Insights into 2D/2D MXene Heterostructures for Improved Synergy in Structure toward Next-Generation Supercapacitors: A Review

2D interfacial heterostructures have found an unassailable status in energy storage systems, particularly in supercapacitors citing the intriguing structural and electrochemical characteristics. Exactly a decade ago, MXene, a promising 2D transition metal carbide/nitride/carbonitride was found to possess excellent conductivity, hydrophilicity, laudable charge storage opportunities, and enriched surface functionalities conducive for supercapacitors with inherent challenging shortcomings. To substantially improve, assembled 2D/2D MXene heterostructures exhibit commendable performance backed by the fact of swift increase in research interest. In this review, state-of-the-art research progress in material design and electrochemical performance of 2D/2D MXene heterostructures for supercapacitors are investigated. Discussion is initially on MXene fundamentals including synthesis and energy storage governing properties. Particularly, different preparation including electrostatic assembly, in situ growth, hydrothermal treatment, and objective specific strategies and its implications are elaborated. Especially, the electrochemical interface science, electrode-electrolyte interaction and ion/electron dynamics and synergistic enhancement of MXene/rGO, MXene/LDH, MXene/metal sulfides and timely investigations on other 2D MXene architectures are provided for its compatibility from solid-state to microsupercapacitors for commerciality. To conclude, a well-comprehended outlook, key challenges, and prospective research guidelines stretching from fundamental mechanism investigations to material and electrolyte optimizations are presented to encourage advanced 2D MXene architectures for future generation supercapacitors.