Chronoamperometric Experiments Research Articles

Electrochemical sensor for sensitive detection of an anticancer drug Capecitabine by modified carbon paste electrode with tetrahydrodipyrazolo pyridine derivative and Cu-MCM-41 nanoparticles

In this work, the electrochemical performance of the modified carbon paste electrode with tetrahydrodipyrazolo pyridine derivative as an organic modifier, and Cu-MCM-41 nanoparticles have been investigated to determine Capecitabine (CAP), an anticancer drug. CAP has been used for treating some cancers such as rectal, stomach, breast, pancreatic, and colon cancer. It works by inhibiting cancer cells growth. Herein, an organic modifier was prepared using a green biocatalyst in a biomimetic synthesis, a simple method was used for synthesis of Cu-MCM-41 nanoparticles. The electrochemical parameters such as the transfer coefficient and the number of electrons and protons involved in the redox reaction of the modifier were calculated using cyclic voltammetry (CV). Also, an electrocatalytic reaction was observed for CAP oxidation on the modified electrode surface as a result of a reduction in the CAP species oxidation overvoltage. To measure the CAP species by the modified electrode, some optimizations were performed. The Tafel curve was used to determine the transfer coefficient between the CAP and modifier, which was determined as 0.9. The chronoamperometric experiment was also investigated to obtain the numerical value of the CAP diffusion coefficient (D = 7.67 × 10–6 cm2 s−1). The calibration curve was drawn by the differential pulse voltammetry technique (DPV), and linear ranges of 2.0–80.0 µM and 80.0–800.0 µM, and the detection limit (LOD = 0.144 µM) were obtained. To evaluate the efficiency of the proposed sensor for CAP determination, measurement was done on a real blood serum sample. The proposed sensor displayed good selectivity, repeatability, and stability.

Voltammetry in Microemulsion Formed by Electron Donor Solution in Organic Solvent|Ionic Liquid Microdroplets in Aqueous Electrolyte

Oxygen reduction reaction (ORR)1 or hydrogen evolution reaction (HER)2 at liquid|liquid interface provide the possibility of separation of their products: hydrogen peroxide or hydrogen.3,4 Typically, these reactions are studied at single interface formed between immiscible electrolyte solutions in quiescent conditions. In such geometry the frequency of successful reaction events when highly hydrophobic electron donor (i.e. decamethylferrocene (DMFc) or excited form of decamethylruthenocene (DMRc)) dissolved in organic phase meet proton from aqueous phase is rather limited. Importantly, electrochemical recycling of electron donor at electrode positioned close to the liquid|liquid interface increases efficiency of this reaction.5,6 The use of microemulsion is promising higher efficiency alternative, because of extended interfacial area of numerous organic droplets. As efficient electron exchange between oxidized form of electron donor and the electrode is crucial for biphasic ORR and HER one has to focus on electrochemical studies of DMFc or DMRc in emulsions.are important. Voltammetric signal of various redox probes as ferrocene or ferrocene surfactants in quiescent emulsions is similar to that in single phase with some variation of peak density currents or redox potential.7-11 Other studies focused on chronoamperometric experiments to detect collisions of redox probe (e.g. ferrocene12) containing droplets with the electrode surface. It was found that the addition of an hydrophobic ionic liquid, typically trihexyltetradecyl-phosphonium bis(trifluoro-methylsulfonyl) amide to the organic phase as stabiliser and electrolyte, does not influence the magnitude of the electrochemical signal.13 Here we will report results of electrochemical studies of emulsion prepared from aqueous HClO4 and DMFc or DMRc and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide (IL-PI) solution in toluene. As aqueous phase acid solution was selected, because in biphasic ORR or HER it serves as a source of protons. During the measurements the microemulsion was stirred to achieve faster droplets transport towards the electrode surface. Results will be compared with these obtained in a single organic phase.Voltammograms obtained with glassy carbon disc electrode indicate reversible oxidation/reduction of the redox probe similar to the seen with an electrode immersed in single organic phase. During continuous scanning redox only small change of peak currents is seen. Importantly, when after experiment in emulsion working electrode was transferred to aqueous HClO4, the voltammetric signal is still seen, but the peak currents are significantly smaller. This may indicate the redox reaction in liquid film formed on the electrode surface. Formation of liquid organic film is confirmed by the results of chronoamperometric experiments. When the electrode is set at potential corresponding to the oxidation of the redox probe, of the current is seen after c.a. 100 s drop, what may indicate the gradient of redox probe concentration. As DMFc is insoluble in water this points out on gradient of organic phase close to the glassy carbon surface.14 In turn voltammetric current related to electroreduction of highly hydrophilic hexacyanoferrate(III) is significantly diminished in emulsion as compared to pure aqueous electrolyte indicating partial coverage of the GC surface by hydrophobic film.Other effects related with electrochemical behavior of studied emulsions will be also presented and discussed.

Formic acid electrooxidation on palladium nanostructured electrodes in concentrated solutions

The formic acid oxidation reaction (FAO) was evaluated on palladium nanostructured films supported on glassy carbon in 0.5 M H2SO4 + x M HCOOH solutions, where 0.5 ≤ x ≤ 8.0, in the potential range 0.2 ≤ Es / V ≤ 0.6 vs. RHE at 25 °C. Measurements consisted in chronoamperometric experiments, which were followed by stripping voltammetry in order to evaluate the presence of COad. Open circuit potential (OCP) decay was also employed to analyse the formic acid spontaneous decomposition. The results of OCP experiments showed the formation of β-PdH hydride as well as the absence of COad for all HCOOH concentrations, evidencing that the spontaneous decomposition of HCOOH on palladium is the dehydrogenation reaction, which produces H2 and CO2. It was demonstrated that COad is not directly involved in the kinetic mechanism of the FAO on palladium, and it was also explained the controversy related to the detection of COad in previous studies. Additionally, the highest FAO electrocatalytic activity was observed at x = 2.0 M

Time Transients with Inductive Loop Traces in Metal Halide Perovskites

AbstractMetal halide perovskites are archetypal ionic‐electronic materials with great prospects for optoelectronic applications. Among the rich variety of physics exhibited by ionic‐electronic conduction, here, those most relevant to optoelectronic devices in which ionic mechanisms introduce a kinetic delay in the electronic phenomena are analyzed. The attention is focused on the inductive loop features and a dynamical model is developed to describe the corresponding complex multiscale dynamics in the time domain under experimental conditions, finally explaining the fundamental structure of the current transient responses in halide perovskite semiconductors. Based on complex capacitive and inductive patterns extensively studied in impedance measurements, an adequate interpretation of time domain methods capable of monitoring charge‐carrier dynamics is produced. Therefore, this methodology identifies the characteristic parameters of all types of transient dynamics in metal halide perovskites, providing a suitable connection of correlated techniques, including impedance and chronoamperometric experiments, toward a robust interpretation of the device response. The scope of the method is fairly general, since these counterintuitive transient effects are observable not only in metal halide perovskites, but also in multiple materials and processes, mainly in different research fields pertaining to electrochemistry and electronics.

Highly Sensitive Sensor for the Determination of Riboflavin Using Thionine Coated Cadmium Selenide Quantum Dots Modified Graphite Electrode

In this paper, the electrochemical non-enzymatic detection of Riboflavin (RF) was proposed based on its catalytic reduction in a Thionine-coated Cadmium Selenide Quantum dots (TH@CdSe QDs)-modified paraffin wax-impregnated graphite electrode (PIGE) that was prepared using a novel approach. The synthesized TH@CdSe QDs were confirmed by UV-Vis spectroscopy, Confocal Raman Microscopy and High Resolution Transmission Electron Microscopy (HRTEM) studies. The electrochemical response of the TH@CdSe QDs-modified PIGE was studied by cyclic voltammetry. The voltammetric response of RF at the TH@CdSe QDs-modified PIGE showed higher current than the bare PIGE. Under optimum conditions, the electrocatalytic reduction currents of RF was found to be linearly related to its concentration over the range of 1.6 × 10−7 M to 1.4 × 10−4 M with a detection limit of 53 × 10−9 M (S/N = 3). The TH@CdSe QDs-modified PIGE was utilized as an amperometric sensor for the detection of RF in flow systems was performed by carrying out hydrodynamic and chronoamperometric experiments. The TH@CdSe QDs-modified PIGE showed very good stability and a longer shelf life. The applicability of the fabricated electrode was justified by the quantification of RF in commercial tablets.

Facile synthesis of a ZnO/Fe2O3 heterostructure and its graphene-reinforced composite for boosting the photo-mineralization of crystal violet and phenol

Abstract Herein, a nanostructured ZnO/Fe2O3 heterostructure and its graphene (Gr)-reinforced composite (ZnO/Fe2O3@Gr) have been synthesized via co-precipitation and post-ultrasonication approaches. The formation of heterojunction at the ZnO–Fe2O3 interface reduces the bandgap and keeps the electron-hole pairs apart. The graphene plays multiple roles to boost the dye removal effectively of the ZnO/Fe2O3@Gr composite. The charge transfer aptitude, isolation of charge carriers, and resistance at the ZnO/Fe2O3-Graphene interface were also examined by Mott–Schottky, chronoamperometric, and impedance experiments. The performance of an as-synthesized ZnO/Fe2O3@Gr catalyst was explored for the mineralization of a cationic dye (crystal violet, CV) and phenol in visible-light (λ above 400 nm) for 2 h. The ZnO/Fe2O3@Gr catalyst has mineralized 92.8 % CV dye and 50.86 % phenol after 2 h of visible-light irradiation. Moreover, the mineralization constant (k) comes to be 0.019 min−1, which is 4.2, 2.3, and 1.7 times higher than ZnO, Fe2O3, and ZnO/Fe2O3 catalysts, respectively. Increasing the dosage of the ZnO/Fe2O3@Gr catalyst from 10 mg to 30 mg increased the rate constant from 0.006 min−1 to 0.019 min−1, thereby increasing the efficiency of CV dye mineralization from 58.5 % to 92.8 %. The tuned photocatalytic activity of the ZnO/Fe2O3@Gr is due to the formation of the ZnO–Fe2O3 heterostructure and, preferentially, its conductive graphene. In fact, graphene serves the roles of an efficient electron collector, a transporter, and an effective UV/Vis light absorber, enabling the creation of active species that further boost the photocatalytic performance. According to the results of this study, the easiest and cheapest way to deal with toxic dyes in industrial waste is to make photocatalysts from semiconductive and carbonaceous materials that have integrated properties.

Oriented growth of cobalt electrodeposits assisted by an interfacial flow of bubbles

High-quality Co products are desirable for a variety of applications due to its unique properties. Herein, an interfacial field of flowing bubbles was used to modify the microstructure of Co deposits in the electrowinning process. The effect of flowing bubbles on morphology, crystallographic structure and impurities of Co deposits were investigated. The nucleation and growth of Co deposits were discussed based on chronoamperometric experiments and sampling experiments. The results indicated that the microstructure of Co deposits was effectively modified by an external field of flowing bubbles. The Co deposits prepared in a quiescent electrolyte were porous and inhomogeneous, while the deposits prepared by using the flowing bubbles were compact and uniform. The nucleation and growth modes of Co deposits were also altered by the flowing bubbles. Preferentially oriented grains in the (110) direction were formed by instantaneous nucleation and screw dislocation growth of the deposits. Improvements in microstructure and crystallographic orientation were able to enhance the purity of Co deposits.

Electrochemical Measurement of Interfacial Distribution and Diffusion Coefficients of Electroactive Species for Ion-Exchange Membranes: Application to Br2/Br- Redox Couple.

A novel method has been proposed for rapid determination of principal transmembrane transport parameters for solute electroactive co-ions/molecules, in relation to the crossover problem in power sources. It is based on direct measurements of current for the electrode, separated from solution by an ion-exchange membrane, under voltammetric and chronoamperometric regimes. An electroactive reagent is initially distributed within the membrane/solution space under equilibrium. Then, potential change induces its transformation into the product at the electrode under the diffusion-limited regime. For the chronoamperometric experiment, the electrode potential steps backward after the current stabilization, thus inducing an opposite redox transformation. Novel analytical solutions for nonstationary concentrations and current have been derived for such two-stage regime. The comparison of theoretical predictions with experimental data for the Br2/Br- redox couple (where only Br- is initially present) has provided the diffusion coefficients of the Br- and Br2 species inside the membrane, D(Br-) = (2.98 ± 0.27) 10-6 cm2/s and D(Br2) = (1.10 ± 0.07) 10-6 cm2/s, and the distribution coefficient of the Br- species at the membrane/solution boundary, K(Br-) = 0.190 ± 0.005, for various HBr additions (0.125-0.75 M) to aqueous 2 M H2SO4 solution. This possibility to determine transport characteristics of two electroactive species, the initial solute component and its redox product, within a single experiment, represents a unique feature of this study.

Deciphering Highly Sensitive Non-Enzymatic Glucose Sensor Based on Nanoscale CuO/PEDOT-MoS2 Electrodes in Chronoamperometry

The present work demonstrates fabrication of a non-enzymatic glucose sensor based on CuO nanoparticles deposited over poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer infiltrated with nanoscale MoS2. Structural, morphological and elemental analyses of the fabricated sensor electrodes were performed via different characterization techniques like X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), elemental dispersive X-ray spectroscopy (EDX), and Fourier transform infra-red spectroscopy (FT-IR). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies of the hybrid nanoelectrode (CuO/PEDOT-MoS2) exhibited better redox activity and electron transfer kinetics, as compared with the CuO/PEDOT and CuO only systems. Accordingly, the electrochemical parameters of all the systems were determined and compared at large. The CuO/PEDOT-MoS2 hybrid electrode system offered a significant enhancement in the electroactive area (∼1.47 cm2) and rate constant (0.76 s−1) upon oxidizing glucose into gluconic acid. In the CV responses, an augmented activity was monitored at +0.6 V which was considered as the dc bias potential in the chronoamperometric experiment for detecting glucose suitably. The sensor electrode yielded a low LOD of 0.046 μM and with a sensitivity magnitude as high as 829 μA mM−1 cm−2 over a wide linear range, between 30 μM to 1.06 mM of glucose concentration. Deployment of organic-inorganic nanomaterial based non-enzymatic sensor would find immense scope in non-clinical diagnostics and pharmaceutical applications for fast, convenient and smart sensing.

Metal Selenide Anchored Carbon Nanotube for Boosted Oxygen Evolution Reaction

The oxygen evolution represents an important reaction in electrochemical water splitting and metal-air batteries. To deal with the increasing energy crisis and demand for sustainable clean energy, production of low-cost, high-efficiency, and robust oxygen evolution reaction (OER) electrocatalysts is urgently needed. Recently, transition metal chalcogenides (TMCs) have been used as active electrocatalysts for OER because of their high electrical conductivity and enhanced electrochemical activity. These chalcogenides based electrocatalysts show unprecedented high efficiency for OER exhibiting very low overpotentials, thereby surpassing state-of-the-art precious metal oxides or hydroxide-based catalysts. Carbon nanostructures have been shown to significantly improve their electrocatalytic performance even further. In the present work, nickel selenide nanorods (NRs) were grown inside carbon nanotubes (NiSe@CNT) through chemical vapor deposition (CVD) wherein, the carbon nanotube formed in-situ wrapping around the growing nickel selenide nanorods. Such intimate intermixing is expected to aid in rapid electron transfer from the catalyst composite and yield significantly higher current density. The encapsulation with a CNT shell can also expectedly increase stability of the selenide phase with respect to corrosion and anion leaching. Electrocatalytic behavior was explored by various electrochemical studies, including linear sweep voltammetry (LSV), chronoamperometric experiments, electrochemical surface area determination, and Tafel slope determination, under highly alkaline condition. It was observed that this NiSe@CNT composites showed enhanced electrocatalytic activity for OER. Our results indicate that the self-grown CNT around nickel selenide increases catalytic activity of this hybrid nanostructure due to an increased number of catalytic sites and electronic conductivity of the nanocomposite. The overpotential at 10 mA cm-2 for the as-synthesized NiSe@CNT catalyst is 270 mV which is much better than precious metal based electrocatalysts for OER, such as RuO2 and IrO2. In addition, the current-voltage plots were superimposable before and after 40 h of chronoamperometry test, confirming that the as-synthesized catalyst gives stable electrocatalytic OER activity in 1 M KOH medium for an extended time period. The as-synthesized catalyst was characterized by XRD, Raman spectroscopy, XPS and TEM for morphology, elemental and chemical compositions.Keywords: oxygen evolution reaction, carbon nanotubes, In-situ wrapping Figure 1

Considerations on the use of spectroelectrochemistry in reflection mode for quantitative analysis: Study of the Fe(III)/Fe(II) – orthophenanthroline system

Theoretical and experimental considerations are made about possible analytical applications of spectroelectrochemistry (SEC) in reflection mode using screen-printed electrodes. The system Fe(III)/Fe(II) – orthophenanthroline is taken as a model of electrochemical generation and consumption of a substance that is strongly absorbing: the Fe(II) – orthophenanthroline complex. Different possibilities of quantification are discussed, including cathodic and anodic peaks in cyclic voltammetry and both electrochemical and optical signals acquired in chronoamperometric experiments. Among these, the evolution of absorbance with the square root of time at a constant potential has shown interesting possibilities for the determination of Fe(III)-ion at micromolar level (LOD = 2 10-6 mol L-1). Moreover, this method appears to be resistant to the presence of other electroactive species such as Cu(II)-ions.

Electrochemistry of Praseodymium in Aqueous Solution Using a Liquid Gallium Cathode

The electrochemistry of liquid Ga electrodes in aqueous media was examined in the presence of praseodymium acetate (PrOAc) as an alternate path for low temperature reduction of rare earth elements (REE). This study investigated the aqueous electrochemistry of Ga with and without REEs (Pr). Cyclic voltammetry experiments showed that in the presence of PrOAc, an order of magnitude increase in cathodic current was observed for the Ga electrode, compared to that in the absence of Pr. Decrease in the reduction current with the increase of scan rate, with and without Pr, suggests catalytic reactions following electron transfer, which was attributed to the Ga2O disproportionation reaction. Chronoamperometric experiments performed in Pr containing solutions formed a precipitate. Over 50% of the Pr ions from the aqueous electrolyte were immobilized in the precipitate; a solid Ga-rich phase. Formation of this precipitate was only possible when Ga oxidation was induced. This condition was achieved by circulation of liquid Ga from the pool via external pump and returned dropwise to the liquid Ga pool. When the collected precipitate was leached in dilute HCl, Pr was released with H2 evolved as a byproduct, and Ga returned to its initial liquid metallic state. These preliminary results show encouraging new routes that could be applied for the recovery of diluted REE leachates, such as those obtained from magnets, coal fly ash, and ores.

A generalized Jaeger [formula omitted] integral, resulting from mathematical modelling in electroanalytical chemistry

Eighty years ago J.C. Jaeger et al. introduced a class of improper integrals, currently called “Jaeger integrals” that occur in theoretical models of diverse physical phenomena characterized by cylindrical geometry. One application area is electroanalytical chemistry, where, in particular, the limiting Faradaic current in a potential step chronoamperometric experiment at a cylindrical electrode is described by the Jaeger ℐ(0,1;t) integral. In a recently published paper the first author determined the Laplace transform of the nonlimiting Faradaic current for a reversible charge transfer between members of a redox couple characterized by different diffusion coefficients. In this study we invert the novel Laplace transform and observe that, while it cannot be expressed by any of the Jaeger integrals, it can be perceived as a generalization of the ℐ(0,1;t) integral. We also describe how to compute this integral with the modulus of the relative error close to 10−16 or smaller, using a C++ code employing exclusively standard floating point variables, without resorting to quad precision or other external high precision libraries.

Behavior characterization of hydrogen species on ZnO electrode during electrolytic reduction of water

The behavior of hydrogen production on ZnO electrode during the electrolytic reduction of water was investigated by cyclic voltammetry (CV) and cathode polarization experiments combined with in situ Raman and photoluminescence spectroscopy. CV experiments indicate that hydrogen species prefers to diffuse into the ZnO bulk at negative potentials and occupies oxygen vacancies and interstitial sites. Meanwhile, the H2O reduction is self-enhanced during the electroreduction process, as evidenced by the trace crossing of the CV curves and the chronoamperometric experiment. The influence of the H species on the ZnO electrode during the electrocatalytic processes was characterized by the in situ Raman and photoluminescence spectroscopies. These results help us to understand the hydrogen-related catalytic or electrocatalytic processes on ZnO surfaces.

New Insights on the Sodium Water-in-Salt Electrolyte and Carbon Electrode Interface from Electrochemistry and Operando Raman Studies.

Comprehensive electrochemical and operando Raman studies are performed to investigate the electrochemical stability window (ESW) of supercapacitors filled with normal (salt-in-water) and highly concentrated (water-in-salt, WiSE) electrolytes. Impedance and chronoamperometric experiments are employed and combined with cyclic voltammetry to correctly define the ESW for a WiSE-based device. The total absence of water-splitting resulted in phase angles close to -90° in the impedance data. It is verified that a 17 m NaClO4 electrolyte avoids the water-splitting up to 1.8 V. Furthermore, Raman studies under dynamic and static polarization conditions corroborate the existence of a solvent blocking interface (SBI), which inhibits the occurrence of water-splitting. Also, the reversible nature of the charge-storage process is assessed as a function of the applied voltage. At extreme polarization, the SBI structure is disrupted, thus allowing the occurrence of water-splitting and anionic (ClO4-) intercalation between the graphene sheets.

Structural, morphological and catalytic characteristics of nanostructured palladium catalysts

A new method for the highly active palladium catalyst synthesis on the surface of a Pd-23%Ag film has been developed to increase the material activity with respect to reactions involving hydrogen. Comparison of the electrochemical experiments data of classical palladium black and a new developed nanocatalyst demonstrated a significant increase in catalytic activity in the methanol oxidation reaction (up to 17.09 μA cm−2) for electrodes modified with the latter catalyst. The reason for that is an increase in the number of localized potentially more active surface regions due to the creation of a larger number of active sites in comparison with spherical particles. Estimation of resistance to CO poisoning showed high efficiency of nanocatalysts. Chronoamperometric experiment established the long-term stability and activity of the developed catalyst and confirmed the possibility of its practical use.

Fabrication of Platinum/ Polypyrol-Carbon Nanofiber Nanocomposite Electrocatalyst for Direct Methanol Fuel Cells

A novel electrocatalyst has been developed based on polypyrol-carbon nanofiber (PPy-CNF) support material to increase the stability of Pt/ PPy-CNF/GDL electrocatalyst in direct methanol fuel cell (DMFC). A novel conducting polymer (PPy)-CNF nanocomposites was prepared by a solution dispersion technique and used to support platinum nanoparticles. For preparation of catalyst ink, 20 wt.% Pt/PPy-CNF electrocatalyst with a platinum loading of 0.4 mg cm-2 was prepared by ethylene glycol (EG) method. Physical and electrochemical properties were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) imaging and cyclic voltammetry (CV) experiments. FTIR results prove the existence of PPy in the support. SEM images showed that the one–dimensional CNFs were efficaciously covered by PPy. The TEM characterization revealed that the fine Pt nanoparticles prepared by polyol method were dispersed on the surface of the electrocatalyst successfully. XRD patterns also revealed that the mean size of Pt crystal nanoparticles was about 3.69, 6.51 and 2.91 nm for Pt/PPy-CNF, Pt/CNF and Pt/C electrocatalyst respectively. The size of the PPy on carbon paper has been measured in the range of 35-40nm by AFM. Based on the electrochemical properties and acceleration tests evaluated by cyclic voltammetry measurements and Chronoamperometric experiments it was found that the as prepared Pt/PPy-CNF/GDL electrode exhibited a comparable electrochemical surface are (ECSA), MOR activity and so stability (in the presence of methanol) with respect to the Pt/CNF /GDL and Pt/C/GDL commercial one. A rather significant reduction in the peak potential of methanol electro-oxidation from 0.69V for Pt/C/GDL to 0.76V for Pt/PPy-CNF/GDL electrode indicates that an increase in the activity for MOR is achieved by replacing the C by PPy-CNF. The corresponding ECSA values for the Pt/PPy-CNF/GDL, Pt/CNF/GDL and Pt/C/GDL electrodes were 108.69, 53.93 and 17.98 m2g-1 respectively.

Impediment of Iron Corrosion by N,N′-Bis[2-hydroxynaphthylidene]amino]oxamide in 3.5% NaCl Solution

Hydrazone [N,N′-bis[2-hydroxynaphthylidene]amino]oxamide] derived from the condensation of ethanedihydrazide with 2-hydroxynaphthalene-1-carbaldehyde was synthesized and assessed on the basis of elemental analysis (CHN) and spectral (IR, mass, 13C/1H NMR and UV-Vis) measurements. The influence of N,N-bis([2-hydroxynaphthylidene]amino)oxamide (HAO) in terms of the inhibition of iron corrosion in concentrated sodium chloride solution (3.5 wt.% NaCl) after various exposure periods was assessed. Numerous electrochemical and spectroscopic assessment techniques were performed. Cyclic potentiodynamic polarization experiments indicated that the presence of HAO and its increased concentration decreased the corrosion of iron in NaCl solution by decreasing the corrosion values, anodic and cathodic currents, and corrosion rate. The electrochemical impedance spectroscopy results showed that HAO molecules greatly increased the corrosion resistance. The chronoamperometric experiments performed at −475 mV (Ag/AgCl) revealed that the HAO molecules decreased the absolute currents and reduced the probability of the occurrence of pitting corrosion. The effect of HAO on the inhibition of iron corrosion was also confirmed through scanning electron microscopy micrographs and energy-dispersive X-ray profile analyses, which proved that the surface of the iron sample exposed to chloride solution alone was pitted, while the presence of HAO molecules reduced the severity of the pitting corrosion. The results confirmed that the presence of HAO molecules inhibits the corrosion of iron and this impact increased when the exposure time was increased to 48 h.

Nickel-based electrochemical sensor with a wide detection range for measuring hydroxyl ions and pH sensing

• Nickel-based sensor allows direct quantification of hydroxyl ions in solution. • The nickel-based sensor is applicable in highly alkaline solutions. • The detection range of the sensor is from 0.3 µM to 4.8 M. • The OH ion detection limit is %94 lower than the lowest reported in the literature. • The sensor has a rapid response time of 14 s. The importance of hydroxyl ions concentration measurement in solution necessitates the development of suitable and simple sensing methods for online detection. To address this need, an electrochemical sensor was developed using nickel as the working electrode that enabled specificity towards hydroxyl ions and their successfully quantification. The electrochemical reaction between nickel and hydroxyl ions in solution generates a current which is proportional to the concentration of hydroxyl ions and consequently is also correlated to the pH of the solution. Cyclic voltammetry and chronoamperometry techniques were used to prepare and activate the nickel electrode for detection. The analysis of chronoamperometric experiments in different solutions exhibited three calibration curves between the current and hydroxyl ion concentrations for three regions in the range of 0.3 µM to 4.8 M with a short response time of 14 s. Up to now, no other hydroxyl ion sensor has been reported that can reach this detection limit. This sensor also holds promise to work perfectly in highly alkaline environments where only costly commercial electrodes are available to quantify pH. The results show three linear calibration curves between the current and pH of the solution over the pH range of 7.4 to 14.6. In addition to the wide detection range, the sensor exhibits a relative standard deviation percentage lower than 7% over 9 months of experiments, confirming repeatability of measurements and stability of the electrode. The potential of the proposed method to measure pH in real applications was demonstrated by testing the sensor in solutions containing urea, nitrates, phosphates, and sulfates.

Carbon Nanotube Encapsulated Metal Selenide Eelectrocatalyst for Oxygen Evolution Reaction

The oxygen evaluation represents an important reaction in electrochemical water splitting and metal-air batteries. To deal with the increasing energy crisis, production of low-cost, high-efficiency, and robust oxygen evolution reaction (OER) electrocatalysts is urgently needed. Recently, transition metal chalcogenides (TMCs) have been used as active electrocatalysts for OER because of their high electric conductivity and enriched redox chemistry. These chalcogenide based electrocatalysts show unprecedented high activity surpassing state-of-the-art precious metal oxides or hydroxide-based catalysts. In the present work, nickel selenide nanorods (NRs) were grown inside carbon nanotubes (NiSe@CNT) through chemical vapor deposition (CVD) wherein, the carbon nanostructure formed in-situ wrapping around the growing nickel selenide nanorods. Electrocatalytic behavior was explored by various electrochemical studies, including linear sweep voltammetry (LSV), chronoamperometric experiments, electrochemical surface area determination, and Tafel slope calculation, under highly alkaline condition. It was observed that this NiSe@CNT composites showed enhanced electrocatalytic activity for OER. Our results indicate that the self-grown CNT around Nickel selenide increases catalytic activity of this hybrid due to an increased number of catalytic sites and electronic conductivity of the nanocomposite. The overpotential at 10 mA cm-2 current density for the as-synthesized NiSe@CNT catalyst is 270 mV which is much better than precious metal based electrocatalysts for OER, such as RuO2 and IrO2. In addition, before and after the 40 h chronoamperometry stability test, the LSV curves were almost similar confirming that the as-synthesized catalyst could give stable electrocatalytic OER activity in 1 M KOH medium for the extended time period. The as-synthesized catalyst was characterized by XRD, Raman spectroscopy, XPS and TEM for morphology, elemental and chemical compositions.