A Redox-Additive Electrolyte and Nanostructured Electrode for Enhanced Supercapacitor Energy Density

Abstract

We demonstrate an ultrahigh energy density asymmetric supercapacitor (ASC) having a novel NiCo(CO 3 )-(OH) 2 nanoneedle positive electrode, Fe 2 O 3 /rGO nanocomposite negative electrode, and advanced potassium ferricyanide (K 3 [Fe-(CN) 6 ])/potassium hydroxide (KOH) electrolyte. The electrode materials were synthesized by a hydrothermal technique. The unique positive electrode was first shown to have a remarkable specific capacitance (C sp ) of 3248.9 F g −1 at 1 A g −1 in an electrolyte containing 0.06 M K 3 [Fe(CN) 6 ] and 3 M KOH. The ASC gives a superior energy density of 84.1 W h kg −1 at a power density of 825 W kg −1 . The findings in this work provide a very promising approach toward the development of high-performance energy storage devices. KEYWORDS: NiCo(CO 3 )(OH) 2 , Fe 2 O 3 /rGO, redox-additive electrolyte, supercapacitor, energy density

Enhanced Electrochemical Performance of Bimetallic Doped Ni-Based Metal–Organic Frameworks by Redox Additives in an Alkaline Electrolyte

“…The mechanism by which the redox additive can enhance the charge storage can be summarized as follows: ,, when the electrode is charged, active materials will be oxidized and M 2+ (Ni 2+ , Cu 2+ , and Zn 2+ ) will lose an electron. The whole electrochemical reaction rate will be accelerated supposing that the M 2+ loses an electron faster and then enhance the charge storage capacity of the electrode material.…”

“…It is well known that an electrolyte is also one of the important components of supercapacitors. − Therefore, another interesting method to improve the specific capacity of the CuZnNi–MOF is to add small quantities of redox additives into the conventional electrolytes. , Recently, many outstanding works have proved that the redox additive K 4 Fe­(CN) 6 can further improve the energy density of supercapacitors, , and adding redox additives into the traditional electrolyte is an easy and low-cost approach to prepare a variety of electrolytes. Thus, the introduction of redox additives into electrolytes has been considered as an efficient and economical method compared with other methods.…”

Ionic Liquid Electrolytes for Electrochemical Energy Storage Devices

“…The specific energy of SCs is proportional to the specific capacitance and the operating potential range [ 20 , 21 ]. Initially, research trends focused on the improvement of non-faradaic electric double layer (EDL) capacitance by adopting electrode active materials, which have large surface areas [ 17 ].…”

Coordination Polymer Derived Porous Carbon Activated in Situ by the ZnCl2 Dot: Capacitances Greatly Enhanced by Redox-Activity Additives in Electrolytes

“…10−12 Between carbon electrodes and electrolytes, fast redox reactions at the interfaces ignite remarkable pseudocapacitances, and the existence of redox couples in electrolytes also reduces the overall resistance, which will further promote the supercapacitive performances. 13 Bearing the above ideas in mind, we used ZnCl 2 to react with 4,4′-bis(imidazol-1-yl)-biphenyl (bibp), and one zinc CP [Zn(bibp)Cl 2 ] ∞ (CP-2-ZX) was obtained. Then, highly porous carbon AC-Zn-CP was generated via direct calcination−thermolysis of CP-2-ZX precursor.…”

“…Even with high porosity, excellent recycling stability, good conductivity, and ecofriendly features, the fatally low capacitance and energy density greatly hinder the widespread application of carbon materials in EDLCs. Thereby, scientists turn their eyes to pseudocapacitances and try the combination of two kinds of supercapacitors. − Different from the composite-electrode strategy, the addition of redox-activity additives into electrolytes is an efficient and ingenious approach to integrate the merits of EDLCs and pseudocapacitors. − Between carbon electrodes and electrolytes, fast redox reactions at the interfaces ignite remarkable pseudocapacitances, and the existence of redox couples in electrolytes also reduces the overall resistance, which will further promote the supercapacitive performances …”