Catechol-modified activated carbon prepared by the diazonium chemistry for application as active electrode material in electrochemical capacitor

Unveiling the Role of Electrografted Carbon-Based Electrodes for Vanadium Redox Flow Batteries

Carbon-based electrodes are used in flow batteries to provide active centers for vanadium redox reactions. However, strong controversy exists about the exact origin of these centers. This study systematically explores the influence of structural and functional groups on the vanadium redox reactions at carbon surfaces. Pyridine, phenol and butyl containing groups are attached to carbon felt electrodes. To establish a unique comparison between the model and real-world behavior, both non-activated and commercially used thermally activated felts serve as a substrate. Results reveal enhanced half-cell performance in non-activated felt with introduced hydrophilic functionalities. However, this cannot be transferred to the thermally activated felt. Beyond a decrease in electrochemical activity, a reduced long-term stability can be observed. This work indicates that thermal treatment generates active sites that surpass the effect of functional groups and are even impeded by their introduction.

Facile preparation of covalently functionalized graphene with 2,4-dinitrophenylhydrazine and investigation of its characteristics

This article reports a fast and easy method for simultaneously in situ reducing and functionalizing graphene oxide. 2,4-Dinitrophenylhydrazine hydrate salt molecules are reduced by graphene oxide by reacting with oxide groups on the surface and removing these groups, and 2,4-dinitrophenylhydrazone groups are replaced with oxide groups. The synthesized materials have been investigated using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and UV absorption. Also, the morphology has been examined with a scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) analysis. The result of the photocurrent response and electrochemical behavior of the samples through cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) have been analyzed to investigate the effect of physical and chemical changes compared to graphene.

Barium 5-(tert-butyl)-2,3-dihydroxybenzenesulfonate

Catechols and their derivatives attract great scientific interest due to the broad spectrum of their functional properties, including complexation, redox behavior, association ability and antioxidant activity. Because of the low molecular mass and two-electron redox process, they are considered to be a promising energy storage compound in different types of electrochemical power sources, such as metal-ion batteries or redox flow batteries. Herein, we report a preparation of the sterically hindered sulfonated catechol, namely the barium salt of 5-(tert-butyl)-2,3-dihydroxybenzenesulfonic acid, by the direct sulfonation of 4-tert-butylcatechol, by concentrated sulfuric acid. The proposed procedure is green and atom-economic, providing the desired product in high yield after simple purification. The solvent-free procedure is inexpensive and highly scalable, which enables direct industrial production of the title product. The resulting product was characterized by the 1H and 13C nuclear magnetic resonance (NMR) and ESI-high resolution mass spectrometry (ESI-HRMS).

Covalent functionalization of carbon materials with redox-active organic molecules for energy storage

Carbon-based materials (CBMs) have shown great versatility because they can be chemically combined with other materials for various applications. Chemical modification of CBMs can be achieved via covalent or non-covalent interactions. Non-covalent interactions are weak and fragile, causing structural change and molecule dissociation. Therefore, in this review, we summarize the covalent modification of CBMs via organic chemistry techniques, aiming at forming more robust and stable CBMs. Besides, their application as electrode materials in energy storage systems is also within the scope of this review. Covalent binding of redox-active organic molecules with CBMs improves the transfer rate of electrons and prevents the dissolution of redox-active molecules, resulting in good conductivity and cycle life. Numerous papers on the functionalization of CBMs have been published to date, but some of them lack scientific evidence and are unable to understand from chemistry viewpoint. Reliable articles with adequate evidence are summarized in this review from a synthetic chemistry viewpoint.

Composites and Copolymers Containing Redox-Active Molecules and Intrinsically Conducting Polymers as Active Masses for Supercapacitor Electrodes—An Introduction

In this introductory report, composites and copolymers combining intrinsically conducting polymers and redox-active organic molecules, suggested as active masses without additional binder and conducting agents for supercapacitor electrodes, possibly using the advantageous properties of both constituents, are presented. A brief overview of the few reported examples of the use of such copolymers, composites, and comparable combinations of organic molecules and carbon supports is given. For comparison a few related reports on similar materials without intrinsically conducting polymers are included.

Facile Electrochemical Demethylation of 2-Methoxyphenol to Surface-Confined Catechol on the MWCNT and Its Efficient Electrocatalytic Hydrazine Oxidation and Sensing Applications

Owing to its biological significance, preparation of stable surface-confined catechol (CA) is a long-standing interest in electrochemistry and surface chemistry. In this connection, various chemical approaches such as covalent immobilization (using amine- and carboxylate-functionalized CA, diazotization-based coupling, and Michael addition reaction), self-assembled monolayer on gold (thiol-functionalized CA is assembled on the gold surface), CA adsorption on the ad-layer of a defect-free single-crystal Pt surface, π-π bonding, CA pendant metal complexes, and CA-functionalized polymer-modified electrodes have been reported in the literature. In general, these conventional methods are involved with a series of time-consuming synthetic procedures. Indeed, the preparation of a surface-fouling-free surface-confined system is a challenging task. Herein, we introduce a new and facile approach based on electrochemical demethylation of 2-methoxyphenol as a precursor on the graphitic surface (MWCNT) at a bias potential, 0.5 V vs Ag/AgCl in neutral pH solution. Such an electrochemical performance resulted in the development of a stable and well-defined redox peak at E ^o' = 0.15 (A2/C2) V vs Ag/AgCl within 10 min of preparation time in pH 7 phosphate buffer solution. Calculated surface excess (16.65 × 10^-9 mol cm^-2) is about 10-1000 times higher than the values reported with other preparation methods. The product (catechol) formed on the modified electrode was confirmed by collective electrochemical and physicochemical characterizations such as potential segment analysis, TEM, Raman, IR, UV-vis, GC-MS, and NMR spectroscopic techniques, and thin-layer chromatographic studies. The electrocatalytic efficiency of the surface-confined CA system was demonstrated by studying hydrazine oxidation and sensing reactions in a neutral pH solution. This new system is found to be tolerant to various interfering biochemicals such as uric acid, xanthine, hypoxanthine, glucose, nitrate, hydrogen peroxide, ascorbic acid, Cu²⁺, and Fe²⁺. Since the approach is simple, rapid, and reproducible, a variety of surface-confined CA systems can be prepared.

Large Capacity Enhancement of Carbon Electrodes by Solution Processing for High Density Energy Storage

An inexpensive, solution phase modification of flat carbon electrodes by electrochemical reactions of a 1,8-diaminonaphthalene derivative results in a 120- to 700-fold increase in capacity by formation of a 15-22 nm thick organic film. Modification of high surface area carbon electrodes with the same protocol resulted in a 12- to 82-fold increase in capacity. The modification layer contains 9-15% nitrogen present as -NH- redox centers that result in a large Faradaic component involving one H⁺ ion for each electron. The electrodes showed no capacity loss after prolonged cycling in 0.1 M H₂SO₄ and exhibited significantly higher charge density than similar reported electrodes based on graphene and polyaniline. Investigation of the deposition conditions revealed that N-doped oligomeric ribbons are formed both by diazonium ion reduction and diaminonaphthalene oxidation, and the 1,8 isomer is essential for the large capacity increases. The capacity increase has at least three contributions: increased microscopic surface area from ribbon formation, Faradaic reactions of nitrogen-containing redox centers, and changes in ribbon conductivity resulting from polaron formation. An aqueous fabrication process was developed which both increased capacity and improved stability and was amenable to industrial production. The high charge density, low-cost fabrication, and <25 nm thickness of the diaminonaphthalene-derived films should prove attractive toward practical application on both flat surfaces and in high surface area carbon electrodes.

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

Supercapacitors deliver exceptional power densities, high cycling stability, and inherent safety but suffer from low energy densities. Many methods to enhance the energy density are based on exploring electrode materials with well-developed structures and designing asymmetric systems with wide voltage windows. The energy density is substantially enhanced at the compromise of power density by utilizing the sluggish kinetics of pseudocapacitive materials. Redox-active electrolytes can contribute additional pseudocapacitance from the reactions of redox mediators at the interface, which have attracted increasing attention of researchers. Redox-mediator-enhanced supercapacitors deliver high energy densities while retaining high power densities. This Minireview highlights the recently prominent progresses of single-, dual-, and ambipolar-redox-mediator-enhanced supercapacitors, the challenges they face, and approaches to suppress self-discharge and develop high-concentration redox-active electrolytes for performance promotion.

Effects of Nanoporous Carbon Derived from Microalgae and Its CoO Composite on Capacitance

Nanoporous carbon was synthesized from microalgae as a promising electrode material for electric double layer capacitors due to its large specific surface area and controllable pore structures. The pore textural properties of the algae-derived-carbon (ADC) samples were measured by N₂ adsorption and desorption at 77 K. The performance of the activated carbon (AC) as supercapacitor electrodes was determined by the cyclic voltammetry and galvanostatic charge/discharge tests. The effect of the nanoporous carbon structure on capacitance was demonstrated by calculating the contributions of micropores and mesopores toward capacitance. Capacitance was significantly affected by both pore size and pore depth. To further increase the specific capacity, a single-pot synthesis of porous carbon supported CoO composite (CoO/ADC) electrode material was developed using microalgae as the carbon source and Co(OH)₂ as both a carbon activation agent and CoO precursor. After carbonization, CoO particles were formed and embedded in the ADC matrix. The synergic contributions from the combined CoO and ADC resulted in better supercapacitor performance as compared to that of the pure CoO electrode. The calculated specific capacities of CoO/ADC were 387 and 189 C g^-1 at 0.2 and 5 A g^-1, respectively, which were far more than the capacities of pure CoO electrode (185 C g^-1 at 0.2 A g^-1 and 77 C g^-1 at 5 A g^-1). The cycle stability of CoO/ADC also increased significantly (83% retention of the initial capacity for CoO/ADC vs 63% for pure CoO). This research had developed a viable and promising solution for producing composite electrodes in a large quantity for commercial application.

Hierarchical bicontinuous structure of redox-active organic composites and their enhanced electrochemical properties

The hierarchical bicontinuous structure of redox-active organic composites of crystalline quinone derivatives and conductive polymers was generated through simultaneous etching of the crystal and polymerization of the monomer.

Incorporating conjugated carbonyl compounds into carbon nanomaterials as electrode materials for electrochemical energy storage

This review provided an overview of recent progress on composites of conjugated carbonyl compounds and carbon nanomaterials for energy storage.

Diazonium modification of porous graphitic carbon with catechol and amide groups for hydrophilic interaction and attenuated reversed phase liquid chromatography

Porous graphitic carbon (PGC) is an increasingly popular and attractive phase for HPLC on account of its chemical and thermal stability, and its unique separation mechanism. However, native PGC is strongly hydrophobic and in some instances excessively retentive. As part of our effort to build a library of hydrophilic covalently modified PGC phases, we functionalized PGC with catechol and amide groups by means of aryl diazonium chemistry to produce two new phases. Successful grafting was confirmed by X-ray photoelectron spectroscopy (XPS). Under HILIC conditions, the Catechol-PGC showed up to 5-fold increased retention relative to unmodified PGC and selectivity that differed from four other HILIC phases. Under reversed phase conditions, the Amide-PGC reduced the retentivity of PGC by almost 90%. The chromatographic performance of Catechol-PGC and Amide-PGC is demonstrated by separations of nucleobases, nucleosides, phenols, alkaline pharmaceuticals, and performance enhancing stimulants. These compounds had retention factors (k) ranging from 0.5 to 13.