Redox Additive Electrolyte Study of Mn–MOF Electrode for Supercapacitor Applications

Abstract

The selection of appropriate electrode materials and electrolytes in addition to optimization of their combinations is a key to improve the performance of supercapacitors. Among the new electrode materials, metal‐organic frameworks (MOFs) based electrodes are attracting attention in energy storage devices, including supercapacitors and batteries. In recent years, the redox additive electrolytes have been projected as efficient options over simple aqueous electrolytes. The present work reports the synthesis of a layered MOF, i. e., manganese‐1,4‐ benzene dicarboxylate (Mn‐BDC) and explores its utility as a supercapacitor electrode in the presence of an optimized redox additive electrolyte (0.2 M K3[Fe(CN)6] in 1 M Na2SO4 (0.2 M KFCN)). As demonstrated for the first time in this study, the combined use of the porous Mn‐BDC electrode and KFCN electrolyte has provided a synergistic enhancement in the supercapacitor performance. The present Mn‐BDC/KFCN combination has delivered a high specific capacitance of 1590 F/g at a current density of 3 A/g. Furthermore, the Mn‐BDC electrode could retain around 82% of its initial specific capacitance even after 3000 continuous charge‐discharge cycles. In view of its encouraging electrochemical performance parameters, the proposed system can be touted as an efficient supercapacitor assembly.

Exceptional Capacitance Enhancement of a Non‐Conducting COF through Potential‐Driven Chemical Modulation by Redox Electrolyte

“…[ 30 ] Realizing that this COF‐carbon composite requires substantial capacitance enhancement in charge‐storage to qualify for practical usage, we resorted to a redox electrolyte system. [ 20–28 ] Here, we adopted a distinct strategy involving the use of “redox electrolyte.” We choose KI as a redox additive, owing to its exceptionally low toxicity, environmentally benign nature, and mainly for its ability to form a spectrum of redox‐active species. Under the redox potential, KI can generate stable polyiodide ions (I n ) − with different redox pairs of iodide on the surface of the electrode, such as 3I − /I 3 − , 2I − /I 2 , 2I 3 − /3I 2 , and I 2 /2IO 3 .…”

“…Hence, alternatively, a great enhancement of capacitance can be achieved by introducing redox electrolyte instead of the inert electrolyte. [ 19,20 ] The improved performance in such a system is attributed to high‐speed Faradaic reactions, which impart very high pseudo‐capacitance. A variety of redox‐active electrolytes have been employed, such as Cu 2+ (1335 F g −1 a current density of 60 A g −1 ), iodine (685 F g −1 at a scan speed of 1 mV s −1 ), bromine (572 F g −1 at 2 mA cm −2 ), hydroquinone (901 F g −1 at 2.65 mA cm −2 ), methylene blue for hybrid capacitors (279 F g −1 at 0.88 mA cm −2 ).…”

“…We realized these redox‐active supporting electrolytes could gain an immense advantage when allowed to adsorb into the carbon‐activated porous sponge—the COF. A word of caution: In many reports, the capacitance is determined from three‐electrode measurements, [ 6,7,11,12,14–16,18–22,24,29 ] which may not be accurate. The reason being, a capacitance value relies on a potential difference between two electrodes and not the absolute position of one electrode only, which is measured in a three‐electrode system against a reference electrode.…”

Metal‐organic frameworks‐derived titanium dioxide–carbon nanocomposite for supercapacitor applications

“…Nonetheless, a small redox peak also appeared at slow scan rates (1‐5 mV/s) attributed to the copresence of TiO 2 particles as redox‐active species in the electrode material. The appearance of this redox peak also suggested that the selected system should have a high energy density . As such, the present TiO 2 /C‐1000 composite electrode‐based SC has combined EDLC and Faradaic types of charge storage mechanisms to result in a system with features of both high charge storage capacity and their fast deliveries when needed.…”

Effect of Redox Additive Electrolyte on the Electrochemical Performance of MnO2 Nanorods for Supercapacitor Application

“…Recently, redox additive based electrolytes are used to improve the performance of supercapacitor electrode materials by enhancing faradaic redox reactions inside the electrolyte. From previous reports, the addition of 0.1M K 4 [Fe(CN) 6 ] to the usual KOH electrolyte will enhance the specific capacitance tremendously [9].…”