Current-time Transients Research Articles

A Current Averaging Strategy for Maximizing Analyte and Minimizing Redox Interference Signals with Square Wave Voltammetry.

Square wave voltammetry (SWV) is commonly used in electroanalytical applications to enhance analyte faradaic signals and minimize nonfaradaic processes. However, little attention is given as to how best use SWV to minimize faradaic interference signals that arise from redox species present in solution that have redox potentials that convolute with that of the analyte. In conventional SWV, a series of current-time (i-t) transients are collected, and i is averaged over a specified window of each transient (potentiostat dependent). This average i is reported against the electrode potential, E. As the i-t response is governed by the type of electron transfer reaction under investigation, we show how by collecting all i-t data and through judicious choice of the current averaging window, it is possible to enhance the analyte response while at the same time reducing the interferent signal. We look at three different electron transfer reactions, fast electron transfer outer sphere, metal electrodeposition/stripping, and surface-confined proton-coupled electron transfer (PCET) and demonstrate different i-t behaviors in SWV, visually aided by the use of 3D i-t-E plots. In the case of PCET quinone-based voltammetric sensing of pH in the presence of a heavy metal (here Cu2+), we show that the use of a much earlier current averaging window (2-10% of the i-t response) results in the pH signal being clearly distinguished from that of the overlapping heavy metal.

Effect of Sulfide Addition on the Corrosion Mechanism of Copper in Saline Groundwater Solution

The interaction of copper with sulfide-containing simulated saline groundwater is studied by electrochemical techniques (voltammetry, current-time transients, and electrochemical impedance spectroscopy, EIS) complemented with surface and cross-sectional microscopic observations and energy dispersive spectroscopic analyses. Both experimental findings and quantitative interpretation of EIS data using previously published kinetic models indicate that no continuous adherent barrier-type layer is formed on Cu in sulfide-containing groundwater, thus precluding the possibility of the development of localized corrosion modes.

Nucleation and growth mechanisms in the electrochemical synthesis of Ag/polyaniline nanocomposites

Nucleation and growth mechanisms in the synthesis of polyaniline nanowires (PANI NWs) and of silver nanoparticles (AgNPs) which are assembly to PANI NWs, are proposed. Aniline polymerization proceeds over a graphite electrode at potentials that go from 0.9 V to 1.15 V (vs Ag/AgCl), using: 0.25, 0.15, or 0.05 M of aniline in HNO3 solution. In the polyaniline nucleation and growth is postulated a diffusional 3D model that involves the dendrites formation and the unidirectional growing step. At lowest aniline concentration, the transients displayed the typical peaked shape, characteristic of a 3D nucleation and diffusion-controlled growth. Silver nanoparticles are synthesized on the polyaniline/graphite substrate. Current-time transients at −0.1 V and −0.2 V (vs Ag/AgCl), displayed a decreasing in the current which is fit to Cotrell modified diffusion-limited aggregation model. Nanowires and nanoparticles morphology observed by SEM corroborated the proposed mechanisms.

Effect of hydrogen on electrochemical behavior of additively manufactured 316L in pressurized water reactor primary water

The electrochemical behavior of laser powder bed fusion (LPBF) 316 L stainless steel subject to different heat-treatments (solution annealing and hot isostatic pressing) is compared to nuclear-grade wrought 316 L in pressurized water reactor primary water at 288 °C (with and without dissolved hydrogen) using current-time transients, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Analysis of spectra by the Mixed-Conduction Model revealed slower corrosion rates of LPBF 316 L than wrought 316 L, the effect being more pronounced in the presence of dissolved hydrogen. The characteristics of the barrier layer and the oxide film/coolant interface were irreversibly altered upon removal of dissolved hydrogen.

Nucleation and Growth of Cu2O: Role of Potential, Electrolyte pH, and Substrate

The nucleation and growth mechanism of functional oxides has a direct bearing on the structural and electronic properties of the deposit. We study the effect of electrolyte pH and deposition potential on the nucleation and growth of Cu2O on polycrystalline metal oxide (FTO) & metal (Au) substrates. Modelling of the recorded current-time transients indicates that both instantaneous and progressive nucleation occur with growth limited by diffusion or lattice incorporation of electro-active species or both. The preferred orientation of Cu2O shows a strong dependence on electrolyte pH. The films are (100) oriented on both substrates at pH 9 except at high applied potential on FTO where the orientation changes to (111). Interestingly, irrelevant of electrolyte pH, the grain size of Cu2O decreases with potential on FTO whereas it increases on Au substrates. We attribute this to a difference in the number of active nucleation sites between the two substrates. The nucleation and growth at pH 12 is observed to be dependent both on diffusion and lattice incorporation of electro-active species. Additionally, the films are primarily (111) oriented on both substrates, which is correlated to the availability of OH− ions.

Ammonia sensing characteristics of an ITO-V2O5 based chemoresistive dual-type gas sensors (CDGS) decorated with platinum nanoparticles

A new chemoresistive dual-type gas sensors (CDGS) has been produced and reported. The studied CDGS contains an indium tin oxide (ITO) thin layer, a vanadium (V2O5) thin layer, and platinum (Pt) nanoparticles (NPs) on a chip. The n- and p-type ammonia (NH3) sensing behaviors of the studied Pt NP/ ITO-V2O5 CDGS were systematically investigated. Initially, a high-resolution scanning electron microscopy (HRSEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were employed to investigate the intrinsic properties. In experiments, significantly different current-voltage (I-V) curves of Pt NP/ ITO (Sensor A) and Pt NP/ V2O5 (Sensor B) were obtained in NH3-contained ambiences. The sensing response SR values for Sensors A and B are 7.54 and 1.14, respectively, under 1000 ppm NH3/air gas at 275°C. The various transient current-time (I-t) curves, under 1, 10, 100, and 1000 ppm NH3 /air gas at 275°C, for Sensors A and B were clearly observed. Moreover, both Sensors A and B demonstrated good selectivity toward NH3 gas. Thus, the presented Pt NP/ ITO-V2O5 CDGS provides the prominent potentiality and flexibility for NH3 gas detecting application.

Effect of sulfide on de-passivation and re-passivation of copper in borate buffer solution

The interaction of copper with sulfide-containing borate buffer solution either via direct immersion or by de-passivation following oxide film formation, is studied by electrochemical techniques (voltammetry, current-time transients and electrochemical impedance spectroscopy, EIS) complemented with surface and cross-sectional microscopic observations and energy dispersive spectroscopic analyses. Both experimental findings and quantitative interpretation of EIS data using newly developed and previously published kinetic models indicate that no continuous adherent barrier-type layer is formed on Cu in sulfide solutions, thus precluding the possibility of the development of localized corrosion modes.

Facile synthesis of NiSe2:α-Fe2O3 thin film: Physical, optical and photoelectronic properties

In this study, a highly scalable approach to fabricating NiSe2:α-Fe2O3 heterojunction thin film in the absence of a dehydration step or lattice parameter matching was established. The attachment of NiSe2 to α-Fe2O3 leads to an 82% and 97% decrease in charge transfer resistance (with and without illumination respectively) compared to pristine α-Fe2O3. The magnitude of the open circuit potential increased from approximately -0.30 V to -0.42 V vs Ag/AgCl, providing a stronger electric field for charge carrier separation. Charge transfer efficiency was calculated by using a ratio of charge carriers removed and those produced in the bulk. Scanning electron microscopy coupled with the electrodeposition current-time transients study proved that the attachment process involved the progressive nucleation of NiSe2 and the simultaneous cathodic reduction of α-Fe2O3.

Toward Precision Deposition of Conductive Charge-Transfer Complex Crystals Using Nanoelectrochemistry.

The lack of understanding for precise synthesis and assembly of nano-entities remains a major challenge for nanofabrication. Electrocrystallization of a charge-transfer complex (CTC), tetrathiafulvalene bromide (TTF)Br, is studied on micro/nanoelectrodes for precision deposition of functional materials. The study reveals new insights into the entire CTC electrocrystallization process from the initial nanocluster nucleation to the final elongated crystals with hollow ends grown from the working electrode to the neighboring receiving electrode. On microelectrodes, the number of nucleation sites is reduced to one by lowering the applied overpotential or precursor concentration. Certain current-time transients exhibit significant induction periods prior to stable nucleus growth. The induction regime contains small fluctuating current spikes consistent with stochastic formation of precritical nanoclusters with lifetimes of 0.1-30s and sizes of 20-160nm. Electrochemical analyses further reveal rate, size distribution, and formation/dissipation dynamics of the nanoclusters. Crystal growth of (TTF)Br is further studied on triangular nanoelectrode patterns with thickness of 5-500nm, which shows a mass-transfer-controlled process applicable for precision deposition of functional (TTF)Br crystals. This study, for the first time, establishes CTC nanoelectrochemistry as a platform technology for precise deposition of conductive crystal assemblies spanning the source and drain electrode for sensing applications.

Electrodeposition of Tin-Reduced Graphene Oxide Composite from Deep Eutectic Solvents Based on Choline Chloride and Ethylene Glycol

Some experimental results regarding the direct electrodeposition of tin-reduced graphene oxide composite (Sn-rGO) compared to the electrodeposition of tin metal (Sn) from a deep eutectic solvent (DES), namely using choline chloride-ethylene glycol eutectic mixtures, are presented. Raman spectroscopy demonstrated that GO is also reduced during the tin electrodeposition. Scanning electron microscopy (SEM) confirmed the presence of incorporated graphene related material in the composite film. X-ray diffraction patterns showed that the presence of rGO in the deposit diminished preferred orientation of Sn growth along the planes (101), (211), (301), and (112). The analysis of current-time transients involving Scharifker & Hills model has shown that Sn-rGO composite deposition process corresponds to a nucleation and tridimensional growth controlled by diffusion, with nucleation evolving from progressive to instantaneous upon increasing the overpotential. Diffusion coefficients at 25 °C of 9.4 × 10−7 cm2 s−1 for Sn(II) species in the absence and of 14.1 × 10−7 cm2 s−1 in the presence of GO, were determined. The corrosion performance has been assessed through the analysis of the recorded potentiodynamic polarization curves and of the electrochemical impedance spectra during continuous immersion in aerated 0.5 M NaCl aqueous solution at 25 °C for 144 h. A slight improvement of the corrosion performance in the case of the Sn-rGO composite coatings was noticed, as compared to pure Sn ones. Furthermore, the solderability performance has been evaluated. The solder joints showed a proper adhesion to the substrate with no fractures, and wetting angles around 44° have been determined, suggesting adequate solderability characteristics.

Influence of natural convection on the electrodeposition of copper nanowires in anodic aluminium oxide templates

Templated electrodeposition is a versatile method for preparing metal nanostructures. Among the various parameters of this process, the effect of convection on the deposition process is less explored. The present work is devoted to the experimental and theoretical study of the influence of natural convection near nanoporous anodic aluminium oxide templates on the deposition of nanowires. Electrochemical deposition of copper nanowires was carried out with vertical templates parallel to the gravitational acceleration at various overpotentials. A model of nanowire electrodeposition was developed based on the Navier‒Stokes and diffusion equations. The length profiles of the nanowires, experimentally measured using scanning electron microscopy, were compared with the results of the numerical simulation. The simulation results were also compared with current-time transients recorded during metal electrodeposition into nanopores. In addition, an analytical expression has been proposed to describe the evolution of the deposition current density into nanopores under natural convection conditions.

Effect of Electrosynthesis Potential on Nucleation, Growth, Adhesion, and Electronic Properties of Polypyrrole Thin Films on Fluorine-Doped Tin Oxide (FTO).

Polypyrrole (PPy) is one of the most attractive conducting polymers for thin film applications due to its good electrical conductivity, stability, optical properties, and biocompatibility. Among the technologies in which PPy has gained prominence are optoelectronics and solar energy conversion, where transparent electrodes such as fluorine-doped tin oxide (FTO) or indium tin oxide (ITO) are frequently used. However, FTO substrates have the notable advantage that their components are widely available in nature, unlike those of ITO. Recognizing the importance that the FTO/polypyrrole system has gained in various applications, here, we studied for the first time the nucleation and growth mechanism of electro-synthesized PPy on FTO. Additionally, the effect of the synthesis potential (0.9, 1.0, 1.1, and 1.2 V vs. Ag/AgCl) on the homogeneity, adhesion, conductivity, and HOMO energy levels of PPy films was determined. From current–time transients and scanning electron microscopy, it was found that films synthesized at 0.9 and 1.0 V exhibit 3D growth with progressive nucleation (as well as lower homogeneity and higher adhesion to FTO). In contrast, films synthesized at 1.1 and 1.2 V follow 2D growth with instantaneous nucleation. It was also evident that increasing the polymerization potential leads to polymers with lower conductivity and more negative HOMO levels (versus vacuum). These findings are relevant to encourage the use of electro-synthesized PPy in thin film applications that require a high control of material properties.

Effect of an external magnetic field orthogonal to the electrode surface on the electrocrystallization mechanism of Co-Fe films under pulsed applied potential

Co100−xFex (x = 0; 50; 30; 20) films are prepared by pulse-reverse plating onto Cu foils, in the presence of a magnetic field of 100 mT applied orthogonally to the substrate surface (B100) and in the condition B ~ 0 (B0). Energy-dispersive X-ray spectroscopy studies indicate that the Fe/Co ratios in the films are similar to those in the feed solution. The electrochemical nucleation and growth of Co and Co-Fe films are analyzed for individual, consecutive cathodic pulses, and also considering them as a continuous transient to achieve a steady stationary state. Current-time transient are analyzed applying the generalized Scharifker-Mostany model, assuming that parameters take effective values, describing the non-single-ion diffusion involved. All Co and Co-Fe films exhibit a 3D nucleation regime and diffusion-controlled growth. Films of pure cobalt prepared at B0 exhibit progressive nucleation (3DP) while bimetallic ones an instantaneous regime (3DI) predominates. Current-time transients obtained at B100 undergo changes from 3DI nucleation, for pure Co, turning more progressive 3DP regime for bimetallic, as the iron content increases. Film morphology and microstructure largely depend on Fe/Co composition and the applied magnetic field. For low iron content, films are granular and change to dendritic-like when iron content increases. Besides, for Co70Fe30 and Co50Fe50 compositions, nanowall-like structures at the surface change into whisker-like prisms when the magnetic field is applied. Iron containing films are thinner when deposited at B100 for all compositions. The key factors explaining the influence of the magnetic field and composition on the film deposition mechanisms and microstructure are: micro-magneto-hydrodynamic convection nearby the interface, the H2 desorption and the competence/interplay of Co(II) and Fe(II) ions during the alloy nucleation and growth.

Pitting corrosion behavior of SS-316L in simulated body fluid and electrochemically assisted deposition of hydroxyapatite coating

The pitting corrosion of SS-316L in human body fluid leads the metallic prosthesis to lose its strength along with severe health consequences such as metallosis condition. Hence, an effective alternative for enhancing the biocompatibility of the SS-316L implant is the electrochemical deposition of a bioinert hydroxyapatite (HAP) coating over the metallic surface. A dense HAP coating was successfully developed on SS-316 L in a supersaturated electrolyte containing Ca+2 and PO43− ions. Electrochemical essays and SEM morphological observation showed the SS-316 L pitting corrosion caused by chloride containing body fluid. The effects of the electrodeposition time and the temperature of the supersaturated electrolyte were assessed using current–time transients, scanning electron microscopy, Energy-dispersive X-ray spectroscopy, Raman and X-ray diffraction analyses. The increase in the temperature promotes the HAP coating formation and accelerates the particles nucleation. An instantaneous HAP growth with no evidence for intermediate phase of HAP formation has been noticed.

Electrodeposition from a Graphene Bath: A Sustainable Copper Composite Alloy in a Graphene Matrix

The leaching effect of metals has led to the introduction of government regulations for the safety of the environment and humans. This has led to the search for new alloys with long-lasting sustainability. Herein, we wish to report a new brass alloy containing carbon with a remarkable sustainability produced by electrodeposition from a graphene quantum dots bath. The electrochemical measurements were carried out using cyclic voltammetry, potentiodynamic analysis, and Tafel measurements, and the deposits were characterized by X-ray fluorescence spectroscopy (XRF), Raman imaging, X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) to understand the surface morphology and elemental compositions. The current–time transients in the potential-step electrolysis were used to investigate the nucleation and growth mechanism. The smooth and compact deposit obtained at −0.60 V showed a composition of Cu = 24.33 wt %; Zn = 0.089 wt %; and C = 75.57 wt %. The SEM and energy dispersion X-ray analysis revealed a surface morphology with a uniform distribution of the particles and the presence of Cu, Zn, and C. The corrosion density of the material is very much lower than that of conventional brass, suggesting a higher sustainability.

Revealing Anomalous High Capacitance of Individual Porous Nanoparticles Employing Nano-Impact Electrochemistry

As a class of promising energy storage devices, supercapacitors have attracted great attention, regarding the deployment of high-power output in renewable energy technologies. The electrification of transportation and the dramatic increase of using portable electronic devices, require significant improvement in this field. Electric double-layer capacitors (EDLCs) are an important class of supercapacitors, in which the electrochemical double layer formed at the electrode/electrolyte interface is used to store energy. However, despite their high power density and remarkable cycle life, the prevalent application of EDLCs is limited because of their still insufficient energy density. Therefore, increasing the capacitance of EDLC electrodes is of great interest. One emerging approach for enhancing energy density has been employment of porous structures as novel electrodes for EDLCs [1].From a theoretical point of view, a conventional EDLC electrode can be considered as a parallel-plate capacitor that delivers a capacitance (C) according to C = ε A / d, where ε is the permittivity of the electrolyte, A is the electrode surface area, and d is the thickness of EDL. Consequently, increasing A of the EDLC electrodes using meso- or nanostructured materials is a classic approach toward realizing large specific capacitance and high energy density. Alternatively, it was experimentally proved that confinement effect on d in microporous EDLCs (pore size < 1 nm) leads to an anomalous increase in the specific capacitance as the pore width decreases. These findings suggest non-classical behaviors of EDLs emerged in sub nanometer pores. However, except for a few theoretical simulation results [2], there has been very limited research carried out on the application of the confinement effect in two-dimensional materials as an additional strategy toward high-energy density capacitors [3]. Herein, we propose single particle electrochemistry to study capacitive properties of individual porous nanoparticles, as an ideal candidate for fabrication of EDLCs.Employing “nano-impact” electrochemistry, an enhanced current is measured, which is caused by randomly colliding nanoparticles with a microelectrode [4,5]. In capacitive nano-impacts, the colliding particle causes the perturbation of a portion of the EDL with the subsequent charging-discharging processes which give rise to transient current-time events. This can be related to the electronic properties/capacitance of the particles [6]. Potentially this method will provide a powerful tool to study the properties of individual nanoparticles without any ensemble effects and overlaying effects of neighboring particles. In the present study, capacitance of individual porous platinum nanoparticles is investigated, by using PtNP impacts at platinum microelectrode in aqueous solution. These experiments are exploited to extract physico-chemical information about the structural effects on the energy density of EDLCs. The gained insights will help to improve our fundamental understanding of the EDL formation and will, thus, provide guidance towards the development of new and improved EDLCs.

Electrochemical nucleation and growth of Pt nanoflower particles on reduced graphite oxide with electrooxidation of glucose.

Electrochemical deposition of platinum nanoflower particles (PtNFPs) on reduced graphite oxide, rGO/GCE, using H2PtCl6 electrolyte in H2SO4 solution was investigated by chronoamperometry (CA). The experimental i-t curves measured at different overpotentials were analyzed and compared with theoretical curves obtained for the two limiting cases of the 3D nucleation and growth model, as described by Scharifker and Hills. The effect of deposition overpotential on the deposition process was evaluated. Through comparing potentiostatic current-time transients with the Scharifker-Hills model, a transition from instantaneous to a mixed kind of progressive-instantaneous nucleation was observed when increasing the deposition overpotential. CA results clearly show that the electrodeposition processes are diffusion-controlled (D0 = 2.77 × 10-5 cm2 s-1). A finer distribution of PtNFPs with an average size of ∼70 nm was obtained in 1.0 mM H2PtCl6 electrolyte in a 0.5 M H2SO4 solution. The as-prepared PtNFP/rGO catalyst shows 1.5 times higher activity than rGO/GCE, and the catalytic activity towards glucose oxidation is about many fold higher than that of the rGO/GCE and bare platinum electrode.

Transient characteristics of back-gated multilayer MoS2 and WSe2 channel n-type metal oxide semiconductor field effect transistors: A comparative study

The surface and interface effects of back-gated transition metal dichalcogenide channel MOSFETs are of great importance to device applications. This paper reports the transient current-time (I-t) characteristics of back-gated multilayer MoS2 and WSe2 channel n-type MOSFETs due to the charge trapping into the surface and interface traps of the devices. By investigating the current-voltage and I-t results measured from the devices with a similar structure and bias conditions under ambient and vacuum conditions, we find that the WSe2 devices show more significant surface and interface effects as compared to the MoS2 devices. The comparison of the experimental results with the technology computer aided design simulation shows that a single type trap model can account for the main characteristics of the transient process observed from the MoS2 and WSe2 devices. As compared to the trap on the MoS2 device, the surface trap on the WSe2 device has higher density, lower energy, and smaller trapping time. A further experimental comparison with WS2 devices suggests that the difference is microscopically originated from the chalcogen of Se and S rather than the metal element of Mo and W.

RESPONSE TO ASCORBIC ACID ON POLYPYRROLE FILM MODIFIED BY COPPER PARTICLES

In this work, a modified electrode of copper-polypyrrole (Cu-PPy) is elaborated by charging the polymer matrix by Cu particles. The response to ascorbic acid (AA) of this material was tested. The results show good performances. The results indicated a sensitive oxidation peak current of AA on the modified electrode. The success of this application led us to study the nucleation mechanism of copper on the PPy surface which permits to obtain this response. Nucleation and growth of electrodeposited copper onto PPy substrate have been studied in an aqueous solution of 0.01[Formula: see text]M CuCl2 and 1[Formula: see text]M KCl by means of electrochemical methods: cyclic voltammetry, chronoamperometry, and using atomic force microscopy (AFM). The model described by Scharifker and Hills was used to analyze current-time transients. According to this model, the nucleation and growth kinetics at the initial stages of deposition process involve an instantaneous nucleation followed by three-dimensional (3D) growth mechanism.

Electrochemical behaviour of hydrogen evolution reaction on platinum in anhydrous ethanol containing tetraethylammonium bromide

The electrochemical behaviour of hydrogen evolution reaction (HER) on platinum in anhydrous ethanol-containing tetraethylammonium bromide was investigated using potentiodynamic polarization, open-circuit potential measurement, potentiostatic current–time transient, galvanostatic potential–time transient, impedance and surface appearance observation techniques. The potentiodynamic polarization curves revealed that the HER process had two stages with larger Tafel slopes in this solution. Such higher slopes might result from the presence of adsorbates on the Pt surface which act as a barrier for HER. The study of ultrasonic-wave impact on potentiodynamic polarization indicated that the desorption of the adsorbates including hydrogen atoms could be enhanced by ultrasonic wave. The hydrogen evolution potential (Eh) shifted to more noble values with increasing scanning rate and solution temperature. Surface appearance observations of the Pt surface demonstrated the existence of hydrogen evolution, presenting the growth of the hydrogen evolution. The potentiostatic current–time transients indicated that HER occurred on Pt at potentials more negative than Eh. The galvanostatic potential/time transients showed that the applied negative current density exerted a great influence on the values of Eh. The impedance spectra at potentials more negative than Eh exhibited two time constants at less-negative potentials, but just one time constant at higher negative potentials.