MXene and transition metal chalcogenides-based 2D nanomaterials for next-generation supercapacitors

The advancement of technologies and burgeoning demand for green energy have created a revolution in the domain of energy storage. The requirements of smart electronics, implantable devices, wearable sensors, stretchable screens, and hybrid electric vehicles are distinct from conventional electronics in terms of power and energy. The ongoing quest for nanomaterials exhibiting superior performance is persistent, aiming to match the high power density of traditional capacitors and rival the high energy density of batteries. Although supercapacitors (SCs) can achieve an intermediate performance of these devices, there is still a wide gap in balancing large energy-storing capacity with a high energy-delivering rate. Among various nanomaterials, MXenes and transition metal chalcogenides (TMCs) are gaining significant importance owing to their captivating electrochemical characteristics such as high electric conductivity, tuneable surface chemistry, rich redox active sites, and cyclic stability. The agglomeration and interlayer restacking are, however, challenging aspects of these twodimensional layered nanomaterials, limiting their use in commercialized devices. There is tremendous thrust in devising various modification approaches such as composite fabrication, electrically conductive polymers, metal compounds (transition metal oxides and hydroxides), doping with nitrogen, sulfur, and phosphorous, or using conducting metals to address these issues and augment electrochemical performance. The present review article focuses on emerging electrode nanomaterials, viz., MXenes and TMCs, synthesis techniques, various parameters governing their structure, finely categorized composite fabrication, and electrochemical performance. At the outset, recent advancements in flexible, stretchable, and self-healable SC technology are elucidated.