A critical review of recent advancements in zinc based metal organic framework nanocomposites and their derivatives for supercapacitor applications with future perspectives and challenges

Among various energy storage materials, Zinc-based metal-organic frameworks (Zn-MOFs used as precursors, templates, and shape controllers) act as potential candidates for supercapacitor (SC) applications due to their remarkable properties, such as facile preparation methods, high specific surface area (SSA), large porosity, outstanding power (P_den) & energy density (E_den), astonishing crystallinity, adjustable sizes, exceptional chemical & thermal stability, elongated life-cycle, framework diversity, and tunable structures. The present review focuses on the most recent progress on pristine Zn-MOFs, nanocomposites (with graphene (Gr), carbon nanotubes (CNTs), and polyaniline (PANI)), and their derivatives (metal oxides (MOs) & hydroxides (MHOs), porous carbon (PC) & activated carbon (AC), and metal sulfides (MSs)) as electrode materials to present the most up-to-date overview in this specific field. We first discuss the fundamental charging mechanisms (electric double-layer capacitance and pseudocapacitance) and the electrochemical techniques (cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy) of SCs. We then analyzed different methods with advantages and disadvantages of Zn-based MOF synthesis, such as solvothermal, hydrothermal, sonochemical, microwave heat-assisted, simple stirring, slow evaporation, mechanochemical, and electrochemical. Furthermore, structural, morphological, and electrochemical assessment techniques of reported Zn-based MOFs were examined in detail in three- and two- electrode configurations (asymmetric/symmetric devices with power and energy density). Finally, the ongoing issues and future developments in this field for architecturing supercapacitive devices are also discussed.