Bare Silver Electrode Research Articles

Modeling Bicarbonate Kinetics on Silver Catalysts for CO2 Electrolysis

Low-temperature CO2 electrolyzers transform captured CO2 into more useful chemicals, such as syngas (CO and H2) for systems with silver or gold catalysts and ethylene and other C2+ products for systems with copper catalysts. At low overpotentials, bicarbonate ions act as proton donors and have been shown to have enhanced activity1, leading to nonlinear Tafel slopes for the hydrogen evolution reaction (HER). We have developed a 1D planar electrode model for CO2 electrolysis, similar to the model developed by Gupta et al.,2 including a thin ionomer layer on top of a silver catalyst layer surface. The model includes buffer chemistry and ion transport in the boundary layer as well as the ionomer thin-film layer. Tafel parameters are fit for both bicarbonate and water as proton donors for HER using the model results to account for mass transport in the boundary layer. A comparison against a bare silver electrode shows that the Donnan potential across the ionomer/electrolyte interface has a significant effect on the ion concentrations at the catalyst layer surface, leading to enhanced HER from bicarbonate at low overpotentials. These results are then compared against Butler-Volmer parameters that are derived from a full microkinetic model. The Tafel kinetic parameters were then used in a 1D full-cell membrane electrode assembly (MEA) model, and we found good agreement with experimental data, illustrating that the ionomer in contact with the catalyst layer surface impacts the underlying kinetics both in planar electrodes and industrially-relevant MEA systems.References D. M. Koshy et al., J. Am. Chem. Soc., 143, 14712–14725 (2021) https://doi.org/10.1021/jacs.1c06212.N. Gupta, M. Gattrell, and B. MacDougall, J. Appl. Electrochem., 36, 161–172 (2006). This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was partially supported by a Cooperative Research and Development Agreement (CRADA) between Lawrence Livermore National Laboratory, Stanford University, and TotalEnergies American Services, Inc. (affiliate of TotalEnergies SE) under Agreement No. TC02307 and Laboratory Directed Research and Development (LDRD) funding under project 22-SI-006.LLNL-ABS-857478 Figure 1

CO2 Electrolysis via Surface-Engineering Electrografted Pyridines on Silver Catalysts.

The electrochemical reduction of carbon dioxide (CO2) to value-added materials has received considerable attention. Both bulk transition-metal catalysts and molecular catalysts affixed to conductive noncatalytic solid supports represent a promising approach toward the electroreduction of CO2. Here, we report a combined silver (Ag) and pyridine catalyst through a one-pot and irreversible electrografting process, which demonstrates the enhanced CO2 conversion versus individual counterparts. We find that by tailoring the pyridine carbon chain length, a 200 mV shift in the onset potential is obtainable compared to the bare silver electrode. A 10-fold activity enhancement at −0.7 V vs reversible hydrogen electrode (RHE) is then observed with demonstratable higher partial current densities for CO, indicating that a cocatalytic effect is attainable through the integration of the two different catalytic structures. We extended the performance to a flow cell operating at 150 mA/cm2, demonstrating the approach’s potential for substantial adaptation with various transition metals as supports and electrografted molecular cocatalysts.

Covalent Organic Frameworks Linked by Amine Bonding for Concerted Electrochemical Reduction of CO2

Summary Covalent organic frameworks (COFs) with amine linkage in both three and two dimensions, COF-300-AR and COF-366-M-AR, were synthesized by direct reduction of their corresponding COFs with imine linkage, COF-300 and COF-366-M, respectively. The quantitative reduction was confirmed by Fourier transform infrared and cross-polarization magic angle spinning NMR (both 13C and 15N) spectroscopy. These amine COFs were highly crystalline and exhibited excellent chemical stability in strong acids and bases. The abundant amino groups in the COF-300-AR backbone facilitated the electrochemical reduction of CO2 on silver electrodes in a concerted manner and led to selective generation of CO. Specifically, CO conversion efficiency was raised from 13% to 53% at −0.70 V and from 43% to 80% at −0.85 V (versus a reversible hydrogen electrode) in comparison with that of a bare silver electrode. The porosity of COFs favored molecular diffusion to the electrode surface, and the amine functional groups close to the electrode surface promoted CO2 conversion efficiency by forming carbamate intermediates.

Areca catechu Assisted Synthesis of Silver Nanoparticles and its Electrocatalytic Activity on Glucose Oxidation

In this work, a facile biogenic route for the synthesis of silver nanoparticles (AgNPs) is reported. The aqueous extract of Areca catechu (A. catechu) nuts are used as reducing source. The synthesized AgNPs characterized by UV–Visible (UV–Vis) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) with energy dispersive spectrum (EDS) analysis. The formations of AgNPs are identified from the appearance of yellow color and the surface plasmon resonance absorbance peak between 407 and 437 nm. The FT-IR results exposed that the active biomolecules of A. catechu are responsible for capping of AgNPs. The synthesized AgNPs are distorted spherical shape with 45 nm of size, identified from the HR-TEM. In application, the electrocatalytic activity of AgNPs is analyzed towards glucose oxidation using cyclic voltammetry. The results showed that A. catechu derived AgNPs act as good electrocatalyst than bare bulk silver and glassy carbon electrodes.

Electrocatalytic oxidation of ethanol at silver chloride/ bromide modified carbon paste electrodes

Silver chloride modified carbon paste electrode was prepared as a new electrode and used to electrocatalytic oxidation of ethanol. For the first time, the catalytic oxidation of ethanol was demonstrated by cyclic voltammetry, chronoamperometry and amperometry methods at the surface of this modified carbon paste electrode. Compared to silver chloride modified carbon paste electrode, silver bromide modified carbon paste electrode and bare silver electrode catalysts, silver chloride modified carbon paste electrode exhibited markedly superior catalytic activity for the electrocatalytic oxidation of ethanol. It can be seen that the electrocatalytic efficiency of silver chloride modified carbon paste electrode is higher than the silver bromide modified carbon paste and bare silver electrodes. The catalytic oxidation peak current was linearly dependent on the ethanol concentration. The j0 for silver chloride modified carbon paste and silver bromide modified carbon paste electrodes are 11.2 and 5.4 folds respectively higher than that of the bare silver electrode. For silver chloride modified carbon paste electrode, the charge transfer coefficient (α), the number of electrons involved in the rate determining step (nα) and exchange current density (j0) were calculated as 0.46, 1 and 5.05×10 respectively. The modified electrode possesses high selectivity, good reproducibility and well stability.

Self-forming electrode modification in organic field-effect transistors

High-performance top-gate TIPS-pentacene/PTAA OFETs having low contact resistance were fabricated by mixing PFBT directly into the semiconductor solution and spin-coating the solution on bare silver electrodes.

Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis

Hemoglobin (Hb) and silver–silver oxide (Ag–Ag2O) nanoparticles were co-immobilized on a bare silver electrode surface by cyclic voltammetry, and were characterized by UV–vis reflection spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The immobilized Hb was shown to maintain its biological activity well. Direct electron transfer between Hb and the resulting electrode was achieved without the aid of any electron mediator. The reduction currents to hydrogen peroxide (H2O2) at co-immobilized electrodes showed a linear relationship with H2O2 concentration over a concentration range from 6.0 × 10−6 to 5.0 × 10−2 mol L−1, and a detection limit of 2.0 × 10−6 mol L−1 (S/N = 3).

Surface-enhanced resonance Raman spectroscopic study of yeast iso-1-cytochrome c and its mutant

The structural stability and redox properties of yeast iso-1-cytochrome c and its mutant, F82H, were studied by surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Phenylalanine, which exists at the position-82 in yeast iso-1-cytochrome c, is replaced by histidine in the mutant. The SERRS spectra of the proteins on the bare silver electrodes indicate that the mutant possesses a more stable global structure with regard to the adsorption-induced conformational alteration. The redox potential of the mutant negatively shifts by about 400 mV, relative to that of yeast iso-1-cytochrome c. This is ascribed to axial ligand switching and higher solvent accessibility of the heme iron in the mutant during the redox reactions.

A new piezoelectric response model for protein adsorption kinetics at a solid–liquid interface

A piezoelectric response model on the protein adsorption kinetics at a solid–liquid interface was derived. It was based on the adsorption mechanism of two consecutive reactions and the fact that the thickness-shear-mode acoustic wave sensor responses to the mass accumulation on the sensor surface during the protein adsorption. This model was used to fit the experimental data of frequency shift for the lysozyme adsorption processes onto bare and thioglycollic acid (TGC)-modified silver electrode surfaces and those for the adsorption of bovine serum albumin (BSA) and human serum albumin (HSA) onto bare silver electrode surface. The fitted results were fairly consistent with the corresponding experimental data. The obtained regression values of rate constants, k 1 and k 2, for the lysozyme adsorption on bare silver surface were 5.93×10 −2 and 7.1×10 −4 s −1, respectively. And those for the lysozyme adsorption on TGC-modified surface were 7.46×10 −2 and 1.46×10 −3 s −1, respectively. The values of k 1 and k 2 for BSA adsorption on bare silver were 1.68×10 −2 and 4.52×10 −4 s −1, and those for HSA adsorption on bare silver were 2.13×10 −2 and 4.06×10 −3 s −1, respectively. These results exhibited the difference in adsorption kinetics for these systems.

Monitoring for adsorption of human serum albumin and bovine serum albumin onto bare and polystyrene-modified silver electrodes by quartz crystal impedance analysis

The adsorption of human serum albumin (HSA) and bovine serum albumin (BSA) from PBS (pH 7.4) onto bare and polystyrene (PS)-modified silver electrodes was in situ monitored using quartz crystal impedance analysis. The adsorption characteristics of HSA and BSA were discussed by analyzing piezoelectric parameter simultaneous responses. Experimental results indicated that for both HSA and BSA, the amount adsorbed on bare silver was more than that on PS-modified surface. The BSA amount adsorbed on the two surfaces was more than that of adsorbed HSA. A kinetic model was developed to describe the adsorption process and fitted to the experimental data of frequency shift. It was shown that HSA adsorption could be described by a kinetic equation involving two consecutive reactions. At lower concentration, BSA adsorption only involved the first reaction. At higher concentration, BSA adsorption on PS-modified surface involved two consecutive reactions. All fitted results were well in agreement with the corresponding experimental results. The regression values of reaction rate constants for the HSA and BSA adsorption were obtained. These data exhibited difference in adsorption kinetics under different conditions.

Dynamics and mechanism of the electron transfer process of cytochrome c probed by resonance Raman and surface enhanced resonance Raman spectroscopy

Stationary and time-resolved surface enhanced resonance Raman (SERR) spectroscopic techniques were employed to probe the mechanism and dynamics of the redox process of cytochrome c (Cyt- c) adsorbed on silver electrodes. On the bare silver electrode, the electron transfer steps were found to be coupled with conformational transitions between the native state B1 and a structurally altered state B2 that exhibits a drastic downshift of the redox potential. State B2, that was characterised by comparison with resonance Raman spectra of various Cyt- c states in solution, differs from state B1 by the lack of the axial methionine-80 ligand, which in a fraction of these species is most likely replaced by a histidine. For Cyt- c adsorbed on the bare electrode, the rate constants of the conformational transitions are similar to the formal heterogeneous electron transfer rate constants which for all species are between 2 and 4 s −1. Much faster electron transfer rates were found for Cyt- c adsorbed on coated electrodes covered with self-assembled monolayers (SAM) of ω-carboxyl alkanethiols. For such electrodes, state B2 could only be detected for SAMs with chain lengths shorter than 19 Å, confirming the view that the formation of this state results from electrostatic interactions. The implications of these findings for the biological electron transfer process are discussed.

The voltammetric behavior of concanavalin a at bare silver electrode and analytical application

The voltammetric behavior of concanavalin A at the bare silver electrode is described. Cyclic voltammograms show a pair of well-defined redox peaks for concanavalin A in the medium of phosphate buffer(pH=7.0) with electrochemical reaction rate constant ofK2=0.053 s−1 and electron transfer number ofn=2. Moreover, both the oxidation currents and the reduction currents have linear relationship with concanavalin A concentrations in the range of 1.0×10−6∼2.0×10−5 mol/L, which can be used as an analytical method for determining concanavalin A concentration.

Direct electron transfer reaction of glucose oxidase at bare silver electrodes and its application in analysis

AbstractThe direct electron transfer reaction of glucose oxidase (GOx) at a bare silver electrode is verified. The electron transfer number n = 2, electron transfer coefficient α = 0.45 and rate constant of the electrochemical reaction Ks = 0.1 s−1 are obtained. This communication presents a multimolecular adsorption model to explain the properties of the direct electron reaction between GOx and bare silver electrodes. The residual valence force may be an important factor to ensure a direct electron transfer reaction on the bare electrode. On the basis of the experimental fact that only biologically active GOx exhibits electrochemical activity in solution, a facile analytical method for analyzing the active GOx concentration is developed. The results determined correspond very well to that of a spectrometric method.

Observation of Electron Transfer between a Silver Electrode and Putidaredoxin Using Electromodulated Reflectance Spectroscopy

This paper reports measurements of the redox reaction rate for the {2Fe–2S} protein puditaredoxin (Pdx) on bare and bekanamycin-modified silver electrodes. The electron turnover rates were determined using electroreflectance (ER) and cyclic voltammetry (CV). The measurements were analyzed with two kinetic models: (1) strongly adsorbed protein layer and (2) freely diffusing protein. For the adsorbed layer model, the rates obtained with ER were almost two orders of magnitude greater than the rates obtained with CV. For the freely diffusing model, the rates determined by the two methods were similar, suggesting that this kinetic model is more appropriate. Modification of the Ag electrode with bekanamycin resulted in a negative 0.1-V shift of the Pdx formal potential, but showed only a small increase in the observed redox reaction rates. The measured rate constants were compared with the predictions of the Marcus theory of electron transfer.

A new method for fabricating flexible polymer electrodes and its application to the oxygen-reduction reaction

The fabrication of flexible polymer electrodes using silver-epoxy-coated poly(vinyl chloride) sheet further coated with a thin layer of conducting poly(phenylene oxide) is described. The electrode displayed improved performance for the oxygen-reduction reaction in alkaline solution compared with a bare silver electrode. This electrode is extremely lightweight and is suitable for application in fuel cells for space craft.

Direct electrochemistry of hemoglobin at a bare silver electrode promoted by cetyl pyridinium chloride and its application in analysis

AbstractThe electrochemical redox of hemoglobin at a bare silver electrode promoted by cetyl pyridinium chloride with the cyclic voltammetric technique has been studied. The electrode reaction exhibits such good stability that the peak currents change less than 8.5% (oxidation) and 10.2%(reduction) for a continuing scan of 30 min in a solution containing 1 × 10−7mol/L hemoglobin. The electrode reaction rate constant Ks is 0.0865s−1 with a single electron transfer. Moreover, both the oxidation currents and the reduction currents are linear with the concentration of hemoglobin over the range of 1 × 10 −8−5 × 10−7mol/L. So, it can be used as an analytical method of determining hemoglobin.

Voltammetric Response of Nicotinamide Coenzyme I at a Silver Electrode

The coenzyme dihydronicotinamide adenine dinucleotide (NADH) can be directly oxidized at ∼0.23 V at a bare silver electrode. Not only is the overpotential lower than that at the commonly used carbon or platinum electrodes, but the coenzyme gives a cathodic peak at ∼0.12 V which can be assigned to the reduction of the oxidized form. Since no mediator for the redox reaction of NAD+/NADH is present at the silver electrode surface, the working electrode is obviously stable and the reaction reported here is useful for electrochemical studies of the nicotinamide coenzyme.

Characterization of cytochurome c immobilized on modified gold and silver electrodes by surface-enhanced Raman spectroscopy

Surface-enhanced Raman scattering and surface-enhanced resonance Raman scattering spectroscopies were used to investigate the behavior of cytochrome c immobilized on the surfaces of gold and silver electrodes modified with bis (4-pyridyl) disulfide and 4-mercaptopyridine. The results are consistent with earlier models for the adsorption of cytochrome c at modified gold electrodes. At a bare silver electrode the cytochrome c is in a mixed spin state, but is in the native 6cLS state at the modified silver surface.

Direct electron transfer reaction of hemoglobin at the bare silver electrode

Most blologlcal macromolecules exhlblt rather low rates of electron transfer so that the resultmg currents are observed with difficulty at conventlonal electrodes, even when applymg relatively large overpotentlals Indeed, for many years it was thought that direct electron transfer between electrodes and redox protems was not possible for the reasons ascribed either to their extended three-dlmenslonal structure and the resulting maccesslblhty of the electroactlve center or to their adsorption onto and subsequent passlvatlon of the electrode surface Only relatively recently has the feaslblhty of studymg the electron transfer reactions of redox proteins at an electrode surface been viewed with any real optlmlsm Essentially, three different approaches have been tried to achieve direct electrode responses of the redox proteins The group of Hill and coworkers [1,2] has been at the forefront of developmg efficient and, possibly, speclflc promoters of bloelectrochemistry Baldwm 131, Dong [41 and other workers have devoted themselves to the fmdmg of the medlators which will catalyze the redox reactions of the proteins However, Hagen [Sl, Hawkrldge [61 and others have taken the approach to do without promoters or mediators by developing special pretreatment procedures and experlmental protocol for the use of bare electrodes Obviously, the last method may be the most appropriate, though unpromoted or unmediated bloelectrochemistry on bare electrodes 1s usually more difficult to obtam, because the data mterpretatlon may be hampered when the responses are determined speclflcally by the properties mtrmslc to the promoters

Binding and orientations of O 2 on Ag(100) and Pb/Ag(100) : Relationships to O 2 reduction by UPD lead on a silver electrode

Molecular orbital calculations using the atom superposition and electron delocalization method predict that O 2 favors binding parallel to the Ag(100) surface on the high-coordinate 4-fold site with its axis oriented in such a way that the O-ends point toward the neighboring 2-fold surface sites. In this orientation, the filled O 2 5σ and π u Orbitals donate to the Ag sd-hybrid orbitals and the surface back-donates to the half-filled O 2 π g orbitals. For the Pb-covered Ag(100) surface, the calculations show that the favored binding site and orientation for O 2 depend on the adatom coverage. At low coverages (θ pb≈ 1 4 ) , O 2 is predicted to bind perpendicular to the surface on the top of a Pb atom, whereas at higher coverages (θ pb≳ 1 2 ) , a lying-down O 2 with its axis bridging two nearest-neighbor Pb atoms on the surface is favored. These results for O 2 adsorption are related to the electrochemical results for O 2 reduction on the bare and UPD Pb-covered silver electrodes.