Cathodic Pretreatment Research Articles

Voltammetric determination of the antifungal drug posaconazole in the presence of an anionic surfactant on a boron-doped diamond electrode

This study describes a new, fast and simple procedure of electrochemical assay of posaconazole (PCZ), which is currently regarded as one of the most important antifungal agents, recommended in the treatment of systemic infections, effective even against rare and atypical kinds of fungi. PCZ is very effective and safe, displaying much lower toxicity than other traditional antifungal drugs. A new, attractive procedure of assaying the compound on boron-doped diamond (BDD) electrode after cathodic pretreatment in the presence of sodium dodecyl sulfate (SDS) is presented in the work. The anionic surfactant SDS was selected after the comparative analysis of various cationic surfactants. PCZ gave a single irreversible oxidation peak at the potential of 0.59 V. The addition of SDS resulted in an almost 5-fold growth in the value of recorded currents as compared to those observed in the absence of the surfactant. The highest peak was obtained in Britton-Robinson buffer at pH 3.78. The calibration curve of PCZ plotted using the SWV technique was linear in the concentration range from 1.34·10−8 mol/L to 1.44·10−6 mol/L. The limit of detection and limit of quantification were 3.78·10−9 mol/L and 1.14·10−8 mol/L, respectively. The value of relative standard deviation of the measurements did not exceed 4.42 %, which proves good precision of the proposed method. The proposed procedure was successfully used in assaying PCZ in simulated gastric juice.

Interfacial bonding and corrosion inhibition of 2-mercaptobenzimidazole organic films formed on copper surfaces under electrochemical control in acidic chloride solution

The interfacial bonding and the layered structure of 2-mercaptobenzimidazole (2-MBI) organic films adsorbed on electrochemically controlled copper surfaces and their corrosion inhibition effects in acidic chloride aqueous solution were investigated using an integrated approach of electrochemical methods and advanced surface analyses by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. It is shown that organic films formed on the copper surfaces are bi-layered with a chemisorbed inner layer and a physisorbed outer layer. In the chemisorbed inner layer, 2-MBI is bonded primarily by its nitrogen atoms with metallic and oxidized copper surfaces. Sulphur atoms are also involved in the bonding mechanism when metallic copper is directly accessible to the 2-MBI molecules. The initial presence of native copper oxides at the interface promotes the formation of Cu(I)-2-MBI metal-organic complexes in the chemisorbed inner layer using cathodic reduction to dissociate the oxide. Metal-organic complexes also form upon anodic polarisation due to Cu(I) ions generated by oxidation of the copper metal. 2-MBI effectively inhibits copper anodic dissolution in varying degrees, between 84% and 93%, depending on the pre-treatment used for the formation of the organic bi-layers. An enhanced protection of the substrate is obtained by adsorbing the 2-MBI inhibitor on an initially oxide-free surface, which is achieved by cathodic pre-treatment in absence of the inhibitor followed by 1 hour exposure to the inhibitor.

A simple and reliable electrochemical method employing an unmodified boron-doped diamond electrode for the determination of triclocarban

Since the advent of the COVID-19 pandemic, triclocarban-containing cleaning products have been increasingly consumed. As triclocarban is an emerging compound, it is necessary to develop new sensors for its monitoring. So, a simple and reliable electroanalytical method for the determination of triclocarban using an unmodified boron-doped diamond electrode was developed. The application of a cathodic pretreatment (−2.0 V, 30 min, 0.5 mol L−1 H2SO4) on the electrode surface provided higher current intensities and lower resistance to charge transfer in contrast to the non-treated surface. On the diamond electrode surface, the triclocarban showed an irreversible behavior with two oxidation peaks at +1.10 and +1.40 V vs. Ag/AgCl, KCl(sat). The hypothesis for removing hydrogens of both amide groups of the triclocarban structure was supported by computational methodology which also explained the broadened oxidation peaks and the distance between them. The calibration curve for triclocarban, obtained by using differential pulse voltammetry in a supporting electrolyte composed of McIlvaine buffer (pH 3.0) and ethanol (80:20 v/v), covered a concentration range of 1.0 to 50 μmol L−1, and it exhibited a detection limit of 0.31 μmol L−1 under optimized experimental conditions. Using an accumulation time of 120 s at open circuit potential, a calibration curve by differential pulse adsorptive stripping voltammetry was constructed in a range of 0.05 to 20 µmol L−1 of triclocarban, with a detection limit of 18 nmol L−1. Triclocarban quantification assays were carried out on samples of antibacterial soaps and river water, and data were recorded with acceptable precision and accuracy.

Adsorption of 2-Mercaptobenzothiazole Organic Inhibitor and Its Effects on Copper Anodic Oxidation in Alkaline Environment

2-Mercaptobenzothiazole (2-MBT) is well established as an effective organic corrosion inhibitor for the protection of copper and other metals. The presence of heteroatoms (2 sulphur and 1 nitrogen) in its structure, enables it to bond to the metallic substrate and form a protective barrier layer on the surface which restricts the pathways for the corrosive ions to the metal surface. However, despite numerous works discussing the inhibiting properties on copper, several questions remain, notably regarding the role played by the surface native oxide on the bonding mechanisms, the stability, and the inhibition efficiency of the organic film formed in various environments.In this work, the adsorption of 2-MBT on copper and its effects on anodic oxide growth in a strong alkaline medium (0.1 M NaOH solution) were investigated. Various cathodic pre-treatment methods were applied to modify and control the native oxide-covered Cu surface during the formation of the inhibitor layer. Cyclic voltammetry (CV) tests were performed to determine how the growth of anodic Cu(I) oxide is altered by the 2-MBT organic inhibitor layers pre-adsorbed in different pre-treatment conditions. Additionally, X-ray photoelectron spectroscopy (XPS) and time-of-flight – secondary ion mass spectrometry (ToF-SIMS) were used to investigate the bonding mechanisms of the 2-MBT molecule to the copper surface, including the role of surface native oxides in the formation of the interface with the inhibitor, the effect of increased exposure time to the inhibitor, the stability of the organic inhibitor layer upon anodic polarisation, and the oxide growth upon anodic polarization. The absence of chlorides eliminates their interference in the understanding the oxidation process in a 2-MBT-containing alkaline solution. Additionally, anodic oxidation is studied in the Cu(I) potential range, which allows us to evaluate the effects of 2-MBT on the oxide layer that forms directly on the bare metallic substrate.The results show that 2-MBT significantly impedes the growth of the passivating Cu(I) oxide by forming a multilayered organic film with the inner layer chemisorbed to the surface. A major factor influencing the formation and properties of the organic barrier layer is the presence and structure of the interfacial native oxides on which it forms. The 2-MBT molecules bond to the copper substrate mostly via its sulphur atoms along with a small fraction of the nitrogen atoms also bonding to the metallic substrate. Additionally, there is an interaction between the inhibitor molecules and copper released from the surface to form metal-organic complexes in the outer layers of the thicker films. Longer exposure times to the inhibitor of a surface with negligible oxides increased the efficiency of the organic barrier layer in impeding the growth of anodic oxide.Upon anodic polarisation, the 2-MBT barrier layer grows in thickness, with inclusion of Cu-2-MBT complexes. It is proposed that the thiolate form of 2-MBT, which is the dominant conformer in an alkaline environment, allows for additional bonding possibilities to the Cu atoms and Cu(I) ions of or released from the surface oxide, forming Cu-2-MBT complexes that deposit on the surface and thus increasing the thickness of the organic barrier layer. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Advanced grant agreement No. 741123, CIMNAS).

Boron-doped {113}, {115} and {118}-oriented single-crystal diamond electrodes: Effect of surface pre-treatment

In this study, the effect of vicinal crystal orientation ({113}, {115}, and {118}), boron doping level, and surface termination induced by various pre-treatments on electrical and electrochemical properties of single crystal boron-doped diamond (SC-BDD) electrodes was carefully investigated. van de Pauw measurements confirmed Hall concentration to increase with increasing vicinal angle, {118} < {115} < {113}. As-deposited H-terminated surfaces were converted to predominantly O-terminated surfaces (confirmed by X-ray photoelectron spectroscopy) using hot acid, ozone and anodic pre-treatments, or by spontaneous oxidation in air. This conversion was recognized by inhibited heterogeneous electron transfer kinetics of inner-sphere redox markers ([Fe(CN)6]3−/4− and dopamine), by an increase in double layer capacitance and charge transfer resistance values. The most pronounced surface oxidation was recognized for electrodes with the lowest boron content as a result of blocked boron atoms by oxygen functionalities and loss of superficial hydrogen on the surface. Reverse conversion from oxidized to H-terminated surfaces using cathodic pre-treatment led mainly to restoration of electrochemical parameters. Moreover, spontaneous oxidation of electrode surfaces in ambient atmosphere was confirmed, with the fastest being within the first five days. The results show the key role of boron content, and hence the crystal orientation and superficial hydrogen in affecting conductivity and performance of SC-BDD electrodes, which is demonstrated by changes in heterogenous electron transfer kinetics of surface sensitive redox systems.

Electrochemical surface rehydrogenation of boron-doped diamond electrodes after electrochemical polishing

Non-diamond carbon impurity and surface roughness are features that can affect the response of boron-doped diamond (BDD) electrodes. Herein, we report on the electropolishing of BDD electrodes carried out in the presence of acetic and sulfuric acid for different times (1, 2, and 4 h). The wet electrochemical treatment smooths the polycrystalline diamond surface and reduces the non-diamond sp2 carbon impurity content while increasing the surface oxygen content. Changes in surface texture and microstructure were revealed by atomic force microscopy, Raman spectroscopy, and cyclic voltammetry. Subsequently, the surface oxygen content was reduced by increasingly severe cathodic pretreatments (CPTs). This was revealed by changes in the voltametric response for the [Fe(CN)6]3−/4– and ascorbic acid (AA) redox systems, as both exhibit electron transfer kinetics sensitive to the level of oxidation of the BDD surface. For [Fe(CN)6]3−/4–, greater ∆Ep values were obtained for the electropolished (EP-BDD) electrodes, as compared to the as received (AR-BDD) electrode. However, after CPTs the EP-BDD electrodes exhibited smaller ∆Ep values (∼60 mV), which indicate significantly improved electrochemical reversibility and faster electron-transfer kinetics caused by the decreased level of surface oxidation (greater hydrogenation). The increased surface oxygen content brought on by the electropolishing process had also a significant effect on the AA oxidation peak potential (Eap), making it at least ∼140 mV more positive than that for the AR–BDD electrode. However, after CPTs the Eap values for the EP–BDD electrodes became at least ∼0.1 V less positive than that for the AR–BDD electrode, indicating that the surface of the EP-BDD electrodes possesses less surface carbon‑oxygen functional groups (i.e., it is more hydrogenated). The combination of electropolishing and cathodic pretreatment is a way to process the BDD electrode surface to create a smoother, low oxygen surface in much the same way as a hydrogen plasma treatment does.

(Invited) Some Aspects of Electrode Kinetics and Electrolyte Stability in Vanadium Flow Batteries

The redox flow battery (RFB) has seen an explosion in research activity in recent years due to its attractiveness for large-scale energy storage applications (e.g. grid level storage). RFBs1,2 offer many advantages over conventional batteries including their relatively high reliability and long cycle life, as well as the ability to scale their energy and power outputs independently. The vanadium flow battery (VFB)1,3-6 is currently the most promising of these technologies, with a number of large-scale applications and demonstration projects already underway.6 The power density of VFBs is limited primarily by the kinetics of the redox reactions at the carbon electrodes while the energy density is limited primarily by the concentration of vanadium in the electrolyte. In this talk we will review our work on two aspects of VFBs – kinetics on carbon electrodes and thermal stability of electrolytes – which impact these two limitations respectively.We have investigated3,7,8 the kinetics of the VII-VIII, VIII-VIV and VIV-VV redox couples for a range of different carbon materials using a variety of techniques, and it is clear that the kinetic rates depend strongly both on the type of carbon used and on the preparation of the electrode surface. We will discuss our investigations of the effects of anodic and cathodic pretreatments of carbon on electrode kinetics in the VFB. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), we showed for four different types of carbon that electrode treatments at negative potentials enhance the kinetics of VIV-VV and inhibit the kinetics of VII-VIII while electrode treatments at positive potentials inhibit the kinetics of VIV-VV and enhance the kinetics of VII-VIII. These observations may explain conflicting reports in the literature. We examined in detail the potentials required for activation and deactivation of electrodes. The results suggest that interchanging the positive and negative electrodes in a vanadium flow battery (VFB) would reduce the overpotential at the negative electrode and so improve the performance. This is supported by flow-cell experiments.3 Thus, periodic catholyte-anolyte interchange, or equivalent alternatives such as battery overdischarge, show promise of improving the voltage efficiency of VFBs.We have developed9-11 a standard methodology for measuring the thermal stability of vanadium catholytes based on their induction time for precipitation of V2O3. Using this, we have investigated the thermal stability of typical vanadium flow battery (VFB) catholytes at temperatures in the range 30–70°C for VV concentrations of 1.4–2.2 mol dm-3 and sulfate concentrations of 3.6–5.4 mol dm-3. In all cases, V2O5 precipitates after an induction time, which decreases with increasing temperature. Plots of the logarithm of induction time versus the inverse of temperature (equivalent to Arrhenius plots) show excellent linearity and all have similar slopes, yielding a value of 1.791±0.020 eV for the activation energy. The logarithm of induction time also increases linearly with sulfate concentration and decreases linearly with VV concentration. The slopes of these plots give values of concentration coefficients β S and β V5 which quantify the effects of concentration on induction times. Combining these with the Arrhenius slope, we have constructed a model11 to predict the stability of sulfate-based vanadium catholytes. The model can also be used as a basis for accelerated testing12 of electrolyte stability.We have investigated a range of additives and shown that many suggested additives are ineffective. However, the Group V elements phosphorus and arsenic in the +5 oxidation state have a significant stabilizing effect.13 We have also used our methodology for measurement of thermal stability to examine the stability of VFB catholytes under actual operating conditions. Results on the effect of state of charge, and deterioration and recovery of stability will be discussed. REFERENCES M. Skyllas-Kazacos et al., J. Electrochem. Soc., 158, R55 (2011). A. Weber et al., J. Appl. Electrochem., 41, 1137 (2011). M. A. Miller et al., J. Electrochem. Soc., 163, A2095 (2016).D. Oboroceanu et al., J. Electrochem. Soc., 163, A2919 (2016).C. Petchsingh et al., J. Electrochem. Soc., 163, A5068 (2016). Á. Cunha et al., Int. J. Energy Res., 39, 889 (2015).A. Bourke et al., J. Electrochem. Soc., 163, A5097 (2016). A. Bourke et al., J. Electrochem. Soc., 162, A1547 (2015).D. Oboroceanu et al., J. Electrochem. Soc., 163, A2919 (2016).D. Oboroceanu et al., J. Electrochem. Soc., 164, A2101 (2017).D. N. Buckley et al., J. Electrochem. Soc., 165, A3263 (2018).D. N. Buckley et al., J. Electrochem. Soc., 168, 030530 (2021).D. Oboroceanu et al., J. Electrochem. Soc., 166, A2270 (2019).

A comprehensive mechanistic analysis of silver dissolution with the monoethanolamine-copper-ammonium system and the development of a novel leaching technology

In the present research, the novel system of monoethanolamine-copper-ammonium was electrochemically studied to improve our knowledge of the reaction mechanism of silver dissolution. This paper introduces the effect of varying the concentration of monoethanolamine (MEA), ammonium sulfate, copper sulfate and temperature on the silver leaching kinetics and mechanism. The study has been complemented with thermodynamic analysis, characterization techniques (FESEM-EDS), leaching tests with H2O2 as oxidizing agent and electrochemical techniques such as Tafel, linear voltammetry and open circuit potential. The results demonstrate that it is possible to dissolve silver inhibiting the Cu(OH)2 precipitation in the system by increasing the concentration of MEA up to 1.5 M. The anodic polarization of silver reveals that an increase in the MEA concentration from 0.05 to 1.5 M, promotes the silver oxidation kinetics, maintaining the concentrations of 0.3 and 0.8 M of CuSO4 and (NH4)2SO4, respectively. Furthermore, the Tafel analysis shows that an increase in temperature from 15 to 45 °C minimizes the charge transfer coefficient and increases the silver oxidation kinetics using a leaching solution which avoids the precipitation of copper hydroxide species. The electrochemical results reveal the catalytic role of MEA during the silver dissolution and the possibility to eliminate the use of cupric ions while an energetic condition higher than 0.4 V vs SHE is maintained. In the case of silver sulfide dissolution, the results revealed that the reductive decomposition of silver sulfide is favored at a more cathodic potential than −0.6 V vs SHE with the MEA-Na2SO4-(NH4)2SO4 system, this cathodic pre-treatment facilitates the accelerated dissolution of silver from Ag2S using the same MEA leaching system. Finally, it is possible to dissolve 81 % of metallic silver using a conventional batch reactor with the MEA-Na2SO4-(NH4)2SO4-H2O2 novel system at room temperature.

Cathodic Activation of Titania-Fly Ash Cenospheres for Efficient Electrochemical Hydrogen Production: A Proposed Solution to Treat Fly Ash Waste

Fly ash (FA) is a waste product generated in huge amounts by coal-fired electric and steam-generating plants. As a result, the use of FA alone or in conjunction with other materials is an intriguing study topic worth exploring. Herein, we used FA waste in conjunction with titanium oxide (TiO2) to create (FA-TiO2) nanocomposites. For the first time, a cathodic polarization pre-treatment regime was applied to such nanocomposites to efficiently produce hydrogen from an alkaline solution. The FA-TiO2 hybrid nanocomposites were prepared by a straightforward solvothermal approach in which the FA raw material was mixed with titanium precursor in dimethyl sulfoxide (DMSO) and refluxed during a given time. The obtained FA-TiO2 hybrid nanocomposites were fully characterized using various tools and displayed a cenosphere-like shape. The synthesized materials were tested as electrocatalysts for the hydrogen evolution reaction (HER) in 0.1 M KOH solution in the dark, employing various electrochemical techniques. The as-prepared (unactivated) FA-TiO2 exhibited a considerable HER electrocatalytic activity, with an onset potential (EHER) value of −144 mV vs. RHE, a Tafel slope (−bc) value of 124 mV dec−1 and an exchange current density (jo) of ~0.07 mA cm−2. The FA-TiO2′s HER catalytic performance was significantly enhanced upon cathodic activation (24 h of chronoamperometry measurements performed at a high cathodic potential of −1.0 V vs. RHE). The cathodically activated FA-TiO2 recorded HER electrochemical kinetic parameters of EHER = −28 mV, −bc = 115 mV dec−1, jo = 0.65 mA cm−2, and an overpotential η10 = 125 mV to yield a current density of 10 mA cm−2. Such parameters were comparable to those measured here for the commercial Pt/C under the same experimental conditions (EHER = −10 mV, −bc = 113 mV dec−1, jo = 0.88 mA cm−2, η10 = 110 mV), as well as to the most active electrocatalysts for H2 generation from aqueous alkaline electrolytes.

Boosting Oxygen Evolution Reaction on Metallocene-based Transition Metal Sulfides Integrated with N-doped Carbon Nanostructures.

In this study, utilizing metallocene and organosulfur chelating agent, an innovative synthetic route was developed towards electrochemically activated transition metal sulfides entrapped in pyridinic nitrogen-incorporated carbon nanostructures for superior oxygen evolution reaction (OER). Most importantly, the preferential electrochemical activation process, which consisted of both anodic and cathodic pre-treatment steps, strikingly enhanced OER and long-lasting cyclic stability. The substantial increase in OER electrocatalytic activity of Ni9 S8 /Ni3 S2 -NC and Co9 S8 -NC during the activation process was mainly attributed to the increase of faradaic active site density on the catalytic layer resulting from the reconstruction of catalytic interfaces. It was also found that Fe-based metallocene [ferrocene (Fc)]-incorporation in the Co9 S8 -NC and Ni9 S8 /Ni3 S2 -NC nanostructures significantly boosted the OER activity. Thus, the combined effects of Fc-incorporation and the electrochemical activation process reduced the overpotential to about 115 and 95 mV on the Ni9 S8 /Ni3 S2 -NC and Co9 S8 -NC nanostructures to derive a current density of 10 mA cm-2 , respectively. Notably, Fc-Ni9 S8 /Ni3 S2 -NC electrocatalysts required very small overpotentials of around 222, 244, and 280 mV to acquire the current densities of 10, 20, and 50 mA cm-2 , respectively. This work opens up a new avenue for superior OER electrocatalysts by the utilization of metallocene and the preferential electrochemical activation process.

The optimized electrochemical deposition of bismuth-bismuth telluride layered crystal structures

Underpotential deposition, i.e. the cathodic deposition above reversible potential E(Men+/Me), produces an atomic layer of a metal on a semiconductor electrode, such as e.g. bismuth telluride. This phenomenon allows electrodeposition of superlattices formed of building blocks of a layered semiconductor structure joined by biatomic metal interlayer. This work outlines the optimized pulse potential controlled electrodeposition of (Bi2)m(Bi2Te3)n films produced under mentioned above technique. The influence on the morphology of the electrodeposited films of key-parameters as applied pulse frequency, duty cycle, a routine of sodium dodecyl sulfate introduction in the electrolyte is discussed. The optimized procedure comprises a short (about 10 s) cathodic pre-treatment at high overpotential of the cathodic reaction, the subsequent periodic switching for 120 min between potentials of electrodeposition and refinement at 0.1 Hz and 5% duty cycle with addition of surfactant 60 min after the start of the electrodeposition.

A Benzocaine‐Induced Local Near‐Surface pH Effect: Influence on the Accuracy of Voltammetric Cocaine Detection

AbstractThis work describes a local induced near‐surface pH effect (pHS) arising from the presence of one analyte, leading to an influence or even suppression of redox signals of a second analyte present in solution. This concept and its impact on voltammetric sensing is illustrated by focusing on the detection of cocaine in the presence of the common adulterant benzocaine. An in‐depth study on the observed interference mechanism and its specificity for benzocaine and not for other adulterants was performed through the use of multiple electrochemical strategies. It was concluded that the potential shift and loss of intensity of the square‐wave voltammetric cocaine signal in the presence of benzocaine was caused by a local pHS effect. A cathodic pretreatment strategy was developed to nonetheless allow accurate cocaine detection. These insights are useful for explaining unidentified phenomena involving compounds with properties similar to benzocaine in voltammetric electroanalysis.

The effect of CTAB, a cationic surfactant, on the adsorption ability of the boron-doped diamond electrode: Application for voltammetric sensing of Bisphenol A and Hydroquinone in water samples

The present study introduces for the first time the effect of the cationic surfactant, cetyltrimethylammonium bromide (CTAB) on the adsorption capability of the boron-doped diamond (BDD) electrode for the sensing of environmental pollutants bisphenol A (BPA) and hydroquinone (HQ). Cathodic pretreatment of the electrode surface after an anodic pretreatment exhibited a best electrochemical response for these two phenolic compounds. The electrochemical characteristics of BPA and HQ were first sufficiently documented by cyclic voltammetry in aqueous solutions without the addition of surfactant over a shorter and longer potential range. Square-wave voltammetry was employed for a detailed study depending on the operational conditions (e.g., pH and nature of supporting electrolyte, concentration of CTAB, accumulation variables, instrumental parameters, etc.). The sensitivity of the voltammetric measurements for BPA and HQ was increased when CTAB was present in strong acidic media (more effective for BPA) due to its interaction with the neutral forms of the selected compounds on the hydrophobic surface of BDD electrode. Besides, a significant increase in the detecting sensitivity of BPA in CTAB-containing solutions could be obtained after applying an accumulation process. Using square-wave stripping mode (after 30 s accumulation at open-circuit condition) in 0.1 M H2SO4 containing 1 × 10−4 M CTAB, the limits of detection were found to be 0.05 μg/mL (2.19 × 10-7 M), and 0.23 μg/mL (2.09 × 10-6 M) for the simultaneous determination of BPA and HQ, respectively. In this way, modification-free BDD electrode could introduce an alternative to chemically modified electrodes for the analysis of environmental samples.

Sensitive Voltammetric Detection of Chloroquine Drug by Applying a Boron-Doped Diamond Electrode

In this research, a boron-doped diamond (BDD) electrode has been explored to detect the chloroquine drug. The electrochemical performance of BDD electrode towards the irreversible anodic response of chloroquine was investigated by subjecting this electrode to the cathodic (−0.5 A cm−2 by 180 s, generating a predominantly hydrogen-terminated surface) and anodic (+0.5 A cm−2 by 30 s, oxygen-terminated surface) pretreatments. The cathodically pretreated BDD electrode ensured a better-defined anodic peak and higher current intensity. Thus, by applying the cathodically pretreated BDD electrode and square-wave voltammetry (SWV), the analytical curve was linear from 0.01 to 0.25 µmol L−1 (correlation coefficient of 0.994), with sensitivity and limit of detection of 12.2 µA L µmol−1 and 2.0 nmol−1, respectively. This nanomolar limit of detection is the lowest recorded so far with modified and unmodified electrodes.

(Invited) Factors Influencing the Performance of Vanadium Flow Batteries: Electrodes and Electrolytes

There is presently great interest in redox flow batteries1-8 (RFBs) for large-scale energy storage9 due to advantages over other electrical energy storage (EES) technologies, and research activities in this area have grown exponentially in recent years. The vanadium flow battery (VFB), also known as the vanadium redox flow battery (VRFB), is commonly regarded as one of the most promising flow batteries.2-3,10-12 Active areas of research on VFBs include electrolytes,13-16 electrodes,5-7 membranes,8 cell design and modelling,8 and performance and state-of-charge (SoC) monitoring.17-18 In this paper, we will review our work in two areas: kinetics on carbon electrodes and thermal stability of electrolytes.The kinetics of the VII-VIII, VIII-VIV and VIV-VV redox couples have been studied for a range of different carbon materials using a variety of techniques, and it is clear that the kinetic rates depend strongly both on the type of carbon used and on the preparation of the electrode surface. We will discuss our investigations5-7 of the effects of anodic and cathodic pretreatments of carbon on electrode kinetics in the VFB. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), we showed for four different types of carbon that electrode treatments at negative potentials enhance the kinetics of VIV-VV and inhibit the kinetics of VII-VIII while electrode treatments at positive potentials inhibit the kinetics of VIV-VV and enhance the kinetics of VII-VIII. These observations may explain conflicting reports in the literature. We examined in detail the potentials required for activation and deactivation of electrodes. The results suggest that interchanging the positive and negative electrodes in a vanadium flow battery (VFB) would reduce the overpotential at the negative electrode and so improve the performance. This is supported by flow-cell experiments. Thus, periodic catholyte-anolyte interchange, or equivalent alternatives such as battery overdischarge, show promise of improving the voltage efficiency of VFBs.We have developed13-16 a standard methodology for measuring the thermal stability of vanadium catholytes based on their induction time for precipitation of V2O3. Using this, we have investigated the thermal stability of typical vanadium flow battery (VFB) catholytes at temperatures in the range 30–70°C for VV concentrations of 1.4–2.2 mol dm-3 and sulfate concentrations of 3.6–5.4 mol dm-3. In all cases, V2O5 precipitates after an induction time, which decreases with increasing temperature. Plots of the logarithm of induction time versus the inverse of temperature (equivalent to Arrhenius plots) show excellent linearity and all have similar slopes, yielding a value of 1.791±0.020 eV for the activation energy. The logarithm of induction time also increases linearly with sulfate concentration and decreases linearly with VV concentration. The slopes of these plots give values of concentration coefficients β S and β V5 which quantify the effects of concentration on induction times. Combining these with the Arrhenius slope, we have constructed a model to predict the stability of sulfate-based vanadium catholytes. The model can also be used as a basis for accelerated testing of the thermal stability of electrolytes.We have investigated a range of additives and shown that many suggested additives are ineffective. However, the Group V elements phosphorus and arsenic in the +5 oxidation state have a significant stabilizing effect. We have also quantified their effect in the temperature range 30-70°C. REFERENCES A.Z. Weber et al., J. Appl. Electrochem. 41, 1137 (2011)M. Skyllas-Kazacos et al., J. Electrochem. Soc. 158, R55 (2011)M.J. Watt-Smith et al., J. Chem. Technol. Biotechnol. 88, 126 (2013)S. Roe et al., J. Electrochem. Soc. 163, A5023 (2016)A. Bourke et al., J. Electrochem. Soc. 163, A5097 (2016)A. Bourke et al., J. Electrochem. Soc. 162, A1547 (2015)M.A. Miller et al., J. Electrochem. Soc. 163, A2095 (2016)D. Reed et al., J. Electrochem. Soc. 163, A5211 (2016)R. M. Darling et al., Energy Environ. Sci ., 7, 3459 (2014)R. M. Darling et al., J. Electrochem. Soc .,163, A5014 (2016)A. K. Manohar et al., J. Electrochem. Soc., 163, A5118 (2016)A. M. Pezeshki et al., J. Electrochem. Soc., 163, A5202 (2016)D. Oboroceanu et al., J. Electrochem. Soc ., 163, A2919 (2016)D. Oboroceanu et al., J. Electrochem. Society, 164, A2101 (2017)D. N. Buckley et al., J. Electrochem. Society, 165, A3263 (2018) Oboroceanu et al., J. Electrochem. Soc ., 166, A2270 (2019)C. Petchsingh et al., J. Electrochem. Soc. 163, A5068 (2016)D. N. Buckley et al., J. Electrochem. Soc., 161 A524 (2014)

A novel electrochemical strategy for determination of vitamin B12 by Co(I/II) redox pair monitoring with boron-doped diamond electrode

Vitamin B12 supplementation is recommended mainly for people who are vegetarian or vegan. The wide extent of the use of this supplementation should act as a warning sign regarding the quality of commercially available products. In this context, a novel electrochemical strategy is proposed for the determination of vitamin B12, where the Co(I/II) redox pair is monitored using a boron-doped diamond electrode for the analysis of supplementation products. The surface of the boron-doped diamond was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The electrical properties of the electrode are highly influenced by its surface terminations and a cathodic pretreatment of −2.0 V for 30 s in 0.5 mol L−1 H2SO4 before the analysis enhanced the analytical response. The cyclic voltammograms for vitamin B12 obtained at pH 5.0 showed four peaks: two oxidation peaks at −0.74 and +0.18 V, corresponding to Co(I/II) and Co(II/III) oxidations, respectively, and two reduction peaks at −0.12 and −0.75 V, corresponding to Co(III/II) and Co(II/I) reductions, respectively. The experimental parameters (pH, supporting electrolyte, pulse technique) were optimized for the monitoring of the Co(I/II) redox pair. The calibration plot for vitamin B12 was obtained by square wave voltammetry at pH 10.0. It was found to be linear from 0.25 to 5.0 μmol L−1, with a detection limit of 86.0 nmol L−1. A boron-doped diamond electrode with cathodic pretreatment was employed to determine vitamin B12 levels in fortified toothpaste and supplementation tablets. The results were compared with those provided by UV–vis spectrometry. The statistical analysis showed no significant difference between the two methodologies in terms of the precision and accuracy of the data obtained.

Electrochemical reduction of nitrate on boron-doped diamond electrodes: Effects of surface termination and boron-doping level

This study is among the first to systematically study the electrochemical reduction of nitrate on boron-doped diamond (BDD) films with different surface terminations and boron-doping levels. The highest nitrate reduction efficiency was 48% and the highest selectivity in the production of nitrogen gas was 44.5%, which were achieved using a BDD electrode with a hydrogen-terminated surface and a B/C ratio of 1.0%. C–H bonds served as the anchor points for attracting NO3− anions close to the electrode surface, and thus accelerating the formation of NO3−(ads). Compared to oxygen termination, hydrogen-terminated BDD exhibited higher electrochemical reactivity for reducing nitrate, resulting from the formation of shallow acceptor states and small interfacial band bending. The hydrophobicity of the hydrogen-terminated BDD inhibited water electrolysis and the subsequent adsorption of atomic hydrogen, leading to increased selectivity in the production of nitrogen gas. A BDD electrode with a boron-doping level of 1.0% increased the density of acceptor states, thereby enhancing the conductivity and promoting the formation of C–H bonds after the cathodic reduction pretreatment leading to the direct reduction of nitrate.

Voltammetric sensing of E,E-dienestrol in fish tissue by combining a cathodically pretreated boron-doped diamond electrode and QuEChERS extraction method

Food quality control has been a pressing issue in recent years and demands the development of efficient and versatile analytical methods. This paper describes a promising voltammetric assay to monitor the synthetic estrogen E,E-dienestrol (E,E-DNL) in fish tissue, using a cathodically pretreated boron-doped diamond (Cpt-BDD) electrode in combination with QuEChERS extraction method. The electrochemical reactivity of E,E-DNL on Cpt-BDD electrode is strongly pH-dependent, so that a well-defined anodic peak (≈ 0.97 V vs. Ag/AgCl) was recorded in Britton-Robinson buffer (pH = 2.0) due to oxidation of estrogen to quinone. This behavior became much more evident after cathodic pretreatment of the working electrode, since the hydrogen-terminations produced on the active surface improve the charge-transfer process, signal-to-background ratio and fouling resistance. When estrogen oxidation current was observed by square-wave voltammetry under optimum conditions, it was found a linear relationship from 2.30 × 10–7 to 9.69 × 10–6 mol L–1E,E-DNL, with high data correlation (R2 = 0.9987), sensitivity (detection limit of 5.43 × 10–8 mol L–1) and precision (RSD < 5.0% for repeatability and reproducibility tests) of the measurements. The procedure was successfully applied to quantify E,E-DNL in QuEChERS extracts from Nile Tilapia (Oreochromis niloticus) liver tissue (92.3–98.8% recovery), proving its high potential for the quality control of this estrogen in aquatic origin foods.

First voltammetric behavior study of non-narcotic analgesic drug nefopam and its reliable determination on boron-doped diamond electrodes

In the present paper, for the first time, the electrochemical behavior and determination of a highly oxidizable non-opioid painkilling medication Nefopam (NEF) has been reported. The outcomes revealed that NEF presented one diffusion-controlled anodic signal at very positive potential of about +1.7 V in 1 M HClO4 on the boron-doped diamond electrode (BDDE). The impact of the electrochemical (anodic and cathodic) pretreatment of the BDDE surface was evaluated. The cathodic pretreatment after anodic one was considered as the most suitable choice due to the improved charge transfer and the enhanced surface activity. Under optimized experimental conditions and operating parameters, the calibration curves were linear over concentration ranges of 2.00–59.7 μM and 0.99–77.1 μM with similar detection limits of 0.5 μM for differential pulse (DPV) and square-wave (SWV) voltammetry, respectively. Moreover, the electroanalytical determination of NEF in the presence of human urine matrix was also found to be possible in the linear concentration ranges from 3.8 to 64.8 μM and from 4.9 to 47.2 μM with detection limits of 1.7 μM and 1.8 μM for DPV and SWV, respectively. The practical feasibility of the introduced method was successfully confirmed by the quantification of NEF amount in commercial pharmaceutical dosage with the result in a good agreement with that specified in analytical normative documentation. The developed procedure can be easily implemented for control analysis also with the use of miniaturized thick-film BDDE without additional optimization steps.

Simple and rapid voltammetric determination of cephalosporin drug cefixime on boron-doped diamond electrode

A boron-doped diamond electrode was used for the first time in sensitive and selective analysis of cefixime, a third-generation cephalosporin drug, using the square-wave voltammetry technique. The effect of the pretreatment procedure on the current response at the electrode was investigated. The best signals were obtained by polishing the electrode with a polishing pad after applying anodic and cathodic electrochemical pretreatment to the electrode. Cefixime gave a well-defined, irreversible and diffusion-controlled oxidation peak in 0.1 mol dm−3 H2SO4 support electrolyte at + 1.25 V (vs. Ag/AgCl 3 mol dm−3 NaCl). Under the best instrumental conditions and with the pretreatment procedure, a calibration curve was obtained with linearity between 2.2 × 10−6 mol dm−3 and 1.3 × 10−4 mol dm−3 at 5.9 × 10−7 mol dm−3 detection limit. The effect of possible interference substances on the current response for cefixime was investigated and the method was found to have sufficient selectivity. The developed method was successfully applied for the analysis of cefixime from pharmaceutical formulations. The method can be an alternative to the other analytical approaches due to its speed, simplicity, low cost, wide calibration range, and repeatable responses.