Potential Sweep Conditions Research Articles

Utilizing Toray Paper as a Metal‐Free, High Surface Area Electrode for Photosystem I–Driven Mediated Electron Transfer

One challenge in capitalizing on the affordability, sustainability, and accessibility of biohybrid solar energy conversion, including devices based on Photosystem I (PSI), is the identification of metal‐free electrode materials to replace the inorganic substrates commonly found in solar cell development. Herein, commercially available Toray carbon paper (CP) is investigated as a high surface area, carbon electrode for the development of photoactive bioelectrodes consisting of PSI and poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). Mediated anodic photocurrent is achieved at both PSI multilayer and PSI–polymer composite films on CP electrodes subjected to flame pretreatment. Film preparation is optimized by utilizing potential sweep voltammetry in place of potentiostatic conditions for polymerization. The optimized PSI–PEDOT:PSS films achieve a threefold increase in polymer growth under potential sweep conditions, quantified through net charge consumed during electropolymerization, resulting in a fourfold increase in photocurrent density (−53 vs −196 nA cm−2). The ability to prepare photoactive PSI‐polymer films on metal‐free CP electrodes opens the door to a rapidly scalable system for biohybrid energy production ultimately leading to more affordable, sustainable, and accessible energy.

Double Current Maxima Formed under Linear Potential Sweep Conditions in Acetic Acid Solutions at pH < 2.5

The kinetics of hydrogen evolution on a copper electrode in acetic acid solutions is studied by the method of linear potential sweep. At рН < 2.5, double current peaks are observed with the height directly proportional to both √v (v is the potential sweep rate) and the total concentration of proton donors and acceptors. Upon the transition from the copper electrode to the platinum electrode, the overpotential of this process considerably decreases, but the shape of current peaks remains unchanged. The analysis of kinetics of acetic acid dissociation points to the high degree of lability of this system, which allows the relationship between the surface concentrations of its components to be expressed through the corresponding equilibrium constants. At certain potentials, significant changes in the surface pH are observed, which favor the appearance of an additional current peak in the cathodic chronovoltammogram. The Tafel plots normalized with respect to the surface concentration of hydrogen ions allow the following values of kinetic parameters to be obtained: i0 ~ 0.3 nA/cm2 and αc = 0.75. Chronovoltamograms simulated with the use of these values demonstrate double maximums which adequately agree with experimental data.

Potentiodynamic behavior of as-grown and annealed porous anodic alumina films: Current overshoots and oscillations in transients

This work presents the results of investigation of the behavior of as-grown and annealed in air at 200 °C in phosphoric acid alumina films during the first and repeated polarizations in the barrier-type anodizing solution under potential sweep conditions. The current overshoots in transients in the annealed porous alumina films at the second potential sweep were found to be dependent on the magnitude of current, which was interrupted at the first sweep. Assumingly these overshoots were caused by an abrupt drop in the mobility of electrons injected from electrolyte in alumina film upon annealing. These experiments also revealed the current oscillations, following the current overshoot, in the voltammograms of repeated potential sweeps and the origin of this phenomenon was considered.

Electrocatalytic Oxidation of Formaldehyde on Platinum under Galvanostatic and Potential Sweep Conditions Studied by Time-Resolved Surface-Enhanced Infrared Spectroscopy

When formaldehyde is oxidized on a Pt electrode under galvanostatic (constant current) conditions, the electrode potential oscillates spontaneously. The oscillatory behavior has been examined by time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS) for understanding the mechanism and kinetics of the reaction at the molecular scale. SEIRAS reveals that CO and formate are adsorbed on the electrode surface and that their band intensities (coverages) oscillate synchronously with the oscillation of potential. SEIRAS coupled to cyclic voltammetry or linear sweep voltammetry suggests that formaldehyde is oxidized to CO2 via two parallel processes: the direct path via adsorbed formate and the indirect path via adsorbed CO. The two processes are kinetically coupled and autocatalytically activate and deactivate formaldehyde oxidation to yield the potential oscillations. The oxidation of the electrode surface also contributes to the oscillations for large applied currents.

Cathodic Processes in Cu(II) Solutions Containing Glycolic Acid

Voltammetric data for Cu|Cu(II), glycolic acid system, obtained at pH < 4 under potential sweep conditions, is analyzed within a theoretical model describing the mass transport of chemically interacting particles. Accounting for the distribution of the system's components at the electrode surface makes it possible to construct linear Tafel plots normalized to the surface concentration of Cu2+ ions, which are treated as electrically active aqua-complexes. The rate of Cu(II) reduction involving two consecutive reactions (Cu2+ + e → Cu+ and Cu+ + e → Cu) is controlled by the transfer of the first electron with kinetic parameters αc1 = 0.27 ± 0.01 and ks1 = (1.2 ± 0.2) × 10–3 cm/s. Another cathodic reaction is observed at higher cathodic polarizations. Well-defined current peaks located at ca. –0.9 V (SHE) increase with both H+ and ligand concentration. This process presumably results from the reduction of hydronium ions involving glycolic acid as a labile donor of protons.

Electrochemical study of LaNi3.55Mn0.4Al0.3Co0.75 by cavity microelectrode in 7 mol l−1 KOH solution

Abstract The electrochemical behavior of LaNi 3.55 Mn 0.4 Al 0.3 Co 0.75 material was investigated with the help of a cavity microelectrode. The cyclic voltammetry study versus the scan rate evidenced the formation of a passivation layer, which is characterized by a positive current during the cathodic sweep. The performances of the LaNi 3.55 Mn 0.4 Al 0.3 Co 0.75 compound as a negative electrode for nickel–metal hydride (Ni–MH) battery can also be determined with the cavity microelectrode. It was shown that even in drastic potential sweep conditions, the material exhibits a very good reversibility during several thousands of cycles.

Oscillatory Behavior during the Anodization of InP

Spontaneous oscillations in current have been observed during anodization of InP. Oscillations were observed under three significantly different sets of conditions, potential sweep, constant potential, and constant current, for InP in an aqueous (NH 4 ) 2 S electrolyte. Their frequency was found to increase with increasing anodic bias and values in the range of 0.1 to 1.25 Hz were recorded. Frequency was proportional to current density regardless of whether the measurements were carried out during a potential sweep or at constant potential. Thus, the charge passed per oscillation remained constant. A characteristic value of ∼0.3 C cm - 2 was measured under potential sweep conditions, and a similar value was obtained under constant potential conditions. More complex oscillatory behavior was observed under constant current conditions. The current in the oscillatory region corresponds to the continuous growth of a thick porous film on the electrode.

Analysis of stresses generated during hydrogen transport through a Pd foil electrode under potential sweep conditions

In the present work, the stresses generated during cyclic voltammetric measurements on a Pd foil electrode in 0.1 M NaOH solution have been analysed by using a laser beam deflection technique combined with cyclic voltammetry. From the linear relationship between the anodic peak current density and the scan rate on a logarithmic scale, it is recognised that the hydrogen concentration at the electrode surface is determined by the applied potential above the transition scan rate, whereas the change in the hydrogen concentration at the electrode surface with time is specified by the Butler–Volmer equation below the transition scan rate. The deflection transient measured simultaneously with the cyclic voltammogram shows that in the high scan rate range, the compressive deflection increases to a maximum value and then is completely relaxed. In the low scan rate range, however, the deflection transient is characterised by the occurrence of a maximum compressive deflection, a transition of compressive to tensile deflection, a maximum tensile deflection and finally a complete decay of the tensile deflection in sequence. From the hydrogen concentration profile transient simulated under the two constraints at the electrode surface, we simulated the deflection transients as a function of the scan rate. From the coincidence of the calculated deflection transient with that measured, the movement of the deflection in the compressive and tensile directions can be accounted for in terms of the difference in the molar volume of α-PdH δ across the whole electrode, developed during hydrogen diffusion.

Simulation of electrochemical behavior of partially blocked electrodes under linear potential sweep conditions

The paper presents nonlinear model which stands for effective digital simulation of electrochemical behavior of partially blocked electrodes under linear potential sweep and cyclic voltammetry conditions. The model is based on a system of diffusion equations, also involving the Nernst diffusion layer. The mass transport is assumed to be regular in the entire diffusion space. The influence of the thickness of the resist layer on the behavior of the partially blocked electrodes is investigated. The agreement between the theoretical results and experimental ones is obtained to be admirable for several model electrodes with different blocking degree.

Redox and electrocatalytic activity of copper in base at unusually low, premonolayer potentials

The assumption involved in this work is that the formation of monolayer (α) oxide species, which occurs on copper in base at 60 °C at ca. 0.5 V (RHE), is of little relevance to the electrocatalytic behaviour of the metal at low potentials. For many processes occurring at the interface in question the critical potential is ca. −0.1 V (RHE). This is the value where several electrocatalytic oxidation and reduction processes commence or terminate under potential sweep conditions; hydrous oxide films are reduced close to this value and it is possible to produce an active (but transient) state of the metal surface which exhibits a reversible redox response in this region. The results are rationalized in terms of the incipient hydrous oxide/adatom mediator model of electrocatalysis, and the nature of the active site material at the interface is discussed.

Sequential electrodeposition of silver and bismuth on a gold surface

AbstractSequential electrodeposition of Ag and Bi from a single electrolyte on Au (111) was studied by means of voltammetry and ion scattering spectroscopy (ISS). Silver was electrodeposited first under diffusion control. Subsequently, bismuth was deposited under potential sweep conditions. Underpotential deposition of BI on the gold surface modified with five Ag monolayers takes place similar to the deposition on the Ag (111) electrode. The deposited Bi can be electrodissolved completely with Ag remaining on the surface. However, the voltammetric characteristics of this process are different from the one in the case of Bi on the (111) surface of a silver single crystal. The ISS data suggest that this might be due to intermixing at the Ag/Bi interface occurring subsequent to the formation of the initial Bi on Ag structure on Au(111).

The electrocatalytic behaviour of palladium in acid and base

Anomalous oxidation of noble metals such as platinum is now an established feature of metal cluster/ oxygen gas reactions. The same type of process at polycrystalline metal electrodes in aqueous media is assumed to give rise to incipient hydrous oxide formation. This approach was used here to rationalize the electrocatalytic behaviour of palladium, with regard to both oxidations and reductions, in aqueous acid and base. The activity of palladium was not dramatically different to that of platinum, and the presence of an unusual peak at about 0.23 V vs RHE in the case of palladium in acid is rather similar in character to the so-called anomalous hydrogen peak previously described for platinum under similar conditions. For both metals (and a similar claim was made recently for gold) an adatom/incipient hydrous oxide transition is assumed to be involved, and it is interesting that the onset/termination potential for hydrazine oxidation under potential sweep conditions virtually coincided with the potential for this minor peak or transition.

A study of the electrocatalytic behaviour of gold in base using ac voltammetry

In-phase, faradaic ac responses were recorded for gold in base, under potential sweep conditions, at quite low potentials: the results support the view that premonolayer oxidation is a significant feature of this sytem. It was concluded that variations, with the degree of oxidation, of the activity of both the reduced and oxidized state of the low coverage interfacial couple caused major broadening of the reversible response for the adatom/incipient hydrous oxide transition in the double layer region of this system. A survey was carried out of a range of electrocatalytic processes, both oxidations and reductions, previously investigated by dc cyclic voltammetry. The observed ac responses support the view that incipient hydrous oxide species play an important role, both as mediators and inhibitors, in such reactions. In most cases the behaviour of gold in base is only explicable in terms of the premonolayer, hydrous oxide approach.

ChemInform Abstract: STM Observations of the Underpotential Deposition and Stripping of Pb on Au(111) Under Potential Sweep Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

STM Observations of the Underpotential Deposition and Stripping of Pb on Au(111) under Potential Sweep Conditions

We report the observation of electrochemical deposition and stripping of a monolayer of Pb on the surface of Au(111) using an in situ scanning tunneling microscope. Sequential STM scans taken during slow (1 mV/s) potential sweeps show that the Pb layer forms by initial growth at Au step edges followed by Pb island nucleation on Au terraces. When the potential sweep is reversed to remove the Pb monolayer, the surface is restored to a state similar to the original, but the details of the Au topography are modified.

Incipient Hydrous Oxide Species as Inhibitors of Reduction Processes at Noble Metal Electrode

Evidence is presented to illustrate the important role of hydrous oxide species in noble metal electrocatalysis. It was demonstrated, for instance, that in the case of gold in acid the onset/termination potential, under potential sweep conditions, for hydrazine oxidation and persulfate or iodate reduction occurred at the end of the hydrous oxide reduction peak (recorded for a thick film grown by potential multicycling); there was also a maximum in the faradaic ac response for gold in acid in the same region. Both gold and platinum were investigated in acid and base electrolytes. In some cases a range of potential, rather than a discrete value, was found to be involved, different species react with (or are inhibited by) different types (or coverages) of these submonolayer species. In some, possibly electrocatalytically nondemanding, reduction reactions the hydrous oxide seemed to have little effect.

A battery‐powered, microprocessor‐controlled, programmable function generator for field‐based stripping voltammetry with conventional and microsized electrodes

AbstractBattery‐powered, complementary metal oxide semiconductor (CMOS) devices have been used to develop a programmable function generator. When used in conjunction with commercially available, battery‐powered potentiostats or electrometers and recording devices, the technique of field‐based direct current stripping voltammetry becomes available. The instrumental performance of a range of modular, battery‐powered instruments has been evaluated with conventional and microsized electrodes and compared with ac‐powered laboratory instruments using conventionally sized electrodes. Stripping experiments with the field‐based instrument and with microelectrodes can be carried out under linear potential sweep conditions because the limit of detection is similar to that obtained with transient techniques at conventional sized electrodes. Other simplifications to the instrumentation and voltammetric procedures that are valuable in field‐based studies (e.g., neither stirring nor deoxygenation of the solutions is required) also are achieved by using microelectrodes and are illustrated by the determination of copper in a river water sample.

Electrochemical behaviour of oxygen-containing aliphatic compounds adsorbed on platinum in acid medium Part II. Primary alcohols

The electrochemical behaviour of chemisorbed species of propanol-1 in the absence of bulk reaction is studied. A reaction scheme is proposed for the modification and desorption processes observed in the hydrogen potential region. About 0.5 to 0.75 electrons per site are required for these processes. The oxidation of the unmodified chemisorbed propanol-1 (assumed to have the structure C 2 H 4 −x/xC−OH) is complete at 1.6 V under potential sweep conditions and requires about 2 e /site. Oxidation of at least, some the modified species begins at more negative potentials and it is assumed that they have the structure of adsorbed methanol. In the presence of propanol-1 in solution in the supporting electrolyte (0.5 M H 2 SO 4 ), the overall reaction rate in the double layer and in the oxygen region is not determined by the oxidation of the chemisorbed species.

Electrochemical behaviour of oxygen-containing aliphatic compounds adsorbed on platinum in acid medium: Part II. Primary alcohols

The electrochemical behaviour of chemisorbed species of propanol-1 in the absence of bulk reaction is studied. A reaction scheme is proposed for the modification and desorption processes observed in the hydrogen potential region. About 0.5 to 0.75 electrons per site are required for these processes. The oxidation of the unmodified chemisorbed propanol-1 (assumed to have the structure C 2H 4−x/xC−OH) is complete at 1.6 V under potential sweep conditions and requires about 2 e/site. Oxidation of at least, some the modified species begins at more negative potentials and it is assumed that they have the structure of adsorbed methanol. In the presence of propanol-1 in solution in the supporting electrolyte (0.5 M H 2SO 4), the overall reaction rate in the double layer and in the oxygen region is not determined by the oxidation of the chemisorbed species.

The Application of Linear Sweep Voltammetry to a Rotating Disk Electrode for the Reversible Deposition of an Insoluble Species

A Nernst diffusion model was employed to obtain an analytical expression for the transient current response of a reversible deposition reaction with insoluble product occurring on a rotating disk electrode under linear potential sweep conditions. The results indicated that for low sweep rates the current increases monotonically with time. However, at high sweep rates a maximum value for the current density at finite values of time is predicted. The peak current density normalized with respect to the diffusion limiting current density was found to be a linear function of the square root of a dimensionless sweep rate. Furthermore, in this region the response of a rotating disk electrode is the same as that in a stagnant system. An experimental investigation based on the reversible deposition of silver showed good agreement with the theoretical predictions.