A sustainable mediated electrochemical process for the abatement of NOx from simulated flue gas by using Ag(I)/Ag(II) redox mediators

Electrochemical removal of NO and NO₂ by using Ag(I)/Ag(II) redox mediator system in nitric acid medium by two-stage scrubbing process was investigated. Experiments were carried out for the complete removal of NO and NO₂ from the stimulated flue gas at room temperature and atmospheric pressure. The process parameters like current density, Ag(I) concentration, HNO₃ concentration, initial concentration of NO, Ag(I) concentration and temperature were studied and optimized. A removal efficiency of >99% was achieved using this sustainable redox process. Ag(II)/Ag(I) can be regenerated and reused for the scrubbing of waste gases continuously and there is no other gases emission during scrubbing.     

Deep desulfurization of gasoline using ion-exchange zeolites: Cu(I)- and Ag(I)-beta

Solid adsorbents Cu(I) and Ag(I) metal exchanged beta zeolites were prepared by solid-state ion-exchange (SSIE) method. Crystallographic structure of the prepared adsorbents has been characterized by XRD analysis. The texture of the prepared adsorbents was investigated using N₂ sorption. Pyridine IR measurements have been carried out to investigate the nature of the acid sites of the adsorbents. The deep-desulfurization performance of such adsorbents has been evaluated through fixed-bed adsorption technique with model gasoline containing thiophene and benzothiophene at ambient temperature and pressure. The obtained results revealed that the breakthrough capacities of Cu(I)- and Ag(I)-beta zeolite with the optimized Cu⁺ or Ag⁺ content are 0.239 mmol S/g and 0.237 mmol S/g, respectively. The remaining sulfur in the desulfurized gasoline is less than 1 ppmw. Their desulfurization capacity for actual FCC gasoline blend is reduced about 30% due to the competitive adsorption from olefins and aromatics. However, The capacity regeneration of Cu(I)- and Ag(I)-beta zeolite sorbents was carried out for 9 times. It is more than 95% recovery of desulfurization after the first regeneration, and it keeps little reduction after subsequent 8 times of regeneration. Such studies included the effect factors on desulfurization performance, such as metal exchange content, SiO₂/Al₂O₃ ratio, acidity, and other texture properties of the zeolite etc.     

Novel method for removal of NO x and SO2 by sustainable electrochemical process using Ag(I)/Ag(II) redox mediator

The objective of this work was to develop a process for removal of industrial waste gases like NO, NO₂ and SO₂ by electrochemically generated Ag(I)/Ag(II) redox mediator system in aqueous nitric acid medium. 100% removal efficiencies were achieved in these studies for removal of NO _x and SO₂ with Ag(II) ions in room temperature and atmospheric pressure. This Ag(I)/Ag(II) redox mediator system can be regenerated continuously during the scrubbing process.     

Role of Ag and Cu as an interfacial layer on the electrochemical performance of Ni/Ag/ Co3(PO4)2 and Ni/Cu/Co3(PO4)2 electrodes for hybrid energy storage devices

Hybrid energy storage devices unifying the effect of both batteries (high specific energy) and capacitors (high specific power) have emerged in recent years due to their admirable cyclic stability and charge storage capability. Considerable amount of research has been conducted to optimize the electrode materials capable of showing good electrochemical characteristics. Here, we report the influence of interfacial layer of Ag and Cu on the electrochemical performance of cobalt phosphate electrode. Sputtering of Ag and Cu has been amalgamated to improve the interfacial properties of the current collector. After initial structural and morphological study, detailed electrochemical characterizations have been employed for Ni/Ag/Co₃(PO₄)₂ and Ni/Cu/Co₃(PO₄)₂ have been investigated by utilizing various characterizations. Hybrid device was fabricated using the combination Ni/Ag/Co₃(PO₄)₂ since, Ag possess impressive electrochemical characteristics and electrical conductivity. The fabricated device has achieved the energy density of 65.8 Whkg^?1 and power density of 6012 Wkg^-1 along with the 85.6% retention after 1000 GCD cycles showing the device is stable enough. These results make the hybrid device a potential candidate for supercapattery applications.     

Comportement electrochimique et reactivite dy systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—II. Etude du couple carbonate de propylene—II. Etude du couple AgII(bipy)2+/AgI(bipy)+

Due to the reactivity expected in the presence of an excess Ag⁺ with respect to the 1–2 stoichiometry (Ag-bipy), the electrochemical behaviour of the Ag(II)/Ag(I)-bipyridine system has been investigated using voltammetry and coulometry. The change in the current-potential curves has been rationalized taking into account an equilibrium between different species of Ag(I) in neutral or acidic media. Changes of the solution nature (ratio C_bipy/C_Ag) or pH actually led to the formation of reactive species.     

Comportement electrochimique et reactivite du systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—III. Etude du mecanisme et de la cinetique de la reaction d'oxydation catalytique de la bipyridine

The electrochemical behaviour of the Ag(II)/Ag(I)-bipyridine system has been investigated in solutions containing bipyridine in excess with respect to the Ag⁺-bipy: 1–2 stoichiometry. The nature of the coupled chemical reaction indicates a chemical catalysis of an electrochemical reaction. The rate constant of the reaction of destruction of the intermediate complex (k₂ = 1.8 × 10^?3s^?1) has been calculated from measurements performed during electrolysis of Ag^I(bipy)⁺₂-bipy solutions.     

Studying the localized deposition of Ag nanoparticles on self-assembled monolayers by scanning electrochemical microscopy (SECM)

The local deposition of Ag nanoparticles (NPs) on ω-mercaptoalkanoic acid, HS(CH₂)_nCO₂H, (n = 2, 10) self-assembled monolayers (SAMs) by scanning electrochemical microscopy (SECM) is reported. We found that the presence of a SAM had a pronounced effect on Ag deposition. Experiments were conducted by applying different potentials to an Au(1 1 1) substrate either in the presence of a constant concentration of Ag⁺ ions in solution (bulk deposition) or by generating a flux of Ag⁺ from an Ag microelectrode that was positioned close to the Au(1 1 1) substrate (SECM deposition). SECM was used for generating a controlled flux of silver ions by anodic dissolution of an Ag microelectrode close to the SAMs modified Au(1 1 1). We found that the shape of the NPs was affected by the length of the carbon-chain of the SAM. Tetrahedral NPs were obtained on bare Au(1 1 1) surfaces while rod like and cubic Ag NPs were deposited onto 3-mercaptopropanoic acid (MPA) and 11-mercaptoundecanoic acid (MUA) SAMs, respectively. The size and shape of the deposited NPs were influenced by the deposition potential.We conclude that the shape and distribution of locally deposited Ag NPs on Au(1 1 1) can be controlled by modification of the substrate with a SAM and through controlling the Ag⁺ flux generated by SECM.     

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.     

Electrochemical window of molten LiCl-KCl-CaCl2 and the Ag/Ag reference electrode

The electrochemical window of an LiCl-KCl-CaCl₂ eutectic melt (52.3:11.6:36.1 mol%) was determined by cyclic voltammetry and open-circuit potentiometry at 723-873 K. The reaction at the anodic limit was confirmed to be Cl₂ gas evolution. The reaction at the cathodic limit was found to be a liquid Ca-Li alloy formation on the basis of ICP analysis of the deposits. An Ag⁺/Ag reference electrode separated with a Pyrex membrane showed good stability for more than 1 week. The standard electrode potential of Ag⁺/Ag was determined in the temperature range of 723-823 K by measuring the potential of a silver electrode in different concentrations of Ag⁺ ions.     

Formation of double-surface-silvered polyimide films via a direct ion-exchange self-metallization technique: The case of BPADA/ODA and [Ag(NH3)2]+

Double-surface-silvered polyimide (PI) films have been successfully fabricated via a direct ion-exchange self-metallization method using silver ammonia complex cation ([Ag(NH₃)₂]⁺) as silver resource and bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride/4,4′-oxydianiline (BPADA/ODA)-based poly(amic acid) (PAA) as the PI precursor. The alkaline characteristic of the silver precursor dramatically improves the efficiency of the ion exchange and film metallization process. By using an aqueous [Ag(NH₃)₂]⁺ solution with a concentration of only 0.01M and an ion-exchange time of only 5 min, metallized films with desirable performance could be easily obtained by simply heating the silver(I)-doped PAA films to 300°C. The strong hydrolysis effect of the basic [Ag(NH₃)₂]⁺ cations on the flexible and acidic BPADA/ODA PAA chains was observed during the ion exchange process by the quantitative evaluation of the mass loss of PAA matrix. Nevertheless, under the present experimental conditions, the final metallized film essentially retained the basic structural, thermal, and mechanical properties of the pristine PI, which make it a truly applicable material. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Comportement electrochimique et reactivite du systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—IV. Etude du mecanisme de l'oxydation catalytique de la methyl-4 pyridine et de la dimethyl-2,6 pyridine

The reactivity of the Ag(II)/Ag(I)-bipyridine system towards substituted pyridines L (L = 4-Mepy, 2,6-diMepy) has been investigated during electrolysis of the Ag^I(bipy)⁺ complex in various medium conditions. This study, using voltammetry, coulometry and EPR points out the influence of the substrate geometry upon the catalytic oxidation mechanism. The processes, involving mixed complexes of silver(II) Ag^II(bipy)L²⁺_n (n = 1,2), are relevant of a chemical catalysis of electrochemical oxidations.     

Synthesis of 2-D nanostructured BiVO4:Ag hybrid as an efficient electrode material for supercapacitors

2-D BiVO₄ nanosheets with monoclinic phase were synthesized at room temperature, and incorporated with Ag to form BiVO₄:Ag hybrid materials. The experiments demonstrated that doping Ag has largely increased the electrochemical performances of supercapacitor. Furthermore, the specific capacitance can reach up to 109 F g^–1 at 1 A g^–1 (the undoped one is of 27 F g^–1); energy density has enhanced to 15.2 Wh kg^–1 compared with the pristine one without Ag (3.8 Wh kg^–1). Therefore, doping Ag into bismuth-based compound provides us an alternative approach for the synthesis of 2-D nanostructured hybrid as an efficient electrode material for supercapacitors     

Mecanisme de la passivation electrochimique du platine en milieu chlorures fondus premiere partie:: Milieu deoxygene

The mechanism of platinum electrochemical passivation in molten LiCl-KCl at 450°C has been examined by the chronopotentiometry.This passivation due to precipitation of a double platinum and potassium chloride (K₂PtCl₆) allows the verification of two kinds of relationships according to the temperature and current density range. At low temperature (<450°C) and current density (<250 mA/cm²), a faradaic relation (Iτ = Cte) is observed, while at higher temperature (450°C) and current density (250 mA/cm²), a relation I√τ = Cte is established.The activation energies required for the transport process of platinum ions are determined both in the eutectic and in the K₂PtCl₆ crystals. By the comparison of the activation energy necessary for the formation of a passivating layer, it may be concluded that the mechanism of thickening in the solid K₂PtCl₆ layer at high temperature is by means of a diffusion process.On the basis of these results, a theory is proposed. It explains the two kinds of law relevant to experimental conditions. It takes into account the initial conditions and it is based on the vacancy theories characteristic of oxidation.     

Studies on promising cell performance with H2SO4 as the catholyte for electrogeneration of Ag2+ from Ag+ in HNO3 anolyte in mediated electrochemical oxidation process

Electrochemical performance of a divided cell with electrogeneration of Ag²⁺ from Ag⁺ in 6 M HNO₃ anolyte has been studied with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte. This work arose because in mediated electrochemical oxidation (MEO) processes with Ag(II)/Ag(I) redox mediator, HNO₃ is generally used as catholyte, which, however, produces NO _x gases in the cathode compartment. The performance of the cell with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte has been compared in terms of (i) the acid concentration in the cathode compartment, (ii) the Ag⁺ to Ag²⁺ conversion efficiency in the anolyte, (iii) the migration of Ag⁺ from anolyte to catholyte across the membrane separator, and (iv) the cell voltage. Studies with various concentrations of H₂SO₄ catholyte have been carried-out, and the cathode surfaces have been analyzed by SEM and EDXA; similarly, the precipitated material collected in the cathode compartment at higher H₂SO₄ concentrations has been analyzed by XRD to understand the underlying processes. The various beneficial effects in using H₂SO₄ as catholyte have been presented. A simple cathode surface renewal method relatively free from Ag deposit has been suggested.     

Copper Recovery from EDTA − Chelating — Copper Wastewater in a Fluidized Bed

Copper recovery from ethylenediaminetetraacetic acid (EDTA)‐chelating‐Cu wastewater was conducted by means of electrochemical process using a Cu cathode and a PbO₂ anode. In this study, the effects of operating parameters including current density, initial pH, and electrolytic‐cell mode on the quality of copper deposit and current efficiency were studied. It was found that the key factors influencing deposit quality and current efficiency are current density and electrolytic cell mode as well as interactions between them. A better quality of copper deposit with high current efficiency can be obtained at lower current density (2.5 mA/cm²) in this fluidized packed‐bed electrolytic cell.     

Adsorption of Cd(II), Pb(II), and Ag(I) in aqueous solution on hollow chitosan microspheres

Cross‐linked chitosans synthesized by the inverse emulsion cross‐link method were used to investigate adsorption of three metal ions [Cd(II), Pb(II), and Ag(I)] in an aqueous solution. The chitosan microsphere, was characterized by FTIR and SEM, and adsorption of Cd(II), Pb(II), and Ag(I) ions onto a cross‐linked chitosan was examined through analysis of pH, agitation time, temperature, and initial concentration of the metal. The order of adsorption capacity for the three metal ions was Cd²⁺ > Pb²⁺ > Ag⁺. This method showed that adsorption of the three metal ions in an aqueous solution followed the monolayer coverage of the adsorbents through physical adsorption phenomena and coordination because the amino (? NH₂) and/or hydroxy (? OH) groups on chitosan chains serve as coordination sites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

Synthesis and electrochemical performance of Li4Ti5O12/Ag composite prepared by electroless plating

To improve the electrochemical and anti flatulence performance of Li₄Ti₅O₁₂, Ag modified Li₄Ti₅O₁₂ (LTO) with high electrochemical performance as anode materials for lithium-ion battery was synthesized successfully by two-step solid phase sintering and subsequent electroless plating process in the presence of silver. The effect of Ag modification on the physical and electrochemical properties were investigated by the extensive material characterization of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM). The results showed that the samples possessed single spinel structure, it could be observed that the LTO/Ag composite and the pure LTO shared the same vibration frequencies, which indicated that the crystal structure of LTO didn’t change after electroless plating process, and the particles were uniformly and regularly shaped within 0.5–1.0 µm. Electrochemical performance of the samples were evaluated by the charging and discharging, cyclic voltammetry, electrochemical impedance spectroscopy, cycling and rate tests. It's obvious that the LTO/Ag composite prepared at the 10 min of electroless plating showed the highest performance with capacitance of 182.3 mA h/g at 0.2 C current rates. What's more, the LTO/Ag composites still maintained 92% of its initial capacity even after 50 charge/discharge cycles. Modification of appropriate Ag not only benefits the reversible intercalation and deintercalation of Li⁺, but also improves the diffusion coefficient of lithium ion. Besides, modification of appropriate Ag lower electrochemical polarization leads to higher conductivity and cycle performance of LTO, which is consistent with the results of the best reversible capacities.     

Catalytic and electrocatalytic oxidation of propane on V-Mg-O and V-Mg-O (Ag) catalysts

Vanadium magnesium oxide catalysts prepared in this work were found active in selective oxidation of propane to propene. A selectivity as high as 79% was obtained at 10% conversion (813 K). No oxygenated or C₂ products were detected and the catalysts were found to undergo no change in activity over many weeks of operation. Under electrochemical pumping of oxygen (EOP) towards the catalyst (with oxygen present in the feed gas), both conversion and selectivity were found to increase slightly as external current increased, indicating the effect of electrical current can be exhibited by an oxide catalyst. However, in the absence of oxygen in the feed gas, EOP could lead to an even higher selectivity: 84 and 86.9% respectively for a 24 V-Mg-O and a 24 V-Mg-O (Ag) (1/2) catalyst. The overall results obtained suggest that electrochemically supplied oxygen is more selective towards C₃H₆. Mechanisms of both catalytic and electrocatalytic oxidation of propane were tentatively suggested, with surface oxygen ion vacancy identified as active surface species and the rate determining step involving heterolytic splitting of the C₃H₈ molecule to form a surface bonded C₃H ₇ ^– ion and a surface hydroxyl ion. The higher selectivity towards C₃H₆ in case of EOP was explained on this basis. While mixing with Ag powder was found to improve significantly the electrocatalytic performance of vanadium magnesium oxide, its role appears to be non-chemical: it simply gives rise to a larger area of the gas/catalyst/Ag electrode interface.     

Analysis of electrochemical mechanism of coprecipitated nano-Ag4Bi2O5 as super high charge–discharge rate cathode materials for aqueous rechargeable battery

Nano Ag₄Bi₂O₅ as a novel cathode material of rechargeable alkaline batteries was successfully synthesized by precise control of precipitation reaction. KOH solution was used as precipitant and a mixture of AgNO₃ and Bi(NO₃)₃ as Ag–Bi source. The experimental results indicate that concentration of KOH, reaction temperature and PH value have the effects on the structure and electrochemical property of the product. The material was characterized by means of XRD, FSEM and TG–DSC. The results show that the sample is single crystals with 50–100 nm in width and 600–800 nm in length. The electrochemical performances of Ag₄Bi₂O₅ in the alkaline electrolyte were measured by galvanostatic method and cyclic voltammetry tests through film electrode. The sample shows three typical procedures during the charge–discharge, corresponding to Ag(II)–Ag(I), Ag(I)–Ag(0) and Bi(III)–Bi(0) transformation processes. This result is also verified by XRD tests. The Ag₄Bi₂O₅ electrode has excellent electrochemical properties. It undergoes a current density as high as 20 A g^?1, which greatly reduces charge time down to 55.9 s. The electrode offers a cycling capacity of 330 mAh g^?1 and a cycling life more than 400 cycles at 1–2 A g^?1.