Electrochemical Oxidation Of Graphite Research Articles

Graphene-Based Electrochemical Sensing Platform for Rapid and Selective Ferulic Acid Quantification

Due to the multitude of physiological functions, ferulic acid (FA) has a wide range of applications in the food, cosmetic, and pharmaceutical industries. Thus, the development of rapid, sensitive, and selective detection tools for its assay is of great interest. This study reports a new electroanalytical approach for the quantification of ferulic acid in commercial pharmaceutical samples using a sulphur-doped graphene-based electrochemical sensing platform. The few-layer graphene material (exf-SGR) was prepared by the electrochemical oxidation of graphite, at a low applied bias (5 V), in an inorganic salt mixture of Na2S2O3/(NH4)2SO4 (0.3 M each). According to the morpho-structural characterization of the material, it appears to have a high heteroatom doping degree, as proved by the presence of sulphur lines in the XRD pattern, and the C/S ratio was determined by XPS investigations to be 11.57. The electrochemical performances of a glassy carbon electrode modified with the exf-SGR toward FA detection were tested by cyclic voltammetry in both standard laboratory solutions and real sample analysis. The developed modified electrode showed a low limit of detection (30.3 nM) and excellent stability and reproducibility, proving its potential applicability as a viable solution in FA qualitative and quantitative analysis.

Electrochemical Formation of a Covalent–Ionic Stage-1 Graphite Intercalation Compound with Trifluoroacetic Acid

A pure stage-1 graphite intercalation compound (GIC) has been prepared by the electrochemical oxidation of graphite in trifluoroacetic acid (CF3COOH). During the CF3COOH-GIC formation, covalent as well as ionic bonds between the trifluoroacetic acid and graphite layers are formed. Electrochemical reduction of the stage-1 GIC leads to the deintercalation of ionically bonded intercalate, yielding the stage-2 covalent GIC. The interlayer spacing is 8.10 Å for stage-1 and 11.62 Å for stage-2 GIC. Further electrochemical oxidation of stage-1 CF3COOH-GIC does not lead to the exfoliation of the GIC product, and the GIC has relatively high stability in air.

Rapid Synthesis of Yellow Graphite Oxide - One-Step Electrochemical Oxidation of Graphite in Organic Solvents

Graphite oxide is the intermediate in the synthesis of the so-called "miracle material" of the 21st century, graphene. The synthesis of highly oxidized, yellow graphite oxide is hitherto only possible via partially toxic and explosive wet-chemical processes. Therefore, the implementation of the topic graphene in school and university lessons was not possible. Due to the existing risks and the long synthesis time, the currently prevalent synthesis methods of graphite oxide are a major problem not only for teaching but also for scientific research. The authors present a novel electrochemical synthesis process of highly oxidized, yellow graphite oxide, which completely avoids the use of corrosive or toxic substances. The synthesis time is only a few minutes and the preparation of the material can be easily carried out. Therefore, Graphene can now be easily synthesized and taught in school and university.

Effect of preparation conditions on gas permeability and sealing efficiency of graphite foil

Nitrogen permeability of graphite foil (GF) based on expandable graphite with different oxidation degrees was measured. Expandable graphite was obtained by the chemical interaction of graphite and nitric acid with the formation of graphite nitrate of II, III, IV stages and by the electrochemical oxidation of graphite in HNO3 solution followed by water washing. The expandable graphite samples were heat-treated at 800 °C with the formation of exfoliated graphite followed by pressing the exfoliated graphite into GF. The samples of exfoliated graphite and graphite foil were investigated by XRD, SEM, Raman spectroscopy and mercury porosimetry methods. GF nitrogen permeance decreases from 19.7 × 10−10 to 6.7 × 10−10 mol m−2 s−1 Pa−1 with decreasing a stage number of graphite nitrate from IV to II. Gas permeance of GF based on electrochemical expandable graphite decreases by an order of magnitude up to 0.2 × 10−10 mol m−2 s−1 Pa−1 in comparison with GF based on graphite nitrate of II stage. Thus, it is possible to produce the graphite foil material with a wide range of permeability and, respectively, the different sealing efficiency by varying the oxidation degree of the initial graphite matrix in the step of obtaining graphite intercalation compounds and expandable graphite.

Impacts of Kaolin on the Thermal and Electrochemical Properties of Ternary Eutectic Molten Carbonate Electrolyte in the Direct Carbon Fuel Cell (DCFC)

Coal is the second largest energy resource used for electricity production in the world and is expected remain unchanged through 2030. The main problem of using coal in conventional combustion power plants is serious environmental pollution due to CO2 emissions. In this context, electrochemical conversion of solid carbon to generate electricity is one of the most efficient technologies using liquid electrolyte at high temperature which is environmentally friendly. Raw coal as a fuel has some advantages and disadvantages in terms of mineral impurities inhabited in the coal which affect the DCFC performance. Kaolin is a common mineral found in coal fuels which has an advantage over other impurities. It was demonstrated that clay impurities in the coal such as kaolin and montmorillonite react catalytically to enhance graphite oxidation in a half-cell set up DCFC and improve the cell performance [1]. Although other impurities such as alumina, anatase and pyrite have limited impacts on the electrochemical oxidation of graphite, quartz was presented a decline in the current density of electro-oxidation of graphite. Thermal investigation of different coal impurities into ternary eutectic carbonate mixture has been done to show the impacts of these impurities on the melting process and kinetics of the melting process [2]. However it isn’t obvious yet what the impacts of these impurities have on the electrochemical performance of the cell and which disruption or modification will happen with addition of them on eutectic carbonate mixtures. In this work different ratios of kaolinite mineral were purposely added to the ternary eutectic carbonate electrolyte to investigate the thermal properties of the mixture and its melting behaviour. Particularly, DTA data were analysed in terms of changing melting temperature of the mixture and the determination of activation energy using different heating rates to asses these effects. The effect of kaolinite on the half-cell performance of a DCFC was also examined by adding kaolinite with different ratios into the eutectic carbonate electrolyte. The OCP, current density and polarization performance have been measured for the half-cell set up and results compared for different ratios of kaolinite and pure eutectic. Reference: 1-Tulloch, J.; Allen, J.; Wibberley, L.; Donne, S. et al. Influence of selected coal contaminants on graphitic carbon electro-oxidation for application to the direct carbon fuel cell. J. Power Sources 2014, 260,140−14910.1016/j.jpowsour.2014.03.026 2-M.J. Glenn, J.A. Allen, S.W. Donne Thermal investigation of a doped alkali-metal carbonate ternary eutectic for direct carbon fuel cell applications Energy Fuels, 29 (8) (2015), pp. 5423-5433

Graphene-Based Electrocatalysts to Boost Electrocatalytic Reduction of Oxygen in Bioelectrochemical Systems

Microbial fuel cells (MFCs) can be considered as an efficient and flexible platform for integrated waste treatment and energy recovery [1]. The extensive research work devoted to this technology over the past decade demonstrates the promising outlook of MFCs, but practical application is still limited by the high costs associated to the materials used for device assembly, such as cathode materials which accounts for over 50% of the overall MFC capital cost. The sluggish kinetics of oxygen reduction reaction (ORR) has led to the use of expensive catalysts, such as platinum, which is not suitable to be applied to sustainable technologies. Hence, a great variety of materials have been developed for MFC cathodes, including nitrogen-doped activated carbons and non platinum group metal catalysts. Such materials allow achieving ORR rate comparable to Pt, the morphology and structure of the catalysts playing an important role on the efficiency and durability of ORR active sites [2,3]. The development of new carbon nanostructures with highly tunable morphology and structure has led to the use of graphene for several applications, including as component for MFC cathodes [4,5]. However, challenges, such as complexity in synthesis and costs, still limit the applicability of graphene as cathode component of MFCs. Therefore, a facile and efficient approach to develop graphene based catalysts can be considered a promising direction to achieve sustainable wastewater treatment and bioenergy production by BESs. In this work, we report a facile method for large-scale preparation of ORR catalysts based on graphene oxide (GO) obtained by electrochemical oxidation of graphite in aqueous solutions of inorganic salts. We developed different strategies to include nitrogen functionalities in GO structure, including post treatments based on annealing with ammonia gas and one-step nitrogen-doping of GO. By combining the use of atomic force microscopy with electrochemical and spectroscopic techniques, we correlated the different morphology and surface chemistry of GO with catalytic activity towards ORR. Differences in catalytic activity obtained by supporting iron on GO surface were also elucidated, investigating the nature of ORR active sites. The applicability of GO-based materials as ORR cathodes of MFCs was evaluated by assembling single chamber air-cathodes MFCs operating with sodium acetate in phosphate buffer solution. Coulombic efficiency, polarization and power density curves, and voltage generation cycles over time were acquired. The body of results demonstrated the potential ability of GO electrocatalysts to substitute platinum for ORR in MFCs. Acknowledgements. The present work was carried out with the support of the “European Union's Horizon 2020 research and innovation programme” (under H2020-FTIPilot-2015-1, Grant Agreement n. 720367-GREENERNET), the University of Rome Tor Vergata (under the Research Call “Consolidate the Foundations”, project name: BEST WATER), and CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil. References. [1] A. Rinaldi, B. Mecheri, V. Garavaglia, S. Licoccia, P. Di Nardo, E.Traversa. Energ. Environ. Sci., 1 (2008) 417-429. [2] C. Santoro, A. Serov, L. Stariha, M. Kodali, J. Gordon, S. Babanova, O. Bretschger, K. Artyushkova, P. Atanassov, Energ. Environ. Sci. 9 (2016) 2346-2353. [3] A. Iannaci, B. Mecheri, A. D'Epifanio, M. J. Lázaro Elorri, S. Licoccia. Int J Hydrogen Energ. 41 (2016) 19637-19644. [4] H. Yuan, Z. He. Nanoscale 7 (2015) 7022-7029. [5] K. Parvez, S. Yang, Y. Hernandez, A. Winter, A. Turchanin, X. Feng, K. Müllen. ACS Nano. 6 (2012) 9541-9550.

Graphene oxide nanoplatforms to enhance catalytic performance of iron phthalocyanine for oxygen reduction reaction in bioelectrochemical systems

Abstract We report the development of electrocatalysts based on iron phthalocyanine (FePc) supported on graphene oxide (GO), obtained by electrochemical oxidation of graphite in aqueous solution of LiCl, LiClO4, and NaClO4. Structure, surface chemistry, morphology, and thermal stability of the prepared materials were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, atomic force microscopy (AFM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The catalytic activity toward oxygen reduction reaction (ORR) at neutral pH was evaluated by cyclic voltammetry. The experimental results demonstrate that the oxidation degree of GO supports affects the overall catalytic activity of FePc/GO, due to a modulation effect of the interaction between FePc and the basal plane of GO. On the basis of electrochemical, spectroscopic, and morphological investigations, FePc/GO_LiCl was selected to be assembled at the cathode side of a microbial fuel cell prototype, demonstrating a good electrochemical performance in terms of voltage and power generation.

Electrochemical oxidation of graphite in aqueous hydrofluoric acid solution at high current densities

Abstract Electrochemical oxidation of graphite was performed at high current densities in 47% HF aqueous solution. Cyclic voltammetry indicated that covalent C F bonding formed above 2.4 V vs Pb/PbF2. The sample obtained at higher current densities than 200 mA cm−2 was stage 1 type material with an interlayer spacing of 0.55 nm and it contained a considerable amount of oxygen, together with the covalently bonded fluorine. The discharge profile of this sample as a cathode of lithium primary battery was similar to that of C2.5F prepared under F2 gas atmosphere and the capacity reached 550 mAh g−1. This strongly indicated that not only fluorine but also oxygen in this sample was utilized.

Modulation of electrochemical property of carbon nanodot by post-chemical reductions

Abstract Influences of chemical reductions on the electrochemical properties of carbon nanodots (CNDs) were investigated. Sequential electron transfer reactions involving CNDs and several electrochromic molecules were analyzed by titration method to deduce electron accepting capabilities and upper-limit reduction potentials. CNDs prepared by alkali-assisted electrochemical oxidation of graphite were reduced by either sodium borohydride or hydrazine to obtain chemically reduced CNDs. Titration analysis of the electron transfer reactions involving methylviologen cation radicals and CNDs revealed that electron uptake per unit weight of CND increased nearly 30% after chemical reductions. Furthermore, detailed analyses of electron discharge processes involving the electron-filled CNDs and several leuco dyes provided fine estimation of upper-limit reduction potential and evidence of reduction potential shifts of CNDs to negative level by chemical reductions.

Molten Carbonate Composition Effects on Carbon Electro-Oxidation at a Solid Anode Interface

The electrochemical oxidation of graphite is investigated to determine the relative influence of the composition of a molten carbonate electrolyte on a solid anode. The binary eutectics of sodium, lithium and potassium carbonates were investigated as well as ternary mixtures including the eutectic and combinations of systematically varied lithium content. It was seen that the combination of cations included in the carbonate melt can influence the electrochemical performance of graphite with binary combinations performing better than ternary in all cases. Very little change in the mechanistic behavior was observed through tafel analysis; instead it is proposed that the observed kinetic effects are a combination of the catalytic role of all metal cations present as well as the intercalation of lithium into the solid graphite electrode. The effect of lithium intercalation is suggested to lead to a change in the graphite surface polarity which affects product gas bubble formation and dislodgement at the solid anode. Increased lithium concentration, and it is assumed intercalation, encourages smaller bubbles to form which are dislodged at a faster rate than surfaces with less lithium intercalation in the ternary electrolyte. A threshold lithium concentration is reached above approximately 65 % where the electrochemical behavior is significantly changed and bubble formation behavior is no longer observed.

Influence of selected coal contaminants on graphitic carbon electro-oxidation for application to the direct carbon fuel cell

A novel method examining the fundamental electrochemical behaviour of carbon is outlined here involving the use of a half cell set-up and solid sacrificial anode. Using this method, electrochemical oxidation of graphite is assessed using selective contamination of a graphite electrode with major coal contaminants identified in selected Australian black coals using X-ray diffraction. Contaminants identified include anatase, alumina, pyrite, quartz, kaolin and montmorillonite. From the systematic introduction of these contaminants it is shown that clay materials, such as kaolin and montmorillonite, act catalytically to increase the rate of graphite oxidation. Metal oxides and sulfides such as anatase, alumina and pyrite give a limited increase in the normalised current, whereas quartz gives a significant decrease in performance. This demonstrates a clear effect of the solid phase interaction of these contaminants on the electrochemical oxidation of graphite since the same effect is not observed when the contaminants are added instead to the molten carbonate electrolyte.

Electrochemical oxidation of graphite in an intermediate temperature direct carbon fuel cell based on two-phases electrolyte

As a promising intermediate temperature fuel cell, Direct Carbon Fuel Cell (DCFC) with composite electrolyte composed of Samarium-Doped Ceria (SDC) and a binary carbonate phase (67 mol% Li2CO3/33 mol% Na2CO3) has a much higher efficiency compared with conventional power suppliers. In the present work, SDC powder has been synthesized by an oxalate co-precipitation process and used as solid support matrix for the composite electrolyte. Single cell with composite electrolyte layer is fabricated by a dry-pressing technique using LiNiO2/Li2Na2CO3/SDC as cathode and 1:9 (weight ratio) graphite mixture with 67 mol% Li2CO3/33 mol% Na2CO3 molten carbonate as anode. The cell is tested at 600–750 °C using electrolytical graphite mixture as fuel and O2/CO2 mixture as oxidant. A relatively good performance with high power density of 58 mW cm−2 at 700 °C is achieved for a DCFC using 0.8 mm thick composite electrolyte layer. The sensibility of the 1 cm2 DCFC single cell performance to the anode gas nature is also investigated. At temperatures higher than 700 °C, both carbon (C) and carbon monoxide (CO) can be considered as reacting fuel for the DCFC system.

Expandable graphite modification by boric acid

Abstract

Water‐Soluble Fluorescent Carbon Quantum Dots and Photocatalyst Design

Carbon nanostructures are attracting intense interest because of their many unique and novel properties. The strong and tunable luminescence of carbon materials further enhances their versatile properties; in particular, the quantum effect in carbon is extremely important both fundamentally and technologically. Recently, photoluminescent carbonbased nanoparticles have received much attention. They are usually prepared by laser ablation of graphite, electrochemical oxidation of graphite, electrochemical soaking of carbon nanotubes, thermal oxidation of suitable molecular precursors, vapor deposition of soot, proton-beam irradiation of nanodiamonds, microwave synthesis, and bottom-up methods. Although small (ca. 2 nm) graphite nanoparticles show strong blue photoluminescence (PL), definitive experimental evidence for luminescence of carbon structure arising from quantum-confinement effects and size-dependent optical properties of carbon quantum dots (CQDs) remains scarce. Herein, we report the facile one-step alkali-assisted electrochemical fabrication of CQDs with sizes of 1.2– 3.8 nm which possess size-dependent photoluminescence (PL) and excellent upconversion luminescence properties. Significantly, we demonstrate the design of photocatalysts (TiO2/CQDs and SiO2/CQDs complex system) to harness the use of the full spectrum of sunlight (based on the upconversion luminescence properties of CQDs). It can be imagined that judicious cutting of a graphite honeycomb layer into ultrasmall particles can lead to tiny fragments of graphite, yielding CQDs, which may offer a straightforward and facile strategy to prepare high-quality CQDs. Using graphite rods as both anode and cathode, and NaOH/EtOH as electrolyte, we synthesized CQDs with a current intensity of 10–200 mAcm . As a reference, a series of control experiments using acids (e.g. H2SO4/EtOH) as electrolyte yielded no formation of CQDs. This result indicates that alkaline environment is the key factor, and OH group is essential for the formation of CQDs by the electrochemical oxidation process. Figure 1a shows a trans-

The first graphite intercalation compounds containing tris(pentafluoroethyl)trifluorophosphate

Graphite intercalation compounds (GICs) containing the tris(pentafluoroethyl)trifluorophosphate anion, [(C 2F 5) 3PF 3] − are prepared for the first time by electrochemical oxidation of graphite in a nitromethane electrolyte. Powder X-ray diffraction (PXRD) data indicate that products are of stages 2–4 with gallery heights of 0.82–0.86 nm. Intercalate orientation is determined by using a structure model containing an energy minimized anion. GIC compositional parameters are obtained by microwave digestion followed by F elemental analysis, in combination with thermogravimetric analyses.

Electrochemical preparation of graphite intercalation compounds containing a cyclic amide, [CF 2(CF 2SO 2) 2N] −

Graphite intercalation compounds (GICs) containing the cyclo-hexafluoropropane-1,3-bis(sulfonyl)amide anion, [CF 2(CF 2SO 2) 2N] −, are prepared for the first time. Stages 2 and 3 GICs are obtained by electrochemical oxidation of graphite in a nitromethane electrolyte. Gallery heights of 0.85–0.86 nm are determined by powder X-ray diffraction, and the intercalate anion orientation within the intercalate galleries is modeled using an energy minimized anion structure. GIC compositions are determined by thermogravimetric, fluorine and nitrogen analyses. The chemical preparation and bifluoride displacement reactions are compared with a GIC containing the linear bis(trifluoromethanesulfonyl)amide anion, [(CF 3SO 2) 2N] −.

Chemical and electrochemical syntheses of a graphite fluoro-tris(pentafluoroethyl)borate intercalation compound

Graphite intercalation compounds (GICs) of composition C x [FB(C 2F 5) 3] · δF are prepared for the first time by the intercalation of fluoro-tris(pentafluoroethyl)borate anion, [FB(C 2F 5) 3] − , under ambient conditions in 48% hydrofluoric acid containing the oxidant K 2[MnF 6]. Powder XRD data indicate that products are of mixed stages 2 and 3 after reactions for 1–20 h, with a gallery height of 0.87 nm. The intercalate orientation is modeled using an energy-minimized anion structure. Microwave digestion followed by B and F elemental analyses, along with thermogravimetric analyses provide compositional x and δ parameters for the GICs obtained. In addition, C x [FB(C 2F 5) 3] · δCH 3NO 2 with stage 2 is prepared by electrochemical oxidation of graphite in a nitromethane solution and characterized as above.

Preparation, structure and reduction of graphite intercalation compounds with hexachloroplatinic acid

Electrochemical oxidation and exchange intercalation, have been used for the production of graphite intercalation compounds (GICs) with hexachloroplatinic acid. Ternary GICs H 2PtCl 6–HNO 3–graphite and H 2PtCl 6–H 2SO 4–graphite have been synthesized by the incomplete exchange reaction between the parent HNO 3 and H 2SO 4 GICs and hexachloroplatinic acid. Irrespective of the precursor GIC stage, stage-2 GIC with H 2PtCl 6 has been obtained. Attempted synthesis of the single-phase stage-2 GIC via the electrochemical oxidation of graphite in H 2PtCl 6 solutions failed since mixtures of the target products with pure graphite have resulted in all cases. The structure and properties of the samples obtained have been examined by XRD, SEM, TG-DTG, TG coupled with FTIR and EXAFS-XANES. GIC samples were preheated to 200 °C to produce exfoliation (caused by deintercalation of nitric acid), and reduced either with boiling 5% aqueous formaldehyde or hydrogen. This approach gives rise to exfoliated graphite material with platinum nanoclusters distributed on the surface. In contrast to the most other work particles with open surfaces were obtained.

Electrochemical synthesis and physical–chemical characterization of the low-oxidized graphite fluoroxide materials

A process of anodic oxidation of purified natural graphite in aqueous 11–45% HF solutions has been studied at constant voltages 5–7 V. New types of low-oxidized graphite fluoroxide materials (FOG-E) were isolated, prepared under electrochemical synthesis conditions only. Electrochemical oxidation of graphite should include in a first step the reaction of evolving oxygen and O-containing groups with surface carbon atoms on graphite particles and a subsequent formation of C–OH bonds, and in a second step, a partial substitution of the latter groups into C–F groups. Chemical and physical–chemical study of FOG-E showed that they are multiphasic materials. The low-oxidized graphite fluoroxide materials are excellent precursors for the preparation of thermally expanded graphite (TEG).

Preparation of a Graphite Bis(perfluoropinacolato)borate Intercalation Compound

The electrochemical oxidation of graphite in a nitromethane solution containing the (perfluoropinacolato)borate anion, produces a new acceptor-type graphite intercalation compound (GIC). Stage 1-3 GICs are obtained and characterized by electrochemical methods and powder X-ray diffraction. The gallery height, of 14.0-14.5 Å indicates a single intercalate layer between graphene sheets. The GICs are produced at higher charge efficiency and are more oxidatively stable than the previously reported intercalation of from this solvent. The GICs are more stable to ambient exposure than most acceptor-type GICs; even the stage 1 material will persist in air for several hours. © 2003 The Electrochemical Society. All rights reserved.