Cathodic Sweep Research Articles

Discovery of cathodic nitrogen evolution

During cyclic voltammetry studies of the surface electrochemistry of the oxidation of azide ions to N2 at a Pt anode, a large reduction current peak is observed during the cathodic sweep; this is shown to be due to electrolytic reduction of N3– to N2 gas and aqueous NH3.

Adsorptive stripping voltammetry of Ni(II) using fast linear sweeps

Nickel was determined as bis-(dimethylglyoximato)-nickel(II) by fast cathodic linear sweep voltammetry with a rate of 10 V s−1 after adsorption on a static mercury electrode. The peak width at half-height was 60 mV. For determinations down to 1 ppb of Ni(II), only 40 s accumulation time were required without accelerating measures like stirring or potential application. Resolution and sensitivity were thus similar to differential pulse voltammetry but the duration of a measuring cycle was only 45 s (40 s accumulation, 80 ms for sweep and 5 s for readout). The method was tested with 2 industrial waste water samples and urine. The direct determination of Ni(II) in urine failed, whereas it was possible in the waste water. Concurrent adsorption was the main interference.

Ag electrode reaction in NaOH solution studied by in-situ Raman spectroscopy

Ag electrode reaction in NaOH solution has been studied by in-situ measurement of surface enhanced Raman scattering. The Raman spectrum is measured while the electrode potential is swept. During and after the reduction process of oxide layers grown on the electrode surface, we observe Raman lines due to atomic oxygen and hydroxyl species adsorbed on the Ag surface. Atomically adsorbed oxygen which gives a vibrational frequency of 330 cm−1 exists in a limited potential range of the electrochemical reduction process. Two lines are observed at 470 and 860 cm−1 in a wider electrode potential range. These lines are due to the AgO stretching vibration (470 cm−1) and the AgOH bending vibration (860 cm−1) of the adsorbed hydroxyl species. The oxygen atoms migrate through the oxide and Ag film facing the electrolyte and then they become adsorbed on the rough Ag film which grows on the electrode surface during the reduction process. The oxygen atom in this adsorption state is rather unstable and it turns to hydroxyl species. These Raman lines are observed also in the anodic sweep, but the intensities are weaker than in the case of the cathodic sweep. Three additional lines appear at 500, 700 and 1615 cm−1 for an electrode potential more negative than −0.8 V (versus SCE). They are observed even in the potential range for hydrogen evolution. These Raman lines are assigned as vibrations of interfacial water molecules sandwiched between the electrode and Na+ ions located in the outer Helmholtz plane. Photoelectrochemical oxidation of Ag2O grown on the electrode surface to AgO occurs if the thickness of Ag2O exceeds a couple of monolayers.

Cathodic reduction of the anodically formed zinc species as a contribution to the study of the potentiodynamic passivation of zinc in alkaline media

The cathodic part of the potentiodynamic curves obtained for upward-facing horizontal 99.9% zinc electrodes in KOH solutions 0.4, 1.0, 2.0 and 3.0 M and sweep rates in the range 1–100 mV s −1 have been systematically analyzed in order to assign the possible species formed and contribute to the study of the potentiodynamic passivation of Zn in alkaline media. The anodic limit of the potentiodynamic cycles was changed and set for significant points of the total curve (between hydrogen and oxygen evolution). Also, the anodic sweep was interrupted at the potentials corresponding to the anodic limit and the cathodic sweep applied immediately from a potential near that of zero current of the cathodic half-cycle. Only two cathodic peaks have been found for the non-interrupted cycles. The assignation of peaks according to the equilibrium potentials of the reduction of the possible species implied, ie Zn(OH) 2− 4, Zn(OH) 2 and ZnO, is not possible because local pH changes are expected and the zincate concentration near the electrode is unknown. The peak placed at more positive potentials for KOH concentrations 0.4 and 1.0 M is assigned to zincate and that at more negative potentials, to the reduction of the film. Just the opposite assignation has been found for 2.0 and 3.0 M KOH solutions. The experimental results can be interpreted assuming that the product formed at the passivation potential consists of the same chemical species as those corresponding to the first anodic peak, probably Zn(OH) 2 or hydrated ZnO. From calculating the maximum film thickness according to the charge passed and taking into account the recent theoretical analysis made by Chang and Prentice, it is concluded that the direct formation of ZnO on the electrode at the passivation potential as a consequence of local pH changes is not probable.

Analytical methods for the direct determination of inorganic and organic species: Seasonal changes of iron, sulfur, and pedogenic and aquogenic organic constituents in the eurotrophic Lake Bret, Switzerland

The behavior of elements and organic compounds is determined by the properties of their chemical forms. Analytical methods are needed that provide information not only about total concentrations of elements and organic compounds but also about the identities and concentrations of their species. Approaches for the determination of species distributions are outlined. A combination of methods (differential pulse polarography, colorimetry, flame atomic absorption spectrometry, absorbance measurements, fluorescence measurements, cathodic sweep voltammetry, filtration; calculations based on formation, equilibrium, and solubility product constants) was used to identify iron and sulfur species and natural organic matter in the water of Lake Bret, Switzerland. Hydrated Fe 2+, labile Fe(II) species, colloidal Fe(II), particulate Fe(II) and Fe(III), H 2S, HS −, labile S(−II), colloidal S(−II), particulate S(−II), and dissolved and particulate elemental sulfur were identified. The species distribution in the anoxic zone of the lake changed with the seasons. Whereas Fe 2+, H 2S and HS − were the predominant species on 6 August, 1981, colloidal Fe(II) and colloidal S(−II) accounted for most of the iron and sulfur 6 weeks later. Absorbance and fluorescence measurements, responding to largely aromatic pedogenic refractory organic material, indicated that pedogenic material brought into the lake by the River Grenet is not the major source of organic material in the sediments of Lake Bret.

Determination of Humic Substances in Seawater by Electrochemistry (Mechanisms)

Abstract A new method for the measurement of the concentration of humic substances (HS) in seawater is described. The peak obtained by differential cathodic sweep voltammetry after HS adsorption in the presence of traces of molybdenum(VI) can be used for quantitative determination. Measurements using various electrochemical techniques (ACP, CV, ADPV, DPP) would indicate that the film adsorbed onto the electrode is the result of the adsorption of the organic substance in a first step followed in a subsequent step by the formation of a surface complex (Mo(VI)-HS)ads rather than the direct adsorption of the dissolved complex. The electrochemical mechanism corresponds to a one-electron reduction of the adsorbed (Mo(VI)-HS)ads complex to the corresponding (Mo(V)-HS)ads complex.

A surface-enhanced Raman study of the electrochemical reduction of 4-cyanopyridine

The adsorption and electroreduction of 4-cyanopyridine (4CP) on a silver electrode were studied by surface-enhanced Raman (SER) spectroscopy. The SER spectra indicate that the adsorbed 4CP takes end-on orientation on a silver electrode through the nitrogen atom in the pyridine ring. The softening and the cleavage of the C-C bond between the pyridine and the nitrile during the cathodic sweep were observed and discussed.

Reactivite electrochimique de quelques oxydes de vanadium en milieu HCl 1 M

The voltammograms recorded for the oxides V 2O 5, NaVO 3, VOSO 4, NaVO 2 and V 2O 3, when incorporated in carbon paste electrodes with conducting binder, show that the electronic transfer occurs between the electrode and the soluble species. The V(V)/V(IV) and V(III)/V(II) systems are reversible and the electrochemical reactions give anodic and cathodic peaks with quite identical potentials, close to that of the standard potential of these systems. The V(IV)/V(III) couple is irreversible and the reduction, shifted towards negative potentials, coalesces with the V(III) to V(II) reduction process. For the oxides containing V(V), the reduction to V(IV) leads to two peaks: the first one is reversible and due to the reduction of the species coming from the instantaneous dissolution of the finest particles, the second one is irreversible and due to the progressive dissolution of the largest particles occuring during the cathodic sweep.

Anodic Degradation of Beta″‐Alumina in Contact with Mercury

The anodic degradation of β/β″‐alumina of different compositions was studied in cells of the type at 350°C. Single voltage sweeps were applied from the open‐circuit voltage to different voltages of reversal at relatively low sweep rates (mainly 0.1–1 mV/s). The current‐voltage curves display an initial rise of current with voltage between about 2.8 and 3.5V, vs. a Na reference electrode, followed by a small change of the current at voltages to 4.0V. The anodic current is attributed to the formation of at the interface Hg/solid electrolyte. The oxygen is supplied by the anodic degradation of the ceramic. The oxide is decomposed at a slow rate during the cathodic sweep. Structural studies were carried out by light microscopy, x‐ray diffraction, and analytical electron microscopy at the end of the electrochemical runs. These investigations supplied confirming evidence for the chosen predominant reaction and yielded additional information on how the degradation proceeds from a structural point of view.

Impurity effects on the macromorphology of electrodeposited zinc III: Potential sweep analysis

The potential sweep method has been employed to analyse the impurity effects in zinc electrodeposition from solutions of its chloride. It has been pointed out that the peak for zinc deposition from its binary systems disappears because of mutual codeposition with hydrogen and continuous exchange of the reaction rates during the cathodic sweep. It has also been pointed out that a black “burned” zinc deposit always appears at electrode reaction rates higher than the limiting current for zinc electrogrowth in intense hydrogen evolution. The distinction between the spongy and burned zinc has also been made: the former is an autocatalytic mass-transfer process promoted by some impurities, while the latter represents the kinetic effects of the local current density, both being electrocatalytic for the hydrogen evolution reaction. Finally, it has been pointed out that the individual deposition peak for more positive metals disappears whenever intermetallic phase formation occurs and that it naturally leads to underpotential deposition.

Molecular precursors to the formation of hydrogen and the reduction of oxygen at a silver cathode: a surface-enhanced Raman scattering experiment

Surface-enhanced Raman scattering (SERS) has been used to probe the formation of several precursor adsorbates on a Ag cathode prior to and during the generation of gaseous H/sub 2/. The chemical reactions occurring during a cathodic voltage sweep correspond to the sequential protonation of (Ag,Mn)O: (Ag,Mn)O ..-->.. (Ag,Mn)OH ..-->.. (Ag,Mn)HO-H-OH(Ag,Mn), where (Ag,Mn)O denotes a mixed metal oxide. The equilibrium concentration of each species is determined by the interfacial pH which in turn is dependent upon the cathode voltage relative to a saturated calomel electrode, V/sub SCE/. As V/sub SCE/ becomes more negative, the interfacial pH decreases because of electrostatic attraction, and the amount of protonation increases. From a logical extension of this protonation model, the formation of the dioxonium complex, (Ag,Mn)HO-H-OH(Ag,Mn), is postulated from an analysis of the SERS spectra of the adsorbates observed at the onset of H/sub 2/ gas generation. The addition of O/sub 2/ gas to the electrolyte solution has the remarkable effect of reversing the protonation reaction sequence. This occurs because the reduction of O/sub 2/ at the electrode, 4e + O/sub 2/ + 2H/sub 2/O = 4OH/sup -/, effectively increases the interfacial pH which, in turn, shifts the equilibrium to the formation of (Ag,Mn)O. Themore » replacement of 5% of the H/sub 2/O with D/sub 2/O demonstrates that proton exchange is more rapid for the bridge hydrogen than for the terminal hydrogen in (Ag,Mn)HO-H-OH(Ag,Mn).« less

Voltammetry of Sodium Polysulfides at Metal Electrodes

The interaction of sodium polysulfides and candidate metals for the current collector and cell casing in sodium/sulfur cells at 300° and 350°C is explored using cyclic voltammetry. The metals investigated are chromium and molybdenum, and data for voltammetric sweeps at rates of 10–500 mV/s in are reported. The results are compared with those of previous experiments conducted at carbon and platinum electrodes, and mechanisms are proposed to explain the data in terms of specific melt‐metal interactions. A model describing the observed cathodic sweep data is presented.

A cyclic-voltammetric study of glucose oxidation on a gold electrode

An electrochemically formed gold oxide layer on the surface of a gold electrode was found to be a powerful and rather selective catalyst of glucose oxidation. Cyclic-voltammetric techniques were used to investigate the performance of the gold electrode in the presence of glucose at different concentrations up to 500 mg/100 cm 3 (28 m M). A positive current peak due to the presence of glucose occurred during the cathodic sweep. The current values at these maxima showed a highly linear dependence on the concentration of glucose in several regions, depending on the medium composition. Chlorides, amino acids, and human albumin were observed to inhibit the reaction. On the other hand, urea and L-ascorbic acid contributed a stabilizing effect to the performance of the electrode. At 34 mg/100 cm 3 (5.7 m M), urea did not affect the current, whereas ascorbic acid somewhat increased the output. The results of this study suggest that the layer of gold oxide on the gold electrode can be utilized for the detection of glucose, if a proper separation of the inhibitors is achieved.

Use of open-circuit pre-concentration of sulphide ion in stripping voltammetry at the parts per billion level of sample

A procedure based on open-circuit pre-concentration using a silver disc electrode was developed. This procedure allows sulphide to be pre-concentrated at concentrations ranging from 0 to 40 p.p.b., with subsequent stripping through a linear cathodic potential sweep. The procedure is precise and reliable, with a similar sensitivity to and a better selectivity than those of conventional cathodic-stripping voltammetry. The procedure is useful for monitoring parts per billion levels of sulphide in tap water samples with a precision of 2%.

The electrochemistry of [PtH(PEt3)3]+; inverted and amplified cyclic voltammetric waves and catalytic hydrogen production at a mercury electrode

Inverted and amplified waves in cyclic voltammograms of [PtH(PEt3)3]+ at a sitting mercury drop electrode are interpreted in terms of catalytic cycles for hydrogen production from water involving adsorbed species. The adsorption step on the cathodic sweep involves a two-electron reduction to the catalytically inactive species [PtH(PEt3)3]–(ads.). On the reverse (anodic) sweep, a reductive catalytic cycle is initiated by oxidation to [PtH(PEt3)3]˙(ads.) and stops when the potential is insufficiently negative to reduce [Pt(PEt3)3]˙+(ads.){or [PtH2(PEt3)3]˙+(ads.)}. In second and subsequent forward scans the catalytic cycle restarts when the potential is sufficiently reducing to reduce [Pt(PEt3)3]˙+(ads.) or [PtH2(PEt3)3]˙+(ads.) and terminates when [PtH(PEt3)3]˙(ads.) is reduced to [PtH (PEt3)3]–(ads.). Variations in peak shape and position with [PtH(PEt3)3]+(aq.) concentration are interpreted in terms of partial or full desorption of [Pt(PEt3)3](ads.) or [PtH(PEt3)3]˙(ads.) during the catalytic cyclic under certain conditions. Catalysis of hydrogen production at a mercury drop electrode with catalyst turnover numbers up to 2 × 105 h–1 for > 16 h is also described.

導電性固体材料とガラス融液との反応に関する研究 Ｖ 金属とケイ酸塩ガラス融液との分極下における反応について Ｗ，Ｃｒ，Ｆｅ，ＳＵＳ３０４およびＩｎｃｏｎｅｌ ６００

In the previous paper, the electrochemical phenomena of Ni and Mo in a molten silicate glass of the composition 16 Na2O·12 CaO·72 SiO2 in wt% were investigated. In this paper, W, Cr, Fe, SUS 304 and Inconel 600 were chosen as the objects to be measured. Anodic dissolution, passivation and cathodic deposition for these metals were investigated by linear potential sweep voltammetry at various potential sweep rates (5-0.05V/sec) with platinum reference and auxiliary electrodes in Ar gas atmosphere or in air. Moreover, the metal-glass interface after polarization was analysed by EPMA.On cathodic potential sweep of every metal investigated here, silicate anions were easily reduced to silicon element and a kind of silicide layer covered the electrode surface. Since the silicide has high electrical resistance, its formation made the measurement of voltammogram difficult at slower sweep rates.The anodic voltammogram of W at 3V/sec showed a large current peak around 1.7V (relative to Pt reference). The peak potential shifted to more cathodic direction with decreasing sweep rate. The current peak was attributed to the formation of a passsive layer on the W electrode. The occurrence of tungsten oxide layer with 30μm thick on the W electrode was confirmed by EPMA. The oxide layer seemed to be made up by WO3. The broad current peak was observed on anodic voltammogram of Cr due to the formation of chromium oxide Cr2O3. There was no peak on the anodic current-potential curve for the Fe electrode and Fe dissolved rapidly and easily. Both SUS 304 and Inconel 600 were subject to passivation by oxide film formation of Cr2O3 and NiO on anodic polarization.

Hydrous oxide formation on gold in base under potential cycling conditions

The formation of hydrous oxide films on gold in base under potential cycling conditions was investigated and found to be less inhibited than the same type of reaction observed when gold is strongly anodized at high potentials under d.c. conditions at high pH. The overall behaviour on cycling is quite similar to that observed with other metals, e.g. platinum. The importance of the lower limit, for instance, again appears to be related to the need under film thickening conditions to significantly reduce the compact oxide layer formed on the metal surface during the anodic sweep. It was noted that the earlier duplex model for this type of system, i.e. an inner compact and an outer dispersed oxide layer, is not always valid. Under certain conditions about six distinct peaks (suggesting six different states of gold oxide hydration, dispersion or polymerization) were observed in cathodic sweeps recorded for the reduction of thick films grown on gold under potential cycling conditions in base.

Esca study of the state of iridium and oxygen in electrochemically and thermally formed iridium oxide films

X-ray photoelectron spectroscopic measurements on the state of Ir and O species in electrochemically and thermally formed iridium oxide films are reported. The electrochemically formed films were grown to three thicknesses by means of potential cycling. The monolayer oxide film which exhibits electrochemical irreversibility in its formation and reduction already causes a change of electronic state of the Ir substrate surface atoms corresponding to formation of an Ir(OH) 4 species. However, if any electrochemically reversible, thick film oxide, 100×a monolayer is formed, it behaves like bulk IrO 2 powder with regard to 4 f electron shell binding energies. The state of O (1 s ) is also different in this material from that in thinner oxide films, and contains clearly distinguishalbe ionic O 2− rather than OH − , bound water, or adsorbed O 2 , although the latter type of species is also present. Appreciable SO 4 2− ion incorporation or irreversible adsorption can also be detected. No difference in the oxidation state of Ir can be detected on (i.e., over ∼1.5 nm) an oxide film that has been produced electrochemically in its oxidized state or in its reduced state at the end of an anodic or cathodic sweep, respectively, prior to introduction into the electron spectrometer. This is probably due to rapid aerial oxidation of the reduced state of the oxide surface region during the process of transfer of the sample to the spectrometer in ex situ experiments. The electronic characteristics of Ir and O in a thermally formed oxide film are found to be identical with those in the electrochemically formed film only when the latter is thick but are also almost identical with those of Ir and O in chemically prepared IrO 2 powder.

ESCA study of the state of iridium and oxygen in electrochemically and thermally formed iridium oxide films

X-ray photoelectron spectroscopic measurements on the state of Ir and O species in electrochemically and thermally formed iridium oxide films are reported. The electrochemically formed films were grown to three thicknesses by means of potential cycling. The monolayer oxide film which exhibits electrochemical irreversibility in its formation and reduction already causes a change of electronic state of the Ir substrate surface atoms corresponding to formation of an Ir(OH) 4 species. However, if any electrochemically reversible, thick film oxide, 100×a monolayer is formed, it behaves like bulk IrO 2 powder with regard to 4 f electron shell binding energies. The state of O (1 s) is also different in this material from that in thinner oxide films, and contains clearly distinguishalbe ionic O 2− rather than OH −, bound water, or adsorbed O 2, although the latter type of species is also present. Appreciable SO 4 2− ion incorporation or irreversible adsorption can also be detected. No difference in the oxidation state of Ir can be detected on (i.e., over ∼1.5 nm) an oxide film that has been produced electrochemically in its oxidized state or in its reduced state at the end of an anodic or cathodic sweep, respectively, prior to introduction into the electron spectrometer. This is probably due to rapid aerial oxidation of the reduced state of the oxide surface region during the process of transfer of the sample to the spectrometer in ex situ experiments. The electronic characteristics of Ir and O in a thermally formed oxide film are found to be identical with those in the electrochemically formed film only when the latter is thick but are also almost identical with those of Ir and O in chemically prepared IrO 2 powder.

Some observations on the effects of temperature and illumination on the anodic passivation of lead in sulphuric acid

The influence of temperature (−20 to 32.5°C) and illumination on the electrochemical oxidation of lead in 30% aqueous sulphuric acid solution are presented. Measurements of the anodic passivation currents and cathodic linear sweep voltammograms have been analyzed. The passive layer, consisting of photosensitive lead monoxide, appears to be formed by a mechanism of diffusion of oxygen vacancies through the PbO with an apparent activation energy of about 75 kJ mol −1. The photoresponse of the passive layer is shown to be temperature dependent.