarchical porous MXene structure, which also provides a shorter pathway for electrolyte ion transport. P-OR-TiCT displays superb rate performance (88.19 % retention at 100Ag) and ultra-high capacitance (676.7F/g at 2 mV/s and 698.7Fg at 1 Ag) when used as a supercapacitor electrode. Moreover, a symmetric flexible supercapacitor device prepared using P-OR-TiCT and carbon cloth achieves a superb energy density of 32.8Whkg at a power density of 236.5Wkg. This study offers insight into the design of MXenes that exhibit both high capacity and excellent rate performance.