Nanocarbon Electrochemistry and Electroanalysis: Current Status and Future Perspectives

Al-Sehemi A, Alargarsamy S, Gajendran P, Ramachandran R. Development of Different Kinds of Electrocatalyst for the Electrochemical Reduction of Carbon Dioxide Reactions: An Overview

Significant advancements have been made in the development of CO2 reduction processes for applications such as electrosynthesis, energy storage, and environmental remediation. Several materials have demonstrated great potential in achieving high activity and selectivity for the desired reduction products. Nevertheless, these advancements have primarily been limited to small-scale laboratory settings, and the considerable technical obstacles associated with large-scale CO2 reduction have not received sufficient attention. Many of the researchers have been faced with persistent challenges in the catalytic process, primarily stemming from the low Faraday efficiency, high overpotential, and low limiting current density observed in the production of the desired target product. The highlighted materials possess the capability to transform CO2 into various oxygenates, including ethanol, methanol, and formates, as well as hydrocarbons such as methane and ethane. A comprehensive summary of the recent research progress on these discussed types of electrocatalysts is provided, highlighting the detailed examination of their electrocatalytic activity enhancement strategies. This serves as a valuable reference for the development of highly efficient electrocatalysts with different orientations. This review encompasses the latest developments in catalyst materials and cell designs, presenting the leading materials utilized for the conversion of CO2 into various valuable products. Corresponding designs of cells and reactors are also included to provide a comprehensive overview of the advancements in this field.

Highly Occupied Surface States at Deuterium-Grown Boron-Doped Diamond Interfaces for Efficient Photoelectrochemistry

Polycrystalline boron-doped diamond is a promising material for high-power aqueous electrochemical applications in bioanalytics, catalysis, and energy storage. The chemical vapor deposition (CVD) process of diamond formation and doping is totally diversified by using high kinetic energies of deuterium substituting habitually applied hydrogen. The high concentration of deuterium in plasma induces atomic arrangements and steric hindrance during synthesis reactions, which in consequence leads to a preferential (111) texture and more effective boron incorporation into the lattice, reaching a one order of magnitude higher density of charge carriers. This provides the surface reconstruction impacting surficial populations of CC dimers, CH, CO groups, and COOH termination along with enhanced kinetics of their abstraction, as revealed by high-resolution core-level spectroscopies. A series of local densities of states were computed, showing a rich set of highly occupied and localized surface states for samples deposited in deuterium, negating the connotations of band bending. The introduction of enhanced incorporation of boron into (111) facet of diamond leads to the manifestation of surface electronic states below the Fermi level and above the bulk valence band edge. This unique electronic band structure affects the charge transfer kinetics, electron affinity, and diffusion field geometry critical for efficient electrolysis, electrocatalysis, and photoelectrochemistry.

A facile fabrication of ratiometric electrochemical sensor for sensitive detection of riboflavin based on hierarchical porous biochar derived from KOH-activated Soulangeana sepals

Herein, a facile ratiometric electrochemical method was developed for sensitive sensing of riboflavin (RF) based on hierarchical porous biochar (HPB) modified electrode. In this sensing system, the reference paracetamol (PA) was directly added into electrolyte solution without the requirement of complex immobilization process. HPB derived from KOH-activated Soulangeana sepals displays hierarchical porous structure, high specific surface area and rich oxygen-containing functional groups, which is favorable for RF adsorption and enrichment. Besides, the excellent electronic conductivity and superior electrocatalytic activity of HPB can effectively promote the electrooxidation of RF. Moreover, the dual-signal strategy greatly improves the reproducibility and reliability of electrochemical detection. Based on the proposed ratiometric sensing platform, the sensor exhibits a wider linear range of 0.0007-10μM and a lower limit of detection of 0.2 nM. The method also presents good selectivity and has been applied to the determination of RF in milk samples with satisfactory results.

Carbon-Supported Noble-Metal Nanoparticles for Catalytic Applications—A Review

Noble-metal nanoparticles (NMNPs), with their outstanding properties, have been arousing the interest of scientists for centuries. Although our knowledge of them is much more significant today, and we can obtain NMNPs in various sizes, shapes, and compositions, our interest in them has not waned. When talking about noble metals, gold, silver, and platinum come to mind first. Still, we cannot forget about elements belonging to the so-called platinum group, such as ruthenium, rhodium, palladium, osmium, and iridium, whose physical and chemical properties are very similar to those of platinum. It makes them highly demanded and widely used in various applications. This review presents current knowledge on the preparation of all noble metals in the form of nanoparticles and their assembling with carbon supports. We focused on the catalytic applications of these materials in the fuel-cell field. Furthermore, the influence of supporting materials on the electrocatalytic activity, stability, and selectivity of noble-metal-based catalysts is discussed.

Carbon Materials in Electroanalysis of Preservatives: A Review

Electrochemical sensors in electroanalysis are a particularly useful and relatively simple way to identify electroactive substances. Among the materials used to design sensors, there is a growing interest in different types of carbon. This is mainly due to its non-toxic properties, low cost, good electrical conductivity, wide potential range, and the possibility of using it in both aqueous and nonaqueous media. The electrodes made of carbon, and especially of carbon modified with different materials, are currently most often used in the voltammetric analysis of various compounds, including preservatives. The objective of this paper is to present the characteristics and suitability of different carbon materials for the construction of working electrodes used in the voltammetric analysis. Various carbon materials were considered and briefly discussed. Their analytical application was presented on the example of the preservatives commonly used in food, cosmetic, and pharmaceutical preparations. It was shown that for the electroanalysis of preservatives, mainly carbon electrodes modified with various modifiers are used. These modifications ensure appropriate selectivity, high sensitivity, low limits of detection and quantification, as well as a wide linearity range of voltammetric methods of their identification and determination.

Recent trends in the applications of thermally expanded graphite for energy storage and sensors - a review

Carbon nanomaterials such as carbon dots (0D), carbon nanotubes (1D), graphene (2D), and graphite (3D) have been exploited as electrode materials for various applications because of their high active surface area, thermal conductivity, high chemical stability and easy availability. In addition, due to the strong affinity between carbon nanomaterials and various catalysts, they can easily form metal carbides (examples: ionic, covalent, interstitial and intermediate transition metal carbides) and also help in the stable dispersion of catalysts on the surface of carbon nanomaterials. Thermally expanded graphite (TEG) is a vermicular-structured carbon material that can be prepared by heating expandable graphite up to 1150 °C using a muffle or tubular furnace. At high temperatures, the thermal expansion of graphite occurred by the intercalation of ions (examples: SO4 2-, NO3 -, Li+, Na+, K+, etc.) and oxidizing agents (examples: ammonium persulfate, H2O2, potassium nitrate, potassium dichromate, potassium permanganate, etc.) which helped in the exfoliation process. Finally, the obtained TEG, an intumescent form of graphite, has been used in the preparation of composite materials with various conducting polymers (examples: epoxy, poly(styrene-co-acrylonitrile), polyaniline, etc.) and metal chlorides (examples: FeCl3, CuCl2, and ZnCl2) for hydrogen storage, thermal energy storage, fuel cells, batteries, supercapacitors, sensors, etc. The main features of TEG include a highly porous structure, very lightweight with an apparent density (0.002-0.02 g cm-3), high mechanical properties (10 MPa), thermal conductivity (25-470 W m-1 K-1), high electrical conductivity (106-108 S cm-1) and low-cost. The porosity and expansion ratio of graphite layers could be customized by controlling the temperature and selection of intercalation ions according to the demand. Recently, TEG based composites prepared with metal oxides, chlorides and polymers have been demonstrated for their use in energy production, energy storage, and electrochemical (bio-) sensors (examples: urea, organic pollutants, Cd2+, Pb2+, etc.). In this review, we have highlighted and summarized the recent developments in TEG-based composites and their potential applications in energy storage, fuel cells and sensors with hand-picked examples.

Carbon Anode in Carbon History

This study examines how the several major industries, associated with a carbon artifact production, essentially belong to one, closely knit family. The common parents are the geological fossils called petroleum and coal. The study also reviews the major developments in carbon nanotechnology and electrocatalysis over the last 30 years or so. In this context, the development of various carbon materials with size, dopants, shape, and structure designed to achieve high catalytic electroactivity is reported, and among them recent carbon electrodes with many important features are presented together with their relevant applications in chemical technology, neurochemical monitoring, electrode kinetics, direct carbon fuel cells, lithium ion batteries, electrochemical capacitors, and supercapattery.

Effect of Surface Oxygen on the Wettability and Electrochemical Properties of Boron-Doped Nanocrystalline Diamond Electrodes in Room-Temperature Ionic Liquids

This paper reports on how the surface chemistry of boron-doped nanocrystalline diamond (BDD) thin-film electrodes (H vs O) affects the wettability and electrochemical properties in two room-temperature ionic liquids (RTILs): [BMIM][PF₆] and [HMIM][PF₆]. Comparative measurements were made in 0.5 mol L^-1 H₂SO₄. The BDD electrodes were modified by microwave or radio-frequency (RF) plasma treatment in H₂ (H-BDD), Ar (Ar-BDD), or O₂ (O-BDD). These modifications produced low-, medium-, and high-oxygen surface coverages. Atomic O/C ratios, as determined by X-ray photoelectron spectroscopy (XPS), were 0.01 for H-BDD, 0.08 for Ar-BDD, and 0.17 for O-BDD. The static contact angle of ultrapure water on the modified electrodes decreased from 110° (H-BDD) to 41° (O-BDD) with increasing surface oxygen coverage, as expected as the surface becomes more hydrophilic. Interestingly, the opposite trend was seen for both RTILs as the contact angle increased from 20° (H-BDD) to 50° (O-BDD) with increasing surface oxygen coverage. The cyclic voltammetric background current and potential-dependent capacitance in both RTILs were largest for BDD electrodes with the lowest O/C ratio (H-BDD) and smallest contact angle. Slightly larger voltammetric background currents and capacitance were observed in [HMIM][PF₆] than in [BMIM][PF₆]. Capacitance values ranged from 8 to 16 μF cm^-2 over the potential range for H-BDD and from 4 to 6 μF cm^-2 for O-BDD. The opposite trend was observed in H₂SO₄ as the voltammetric background current and capacitance were largest for BDD electrodes with the highest O/C ratio (O-BDD) and smallest contact angle. In summary, reducing the surface oxygen on BDD electrodes increases the wettability to two RTILs and this increases the voltammetric background current and capacitance.

Modeling and Electrochemical Characterization of Electrodes Based on Epoxy Composite with Functionalized Nanocarbon Fillers at High Concentration

This paper deals with the electrochemical characterization and the equivalent circuit modeling of screen-printed electrodes, modified by an epoxy composite and loaded with carbon nanotubes (CNTs), pristine and functionalized NH₂, and graphene nanoplates (GNPs). The fabrication method is optimized in order to obtain a good dispersion even at high concentration, up to 10%, to increase the range of investigation. Due to the rising presence of filler on the surface, the cyclic voltammetric analysis shows an increasing of (i) electrochemical response and (ii) filler concentration as observed by the scanning electron microscopy (SEM). Epoxy/CNTs-NH₂ and epoxy/GNPs, at 10% of concentration, show the best electrochemical behavior. Furthermore, epoxy/CNTs-NH₂ show a lower percolation threshold than epoxy/CNT, probably due to the direct bond created by amino groups. Furthermore, the electrochemical impedance spectroscopy (EIS) is used to obtain an electrical equivalent circuit (EEC). The EEC model is a remarkable evolution of previous circuits present in the literature, by inserting an accurate description of the capacitive/inductive/resistive characteristics, thus leading to an enhanced knowledge of phenomena that occur during electrochemical processes.

Electron Transfer Kinetics at Graphene Quantum Dot Assembly Electrodes

Electrochemical performance of nanostructured carbon electrodes was evaluated using cyclic voltammetry and a simple simulation model. The electrodes were prepared from soluble precursors by anodic electrodeposition of two sizes of graphene quantum dot assemblies (hexabenzocoronene (HBC) and carbon quantum dot (CQD)) onto a conductive support. Experimental and simulated voltammograms enabled the extraction of the following electrode parameters: conductivity of the electrodes (a combination of ionic and electronic contributions), density of available electrode states at different potentials, and tunneling rate constant (Marcus-Gerischer model) for interfacial charge transfer to ferrocene/ferrocenium (Fc/Fc⁺) couple. The parameters indicate that HBC and CQD have significant density of electronic states at potentials more positive than -0.5 V versus Ag/Ag⁺. Enabled by these large densities, the electron transfer rates at the Fc/Fc⁺ thermodynamic potential are several orders of magnitude slower than those commonly observed on other carbon electrodes. This study is expected to accelerate the discovery of improved synthetic carbon electrodes by providing fast screening methodology of their electrochemical behavior.

Electrochemical performance at sputter-deposited nanocarbon film with different surface nitrogen-containing groups

Carbon materials containing nitrogen have been extensively studied as electrode materials for use in non-platinum cathodes of fuel cells due to their high electrocatalytic activity for oxygen reduction. The activity is strongly dependent on the structure of surface nitrogen-containing functional groups. Carbon film containing nitrogen is also suitable for analytical applications because of its low background noise and its electrocatalytic activity, which is superior to that of pure carbon film. Here, we fabricated sputter-deposited nanocarbon film with a nitrogen-containing group and estimated the efficacy of a surface nitrogen-containing group for detecting biomolecules. Two types of carbon films, one rich in graphite-like nitrogen-containing bonds and the other rich in pyridine-like bonds, were successfully fabricated without changing their nitrogen concentration, sp2/sp3 ratio or surface flatness. The carbon film rich in pyridine-like bonds shows a positive oxygen reduction peak of about 250 mV compared with pure carbon film and is also 200 mV more positive compared with film with graphite-like nitrogen-containing bonds. This indicates that pyridine-like bonds contribute more effectively to electrocatalytic activity than graphite-like nitrogen-containing bonds. For detecting biomolecules, carbon film rich in pyridine-like bonds also exhibits more negative peak potentials for the oxidation of NADH and l-ascorbic acid, suggesting that carbon film rich in pyridine-like bonds will show improved performance for detecting electroactive biomolecules.

Conductive diamond: synthesis, properties, and electrochemical applications

This review summarizes systematically the growth, properties, and electrochemical applications of conductive diamond.

Determination of bromate via the chemiluminescence generated in the sulfite and carbon quantum dot system

The authors describe a chemiluminescence (CL)-based assay for the determination of bromate. The method is based on the use of a solution of carbon quantum dots (CQDs) and sulfite. Strong CL (peak at 490 nm) is observed when bromate is injected into the solution. The CL increases linearly in the 0.3 to 10 μmol L^-1 bromate concentration range, giving a 0.1 μmol L^-1 limit of detection (at an S/N ratio of 3). A possible CL mechanism is suggested that involves a redox reaction between the CQDs, bromate and sulfite in the acidic medium. This leads to the formation of hole-injected and electron-injected CQDs. Radiative recombination of oxidant-injected holes and electrons in the CQDs accounts for the occurrence of CL. This mechanism contradicts the previous assumption that the transfer of energy occurs from SO₂* to the CQDs. Although nitrite may interfere in the determination of bromate, its effect can be eliminated by adding sulfamic acid. The assay is sensitive and represents a new tool for the determination of bromate, which is a carcinogen. Graphical abstract Under acidic condition, carbon quantum dots (CQDs) can react with sulfite and bromate transforming to hole-injected CQDs (CQDs^•-) and electron-injected CQDs (CQDs^•+), respectively. Thereafter, strong chemiluminescence (490 nm) aroused from the radiative electron-hole annihilation between CQDs^•- and CQDs^•+.

Development and application of a routine robust graphite/poly(lactic acid) composite electrode for the fast simultaneous determination of Pb2+ and Cd2+ in jewelry by square wave anodic stripping voltammetry

A handcrafted, low cost sustainable electrochemical sensor based on graphite/PLA was developed and applied for the simultaneous quantification of Pb²⁺ and Cd²⁺ in jewelry.

Electrocatalytic Water Oxidation by MnOx /C: In Situ Catalyst Formation, Carbon Substrate Variations, and Direct O2 /CO2 Monitoring by Membrane-Inlet Mass Spectrometry

Layers of amorphous manganese oxides were directly formed on the surfaces of different carbon materials by exposing the carbon to aqueous solutions of permanganate (MnO₄^- ) followed by sintering at 100-400 °C. During electrochemical measurements in neutral aqueous buffer, nearly all of the MnO_x /C electrodes show significant oxidation currents at potentials relevant for the oxygen evolution reaction (OER). However, by combining electrolysis with product detection by using mass spectrometry, it was found that these currents were only strictly linked to water oxidation if MnO_x was deposited on graphitic carbon materials (faradaic O₂ yields >90 %). On the contrary, supports containing sp³ -C were found to be unsuitable as the OER is accompanied by carbon corrosion to CO₂ . Thus, choosing the "right" carbon material is crucial for the preparation of stable and efficient MnO_x /C anodes for water oxidation catalysis. For MnO_x on graphitic substrates, current densities of >1 mA cm^-2 at η=540 mV could be maintained for at least 16 h of continuous operation at pH 7 (very good values for electrodes containing only abundant elements such as C, O, and Mn) and post-operando measurements proved the integrity of both the catalyst coating and the underlying carbon at OER conditions.

Electrochemistry of Carbon Dioxide on Carbon Electrodes

Carbon electrodes have the advantages of being chemically inert at negative potential ranges in all media and high offset potentials for hydrogen evolution in comparison to metal electrodes, and therefore are the most suitable electrodes for electrochemistry and electrochemical conversion of CO₂ into valuable chemicals. Herein we summarize on carbon electrodes the voltammetry, electrochemical and electrocatalytic CO₂ reduction, as well as electron synthesis using CO₂ and carbon electrodes. The electrocatalytic CO₂ reduction using carbocatalyts and the future activities about electrochemical CO₂ conversion are highlighted.

Electrochemical Grafting of Graphene Nano Platelets with Aryl Diazonium Salts

To vary interfacial properties, electrochemical grafting of graphene nano platelets (GNP) with 3,5-dichlorophenyl diazonium tetrafluoroborate (aryl-Cl) and 4-nitrobenzene diazonium tetrafluoroborate (aryl-NO₂) was realized in a potentiodynamic mode. The covalently bonded aryl layers on GNP were characterized using atomic force microscopy and X-ray photoelectron spectroscopy. Electrochemical conversion of aryl-NO₂ into aryl-NH₂ was conducted. The voltammetric and impedance behavior of negatively and positively charged redox probes (Fe(CN)₆^3-/4- and Ru(NH₃)₆^2+/3+) on three kinds of aryl layers grafted on GNP reveal that their interfacial properties are determined by the charge states of redox probes and reactive terminal groups (-Cl, -NO₂, -NH₂) in aryl layers. On aryl-Cl and aryl-NH₂ garted GNP, selective and sensitive monitoring of positively charged lead ions as well as negatively charged nitrite and sulfite ions was achieved, respectively. Such a grafting procedure is thus a perfect way to design and control interfacial properties of graphene.