Layered materials and their heterojunctions for supercapacitor applications: a review

Supercapacitors have recently emerged as a potential technology with superior charge storage capacity and power density. Layered materials, by the virtue of their morphology and high surface area, are deemed to be potential candidates for storing charge or energy. In this review, the supercapacitive properties and electrochemical stability of different layered materials (MnO₂, graphene, g-C₃N₄, MoS₂, and MXenes) in a wide range of electrolytes is discussed. Moreover, an overview of the heterojunctions or composites of these 2D materials is included, emphasizing their synergistic effect towards improved supercapacitive performance and cyclic stability. Most importantly, the capacitive behavior dependence on the working electrode morphology, crystal structure, and type of electrolyte is explained. A future perspective on the design and use of these layered materials and their heterojunctions for commercial applications is presented.