硫酸溶液中Ag+离子对Mn2+离子阳极氧化的催化作用

Anodic oxidation of Mn2+ and Ag+ ions and anodic oxidation of Mn2+ ion on platinum electrode in H2SO4 solution catalyzed by Ag+ ion are studied by using RRDE and triangle voltammetry techniques. Mn2+ ion is oxidized on the anode surface with adsorped OH group to form a certain compound containing Mn3+, which causes Mn2+difficult to be oxidized directly on anode. Near the potential of oxygen evolution from H2O decomposition, Ag+ ion is oxidized to form Ag2+ ion. This is the main reaction on anode because of its reversability. At higher potential silver oxide is formed on the anode. The oxide catalyzes the decomposition of H2O strongly. The anodic oxidation of Mn2+ion catalyzed by Ag+ takes place and Ag2+ ion and silver oxide are no longer the product of Ag+ anodic oxidation when Mn2+ exists in solution at the potential for Ag+ anodic oxidation. It is confirmed that the catalysis reaction is homogeneous and very fast.     

Electroprecipitation of Ag(II)/Ag(III) tetraphenylsulfonate porphyrin and electrocatalytic behavior of the films

The electrochemical precipitation on glassy carbon and gold electrodes of Ag(II) tetraphenylsulfonate porphyrin (Ag(II)TPPS) from aqueous HClO₄ solutions, is reported. Electrochemical quartz crystal microbalance (EQCM) results indicate the possible formation of an Ag(II)–Ag(III) porphyrin dimer species. This species is oxidized and reduced in two consecutive steps: oxidation at +0.31 and +0.36 V (vs. SCE) and reduction at +0.11 and +0.07 V. The films show catalytic behavior toward O₂ reduction in 10⁻² M HClO₄ at relatively low potentials (E<−0.1 V) but catalyze NO reduction at relatively high-reduction potentials (E<0.4 V). The electrochemical results seem to indicate that the catalytic cycle in the case of NO involves formation of Ag(II)TPPS–Ag(II)TPPS(NO)⁺ and its electroreduction to regenerate Ag(II)TPPS–Ag(III)TPPS and NO-reduction products.     

Correction to: The effect of small silver inclusions on the palladium activity in formicacid oxidation reaction and corrosion stability

A PdAg deposit containing ~ 25 at.% Ag is obtained by the electrochemical codeposition from an aqueous solution of Pd and Ag sulfates (Au support, 0.5 M H₂SO₄). The deposit is characterized by means of various physical, physicochemical, and electrochemical methods. The PdAg deposit demonstrates the ~ 2 times higher specific activity (per the electrochemically active surface area (EASA) of Pd) in the formic acid oxidation reaction (FAOR) as compared with the individual Pd deposit prepared under the same conditions. The effect of silver additions on the palladium activity depends on many factors. The corrosion stability of PdAg is studied in 0.5 M H₂SO₄ solution based on the overall cyclic voltammograms (CVAs) and also on anodic and cathodic half-cycles in the region E = 0.3 − 1.25 V (vs. reversible hydrogen electrode (RHE)). The electrochemical estimates are compared with the results of direct analytical determination of dissolution products in solution after anodic polarization of deposits. The total amounts of Pd dissolved substantially increase with incorporation of Ag, which is associated, first of all, with the considerable increase in the EASA; at the same time, the specific dissolution of Pd also substantially increases. The possible factors determining the active dissolution of PdAg deposits are discussed; in particular, the specific mechanism of their dissolution via silver adatoms is proposed.

     

Dealloying to Nanoporous Silver and Its Implementation as a Template Material for Construction of Nanotubular Mesoporous Bimetallic Nanostructures

Nanoporous silver (NPS) is fabricated by selectively dissolving Al from AgAl alloys in corrosive electrolytes at room temperature. Electron spectroscopy characterizations demonstrate that the NaOH electrolyte is beneficial to the formation of a three‐dimensional bicontinuous porous nanostructure with uniform and tunable pore and ligament dimensions of a few tens of nanometers, while processing in HCl electrolyte easily lead to coarsened porous nanostructures. The high‐surface‐area Ag nanostructures are demonstrated as novel effective template materials to the construction of nanotubular mesoporous Pt/Ag and Pd/Ag alloy structures, which are realized via room temperature galvanic replacement reactions with H₂PtCl₆ and K₂PdCl₄ solutions by adding a high concentration of Cl^? ions as a coordinating agent. Electrochemical measurements indicate that the resulting hollow and porous bimetallic nanostructures show enhanced electrocatalytic activities and CO‐tolerance with better durability toward methanol and formic acid oxidation due to alloying with Ag.     

Study of electrooxidation of binary electrolytic deposit palladium–bismuth deposited on graphite electrode surface

The phase structure of palladium–bismuth binary electrolytic deposit was studied. The electrodeposition of deposit components on the surface of a graphite electrode (GE) was carried out in situ. On current–voltage curves, the peak of bismuth electrooxidation, the peak of palladium electrooxidation and an additional peak at 0.15 V vs. Ag/AgCl are observed. The peak current at 0.15 V depends both on the concentration of palladium(II) ions and on that of bismuth(III) ions. The thermodynamic theory of alloys in the approximation of the theory of regular solutions was used for calculations. The mixing heat of the binary alloy components and the equilibrium potential of bismuth in the bismuth–palladium alloy are calculated. The calculated equilibrium potential of bismuth in an alloy with palladium is 0.12 V vs. Ag/AgCl which corresponds to the Bi₂Pd intermetallic compound (IMC). Investigation of the surface of a GE with a palladium–bismuth deposit with use of scanning electron microscope showed that the electrolytic deposit contains bismuth, palladium and the Bi₂Pd IMC. Peak at the potential of plus 0.15 V vs. Ag/AgCl is due to selective bismuth electrooxidation from the Bi₂Pd IMC.     

Kinetics of electrochemical reactions on the Ag(Hg)/Ag4RbI5 interface

The electrochemical behaviour of the Ag(Hg)/Ag₄RbI₅ interface is investigated by a potentiostatic pulse method. It is found that the rate-determining step of the electrode reaction is electron transfer with an exchange current density of 68 mA cm^–2 and a transfer coefficient of approximately 0.45. The order of the electrochemical reaction for silver oxidation is estimated from polarization investigations of silver amalgam in various concentrations. From this it is deduced that the mercury is ionized and is implanted in the electrolyte together with silver under anodic polarization: 15Ag+85Hg–100e^–→15Ag⁺+85Hg⁺. From comparison of the electrochemical behaviour of the Ag(Hg)/Ag₄RbI₅ and Ag/Ag₄RbI₅ interfaces it is concluded that the rate of anodic silver dissolution on the Ag/Ag₄RbI₅ interface is limited by crystallization effects. Electronic Publication     

Destruction of butyraldehyde isomers using silver catalyzed electrochemical oxidation

The destruction of butyraldehyde isomers has been studied using a silver catalyzed electrochemical oxidation technique. The destruction rates of nand iso-butyraldehydes were measured as a function of the concentrations of butyraldehyde isomers, silver and nitric acid in aqueous solutions, anode potential and temperature. More than 99% of n-butyraldehyde in 3M nitric acid was destroyed within 50 minutes by electrochemical oxidation at the anode potential of 1.6V versus a reference saturated calomel electrode (SCE). The process was found to be applicable to the destruction of butyraldehyde isomers in nitric acid solutions.     

Electrochemical oxidation of californium in carbonae solutions

The electrolysis of trivalent californium, terbium and praseodimium in 2M K₂CO₃ solutions at pH 13.2 results in a partial oxidation of the trivalent ions to a higher oxidation state. Absorption spectra of Cf/III/ in 1M HCLO₄ and in 2M K₂O₃ and that of oxidized californium in carbonate solution have been recorded. Incomplete oxidation is accounted to a reducing species generated at high anode potentials.     

Cyclic voltammetry on Ag(111) and Ag(100) faces in sodium hydroxide solutions

The electrochemical behavior of silver (100) and (111) single crystal surfaces was examined by cyclic voltammetry in aqueous NaOH solution. In the `double layer' region (between −1.2 and 0.1 V (SCE)) adsorption of OH⁻ ions followed by phase transformation into an Ag–OH monolayer was found to take place. The difference in peak potentials recorded in 0.1 and 0.01 mol dm⁻³ NaOH solutions of about 60 mV indicates that one electron is exchanged in the overall electrochemical reaction, implying a complete charge transfer between OH⁻ ions and the silver surface. The adsorption process has been modeled to a Frumkin adsorption isotherm. Further oxidation of silver into Ag₂O takes place at more positive potentials. The formation of bulk Ag₂O results in considerable change to the original single crystal surface. This is likely to be due to roughening of the silver surface as a consequence of the formation and reduction of the oxide.     

Silver migration at the Ag|Sm0.2Ce0.8O1.9 interface

The behavior of a silver electrode contacting Ce_0.8Sm_0.2O_1.9 (samaria-doped ceria or SDC) electrolyte under external cathodic polarization in the temperature range 350–700 °C was examined by means of long-term polarization experiments, scanning electron microscopy, and electrochemical impedance spectroscopy. A silver deposit is formed around the silver cathode via a surface migration mechanism without the occurrence of the gas-phase transport phenomenon during polarization. This results in an increase in both the electrode-electrolyte contact area and the triple-phase boundary length, which in turn causes decreases in charge transfer resistance and electrolyte resistance.     

Morphology of silver electrolytically precipitated from acetonitrile solutions of silver nitrate

The electrochemical deposition of silver was investigated from 0.01–0.1 M acetonitrile solutions of Ag NO₃ by stationary and pulse current. An effect of the main parameters of the pulse current (duration and pause of pulse), concentrations of silver ions, time of electrolysis, and nature of support was considered on form and size of structural particles of deposit.     

Decomposition Studies of Aqueous Phase Ligands Used in Advanced Reprocessing Flowsheets

Two potential methods for decomposing organic ligands in nitric acid have been studied using acetic acid and diethylenetriaminepentaacetic acid (DTPA) as examples; these methods were oxidation by nitric acid at elevated temperatures (70-110 °C) and electrochemical oxidation, both direct and mediated electrochemical oxidation. Based on total carbon measurements, acetic acid proved to be rather stable against nitric acid oxidation whereas 60-80% of DTPA was decomposed at 100-110°C. Electrochemical oxidation methods were generally more effective in decomposing acetic acid and DTPA with mediated electrochemical oxidation using Ag(II) ions the most effective method under the conditions tested, with ∼80 and >90% loss of carbon from acetic acid and DTPA solutions respectively, at ambient temperature in 6 M HNO₃.     

Nature of the silver precipitation obtained by cementation from thiosulphate solutions

The morphology and composition of the deposits formed on the surface of magnesium disk during cementation from thiosulphate solutions (0.0025–0.1M) [Ag(S₂O₃)₂]³⁻ + 0.5M S₂O₃ ²⁻ have been studied. A porous deposit with low adhesion is formed on the surface of the magnesium metal substrate. Within a wide range of [Ag(S₂O₃)₂]³⁻ ion concentrations, sulfur as well as silver are constituents of the deposit at the initial stages of cementation and at the end of the reaction. This is attributed to the electrochemical behaviour of magnesium in thiosulphate solutions resulting in the exceeding of current limit on cathode for pure silver reduction. Hence, parallel electrochemical reactions take place that are very close in their values to the standard redox potentials of reduction of [Ag(S₂O₃)₂]³⁻ ions to Ag⁰ and S₂O₃2− ions to S²⁻. Sulfur content in the cement deposits increases with the decrease in [Ag(S₂O₃)₂]³⁻ ion concentration and increase in cementation time. This tendency is also observed with the decreasing solution temperature.     

Effect of process parameters on the concentration,current efficiency and energy consumption of electro-generated silver(II)

Electro-membrane generation of Ag(II) in nitric acid was experimentally explored in a three-electrode laboratory cell with respect to various operating parameters. DSA-O₂, titanium plate and saturated Ag/AgCl were employed as the anode, cathode and reference electrode, respectively. The considered process parameters included anolyte temperature and Ag(I) initial concentration, electrolysis time, current density and supporting electrolyte concentration. Parameter effect on the Ag(II) concentration, current density and energy consumption were determined by the Taguchi and ANOVA methods for test design and data analysis, respectively. The results revealed that current density, AgNO₃ concentration and temperature had noticeable effect on the generation of Ag(II). On the other hand, AgNO₃ concentration and current density showed the most dominant effect on the Ag(II) current efficiency: 48.5% and 30.3%, respectively. AgNO₃ concentration and current density were also found to have the highest effect on the energy consumption: 72.4% and 15.9%, respectively. Validity of the Taguchi method was also assessed by collecting the actual data.     

Polyaniline‐Modified Silver and Binary Silver‐Cobalt Catalysts for Oxygen Reduction Reaction

Novel dendrite‐like silver particles were electrodeposited on Ti substrates from a supporting electrolyte‐free 30 mmol L^?1 Ag(NH₃)₂⁺ solution, to synthesize the den‐Ag/Ti electrode. Binary Ag_xCo_y/Ti electrodes with different Ag:Co atomic ratios were further obtained by electrodeposition of Co particles on the den‐Ag/Ti electrode. Polyaniline (PANI) modified den‐Ag/Ti and Ag_xCo_y/Ti electrodes, PANI(n)‐den‐Ag/Ti and PANI(n)‐Ag_xCo_y/Ti, were also obtained by cyclic voltammetry at different numbers of cycles (n) in acidic and alkaline solutions containing aniline, respectively. All these electrodes exhibit high electroactivity for oxygen reduction reaction (ORR) in alkaline solution and their electroactivities follow the order: PANI(15)‐Ag₃₁Co₆₉/Ti>Ag₃₁Co₆₉/Ti>PANI(20)‐den‐Ag/Ti>den‐Ag/Ti. Among them, PANI(15)‐Ag₃₁Co₆₉/Ti displays the highest electrocatalytic activity for ORR with a much positive onset potential of 0 V (vs. Ag/AgCl) and a high ORR current density of 1.2 mA cm^?2 at ?0.12 V (vs. Ag/AgCl). The electrocatalysts are electrochemically insensitive to methanol and ethanol oxidation, and, as cathode electrocatalysts of direct alcohol fuel cells, can resist poisoning by the possible alcohol crossover from the anode.     

Lead(II) Sulfide. Synthesis in Lead(II) Tetraoxophosphate(V) Gelatin-immobilized Matrix Implantates and Sorption Activity Toward Silver(I) Ions

Processes that occur in lead(II) tetraoxophosphate(V) gelatin-immobilized matrix systems on their contact with aqueous solutions containing the sulfide anion S₂ ^- were studied. As a result of this contact, lead(II) sulfide is formed. The sorption activity of the resulting metal sulfide gelatin-immobilized matrix systems with respect to Ag(I) ions is associated with substitution of Pb(II) by Ag(I) ions.     

Composite cathode materials Ag-Ba0.5Sr0.5Co0.8Fe0.2O3 for solid oxide fuel cells

Silver-Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) cathodes were prepared in two ways. In the first method, Ag-BSCF composite powder was prepared in ethanol solution, where Ag nanoparticles serving as a component in the preparation of Ag-BSCF composite cathodes had been previously obtained via one-step synthesis in absolute ethanol using a neutral polymer (polyvinylpyrrolidone). To the best of our knowledge, this is the first study to use a Ag sol obtained by the above method for preparation of Ag-BSCF composite powder. Then, a paste containing this powder was screen-printed on a Sm_0.2Ce_0.8O_1.9 electrolyte and sintered at 1,000 °C. In the second technique, an aqueous solution of AgNO₃ was added to a previously sintered BSCF cathode, which was then sintered again at 800 °C. The oxygen reduction reaction at the quasi-point BSCF cathode on the Sm_0.2Ce_0.8O_1.9 electrolyte was tested by electrochemical impedance spectroscopy at different oxygen concentrations in three electrode setup. The continuous decrease of polarization resistance was observed under polarization ?0.5 V at 600 °C. The comparative studies of both obtained composite Ag-BSCF materials were performed in hydrogen-oxygen IT-SOFC involving samaria-doped ceria as an electrolyte and Ni-Gd_0.2Ce_0.8O_1.9 anode. In both cases, the addition of silver to the cathode caused an increase in current and power density compared with an IT-SOFC built with the same components but involving a monophase BSFC cathode material.     

Role of adsorption phenomena in the electrocatalytic reduction of nitric acid at a platinized platinum electrode

The electrocatalytic reduction of nitric acid was studied at a platinized platinum electrode in the presence of different supporting electrolytes. It has been found that at low HNO₃ concentrations the polarization behaviour, the shape of the polarization curves and the reduction rate depend significantly upon the supporting electrolyte. (For instance, one maximum in HClO₄, two maxima in H₂SO₄.)With increasing nitric acid concentrations the differences in the character of the polarization curves gradually disappear. The phenomena observed can be explained by the role of competitive adsorption between nitric acid and ions of the supporting electrolyte. Strongly adsorbing chloride ions exert a very pronounced influence on the reduction rate and induce periodical phenomena under certain experimental conditions. The adsorption of chloride ions was studied by a radiotracer method. Results of this study confirm the view on the importance of adsorption competition in the polarization behaviour. On the basis of simple adsorption models an attempt was made to explain the phenomena observed.     

Investigation of the anodic decomposition of the solid electrolyte RbCu4Cl3I2

The process of electrochemical decomposition of the solid electrolyte RbCu₄Cl₃I₂ at a vitreous carbon electrode has been investigated. The anodic decomposition of the electrolyte occurs in two steps. At first, the oxidizing electrode reaction of Cu⁺ ions to Cu²⁺ ions takes place at potentials higher than 0.57 V and a layer of decomposition products is formed on the electrode surface, including the divalent copper compound RbCuCl₃. Then the oxidizing reaction of I^– ions occurs at potentials higher than approximately 0.67 V, with deposition of an iodine layer onto the electrode surface. The deposition rate of the layers of decomposition products is controlled by instantaneous nucleation and two-dimensional growth of the deposit. The total thickness of the passivating layer of decomposition products on the anode is equal to ca. 1 μm. Electronic Publication     

Silver as anode in cryolite—alumina-based melts

The anodic behaviour of silver was investigated in cryolite—alumina-based melt. Silver has a lower melting point (ca. 960°C) than the other metals considered as possible inert materials for aluminium electrolysis. The working temperature used in aluminium industry is approximately 960°C, depending on the melt composition. Therefore, the stability of silver during the anodic process was tested at 870°C in an acidic electrolyte consisting of 65.5 mass % Na₃AlF₆ + 22.9 mass % AlF₃ + 5.7 mass % CaF₂ + 3.9 mass % LiF + 2 mass % Al₂O₃ with the melting point ca. 850°C. The electrolyte without alumina was prepared as well, with the melting point ca. 860°C. The resulting cryolite ratio (CR = n(NaF)/n(AlF₃)) for both electrolytes was equal to 1.6. The behaviour of the silver anode was studied by voltammetry measurements. The electrochemical study showed that an oxidation reaction occurred at a potential below the oxygen evolution potential. Silver was not found to be stable under oxygen evolution. The degradation of the silver anode was apparent after electrolysis.