Application of ultrasound in electrochemistry. An overview of mechanisms and design of experimental arrangement

An overview of possible mechanisms by which sonication can influence electrochemical processes is given. Four mechanisms are discussed:

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acoustic streaming;

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microstreaming and turbulence due to cavitation;

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formation of microjets in the course of collapse of cavitation bubble;

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shock waves;

and possible effects are illustrated on several examples. The most effective process is formation of microjets, which can not only decrease diffusion layer thickness under 1 μm, but also activate (depassivate) electrode surface. Design of experimental arrangement with maximum participation of microjets is proposed. Two approaches are proposed:

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focusing of ultrasound on the working electrode and reduction of energy losses by over-pressure;

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“tuning” the reactor to obtain resonance, i.e. formation of stationary waves by activating reactor in its resonant mode.

     

A lasing wavelength stabilized simultaneous multipoint acoustic sensing system using pressure-coupled fiber Bragg gratings

A fiber Bragg grating (FBG) sensor head, using a pressure coupling mechanism, was designed for broadband frequency response and structural strain-free characteristic. The pressure-coupled sensor heads were connected to a simultaneous multipoint acoustic sensing system based on a tunable laser. An intelligent lasing wavelength stabilization algorithm capable of identifying the direction of spectrum movement, the wavelength shifting speed, and a fiber bending event was developed so that the simultaneous multipoint acoustic sensing system could be used in environments with rapid temperature variations. The lasing wavelength feedback control algorithm updated the lasing wavelength into the steep slope of the FBG spectrum even under conditions of rapid temperature change. The averaging lasing wavelength updating time was only 21 s because the system can decide a minimal size in scan window by finding the FBG spectrum shifting speed and direction in real time. The system was able to update the lasing wavelength which missed the steep slope of the FBG spectrum under maximum temperature variation rates 0.3014 and −0.3246 °C/s. The proposed system detected simultaneous impact waves at multiple points under conditions of rapid temperature change and change in dynamic strain.     

Ordered fluorite phases in the Bi2O3-Ta2O5 system: A structural and electrical investigation

Structure and electrical behaviour are reported for the system Bi_1-xTa_xO_1.5 + x (0.167 ≤ x ≤ 0.250). In the compositional range 0.200 < x ≤ 0.250 an incommensurately modulated pseudo-cubic phase (type II) is observed, with the appearance of a larger pseudo-cubic phase in the region 0.167 ≤ x ≤ 0.200. Structural analysis of the type II phases by neutron diffraction reveals subtle changes in the oxide ion distribution with temperature, associated with changes in the incommensurate modulation parameter. Analysis of the defect structure of the type II phase reveals chains of tantalate octahedra as a likely structural motif. It is proposed that these chains facilitate an electronic contribution to total conductivity at low temperatures through electron hopping along the chains. Changes in oxide ion vacancy ordering may explain the observed non-linear behaviour in the thermal expansion of lattice parameter and Arrhenius plots of total conductivity.     

Ultrasonic and spectroscopic studies on hydrogen bonded complexes of aromatic amine and aryl ketones in n-hexane at 303.15 K

Viscometric and ultrasonic studies have been carried out in n-hexane solutions, containing equimolar concentration from 0.02 to 0.2 M of aromatic ketones and N-methylaniline (NMANI), at 303.15 K and at atmospheric pressure. The ketones studied in the present investigation are acetophenone (ACP), 4-chloroacetophenone (ClACP) and 4-methylacetophenone (MACP). The behaviour of measured ultrasonic velocity (u), density (ρ) and viscosity (η) and also the computed acoustic parameters provide strong evidence for the presence of strong solute-solute interactions in the three ternary systems. Excess molar volume and excess thermo acoustic parameters reveal the existence of hydrogen bonded complexes between the solute molecules, ketones and secondary amine. The variation of these parameters with the concentration shows that the existing interactions are influenced by the structure of components and functional groups of the components involved. An attempt has been made to confirm the formation of 1:1 complexes in these systems through UV-visible spectroscopic method at 303.15 K. The calculated values of formation constants of the charge transfer complexes both by acoustic and optical methods agree satisfactorily. The variation in the values of formation constant reveals that electron releasing substituent in the acetophenone molecule enhances the stability while electronegative substituent decreases the stability of the complex. The negative values of free energy of formation of these three complexes indicate that these complexes are thermodynamically stable.     

Electrochemical sensitive determination of acetaminophen in pharmaceutical formulations at iron oxide/graphene composite modified electrode

Acetaminophen (AC) is one of the most commonly prescribed analgesic and antipyretic drug, which is considered to be safe as well as effective. Rational use of AC does not pose any toxicity or adverse effects, however, an overdose or prolonged use could lead to nephrotoxicity and severe hepatoxicity. Thus, monitoring of AC is essential for drug safety. In this work, a facile Fe₂O₃/reduced graphene oxide (Fe₂O₃/RGO) nanocomposite was synthesized for improved electrochemical detection of AC. The material was synthesized through a simple one-step process. For characterization of synthesized Fe₂O₃/RGO composite, energy-dispersive X-ray spectroscopy (EDX), field emission-scanning electron microscopy (FE-SEM) and electrochemical impedance spectroscopy (EIS) were employed. To verify the electrochemical performance of Fe₂O₃/RGO nanocomposite, GCE was modified with this nanocomposite and utilized for quantification of AC. The detection limit of AC was 21 nM in a linear range from 1.0 × 10⁻⁷ to 74 × 10⁻⁶ M. Furthermore, the sensor also unveiled good stability, promising sensitivity and selectivity. Hence, Fe₂O₃/RGO could be applied as a sensing material for electrochemical detection of AC. Finally, the analytical utility of the method was also verified in human urine and drug samples with some preliminary treatments.     

Graphene and Graphene/Polymer Composites as the Most Efficient Protective Coatings for Steel,Aluminum and Copper in Corrosive Media: A Review of Recent Studies

The metal corrosion is considered as a severe threat to the national economy and industry structure, capable of triggering significant economic losses and severe damages, involving innumerable fields in daily life and industries. This review provides an overview of the physioelectrochemical studies on anticorrosive properties of various types of graphene coatings. Required electrochemical techniques for the investigation of anticorrosive efficiency, various types of graphene‐based materials coatings along with different routes to provide desirable coated layers are discussed in detail. After all, we intend to show that the modified graphene nanosheets can be regarded as effective protective layers against metal corrosion not only because of their extraordinary mechanical strength and toughness, which can be reached with a vastly thin layer, but also for their high transparency, cost‐efficiency and stability.     

Local electrochemical impedance spectroscopy: A window into heterogeneous interfaces

The ability to probe surface reactivity on a local scale has led to a new insight into the comprehension of the electrochemical reactivity in relation with the microstructure of the surface. Among the different techniques developed in recent years, local electrochemical impedance spectroscopy has the advantage of using a transient approach to locally characterize a stationary electrochemical system without the need to add any redox mediator in solution, which is a great advantage for the study of different systems.In this review, particular attention is paid to the different ways of measuring the local impedance, and the technique implementing a local current measurement in solution is deeply discussed. This local electrochemical impedance spectroscopy journey also encompasses a discussion about technical and experimental limitations.     

表面修饰的TiO_2太阳能电池界面特性研究

用水热法制备了具有典型锐钛矿晶型的TiO2纳米材料,采用Cr(NO3)3对TiO2薄膜电极进行修饰改性。用X射线衍射(XRD)、扫描电子显微镜(SEM)和光电子能谱(XPS)测试电极的物相及表面结构,结果显示TiO2薄膜表面包覆一层粒径较大的氧化铬颗粒,整个电极仍保持均匀的多孔结构。电流-电压(I-V)曲线测试结果显示,改性后最佳电极的短路电流和光电转换效率分别比改性前提高了31.1%和40.4%。用电化学阻抗谱(EIS)测试电池的界面特性,从测试结果可以看出,相同偏压下,改性后电池的TiO2/染料/电解质界面电阻更大,说明氧化铬包覆层在一定程度上抑制了界面的电子复合,改善了电池的光电输出特性。     

Ultrasonic investigation on aqueous polysaccharide (starch) at 298.15 K

The ultrasonic velocity, density and viscosity at 298.15 K have been measured in the binary system of starch in aqueous medium. The acoustical parameters such as adiabatic compressibility (β), free length (L_f), free volume (V_f), internal pressure (π_i), acoustical impedance (Z), relative association (R_A), Rao’s constant (R), Wada’s constant (W), classical absorption coefficients (α/f²), relaxation time (τ) and relaxation strength (r) are calculated. The results are interpreted in terms of molecular interaction between the components of the mixtures.     

A sensitive and label-free impedimetric biosensor based on an adjunct probe

A highly sensitive and label-free impedimetric biosensor is achieved based on an adjunct probe attached nearby the capture probe. In this work, the adjunct probe was co-assembled on the surface of gold electrode with the capture probe hybridized with the reporter probe, and then 6-mercapto-1-hexanol was employed to block the nonspecific binding sites. When target DNA was added, the adjunct probe functioned as a fixer to immobilize the element of reporter probe displaced by the target DNA sequences and made the reporter probe approach the electrode surface, leading to effective inhibition of charge transfer. The increase in charge transfer resistance is related to the quantity of the target DNA in a wide range. The linear range for target DNA with specific sequences was from 0.1 nM to 0.5 μM with a good linearity (R = 0.9988) and a low detection limit of 6.3 pM. This impedimetric biosensor has the advantages of simplicity, sensitivity, good selectivity, and large dynamic range.