Flexible MXene/Graphene Films for Ultrafast Supercapacitors with Outstanding Volumetric Capacitance

TLDR

The authors present a strategy to fabricate flexible, conductive MXene/graphene supercapacitor electrodes by electrostatic self‑assembly of positively charged rGO (modified with PDADMAC) and negatively charged TiC MXene nanosheets. Electrostatic assembly inserts rGO nanosheets between MXene layers, preventing restacking, expanding interlayer spacing, and accelerating electrolyte ion diffusion to expose more electroactive sites. The resulting freestanding MXene/rGO‑5 wt % electrode delivers a volumetric capacitance of 1040 F cm⁻³ at 2 mV s⁻¹, retains 61 % at 1 V s⁻¹, and the symmetric device achieves 32.6 Wh L⁻¹, among the highest for aqueous MXene/carbon supercapacitors, demonstrating the critical role of interlayer spacing for high‑performance flexible energy storage.

Abstract

A strategy to prepare flexible and conductive MXene/graphene (reduced graphene oxide, rGO) supercapacitor electrodes by using electrostatic self‐assembly between positively charged rGO modified with poly(diallyldimethylammonium chloride) and negatively charged titanium carbide MXene nanosheets is presented. After electrostatic assembly, rGO nanosheets are inserted in‐between MXene layers. As a result, the self‐restacking of MXene nanosheets is effectively prevented, leading to a considerably increased interlayer spacing. Accelerated diffusion of electrolyte ions enables more electroactive sites to become accessible. The freestanding MXene/rGO‐5 wt% electrode displays a volumetric capacitance of 1040 F cm −3 at a scan rate of 2 mV s −1 , an impressive rate capability with 61% capacitance retention at 1 V s −1 and long cycle life. Moreover, the fabricated binder‐free symmetric supercapacitor shows an ultrahigh volumetric energy density of 32.6 Wh L −1 , which is among the highest values reported for carbon and MXene based materials in aqueous electrolytes. This work provides fundamental insight into the effect of interlayer spacing on the electrochemical performance of 2D hybrid materials and sheds light on the design of next‐generation flexible, portable and highly integrated supercapacitors with high volumetric and rate performances.