Glassy Carbon Working Electrodes Research Articles

High-Throughput Activity Screening of Oxygen Reduction and Oxygen Evolution Catalysts

High-throughput techniques are being actively studied to expedite the evaluation of the electrocatalytic activity of newly developed materials. These techniques include the use of optical sensing or electrochemical array cells in stagnant or hydrodynamic aqueous electrolytes [1-2]. A new high-throughput electrochemical cell has been developed utilizing multiple glassy carbon working electrodes with dimensions comparable to those of a conventional ring-disk electrode (RDE) that are inserted into a channel flow cell (Figure 1) comprised of two PEEK blocks separated by a gasket that defines the electrolyte channel depth. This cell enables evaluation of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) activity as a function of the potential of multiple catalyst samples simultaneously that are deposited on the glassy carbon electrodes using standard methods used for RDE electrodes (e.g., using a hand-held micropipette). As shown in Figure 1, a common reference electrode is located in the lower cell block across an electrolyte channel from the working electrodes and a common counter electrode is located in the electrolyte outlet. Electrolyte flow has been simulated to ensure that the electrolyte is evenly distributed throughout the shallow flow channel with uniform laminar electrolyte flow and identical flow rate for all working electrodes. The new cell is coupled with a Bio-logic multichannel Potentiostat (VSP) that allows the use of multiple working electrodes simultaneously with a common counter electrode and common reference electrode. The catalyst activity and stability results obtained with the new cell have been verified by comparison with RDE measurements for the same catalysts. Acknowledgments This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.

Low Overpotential Amperometric Sensor Using Yb2O3.CuO@rGO Nanocomposite for Sensitive Detection of Ascorbic Acid in Real Samples.

The ultimate objective of this research work is to design a sensitive and selective electrochemical sensor for the efficient detection of ascorbic acid (AA), a vital antioxidant found in blood serum that may serve as a biomarker for oxidative stress. To achieve this, we utilized a novel Yb2O3.CuO@rGO nanocomposite (NC) as the active material to modify the glassy carbon working electrode (GCE). The structural properties and morphological characteristics of the Yb2O3.CuO@rGO NC were investigated using various techniques to ensure their suitability for the sensor. The resulting sensor electrode was able to detect a broad range of AA concentrations (0.5-1571 µM) in neutral phosphate buffer solution, with a high sensitivity of 0.4341 µAµM-1cm-2 and a reasonable detection limit of 0.062 µM. The sensor's great sensitivity and selectivity allowed it to accurately determine the levels of AA in human blood serum and commercial vitamin C tablets. It demonstrated high levels of reproducibility, repeatability, and stability, making it a reliable and robust sensor for the measurement of AA at low overpotential. Overall, the Yb2O3.CuO@rGO/GCE sensor showed great potential in detecting AA from real samples.

Spectroscopic and electrochemical investigation of mixed – ligand transition metal complexes with 2N-salicylidine-5-(p-nitrophenyl)-1, 3, 4-thiadiazole and 5, 5’-Me2bipy in aqueous medium

Herein we reported the spectroscopic and electrochemical investigation of four transition metal complexes viz. VO(II), Co(II), Ni(II) and Cu(II) of 2N-salicylidine-5-(p-nitrophenyl)-1, 3, 4-thiadiazole Schiff base ligand (L) and 5,5’-dimethyl-2,2’-bipyridine (Me2bipy) in the aqueous (1: 1: 1 molar ratio) medium. Transition metal complexes were characterized by microanalysis, FT-IR, electronic absorption and mass spectroscopy. Electrochemistry of transition metal complexes was studied in aqueous medium by using cyclic voltammetry (CV) at glassy carbon working electrode (GCE) versus Ag/AgCl. The reduction potential of the VO (II) and Cu (II) becomes more negative with increasing scan rate while Co (II) and Ni (II) positive show easier reduction.

Determination of hydroquinone and benzoquinone in pharmaceutical formulations: critical considerations on quantitative analysis of easily oxidized compounds.

Hydroquinone is a skin-lightening agent used as an active ingredient in topical dermatological formulations prescribed for treating cutaneous diseases caused by hyperpigmentation. Despite being widely used, some toxicological aspects have been associated with these products, mainly due to overdosage and long-term use combined with the easy oxidation of hydroquinone. In this work, an investigative study has been done to gather enough data for selecting a quantitative analytical method for quality control purposes that considers the ease of oxidation not only within the product but also during the experimental procedures. After studying the influence of pH, reversibility, sampling, and standard solution preparation on the redox reaction between hydroquinone and benzoquinone by using spectroscopic, electrophoretic, and electroanalytical measurements, a reliable, fast, and selective chronoamperometric method was achieved. The optimized method was used for the analysis of samples, previously diluted in Britton-Robinson (BR) buffer (pH 5.5) and methanol (1 : 9, v/v), by applying a potential fixed at 0.4 V. A glassy-carbon working electrode, lab-made Ag/AgCl(sat) and platinum wire as a reference electrode and auxiliary electrodes, respectively, and BR buffer (pH 5.5) as supporting electrolyte were the additional experimental conditions used. Analytical performance parameters were verified to confirm the applicability of the new method (LOD 4.22 μmol L-1 and LOQ 14.1 μmol L-1; recovery mean value of 100% with 0.22% RSD). A gel topical formulation containing 4% (w/w) hydroquinone was analyzed through the developed method for determination of dosage and oxidation traces, and a content of 3.53 ± 0.095% (w/w) was found with no indications of degradation.

Atomically Precise Ni-Pd Alloy Carbonyl Nanoclusters: Synthesis, Total Structure, Electrochemistry, Spectroelectrochemistry, and Electrochemical Impedance Spectroscopy.

The molecular nanocluster [Ni36–xPd5+x(CO)46]6– (x = 0.41) (16–) was obtained from the reaction of [NMe3(CH2Ph)]2[Ni6(CO)12] with 0.8 molar equivalent of [Pd(CH3CN)4][BF4]2 in tetrahydrofuran (thf). In contrast, [Ni37–xPd7+x(CO)48]6– (x = 0.69) (26–) and [HNi37–xPd7+x(CO)48]5– (x = 0.53) (35–) were obtained from the reactions of [NBu4]2[Ni6(CO)12] with 0.9–1.0 molar equivalent of [Pd(CH3CN)4][BF4]2 in thf. After workup, 35– was extracted in acetone, whereas 26– was soluble in CH3CN. The total structures of 16–, 26–, and 35– were determined with atomic precision by single-crystal X-ray diffraction. Their metal cores adopted cubic close packed structures and displayed both substitutional and compositional disorder, in light of the fact that some positions could be occupied by either Ni or Pd. The redox behavior of these new Ni–Pd molecular alloy nanoclusters was investigated by cyclic voltammetry and in situ infrared spectroelectrochemistry. All three compounds 16–, 26–, and 35– displayed several reversible redox processes and behaved as electron sinks and molecular nanocapacitors. Moreover, to gain insight into the factors that affect the current–potential profiles, cyclic voltammograms were recorded at both Pt and glassy carbon working electrodes and electrochemical impedance spectroscopy experiments performed for the first time on molecular carbonyl nanoclusters.

Novel Aluminum-Ion Based Non-Aqueous Redox Flow Battery

The global implementation of renewable energy technologies requires sustainable large-scale manufacturing by using locally available materials. The urgent need to achieve a climate-neutral society encouraged researchers to find sustainable and innovative ways to store electrical energy. Currently, Li-ion battery (LIB) technology is the largest implemented commercial level battery for energy systems. The LIBs' upstream supply chain comprises specific materials, including lithium, cobalt, iron, and phosphate. The latter poses a challenge as they are geographically limited to fewer countries. Therefore, as the LIB production growth rate increases rapidly, balancing the raw material supply and resource circulation is required.In contrast to the intercalation-based electrochemistry of the LIBs, the redox flow battery (RFB) store electrical energy in the form of chemical energy directly into the electrolyte. The amount of energy stored in the battery is proportional to the concentration of redox species or simply to the amount of the electrolyte used. The redox reactions happen at the electrode surface assembled inside the battery, and the electrolyte containing the active redox species flows across the electrodes from the adjacent reservoirs. Minimal single cell design variations are required to use different electrolyte chemistries, barring the widely and commonly used Vanadium redox ions. This flexibility enables adjusting the active redox species comprised on the electrolyte, with locally abundant transition metals. The redox potentials of the mentioned metallic compounds lie outside the electrochemical stability range of aqueous electrolytes. The research community addresses increment in electrochemical operation range by introducing the non-aqueous RFB (NAqRFB) technology.The latter allowed to explore more promising redox ions for NAqRFB. An ideal redox ion should i) have great abundancy; ii) be cheap, iii) provide fast multiple electron transfer per reacting molecule, and iv) possess reversible kinetics mechanisms, therefore not compromising the system's stability by generating irreversible side reactions. This thirst is quenched by Aluminum-ions (Al3+), which demonstrate the mentioned features besides having high energy density and high value of negative redox potential, i.e., -1.7 V vs. Ag/Ag+ allow higher cell potential. In this regard, an aluminum-ion-based non-aqueous redox flow battery was introduced in this study as a proof-of-concept. The aluminum redox ion is used as negolyte coupled with the posolyte based on the redox ions of metal acetylacetonates - M(acac) (where, M = Cr, Fe) - and Ferrocene (Fc). The insertion of the mentioned metals at the posolyte while keeping aluminum ion at the negolyte ensured the generation of novel chemistries for NAqRFBs, in detail Al||Cr, Al||Fc, and Al||Fe with cell potential differences of 3.2 V, 1.26 V, and 0.8 V, respectively.The reversibility of the redox ions in the electrolyte is compulsory and crucial for the operation of RFB. Cyclic voltammetry (CV) was performed for the non-aqueous electrolytes with acetonitrile as solvent and TEABF4 as supporting electrolyte. The redox ions of Al/Al3+, Cr4+/Cr5+, Fc/Fc+, and Fe3+/Fe4+ were used as active species and proved to be reversible on a glassy carbon working electrode (GCE); said attained redox couple potentials (vs. Ag/Ag+) were -1.7 V, 1.5 V, 0.1 V, and -0.9 V, respectively. Detailed electrochemical characterization was performed in a single NAqRFB, using polarization curve analysis, electrochemical impedance spectroscopy (EIS), and charge-discharge cycling (CDC) – Table 1. Post-mortem CVs of the electrolyte using GCE highlight the stability of the electrolyte after intensive CDC.The RFB assembled with Al||Cr offered the capacity and energy density performance. The CV results highlight that the redox reaction is quasi-reversible, affecting the battery performance and stability. The RFB composed of Al||Fc offers the highest capacity and energy density than others and is three times more than reported Al||Cr NAqRFB. The post-mortem analyses on the posolyte signify that there was crossover through the membrane, which ended up with a contaminated electrolyte (mixture with negolyte chemistry) that affected the extended capacity of the cell. Reinforced membranes permit to decrease the permeability of the membrane toward smaller ions of Al3+ as compared to Fc+. Further optimization of the membrane is required to improve the promising Al||Fe RFB, perhaps to reach the energy efficiency of 90%. Furthermore, the Al||Fe battery demonstrated a stable performance up to 50 cycles and the second-highest energy density ca. 25.9 mWh.g-1 compared to other versions of aluminum-ion-based non-aqueous redox flow batteries. This work is still in progress for in-depth study covering other aspects and ascertaining the feasibility of Al based RFB to be the new generation of NAqRFBs. Figure 1

Step Toward Eco-Friendly Green Source of Non-Aqueous Electrolytes for Redox Flow Battery

The efficient utilization of energy from non-exhaustive resources without adverse effects on the environment is a way forward for the sustainable development of society. The intermittent nature of renewable energy from non-exhaustive resources such as solar, wind, etc., requires a large-scale and advanced energy storage system to eliminate the impact of intermittency on the power grid. Redox flow battery (RFB) technology is one of the promising candidates for large-scale grid systems. Present commercial RFB technology is based on the redox reactions of electroactive metals, which are constrained by material abundance, cost, and environmental issues. These issues are prompting scientists to look into organic-based technologies as potential metal-free battery alternatives. Organic-based materials offer structural diversity of organic molecules to adjust the electrolyte materials' thermodynamics and redox characteristics, in addition to low cost and scalability. This opens the door to the development of green and sustainable energy storage devices.Despite development over the last decade, organic compound exploitation for RFB remains limited. Organics with limited ionic conductivity and poorly defined conducting channels have poor voltage efficiency and cyclability. In aqueous flow batteries, the cell potential is also limited by the electrolysis of water. The scientific community, on the other hand, is addressing this issue by introducing the non-aqueous RFB (NAqRFB).Quinones are the most redox-active moieties found in natural organic materials, and they play a critical role in biological electron transport. They are a class of molecules that are formed from aromatic compounds like benzene or naphthalene and have a fully conjugated cyclic diketone structure with a redox reaction based on the rearrangement of the conjugated double bond. 1,4-naphthoquinone (NQ) is investigated as a possible negolyte candidate. NQ as metal-free organic negolyte was coupled with metal acetylacetonate-based posolytes, M(acac), where M = Cr, V, Mn. Both types of redox species (metal & metal-free) have good solubility in the solvent - Dimethylacetamide (DMA) - and ionic conductivity was enhanced using the supporting electrolyte of TEABF4. Cyclic voltammetry (CV) analysis using glassy carbon working electrode (GCE) highlighted that NQ offers reversibility; the high value of negative redox potential -1.75 V vs. Ag/Ag+ enables higher cell potential and posses no irreversible side reactions.The electrochemical stability of the negolyte was further tested using the symmetrical cell having an electrolyte of 0.06 M concentration of NQ as redox species. The electrolyte flow from the reservoir, cathode, and anode in a series arrangement. The redox species are reduced at the cathode and then oxidized at the anode, which helps maintain the state-of-charge (SOC) at 50 %. The cell was operated for 50 cycles at the C-rate = 1C, i.e., 2.75 mA⋅cm-2 at the cutoff potentials of ±0.3 V. The energy efficiency of that symmetric cell was 99.7 %, and discharge capacity retention was 99.967%. These results are validated from the reported study by Yu Ding, 2016. This strengthen the motivation of using the NQ as metal-free organic negolyte for single NAqRFB-cell. The insertion of the mentioned metals (Cr, V, Mn) at the posolyte while keeping NQ ion at the negolyte ensured the generation of novel chemistries for NAqRFBs, in detail NQ||Cr, NQ||V, and NQ||Mn, with cell potential differences of 3.25 V, 2.2 V, and 2.45 V, respectively.Detailed characterization was performed using polarization, EIS, and charge-discharge cycling (CDC) – Table 1. Post-mortem CVs of the electrolyte using GCE highlight the stability of the electrolyte after intensive CDC. The RFB assembled with NQ||Cr offered the highest capacity and energy density. However, it was faced with lower energy efficiency. The post-mortem analyses on the posolyte signify that there was crossover through the membrane, which ended up with a contaminated electrolyte (mixture with negolyte chemistry) that affected the extended capacity of the cell. The RFB composed of NQ||V offers the 2nd highest capacity and energy density than others and is two times more than reported V||V NAqRFB. Reinforced membranes permit to decrease the permeability of the membrane toward smaller ions of NQ as compared to V2+ redox ions. Furthermore, the NQ||Mn battery demonstrated a stable performance up to 25 cycles having higher efficiencies and with a decent energy density of ca. 60 mWh.g-1 . NQ has high solubility of 1.5 M in DMA and future work at higher capacities is in progress for in-depth study covering other aspects. The study may ascertain the feasibility of NQ-based RFB to be the eco-friendly green alternate battery chemistry. Figure 1

A biosensor for the sensitive and specific measurement of arsenite using gold nanoparticles

An electrochemical biosensor for arsenite concentration determination is developed in this study using arsenite oxidase (ArOx). Gold nanoparticles (AuNP) were used in this study to improve the analytical characteristics of the biosensor by providing a suitable nano-environment for the enzyme activity. The enzyme and the nanoparticles were electrodeposited on the glassy carbon (GC) working electrode to prepare the GC-AuNP-ArOx electrode. The linear measurement range of the biosensor was between 101 and 104 nM, while its detection limit was obtained equal to 5 nM. The effects of enzyme concentration, pH, storage temperature, and storage time on the biosensor’s performance were investigated. Results showed that an enzyme concentration of 7 μM at the physiological pH exerted the highest biosensor response (7 μA anodic current/10 nM arsenite). No undesirable interference of heavy metals was observed on the biosensor response, and the biosensor showed excellent reproducibility compared to a conventional chemosensor.

Cu(OH)2-Ni(OH)2 engulfed by zeolite-Y hydroxyl nest and multiwalled carbon nanotube for effective methanol oxidation reaction

Cu(OH)2-Ni(OH)2 supported on zeolite-Y and combined with multi-walled carbon nanotube (MWCNT), M(OH)2-Y-CNT (M = Cu, Ni) was found to be an excellent multicomponent hybrid system for methanol oxidation reaction (MOR). The formation of metal hydroxyl nest interconnected through MWCNT produced a high current density of 5.5 A/mg with significant durability up to 11.1 h. The electrochemical oxidation of methanol was found to be significant with maximum current density when the Cu:Ni ratio was 3:1. The surface hydroxyl group of zeolite-Y and -COOH functional group of MWCNT interacted strongly with Cu(OH)2 and Ni(OH)2 and provided a strong metal to surface interaction. From the temperature programme desorption (TPD) study and pyridine adsorption FTIR analysis, it was evident that both the acidity and basicity of Cu(OH)2-Ni(OH)2-Y catalyst was influenced by the MWCNT and consequently helped in MOR. Modification with MWCNT also lead to the change in the binding energy values of Cu and Ni and thereby effected the overall MOR activity of the electrocatalyst. The MOR activity of the hybrid material was tested by modifying the glassy carbon working electrode (GCE) as well in Pt working electrode. The MOR activity was found to be much better with Pt-electrode in comparison to GCE in terms of current density, durability and stability. The Pt-electrode modified with the hybrid M(OH)2-Y-MWCNT exhibited high CO tolerance in comparison to commercial Pt/ C electrocatalyst.

Polymeric membrane-modified voltammetric sensors for lipophilic analytes with nanomolar detection limit: Key parameters influencing the response characteristics

Thin plasticized PVC membrane-coated glassy carbon working electrodes have been used for the voltammetric measurement of highly lipophilic, electroactive drugs. Compared to conventional working electrodes, these membrane-coated electrodes exhibit remarkable detection limit and selectivity and are less prone to electrode fouling. The unique performance characteristics of these sensors are related to the large partition coefficient of the analyte in the membrane coating where it is oxidized in a non-aqueous membrane phase. To analyze the influence of the key parameters of the response of membrane-coated sensors, we derived theoretical expressions on the voltammetric response of the sensors. In our analysis we considered 1) the partition coefficient (Pmw) of the analyte between the aqueous sample and the organic membrane, 2) the membrane volume to sample volume ratio (Vm/Vw), and 3) the binding constant of constituents in the sample that bind the analyte (K). The results of our theoretical analysis have been tested through voltammetric measurement of highly lipophilic analytes with logPow values (logarithm of the partition coefficient between octanol and water) ranging between 0.3 and 7.5. By understanding of the influence of the sensor design parameters on the overall sensor response, these parameters can be tuned for optimized response slope, detection limit, etc., for solving specific analytical tasks.

Synthesis, characterization, biological (in vitro) activity and electrochemical studies of mixed-ligand copper (II) and cobalt (II) complexes with picolinic acid and imides

• Synthesis of mixed ligand copper (II) and cobalt (II) complexes with imides and picolinic acid. • Characterized by FT-IR, UV–visible spectroscopy. • Electrochemical behavior of mixed-ligand copper (II) and cobalt (II) complexes (1–4) by using cyclic voltammetry (CV). • Biological activity of mixed-ligand copper (II) and cobalt (II) complexes (1–4). Mixed ligand copper (II) and cobalt (II) complexes viz; [Cu(6-pic) 2 (succinimie) 2 ] 1; [Cu(6-pic) 2 (phthalimide) 2 ] 2; [Co(6-pic) 2 (succinimide) 2 ] 3; [Co(6-pic) 2 (phthalimide) 2 ] 4 have been synthesized with picolinic acid (6-picolinic acid) and imides (imides = succinimide and phthalimide), used as primary and secondary ligands respectively. All these mixed-ligand complexes (1–4) were characterized by elemental analysis (C H N), molar conductance, room temperature magnetic susceptibility, FT-IR, and UV–visible spectroscopy. The electrochemical study of all these complexes were performed in aqueous medium, containing 0.2 M NaClO 4 as supporting electrolyte at glassy carbon working electrode (GCE) vs Ag/AgCl reference electrode by using cyclic voltammetric (CV). The complexes 1, 2 and 3, 4 were exhibited Cu 2+/+ and Co 3+/2+ / Co +/2+ diffusion controlled quasi-reversible single electron transfer redox couples. The cobalt (II) complexes 3 and 4 are biologically (in vitro) more active compare to copper (II) complexes 1 and 2 against microorganisms with antibacterial and antifungal drugs.

High Energy Density Non-Aqueous Organic Redox Flow Batteries

Renewable energy sources such as wind and solar are replacing fossil fuels for electricity generation. However, intermittency of wind and solar limits their wide-spread adoptions. The energy fed into the power grid must be matched with the consumer energy demand to prevent blackouts and destabilization of the grid [1, 2]. Recently, redox flow batteries (RFBs) have gained practical interest among the other energy storage technologies in light of their long lifetime, independent sizing of power and energy, high round-trip efficiency, scalability and design flexibility, fast response, and low environmental impact [3-5]. Organic redox-active materials have recently received attention as they provide competitive electrochemical characteristics, flexible design, and they are abundant in nature [6]. Aqueous designs face commercial difficulty because RFBs have low energy and power density due to the limited cell voltage of 1.23 V. The limited voltage is due to the evolutions of hydrogen and oxygen in the water electrolysis [7]. Solvent substitution is one solution to enable higher energy densities in RFBs, using non-aqueous solution also provides a large design space for enhancement of material solubility, cell potential and the number of electrons stored in the redox species [7-8].In this study, a new organic redox molecule, tetra amino anthraquinone (Disperse Blue 1: DB-1), is evaluated and compared with other organic systems reported in the literature [5, 7] such as benzoquinone (BQ), naphthoquinone (NQ), anthraquinone (AQ), tetramethyl piperidinyloxyl (Tempo), and phenylenediamine (PD) in non-aqueous solvent by means of cyclic voltammetry. A three-electrode system was utilized to conduct cyclic voltammetry (CV) experiments using glassy carbon working electrodes. The battery performance was evaluated using a flow cell with an electrode area of 2.5 cm2. The electrolytic solution, containing 40 mM DB-1 solution in dimethyl sulfoxide solvent (DMSO) and 1 M Bis (trifluoromethane) sulfonimide lithium salt, was circulated through the cell at a flow rate of 10 cm3 min-1. Graphite felt and Nafion 115 were used as the electrode and membrane, respectively.In addition, density functional theory (DFT) calculations were used to better understand the electrochemical behavior of the active quinone molecules at different oxidation states. Figure 1 shows the molecular orbital energy levels (HOMO and LUMO) of the DB-1 organic dye and other similar organic molecules obtained by DFT calculations in DMSO. A relatively small HOMO-LUMO gap means a lower overpotential required for the oxidation and reduction processes [8]. The DB-1 had narrower bandgaps (<3 eV) than other quinone molecules (> 3.9 eV), suggesting that the selected molecule has better kinetics than other organic molecules. The result describes a systematic evaluation of DB-1 as a redox active material for energy storage applications by means of electronic structures, electrochemical properties, and flow cell studies. Voltammetric studies and DFT calculations (in DMSO solvent) demonstrated that this was capable of forming both anions and cations at electrode potentials ranging from 1.7 to 4.4 V vs. Li, involving up to 6 electron-transfers and exhibiting one of the highest electrode potentials (up to 4.4 V vs. Li) in the literature. Since these quinone derivatives can be extracted from biomass materials, the proposed organic RFB system provides a greener and more sustainable option for grid-scale energy storage applications than metal based redox systems. The proposed chemistry in this work showed high energy efficiency (ca. 68 %) at a current density (20 mA cm-2) with close to 100% capacity retention. These results reveal that the molecular tuning of quinone structures is promising for RFBs applications. Figure 1

Electrochemiluminescence of Bare Glassy Carbon with Benzoyl Peroxide as the Coreactant in N,N-Dimethylformamide

The electrochemiluminescence (ECL) properties of many carbon materials have been reported with glassy carbon (GC), Pt, Au or indium tin oxide (ITO) as the working electrode (WE). As one type of carbon materials, GC itself can generate ECL signal. Some research groups have already noticed the ECL signal from GC WE and reported the results of GC WE with respect to their luminophores. However, comprehensive analyses of ECL properties of GC WE are rare. Herein, the ECL properties of GC WE in organic electrolyte with benzoyl peroxide as the coreactant are reported. Our results are of great importance to distinguish the true ECL data of luminophores from that of GC. Sky-blue light was generated in the electrochemiluminescence process of bare glassy carbon working electrode with benzoyl peroxide as the coreactant.

Experimental and Computational Studies of Disperse Blue in Organic Non-Aqueous Redox Flow Batteries

Renewable energy sources such as wind and solar are replacing fossil fuels for electricity generation. However, intermittency of wind and solar limits their wide-spread adoptions. The energy fed into the power grid must be matched with the consumer energy demand to prevent blackouts and destabilization of the grid [1, 2]. Converting this intermittent power into a base-load power is a challenge in the energy sector. Energy storage systems (ESSs) can store and supply large scale energy as required to address this challenge. Recently, redox flow batteries (RFBs) have gained practical interest among the other energy storage technologies in light of their long lifetime, independent sizing of power and energy, high round-trip efficiency, scalability and design flexibility, fast response, and low environmental impact [3-5]. Redox-active materials is an important constituent of RFBs since battery cycling performance is highly dependent on redox-active properties such as solubility, redox potential, chemical stability, and cost. Organic redox-active materials have recently received attention as they provide competitive electrochemical characteristics, flexible design, and they are abundant in nature [6]. Aqueous designs face commercial difficulty because RFBs have low energy and power density due to the limited cell voltage of 1.23 V. The limited voltage is due to the evolutions of hydrogen and oxygen in the water electrolysis [7]. Solvent substitution is one solution to enable higher energy densities in RFBs, using non-aqueous solution also provides a large design space for enhancement of material solubility, cell potential and the number of electrons stored in the redox species [7-8].In this study, a new organic redox molecule, tetra amino anthraquinone (Disperse Blue: DB), is evaluated and compared with other organic systems reported in the literature [5, 7] such as benzoquinone (BQ), naphthoquinone (NQ), anthraquinone (AQ), tetramethyl piperidinyloxyl (Tempo), and phenylenediamine (PD) in non-aqueous solvent by means of cyclic voltammetry. A three-electrode system was utilized to conduct cyclic voltammetry (CV) experiments using glassy carbon working electrodes. The battery performance was evaluated by using a flow cell design with an electrode area of 2.5 cm2. The electrolytic solution: 40 mM DB solution in dimethyl sulfoxide solvent (DMSO) and 1 M Bis (trifluoromethane) sulfonimide lithium salt, was circulated through the cell at a flow rate of 10 cm3 min-1. Graphite felt and Nafion 115 were used as the electrode and membrane, respectively.In addition, density functional theory (DFT) calculations were used to better understand the electrochemical behavior of the active quinone molecules at different oxidation states. Figure 1 shows the molecular orbital energy levels (HOMO and LUMO) of the DB organic dye and other similar organic molecules obtained by DFT calculations in DMSO. A relatively small HOMO-LUMO gap means a lower overpotential required for the oxidation and reduction processes [8]. The DB had narrower bandgaps (<3 eV) than other quinone molecules (> 3.9 eV), suggesting that the selected molecule has better kinetics than other organic molecules. The results of the CV and charge-discharge experiments will be presented demonstrating that this organic molecule can improve RFBs energy density.[1] J. Winsberg, C. Stolze, S. Muench, F. Liedl, M.D. Hager, U.S. Schubert., TEMPO/Phenazine Combi-Molecule: A Redox Active Material for Symmetric Aqueous RedoxFlow Batteries, ACSEnergyLett. 2016, 1, 976−980.[2] E.S. Beh, D.D Porcellinis, R.L. Gracia, K.T. Xia, R.G. Gordon, M.J. Aziz, A Neutral pH Aqueous Organic− Organometallic Redox Flow Battery with Extremely High Capacity Retention, ACS Energy Lett. 2017, 2, 639−644.[3] X. Wei, W. Duan, J. Huang, L. Zhang, B. Li, D. Reed, W. Xu,V. Sprenkle, Wei Wang, A High-Current, Stable Nonaqueous Organic Redox Flow Battery, ACS Energy Lett. 2016, 1, 705−711.[4] K.H. Hendriks, C.S. Sevov, M.E. Cook, M.S. Sanford., Multielectron Cycling of a Low-Potential Anolyte in Alkali Metal Electrolytes for Nonaqueous Redox Flow Batteries, ACSEnergyLett. 2017, 2, 2430−2435.[5] P. Leung., A.A. Shah., L. Sanz., C. Flox., J.R. Morante., Q. Xu., M.R. Mohamed., C. Ponce de León., F.C. Walsh., Recent developments in organic redox flow batteries: A critical review, Journal of Power Sources., 360, 243 – 283, 2017.[6] Wei, X., Pan, W., Duan, W., Hollas, A., Yang, Zh., Li, B., Nie, Z., Liu, J., Reed, D., Wang, W., Sprenkle, V., Materials and Systems for Organic Redox Flow Batteries: Status and Challenges, ACS Energy Lett. vol. 29, 2187-2204, 2017.[7] R. Emanuelsson, M. Sterby, M. Strømme, M.S. din, An All-Organic Proton Battery, J. Am. Chem. Soc. 2017, 139, 4828−4834[8] P. Leung., J. Bu., P.Q. Velasco., M.R. Roberts., N. Grobert., P.S. Grant., Single-Step Spray Printing of Symmetric All-Organic SolidState Batteries Based on Porous Textile Dye Electrodes, Adv. Energy Mater., 1901418, 2019. Figure 1

Studies on Electrochemical Generation of Ceric Ions in Nitric Acid Medium

AbstractCerous/ceric redox couple is considered as a potential Mediated Electro Oxidative (MEO) catalyst in the electro‐oxidative dissolution of difficult‐to‐dissolve trans‐uranic elements in the concentrated nitric acid medium. The electrochemical oxidation behavior of CeIII in 11.5 M HNO3 was investigated by cyclic voltammetry (CV) using two different working electrodes platinum (Pt) and glassy carbon (GC) at 298 K. At higher acidity, cerous to ceric oxidation on GC working electrode was found to be a reversible process contrary to a quasi‐reversible observed at Pt working electrode. To compare the current efficiency in electrochemical cells for the oxidation of CeIII ions, lab and bench scale oxidation of 0.05 and 0.5 M CeIII in 11.5 M nitric acid was performed in divided and undivided cell assemblies using Pt electroplated Ti (PET) or pure Pt gauze as anodes. Almost 100% yield for CeIV could be achieved in divided cells and under identical conditions; the conversion efficiency was 30% lower in undivided cells. These studies revealed the concentration dependence of CeIII besides cell potential and temperature on the rate of oxidation.

An ultra-sensitive non-enzymatic hydrogen peroxide sensor based on SiO2-APTES supported Au nanoparticles modified glassy carbon electrode

A novel electrochemical sensor based on (3-aminopropyl)triethoxysilane (APTES) functionalized SiO2 supported Au nanoparticles and Nafion (Nf) as the protective membrane was fabricated for the electrochemical determination of H2O2 in contact lens-cleaning solution. The modification steps of glassy carbon working electrode (GCE) were evaluated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The amperometric results showed that Nf/Au@SiO2-APTES/GCE sensor can be used to determine H2O2 in contact lens solutions with the linear ranges of 14–180 μM and 0.18–7.15 mM, excellent sensitivities of 2514.6 and 894.2 μA mM cm−2, and a low limit of detection (LOD) of 4.25 μM depending upon signal-to-noise ratio of 3. Nf/Au@SiO2-APTES/GCE exhibited excellent repeatability with relative standard deviation (RDS) of 2.66% and acceptable reproducibility with RSD of 3.35%. The sensor displayed reasonable selectivity in the presence of uric acid, dopamine, ascorbic acid, glucose, mannose, glycine, fructose, histidine, and arginine with RSD less than 2.5%. The fabricated Nf/Au@SiO2-APTES/GCE sensor has been successfully applied to detect H2O2 in contact lens cleaning solutions.

Voltammetric determination of glycopyrrolate in a pharmaceutical formulation

The electrochemical activity of glycopyrrolate was studied. Different voltammetric techniques were applied in this study, including cyclic voltammetry (CV), differential pulse voltammetry (DPV), and linear sweep voltammetry (LSV). Glassy carbon and platinum working electrodes were utilized. CV indicated that glycopyrrolate has a reversible redox reaction on the working electrode surface, with an anodic peak current at approximately 1.05 V and a cathodic peak at 0.80 V. Several parameters that affect the sensitivity of these methods were optimized for the quantitation of glycopyrrolate. LSV showed a better correlation coefficient than DPV did, with a value of ca. 0.9990 in the range of 0.1-0.5 mg/mL. The LSV and DPV recovery and relative standard deviation (RSD) results fell within the accepted range, with a better recovery (102.07%) for DPV and a better RSD (0.511%) for LSV. The limits of detections were ca. 16 and ca. 25 μg/mL for LSV and DPV, respectively.

Graphene Doped Mn2O3 Nanofibers as a Facile Electroanalytical DNA Point Mutation Detection Platform for Early Diagnosis of Breast/Ovarian Cancer

AbstractThis paper demonstrates a simple, label‐free detection methodology for detecting single point DNA mutations. Single point mutation detection is a key enabler for diagnosis and prevention of several genetic disorders that manifest into cancers. Specifically for this purpose, herein, an electrochemical biosensor utilizing electrospun graphene doped manganese III oxide nanofibers (GMnO) is developed. The charge transfer resistance offered by GMnO is extremely sensitive to the localized change in the conductivity. This sensitivity, attributed to the low band gap of Mn2O3 and high charge transfer kinetics of graphene, is explored in the proposed mutation detection platform. As a proof of concept, ultrasensitive detection of BRCA1 gene specific point mutation is demonstrated. The target specific single stranded probe DNA is immobilized onto GMnO modified glassy carbon working electrodes via chemisorption. Post target‐DNA hybridization, differential pulse voltammetry is employed to facilitate detection of targeted point mutation, wherein, difference in peak currents is used to distinguish the target DNA as normal or mutant. Efficiency of the proposed method is evaluated against a target concentration ranging from 10 pM−1 μM. With respect to the mutated target DNA, the LoD of the proposed device is found to be 0.8±0.069 pM. The proposed approach can be extended for detecting any mutation/hybridization of interest by simply adapting an appropriate functionalization protocol.

Immobilization of functionalized iron(II) clathrochelates with terminal (poly)aromatic group(s) on carbonaceous materials and their detailed cyclic voltammetry study

The detailed cyclic voltammetry (CV) study of the iron(II) clathrochelates with one, two or six terminal (poly)aromatic group(s) in a wide range of scan rate of the potential using glassy carbon (GC) and Pt working electrodes was performed. Their CVs contain the single one-electron quasireversible Fe2+/+ reduction wave in the cathodic potential range and one or two oxidation waves in the anodic range, assigned to a metal-centered Fe2+/3+ process and to oxidation of their polyaromatic terminal group(s). The potentials of both the reduction Fe2+/+ and oxidation Fe2+/3+ processes are shifted in the cathodic range as compared with their halogenoclathrochelate precursors and the values of shifts are substantially affected by a material of the working electrode; the electrochemical characteristics of the metal-centered waves suggest their diffusion-controlled character. Plots of the current peaks versus υ1/2 for the second anodic waves suggest a more complex diffusion – kinetic controlled character of these oxidations; for the dipyrenyl-terminated cage complex, the plots of the peak potentials versus lnυ allowed to obtain the corresponding average values of the apparent charge transfer coefficient α for both these electrodes, which are evidenced a very slow rate and irreversible character of this redox process. CVs of the hexafunctionalized clathrochelates contain an additional peak between the first and second (or after the second) anodic oxidation waves, an intensity of which linearly depends on a scan rate; the shapes of these CVs and the presence of an additional oxidation wave or plateau suggest their strong adsorption. The quantitative data about the physical adsorption of the iron(II) clathrochelate on activated carbon (AC) and reduced graphene oxide (RGO) were obtained. Using UV–vis spectral method; the Langmuir adsorption isotherms were used to calculate the corresponding adsorption equilibrium constants K. The observed changes of a free Gibbs energy are characteristic of the processes of physical adsorption via the stacking and Van-der-Waals interactions. Their limiting adsorption on AC decreases with increase in the number of the polyaromatic group(s) per a molecule from approximately 3·10−4 to 5.65·10−5 mol l−1, whereas in the case of RGO as an adsorbent that increases from 2.57·10−4 to 3.16·10−1 mol l−1. Values of K for AC also decrease with their number, while in the case of RGO as a substrate, its maximal value was observed for the difunctionalized iron(II) cage complex. Therefore, the physical adsorption of these clathrochelates is a structure-dependent process, which is strongly affected by the number of the functionalizing substituents at a cage framework. The value of K is determined by energy of the supramolecular binding of an adsorbate to an adsorbent. In the case of the diphenanttheryl-terminated iron(II) cage complex, its supramolecular binding with a surface of AC is stronger, thus suggesting a higher adsorption energy, while the hexafunctionalized cage complex forms the more strong supramolecular assemblies on a surface of RGO. This effect is explained by the presence of wedge-shaped pores in a macrostructure of RGO, both the size and the form of which is favorable for the physical adsorption of bulky molecules of the hexaphenanthrenyl-terminated macrobicyclic complex, while the size and the form of mesopores of AC are favorable for that of the difunctionalized iron(II) clathrochelate.

Electrochemical Determination of the Levels of Cadmium, Copper and Lead in Polluted Soil and Plant Samples from Mining Areas in Zamfara State, Nigeria

&lt;p class="PaperAbstract"&gt;&lt;span lang="EN-GB"&gt;The concentrations of lead, copper and cadmium in soil and plant samples collected from Abare and Dareta villages in Anka Local Government Area of Zamfara State, Nigeria have been electrochemically determined. The study was carried out because of the high mortality of women and children under five, reported for these areas in June 2010. The cause was ascribed to the lead poisoning which has been related to the mining and processing of gold-containing ores. Linear sweep anodic stripping voltammetry technique was used with the glassy carbon working, Ag/AgCl reference and platinum auxiliary electrodes. Voltammetric peaks for lead, copper and cadmium that were observed at -495 mV, -19.4 mV and -675 mV, respectively, have formed a basis for construction of the corresponding calibration plots. The concentrations (in mg/kg) of lead, copper and cadmium in the soil samples were found in the ranges of 18.99−26,087.70, 2.96−584.60 and 0.00−1354.25, respectively. The concentration values for lead were far above already established USEPA (2002) and WHO (1996) maximum permissible limits for residential areas. The concentrations of lead, copper and cadmium in the food samples ranged between 5.70−79.91, 11.17−41.21 and 0.00−5.74 mg/kg. Several of these values are found well above the FAO/WHO limits of 0.1, 2 and 0.1 mg/kg, respectively. The results indicate that in addition to the lead poisoning, copper and cadmium poisoning may also be responsible for sudden and high mortality in this population.&lt;/span&gt;&lt;/p&gt;