Polycrystalline Silver Electrode Research Articles

Efficient Electrocatalytic Reduction of Carbon Dioxide in 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate and Water Mixtures

The catalytic activity of room-temperature ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]) for carbon dioxide (CO2) reduction is reported on a polycrystalline silver electrode as a function of the water content and solution pH. The optimal aqueous dilution was determined to be ca. 10% (v/v), resulting in a reduction of the overpotential required to reduce CO2 in [EMIM][OTf] by 400 mV. The reduction process and products are largely insensitive to pH. CO2 reduction in [EMIM][OTf] with 10% 0.1 M NaHCO3 is achieved with high selectivity for CO with 93.0 ± 4.6% Faradaic efficiency. Hydrogen evolution reaction (HER) is suppressed in the range of neat [EMIM][OTf] (500 ppm water content) to a [EMIM][OTf]/H2O mixture of 10% water content. Conductivity and viscosity of the [EMIM][OTf]/H2O mixture suggest that the ionic liquid ion pair fully dissociates, analogous to dilute KCl solution, where each ion is completely hydrated by water molecules.

Insights of glycerol electrooxidation on polycrystalline silver electrode

This work presents a detailed study of silver electrode activity toward glycerol electrooxidation reaction (GEOR) in alkaline media. The effect of pH and glycerol concentration on GEOR kinetics was investigated by cyclic voltammetry technique. It has been found that hydroxyl ions concentration leads to an oxidation current increase, which indicates that glyceroxide could be the active species for GEOR. The presence of silver oxide layer inhibits the glycerol oxidation process, reaching maximum current densities of 2.3mAcm−2 (1M glycerol in 1M NaOH). HPLC studies indicate that formic, glycolic and glyceric acids are the main products.

Kinetic Implication from Temperature Effect on Hydrogen Evolution Reaction at Ag Electrode

Hydrogen evolution reaction (HER) at polycrystalline silver electrode in 0.1 mol/L HClO4 solution is investigated by cyclic voltammetry in the temperature range of 278–333 K. We found that at electrode potential φ<PZC (potential of zero charge), the apparent activation energy Ea, app decreases with φ, while pre-exponential factor A remains nearly unchanged, which conforms well the prediction from Butler-Volmer equation. In contrast, with φ negative shifts from the onset potential for HER to the potential of zero charge (PZC≈− 0.4 V), both Ea,app and A for HER increase (e.g., Ea,app increases from 24 kJ/mol to 32 kJ/mol). The increase in Ea,app and A with negative shift in φ from −0.25 V to PZC is explained by the increases of both internal energy change and entropy change from reactants to the transition states, which is correlated with the change in the hydrogen bond network during HER. The positive entropy effects overcompensate the adverse effect from the increase in the activation energy, which leads to a net increase in HER current with the activation energy negative shift from the onset potential of HER to PZC. It is pointed out that entropy change may contribute greatly to the kinetics for electrode reaction which involves the transfer of electron and proton, such as HER.

Comparison of Oxygen Reduction Reaction at Silver Nanoparticles and Polycrystalline Silver Electrodes in Alkaline Solution

Adenosine 5′-triphosphate capped silver nanoparticles (ATP-Ag NPs) with diameters of 4.5 ± 1.1 nm were synthesized using a one-pot chemical reduction route. After removal of the ATP capping ligands, the electrochemical activity of these NPs for the oxygen reduction reaction (ORR) in aqueous alkaline solution (0.1 M NaOH) was studied in a single layer-by-layer (1 L LbL) film of NPs and compared with bulk polycrystalline Ag using cyclic voltammetry (CV) and rotating disk electrode (RDE) experiments. For the NPs in the 1 L LbL film, the active area of catalyst available for the ORR was calculated using the charge for the underpotential deposition (UPD) of lead (Pb) on the NPs. RDE data were analyzed to determine the ORR rate constant and the number of electrons (n-value) involved in oxygen reduction. Analysis of Koutecky–Levich (K–L) plots indicates an n-value between 3 and 4 with a higher n-value under some conditions for the NPs than for bare polycrystalline Ag. Possible origins of the variation of n-value...

Multistep Reduction of Oxygen on Polycrystalline Silver in Alkaline Solution

Abstract Oxygen reduction on a polycrystalline silver electrode was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The reaction occurred by a two-electron pathway. The steps in the mechanism were observed in the cyclic voltammograms recorded with different scan rates. The intermediates formed in the steps were detected by electrochemical impedance spectroscopy.

Oxidation of the Borohydride Ion at Silver Nanoparticles on a Glassy Carbon Electrode (GCE) Using Pulsed Potential Techniques

Direct oxidation borohydride fuel cells are very attractive energy conversion devices. Silver has been reported as one of the few materials which can catalyze an 8-electron oxidation. Potential step amperometric pulse techniques to synthesize nanostructured silver material on flat glassy carbon electrodes is reported and significant differences with bulk silver deposit have been observed. The oxidation of borohydride ion on the silver particles occurs at -0.025 V vs. SCE and the potential decreases towards negative values at longer cycle times. The oxidation current also decreases with the number of cycles, suggesting that the silver active sites become partially blocked by oxidation products of borohydride. The electroactive area per unit electrode area of silver was relatively low for particles deposited using potential step amperometric techniques on glassy carbon (0.002 cm2 per cm-2) compared with the area found at a polycrystalline silver electrode (0.103 cm2 per cm-2).

Tailoring the morphology and electrocatalytic properties of electrochemically formed Ag/TiO2 composite deposits on titanium surfaces

Three different forms of Ag/TiO2 composite layers, which have whisker-, dot- and island-like distribution of silver were obtained on a mechanically polished titanium surface by adjusting the conditions of silver deposition from an aqueous AgNO3 solution. The deposit morphology was the result of both the program of electrode polarization and the template action of the simultaneously formed TiO2 layer. The catalytic activity of the composite layers toward the oxygen reduction reaction was studied in aqueous 0.1 M NaOH solutions and found to be a function of both the surface loading of silver and the type of silver distribution within the Ag/TiO2 composite layers. The reaction path of oxygen reduction on the composite layers was found to be always a 4e- one, characteristic otherwise of polycrystalline silver electrodes.

Specific adsorption of bromide and iodide anions from nonaqueous solutions on controlled-surface polycrystalline silver electrodes

Abstract A systematic investigation was performed on the specific adsorption of bromide and iodide anions on controlled-surface polycrystalline silver electrodes, from three organic solvents (acetonitrile, propylene carbonate, and dimethylformamide), combining differential capacity and impedance experiments with a recently proposed “indirect” voltammetric method based on the monitoring of the negative shift of the reduction peak potential of a “probe” organic halide molecule induced by progressive additions of halide anions, resulting in increasing adsorption competition. Bromide and iodide ions are specifically adsorbed onto polycrystalline silver electrodes in the three organic solvents studied. The adsorption process, which is slow and it is characterised by a partial charge transfer and by a slow diffusion step, is modulated by the different coordination abilities of the solvents for the species involved in the adsorption. The three experimental methods provide consistent results. In particular, the strength of halide adsorption increases in the halide sequence Br−

The Mechanism of Silver(I) Oxide to Silver(II) Oxide Formation on Polycrystalline Silver Electrodes in 8 M KOH Solution

The kinetics of silver(II) oxide formation on polycrystalline silver electrodes in 8 M KOH solution was investigated by cyclic voltammetry, potentiostatic and galvanostatic techniques, and by the morphology of the silver(II) oxide structures determined by scanning electron microscopy. Potentiostatic investigations revealed unambiguously that the silver(II) oxide formation proceeded via a nucleation and 3-D growth process. Microscopic examinations provided undoubted evidence that nucleation, 3-D growth, and Ostwald ripening processes are involved in the stage of silver(II) oxide formation. In addition, it was found that two types of silver(II) oxide morphologies might be formed by progressive and instantaneous nucleation process in the silver(I) oxide layer covering the silver substrate.

Adsorption of pyridine carboxylic acids on silver surface investigated by potential-dependent SERS

The potential-dependent surface enhanced Raman scattering (SERS) of the three-pyridine carboxylic acids (picolinic acid, isonicotinic acid and nicotinic acid) on polycrystalline silver electrode are studied in this paper. Their surface geometries may be detected from the high-quality potential-dependent SERS signals. With the varying of potential the adsorption behavior of picolinic acid is invariant, perpendicularly standing on the silver surface with both N-atom of the heteroaromatic ring and carboxylate group, while the adsorption behavior of isonicotinic acid and nicotinic acid may change. At higher potential values, both isonicotinic acid and nicotinic acid stand perpendicularly on silver surface via carboxylate group. At low potential values, the former lie flat on the silver surface and the latter edge on the silver surface via oxygen lone pair electrons. The probable reasons are given.

Bi<Sub>2</sub>O3를 첨가한 8M KOH용액에서 다결정 Ag전극의 전기화학적 거동

[ <TEX>$Bi_2O_3$</TEX> ]를 첨가한 8M KOH용액에서 다결정 Ag전극의 전기화학적인 거동과 생성된 산화물들의 미세조직 변화를 분석하였다. <TEX>$Bi_2O_3$</TEX>를 첨가한 8M KOH용액에서 Ag 산화물뿐만 아니라 새로운 Ag-Bi-O화합물들이 생성되는 것을 알 수 있었다. Ag(I) 산화물 생성 전위 영역에서는 <TEX>$Ag_2O$</TEX> 이외에, Ag-Bi-O 화합물이 핵 생성과 3D성장 과정에 의해서 생성되고, Ag(II)산화물 생성 전위 영역에서는 AgO뿐만 아니라 새로운 Ag-Bi-O화합물들이 핵 생성과 3D성장 과정에 의해서 생성되었다. Ag(I) 산화물 생성 전위에서 두 가지 형상의 Ag(I) 산화물이 생성되는 것을 SEM 조직에 의해 관찰하였다. The electrochemical behaviors of polycrystalline silver electrodes in 8M KOH solutions containing <TEX>$Bi_2O_3$</TEX> were studied under various conditions by cyclic voltammetry, potentiostatic and galvanostatic techniques as well as the morphology of the silver oxide structures by SEM. It was found that three new compounds comprising silver, bismuth, and oxygen as well as <TEX>$Bi_2O_3,\;Ag_2O$</TEX> and AgO were formed during the electrochemical oxidation of silver. In addition, the potentiostatic current transients were characterized by the appearances of the first current peaks corresponding to the formation of silver oxides, and the second current peaks corresponding to the Ag-Bi-O compounds, indicating the presence of the nucleation and 3D growth mechanism, in the potential regions of <TEX>$Ag_2O$</TEX> and AgO, respectively. Microscopic examinations showed that two types of silver (I) oxide morphologies are formed in the potential region of <TEX>$Ag_2O$</TEX>.

Characterization and electrocatalytic application of silver modified polypyrrole electrodes

Silvermodified polypyrrole electrodes were prepared with the aim of testing them for the electro oxidation of formaldehyde in alkaline solution. The modification of polypyrrole by immersion in aqueous AgNO3 solution was studied by cyclic voltammeter and vacuum techniques (AES and XPS). The influence of time of immersion and the thickness of the polypyrrole film, prepared by electrochemical polymerization, on the modification of the polymer were examined. The results acquired from both electrochemical and spectroscopic examinations show that immersion of a polypyrrole electrode in a AgNO3 solution results in its modification with silver, which is deposited in the elemental state on the surface. The quantity of silver deposited depends not only on the immersion time but also on the thickness of the polymer film. A modified PPy/Ag electrode exhibits catalytic activity for the electro oxidation of CH2O in NaOH. In spite of the low quantity of silver, the activity of the electrode for this reaction is comparable to that of a polycrystalline silver electrode.

Adsorption of urea on a polycrystalline silver electrode; comparison of electrochemical and radiometric methods

The adsorption of urea on a polycrystalline silver electrode was studied by radiometry and impedance spectroscopy. The differential capacity of the silver electrode in 0.01 M NaClO4 solution containing urea in concentrations from 10−6 to 5×10−4 M has been determined. The isotherms of urea adsorption, found from the capacitance and radiometric measurements have been compared. The experimental data were described by the Langmuir isotherm, and the Gibbs energy of adsorption was calculated. The urea adsorption takes place in the entire range of the applied potential. The process is reversible with respect to the electrode potential and the bulk urea concentration.

Mechanism of Silver(I) Oxide Formation on Polycrystalline Silver Electrodes in 8 M KOH Solution

The kinetics of silver(I) oxide formation on polycrystalline silver electrodes in 8 M KOH solution was investigated by cyclic voltammetry, potentiostatic and galvanostatic techniques as well as the morphology of the silver(I) oxide structures by scanning electron microscopy. Potentiostatic investigations revealed unambiguously that the silver(I) oxide may be nucleated in the second stage as well as in the third stage of silver(I) oxide formation. Cyclic voltammograms showed that the second peak current could be larger than the third peak current with repetitive cycling. Microscopic examinations provided undoubted evidence that electrodissolution, nucleation, three-dimensional (3D) growth, and Ostwald ripening processes are involved in the initial stage of silver(I) oxide formation. In addition, it was found that two types of silver(I) oxide morphologies were formed by progressive nucleation and instantaneous nucleation process. On the basis of the experimental results, a model of silver(I) oxide formation involving electrodissolution, progressive nucleation, instantaneous nucleation, and 3D growth processes is proposed. © 2004 The Electrochemical Society. All rights reserved.

Anion-induced adsorption of thallium complex on silver electrodes

The interfacial behavior of thallium ions on polycrystalline silver electrodes is analyzed using cyclic voltammetric and chronocoulometric and impedance studies. The specificity associated with bromide ions leading to the anion-induced adsorption of the thallium complex is pointed out and the stoichiometry of the thallium complex is deduced.

Surface enhanced Raman spectroscopy study of the potential dependence of thymine on silver electrodes

The potential-induced changes in thymine coordination on polycrystalline silver electrodes are studied by surface enhanced Raman spectroscopy (SERS) for potentials positive to the potential of zero charge up to the end of the double layer range. Two distinct sets of spectra could be obtained in the range of potentials studied. Both states correspond to chemisorbed phases of thymine on silver, where a distinct heteroatom is deemed responsible for the bond with the surface. At less positive potentials, one of the ring oxygen atoms is responsible for the chemical bond and the molecule assumes a tilted position. At more positive potentials, one of the ring nitrogen atoms, possibly deprotonated, establishes a new bond with the surface, aligning the molecule's axis closer to the surface normal.

Electrolyte electroreflectance study of carbon monoxide adsorption on polycrystalline silver and gold electrodes

We have carried out an electrolyte electroreflectance (EER) study of the adsorption of CO on polycrystalline Ag and Au electrodes. EER proved to be a very sensitive tool for detecting the presence of chemisorbed CO on the surface of the Ag electrode, clearly distinguishing between strong adsorption (chemisorption) and weak adsorption (physisorption). In the case of Au, onto which CO chemisorbs in both alkaline and acid media, EER also detects the presence of this chemisorbed CO. However, while in alkaline medium CO adsorption provokes major changes in the EER spectrum of Au, in acid medium only minor changes are observed, since the CO coverage is 10 times lower than that in the former case. An analysis of the EER spectra of CO-covered Au provided valuable information regarding the surface electronic levels involved in the formation of the chemisorption bond.

Electroreduction of Heptyl Viologen on Polycrystalline Silver : Formation and Layer-by-Layer Dissolution of the Bromide Salt of the Cation Radical Film

The formation of a film by the bromide salt of the cation radical of heptyl viologen, on a polycrystalline silver electrode under potentiostatic conditions can be interpreted in the light of an adsorption-nucleation mechanism and a diffusion-controlled growth mechanism. On the other hand, the dissolution of such a film can be interpreted with the aid of a mathematical model based on a progressive hole-nucleation and layer-by-layer growth of vacancies that considers dissolution of incomplete monolayers. © 2002 The Electrochemical Society. All rights reserved.

Investigation of the Adsorption of l-Cysteine on a Polycrystalline Silver Electrode by Surface-Enhanced Raman Scattering (SERS) and Surface-Enhanced Second Harmonic Generation (SESHG)

The adsorption of L-cysteine (L-Cys) onto a polycrystalline silver electrode surface was investigated by in situ spectroelectrochemical methods. Surface-enhanced Raman spectroscopy (SERS) and surface-enhanced second-harmonic generation (SESHG) measurements were performed in a 0.2 M KCl solution in the presence and absence of L-Cys. The experimental results indicated that L-Cys strongly adsorbs onto silver and remains on the surface at potentials as negative as -900 mV (vs Ag/AgCl). A peak around -650 mV was observed in the SESHG intensity versus applied potential plots obtained in the presence of L-Cys. The peak was indicative of an abrupt change in the electronic properties of the interface at that potential. The SERS spectra at potentials more negative than ca. -650 mV showed an increase in the intensity of vibrational modes assigned to the carboxylate group of L-Cys. The combination of the SERS and the SESHG results suggests a potential-induced reorientation of the adsorbed L-Cys molecules for potentials more negative than -650 mV. The data interpretation considered the different possible conformational forms of L-Cys adsorbed on the Ag surface. At potentials more positive than ca. -650 mV, L-Cys molecules adsorb with the protonated amino group pointing toward the surface. In this case, the positively charged amino group is stabilized by the coadsorbed chloride anions. The molecule changes its conformation at potentials more negative than -650 mV as the chloride ions leave the surface. The C α -C β bond rotation brings the carboxylate group closer to the surface at these potentials.

Electrocatalysis at polycrystalline silver in base: an example of the complexity of surface active state behaviour

Four low-level redox responses, attributed to the involvement of four different types of active surface state (or site) transitions, were observed within the double layer region in the case of polycrystalline silver electrodes in base; there is now independent evidence for such premonolayer behaviour in data reported by other authors. The potentials for each of these transitions were correlated with the onset/termination potentials of different electrocatalytic processes, usually for oxidations or reductions but in some cases for both types. The data obtained are in good agreement with the IHOAM model of electrocatalysis which was outlined earlier for the other Group 11 metals, gold and copper.