Reduction Peak Research Articles

Cyclic Voltammetry Study of Noble Metals and Their Alloys for Use in Implantable Electrodes.

Innovation in the application and miniaturization of implantable electrodes has caused a spike in new electrode material research; however, few robust studies are available that compare different metal electrodes in biologically relevant media. Herein, cyclic voltammetry has been employed to compare platinum, palladium, and gold-based electrodes’ potentiometric scans and their corresponding charge storage capacities (CSCs). Ten different noble metals and alloys in these families were tested under pseudophysiological conditions in phosphate-buffered saline (pH 7.4) at 37 °C. Charge storage capacity values (mC/cm2) were calculated for the oxide reduction, hydrogen adsorption, hydrogen desorption, and oxide formation peaks. Five scan rates spanning 2 orders of magnitude (10, 50, 100, 500, and 1000 mV/s) in both sparged and aerated environments were evaluated. Materials have been ranked by their charge storage capacities, reversibility, and trends discussed. Palladium-based alloys outperformed platinum-based alloys in the sparged condition and were ranked equally as high in the aerated condition. The Paliney 1100 (Pd-Re) alloy gave the highest observed calculated CSC value of 0.64 ± 0.02 mC/cm2 in the aerated condition, demonstrating 73 ± 5% reversibility. Trends between metal electrode families elicited in this study can afford valuable insight into future engineering of high performing implantable electrode materials.

High-fidelity simulation of the effects of street trees, green roofs and green walls on the distribution of thermal exposure in Prague-Dejvice

We investigate the heat stress mitigation potential of greening strategies in Prague using a configuration of the PALM-4U model that has been rigorously evaluated with measurements. Three greening scenarios were evaluated using the Universal Thermal Climate Index (UTCI). The UTCI reduction effect of broad-leaf or coniferous trees in a complex urban environment was found to be strongly local, with minor domain-average UTCI reductions; −4.1K under tree crowns and −0.6K on average in the neighbourhood as a day-time average, peaking at about twice these values near midday. During daytime the UTCI reduction potential of trees increases with the intensity and duration of solar exposure; −15.1K is the spatial maximum across all scenarios. For trees fully shaded by buildings, UTCI reduction was low (−0.5K as maximum). Tree planting reduces air temperature by more than 5K in some locations under trees, and reduces neighbourhood-average air temperature by up to 0.3K, with cooling peaking in the early evening about 8 h after the corresponding peak in UTCI reduction. Results emphasize the highly localized microclimate effects of trees for pedestrian thermal exposure reduction. The combination of green walls and roofs yielded negligible results in terms of UTCI reduction and only small air temperature effects. • UTCI reduction effect of broad-leaf or coniferous trees was −4.1K under tree crowns. • In the neighbourhood was day-time average UTCI reduction effect −0.6K • Trees fully shaded by buildings reduce UTCI about −0.5K as maximum. • Microclimate effects of trees for thermal exposure reduction are highly localized. • The combination of green walls and roofs yielded negligible results of UTCI reduction.

Electrochemical analysis of ferrocene in bicontinuous microemulsions using β- cyclodextrin modified monolayer graphene electrodes

• The reduction peak of ferrocene increased significantly by modifying β-CD in BME. • Modification density of β-CD on a monolayer graphene exceeds a coverage of 0.5. • Small water domains around β-CD forms a concentration field for ferrocenium ions. A monolayer graphene electrode modified with β-cyclodextrin (β-CD) was produced via a one-step reaction using an originally synthesized pyrene derivative of β-CD (py-β-CD). A py-β-CD-modified graphene electrode with a high modification density exceeding a coverage of 0.5 was obtained. Using this electrode, the electrochemical behaviors of water-insoluble ferrocene (Fc) and of a water-soluble ferrocene derivative in a bicontinuous microemulsion (BME) solution, consisting of a phosphate buffer (pH = 7.4), sodium dodecyl sulfate (SDS), 2-butanol, and toluene, were analyzed to investigate the effects of β-CD modification on the redox reactions of these species. In the reduction reaction of water-insoluble Fc, almost no peak was observed for the unmodified graphene electrode, whereas a high peak current increase was observed for the β-CD-modified electrode. The mechanism of the increase in the peak current of the reduction reaction can be derived from many small water domains formed around the β-CD molecules on the graphene surface. These water domains form many oil–water interfaces on the surface of the graphene electrode, which act as an [Fc] +1 concentration field by interacting with SDS.

Formaldehyde electrochemical sensor using graphite paste-modified green synthesized zinc oxide nanoparticles

• The ZnO NPs were synthesized via green synthesis route. • The ZnO NPs have irregular sponge-like shapes. • The GPE/ZnO NPs electrode performed a faster electron transfer rate. • The GPE/ZnO NPs is more accessible than other formaldehyde analytical methods. • The GPE/ZnO NPs was employed in formaldehyde electrochemical sensor in tofu sample. The green synthesis route of metal oxide nanoparticles using plant derivative extract has attracted the attention of researchers due to the simplicity, low cost, use less chemical reagents, produce less toxic waste, as well ready conducted in ambient conditions. In this study, zinc oxide nanoparticles (ZnO NPs) were successfully prepared via the facile green synthesis route using orange ( Citrus sinensis ) peel waste aqueous extract (OPE) as the bio-complexing agent. The prepared ZnO NPs showed a broad Ultra-Violet (UV) peak at around 358 nm, indicating the significant excitation binding energy of the ZnO NPs. Further characterization using Fourier-transform infrared (FTIR) confirmed that flavonoids in the OPE play the primary role in nanoparticle formation. Moreover, the scanning electrode microscopy-energy dispersive X-ray (SEM-EDX) and transmission electron microscopy (TEM) images showed that the prepared ZnO NPs have irregular sponge-like shapes, while the X-ray diffraction (XRD) confirmed the structure of ZnO was hexagonal wurtzite with a crystalline size of 11.58 nm. The electrochemical behavior study of the ZnO NPs-modified graphite paste electrode (GPE/ZnO NPs) using the ferro ferricyanide system was also performed, revealing that the ZnO NPs modification did not increase the mass transfer rate but successfully increased the electron transfer rate compared to the bare GPE. The cyclic voltammogram showed the optimum pH of 9 for the electrooxidation of formaldehyde (HCHO) on the GPE/ZnO NPs with an HCHO oxidation peak at 0.191 V vs. Ag/AgCl, while there was no reduction peak observed. Furthermore, in the phosphate buffer pH of 9 media, the linear correlation study between the square root of scan rate and the anodic peak current showed that the mass transfer of HCHO on the surface of GPE/ZnO NPs was mainly controlled by diffusion. The feasibility as the electrochemical sensor of HCHO is demonstrated by a limit of detection of less than 18 µM, linearity ranges from 0 to 100 mM, a ratio value of 0.38 of %relative standard deviation (RSD) to %RSD Horwitz, % recovery up to 103.9% in the real tofu sample, and the high selectivity toward HCHO instead of ethanol.

Fabrication of copper incorporated graphene oxide nanocomposites used for electrochemical determination of methyl parathion contaminants

lectrochemical studies of methyl parathion on novel nanocomposites electrode surface systems reached distinction in recent years because of their application in trace determination. Cyclic voltammetric behaviours of methyl parathion on nanocomposites modified glassy carbon electrodes at different pH in aqueous ethanol media were carried out. Influence of pH led to the selection of pH 1.0 as the best pH for the electroanalysis of methyl parathion. Voltamogram of pesticide exhibits two cathodic and one anodic peak responding at all pH media with the novel modified electrode system. The modified electrode shows one redox couple around the potential range from 0.1 to 0.3 V and one reduction peak around at - 0.75 V with higher peak current responding to the modified electrode. The reduction peaks were selected for stripping analysis owing to their maximum current response. The experimental parameters were optimized using the differential pulse stripping mode. A calibration plot was made. The determination limit and standard deviations were arrived. The applicability of the method was also verified in a sample soil analysis.

Phenyl Vinylsulfonate, a Novel Electrolyte Additive to Improve Electrochemical Performance of Lithium-Ion Batteries

Irreversible capacity fading, originating from the formation of the solid electrolyte interphase (SEI), is a common challenge encountered in lithium-ion batteries (LIBs) containing an electrolyte based on ethylene carbonate (EC). In this research, phenyl vinyl sulfonate (PVS) is examined as a novel electrolyte additive to mitigate this issue and subsequently enhance the cyclic stability of LIBs. As evidenced by density functional theory (DFT) calculations, PVS has a higher reduction potential than that of EC, which is in accordance with the cyclic voltammetry (CV) measurements. Accordingly, the PVS-containing electrolyte demonstrated a reduction peak at ~1.9 V, which was higher than that of the electrolyte without an additive (at ~1.7 V). In contrast to the SEI derived from the reference electrolyte, the one built-in PVS-containing electrolyte was capable of completely inhibiting the electrolyte reduction. In terms of the Raman spectroscopy and electrochemical impedance spectroscopy (EIS) analysis, SEI formation as the result of PVS reduction can lead to less structural disorder in the graphite electrode; the battery with the additive showed less interfacial and charge transfer resistance. The Li/graphite cell with 1 wt % of PVS delivered capacity retention much higher than that of its counterpart without the additive after 35 cycles at 1 C.

Electrochemical oxidation of ketorolac at graphene oxide-based sensor

An electrochemical study of an anti-inflammatory drug Ketorolac (KTC) was carried out at graphene oxide modified CPE using electrochemical technique like voltammetry. Phosphate buffer solution (PBS) with an ionic power of 0.2 M was opted as an electrolytic solution and pH 3.8 was found to be optimum. The KTC was electrochemically oxidised giving two well defined oxidation peaks at 1.114 V and 1.474 V with peak strength 9.87 µA and 29.75 µA. The obtained peak current was very much higher than that of bare CPE and the absence of reduction peak confirms the process was irreversible. Surface characterisation of GO/CPE was studied by employing scanning electron microscopy (SEM) and atomic force microscopy (AFM). Scan rate studies gave the insights about reaction mechanism which involves two electrons and one proton transfer. The process was predominantly controlled by diffusion. The limit of detection (LOD) and limit of quantification (LOQ) was calculated to be 4.92 × 10-8 M and 16.41 × 10-8 M respectively. The proposed sensor was used in analysis of pharmaceutical and spiked urine samples, which showed the high recovery rate proving the applicability of the developed sensor.

Amino-Functionalized Laponite Clay Material as a Sensor Modifier for the Electrochemical Detection of Quercetin.

In this work, an electrode modified with an amino-functionalized clay mineral was used for the electrochemical analysis and quantification of quercetin (QCT). The resulting amine laponite (LaNH2) was used as modifier for a glassy carbon electrode (GCE). The organic–inorganic hybrid material was structurally characterized using X-ray diffraction, Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and CHN elemental analysis. The covalent grafting of the organosilane to the clay backbone was confirmed. The charge on the aminated laponite, both without and with the protonation of NH2 groups, was evaluated via cyclic voltammetry. On the protonated amine (LaNH3+)-modified GCE, the cyclic voltammograms for QCT showed two oxidation peaks and one reduction peak in the range of −0.2 V to 1.2 V in a phosphate buffer–ethanol mixture at pH 3. By using the differential pulse voltammetry (DPV), the modification showed an increase in the electrode performance and a strong pH dependence. The experimental conditions were optimized, with the results showing that the peak current intensity of the DPV increased linearly with the QCT concentration in the range from 2 × 10−7 M to 2 × 10−6 M, leading to a detection limit of 2.63 × 10−8 M (S/N 3). The sensor selectivity was also evaluated in the presence of interfering species. Finally, the proposed aminated organoclay-modified electrode was successfully applied for the detection of QCT in human urine. The accuracy of the results achieved with the sensor was evaluated by comparing the results obtained using UV–visible spectrometry.

A stable glucose sensor with direct electron transfer, based on glucose dehydrogenase and chitosan hydro bonded multi-walled carbon nanotubes

Direct electron transfer (DET) glucose sensors are third-generation biosensors, which allow the enzyme to directly transfer electrons by glucose oxidation without a mediator. In previous studies, many researchers have focused on the glucose oxidase (GOx)-based DET glucose sensor; however, an efficient DET glucose sensor using flavin adenine dinucleotide (FAD)-glucose dehydrogenase (GDH) has not been developed. In the present study, we bound FAD-GDH and multi-walled carbon nanotubes (MWCNT), using chitosan (CS) compounds that support hydrogen bonding, van der Waals forces, and 3D structural adsorption. The GDH/CS-MWCNT-5 composite, which had a GDH concentration of 75 wt%, was physically adsorbed on screen-printed carbon electrodes (SPCEs), and cyclic voltammetry indicated that its oxidation and reduction peaks were at − 0.422 V and − 0.543 V (vs Ag/AgCl), respectively. In addition, the electrochemical results confirmed that the prepared GDH/CS-MWCNT/SPCEs were not affected by other interfering substances or oxygen at pH of 7. The GDH/CS-MWCNT/SPCEs displayed oxidation catalytic currents, which increased according to glucose concentrations across a range of 0–5.5 mM. Finally, the short-term stability of glucose, assessed for 10 days, was maintained at 80% of the GDH enzyme activity for 6 days, and it reduced to 50% of the initial activity for the remaining 4 days. Here, we illustrate the potential utility of the FAD-GDH-based DET method in continuous glucose monitoring sensors.

Anodic TiO2 nanotube layers decorated by Pd nanoparticles using ALD: An efficient electrocatalyst for methanol oxidation

Herein, we report the performance of Pd nanoparticles (NPs) prepared by Atomic Layer Deposition (ALD) as a catalyst for methanol electro-oxidation. Pd NPs were decorated onto anodic TiO2 nanotube (TNT) layers as supporting material that possess a large available surface area and direct electrical contact via the underlying titanium foil. Different Pd loadings (150 – 300 – 450 – 600 ALD cycles) show different particles sizes ranging between 7 and 12 nm, as revealed by transmission electron microscopy. Coalescence dominated visibly from 450 ALD cycles, which led to a porous Pd layer all along the TNT walls rather than the growth of individual particles. Electrocatalytic performance was investigated by cyclic voltammetry (CV), where the catalytic activity increased proportional with Pd loading up to the highest values for 400 and 450 cycles, whereas a further increase in the number of ALD cycles (NALD) did not show any additional improvement in methanol oxidation current densities. TNT layers decorated with 400, 450 and 600 Pd ALD cycles show featureless curves suggesting complete anti-poisoning ability or possibly a proof of a direct conversion from CH3OH to CO2 (without any intermediate byproducts). The lack of an oxidation peak during the anodic scan and therefore a reduction peak during the cathodic scan, confirms Pd NPs (stabilized by TiO2) efficiently utilize OHads and chemisorbed CH3OH in a way that its CO poisoning was inhibited. As a result, the tuned high surface area TNT layers exhibited excellent performance as a supporting material for Pd NPs against formation of electrochemical poisoning species. Finally, the mechanism of the TNT layers interaction with Pd NPs, which led to the propelling methanol oxidation reaction without loss in performance over cycling is postulated.

Cyclic square-wave voltammetric discrimination of the amphetamine-type stimulants MDA and MDMA in real-world forensic samples by 3D-printed carbon electrodes

3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA), called as “ecstasy”, are the main seized amphetamine-type stimulants consumed worldwide. Based on the voltammetric profiles of MDMA and MDA on 3D-printed carbon-black integrated polylactide, we propose a cyclic square-wave voltammetric (CSWV) approach to detect and discriminate both molecules in saliva and seized samples. CSWV combines enhanced sensitivity of pulsed techniques and mechanistic insights of cyclic voltammetry and herein we propose cyclic scans from 0.0 to +1.5 V and back to 0.0 V in Britton-Robinson buffer (0.12 mol L−1 pH=6.0). The first scan showed oxidation peaks at around +1.1 V for both MDMA and MDA, however, only MDMA showed a second oxidation peak at +1.35 V (stabilization of a cation radical). The reverse scan displayed a reduction peak only for MDA at around +0.2 V (the oxidation product from MDA is only electroactive in the reverse scan). Thus, MDMA can be selectively detected in the forward scan and MDA in the reverse scan. CSWV provided linear ranges from 5.8 to 35.0 µmol L−1 and 3.1 to 21.8 µmol L−1 (r2>0.99) for MDMA and MDA, respectively. Intra-day precision studies (n=10) showed that potential peaks (RSD<0.8%) and current intensity (RSD<3.8%) for all electrochemical processes are repetitive, with LODs lower than 1.8 µmol L−1. Paracetamol, caffeine, amphetamine, methamphetamine, ephylone, lysergic acid diethylamide and a phenethylamine drug (found in ecstasy-like tablets) did not interfere in the detection of MDMA and MDA. Analysis of seized tablets showed results similar to GC-MS. Spiked saliva samples were analyzed (recovery of 83-106%) after dilution in electrolyte. The combination of CSWV and 3D-printed electrodes (disposable devices easily produced in large scale at reduced cost) is highly promising for selective, fast, simple, low-cost, and on-site screening forensics analyses.

Electrochemical detection of hydrogen peroxide using micro and nanoporous CeO2 catalysts

In this research work, focus has been made on a glassy carbon electrode (GCE) modified commercial micro and synthesized nano-CeO2 for the detection of hydrogen peroxide (H2O2). Firstly, CeO2 nanoleaves were prepared by solvothermal route. Both commercially available micro CeO2 and synthesized nano-CeO2 structures were analyzed by different characterization techniques. The Raman spectra of synthesized nano CeO2 has more oxygen vacancies than micro CeO2. SEM images revealed that the synthesized CeO2 acquired leaf-like morphology. The catalyst nano CeO2 offered mesoporosity from nitrogen adsorption-desorption isotherms with massive sites of activation for increasing efficiency. Experiments on determining H2O2 using micro CeO2 or nano-CeO2/GCE was conducted using cyclic voltammetry (CV) and amperometry. Enhanced H2O2 reduction peak current with lower potential was observed in nano-CeO2/GCE. The influence of scan rate and H2O2 concentration on the performance of nano-CeO2/GCE were also studied. The obtained results have indicated that nano-CeO2/GCE showed improved electrochemical sensing behavior towards the reduction of H2O2 than micro-CeO2/GCE and bare GCE. A linear relationship was obtained over 0.001 μM–0.125 μM concentration of H2O2, with good sensitivity 141.96 μA μM−1 and low detection limit of 0.4 nM. Hence, the present nano-CeO2 system will have a great potential with solvothermal synthesis approach in the development of electrochemical sensors.

Electroanalytical measurements of lanthanum (III) chloride in molten calcium chloride and molten calcium chloride and lithium chloride

Cyclic voltammetry (CV), square wave voltammetry (SWV) and other electroanalytical methods have been applied to molten chloride salts to study metal ion behavior. These studies have been useful for understanding and optimizing the electrowinning of metals. Notable ions that have been studied are rare earth and actinide metal ions in LiCl-KCl salts. However, the behavior of lanthanum (La3+) ions in some molten chlorides or chloride mixtures (e.g., CaCl2) has not been studied. CV experiments were conducted to evaluate La3+ behavior in CaCl2-LiCl and CaCl2 and were compared to La3+ behavior in LiCl-KCl and CaCl2-NaCl eutectics from other studies. The electrochemical reaction was checked for reversible, quasi-reversible, and irreversible transitions in scan rate by examining the relationship between the scan rate applied and the peak current and potential for La3+ reduction. Properties such as diffusion coefficient (Do) and electrons exchanged (n) were calculated from data. The electrochemical setup was also checked for radial diffusion based on the calculated La3+ diffusion coefficient and electrode radius, which led to the observation that natural convection possibly affected the La3+ reduction peak at low scan rates. For more accurate electroanalytical measurements of La3+ reduction, CV curves with and without LaCl3 added to CaCl2 and CaCl2-LiCl were compared to establish baselines for the La3+ reduction peak. The impact of resistance (IR) compensation on the La3+ reduction peak was also explored. Techniques and practices that improved electroanalytical measurements include placing the electrolytic cell in a Faraday cage, distancing electrodes from the heating coils, and melting the chlorides twice prior to measurements.

A nonenzymatic reduced graphene oxide-based nanosensor for parathion.

Organophosphate-based pesticides (e.g., parathion (PT)) have toxic effects on human health through their residues. Therefore, cost-effective and rapid detection strategies need to be developed to ensure the consuming food is free of any organophosphate-residue. This work proposed the fabrication of a robust, nonenzymatic electrochemical-sensing electrode modified with electrochemically reduced graphene oxide (ERGO) to detect PT residues in environmental samples (e.g., soil, water) as well as in vegetables and cereals. The ERGO sensor shows a significantly affected electrocatalytic reduction peak at −0.58 V (vs Ag/AgCl) for rapid quantification of PT due to the amplified electroactive surface area of the modified electrode. At optimized experimental conditions, square-wave voltammetric analysis exhibits higher sensitivity (50.5 μA·μM−1·cm−2), excellent selectivity, excellent stability (≈180 days), good reproducibility, and repeatability for interference-free detection of PT residues in actual samples. This electrochemical nanosensor is suitable for point-of-care detection of PT in a wide dynamic range of 3 × 10−11–11 × 10−6 M with a lower detection limit of 10.9 pM. The performance of the nanosensor was validated by adding PT to natural samples and comparing the data via absorption spectroscopy. PT detection results encourage the design of easy-to-use nanosensor-based analytical tools for rapidly monitoring other environmental samples.

Selective Catalytic Removal of High Concentrations of NOx at Low Temperature

Three vanadium-based catalysts were used to remove high concentrations of nitrogen oxides, and the catalysts’ performance of de-NOx and anti-H2O under the high concentrations of NOx were investigated. The V-Mo-W/TiO2 catalysts were tested under 1500 mL/min gas flow (GHSV = 500 h−1, 2.4% NO2, 4.78% NH3, 13% O2, 4% H2O, 5% CO2) and characterized by BET, SEM, EDS, XRD, XPS, H2-TPR, and NH3-TPD; then, their physical and chemical properties were analyzed. The results showed that under the influence of H2O, the NOx conversion of the V-Mo-W/TiO2 catalysts remained above 97% at 200–280 °C indicating that the catalysts had high catalytic activity and strong water resistance. The analysis of the characterization results showed that the larger specific surface area of the catalyst, the higher acid content, stronger redox ability, and higher V4+ and V3+ content were the reasons for the high NOx conversion. The surface area decreased and the microstructure become smoother after the reaction, which may be caused by thermal sintering, but the overall morphology did not change. Comparing the H2-TPR and NH3-TPD of V1.6Mo1.7W1.8/TiO2 before and after NH3-SCR reaction, it was found that the reduction peak and the intensity of the acid sites of the sample had not changed, which indicated that the catalyst had good anti-sintering performance and a long lifetime. This is significant for followup long-term engineering application experiments.

Electrochemical sensor based on Ca-doped ZnO nanostructured carbon matrix for algicide dichlone

As many new pollutants continue to be introduced into the environment, environmental pollution has become the biggest concern in the current era. It requires the development of a more sensitive, effective and selective, cost-efficient modified electrode. We designed a sensitive and effective voltammetric sensor with synthesized calcium-doped zinc oxide (Ca-ZnO/CPE). The cyclic voltammetry (CV) method was employed to determine the electrochemical behavior of dichlone (DCN), referred to as fungicide and algaecide. The surface morphology of the developed sensor's matrix was carried out employing SEM, TEM, and XRD techniques. The Ca-ZnO NPs as a modifier in the carbon paste efficiently enhanced both the oxidative and reduction peak current of DCN in CVs. The effect of electrolyte pH and scan rate variation investigation results were used to determine the total number of electrons in the DCN electro-oxidation mechanism, the number of protons, charge transfer coefficient, and heterogeneous rate constant. Additionally, kinetic and thermodynamic aspects of DCN were investigated. The square wave voltammetry technique (SWV) showed the lowest detection limit (DL) of 5.98 × 10–8 M and a wide linearity range (3.5 × 10–7 M to 7.2 × 10–4 M). The environmentally-based approach successfully quantifies DCN in water and soil samples.

Electrochemical behavior of chromium carbide MXene modified electrodes: Hydrazine sensing

Electrochemical characteristics of few-layered two dimensional chromium carbide MXene (FL-Cr2CTx) modified electrode towards the detection of hydrazine (HZ) is reported for the first time in this paper. The modified electrode was fabricated using binder-free and mechanically immobilized FL-Cr2CTx onto the surface of paraffin impregnated graphite electrode. Electrochemical behavior of modified electrode was investigated by cyclic voltammetric studies and the effect of supporting electrolytes, scan rate and stability was also examined. The modified electrode exhibited multiple quasi-reversible peaks with three reduction peaks at − 0.39 V, − 0.88 V and − 1.20 V and two oxidation peaks at − 0.56 V and 0 V respectively, corresponding to surface oxy and hydroxyl groups in FL-Cr2CTx and due to the variable oxidation states of chromium as well. The electrode was utilized for electrochemical sensing of HZ, which exhibited a high sensitivity of 1.810 ± 0.013 µA µM−1 with a detection limit of 6.60 × 10−7 M (at S/N = 3). The developed sensor was further used for quantitatively analyzing HZ liquid propellant spiked in water, as a part of real sample analysis and the results were found satisfactory. The plausible mechanism suggests that the surface adsorption/desorption redox process of Cr2COx/Cr2COxH2 is responsible for the detection of HZ.

Bio-Electrocatalytic Reduction of Hydrogen Peroxide by Peroxidase from Guinea Grass (Panicum Maximum) Immobilized on Graphene and Graphene Oxide Screen-Printed Electrodes

Objective: In this article a comparison was made between graphene (SPGE) and graphene oxide screen-printed electrodes (SPGOE) to study the bio-electrocatalytic reduction of hydrogen peroxide (H2O2) by guinea grass peroxidase (GGP). Methods and materials: GGP was immobilized onto SPGE and SPGOE by a drop-casting procedure. Electrochemical techniques were carried out to monitor the electrochemical behavior of GGP and the efficiency of electrocatalytic reduction of H2O2. Results and discussion: GGP adsorbed on both electrodes exhibited a couple of well-defined redox peaks at 120 mV/10.5 mV and 184 mV/59 mV for anodic and cathodic peaks, respectively. Linearity between scan rates root and oxidation and reduction peak currents for both electrodes suggest a surface-controlled process. The GGP-modified electrodes exhibited a good electrocatalytic activity to H2O2 reduction at a redox potential of -0.6 V and -0.5 V for SPEG and SPEGO, respectively. Conclusions: SPGE and SPGOE electrodes modified with GGP showed excellent analytical performance towards different concentrations of hydrogen peroxide. This is a preliminary step to developing a bio-analytical portable system based on GGP for the detection of H2O2 in real environmental samples.

Depolarization of Cu Electrodeposition in the Presence of Ag: A Cyclic-Voltammetry Study

During our investigation of Cu-Ag alloy electrodeposition from acidic sulfate bath, peculiar behavior of Cu reduction was found in the CV profiles when the Cu deposition overpotential is very small. An early Cu(II) reduction peak, which is revealed to be a full reduction of Cu(II) to Cu(0) based on the EQCM-CV measurement, was observed in addition to the main Cu(II)/Cu(0) deposition peak. To our surprise, this early Cu deposition peak occurs when the deposition bath contains Ag(I) cations, or the substrate contains Ag metals.EQCM-CV profile shows that the early Cu deposition peak is associated with a 65% deposition efficiency, slightly smaller than that of the main Cu(II)/Cu(0) reduction peak (~78%). The amount of Cu deposited associated with the early Cu reduction peak is estimated based on the total charge associated with this peak. The early Cu reduction peak is associated with Cu deposit thicker than 3 nm, with the thickness increases with decreasing scan rate or increasing Ag(I) concentration in the electrolyte. Meanwhile, from the CV profiles, the early Cu reduction peak is associated with a Tafel slope ~30mV/dec. We hypothesize that by the catalytic effect of Ag, either in the substrate or in the initial deposit, on the intermediate reduction step of Cu(II)/Cu(I) causes the early Cu reduction peak by shifting rate determining step of Cu(II)/Cu(0) deposition from Cu(II)/Cu(I) to Cu(I)/Cu(0). Disclaimer: This work has been submitted at Electrochimica Acta (manuscript id: EA21-4167RR1), with title "Depolarization of Cu electrodeposition in the presence of Ag: a cyclic-voltammetry study". Figure attached is chosen from this manuscript. Figure. Cyclic voltammograms at electropolished Cu substrate from 0.3 M CuSO4 + 0.5 M H2SO4 (a) with or without 0.5 mM NaNO3, and (b) with 0-0.5 mM AgNO3. Figure 1

(Digital Presentation) Synthesis of Conjugated Polymer Alloy Prepared By Electrochemical Polymerization in Chiral Liquid Crystal

In this research, we synthesized polymer alloy by electrochemical polymerization in chiral liquid crystal. Homopolymers and the copolymer can be synthesized when electrochemical polymerization was conducted in the presence of several types of monomers. The polymer alloy thus prepared contains both blend of homopolymers and copolymers. The polymer alloy shows optical activity. The chirality derived from transcription of liquid crystal during the polymerization reaction results to show optical activity. The polymer alloy can show optical activity with no asymmetric centers. The optical activity is due to existence of charge carriers (polarons) in the main chain as a form of conjugated polymers. This is called chiral charge carrier “chiralions”. This research found that the chiral polymer alloy has chiralions.Polymer alloys have been prepared by blending several kinds of polymers in the reaction. Polymer alloys also can be prepared by melt method. Unsubstituted conjugated polymers have poor solubility and fusibility because of the rigid π-bonds in the skeleton, which is drawback for preparation of π-conjugated polymer-based alloys. We have studied on preparation of chiral conjugated polymer alloys with combination of achiral polymers and chiral polymers.In the present study, conjugated polymer alloys were synthesized with the method described in Figure 1a. Cholesteryl acetate (chiral inducer), 2,7-di(2-thienyl)fluorene (mono1), N-methyl-3,6-di(2-thienyl)carbazole (mono2) and TBAP (supporting salt) were dissolved in 4-cyano-4'-pentylbiphenyl (5CB) as a host liquid crystal to prepare a chiral liquid crystal electrolyte. The electrolyte exhibited a fingerprint structure under observation of polarizing optical microscopy. For the electrochemical polymerization reaction, the electrolyte solution is charged in the cell consisted of two indium-tin-oxide (ITO) glass plates as electrodes and a poly(tetrafluoroethylene) spacer (200 μm thickness). Next, dc voltage of 3.0 V was applied to the ITO glass cell for 30 min for electrochemical polymerization. The polymer was deposited on the anode electrode as a thin film form. After polymerization, the remaining electrolyte solution on the ITO glass electrode was carefully washed with a large amount of hexane, yielding dark blue film. This film is abbreviated as Alloy1. The molecular structure was confirmed by infrared spectroscopy with the KBr method. Alloy1 shows a fingerprint structure under POM observations (Figure 1b). The macroscopic structure of cholesteric liquid crystal was transcribed from the liquid crystal electrolyte solution to Alloy1. Synchrotron XRD measurement was carried out. The peak at 10.3 Å is derived from monomer repeat units. The XRD signal at 5.1 Å and 3.4 Å can be derived from π-stacking of Alloy1. Alloy1 shows UV-vis absorption due to the three signals derived from π-π* transition of the main chain, polarons (radical cations) and bipolarons (radical dications). Electrochemical properties of Alloy1 were evaluated by the cyclic voltammetry (CV). Alloy1 film deposited on the ITO glass was used as a working electrode. An Ag/Ag+ electrode and a platinum wire served as the reference and counter electrodes, respectively. A propylene carbonate solution with 0.1 M of TBAP was employed as an electrolyte solution for the CV measurements. Cyclic voltammograms of Alloy1 shows the oxidation peak and reduction trough (Figure 1c). Plots of the oxidation peak current (I pa) and the reduction peak current (I pc) as a function of the square root of the scan rate show a linear shape of the anodic and cathodic peak current values when scan rates from 10 to 100 mV/s with intervals of 10 mV/s. This result indicated that the redox reaction of Alloy1 was reversible and controlled by electron transfer processes. In-situ circular dichromism (CD) and in-situ optical rotatory dispersion (ORD) spectra of Alloy1 with application of voltages were examined in a propylene carbonate solution with 0.1 M of TBAP. The application voltages were between 0-1.2 V (vs. Ag/Ag+) with intervals of 0.1 V. A negative Cotton effect was observed from the in-situ CD, indicating Alloy1 has left-handed helical structure. The ORD shows negative signals, and changes with applied voltage. The ellipticity signal in the CD and optical rotation in the ORD could control in the electrochemical method, accompanied by electrochemical redox process.We synthesized the polymer alloy by electrochemical polymerization in chiral liquid crystal. The conjugated polymer alloy showed chirality with no chiral centers in the main chain. The CD and ORD bands at NIR range are assigned to doping band as a form of polarons (radical cations). This research evaluated electrochemical control of “chiralions”. Figure 1