rGO Functionalized with a Highly Electronegative Keplerate‐Type Polyoxometalate for High‐Energy‐Density Aqueous Asymmetric Supercapacitors

Abstract

Keplerate-type polyoxometalates represent a large series of high nuclear molecular clusters; for example, (NH ) [Mo Mo O (CH COO) (H O) ] ({Mo }) is a kind of spherical heteropoly blue with a large overall negative charge and an electron density and topological structure similar to C . {Mo } is a good bifunctional material that can be used as an electron acceptor or donor, which is advantageous to accelerate electron transmission in supercapacitors. Herein, a nanocomposite of rGO functionalized with a Keplerate-type polyoxometalate {Mo } was prepared by a facile chemical reduction method and used to construct supercapacitors for the first time. The electrochemical performance of the supercapacitors can be significantly improved due to the excellent redox properties, high electronegativity, and hollow porous structures of {Mo }, in addition to the outstanding conductivity of rGO. The {Mo }-rGO nanocomposite electrode exhibited an excellent gravimetric specific capacitance of 617.3 F g at a current density of 5 A g in 1 m Li SO electrolyte. An aqueous asymmetric supercapacitor with a voltage range of 2.1 V, with the {Mo }-rGO nanocomposite as the negative electrode and modified activated carbon as the positive electrode, exhibited a high energy density of 31.6 Wh kg with a power density of 207.7 W kg and favorable cycling stability.

Redox‐Mediator‐Enhanced Electrochemical Capacitors: Recent Advances and Future Perspectives

“…The third strategy is to attach redox mediators to the electrode materials through covalent or non‐covalent binding . The easiest method is immersing the electrode materials, always carbons, into the solution containing the redox mediators for several hours.…”

“…Organic mediators, such as, anthraquinone, alizarin, and even metal complexes (e.g., K 3 [Fe(CN) 6 ]) are successfully adsorbed into the pores of carbons with the help of π–π and electrostatic interactions. Metal oxide clusters, such as phosphotungstate and phosphomolybdate, are also combined with graphene and polymers materials by mixing and sonicating . Hydrothermal treatments also can decorate redox mediator on carbons .…”

“…The third strategy is to attach redox mediators to the electrode materials through covalento rn on-covalentb inding. [87][88][89][90][91][92][93][94][95][96][97][98][99][100][101] The easiest method is immersing the electrode materials, always carbons, into the solution containing the redox mediators for several hours.O rganicm ediators, such as, anthraquinone, [87] alizarin, [88] and even metal complexes (e.g., K 3 [Fe(CN) 6 ]) [89] are successfully adsorbed into the pores of carbons with the help of p-p and electrostatic interactions. Metal oxide clusters, such as phosphotungstate and phosphomolybdate, are also combined with graphene and polymers materials by mixinga nd sonicating.…”

“…Metal oxide clusters, such as phosphotungstate and phosphomolybdate, are also combined with graphene and polymers materials by mixinga nd sonicating. [90][91][92] Hydrothermal treatments also can decorate redoxm ediatoro nc arbons. [93] Electropolymerization is mainly used to modify polymer materials with redoxactive polymers.…”

Proton-Conducting Polyoxometalates as Redox Electrolytes Synergistically Boosting the Performance of Self-Healing Solid-State Supercapacitors with Polyaniline

“…[8][9][10] According to the equation E = 1/2 CV 2 , 11 the energy density can be improved by increasing the capacitance of SCs. 12 To increase the SCs capacitance, a few investigations have been conducted on the design of electrode materials with hierarchical porous structure or introduced heteroatoms. [13][14][15] However, so far, the performance of SCs using traditional electrolytes is still much lower than their theoretical capacity.…”