This review describes recent advances in electrochemical impedance spectroscopy (EIS) with an emphasis on its novel applications to various electrochemistry-related problems. Section 1 discusses the development of new EIS techniques to reduce measurement time. For this purpose, various forms of multisine EIS techniques were first developed via a noise signal synthesized by mixing ac waves of various frequencies, followed by fast Fourier transform of the signal and the resulting current. Subsequently, an entirely new concept was introduced in which true white noise was used as an excitation source, followed by Fourier transform of both excitation and response signals. Section 2 describes novel applications of the newly developed techniques to time-resolved impedance measurements as well as to impedance imaging. Section 3 is devoted to recent applications of EIS techniques, specifically traditional measurements in various fields with a special emphasis on biosensor detections.

Electrochemical Impedance Spectroscopy

Diamond-like carbon: state of the art

Here we report that photostability and photoactivity of WO3 for water oxidation can be simultaneously enhanced by controlled introduction of oxygen vacancies into WO3 in hydrogen atmosphere at elevated temperatures. In comparison to pristine WO3, the hydrogen-treated WO3 nanoflakes show an order of magnitude enhanced photocurrent, and more importantly, exhibit extraordinary stability for water oxidation without loss of photoactivity for at least seven hours. The enhanced photostability is attributed to the formation of substoichiometric WO3−x after hydrogen treatment, which is highly resistive to the re-oxidation and peroxo-species induced dissolution. This work constitutes the first example where WO3 can be stabilized for water oxidation in neutral medium without the need for oxygen evolution catalysts. The demonstration of electrochemically stable WO3 could open up new opportunities for WO3 based photoelectrochemical and photocatalytic applications.

Hydrogen-treated WO3 nanoflakes show enhanced photostability

An electrochemical impedance spectroscopy study of the corrosion behaviour of PVD coated steels in 0.5 N NaCl aqueous solution: Part II.: EIS interpretation of corrosion behaviour

Passivity breakdown, pit initiation and propagation of pits in metallic materials – Review

A local electrochemical impedance spectroscopy (LEIS) technique for mapping the ac impedance distribution, as a function of frequency, of an electrode has been developed. In LEIS, as in traditional ac impedance methods, a sinusoidal voltage perturbation between the working and reference electrode is maintained by driving an ac current between the working electrode and a distant counterelectrode with a potentiostat. Local ac impedances are then derived from the ratio of the applied ac voltage and the local ac solution current density. The local ac current density is obtained from potential difference measurements near the electrode surface using a probe consisting of two micro‐electrodes. By measuring the ac potential difference between the micro‐electrodes, and knowing their separation distance and the solution conductivity, the local ac solution current density is derived. The accuracy of the local ac impedance data generated with this technique was established by investigating two model systems. The first provided a homogeneous electrode which allowed LEIS measurements to be compared to traditional EIS, while the second system provided a heterogeneity of known size and location whose components were easily characterized with traditional techniques. It is shown that area‐normalized scanning ac impedance measurements of the homogeneous electrode agreed well with traditional results. In addition, because LEIS maps the impedance properties of an electrode, the defect in the heterogeneous electrode was easily detected, while traditional ac impedance of this electrode gave little indication of its presence.

https://iopscience.iop.org/article/10.1149/1.2069332/pdf

A Novel Method for Generating Quantitative Local Electrochemical Impedance Spectroscopy

Surface enhanced Raman spectroscopy (SERS) data of W in acidic solution were characterized by modes associated with hydration (WO{sub 3}(H{sub 2}O){sub x}, 942 cm{sup {minus}1}) as well as modes characteristic of WO{sub 3} (816 cm{sup {minus}1}). At applied anodic potentials, the WO{sub 3}(H{sub 2}O){sub x} content in the oxide was greater than the WO{sub 3} content, while at applied cathodic potentials the WO{sub 3} content was larger. These results are consistent with a bilayer film on W in acidic solution which consists of a compact inner layer of WO{sub 3} and an outer layer of WO{sub 3}(H{sub 2}O){sub x}. Rotating disk electrode experiments (RDE) demonstrated that the passive dissolution (i{sub pass}) of W in acidic solution increased with the angular velocity of the electrode. An increase in i{sub pass} and a corresponding decrease in the thickness of the surface layer with increasing angular velocity is consistent with a reversible dissolution mechanism where dissolution is limited by the mass transport of a loosely bound WO{sub 3}(H{sub 2}O){sub x} layer from the surface. Electrochemical impedance spectroscopy measurements found that W dissolution in acidic solution was associated with an adsorption pseudocapacitance presumably due to the outer WO{sub 3}(H{sub 2}O){sub x} layer. The valuemore » of this pseudocapacitance increased with increasing angular velocity, indicating thinning of the layer consistent with RDE and SERS results. Results for W in alkaline solution are also presented.« less

The Nature of Oxide Films on Tungsten in Acidic and Alkaline Solutions

The corrosion behavior of Mg is of interest because of its growing use as an alloy in the transportation industry and also because it is a major component of some intermetallic phases in Al alloys, such as the deleterious S (Al 2 CoMg)-phase found in AA2024-T3. Pure Mg corrodes rapidly in a chloride-containing solution and even dissolves in water if the surface hydroxide is damaged by scratching the surface, for example. Uniform dissolution is drastically reduced in NaCl solutions (from 0.01 to 0.5 M) with the addition of very dilute concentrations of dichromate (10 -4 M). However, it is replaced by a strong localized attack in the form of fast filiform-like attack. On a large-grained sample with a defined defect structure, the attack can be seen to propagate at twin boundaries. Orientation imaging microscopy analysis found that corrosion was limited to planes near {0001} orientations with propagation being in prismatic directions. Auger electron spectroscopy analysis shows that interaction of chromate with the Mg hydroxide results in incorporation of reduced chromium ions in the hydroxide surface layer. Formation of a more resistant surface film could explain the very local nature of the corrosion in this case. The interaction between dichromate ions and Mg hydroxide can also explain the higher corrosion resistance of S-phase particles in chloride solutions containing dilute dichromate, although differences in the surface film formed compared to pure Mg are observed. Sputter-etching of the surface in order to assess the depth of the attack revealed that very hard or isolating corrosion products difficult to sputter are produced along the filiform path and that chromium compounds are not integrated in the corrosion products. Focused ion beam sectioning followed by scanning electron microscopy investigation of the sectioned area, demonstrates the presence of a continuous protective surface film. Adhesion between the Mg hydroxide and the metal is lost at the location of the corrosion filament, suggesting that the mechanism of propagation is similar to filiform corrosion under a coating. The depth of attack is a couple of micrometers with large cracks present within the corroded area that could induce severe surface damage.

/pdf/influence-of-dichromate-ions-on-corrosion-processes-on-pure-29az5gsitw.pdf

Influence of Dichromate Ions on Corrosion Processes on Pure Magnesium

Factors controlling the initiation and propagation of crevice corrosion on alloy 625 (UNS N06625) in ocean water of ambient temperature were explored within the contexts of the Oldfield-Sutton model for critical crevice corrosion solution (CCS) development and the ohmic criterion for crevice corrosion initiation. Data supported an earlier claim that a critical potential drop must be exceeded to initiate crevice corrosion. Steady-state crevice corrosion propagation was found to be under ohmic control. Chlorine decreased the time required for initiation and possibly raised propagation rates in ASTM artificial ocean water. Addition of molybdate (MoO42−) to ocean water (simulating the dissolution of alloyed molybdenum [Mo]) delayed initiation and reduced propagation rates temporarily, but not sufficiently to explain fully the inhibiting effects of alloyed Mo. Beneficial effects on crevice corrosion susceptibility of alloyed Mo and equivalent chromium (Creq) concentration were examined critically in t...

Crevice Corrosion of Alloy 625 in Chlorinated ASTM Artificial Ocean Water

Local electrochemical impedance spectroscopy (LEIS) was used to locate and examine the electrochemical properties of artificial and natural defects in a heat-cured, urea-formaldehyde modif...

R. S. Lillard

Papers

A Novel Method for Generating Quantitative Local Electrochemical Impedance Spectroscopy

The Nature of Oxide Films on Tungsten in Acidic and Alkaline Solutions

Influence of Dichromate Ions on Corrosion Processes on Pure Magnesium

Crevice Corrosion of Alloy 625 in Chlorinated ASTM Artificial Ocean Water

Using local electrochemical impedance spectroscopy to examine coating failure