Metal–organic frameworks have received increasing attention as promising electrode materials in supercapacitors. In this study, we have successfully synthesized a novel accordion-like Ni-MOF superstructure ([Ni₃(OH)₂(C₈H₄O₄)₂(H₂O)₄]·2H₂O), for the first time, and used it as an electrode material for supercapacitors. The supercapacitors with the novel electrode exhibited excellent electrochemical performance. For example, the accordion-like Ni-MOF electrode showed specific capacitances of 988 and 823 F g⁻¹ at current densities of 1.4 and 7.0 A g⁻¹, respectively, while maintaining outstanding cycling stability (capacitance retention of 96.5% after 5000 cycles at a current density of 1.4 A g⁻¹). More importantly, the accordion-like Ni-MOF and activated carbons were assembled into a high-performance flexible solid-state asymmetric supercapacitor with a specific capacitance of 230 mF cm⁻² at a current density of 1.0 mA cm⁻². The cycle test showed that the device can offer 92.8% capacity of the initial capacitance at 5.0 mA cm⁻² after 5000 cycles with little decay. The maximum energy density of the device can achieve 4.18 mW h cm⁻³ and the maximum power density can also achieve 231.2 mW cm⁻³.

Of the two major capacitances contributing to electrochemical storage devices, pseudo-capacitance, which results from the reversible faradaic reactions, can be much higher than the electric double layer capacitance. Transition metal compounds are emerging electrode materials for pseudo-capacitors due to their multiple oxidation states and different ions. As one of the most well-known electroactive inorganic materials, nickel based materials are being developed for this purpose. Nickel based materials have been intensively investigated and evaluated as potential electrode materials for pseudo-capacitors due to their thermal stability and chemical stability, high theoretical specific capacity, low price and environment friendliness. A variety of synthetic methods such as hydrothermal/solvothermal methods, sol–gel, electrodeposition, and the spray deposition method have been successfully applied to prepare nickel based compounds and composite materials. In this review, comprehensive summaries and evaluations have been given to show the recent progress. And we introduce the nickel based compounds and composites electrode materials for supercapacitors via synthesis methods, the electrochemical performances of the electrode materials and the devices.

Graphitic carbon nitride (g-C ₃ N ₄ ), with a unique structure analogous to graphite, has attracted ever-increasing attention for electrochemical energy storage due to its high surface area, metal-free characteristic, low cost and facile synthesis.

This review comprehensively summarizes and evaluates the recent progress in the research of noble metals and their composite electrode materials for supercapacitors.