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Summary The Pt surface-based hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) are the two most basic electrochemical reactions. However, an accurate quantitative microkinetic model of HER and HOR on Pt surface is still missing. In the current work, the charge transfer coefficient and potential-dependent reaction barriers are obtained via grand canonical fixed-potential calculations to predict such polarization curves. Excellent agreements between the prediction and experiments have been obtained. We found that the common practice of relating a Tafel slope to one specific prominent reaction channel is not reliable. Instead, the balance of several pathways might determine the Tafel slope. Our work demonstrated the important roles of the fixed-potential approach, the explicit water layer structure, and the cations in predicting the Pt-HER/HOR accurately. The proposed computational framework can be generally applied to other electrochemical processes.

MoS2-GO composites were fabricated by an ultrasonication method at room temperature. Raman spectra, emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM) images were used to study the structural characteristics, morphologies, and sizes of the synthesized materials. An MoS2-GO/SPE (screen-printed electrode) was prepared by a facile dropping method and acted as an effective electrochemical sensor toward clenbuterol (CLB) and 4-nitrophenol (4-NP) detection. Based on the obtained results, the influence of analyte molecular structure on the adsorption ability and electronic interoperability between the targeted analyte and electrode surface were investigated in detail and discussed as well, through some electrochemical kinetic parameters (electron/proton-transfer number, electron transfer rate constant (ks), charge transfer coefficient, and adsorption capacity (Γ)). In particular, it should be stressed that 4-NP molecules possess a simple molecular structure with many positive effects (electronic, conjugation, and small steric effects) and flexible functional groups, resulting in fast electron transport/charge diffusion and effective adsorption process as well as strong interactions with the electrode surface. Therefore, 4-NP molecules have been facilitated better in electrochemical reactions at the electrode surface and electrode-electrolyte interfaces, leading to improved current response and electrochemical sensing performance, compared with those of CLB.

The significant aspect of this work is to develop a nanocomposite biosensor based on the combination of Fe3O4 nanoparticles (NPs)—multi-walled carbon nanotubes (MWCNTs) (Fe3O4-MWCNTs), tyrosinase (TYR), and silica sol–gel (SiSG). The obtained material was drop cast on the glassy carbon electrode (GCE) to attain a nanocomposite biosensor (SiSG-TYR/Fe3O4-MWCNTs/GCE). The surface morphology of Fe3O4-MWCNTs was characterized by FE-SEM, TEM, and EDS techniques. The analytical performance of the electrochemical biosensor was evaluated by using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The SiSG-TYR/Fe3O4-MWCNTs/GCE was applied as an efficient biosensor for the simultaneous determination of catechol (CC) and hydroquinone (HQ). A good linear relationship was figured out between the peak currents and analyte concentrations from 1.5 to 30 μM and 1.5–40 μM for CC and HQ with detection limits down to the concentrations of 0.055 and 0.057 μM, respectively. Several kinetic parameters such as charge transfer coefficient, the heterogeneous rate constant, and the number of electrons involved were successfully calculated. The developed biosensor exhibited satisfactory repeatability, reproducibility, good stability, and anti-interference performance. The proposed biosensor was efficiently used for the detection of CC and HQ in spiked local tap water with satisfactory results.

In the last twenty years, direct electro-reduction of solid oxides in molten salt has been investigated extensively. Compared with thermodynamics, kinetics of this solid-to-solid reaction is far less concerned. In this work, Butler-Volmer model was adapted for cyclic voltammetric study of this reaction. Film electrode with three kinds of geometry was proposed to obtain kinetic parameters from the current-overpotential equations. AgCl reduction in 0.5 M KCl–0.5 M NaNO3 was chosen as a model system. The main predictions of planar electrode and cylindrical electrode (inward) were well demonstrated by the electrodes constructed in this work, and the characteristics of cylindrical electrode (outward) were revealed by experimental results from literature. With the obtained relations, kinetics of AgCl/Ag reaction was carefully examined. By in-situ formation of UO2 film on a planar surface in LiCl-KCl-UO2Cl2, the charge transfer coefficient and exchange current density for UO2/U reaction were obtained as 0.19 and 20 mA cm−2, respectively. With the model, electron transfer in an irreversible solid state reaction can now be quantitatively described.

Epinephrine (EP) is one of the key neurotransmitter, which plays a vital role in the central nervous system. Current research report designates the development of biosensor based on the modification of glassy carbon electrode (GCE) with multi walled carbon nano tubes (MWCNTs) followed by drop casting of Tyrosinase (Ty) enzyme (Ty/MWCNTs/GCE) towards the sensitive monitoring of EP. The electrochemical behavior of EP at Ty/MWCNTs/GCE biosensor was examined and the redox mechanism was proposed. The developed Ty/MWCNTs/GCE was characterized by electrochemical techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and tafel plot studies. The influence of pH of phosphate buffer solution (PBS) on the electrochemical redox behavior of EP was observed and pH-7.0 was identified as optimal pH value. The electrochemical kinetic parameters such as heterogeneous rate constant, diffusion coefficient and charge transfer coefficient values were evaluated. The limit of detection and limit of quantification values were evaluated. The low apparent Michaelis – Menten constant (Kmapp) was determined as 0.159 mM, demonstrating the immense catalytic activity of Ty enzyme. Repeatable, reproducible and stable nature of the fabricated Ty/MWCNTs/GCE was successfully examined. Finally, the developed biosensor was tested for the practical application in quantification of EP in human serum samples.

Two representative parameters, exchange current density (j0) and charge transfer coefficient (α), in a standard fuel cell model of polymer electrolyte membrane fuel cells (PEMFCs) were experimentally investigated. The polarization characteristics and the corresponding electrochemical impedance spectra of the normal PEMFCs were measured and Tafel curves were calculated from them, where j0 and ? were finally calculated. As a result, the calculated j0 was 0.11- 0.70 A/cm2, while the α was 0.056-0.023, depending on the operating temperature. Here, the j0 is extremely overestimated while α is underestimated as compared with those in literature. Although the reason for such difference is not clear, it is expected that it could affect the predicted performance by the model significantly if the fuel cell performance is improved highly in the future so the activation overvoltage corresponding to identical current is lowered.

Series of synthesized 4-[({2-hydroxy-5-[2-(substituted methyl phenyl) diazen-1-yl] phenyl} methylidine) amino] N-(1,3-thiazol-2 yl)/ 4-amino-N-(5-methyl-1,2-oxazol -3-yl) benzene-1-sulphonamides schiff base derivatives were analysed for their voltammetric behaviour on dropping mercury (DME) and solid electrodes using differential pulse polarography, cyclic voltammetry and Coulometry techniques. The data revealed that the electrode process is irreversible and diffusion controlled. The kinetic parameters, i.e. charge transfer coefficient ( α n a ), formation constant ( k ° f , h ) and diffusion coefficient were calculated

A highly sensitive and electroactive reduced graphene oxide is achieved by directly reducing the ionic medium supported graphene oxide on the electrode surface. The ionic medium supported reduced graphene oxide (im-rGO) has revealed enhanced electrochemical activity compared to water medium reduced graphene oxide under the same set of conditions. The im-rGO has revealed excellent kinetics. The ionic medium supported reduced graphene oxide modified graphite pencil electrode (im-rGO/GPE) was used for selective trace level quantification of dopamine (DA) in human urine. The developed sensor was comprehensively investigated by field emission-scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). The im-rGO on the electrode surface has effectively increased the electroactive surface area for DA from 0.063 to 0.631 cm2. The charge transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (ks) were calculated to be 0.61 and 5.81 s−1, respectively. A very low LOD of 95 nM was achieved without using any noble or precious metals in combination. The im-rGO/GPE has shown an excellent capability to sense dopamine in the presence of a high concentration of ascorbic acid. The ionic medium supported reduction of GO is the fastest and most cost-effective approach to enhance the sensitivity of the sensor for dopamine in a short time.

The development of an accurate, sensitive and selective sensor for the detection of bisphenol A (BPA) based on the incorporation of a new phthalocyanine derivative, cobalt phthalocyanine, C,C,C,C-tetracarboxylic acid-polyacrylamide (CoPc-PAA) into a carbon-paste matrix is presented using voltammetry and constant potential techniques. The influence of measuring parameters such as pH and scan rate on the analytical performance of the sensor was evaluated. Several kinetic parameters such as electron transfer number (n), charge transfer coefficient (α), electrode surface area (A) and diffusion coefficient (D) were also calculated. Under optimum conditions, particularly at pH 7.2, the BPA sensor resulted in a wide linear range from 25 × 10−11 M to 2.5 × 10−7 M and a limit of detection as low as 63.5 pM. Based on these findings, it can be concluded that our sensor can be substantially utilized for detecting BPA in spiked milk samples.

The direct electron transfer behavior of hemoglobin that is immobilized onto screen-printed carbon electrode (SPCE) modified with silver nanoparticles (AgNPs) and chitosan (CS) was studied in this work. Cyclic voltametry and spectrophotometry were used to characterize the hemoglobin (Hb) bioconjunction with AgNPs and CS. Results of the modified electrode showed quasi-reversible redox peaks with a formal potential of (-0.245V) versus Ag/AgCl in 0.1M phosphate buffer solution (PBS), pH7, at a scan rate of 0.1Vs-1. The charge transfer coefficient (α) was 0.48 and the apparent electron transfer rate constant (Ks) was 0.47s-1. The electrode was used as a hydrogen peroxide biosensor with a linear response over 3 to 240 µM and a detection limit of 0.6 µM. As a result, the modified biosensor here has exhibited a high sensitivity, good reproducibility and stability.

A modified carbon paste electrode (CPE) with AgBr nanoparticles (NPs) showed an increased anodic current in cyclic voltammetry (CV) when methanol or ethanol was added to the supporting HCl electrolyte at pH 2.5. This work was focused to study the kinetic aspects of the modified AgBr NPs-CPE electrode in the absence and presence of the mentioned alcohols. The electrode showed an irreversible response because difference between the peak potentials was about 135 mV and ratio of Ipa/Ipc was 0.88 for the proposed AgIBr/AgIIBr redox process. The surface coverage concentration of the electrode, Γ, was estimated about 13.0 µmol AgBr cm−2. The charge transfer coefficient, α, was changed from 0.72 in HCl to 0.53 and 0.61 when methanol or ethanol was added to HCl solution in CV experiments, while when Tafel plots were studied in LSV (linear sweep voltammetry) its value was changed from 0.72–0.56 and 0.67, respectively. Similarly, the rate constant value was changed from 0.34 s−1 to 0.78 and 0.67 s−1 in CV experiments and from 0.31 s−1–0.83 and 0.68 s−1 in LSV experiments by adding the mentioned alcohols, respectively, confirming a faster reaction rate in the presence of the alcohols.

In this paper a systematic understanding of how charge transfer coefficient (CTC) and exchange current density contributes to polarization and performance characteristics of PEM electrolyzer has been investigated. A detail discussion on the role played by charge transfer coefficient in influencing operating characteristics of PEM electrolyzer has been presented in this article. Experimental data was used to validate the accuracy of the finding of this research. Main interesting insights are that at CTC of 0.5 and 0.2 for anode and cathode respectively, the operating voltage at 1 A/cm2 (current density) is around 2.0 V, however at CTC of 2 and 0.5 for anode and cathode respectively, there was significant drop in operating voltage up to 1.62 V with current density of 1 A/cm2, this accounts for about 27% reduction in operating voltage. It was also discovered that with exchange current density of 1 × 10–7 for a Pt–Ir anode based electrode the CTC value for anode increase from 0.27 to 0.34 at current density of 0.05 A/cm2 to 2 A/cm2 respectively, whereas for Pt cathode catalyst with exchange current density of 1.8 × 10–3 the CTC values for cathode increased from 0.02 to 0.14 at current density of 0.1 A/cm2 to 2 A/cm2 respectively, these findings were in agreement with the CTC values reported in the literature.

We designed a hydrogen peroxide biosensor. The electrochemical detection of H2O2 was performed based on immobilization of cobalt nanoparticles–ferritin (CoNPs–Fer) onto multiwalled carbon nanotubes (MWCNTS) ensnared into chitosan (CS) matrices. Electrochemical techniques such as differential pulse voltammetry (DPV) and cyclic voltammetry (CV) was used to check the property of biosensor. Energy-dispersive X-ray spectroscopy (EDXS) and field emission scanning electron microscopy (FESEM) techniques showed the prosperous immobilization of CoNPs–Fer on the modified GC electrode surface. The hydrogen peroxide-designed biosensor displayed a linear range from 0.2 to 14 nM (R2 = 0.99), a detection limit of 1.29 nM (S/N = 3) and sensitivity of –0.1105 μA/nM.The apparent heterogeneous electron transfer rate constant (Ks) and the charge transfer coefficient (α) were gained 4.19 s–1 and 0.49, respectively. This biosensor can detect hydrogen peroxide with high sensitivity, selectivity, and low detection limit.

In this work, Fe3O4@ZnO core/shell magnetic nanoparticles (MNPs) were prepared by a facile method and used as an excellent electrocatalyst to construct an electrochemical sensor for simultaneous determination of quercetin (Qu) and rutin (Ru) in some pharmaceutical herbs including Borage, Chamomile, Asparagus, Teucrium, Tarragon and Pennyroyal. The morphology and structure of the nanoparticles were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Compared with the bare glassy carbon electrode, Fe3O4@ZnO MNPs modified carbon paste/glassy carbon electrode exhibited much higher electrocatalytic activity toward the oxidation of Qu and Ru with increasing of peak currents and decreasing of oxidation overpotentials. Under the optimized condition, the electrochemical parameters such as the effective surface area, charge transfer coefficient, electron transfer rate constant and diffusion coefficient were calculated. A good linearity was obtained in the concentration range of 2.9 × 10–7–6.47 × 10–5 M for Qu and 9.9 × 10–8–9.9 × 10–5 M for Ru. The limits of detection (S/N = 3) of Qu and Ru were 1.4 × 10–7 M and 7 × 10–8 M, respectively. The experimental results demonstrated that the proposed method shows a promising prospect in determination of Qu and Ru in pharmaceutical herbs.

Climate engineering solutions with emphasis on CO2 removal remain a global open challenge to balancing atmospheric CO2 equilibrium levels. As a result, warnings of impending climate disasters are growing every day in urgency. Beyond ordinary CO2 removal through natural CO2 sinks such as oceans and forest vegetation, direct CO2 conversion into valuable intermediaries is necessary. Here, a direct electrosynthesis of the peroxydicarbonate anion (C2O62–) was investigated by the reaction of CO2 with the superoxide ion (O2·–), electrochemically generated from O2 reduction in bis(trifluoromethylsulfonyl)imide [TFSI–] anion derived ionic liquid (IL) media. This is the first time that the IL media were employed successfully for CO2 conversion into C2O62–. Moreover, the charge transfer coefficient for the O2·– generation process in the ILs was less than 0.5, indicating that the process was irreversible. Voltammetry experiments coupled with global electrophilicity index analysis revealed that, when CO2/O2 was contac...

A flexible and promising amperometric glucose biosensor was reported using direct immobilization of glucose oxidase (GOx) on chitosan supported mesoporous carbon (MPC-CHT) nanocomposite. The availability of more functional groups particularly amine groups, the CHT was selected as an immobilization matrix as well as cross linker for GOx. The MPC-CHT-GOx composites were characterized well and discussed in details. The MPC-CHT-GOx modified electrode accelerates fast electron transfer on the electrode surface due to the excellent intermolecular interaction between the CHT and GOx molecule. Besides, the MPC-CHT-GOx composite showed well-defined redox behavior with enhanced direct electron transfer (DET) of GOx in PBS, pH 7. Amperometric response of MPC-CHT-GOx modified electrode displayed a good linear response over the glucose concentration ranges from 250 μM to 3 mM with a detection limit (LOD) and sensitivity of 4.1 μM and 56.12 μA mM−1 cm−2, respectively. The MPC-CHT-GOx modified electrode also displayed good charge transfer coefficient (α) and heterogeneous rate constant (ks) values are 0.56 and 2.2182 s−1. Besides, the MPC-CHT-GOx modified electrode exhibited good bio-catalytic activity with the Michaelis-Menten saturation (Kmapp) value was about 2.14 mM. The practicability of the sensor was evaluated in biological real samples with satisfactory recoveries.

The electrochemical reduction of thymine (T) and thymidine (Thy) in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid at room temperature is investigated using cyclic voltammetry (CV). The CV of thymine shows one-electron reduction peak at − 0.67 V vs Fc/Fc+, while thymidine exhibited two reduction peaks corresponding to − 1.54 V and at − 2.06 V vs Fc/Fc+. The difference in the reduction peaks of thymine and thymidine observed suggests a single-step and two-step reductions, respectively. The experimental voltammogram was convoluted for the the estimation of diffusion coefficient, charge transfer coefficient, kinetics, and energetics of thymine and thymidine. The theoretical prediction using semi-integral technique suggests that thymidine at the reduction peak − 1.54 V vs Fc/Fc+ proceeds a one-electron reductive cleavage of N–C glycosidic bond (nitrogen–carbon) via concerted dissociative electron-transfer mechanism while thymine.

The charge transfer reaction is the fundamental reaction for rechargeable batteries. The energy landscape of this reaction depicts the equilibrium and kinetics of the electrochemical process. Typically, a Li-metal electrode is always covered by a thin layer of solid electrolyte interphase (SEI), forming a complex Li/SEI/electrolyte interface. In this paper, a new modeling framework was developed to predict the energy landscape of the lithiation/delithiation charge transfer reaction at a Li/Li2CO3/EC-electrolyte interface, with combined density functional theory (DFT) and tight-binding (DFTB) calculations. It was found that Li+ ions are much more energetically favorable to be dissolved in the electrolyte on a zero-charged Li-metal electrode, indicating that the SEI is a necessary kinetic barrier to prevent complete solvation of Li-metal into the electrolyte. During delithiation, Li+ ions would be stripped from the surface non-uniformly and form a large void on the Li-metal surface. During lithiation, it was demonstrated that the annihilation of Li+ ions and electrons occurs at the Li/SEI interface, for an idealized defect free SEI. Furthermore, at the experimentally defined zero voltage for Li+/Li0, the Li-metal surface is negatively charged (−0.62 ± 0.12 e nm−2) to maintain the electrochemical equilibrium. The electric field created by the negatively charged surface can reorient the electrolyte into an ordered structure, lower the Li+ ion desolvation energy barrier, and help the Li+ ion transport through the SEI. The charge transfer coefficient, α, in the Butler–Volmer equation was directly computed to be ∼0.22 from the simulated energy landscape, consistent with the experimental measurements. Thus, this model enables a bottom-up multiscale modeling approach for ion-transfer electrochemical reactions.

A simple and robust sensor (fMWCNT-Nafion®0.5%/GCE) for determination of imidacloprid (IMI), a widely used neonicotinoid, was developed using a glassy carbon electrode (GCE) modified with functionalized multi-walled carbon nanotubes (fMWCNT) and Nafion®. The obtained data suggest that IMI reduction is an irreversible process, due to the reduction of the nitro group to hydroxylamine derivatives, with the participation of two protons and four electrons, and a charge transfer coefficient of 0.141. The optimized square-wave voltammetric conditions were: McIlvaine buffer at pH 6.0, 0.5% of Nafion® in the fMWCNT suspension, -0.6 V and 180 s as accumulation potential and time, respectively. A linearity in the range of 2.00 × 10-7 to 1.77 × 10-6 mol L-1 IMI, with the values of limit of detection and limit of quantification were equal to 3.74 × 10-8 mol L-1 and 1.25 × 10-7 mol L-1, respectively. Repeatability and reproducibility displayed relative standard deviations lower than 5%. Recovery tests performed in tap water, melon, and shrimp yielded mean values of 94 ± 6%, 97 ± 10% and 93 ± 10%, respectively. Moreover, several inorganic and organic compounds did not significantly interfere (0.6 to 4.5%) on the IMI signal, proving the selectivity and applicability of the developed sensor for IMI detection in complex samples.

In this study the effect of thermomechanical treatments in chloride induced pitting corrosion is presented for carbon steel rebars exposed to synthetic fly ash (FA) pore solution. Due to the likely phase transformations that steel reinforcements in concrete experience during the event of a fire, the understanding of the corrosion behavior of such phases is key in predicting the stability of the structure. The motivation for this study arrives from the scarce literature regarding the corrosion behavior of thermomechanically treated steel reinforcements in FA environments and the need for further investigation to understand its mechanism. In order to better understand the effects on the corrosion behavior electrochemical measurements including cyclic potentiodynamic polarization curves (CPP) and electrochemical impedance spectroscopy (EIS) were used. It was found that quenched specimens showed enhanced corrosion kinetics as their icorr values were higher, being of 3.18 × 10−5 and 2.20 × 10−5 A/cm2 for water and oil quenched compared to 2.13 × 10−6 A/cm2 for the as-received. Furthermore, the effective capacitance of the double layer (Ceff,dl) showed the lower stability of the passive film for the quenched specimens, with values of 1.11 × 10−3 µF/cm2 for the as-receive sample that decreased to 8.12 × 10−4 µF/cm2 for the water quenched sample. The anodic charge transfer coefficient in the synthetic FA alkaline pore solution changes from 0.282 to 0.088, for the as-received and water quenched rebars specimens, respectively. These results indicate a lower energy barrier for the anodic dissolution reaction of quenched specimens, indicating that martensite and bainite microstructures promote corrosion process. Enhanced corrosion was found on quenched samples presenting martensite and bainite microstructure as showed by the increased pith depth, with values of 5 μm compared to 1 μm observed in the as-received samples.

Background: With the development of advanced characterization techniques, lithium-ion battery non-linearities have recently gained increased attention which can benefit battery health diagnosis and ageing mechanism identification. In comparison to conventional single sine wave-based methods, the multisine-based non-linear characterization method has the advantage of capturing the dynamic voltage response within a short testing duration, and therefore has further development potential for on-board applications. However, understanding lithium-ion battery electrochemical processes that contribute to battery non-linearities is still unclear. Methods: In this paper, the sensitivity of the Doyle–Fuller–Newman model parameters are analysed in the frequency domain to investigate the electrochemical processes that contribute to the non-linear dynamics of the voltage response. To begin with, the non-linearities of the Doyle–Fuller–Newman model with validated parameters are characterized and compared to experimental data from a commercial cell. This demonstrated a significant difference between the mathematical model and the non-linearities determined experimentally. Then, a global sensitivity analysis is applied to determine the most sensitive parameter contributing to battery non-linearities. Finally, the appropriate value of the most sensitive parameter which results in the closest non-linear response to the commercial battery is estimated through minimizing the root mean square error. Results: The results show that the charge transfer coefficient is the most sensitive parameter contributing to battery non-linearities among the Doyle–Fuller–Newman model parameters. The non-linear response of the Doyle–Fuller–Newman model is validated with good agreement with the experimental results, when the Butler–Volmer kinetic is asymmetrical due to the unequal anodic and cathodic charge transfer coefficients.

Despite arsenite can be reduced to As(0) and deposited at the surface of solid electrodes such as gold, platinum, or copper, it cannot form amalgams with mercury, and so the addition of other metal ions is required for its deposition. In this manuscript, mechanistic analysis of the cathodic stripping square-wave voltammetric response of the system copper‑arsenic is presented. For the analysis of experimental responses, a mathematical model is used to consider that a surface-active reagent undergoes a charge transfer step followed by a chemical reaction. The dependences of the differential peak current, and the respective peak potential and half-peak width on the square-wave frequency were used to estimate the apparent stability constant of arsenide formation and that the electrode reaction would involve the direct transfer of 2 electrons, while the simulation and fit of forward and backward voltammetric responses have been useful for inferring other parameters such as the formal charge transfer rate constant of the global electron transfer reaction, a pseudo-first order homogeneous rate constant associated with arsenide formation, and the charge transfer coefficient of the global electron transfer reaction. Besides the values estimated for each of those parameters, all simulations indicate that the reduction of copper instead of arsenic would be taking place during the cathodic stripping scan. Accordingly, the trace-analysis reaction of arsenic in the presence of copper would be based on the surface accumulation of a metal complex, where Cu2+ would be the metal cation and an arsenide species the ligand. The stability of that complex at the surface of a mercury electrode would depend not only on the applied potential, but also on the ratio between copper, arsenic, and protons. Fil: Gómez Avila, Jenny. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Pontificia Universidad Católica Madre y Maestra; República Dominicana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Burgos Gómez, Jhan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Heredia, Angelica Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; Argentina Fil: Crivello, Mónica Elsie. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; Argentina Fil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

This paper proposes an optimization model that identifies the parameters of a detailed electrochemical model for a Proton Exchange Membrane (PEM) electrolyzer. The identification procedure is based on current-voltage (I-V) measurements. The proposed model aims to identify the values of seven modelling parameters of the electrolyzer electrochemical model. These parameters include: change in Gibbs free energy, exchange current density for anode and cathode, charge transfer coefficient of both anode and cathode, conductivity of the membrane, and limiting current density. The parameter identification problem is formulated based on a nonlinear least-squares objective function. The optimization problem is solved using the MATLAB optimization toolbox. Comparisons of results and analysis between experimental and estimated data are presented for different operating conditions of temperature and pressure. The results provide a Root Mean Square Error (RMSE) in the range of 106 which demonstrates the accuracy of the proposed model. To affirm the model’s superiority, the proposed model is compared with other electrolyzer parameter identification models found in existing literature.

Direct flame fuel cells were developed in 2004 and there have been many iterations of them ever since. One of the latest iterations are the micro-tubular flame-assisted fuel cells. Even though there has been significant experimental research characterizing the performance and polarization losses of flame-assisted fuel cells, there is no model that describes their polarization losses. A model is thus developed and presented in this paper to assess the polarization losses and performance of flame-assisted fuel cells. Voltage and power density variation with current density are the main parameters that are analyzed in this paper. A model for calculating activation, ohmic and polarization losses is developed. Experimental parameters from previously published work like dimensions of the fuel cell layers, the fuel and oxidizer flow rates, the charge transfer coefficient and the exchange current density are used to optimize the model. The FFC is assumed to be a lumped system and a zero dimensional model is thus developed. The model was able to achieve an accuracy up to 95%, which adds to its credibility. The fuel-rich combustion exhaust composition is predicted using chemical equilibrium analysis for the equivalence ratios of 1.25 to 1.4 with intervals of 0.5 at 800°C. The model predicts that the open circuit voltage decreases from 0.94 to 0.89 for the equivalence ratios of 1.4 to 1.25, respectively, which matches experimental results. The model also predicts that the maximum power density decreases with decrease in equivalence ratio. Negligible activation loss was observed in the results while the ohmic loss didn‘t vary significantly with equivalence ratio. The concentration loss increased with decrease in equivalence ratio, which also matches with experimental results.

The electrochemically functionalized multiwalled carbon nanotubes/copper nanoparticles (fMWCNT/CuNPs) carbon paste electrode (fMWCNT/CuNPs-CPE) was successfully modified by silver nanoparticles (AgNPs) via electrocatalytic process. The formation of modified electrode (AgNPs/fMWCNT/Cu NP-CPE) was observed by Field Emission Scanning Electron Microscopy and X-ray diffraction techniques. The as-prepared electrodes were explored for the trace recognition of calcium channel blocker drug amlodipine besylate (ADB) using cyclic voltammetry and electrochemical impedance spectroscopy measurements. Kinetic parameters like electron transfer coefficient (α), charge due to adsorption (Qads), surface coverage (Γ), charge transfer coefficient (Rct), and apparent electron-transfer rate constant (kapp) for the designed electrodes were evaluated. The nanoparticles based electrochemical sensor displayed high sensitivity, good selectivity and favorable catalytic ability for the oxidation of amlodipine besylate. The fabricated electrodes showed good reproducibility and stability towards the determination of anti-hypertensive drug ADB.

A common basis for investigations of the properties of electrode reactions is provided. The basic equations of electrostatics and electrodynamics and the assumption that electrode reactions are relaxation processes, are used to develop the equations for the electrical behavior of electrode systems. Thus electrode reaction processes are characterized as two states separated by an energy barrier. The application of static and alternating fields to electrode systems is interpreted in terms of the kinetic parameters of the electrode reactions. The equations for impedance are applied to silver and cadium electrode systems reported in the literature. The agreement of experiment and theoretical expectation is excellent. The equations are also applied to the interpretation of the impedance of LeClanché cells. The kinetic analysis of a simple unimolecular reaction is used to illustrate the kinetic interpretation of experimental information. This simple analysis may be extended to more complex reactions.

Here, the effect of morphology on the electrocatalytic activity of metal-organic framework (MOF) was investigated. Post synthetic gold (Au) insertion was done into hollow PCN-222 (HPCN-222) and solid PCN-222 (SPCN-222) frameworks by a simple hydrothermal method. The crystalline nature, chemical composition, and morphologies of the synthesized MOFs were characterized by PXRD, XPS, and TEM. Electrochemical characterizations were done by cyclic voltammetry and electrochemical impedance spectroscopy. The excellent electrocatalytic activity of highly small-sized Au(0) with the enhancement of electrical conductivity through a hopping mechanism combined with a hollow structure and high surface area in the HPCN-222 MOF hugely alters the electrochemical properties. Overall, a better electrocatalytic surface area, charge transfer coefficient, and catalytic activity were generated at the modified electrode. The hollow structure MOF showed better electrocatalytic activity than solid structured MOF. The AuHPCN-222 modified glassy carbon electrode (AuHPCN-222/GCE) electrochemical sensor was employed for the analytical analysis of estradiol (ED) in an optimum experimental condition. AuHPCN-222 showed selective and better electrocatalytic activity toward ED than GCE. The differential pulse voltammetric measurements by the fabricated sensor showed two linear determination ranges for ED; those are 0.01-1 and 1-220 μM. The measured limit of detection (m-LOD) was found to be 0.5 nM with the highest sensitivity of 2.2 μA μM cm-2. The analytical performances for the detection of ED in human urine and serum samples were done with reasonable recoveries (98%-103%) using the standard addition method. Also, the sensor showed better reproducibility and repeatability with stability.

Despite the significant experimental work in flame-assisted fuel cells (FFCs), a detailed model of FFC polarization losses does not exist in the literature. This paper thus presents a combination of theoretical and empirical models to describe the performance of FFCs. Previous models for solid oxide fuel cell (SOFC) polarization losses typically assumed values of the charge transfer coefficient (α) of 0.5 and a Nernst diffusion layer thickness (δ) equal to the anode thickness. The theoretical model developed in this work, parametrized in α and δ, is empirically fitted to the experimental polarization curves to understand the variation of these parameters while the FFC operates with different fuel partial pressures. Model results indicate that at low fuel concentrations (CR,0), the current density of the fuel cell (j) is limited by mass transfer limitations. As CR,0 increases, j is then limited by activation due to the limited number of activation sites in the fuel cell. Activation loss (ɳact) remains constant at low CR,0 (concentration limited) and increases rapidly with an increase in CR,0 under activation-limited conditions. The value of α, which varies significantly from 0.5, under concentration-limited conditions remains constant at ~0.24 and decreases rapidly with CR,0 under activation-limited conditions. The value of δ, which is much smaller than anode thickness, remains constant at ~10 µm under concentration-limited conditions and increases to a constant value of ~17.5 µm under activation limitations. Overcoming activation losses under high CR,0 conditions requires further investigation of FFCs.

Polypyrrole-carbon (PPy-C) composites having different amounts of carbon (5–35 wt.%) decorated with platinum nanoparticles (Pt/PPy-C) were prepared and investigated for borohydride oxidation reaction (BOR) in alkaline medium and for hydrogen peroxide reduction reaction (HPRR) in acidic medium. Structural and morphological properties and composition of these electrocatalysts were determined by FTIR, Raman, XPS, SEM/EDS, TEM and ICP-MS analyses. Pt/PPy-C electrocatalysts were evaluated for BOR and HPRR by cyclic voltammetry and chronoamperometry. Faradaic and kinetic parameters, such as the number of exchanged electrons, n, charge transfer coefficient, α, apparent activation energy, Eaapp, and order of reaction, β, were calculated. n for BOR ranged from 6.0 to 7.6, while n for HPRR ranged from 1.0 to 2.0. Eaapp was found to range from 10 to 18 kJ mol−1 for BOR and from 8 to 14 kJ mol−1 for HPRR. The BOR was found to be a 1st order reaction with respect to BH4−. Pt/PPy-C35% electrocatalyst showed the best activity for both reactions. Fuel cell tests were done with Pt/PPy-C electrodes as anode, as cathode and as both anode and cathode in a direct borohydride-peroxide fuel cell (DBPFC). DBPFC with Pt/PPy-C35% as anode electrocatalyst gave the highest peak power density of 1432 W gPt−1 at current density of 2046 A gPt−1 and cell voltage of 0.70 V.

The oxidative dissolution of chalcopyrite in aqueous solutions is an electrochemical process. Such processes can be evaluated as coupled anodic and cathodic reactions using electrochemical techniques. The chalcopyrite dissolution reaction has been studied in ammonia-ammonium sulphate solutions using potentiostatic and potentiodynamic methods. Anodic current densities in the vicinity of the mixed potential have been found to increase with an increase in total ammonia (NH3 + NH4+) from 1 M to 3 M, and the order of reaction was found to be 1st order with respect to ammonia. The reaction was found to be zero order with respect to [OH−] at a pH between 9 and pH 10. An analysis of the Tafel slopes suggested an average charge transfer coefficient of 0.61. The rate controlling step was concluded to be a single electron transfer reaction, which supports the formation of a copper depleted intermediate surface that is rapidly oxidised in subsequent electron transfer reactions. The anodic sweeps and constant potential tests did not support the formation of a passivating surface deposit on the oxidising chalcopyrite surface.

The graphene or graphite analogous transition metal dichalcogenides have been received as an exciting new type of electrode materials in various electrochemical applications. In this work, we have demonstrated the synthesis of europium doped molybdenum diselenide nanoflower (EuMoSe2) by using the simple hydrothermal method and characterized by using different analytical techniques. Especially, the XRD and Raman spectroscopy techniques provided the information on the crystal structure of EuMoSe2. And also, the flower-like nanostructure with protruded few-layer nanosheets of EuMoSe2 was clearly observed by using SEM and TEM analysis. Further, the EDX and XPS analysis also evidently scrutinized the formation of EuMoSe2 nanoflower. Furthermore, electrochemical activity of EuMoSe2 nanoflower towards the detection of diphenylamine (DPA) was studied by using various electrochemical methods such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV). As the result, the EuMoSe2 modified glassy carbon electrode (EuMoSe2/GCE) exhibited an excellent electrocatalytic activity for the detection of DPA with a low detection limit (8.8 nm), which is strongly associated to the calculated low charge transfer resistance (10.23 Ω), excellent active surface area (0.117 cm2), and charge transfer coefficient (0.58). Finally, the real-time application of EuMoSe2/GCE was also tested by using apple juice.

Although the activity coefficients and diffusion coefficients of LaCl3 in molten LiCl KCl salt have been extensively studied, the data on the electrochemical properties of La(III)/La reaction in the melt are very scarce. Among the few measurements, up to five orders of magnitude discrepancies for the reaction rate constant k 0 have been reported. In the present study, potentiodynamic polarization measurements at different LaCl3 concentrations (1–6 wt%) and temperatures (723–823 K) are conducted to obtain accurate values of the exchange current density i 0 and charge transfer coefficient α . The data are analyzed using non-simplified electrode kinetic equations through the optimization fitting procedures, and conventional Tafel and linear polarization (LP) methods. The concentration dependence of i 0 obtained from the optimization fitting method is examined, showing agreement with the theoretical correlation i 0 = n F k 0 c ( 1 − α ) . The corresponding values of k 0 are 1.76–3.22 × 10−5 cm s−1 in 723–823 K.

Valacyclovir (VCH) is an antiviral drug, used in the management of viral infections such as herpes simplex and varicella-zoster in humans. It is rapidly converted to acyclovir which has antiviral activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) and Varicella-zoster virus (VZV) both in vitro and in vivo. Electrochemical behavior was studied using cyclic voltammetric method, and the analytical application was studied using differential pulse voltammetric technique. The process on the surface of electrode was found to be irreversible and diffusion controlled. The charge transfer coefficient, heterogeneous rate constant, the number of electron transferred and activation parameters were calculated. Possible free radical reaction mechanism taking place on the surface of electrode was proposed. Calibration plot constructed using differential pulse voltammetric technique and applied for quantitative analysis in pharmaceutical and human urine sample. Limit of detection (LOD) and limit of quantification (LOQ) were calculated and found to be 0.028 and 0.09 μM, respectively. The present work describes the electrochemical behavior of an antiviral drug, VCH and its determination in pharmaceutical samples. The method shows the development of a sensor for selective and sensitive determination of VCH.