Electrochemical study of TiO2 modified with silver nanoparticles upon CO2 reduction

A systematic cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) study on titanium dioxide (TiO₂) and silver–TiO₂ surfaces was performed in order to decouple electrochemical reduction processes of carbon dioxide in aqueous solutions. CV studies indicate cathodic current increase on Ag–TiO₂ compared to bare TiO₂ surfaces. An equivalent circuit based on transmission line model was applied in order to adjust EIS data, and a modification of this model was made to account for Ag particle interaction with the electrolyte solution. Electrochemical processes were then decoupled upon applied potential where the role of TiO₂ surface states was identified and separated from (a) silver reduction, (b) electronic transport on TiO₂, and (c) charge transfer on TiO₂ and Ag surfaces. The Ag–electrolyte interface impedance has considerably lower values than the TiO₂–electrolyte interface, suggesting that the silver particles may be considered as favorable reaction sites for the electrochemical reduction of water and carbon dioxide.     

Electrochemical recovery of silver from waste aqueous Ag(I)/Ag(II) redox mediator solution used in mediated electro oxidation process

The paper presents a process for the electrochemical recovery of silver(Ag) by electro deposition on the electrode surface from the waste solutions of Ag(I)/Ag(II) redox system in nitric acid medium used for the mediated electrochemical process. Electrochemical recovery was carried out in an undivided cell with DSA-O₂ electrodes at room temperature condition. At an optimized current density of 12 A/dm², 99% of Ag recovery efficiency was achieved with high yield and low energy consumption. Experimental runs were made in order to observe the performance of the Ag recovery process. The operating conditions like current density, temperature and Ag(I) concentration of the electrolyte, the acid concentrations, agitation rate and inter-electrode distance were optimized.     

Ag nanowires and its application as electrode materials in electrochemical capacitor

Silver nanowires were synthesized on a large scale by using anodic aluminum oxide (AAO) film as templates and serving ethylene glycol as reductant. Their morphological and structural characterizations were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and selected area electron diffraction (SAED). The electrochemical properties of silver nanowires as electrode materials for electrochemical capacitors were investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge technique in 6 M KOH aqueous electrolyte. The Ag₂O/Ag coaxial nanowires were formed by the incomplete electrochemical oxidation during the charge step. The maximum specific capacitance of 987 F g^?1 was obtained at a charge–discharge current density of 5 mA cm^?2.     

Development of a Ag/Ag micro-reference electrode for electrochemical measurements in ionic liquids

We report on a novel miniaturized Ag/Ag⁺ reference electrode (RE) design suitable for electrochemical measurements in room temperature ionic liquids (RTILs). The electrode is based on capillaries with an outer diameter of 365 μm and contains a 10 mmol/l solution of a silver salt in a RTIL. The silver salt bears the same type of anion as the RTIL. While potential shifts of several hundred millivolts have been observed for common platinum or silver pseudo-reference electrodes, our Ag/Ag⁺ micro electrode provides a stable and reliable reference potential over a period of more than two weeks, if protected from light and stored in a nitrogen atmosphere. Due to the small dimensions of the RE, it can be placed close to the working electrode (WE) and it is well-suited for application in electrochemical micro cells as well as for potential-controlled in situ AFM, STM or electrochemical impedance measurements. The electrode characteristics were determined by voltammetric measurements on ferrocene and cobaltocenium hexafluorophosphate dissolved in a RTIL. The highest expected contamination of the sample with Ag⁺ ions was calculated and found to be below 4 ppm.     

Ag(I)/Ag electrode reaction in amide-type room-temperature ionic liquids

Ag(I)/Ag electrode reaction was investigated in some amide-type room-temperature ionic liquids composed of different cations. The morphology of silver deposits and the electrochemical behavior were not sensitive to the difference in the cations of ionic liquids. On the other hand, it was suggested that the adsorption of bis(trifluoromethylsulfonyl)amide (TFSA⁻) is more important for electrodeposition of silver in both ionic liquids and aqueous solutions. The diffusion coefficients of silver cation in the ionic liquids indicated the silver cation is surrounded by TFSA⁻ to form a bulky species. The rate of crystal growth of silver particles in the ionic liquids by electrochemical Ostwald ripening was much slower than that in a nitrate aqueous solution, suggesting the charge transfer in the ionic liquids is slower than that in the aqueous solution.     

Electrochemical Pretreatment of Polymers with Dilute Nitric Acid Either Alone or in the Presence of Silver Ions

X-ray Photoelectron spectroscopy (XPS) was used to detect major changes to the surface chemistry of polypropylene (PP), high density polyethylene (HDPE) and styrene-butadiene block copolymer (SBS) caused by electrochemical treatment using dilute nitric acid as electrolyte. Large increases in adhesion levels were observed with PP and HDPE. The method has the potential to be a commercial pretreatment that is inexpensive and safe. Further treatments were carried out in which the complex ion (AgNO₃)⁺ was generated electrochemically. Effective pretreatment was achieved even with dilute solutions (0.001 M w.r.t. silver nitrate). Mechanisms are tentatively proposed for the electrochemical treatment when simply using an electrolyte of dilute nitric acid or where the anolyte consists of a solution of silver nitrate in dilute nitric acid.     

Strategy for the syntheses of isolated fine silver nanoparticles and polypyrrole/silver nanocomposites on gold substrates

In this work, isolated fine silver nanoparticles and polypyrrole/silver nanocomposites with diameters of about 10 nm on gold substrates were first prepared by electrochemical methods. First, an Ag substrate was cycled in a deoxygenated aqueous solution containing 0.1 M HCl from −0.30 to +0.30 V versus Ag/AgCl at 5 mV/s with 30 scans. Subsequently the Ag working electrode was immediately replaced by an Au electrode and a cathodic overpotential of 0.2 V was applied under controlled sonication to synthesize Ag nanoparticles on the Au electrode. Then pyrrole monomers were encouragingly found to be polymerized on the deposited Ag nanoparticles. This polymerization is distinguishable from the known chemical or electrochemical one, due to the electrochemical activity of unreduced species of Ag_n⁺ clusters inside the nanoparticles. Also, this polymerization may be ascribed to the oxidizing agent of AuCl₄⁻, which is present on the Au electrode.     

Electrochemical silver microcoulometers with fluoroborate electrolyte

The results of some electrochemical investigations on a silver microcoulometer with an electrolyte consisting of Ag⁺ in concentrated fluoroboric acid are reported. The advantages of this system are confirmed as wide ranges of current and charge, low resistance and low influence of temperature. The investigated solution may also be used in other electrochemical investigations.     

流化床电化学反应器回收铜电解液中的银

采用流化床电化学反应器，分别对实验室配制的Ag十溶液和铜生产厂取样涂进行了银回收实验，表明该工艺技术可行、经济合理，有工业化应用前景     

Effect of electrolysis conditions on the deposition of silver–bismuth alloys

The electrochemical deposition and dissolution of silver, bismuth and silver–bismuth alloy from a cyanide–tartrate electrolyte were studied by means of cyclic voltammetry. The influence of the electrolyte composition on the electrochemical reactions is discussed. The deposition potentials of the two metals could be maintained close to each other by means of appropriate complex forming agents, leading to their codeposition. Silver deposition is the predominant reaction in the electrolyte studied and the bismuth content in the coating increases with increased current density. The dissolution potentials of the two metals are quite distinct; they differ by more than 0.5 V. In the presence of a free complex forming agent, both the deposition and the dissolution potentials of silver can be shifted in the negative direction. Depending on the type and amount of the complex forming agent, they can become more negative than the deposition and dissolution potentials of bismuth. Predominant deposition of bismuth is realized in this case and the codeposition of silver is enhanced at higher current densities. By varying the amount of the complex forming agent, silver–bismuth coatings of any desired composition can be obtained.     

A cyclic voltammetric study of ferrocyanide-thiocyanate silver electrodeposition electrolyte

The electrochemical behaviour of ferrocyanide-thiocyanate electrolytes for silver electrodeposition was studied by cyclic voltammetry. The differences in the electrolyte preparation procedure do not affect their electrochemical behaviour at identical silver concentrations. The silver electrodeposition is characterized by two cathodic current maxima and by charge transfer limitations with a preceding chemical reaction. The dissolution of the electrodeposited silver is characterized by the formation of AgCN on the electrode and further dissolution by passivation and formation of oxide products, which are reduced during the next cathodic scan. The redox processes of iron from the ferrocyanide complex on Pt- and Ag-substrates, as well as the effect of the complex forming agents like SCN^–- and CN^–- ions are shown.     

One-step large-scale synthesis of micrometer-sized silver nanosheets by a template-free electrochemical method

We have synthesized micrometer-sized Ag nanosheets via a facile, one-step, template-free electrochemical deposition in an ultra-dilute silver nitrate aqueous electrolyte. The nanosheet growth was revealed to occur in three stages: (1) formation of polygonal Ag nuclei on a substrate, (2) growth of {112}-faceted nanowire from the nuclei, and (3) anisotropic growth of (111)-planar nanosheets, approximately 20 to 50 nm in thickness and 10 μm in width, in the <112>−direction. The vertical growth of the facet nanowire was induced by the strong interface anisotropy between the deposit and electrolyte due to the ultra-dilute concentration of electrolyte and high reduction potential. The thickness of Ag nanosheets was controllable by the adjustment of the reduction/oxidation potential and frequency of the reverse-pulse potentiodynamic mode.     

In situ FTIR monitoring of Ag and Au electrodeposition on glassy carbon and silicon

Formation of Ag, Au and Ag-Au alloys on Si and Glassy Carbon (GC) electrodes from alkaline cyanide electrolytes was investigated using a combination of electrochemical and spectroscopic techniques. Metal deposition and dissolution processes could be studied in situ by monitoring the ν(CN) bands of the metal complexes and the free cyanide ion in the region between 2000 and 2200 cm⁻¹ using FTIR reflectance spectroscopy. Under the experimental conditions, two different silver complexes, namely [Ag(CN)₂]⁻ and [Ag(CN)₃]²⁻ (whilst only one gold complex, namely [Au(CN)₂]⁻), were identified. In the case of the Ag-Au alloys, both species co-deposit even in the activation region, where Ag reduction is expected to be the main reaction. Experimental results indicate that in a mixed electrolyte containing equal amounts of Ag and Au, Ag deposition is thermodynamically favoured (), while Au deposition is kinetically favoured. The Ag-Au alloy deposition follows a progressive nucleation mechanism even at relatively high negative potentials. The morphology and adhesion of all deposits, as well as the alloy composition, were found to be strongly dependent on the deposition conditions. A better adhesion of the films with a higher Au content was observed, due to the formation of a more stable AuSi bond.     

Electrochemical behaviour of chalcopyrite in the presence of silver and Sulfolobus bacteria

The electrochemical behaviour of massive chalcopyrite electrodes has been studied in an acid medium (pH1.5) containing silver ions (0.02gdm–3Ag+) and thermophilic bacteria (68°C). Preliminary tests on particulate electrodes made from graphite, elemental sulfur and Ag2S were included to determine the electrochemical response of reactants (Ag+) and products (S° and Ag2S) associated with the dissolution of chalcopyrite in the presence of silver. Massive chalcopyrite electrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solution and [Ag+]. As well as Ag2S, metallic silver was detected on the chalcopyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopyrite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of the electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two weeks did not improve the surface reactivity. However, in the initial stages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganisms.     

Synergic effect of benzotriazole and chloride ion on Cu passivation in a phosphate electrochemical mechanical planarization electrolyte

In this study, the effect of chloride ion (Cl⁻) in phosphate electrolytes of pH 2 containing benzotriazole (BTAH) developed for use in electrochemical mechanical planarization (ECMP) was investigated at various anodic potentials. According to D.C. and A.C. electrochemical analyses, the inhibition effect of the BTAH passive film formed in phosphate electrolyte containing both BTAH and Cl⁻ was superior to that formed in phosphate electrolytes containing BTAH alone, even at high anodic potential. The effective window for BTAH passivation reached ∼1.3 V vs. Ag/AgCl nearly three times that of the ∼0.5 V vs. Ag/AgCl recorded for electrolyte containing BTAH alone. According to analyses conducted by atomic force microscopy (AFM) and secondary ion mass spectrometer (SIMS), the thickness of the passive film grown from the BTAH-only electrolyte at 0.3 V vs. Ag/AgCl was ∼52 ± 7 nm and ∼55 nm, respectively. As for the passive film grown from the BTAH and Cl⁻ electrolyte, the thickness increased to ∼104 ± 18 nm and ∼106 nm, respectively. The mechanism for the enhanced inhibition capability was that the passive film grown from the BTAH and Cl⁻ electrolyte was thicker compared to that formed from the BTAH-only electrolyte due to the incorporation of Cl⁻ into the BTAH passive film. The ECMP polishing results also demonstrated an obvious step height reduction of ∼1000 nm in a patterned structure for only 60 s polishing at a high potential of 1.0 V vs. Ag/AgCl under a low downward pressure (∼0.5 psi). Subsequently, this study proposes that the control of Cl⁻ in a phosphate ECMP electrolyte of pH 2 may be useful in enhancing the passivation capability of BTAH passive film, thus expanding the operating potential window.     

Electrochemical behaviour of chalcopyrite in the presence of silver and Sulfolobus bacteria

The electrochemical behaviour of massive chalcopyrite electrodes has been studied in an acid medium (pH1.5) containing silver ions (0.02gdm?3Ag+) and thermophilic bacteria (68°C). Preliminary tests on particulate electrodes made from graphite, elemental sulfur and Ag2S were included to determine the electrochemical response of reactants (Ag+) and products (S° and Ag2S) associated with the dissolution of chalcopyrite in the presence of silver. Massive chalcopyrite electrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solution and [Ag+]. As well as Ag2S, metallic silver was detected on the chalcopyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopyrite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of the electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two weeks did not improve the surface reactivity. However, in the initial stages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganisms.     

Double-layer capacitors composed of interconnected silver particles and with a high-frequency response

Porous and multi-layer network of interconnected silver particles is deposited by galvanic displacement on a technologically relevant substrate, silicon with an aluminum/copper film. The mean particle diameter is approximately 200 nm and the particle density in a single layer is 10⁹ particles per cm². Cyclic voltammetry and electrochemical impedance spectroscopy reveal that capacitance normalized to the electrode geometric area reaches a value of 1.7 ± 0.2 mF/cm², which is about two orders of magnitude higher than that observed on a smooth silver/electrolyte interface. The specific surface area of silver particles, which are assumed to be spherical, is 2.7 m²/g. The electrolyte accessible surface area is slightly larger (3.5 m²/g) due to the surface roughness of silver particles. The frequency response of the porous network of silver particles is analyzed using the transmission line model. The “knee” frequency is determined to be around 200 Hz. The described capacitor could find applications for special electronic circuits where a high-frequency response is needed.     

卤族元素对Ag电极电催化还原CO2的影响

通过在电解液中加入卤族元素，系统地研究了卤族元素对于CO的选择性和反应速率的影响。结果表明，卤族元素对于CO₂的还原反应具有促进作用，并按照Cl^- < Br^- < I^-的顺序递增。Cl^-和Br^-对CO₂还原反应和析氢反应都具有催化作用，而I^-的存在加快了CO的生成，对析氢反应没有明显影响。在过电势为590 mV时，CO在有I-溶液中的选择性是无I^-溶液的28倍。经过表征和分析后得出，I^-具有较强的吸附性能，通过化学吸附使催化剂表面形貌发生改变，CO的活性位增多，加快其反应速率。同时，I^-在反应过程中易向反应表面传输负电荷，增加与碳原子的相互作用，从而提高CO的生成速率。     

Electrochemical and spectroscopic measurements for stable nitroxyl radicals

A nitroxyl radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), is known to be oxidized electrochemically at 3.5 V versus lithium [4] and [5]. Since this reaction is reversible in the aprotic electrolyte, we can use it as a cathode reaction in lithium rechargeable battery. Some nitroxyl radical compounds which have different structures have been prepared and their electrochemical behavior and spectroscopic properties have been studied. The electrochemical measurements in aprotic electrolyte revealed that most nitroxyl radical compounds show reversible redox behavior similar to that of TEMPO independent of their structures in the range of −0.15-0.20 V versus Ag/Ag⁺ (3.69-4.04 V versus Li/Li⁺). The redox potentials for these materials were found to be predictable approximately by quantum calculations. Thus, various molecular designs tailored to desired redox potentials would be possible as active materials for lithium rechargeable batteries, and their specific capacities, mechanical properties and colors can be controlled within limits.     

Electrochimie du polynitrure de soufre dans les solvants non aqueux—I. Comportement dans l'acetonitrile

The electrochemical behaviour of polysulphur nitride was studied by cyclic voltametry in alkaline and silver salt acetonitrile solutions. In an alkaline salt solution during the cathodic polarization, superficial degradation of (SN)_x probably gives S₇N^? ions. In a silver perchlorate solution silver deposition was observed. It can be dissolved anodically. During the first anodic polarization, oxidation pic occurs. The quantity of electricity involved during this reaction is a function of the association constant of the electrolyte.