Faradaic-dominated intercalation pseudocapacitance in bimetallic ultrathin NiMn-MOF nanosheet electrodes for high-performance asymmetric supercapacitors

Specialized electrochemical characteristics of layered materials are concentrated in the interlayer regions. However, total performance is limited by slow kinetics and unstable cycles. Interfacial alteration of layered materials can significantly enhance charge storage by allowing the development of intercalation pseudocapacitance. The emergence of intercalation pseudocapacitance represents a new energy storage mechanism that bridges the gap between supercapacitors (SCs) and batteries in terms of energy and power density. In this study, bimetallic MOFs of Ni and Mn are synthesized to create a NiMn-MOF electrode with a unique 2D layered structure with ample voids and pores that enable rapid intercalation of electrolyte ions followed by Faradaic redox reactions to promote intercalation pseudocapacitance. Especially, the multiple oxidation states of the metal-ions facilitate better electrochemical activity. The NiMn-MOF electrode material is synthesized by a simple hydrothermal route. The resulting electrode exhibits a high specific capacity of 502 C/g (1025 F/g) at 1 A/g current density, along with 97.5 % capacity retention over 10,000 GCD cycles. Furthermore, an asymmetric supercapacitor (ASC), constructed using NiMn-MOF as the positive electrode and commercially available activated carbon (AC) as the negative electrode, demonstrates a high specific capacitance of 160 F/g, an energy density of 55.0 Wh/kg and a power density of 785 W/kg with a capacitance retention of 94 % over 5000 GCD cycles. This innovative nanocomposite electrode with a novel charge storage mechanism shows great potential for advancing energy density, power density, and rate performance in advanced energy storage systems.