Nitrogenous MOFs and their composites as high-performance electrode material for supercapacitors: Recent advances and perspectives

The unsatisfactory performance of energy-storage devices often stymies future advancements in a broad spectrum of industries, including portable gadgets, transportation, and green energy. By taking advantage of porous crystalline materials, a novel class of materials i.e., metal–organic framework (MOF) has perceived a remarkable upsurge of attention in versatile applications since their birth. Among MOFs, nitrogenous MOFs (self-assembled metal ions/clusters by nitrogen-containing organic ligands) are considered as one of the most promising electrode materials for supercapacitor applications owing to their ultrahigh specific surface area (SSA), wide pore-size distribution, adjustable crystal structure and morphology, open metal sites, and high self-doped nitrogen content. Indeed, nitrogenous MOFs and their derivatives and composite materials exhibit diverse structures, relatively high conductivity, excellent electrochemical performances, and stability. Despite their excellent features and extensive research, there has been no critical review reported solely focusing on nitrogenous MOF, their derivative and composite materials applied in supercapacitors. This review firstly discusses the comprehensive introduction, types and charge storage mechanism of supercapacitors, and the effect of nitrogen on the physicochemical properties. Followed by the well-known synthesis methods, the effect of dimensionality and morphology of MOFs on electrochemical performance and stability has been critically discussed. Then, the latest advancements in nitrogenous mono-and mixed-metallic MOFs and their derivative and composite materials have been explored in terms of their basically required characteristics including chemical composition, surface area, nitrogen content, porous structure, and tunable morphologies in supercapacitors. Finally, based on a comprehensive understanding of recent advancements, underlying challenges, guidelines, and perspectives on boosting the electrochemical performance of nitrogenous MOF materials for next-generation supercapacitors have also been documented.