Faradaic-dominated intercalation pseudocapacitance in bimetallic ultrathin NiMn-MOF nanosheet electrodes for high-performance asymmetric supercapacitors Mohan Reddy Pallavolu a , Arghya Narayan Banerjee b,* , Nipa Roy b , Dhananjaya Merum b , Jyothi Nallapureddy b , Sang Woo Joo b,* a School of Chemical Engineering, Yeungnam University, Gyeongsan 38541, Republic of Korea b School of Mechanical Engineering, Yeungnam University, Gyeongsan 38541, Republic of Korea A R T I C L E INFO Keywords: NiMn-MOF Intercalation pseudocapacitance 2D layered structure Fast ion-diffusion Asymmetric supercapacitors ABSTRACT 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 pseudocapa- citance. 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 acti- vated 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. 1. Introduction Currently, rapid research is being performed on effective energy storage devices due to the fast growth in energy demand. Particularly, supercapacitors (SCs) have emerged as one of the potential energy storage devices with quick recharge capabilities and high energy den- sities [1,2]. To improve electrochemical performance, it is important to rationally design new structures and develop new materials with high surface area. Electrode materials with high surface areas can reduce the hydroxyl ion (OH  ) diffusion pathways, thus increasing charge storage [3]. Although SCs exhibit higher power density and outstanding rate performance due to the electrochemical double layer capacitance (EDLC) and surface Faradaic redox pseudocapacitance (both of which are mainly manifested by surface-controlled charge storage mecha- nism), their corresponding energy density is quite low compared to conventional batteries (like Li-ion, Na/K-ion, Ni-Cd, Pd-acid, Ni-MH batteries, etc.). On the other hand, due to the sluggish diffusion- controlled mechanism of ion insertion into the bulk of the active ma- terial, the rate performance of batteries (which follow the three main charge storage mechanisms of alloying, conversion, and intercalation) is found to be unusually low, although their energy density is much higher than SCs. Recently, a new type of electrochemical energy storage mechanism has evolved where the active ions are intercalated within the bulk (internal structure) of the active electrode through a diffusion- controlled process. Yet, instead of sluggish battery-type intercalation, rapid intercalation of ions into the redox-active inner sites occurs, fol- lowed by fast Faradaic charge transfer, resulting in pseudocapacitive * Corresponding authors. E-mail addresses: arghya@ynu.ac.kr (A. Narayan Banerjee), swjoo@yu.ac.kr (S. Woo Joo). Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej https://doi.org/10.1016/j.cej.2024.155240 Received 7 June 2024; Received in revised form 20 August 2024; Accepted 26 August 2024 Chemical Engineering Journal 498 (2024) 155240 Available online 1 September 2024 1385-8947/© 2024 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.