Scanning vibrating electrode technique (SVET), also known as vibrating probe within the field of biology, is a scanning probe microscopy (SPM) technique which visualizes electrochemical processes at a sample. It was originally introduced in 1974 by Jaffe and Nuccitelli to investigate the electrical current densities near living cells. [1] Starting in the 1980s Hugh Isaacs began to apply SVET to a number of different corrosion studies. [2] SVET measures local current density distributions in the solution above the sample of interest, to map electrochemical processes in situ as they occur. It utilizes a probe, vibrating perpendicular to the sample of interest, to enhance the measured signal. [1] It is related to scanning ion-selective electrode technique (SIET), which can be used with SVET in corrosion studies, [3] and scanning reference electrode technique (SRET), which is a precursor to SVET. [4]
Scanning vibrating electrode technique was originally introduced to sensitively measure extracellular currents by Jaffe and Nuccitelli in 1974. [1] Jaffe and Nuccitelli then demonstrated the ability of the technique through the measurement of the extracellular currents involved with amputated and re-generating newt limbs, [5] developmental currents of chick embryos, [6] and the electrical currents associated with amoeboid movement. [7]
In corrosion, the scanning reference electrode technique (SRET) existed as the precursor to SVET, and was first introduced commercially and trademarked by Uniscan Instruments, [8] now part of Bio-Logic Science Instruments. [9] SRET is an in situ technique in which a reference electrode is scanned near a sample surface to map the potential distribution in the electrolyte above the sample. Using SRET it is possible to determine the anodic and cathodic sites of a corroding sample without the probe altering the corrosion process. [10] SVET was first applied to and developed for the local investigation of corrosion processes by Hugh Isaacs. [2]
SVET measures the currents associated with a sample in solution with natural electrochemical activity, or which is biased to force electrochemical activity. In both cases the current radiates into solution from the active regions of the sample. In a typical SVET instrument the probe is mounted on a piezoelectric vibrator on and x,y stage. The probe is vibrated perpendicular to the plane of the sample resulting in the measurement of an ac signal. The resulting ac signal is detected and demodulated using an input phase angle by a lock-in amplifier to produce a dc signal. [1] [11] [12] The input phase angle is typically found by manually adjusting the phase input of the Lock-in Amplifier until there is no response, 90 degrees is then added to determine the optimum phase. [13] The reference phase can also be found automatically by some commercial instruments. [14] The demodulated dc signal which results can then be plotted to reflect the local activity distribution.
In SVET, the probe vibration results in a more sensitive measurement than its non-vibrating predecessors, [1] as well as giving rise to an improvement of the signal-to-noise ratio. [13] The probe vibration does not affect the process under study under normal experimental conditions. [15] [16]
The SVET signal is affected by a number of factors including the probe to sample distance, solution conductivity, and the SVET probe. The signal strength in a SVET measurement is influenced by the probe to sample distance. When all other variables are equal a smaller probe to sample distance will result in the measurement of a higher magnitude signal. [17] The solution conductivity affects the signal strength in SVET measurements. With increasing solution conductivity, the signal strength of the SVET measurement decreases. [18]
Corrosion is a major application area in for SVET. SVET is used to follow the corrosion process and provide information not possible from any other technique. [19] In corrosion it has been used to investigate a variety of processes including, but not limited to, local corrosion, self-healing coatings, Self-Assembled Monolayers (SAMs). SVET has also been used to investigate the effect of different local features on the corrosion properties of a system. For example, using SVET, the influence of the grains and grain boundaries of X70 was measured. A difference in current densities existed between the grains and grain boundaries with the SVET data suggesting the grain was anodic, and the boundary relatively cathodic. [20] Through the use of SVET it has been possible to investigate the effect of changing the aluminum spacer width on the galvanic coupling between steel and magnesium, a pairing which can be found on automobiles. Increasing the spacer width reduced the coupling between magnesium and steel. [21] More generally localized corrosion processes have been followed using SVET. For a variety of systems it has been possible to use SVET to follow the corrosion front as it moves across the sample over extended periods, providing insight into the corrosion mechanism. [22] [23] [24] A number of groups have used SVET to analyze the efficiency of self-healing coatings, mapping the changes in surface activity over time. When SVET measurements of the bare metals are compared to the same metal with the smart coating it can be seen that the current density is lower for the coated surface. Furthermore, when a defect is made in the smart coating the current over the defect can be seen to decrease as the coating recovers. [25] [26] [27] Mekhalif et.al. have performed a number of studies on SAMs formed on different metals to investigate their corrosion inhibition using SVET. The SVET studies revealed that the bare surfaces experience corrosion, with inhomogeneous activity measured by SVET. SVET was then used to investigate the effect of modification time, [28] and exposure to corrosive solution. [29] When a defect free SAM was investigated SVET showed homogeneous activity. [30] [31]
In the field of biology the vibrating probe technique has been used to investigate a variety of processes. Vibrating probe measurements of lung cancer tumor cells have shown that the electric fields above the tumor cell were statistically larger than those measured over the intact epithelium, with the tumor cell behaving as the anode. Furthermore, it was noted that the application of an electric field resulted in the migration of the tumor cells. [32] Using vibrating probe, the electrical currents involved in the biological processes occurring at leaves have been measured. Through vibrating probe it has been possible to correlate electrical currents with the stomatal aperture, suggesting that stomatal opening was related to proton efflux. [33] Based on this work further vibrating probe measurements also indicated a relationship between the photosynthetic activity of a plant and the flow of electrical current on its leaf surfaces, with the measured current changing when it was exposed to different types of light and dark. [34] [35] As a final example, the vibrating probe technique has been used in the investigation of currents associated with wounding in plants and animals. A vibrating probe measurement of maize roots found that large inward currents were associated with wounding of the root, with the current decreasing in magnitude away from the center of the wound. [36] When similar experiments were performed on rat skin wounds, large outward currents were measured at the wound, with the strongest current measured at the wound edge. [37] The ability of the vibrating probe to investigate wounding has even lead to the development of a hand held prototype vibrating probe device for use. [38]
SVET has been used to investigate the photoconductive nature of semiconductor materials, by following changes in current density related to photoelectrochemical reactions. [39] Using SVET the lithium/organic electrolyte interface, as in lithium battery systems has also been investigated. [40]
Although SVET has almost exclusively been applied for the measurement of samples in aqueous environments, its application in non-aqueous environments has recently been demonstrated by Bastos et al. [41]
Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very-high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit.
Scanning probe microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. SPM was founded in 1981, with the invention of the scanning tunneling microscope, an instrument for imaging surfaces at the atomic level. The first successful scanning tunneling microscope experiment was done by Gerd Binnig and Heinrich Rohrer. The key to their success was using a feedback loop to regulate gap distance between the sample and the probe.
Dielectric spectroscopy measures the dielectric properties of a medium as a function of frequency. It is based on the interaction of an external field with the electric dipole moment of the sample, often expressed by permittivity.
Kelvin probe force microscopy (KPFM), also known as surface potential microscopy, is a noncontact variant of atomic force microscopy (AFM). By raster scanning in the x,y plane the work function of the sample can be locally mapped for correlation with sample features. When there is little or no magnification, this approach can be described as using a scanning Kelvin probe (SKP). These techniques are predominantly used to measure corrosion and coatings.
Buckypaper is a thin sheet made from an aggregate of carbon nanotubes or carbon nanotube grid paper. The nanotubes are approximately 50,000 times thinner than a human hair. Originally, it was fabricated as a way to handle carbon nanotubes, but it is also being studied and developed into applications by several research groups, showing promise as vehicle armor, personal armor, and next-generation electronics and displays.
Cobalt sulfide is the name for chemical compounds with a formula CoxSy. Well-characterized species include minerals with the formulas CoS, CoS2, Co3S4, and Co9S8. In general, the sulfides of cobalt are black, semiconducting, insoluble in water, and nonstoichiometric.
Water oxidation is one of the half reactions of water splitting:
Zinc–cerium batteries are a type of redox flow battery first developed by Plurion Inc. (UK) during the 2000s. In this rechargeable battery, both negative zinc and positive cerium electrolytes are circulated though an electrochemical flow reactor during the operation and stored in two separated reservoirs. Negative and positive electrolyte compartments in the electrochemical reactor are separated by a cation-exchange membrane, usually Nafion (DuPont). The Ce(III)/Ce(IV) and Zn(II)/Zn redox reactions take place at the positive and negative electrodes, respectively. Since zinc is electroplated during charge at the negative electrode this system is classified as a hybrid flow battery. Unlike in zinc–bromine and zinc–chlorine redox flow batteries, no condensation device is needed to dissolve halogen gases. The reagents used in the zinc-cerium system are considerably less expensive than those used in the vanadium flow battery.
Bipolar electrochemistry is a phenomenon in electrochemistry based on the polarization of conducting objects in electric fields. Indeed, this polarization generates a potential difference between the two extremities of the substrate that is equal to the electric field value multiplied by the size of the object. If this potential difference is important enough, then redox reactions can be generated at the extremities of the object, oxidations will occur at one extremity coupled simultaneously to reductions at the other extremity. In a simple experimental setup consisting of a platinum wire in a weighing boat containing a pH indicator solution, a 30 V voltage across two electrodes will cause water reduction at one end of the wire and a pH increase and water oxidation at the anodic end and a pH decrease. The poles of the bipolar electrode also align themselves with the applied electric field.
Scanning electrochemical microscopy (SECM) is a technique within the broader class of scanning probe microscopy (SPM) that is used to measure the local electrochemical behavior of liquid/solid, liquid/gas and liquid/liquid interfaces. Initial characterization of the technique was credited to University of Texas electrochemist, Allen J. Bard, in 1989. Since then, the theoretical underpinnings have matured to allow widespread use of the technique in chemistry, biology and materials science. Spatially resolved electrochemical signals can be acquired by measuring the current at an ultramicroelectrode (UME) tip as a function of precise tip position over a substrate region of interest. Interpretation of the SECM signal is based on the concept of diffusion-limited current. Two-dimensional raster scan information can be compiled to generate images of surface reactivity and chemical kinetics.
Scanning Flow Cell (SFC) is an electrochemical technique, based on the principle of channel electrode. The electrolyte is continuously flowing over a substrate that is introduced externally on translation stage. In contrast to the reference and counter electrode that are integrated in the main channel or placed in side compartments connected with a salt bridge.
A solid dispersion redox flow battery is a type of redox flow battery using dispersed solid active materials as the energy storage media. The solid suspensions are stored in energy storage tanks and pumped through electrochemical cells while charging or discharging. In comparison with a conventional redox flow battery where active species are dissolved in aqueous or organic electrolyte, the active materials in a solid dispersion redox flow battery maintain the solid form and are suspended in the electrolyte. Further development expanded the applicable active materials. The solid active materials, especially with active materials from lithium-ion battery, can help the suspensions achieve much higher energy densities than conventional redox flow batteries. This concept is similar to semi-solid flow batteries in which slurries of active materials accompanied by conductive carbon additives to facilitate electrons conducting are stored in energy storage tanks and pumped through the electrochemical reaction cells. Based upon this technique, an analytical method was developed to measure the electrochemical performance of lithium-ion battery active materials, named dispersed particle resistance (DPR).
Dispersed particle resistance (DPR) is a measured parameter to characterize battery active materials. It is seen as an indicator of lithium-ion battery active material rate capability. It is the slope of voltage-current linear fit for active material samples in suspensions. It can be obtained by applying different voltages on a suspension and measuring the currents, after which the data points are plotted. The slope of the plot is referred to as dispersed particle resistance. It can also be done in the opposite way where different currents are applied and voltages are measured. The key advantage of this dispersed particle resistance technique is fast and accurate comparing with the conventional characterization method for which batteries need to be fabricated and tested for a long time.
Electrochemical AFM (EC-AFM) is a particular type of Scanning probe microscopy (SPM), which combines the classical Atomic force microscopy (AFM) together with electrochemical measurements. EC-AFM allows to perform in-situ AFM measurements in an electrochemical cell, in order to investigate the actual changes in the electrode surface morphology during electrochemical reactions. The solid-liquid interface is thus investigated. This technique was developed for the first time in 1996 by Kouzeki et al., who studied amorphous and polycrystalline thin films of Naphthalocyanine on Indium tin oxide in a solution of 0.1 M Potassium chloride (KCl). Unlike the Electrochemical scanning tunneling microscope, previously developed by Itaya and Tomita in 1988, the tip is non-conductive and it is easily steered in a liquid environment.
David Zitoun is an Israeli chemist and materials scientist.
Doron Aurbach is an Israeli electrochemist, materials and surface scientist.
Electro-oxidation(EO or EOx), also known as anodic oxidation or electrochemical oxidation (EC), is a technique used for wastewater treatment, mainly for industrial effluents, and is a type of advanced oxidation process (AOP). The most general layout comprises two electrodes, operating as anode and cathode, connected to a power source. When an energy input and sufficient supporting electrolyte are provided to the system, strong oxidizing species are formed, which interact with the contaminants and degrade them. The refractory compounds are thus converted into reaction intermediates and, ultimately, into water and CO2 by complete mineralization.
Screen-printed electrodes (SPEs) are electrochemical measurement devices that are manufactured by printing different types of ink on plastic or ceramic substrates, allowing quick in-situ analysis with high reproducibility, sensitivity and accuracy. The composition of the different inks used in the manufacture of the electrode determines its selectivity and sensitivity. This fact allows the analyst to design the most optimal device according to its purpose.
Raman spectroelectrochemistry (Raman-SEC) is a technique that studies the inelastic scattering or Raman scattering of monochromatic light related to chemical compounds involved in an electrode process. This technique provides information about vibrational energy transitions of molecules, using a monochromatic light source, usually from a laser that belongs to the UV, Vis or NIR region. Raman spectroelectrochemistry provides specific information about structural changes, composition and orientation of the molecules on the electrode surface involved in an electrochemical reaction, being the Raman spectra registered a real fingerprint of the compounds.
Electrochemical quartz crystal microbalance (EQCM) is the combination of electrochemistry and quartz crystal microbalance, which was generated in the eighties. Typically, an EQCM device contains an electrochemical cells part and a QCM part. Two electrodes on both sides of the quartz crystal serve two purposes. Firstly, an alternating electric field is generated between the two electrodes for making up the oscillator. Secondly, the electrode contacting electrolyte is used as a working electrode (WE), together with a counter electrode (CE) and a reference electrode (RE), in the potentiostatic circuit constituting the electrochemistry cell. Thus, the working electrode of electrochemistry cell is the sensor of QCM.
{{cite journal}}
: Cite journal requires |journal=
(help)