Silver Cathode Research Articles

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction.

Invited for this month's cover is the group of Tom Rufford at the University of Queensland. The image shows how choline chloride and urea in a reline solution interact with the surface of a silver cathode to enhance the selectivity of electrochemical CO2 reduction to CO. The Full Paper itself is available at 10.1002/cssc.201902433.

Direct Electrochemical Reduction of Acetochlor at Carbon and Silver Cathodes in Dimethylformamide

Cyclic voltammetry and controlled-potential (bulk) electrolysis have been employed to investigate the direct electrochemical reduction of acetochlor (1) at carbon and silver cathodes in dimethylformamide. Voltammograms of 1 exhibit a single irreversible cathodic peak at both cathode materials. Catalytic properties of silver towards carbon–halogen bond cleavage are evidenced by a positive shift in the reduction of acetochlor as compared to the more inert glassy carbon electrode. Voltammograms in the presence of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and comparisons of calculated relative interaction energies between acetochlor, possible intermediates, and deschloroacetochlor in the presence of different proton donors, suggest strong hydrogen-bonding interactions between HFIP and a carbanion intermediate. Addition of HFIP to electrolysis conditions promotes complete reduction at both cathode materials, with formation of deschloroacetochlor in high yields. In deuterium labelling studies, the use of DMF-d7 led to no evidence for deuterium atom incorporation. However, when HFIP-OD or D2O were employed as a proton source, substantial amounts of deuterated deschloroacetochlor were observed. A mechanism for the reduction of acetochlor is proposed, in which radical intermediates do not play a significant role in reduction, rather a carbanion intermediate pathway is followed.

Cathodic electrochemical deposition: a new strategy to enhance the activity and stability of silver cathodes for thin-film solid oxide fuel cells

Cathodic electrochemical deposition-treated silver cathodes for solid oxide fuel cell achieved 40% enhanced peak power density and 50 hour thermal stability.

Reduction of carbon dioxide at a plasmonically active copper-silver cathode.

Electrochemically deposited copper nanostructures were coated with silver to create a plasmonically active cathode for carbon dioxide (CO2) reduction. Illumination with 365 nm light, close to the peak plasmon resonance of silver, selectively enhanced 5 of the 14 typically observed copper CO2 reduction products while simultaneously suppressing hydrogen evolution. At low overpotentials, carbon monoxide was promoted in the light and at high overpotentials ethylene, methane, formate, and allyl alcohol were enhanced upon illumination; generally C1 products and C2/C3 products containing a double carbon bond were selectively promoted under illumination. Temperature-dependent product analysis in the dark showed that local heating is not the cause of these selectivity changes. While the exact plasmonic mechanism is still unknown, these results demonstrate the potential for enhancing CO2 reduction selectivity at copper electrodes using plasmonics.

Electrochemical Properties of Silver-Zinc Secondary Battery

The forthcoming green energy era strongly demands a next generation energy storage systems with much higher energy/power density, environmental friendliness, stability, etc. In relation to this, much effort has been made to explore the possible use of conventional primary battery in an electrically rechargeable form. Various alkaline batteries have been proposed as a candidate. Among this, silver-oxide battery draws a special attention because it has flat discharge voltage, high energy density (200 Wh/kg, 750 Wh/dm3) and superior rate performance. In addition, it is much safer and easier to recycle, as compared to lithium-ion batteries. A silver-oxide battery is often called a silver-zinc battery when it is designed to be electrically rechargeable. Like its primary form, it is desirable to minimize the content of expensive silver, i.e., the design needs to be cathode-limited. Accordingly, the characteristics of silver-zinc battery might be strongly affected by the behavior of silver cathode. Based on the works on the silver anodization, it has been reported that silver is transformed to Ag2O and then AgO during anodic oxidation and the latter AgO formation needs relatively large driving force. In spite of many data on the anodization process of silver, however, there has been little information about the battery performance of silver-zinc secondary battery. Moreover, as far as we know, the systematic study on its electrochemical characteristics is extremely lacking. The work provides an in-depth investigation of silver-zinc battery. In particular, the electrochemical properties and battery performance were systematically investigated at different charging/discharging rate, operating temperature, state of charge (SoC), etc. For this purpose, cathode-limited silver-zinc battery was fabricated using well-defined silver thin film and was analyzed by a variety of electrochemical techniques such as galvanostatic/potentiostatic methods, cyclic voltammetry, and impedance spectroscopy. From the combination of electrochemical, compositional, and structural analyses, the transformation of silver to Ag2O and AgO, and vice versa process was thoroughly investigated. For example, figure shows the SEM images and the corresponding XRD patterns of silver cathode at different SoCs. Porosity of products (Ag2O, AgO) gets increased with the SoC and the diffraction intensities of substrate and products are accordingly varied. In this presentation, the charging/discharging mechanism of silver-zinc battery will be systematically explored and its uniqueness will be highlighted from the viewpoint of the kinetics of electrochemical reactions. Moreover, the cycling performance and the factors governing the capacity and efficiency degradation will be discussed. Figure 1

Electrocatalytic Processes for the Valorization of CO2: Synthesis of Cyanobenzoic Acid Using Eco-Friendly Strategies

Carbon dioxide (CO2) is a known greenhouse gas, and is the most important contributor to global warming. Therefore, one of the main challenges is to either eliminate or reuse it through the synthesis of value-added products, such as carboxylated derivatives. One of the most promising approaches for activating, capturing, and valorizing CO2 is the use of electrochemical techniques. In the current manuscript, we described an electrocarboxylation route for synthesizing 4-cyanobenzoic acid by valorizing CO2 through the synergistic use of electrochemical techniques (“green technology”) and ionic liquids (ILs) (“green solvents”)—two of the major entries in the general green chemistry tool kit. Moreover, the use of silver cathodes and ILs enabled the electrochemical potential applied to be reduced by more than 0.4 V. The “green” synthesis of those derivatives would provide a suitable environmentally friendly process for the design of plasticizers based on phthalate derivatives.

Electrochemical Reduction of Acetochlor at Carbon and Silver Cathodes in Dimethylformamide

Chloroacetamides are a popular class of herbicides often used against weeds in a variety of major crops, such as corn, cotton, rice, and soybeans.1 One such herbicide is acetochlor or 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide that, since its registration in 1994, has become commonly used in the United States.2 Although acute and chronic toxicological effects in humans of acetochlor at low environmental exposures are still unknown, animal tests have shown in some species the development of lung tumors, nasal epithelia, and thyroid cancer; for that reason, the U.S. EPA classifies acetochlor as likely to be carcinogenic in humans.3,4 This project’s primary objective is to investigate the electrochemical behavior of acetochlor and to develop a possible degradation method for acetochlor as well as other chloroacetamide-type herbicides. To the best of our knowledge, previous electrochemical studies of acetochlor have been performed only via anodic Fenton treatment;5 electrochemical reduction has not yet been pursued. In the present study, we have conducted cyclic voltammetry to evaluate the electrochemical behavior of acetochlor at carbon and silver cathodes in dimethylformamide (DMF) containing 0.05 M tetramethylammonium tetrafluoroborate (TMABF4). Glassy carbon is a traditional electrode material and silver has been shown to be catalytic for the cleavage of carbon–halogen bonds. Reduction of acetochlor at silver (–0.95 V vs. Cd/Hg) occurs at more positive potentials than at carbon (–1.4 V vs. Cd/Hg) and affords primarily the dechlorinated parent compound, N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide. In addition, reduction of acetochlor in the presence of electrogenerated nickel(I) salen (–0.95 V vs. Cd/Hg) indicates that nickel salen complexes can be an alternative to silver in order to achieve catalytic reduction. Controlled-potential (bulk) electrolysis coupled with traditional analytical methods such as gas chromatography–mass spectrometry (GC–MS) led to the identification and quantitation of reduction products. References Lamberth, C. Chloroacetamide Herbicides. In Bioactive Carboxylic Compound Classes, Pharmaceuticals and Agrochemicals, Lamberth, C., Dinges, J., Eds.; Wiley: Germany, 2016; pp 293–302.Lerro, C. C.; Koutros, S.; Andreotti, G.; Hines, C. J.; Blair, A; Lubin, J.; Ma, X.; Zhang, Y.; Beane Freeman, L. E. Int. J. Cancer. 2015, 137, 1167–1175.U.S. Environmental Protection Agency. Acetochlor (Harness) Pesticide Petition Filing 1/00. Fed Regist. 2000, 65, 3682–3690. Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress and Risk Management Decision (TRED) for Acetochlor. EPA 738-R-00-009; U.S. Environmental Protection Agency (U.S. EPA): 2006, 1–9.Friedman, C. L.; Lemley, A. T.; Hay, A. J. Agric. Food Chem. 2006, 54, 2640–2651.

Electrochemical Reduction of Chlorpyrifos at Silver Cathodes in Dimethylformamide

Once a widely popular insecticide, Chlorpyrifos (O,O-diethyl-O-3,5,6-trichloropyridin-2-yl phosphorothioate) has been the center of controversy in recent years. Rauh and co-workers found the compound to be neurotoxic; severe developmental defects were found in children up to three years of age.1 Regardless of these findings, a political divide over continued use of the compound has led to inaction over its regulation. In 2015, the EPA responded to a petition filed in 2007 by proposing a complete ban on the compound for use on food crops. However, the EPA reversed course in 2017, denying the proposed ban and deciding to study further the pesticide’s possible toxicity until 2022.2 Given our laboratory’s long-standing history of environmental remediation, we decided to be proactive and to investigate the electrochemistry of Chlorpyrifos, with the hope of degrading the compound into some compound less harmful to the environment. Cyclic voltammetry at silver cathodes in dimethylformamide containing 0.10 M tetramethylammonium tetrafluoroborate shows four reduction events at –1.05 V, –1.25 V, –1.43 V, and –1.75 V, all versus a cadmium-mercury amalgam (Cd/Hg) reference electrode. As a means of comparison, cyclic voltammetric behavior of TCPy (3,5,6-trichloro-2-pyridinol), a metabolite of Chlorpyrifos, was also investigated. A single cathodic peak was observed at –1.77 V vs. Cd/Hg. Surprisingly, controlled-potential (bulk) electrolyses conducted at silver cathodes showed unreduced Chlorpyrifos as the major product with less than one electron transferred per molecule of substrate (n < 1), regardless of the potential applied. However, bulk electrolyses performed in the presence of a suitable proton donor result in a substantial increase in the n value as well as a wide range of products including, but not limited to, dechlorinated, monochlorinated, and unreduced Chlorpyrifos. Rauh, V. A.; Garfinkel, R.; Perera, F. P.; Andrews, H. F.; Hoepner, L.; Barr, D. B.; Whitehead, R.; Tang, D.; Whyatt, R. W. Pediatrics 2006, 118, 1845–Erickson, B. E. Eng. News 2017, 95, 26–30.

Galvanic Dissolved Oxygen Sensor Based from Inkjet Printed Silver Cathode and Electrodeposited Zinc Anode

Inkjet printing has been gaining widespread application in printed electronics research. However, there are certain metals that cannot be printed easily without being oxidized in ambient air during post-print processing. One such example that has been thoroughly researched is sintering of printed copper nanoparticles or copper salts, which gets oxidized when exposed to sintering temperature in the presence of oxygen in air. There have been successful examples of workaround for printing copper inks. However, metals that are more reactive than copper, in terms of the activity series, is going to be a challenge to print and anneal. In such a case, we explore the use of electrodeposition, another well-established additive manufacturing technology. This study investigates the use of electrodeposition of zinc metal on inkjet-printed silver seed layer for use in printed electronic applications where the chemistry of zinc is desirable, such as in galvanic dissolved-oxygen (DO) sensors. There are a couple of literature that demonstrate inkjet-printed polarographic DO sensors using silver anode and gold cathode. However, commercial polarographic DO sensors do require more frequent maintenance compared to commercial galvanic DO sensors due to tarnishing of the gold cathode, which then requires physical polishing. In the case of galvanic DO sensors, the zinc hydroxide/ zinc oxide that results from oxidation of zinc anode is porous and thus flakes off by itself requiring less maintenance. Another advantage of a galvanic DO sensor is that the dissolved oxygen is directly measured as a potential between the anode and cathode, whereas a polarographic sensor requires an external potential sweep between the anode and cathode to measure the current produced by the sensor. This necessitates a slightly more complex measuring equipment and a longer scan time for polarographic DO sensors. The sensor was fabricated as such. Silver ink (Silverjet DGP 40LT-15C) electrodes (final silver cathode and anode seed layer), conducting wires, and contact pads were inkjet printed on flexible PEN substrate (150 microns, Dupont Teijin PQA1) followed by annealing at 180oC. The silver seed layer for the anode was then electrodeposited with zinc using zinc acetate dihydrate (Sigma-Aldrich ACS reagent, >99.0%) electroplating solution and zinc plate anode (acquired from Panasonic size D Zinc-Carbon battery). XRD pattern of printed silver coincides with diffraction peaks of face-centered cubic silver (JCPDS PDF # 01-087-0720), while XRD pattern of electrodeposited zinc matches with diffraction peaks of hexagonal zinc (JCPDS PDF # 00-004-0831). Preliminary devices have shown issues such as delamination of silver seed layer during zinc plating, or curling of electroplated zinc layer during galvanic operation. This was addressed by anchoring the silver seed layer to the PEN substrate by inkjet printing PMMA layer (Sigma-Aldrich 15,000 Mw PMMA; dissolved in NMP solvent at 15% wt/wt) prior to electrodeposition of zinc. In addition, PMMA ink was printed over the silver conducting wires to act as an insulator. Immersing the electrodes (both 2.0mm x 1.5mm in dimension) in 0.5M KOH electrolyte solution results in a galvanic micro-battery which yields an open circuit voltage of 1.43 V and short circuit current of 1.5 µA. Lastly, we show a proof-of-concept galvanic dissolved oxygen probe using the electrodeposited zinc anode, inkjet printed silver cathode, 0.5 M KOH as the electrolyte, PTFE membrane (Hannah DO screw cap membrane; product # HI76407A/P) as the gas permeable membrane, and bonded acrylic sheets as water tight housing. This device has an output voltage of 62.5 mV when calibrated in saturated 100% humidified air and a voltage of 0.3 mV when calibrated in 0% calibration solution (Atlas Scientific DO test solution; part # CHEM-DO). This is comparable to the working potential of a commercially available galvanic DO probe (Atlas Scientific Dissolved Oxygen probe, part # ENV-40-DO), which puts out 61.8 mV when saturated with air and 0.9 mV in 0% calibration solution. Figure 1

Electrochemical Investigation of Halogenated Hydroxybenzonitriles at Silver Cathodes in Dimethylformamide

Chloroxynil (3,5-dichloro-4-hydroxybenzonitrile), Bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), and Ioxynil (3,5-diiodo-4-hydroxybenzonitrile) belong to a group of halogenated phenols commonly used as herbicides to control broad-leaved weeds. Functioning as disruptors of oxidative phosphorylation, these compounds have grown in popularity in recent years as alternatives to atrazine, particularly bromoxynil (1800–2200 tons applied per year).1,2 In the environment, all three herbicides can undergo hydrolysis as well as enzymatic degradation to the corresponding benzamide (3,5-dihalo-4-hydroxybenzamide) and subsequently to the benzoic acid (3,5-dihalo-4-hydroxybenzoic acid), both of which have the possibility of persisting in soil.3,4 As a result, an efficient means of degrading the parent compounds is necessary. Sokolova and co-workers5 have investigated the electrochemical reduction of these hydroxybenzonitriles; however, their studies employed mercury working electrodes, which are known to be extremely toxic and hazardous. Silver has long been praised as an advantageous cathode for remediation of environmental pollutants due to its affinity for halides.6 In the present study, we propose to use silver cathodes to investigate the electrochemical behavior of chloroxynil, bromoxynil, and ioxynil in dimethylformamide (DMF). Cyclic voltammograms for each compound in DMF containing 0.05 M tetramethylammonium tetrafluoroborate (TMABF4) show widely different behavior between the three herbicides: chloroxynil exhibits one cathodic peak (–0.74 V), whereas bromoxynil displays four cathodic peaks (–0.40 V, –0.65 V, –1.23 V, and –1.51 V) as does ioxynil (–0.20 V, –0.30 V, –0.58 V, and –1.66 V). All potentials are versus a cadmium-mercury amalgam reference electrode. Bulk electrolyses performed with 0.05 M TMABF4–DMF result in a wide product distribution in addition to different n values for each substrate. Holtze, M.; Sorensen, S. R.; Sorensen, J.; Aamand, J. Environ. Pollut. 2008, 154, 155–168.Lovecka, P.; Thimova, M.; Grznarova, P.; Lipov, J.; Knejzlik, Z.; Stiborova, H.; Nindhia, T. G. T.; Demnerova, K.; Ruml, T. BioMed Res. Int. 2015, 2015, 1–9.Nielsen, M. K. K.; Holtze, M. S.; Svensmark, B.; Juhler, R. K. Pest Manag. Sci. 2007, 63, 141–149.Roberts, T. R.; Hutson, D. H.; Lee, P. W.; Nicholls, P. H.; Plimmer, J. R., Metabolic Pathways of Agrochemicals: Part 1: Herbicides and Plant Growth Regulators. 1998.Sokolova, R.; Hromadova, M.; Fiedler, J.; Pospisil, L.; Giannarelli, S.; Valasek, M. J. Electroanal. Chem. 2008, 622, 211–218.Martin, E. T.; McGuire, C. M.; Mubarak, M. S.; Peters, D. G. Chem. Rev. 2016, 116, 15198–15234.

Electrodeposition of Silicon with a Liquid Gallium Cathode in Molten Salts

Further development of solar power depends largely on the availability of inexpensive solar grade silicon. Electrodeposition is a candidate method to produce high purity silicon at a reasonable cost. We have previously studied electrodeposition of silicon from molten calcium chloride based electrolytes and molten fluoride electrolytes. Recent experiments were carried out by using a liquid gallium cathode. The approach is based on studies by Stephen Maldonado and coworkers [1] of electrodeposition of silicon by using a liquid gallium cathode in an organic based electrolyte. Silicon has a low tendency to alloy with gallium. Electrochemical studies and electrolysis to deposit silicon from molten eutectic KCl – KF with 2 mol% K2SiF6 were carried out at 650 oC. Silver wire and glassy carbon rod were used as working electrodes, while glassy carbon rod or silver wire were counter electrodes. A silicon flag reference electrode was used. Liquid gallium in a small alumina tube with tungsten lead was the cathode during electrolysis while glassy carbon or silicon was the anode. Silicon deposition is diffusion controlled on silver cathode, while silicon deposition is charge transfer controlled on liquid gallium cathode. Silicon was found to deposit using a liquid gallium cathode, both during galvanostatic and potentiostatic electrolysis. The current efficiency was found to be quite high, and consistently above 80 %. Some silicon particles were found on top of gallium after cooling down. A much larger amount of gallium was used in recent experiments. This helped to form silicon particles inside the liquid gallium cathode. Silicon was recovered after experiments by physical separation from liquid gallium followed by dissolution of gallium in concentrated HNO3. High purity silicon was obtained. Gallium can form alloys with many impurity elements which may cause a refining effect of silicon. The use of a liquid gallium cathode is promising for the prospect of developing a new process for producing high purity silicon by electrolysis in molten salts.

Analysis of Instability Phenomena at Current Interruption in Vacuum Arc Discharge Compared With Silver or Copper Electrode

Vacuum circuit breakers have an issue of instability arc current and chopping phenomena when the current is cut off from the circuit. To clarify the effect of the instability low-current vacuum arc for circuit breaker development, the instability mechanism of low-current vacuum arc for various parameters was proposed to verify consequent affecting circuit breaker capacity in this paper. This paper used the cathode spot model neglect the transition region between the collisionless sheath and collisional plasma region. The eight equations were used for solving the dependent variable of plasma parameters for both silver and copper electrode materials. The low ionization was supposed in the cathode spot model. The results showed that the changes in the work function and ion current fraction at ambient temperature did not have the main influence on the arc stability limit current both in the silver electrode and copper electrode. On the contrary, the changes in the heat conductivity at ambient temperature affecting the arc stability limit current significantly both in the silver and copper electrodes. Furthermore, the results were found out that the cathode spot can be confirmed unstable current phenomena when the current below 19 A for copper cathode and below 19.4 A for the silver cathode. These phenomena can be explained that the reversed electrons flow from the plasma side to sheath region affecting the electric field at cathode spot become negative zone; thus, the starting noise on the current trace appears before chopping current.

Transforming Ionene Polymers into Efficient Cathode Interlayers with Pendent Fullerenes

AbstractA new and highly efficient cathode interlayer material for organic photovoltaics (OPVs) was produced by integrating C60 fullerene monomers into ionene polymers. The power of these novel “C60‐ionenes” for interface modification enables the use of numerous high work‐function metals (e.g., silver, copper, and gold) as the cathode in efficient OPV devices. C60‐ionene boosted power conversion efficiencies (PCEs) of solar cells, fabricated with silver cathodes, from 2.79 % to 10.51 % for devices with a fullerene acceptor in the active layer, and from 3.89 % to 11.04 % for devices with a non‐fullerene acceptor in the active layer, demonstrating the versatility of this interfacial layer. The introduction of fullerene moieties dramatically improved the conductivity of ionene polymers, affording devices with high efficiency by reducing charge accumulation at the cathode/active layer interface. The power of C60‐ionene to improve electron injection and extraction between metal electrodes and organic semiconductors highlights its promise to overcome energy barriers at the hard‐soft materials interface to the benefit of organic electronics.

Transforming Ionene Polymers into Efficient Cathode Interlayers with Pendent Fullerenes.

A new and highly efficient cathode interlayer material for organic photovoltaics (OPVs) was produced by integrating C60 fullerene monomers into ionene polymers. The power of these novel "C60 -ionenes" for interface modification enables the use of numerous high work-function metals (e.g., silver, copper, and gold) as the cathode in efficient OPV devices. C60 -ionene boosted power conversion efficiencies (PCEs) of solar cells, fabricated with silver cathodes, from 2.79 % to 10.51 % for devices with a fullerene acceptor in the active layer, and from 3.89 % to 11.04 % for devices with a non-fullerene acceptor in the active layer, demonstrating the versatility of this interfacial layer. The introduction of fullerene moieties dramatically improved the conductivity of ionene polymers, affording devices with high efficiency by reducing charge accumulation at the cathode/active layer interface. The power of C60 -ionene to improve electron injection and extraction between metal electrodes and organic semiconductors highlights its promise to overcome energy barriers at the hard-soft materials interface to the benefit of organic electronics.

Energy transfer-enhanced external power conversion efficiency in blended polymeric thin film solar devices

In this paper, the spectral and electrical properties of a conjugated polymer poly [(9, 9-dioctyl-2, 7-divinylenefluorenylene)-alt-co-(1, 4-phenylene)] (PFO–MEH–PPV) with poly[3-(2-ethyl-isocyanato-octadecanyl) thiophene] (PECOD) in thin films have been studied. First, PFO–MEH–PPV and PECOD were dissolved in tetrahydrofuran and chloroform respectively for different concentrations. These solutions were deposited on glass substrates to form thin films with different thicknesses. The absorbance and photoluminescence spectra for each individual pure polymer were recorded and contrasted with those for blended conjugated polymer’s films to determine the effect of blending on the absorption and photoluminescence. Finally, we present a study on the processing and characterization of organic solar cells fabricated by spin coating pure PFO–MEH–PPV, PECOD and their blend as the organic active layer onto indium tin oxide layer (150 nm), followed by the evaporation of silver cathode (110 nm). The current–voltage characteristics of these cells were determined and external quantum efficiency. Upon blending the two polymers in solid forms, it could be seen that the efficiency (6.25%) for the cells based on a blend layer is higher than the ones without blending (4.4%). Finally, we demonstrated here that the combination/blending of conjugated polymers has resulted in optimized solar device function, with reasonably quantum efficiency higher than 10%.

Electrochemical Synthesis of Ammonium Persulfate (NH4)2S2O8 Using Oxygen-Depolarized Porous Silver Cathodes Produced by Powder Metallurgy Methods

The stage-by-stage mechanism of the reduction process proceeding in an acidic environment in the cathodic depolarization of ammonium sulfate (NH4)2SO4 (including the primary process such as synthesis of hydrogen peroxide H2O2 on a porous silver cathode by equation $$ 2{\mathrm{H}}_2{\mathrm{O}}_2+2{\mathrm{S}\mathrm{O}}_4^{2-}=={\mathrm{S}}_2{\mathrm{O}}_8^{2-}+{\mathrm{O}}_2\uparrow +{\mathrm{H}}_2\mathrm{O} $$ and the main final process such as $$ 2{\mathrm{NH}}_4^{2+}+{\mathrm{S}}_2{\mathrm{O}}_8^{2-}=\left({\mathrm{NH}}_4\right){}_2{\mathrm{S}}_2{\mathrm{O}}_8\Big) $$ along with the anodic reaction, $$ 4{\mathrm{H}\mathrm{O}}_2^{-}=3{O}_2\uparrow +2{\mathrm{H}}_2\mathrm{O}+4\mathrm{e} $$ , on a platinum plate has been established. The silver cathodes were produced by powder metallurgy methods (compaction of silver nanopowder with particles 10–30 nm in diameter at 44.13 MPa followed by sintering of the samples in a purified hydrogen atmosphere at 450°C). The silver nanopowder was obtained as individual acicular nanocrystals that branched out and were held in pairs on the Pt plate in electrolysis in a 2% AgNO3 solution with addition of 1% nitric acid. The nanostate of the silver powder was verified with the BET method (Brunauer, Emmett, Teller) by low-temperature nitrogen adsorption. The ammonium persulfate synthesis kinetics and mechanism indicate that the replacement of commercial lead cathodes with oxygen-polarized silver cathodes leads to a 17.5% decrease in the electricity consumed. The polarization properties of the cellular silver cathode remain unchanged for 100 h of (NH4)2SO4 electrolysis.

Electrocarboxylation of 1-chloro-(4-isobutylphenyl)ethane with a silver cathode in ionic liquids: an environmentally benign and efficient way to synthesize Ibuprofen.

Electrocarboxylation of organic halides is one of the most widely used approaches for valorising CO2. In this manuscript, we report a new greener synthetic route for synthesising 2-(4-isobutylphenyl)propanoic acid, Ibuprofen, one of the most popular non-steroidal anti-inflammatory drugs (NSAIDs). The joint use of electrochemical techniques and ionic liquids (ILs) allows CO2 to be used as a C1-organic building block for synthesising Ibuprofen in high yields, with conversion ratios close to 100%, and under mild conditions. Furthermore, the determination of the reduction peak potential values of 1-chloro-(4-isobutylphenyl)ethane in several electrolytes (DMF, and ionic liquids) and with different cathodes (carbon and silver) makes it possible to evaluate the most “energetically” favourable conditions for performing the electrocarboxylation reaction. Hence, the use of ILs not only makes the electrolytic media greener, but they also act as catalysts enabling the electrochemical reduction of 1-chloro-(4-isobutylphenyl)ethane to be decreased by up to 1.0 V.

Synergic effect of ionic liquid grafted titanate nanotubes on the performance of anion exchange membrane fuel cell

Titanate nano tubes, prepared by hydrothermal method, are covalently bonded with a basic ionic liquid (1-Methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride) resulting in an ion exchange behaviour. The ionic liquid bonded Titanate nano tubes are characterised by SEM, TEM, XRD studies for their nano tube morphology and covalent bond between them which are confirmed by solid state NMR and FTIR. This synthesised filler, in various concentrations (1, 3, 5 and 7 wt%), are incorporated into quaternised polysulfone leading to the fabrication of nano composite membranes with high ion exchange capacity. The fabricated nano composite membranes are characterised by SEM, XRD, water uptake, ion exchange capacity and hydroxyl conductivity studies to evaluate their suitability as an electrolyte in alkaline fuel cell applications. Upon testing these membranes in fuel cell setup with platinum anode and silver cathode, amongst the various composites, the membrane with 5% wt filler exhibits the most optimum properties for application in alkaline fuel cells with a power density of 302 mW/cm2. The existence of ion exchange behaviour as well as the hollow nature of titanate nano tubes leads to synergistic effect in conducting the hydroxyl ions via both Grotthus (through water molecules) and hopping (through ion exchange groups) mechanisms.

Electrochemical reduction of p-chloronitrobenzene (p-CNB) at silver cathode in dimethylformamide

Chloronitrobenzenes (CNBs) are a group of extensively used raw materials in the production of many important chemicals, which also belong to among the common pollutants in the environment. Electrochemical reduction is recognized as an important and promising strategy widely applied in the environment and synthesis fields. However, few studies on the possible electrochemical reduction of CNBs have been reported before; in particular, the effects of proton donor on the reduction mechanisms have not been fully addressed. In this work, cyclic voltammetry and bulk electrolyses have been investigated for the electrochemical reduction of p-CNB at silver (Ag) cathode in DMF under different solvent conditions. Voltammetric reduction of p-CNB at Ag electrode shows two successive reduction peaks and three anodic waves in the return cycle, the first reduction peak of which is attributed to the sequential reduction of p-CNB to p-chlorophenylhydroxylamine (p-CPHA), while the second one is assigned to the further reduction to p-chloroaniline (p-CAN). No catalytic effect of Ag was observed for the reduction of p-CNB with respect to GC electrode, which was mainly due to the reversible nature of both reduction waves in the cyclic voltammetry. The presence and the type of proton donor (e.g., acetic acid and water) was found to have significant effects on the reduction of p-CNB. The general observation is that the first reduction peak develops at the expense of the second one with increasing concentrations of proton donors at Ag cathode. Bulk electrolysis of p-CNB shows that three principal reduction mechanisms of sequential reduction, condensation and radical anions’ coupling reactions were involved. The primary electrolysis products were 4,4′-dichloroazoxybenzene (DOB) and 4,4′-dichloroazobenzene (DAB), as well as a small amount of p-CAN, and the product selectivity was dependent on the solvent conditions. This work may provide an effective tool for the reduction of p-CNB and other CNBs by obtaining useful compounds (e.g., chlorinated azo-benzenes).

Nanoporous silver cathode surface-treated by aerosol-assisted chemical vapor deposition of gadolinia-doped ceria for intermediate-temperature solid oxide fuel cells

Herein, a nanoporous silver surface treated with gadolinia-doped ceria (GDC) is evaluated as a cathode for intermediate-temperature solid oxide fuel cells operating below 500 °C. For uniform surface treatment on the porous silver, aerosol-assisted chemical vapor deposition (AACVD) is used; it is a non-vacuum process and is considered as an economical alternative to the expensive vacuum-environment thin-film fabrication methods. Consequently, a uniform coating of AACVD GDC on the Ag surface is successfully achieved, which is confirmed by high-resolution transmission electron microscopy. The optimized amount of AACVD GDC enhances fuel cell performance compared to cells with bare Ag, in terms of the power and long-term stability measured by current–voltage characteristics, electrochemical impedance spectroscopy, and potentiostatic amperometry. This performance is even more significant than that from the cell with a platinum cathode, which, to our best knowledge, is known as the best-performing catalyst for solid oxide fuel cells in the intermediate- and low-temperature regimes. The power enhancement is attributed to the improved kinetics with the GDC surface coating; moreover, this oxide decoration is proven effective in preventing the thermal agglomeration of Ag, as confirmed by the morphology comparison before and after the long-term test.