Potentiostatic Oxidation Research Articles

Novel oxidative routes to N-arylpyridoindazolium salts.

A novel facile approach to N-arylpyridoindazolium salts is proposed, based on direct oxidation of the ortho-pyridine substituted diarylamines, either using bis(trifluoroacetoxy)iodobenzene as an oxidant, or electrochemically, via potentiostatic oxidation. Electrochemical synthesis occurs under mild conditions; no chemical reagents are required except electric current. Both approaches can be considered as a late-stage functionalization; easily available ortho-pyridyl-substituted diarylamines are used as the precursors.

Exploiting synergistic interaction in Cu-Zn-Ni alloy oxide films prepared by one-step anodizing for a highly sensitive non-enzymatic glucose sensor

A highly sensitive and precise electrochemical biosensor for glucose detection was developed by coupling synergetic catalysis of Cu-Zn-Ni oxide films. To enhance the catalytic performance of alloy, potentials between −0.5 V and 1.5 V are selected for potentiostatic oxidation. Notably, the oxidation process reveals the influence of Cl− in the electrolyte, leading to electrode surface etching, with increasing etching and grain boundary collapse at higher potentials. The electrochemical performance of the electrode was comprehensively evaluated using cyclic voltammetry (CV) and amperometric response in alkaline conditions. The catalytic electrode has an impressive linear response in the concentration range of 0.1 ∼ 1.0 mM glucose, with a sensitivity of 3775.11 μA·mM−1. Furthermore, the electrode exhibits remarkable stability and anti-interference properties, rendering it suitable for non-enzymatic glucose sensing applications.

Thermo-electro dually activated carbon cloth as cathode material for aqueous hybrid zinc ion supercapacitor with ultrahigh stability and dramatically enhanced areal capacitance

The facile and low-cost technology for the fabrication of high-performance electrode material for supercapacitors is very important for green energy storage. Herein, the commercial carbon cloth (CC) with poor capacitance is subjected to thermal treatment at 430°C, followed by a potentiostatic oxidation at a constant potential of 2 V. Through the thermal activation process, the capacitance is increased to 1310 mF cm−2, and further enhanced to 2421 mF cm−2 after the additional potentiostatic activation. Nitrogen adsorption experiment and X-ray photoelectron spectroscopy analysis show that the prominent increase in specific surface area upon thermal-activation and the formation of oxygen-containing groups after electrochemical-activation are responsible for the greatly improved capacitive properties. The aqueous hybrid zinc ion supercapacitor (HZSC) constructed using the thermal-electro dually activated CCs cathode and Zn plate anode shows a high energy density of 1.21 mWh cm−2 at a power density of 4.75 mW cm−2. The HZSC displays superior long period stability with 94.65% capacitance retention after 8000 galvanostatic charge-discharge cycles. This work proposes a facile route to transform commercial carbon cloths into high performance self-standing cathode for the aqueous HZSCs, which will have noticeable effect on energy storage technology due to its stability, low-cost, environmental friendliness and safety.

Pom-pom-like nanowire clusters prepared by potentiostatic oxidation of copper in NH4HCO3 solution

Formation of hemispherical pom-pom-like clusters of nanowires during potentiostatic oxidation of copper in NH 4 HCO 3 is reported. High-purity copper was oxidized in a three-electrode setup at constant electrode potential ranging from 200 mV to 1000 mV vs. Ag|AgCl|sat. KCl for 14 h. The obtained clusters of nanwires were examined using FE-SEM, XRD and XPS techniques. The diameter of nanowires, composed mainly of CuO, Cu 2 O, Cu(OH) 2 , and Cu 4 O 3 , was ca. 50–70 nm. The diameter of the clusters strongly depends both on the applied potential and the time of electrooxidation, and was found to be in the range of 1–3 μm. The mechanism for the formation of such nanowires clusters is proposed. • Clusters of nanowires form on copper during potentiostatic oxidation in NH 4 HCO 3 . • The outer layer of nanowires is composed of mostly Cu(OH) 2 and CuO. • Cu 2 O, CuO, Cu(OH) 2 , Cu 4 O 3 and Cu 2 CO 3 (OH) 2 are present in internal layer. • The cluster diameter depends on the applied potential and time of oxidation.

Extension of the potential intervals of high redox activity and electronic conductivity of polypyrrole films on electrode surface via their electrochemical multi-cycle treatment in monomer-free solution

Thin polypyrrole films (thickness: about 30 nm) have been deposited at electrode surface via potentiostatic oxidation of dilute (1 mM) pyrrole solution in acetonitrile (AN). It has been shown that their subsequent treatment by means of multi-cycle voltammetry within a broad potential range (up to -2.0 V vs. Ag/Ag+ in AN) leads to their "activation", i.e. to a very strong extension of their redox response region in the negative direction as well as to almost uniform distribution of the redox activity within this potential range. Region of their high conductivity under in situ conditions has also extended significantly. Spectral and electrocatalytic properties of such PPy films before and after their "activation" have been analyzed. Two parameters for characterization of the variation of film's properties in the course of its "activation" (redox efficiency of polymerization and width of electroactivity region) have been proposed. Comparison of films deposited at different potentials (from 0.6 V to 0.8 V) has revealed that the effect of their "activation" increases for lower polymerization potential. Films deposited at 0.6 V possess after their "activation" a very broad electroactivity range (almost 2.5 V) and a record high redox charge per monomer unit (its oxidation degree) inside the film in contact with AN solution, 0.45. Such unusual properties of "activated" PPy films make them prospective materials for various applications.

Potentiostatic oxidation of N-doped algae-derived carbon for P-nitrophenol sensitive determination

Abstract A p-nitrophenol (4-NP) sensor based on Enteromorpha algae-derived carbon is conducted in the presented work. Nitrogen doping and potentiostatic oxidation are implemented to optimize the electrochemical performance of Enteromorpha algae-derived porous carbon. A series of techniques including Electrochemical Impedance Spectroscopy, Scanning Electron Microscope, Raman spectroscopy and X-ray photoelectron spectroscopy are exploited to evaluate the physicochemical properties of materials after doping and oxidation. The results show that the introduction of nitrogen atoms not only generates more active sites on the electrode but also enhances its adsorption of 4-NP, which is verified by the analysis of molecular dynamics simulations. It is also determined that oxygenated functional groups are introduced after electrochemical oxidation, enhancing the catalytic and hydrophilic nature of the electrode. Under the optimal experimental conditions, the prepared electrode shows a current response of over 400 μA at 4-NP concentration of 100 μM, which is about 7 times higher than the undoped or unoxidized electrode. A good linear relation to 4-NP over the range of 0.5–10 μM and log-linear relationship within 10–500 μM are obtained. In the practical sample detection, N-PCOx also showed sufficient practicability and excellent anti-interference ability.

Effect of 6‐thioguanine, as an electrolyte additive, on the electrochemical behavior of an Al–air battery

AbstractIn this study, the electrochemical behavior of an Al–air battery is improved by mixing 6‐thioguanine into 4.0 M NaOH electrolyte. The electrochemical performance of the Al electrodes is analyzed using potentiodynamic polarization, potentiostatic oxidation, and electrochemical impedance spectroscopy. The surface morphology of the Al electrodes after discharging for 1,000 s is characterized using scanning electron microscopy coupled with X‐ray elemental mapping for Al, O, C, N, and S. Furthermore, the utilization efficiencies of these samples are also determined. The results show that the corrosion resistance of the Al electrodes initially increases and then decreases with an increase in 6‐thioguanine concentration. The presence of 6‐thioguanine enhances the corrosion resistance to the maximum, with a corrosion current density (Icorr) of 6.170 mA/cm2, and corrosion inhibition efficiency (η) of 36.56%, at 0.5 mM of 6‐thioguanine.

Influence of histidine as an electrolyte additive on the electrochemical performance of Al electrodes in 4.0 M KOH electrolyte

AbstractIn this study, the influence of histidine as an electrolyte additive on the electrochemical performance of Al electrodes in 4.0 M KOH electrolyte is studied by measuring open‐circuit potential–time curves, potentiodynamic polarization, potentiostatic oxidation, and electrochemical impedance spectroscopy. The surface morphology of Al electrodes is characterized by scanning electron microscopy. The results show that the battery performance is significantly improved by adding histidine. Samples with 50 mM histidine exhibit the highest corrosion resistance and discharging current density among all the specimens, with the corrosion current density (Icorr) being 7.471 mA/cm2 and corrosion inhibition efficiency (η) being 43.33%.

Performance of Modified Graphite Felt as Cathode in the Electro-Fenton System

The graphite felt (GF) was modified by the impregnation method and the potentiostatic oxidation method to improve its application performance in the electro-Fenton (E-Fenton) system. Sulfuric acid and ammonia water were used as modifying reagents. After the GF was modified, its conductivity, adsorption performance and hydrogen peroxide production performance were improved. The original graphite felt (GF0) and the modified GF were used as cathode to degrade methylene blue in the E-Fenton system to explore the practical application performance. The reaction kinetics of the methylene blue degradation process was fitted. The results showed the degradation of methylene blue followed the first-order kinetics. The GF was modified by the potentiostatic oxidation with ammonia as modifying reagent (GFEN) had the best application performance in the E-Fenton system. Degradation of methylene blue for 30 min, the reaction rate constant of GFEN cathode system was 1.71 times higher than GF0 cathode system. The GFEN electrode was reused 10 times in the E-Fenton system, the removal rate of methylene blue was only decreased by 7.14%, and the current was only decreased by 4 mA, which showed its good stability. Finally, the comparison of the electrical energy per order (EE/O) values showed that GFEN can significantly improve the current efficiency of the E-Fenton system.

Effects of the addition of Na2SnO3 to NaCl electrolytes on Mg‐14Li‐3Al‐1Gd electrode electrochemical behavior

AbstractWe report on the electrochemical performance of Mg‐14Li‐3Al‐1Gd electrodes prepared by the accumulation roll bonding technique in a 0.7 M NaCl solution. To explore the effects of adding different concentrations of Na2SnO3 to 0.7 M NaCl solutions, potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance spectroscopy, and scanning electron microscopy were utilized. The results show that the addition of Na2SnO3 to a 0.7 M NaCl solution increases the corrosion potential of the Mg‐14Li‐3Al‐1Gd electrodes. Samples with 0.1 mM Na2SnO3 retained the highest discharging current density and lowest polarization resistance of all the specimens. Electrodes in an electrolyte solution mixed with 0.1 mM Na2SnO3 presented a larger active reaction area, deeper channels, and higher discharging currents than those with other additive concentrations. In conclusion, to improve the electrochemical behavior of Mg‐14Li‐3Al‐1Gd electrodes in a 0.7 M NaCl solution, the optimal concentration of Na2SnO3 is 0.1 mM.

Effect of distribution of polytetrafluoroethylene on durability of gas diffusion backing in proton exchange membrane fuel cell

Gas diffusion backing (GDB) in proton exchange membrane fuel cell played an important role in conducting electricity, conducting air and draining water, and its durability had not been widely valued. In order to improve its durability, the ultrasonic immersion method was tried during the hydrophobic treatment of GDB and the characteristic parameters of the GDBs by different immersion methods and their effects on the performance of the single fuel cell were compared by scanning electron microscopy, sectional fluorine line-scanning and map-scanning, pore size distribution, gas permeability and fuel cell performance. Besides, the hydrophobic stability of the GDBs by different immersion methods was measured by potentiostatic oxidation and ultrasonic water washing tests. It was found that ultrasonic immersion method improved the content and the uniform distribution of polytetrafluoroethylene (PTFE) in the section of GDB, resulting in the better fuel cell performance and hydrophobic stability.

In situ determination of polysulfides in alkaline hydrogen sulfide solutions

A method was developed to determine low concentrations of polysulfide ions (Sn2− expressed as zero-valent sulfur) in situ and in the presence of high concentrations (0.5 mol dm−3) of hydrogen sulfide ions, HS−, at pH 14. UV–visible spectrophotometry was used to determine absorbances at 295 and 420 nm using an immersion probe, designed for highly corrosive environments. Three absorbance trends were found, corresponding to three concentration ranges of zero-valent sulfur: low (0–1.2 × 10−3 mol dm−3), medium (1.2–3.6 × 10−3 mol dm−3) and high (3.6–10 × 10−3 mol dm−3). The non-linear dependence of absorbance on concentration over the range studied was due to disproportionation of polysulfides. Determination of these species is well known to be problematic at low concentrations due to the effects of adventitious oxygen in solution, meta-stability and speciation of polysulfide species: S22− – S82−. Oxygen concentrations must be minimised in the inert gas used to de-oxygenate sulfide solutions and for the same reason, their contact with atmospheric oxygen should be minimised. During potentiostatic oxidation of alkaline solutions containing HS− ions in the anolyte of electrochemical reactors incorporating cation-permeable membranes, temporal changes in anolyte absorbance and charge were used to estimate polysulfide concentrations. Charge yields for sulfide to polysulfide oxidation were close to unity, confirming the utility of the technique developed. Molar attenuation coefficients of the predominant polysulfide ions S32− at 420 nm and S42− at 295 nm were also estimated as 289 and 3609 dm3 mol−1 cm−1, respectively, and comparable to values of (190, 206) and (3420, 3690) dm3 mol−1 cm−1 reported previously.

Passivation of a corrosion resistant high entropy alloy in non-oxidizing sulfate solutions

The passivation behavior of a novel high entropy alloy (HEA) of composition 38Ni-21Cr-20Fe-13Ru-6Mo-2W at.% (33Ni-16Cr-17Fe-19Ru-9Mo-6W wt.%) was investigated in sulfate solutions of various pH levels. The HEA was compared to a commercially available Ni-Cr-Mo-W-Fe alloy, C-22. Experiments were conducted using in-situ electrochemical and ex-situ surface-sensitive methods to probe the growth and dissolution of the passive layer. The HEA exhibited excellent corrosion resistance in highly acidic and highly alkaline solutions, maintaining passivity through a broad range of potentials below the Cr transpassivity range. Extremely rapid and efficient oxide formation and lower quasi-steady passive current densities were observed during oxide growth in the passive range compared to commercial alloy C-22. Ex-situ characterization of the passive film by atom probe tomography and X-ray photoelectron spectroscopy provided insight into the oxide composition, thickness, and elemental valence states of potentiostatically-grown and air-formed oxides. All elements in the alloy were oxidized following potentiostatic oxide growth. Instead of distinct stoichiometric compounds (i.e. with integer cation ratios) and oxide phases, a non-stoichiometric oxide solid solution was observed with significant enrichment in Cr and Ru, as well as depletion of Fe and Ni. The behavior of Cr was modeled with a modified surface enrichment model. The oxide thickness was estimated to be 3–4 nm thick. The connection between the solid solution oxide, enrichment of Cr in the passive layer, the presence of Mo and W, and excellent passivity is discussed.

Combined Galvanostatic and Potentiostatic Plasma Electrolytic Oxidation of Titanium in Different Concentrations of H2SO4

We report on plasma electrolytic oxidation of titanium, employing a technique with combined potentiostatic and galvanostatic control. The effect of different H 2 SO 4 electrolyte concentrations on the titanium oxide formation was studied sytematically. The titanium oxide consisted of two distinguishable layers. The upper layer is porous, up to few micrometers thick and primarily rutile, while the interlayer is compact, comparatively thin and is associated to anatase formation. The electrolyte concentration changed substantially layer thickness, porosity and phase composition, as deduced from scanning electron microscopy, X-ray diffraction and Raman spectroscopy.

The electrochemical behaviors of Mg-5Li-3Al-1La and Mg-8Li-3Al-1La alloys in sodium chloride solution

The electrochemical behaviors of Mg-5Li-3Al-1La and Mg-8Li-3Al-1La electrodes in NaCl solution are investigated by means of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). It is found that the Mg-8Li-3Al-1La electrode is of higher discharge activity than the Mg-5Li-3Al-1La electrode in 0.7 mol L−1 NaCl solution, which is consistent with the results observed from SEM images. The composition of the discharging products is also analyzed by means of XRD diffraction. This result shows that the Mg-8Li-3Al-1La alloy displays better compatibility with salt than the Mg-5Li-3Al-1La alloy, and the electrolyte can easily permeate the electrode, which enlarges the reaction zone and improves the activity of the electrode. The continuous discharging utilization efficiency of the Mg-5Li-3Al-1La and Mg-8Li-3Al-1La electrodes is 47.36 and 50.46%, respectively. The utilization of the Mg-Li-Al-La electrode is increased by 3.10% with the amount of Li increased from 5 to 8%. Meanwhile, the interval discharging utilization efficiency of the two electrodes is 46.13 and 49.88%, respectively, and the increase in the amount of Li in the electrode also brings a favorable effect on the interval electrochemical properties of the electrode.

Electrochemical behavior of alloy AgCu50 during oxidation in the presence of chlorides and benzotriazole

Abstract The presence of chloride ions in concentrations higher than 0.01 mol × dm−3 significantly intensifies anodic processes at AgCu50 alloy. In order to slow down this reaction, it was looked for the possibility of using benzotriazole known as an effective corrosion inhibitor for copper. This paper shows the influence of benzotriazole in a wide range of concentrations on inhibition of anodic processes as well as its influence on mechanism of the reactions such as formation of copper and silver oxides and chlorides. To determine this influence, open circuit potential measurements, anodic polarization and potentiostatic oxidation followed by optical microscopy were used. It was discovered that benzotriazole in concentrations higher than 0.005 mol × dm−3 almost completely passivates the mentioned alloy in alkaline solutions in the presence of chloride ions in a concentration range from 0.01 to 0.02 mol × dm−3.

Tuning inner-layer oxygen functional groups of reduced graphene oxide by potentiostatic oxidation for high performance electrochemical energy storage devices

The electrochemical lithiation/delithiation of oxygen-containing functional groups (OCFGs) of nanocarbon materials, particularly graphene, have attracted intensive interest in recent years. Here, we propose a controllable potentiostatic oxidation approach to tune the OCFGs of as-prepared reduced graphene oxide (rGO) in a carbonate-based electrolyte to improve the specific capacity and rate capability. By X-Ray absorption spectroscopy in total fluorescence yield mode and X-Ray diffraction, we confirm that potentiostatic oxidations generate new OCFGs in the inner-layer of rGO. The content of OCFGs increases as oxidation potential being elevated. Such increasing of OCFGs in quantity significantly enhances the capacity. For instance, the specific capacity of 170.4mAhg−1 for pristine rGO electrode is increased to 290.5mAhg−1 after the oxidation at 5.0V. We demonstrate that oxidations at moderate potentials can reduce the electrochemical and ohmic polarizations of rGO electrodes without deteriorating diffusion dynamic, thereby improving rate capability. After the optimal oxidation at 4.7V, rGO electrode exhibits an excellent rate capability, delivering 58.4mAhg−1 at 20Ag−1.

Electrochemical behavior of AgCu50 in alkaline media in the presence of chlorides and 2-mercaptobenzothiazole

Electrochemical behavior of an alloy AgCu50, pure copper, and pure silver, respectively, was investigated by measuring the open circuit potentials using anodic potentiodynamic polarization and potentiostatic method in 0.1 moldm-3 NaOH + 0.02 moldm-3 NaCl solution, without and with adding 2-mercaptobenzothiazole in various concentrations (0.00001 - 0.001 moldm-3). Anodic polarization curves for AgCu50 alloy, showed four current peaks. Potentiostatic curves showed that values of the stationary current densities drop down with the increase of 2-mercaptobenzothiazole concentration in the electrolyte. The electrode surface was analyzed by optical microscopy after the potentiostatic oxidation. Micrographs confirmed that 2-mercaptobenzothiazole has got the inhibitory effect by forming the film of CuMBT and AgMBT which protect the electrode surface from corrosion.

Synthesis of facetted Pt nanoparticles on SnO2 as an oxygen reduction catalyst

Fuel cells are an important technology to match the volatile energy production with the energy demand in a sustainable energy system. One crucial task is to raise the Pt mass specific activity of Pt oxygen reduction catalysts in fuel cells and to increase their stability. Therefore, different approaches are investigated like the facetting of Pt nanoparticles and the use of supporting particles like SnO2, which stabilize Pt. For the first time, the growth of facetted Pt nanoparticles on SnO2 nanoparticles is reported which combines both approaches. The synthesis is based on a polyol process and employs Ag ions to influence the shape evolution of the Pt nanoparticles. The samples were studied by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and cyclic voltammetry (CV). Since SnO2 is etched during the original synthesis, KOH is added to compensate the protons released. The fraction of the facetted Pt nanoparticles is lowered in the presence of SnO2 likely due to adsorption of Ag on the SnO2 surface and, thus, a decrease of the Ag concentration in the bulk solution. Consequently, the Ag concentration was increased leading to the generation of a fair amount of facetted Pt nanoparticles. To avoid the occupation of Ag redeposited on the Pt catalyst's surface and, thus, lowering of its catalytic activity, a cleaning procedure consisting of potentiostatic oxidation of Ag and replacement of the electrolyte was applied.

Mechanistic study on the interfacial variation of carbon electrode under electrochemical oxidation

Previously, we have reported that different procedures employed for electrochemical oxidation of glassy carbon (GC) can lead to remarkably different interfaces for the redox reactions of copper species in the presence of Cl− anion. In this article, we further investigated the interfacial variation mechanism of other carbon electrodes employing both cyclic and potentiostatic oxidation methods in H2SO4 solution. The electrochemical studies were limited to the end-edge planes of vertically aligned multi-walled carbon nanotubes (eVAMWCNTs) and the edge planes of highly oriented pyrolytic graphite (eHOPG). Differences in the pristine surfaces and bulk structures of these two sp2 carbon electrodes were merely resulted from the arrangements of graphene multilayers by rolling seamlessly or parallel alignment. Experimental results showed that cyclic oxidation favored the generation of oxygen-containing groups at eVAMWCNTs, due to that rigid MWCNT surface and bulk structures were unfavorable for the intercalation reaction of SO42− anion. On the other hand, potentiostatic oxidation was found to cause the oxidation of eVAMWCNTs via a different reaction route. By contrast, the oxidation of the soft eHOPG predominantly involved the intercalation of SO42− anion into the gaps between graphene layers, which might restrain the increase of oxygen-containing groups at eHOPG. As probed by Raman spectroscopy and the redox reactions of copper species, significant differences in the interfacial variation with two oxidation methods were observed for eVAMWCNTs. As indicated by an abnormal behavior of metallic copper deposition/dissolution, only the cyclic oxidation could quickly generate a very high ratio of oxygen-containing groups to other electron transfer sites (edge steps and defect sites) at the eVAMWCNT interfaces, similar to the previous observations for GC. Due to limitation in the increase of oxygen-containing groups at the eHOPG interfaces, two oxidation methods would not cause significant differences in the electrode responses for the redox reactions of copper species.