Increase In Electron Transfer Rate Research Articles

3D hierarchical Co3O4@Co3S4 nanoarrays as anode and cathode materials for oxygen evolution reaction and hydrogen evolution reaction.

With the increasing energy demand and environmental pollution, hydrogen production by water splitting is one of the best ways to solve the energy shortage. Three-dimensional (3D) hierarchical Co3O4@Co3S4/NF was first synthesized directly in situ, grown on the nickel foam through a simple hydrothermal process, and the anion-exchange reaction and the Ostwald ripening mechanism were investigated by adjusting the reaction time. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities of Co3O4@Co3S4/NF-24 h were investigated, and the required overpotentials were 270 mV and 143 mV, when the current density was 100 mA cm-2 and 20 mA cm-2, respectively. Subsequently, the overall water splitting activity of Co3O4@Co3S4/NF-24 h was investigated; when the current density was 10 mA cm-2, the low cell voltage was 1.53 V, which, to our knowledge, was among the smallest values reported for electro-driven water splitting so far. This high catalytic activity is attributed to the construction of the O-S interface and the increased electron transfer rate at the beginning of the reaction. Through XRD, SEM and XPS characterization, it is proven that Co3O4@Co3S4/NF-24 h is relatively stable and is expected to be an efficient and stable water splitting catalyst.

Coherent polyaniline/graphene oxides/multi-walled carbon nanotubes ternary composites for asymmetric supercapacitors

A coherent polyaniline (PANI)/graphene oxides (GOs)/multi-walled carbon nanotubes (MWCNTs) composite was prepared by in-situ solution polymerization as a positive electrode of supercapacitors. The orderly growth of PANI nano-dots on GOs led to the formation of the nano-ravines that can enhance ions diffusion efficiency. MWCNTs surrounded by PANI connected all components, and thus the conductivity with the increasing electron transfer rate was improved. The results showed that the electrode exhibited the outstanding electrochemical performances with the specific capacitance up to 696Fg−1 at 20mVs−1. The KOH-activated GOs/MWCNTs were used as a negative electrode to assemble an asymmetric supercapacitor (ASC). The ASC possessed an extended working potential (1.6V), a good rate capability (58% capacitance retention even after the current density being increased by 10 times), an excellent cycling stability (89% capacitance retention after 3000 cycles), and a decent average energy and power density (69Wh/kg and 6.4kW/kg).

Surface Modification for Enhanced Biofilm Formation and Electron Transport in Shewanella Anodes

In this study a simple, fast and effective surface modification method for enhanced biofilm formation, increased electron transfer rate and higher current density generation from microbial fuel cell (MFC) has been demonstrated. This method consists of partial oxidation of carbon felt material by UV/O3 treatment. Results from the electrochemical studies performed suggest that Shewanella oneidensis MR-1 biofilm formation is favored on UV/O3 treated carbon felt electrodes when subjected to an applied potential of −0.3 V vs. Ag/AgCl. Carbon electrodes exposed to 45 min of UV/O3 treatment provided the best electrochemical results and richer bacterial cell attachment. Ozone exposure above 45 min presented decreased MFC performance and current generation. Visual confirmation via SEM images indicated a link between the current generation and the presence of biomass attached to the working electrodes. In addition, we have shown enrichment of the electrode surface with flavin, which correlates with the increased anodic performance.

Improved performance of CdS/CdSe quantum dots sensitized solar cell by incorporation of ZnO nanoparticles/reduced graphene oxide nanocomposite as photoelectrode

Here we present novel quantum dot sensitized solar cells (QDSSC) based on ZnO nanoparticles (NPs)/reduced graphene oxide (RGO) nanocomposite photoanodes for better light harvesting and energy conversion. Photoelectrodes are prepared by doctor blading ZnO NPs/GO nanocomposite paste on a fluorine doped tin oxide substrate which are then sintered at 450 °C to obtain ZnO NPs/RGO nanocomposites. The partial reduction of GO after thermal reduction, is studied by Fourier transform infrared and Raman spectroscopies. Cadmium sulfide (CdS) and cadmium selenide (CdSe) quantum dots are deposited on the films through successive ionic layer adsorption and reaction and chemical bath deposition methods, respectively. The unique properties of ZnO NPs/RGO photoanodes, lead to a significant enhancement in the photovoltaic properties of solar cells in comparison with bare ZnO photoanodes. Current–voltage characteristics of cells are studied and the best results are obtained from ZnO NPs-RGO/CdS/CdSe with photoelectric conversion efficiency of 2.20% which is almost two times higher than cells which are made by pure ZnO NPs as photoanode (1.28%). Electrochemical impedance measurements show that the enhancement can be attributed to the increase of electron transfer rate in the ZnO NPs/RGO nanocomposite photoanode which arises from the ultrahigh electron mobility in graphene (RGO) sheets.

Electrochemical detection of trace cadmium in soil using a Nafion/stannum film-modified molecular wire carbon paste electrodes

In this paper, a novel Nafion polymer-coated stannum film-modified carbon paste electrode was developed for the analysis of trace cadmium by square wave anodic stripping voltammetry. The electronic conductive material—molecular wire (diphenylacetylene)—was employed as the binder instead of traditional mineral oil for fabricating this electrode. It was found that the prepared electrode possessed excellent electrochemical performance and increased electron transfer rate due to the introduction of molecular wire as a binder, and exhibited a better sensitivity and stability as well as high resistance to surfactants due to the synergistic effect of Nafion and stannum film. Under the optimal conditions, the stripping peak currents showed a good linear relationship with the Cd(II) concentration in the range from 1.0 to 80.0 μg L−1 with a detection limit of 0.13 μg L−1 (S/N = 3). The developed electrode was further applied to the determination of Cd(II) in soil extracts with satisfactory results.

Layer-by-layer assembled gold nanoparticles modified anode and its application in microbial fuel cells

Microbial fuel cells (MFCs) as one type of “green” energy source are drawing great attention among researchers. Anode performance is an important factor limiting the power output of MFCs for practical application. In this paper, the gold nanoparticles (Au NPs) modified carbon paper electrode was successfully constructed by layer-by-layer assembly technique for the first time. UV–vis spectroscopy was used to monitor the regular layer growth of the {PEI/Au}10 multilayer. The results of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in Fe(CN)63−/4− solution demonstrated that the Au NPs modified carbon paper electrode exhibited better electrochemical behavior than the bare carbon paper electrode, including relatively high electroactive surface areas, increased electron transfer rate and decreased interfacial electron transfer resistance. A two-chambered MFC equipped with the modified anode achieved a maximum power density of 346mWm−2 and a start-time for the initial maximum stable voltage of 175h, which were respectively 50% higher and 36% shorter than the corresponding values of the MFC with the unmodified anode. All the results indicated that the LBL assembly Au NPs-based modification on the anode was a simple but efficient method to incorporate Au NPs onto carbon paper electrodes and promoted the electricity generation of MFCs.

Role of Solvent and Dendritic Architecture on the Redox Core Encapsulation

Dendrimers with redox cores can accept, donate, and/or store electrons and are used in nanoscale devices like artificial receptors, magnetic resonance imaging, sensors, light harvesting antennae, and electrical switches. However, the dendrimer molecular architectures can significantly alter the encapsulation of the redox core and charge transfer pathways, thereby changing the electron transfer rates. In this study, we used molecular dynamics simulations to investigate the role of solvent and peripheral groups on molecular structure and core encapsulation of iron-sulfur G2-benzyl ether dendrimers in polar and nonpolar solvent. We found that the dendrimer branches collapse in water and swell in chloroform. The presence of the long hydrophobic alkyl groups at the periphery deters the encapsulation of the core in water which may cause an increase in electron transfer rate. However, in chloroform, the dendrimer branches remain in the extended form, which leads to an increased radius of gyration. Our results suggest that peripheral alkyl chains in dendrimers cause steric hindrance, which prevents branches from back folding in chloroform solvent, but in water it reverses the trend. Overall, the presence of a hydrophobic interior and hydrophilic periphery in a dendrimer improves core encapsulation in water while hindering encapsulation in chloroform.

Photoinduced electron transfer in covalent ruthenium–anthraquinone dyads: relative importance of driving-force, solvent polarity, and donor–bridge energy gap

Four rigid rod-like molecules comprised of a Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) photosensitizer, a 9,10-anthraquinone electron acceptor, and a molecular bridge connecting the two redox partners were synthesized and investigated by optical spectroscopic and electrochemical means. An attempt was made to assess the relative importance of driving-force, solvent polarity, and bridge variation on the rates of photoinduced electron transfer in these molecules. Expectedly, introduction of tert-butyl substituents in the bipyridine ligands of the ruthenium complex and a change in solvent from dichloromethane to acetonitrile lead to a significant acceleration of charge transfer rates. In dichloromethane, photoinduced electron transfer is not competitive with the inherent excited-state deactivation processes of the photosensitizer. In acetonitrile, an increase in driving-force by 0.2 eV through attachment of tert-butyl substituents to the bpy ancillary ligands causes an increase in electron transfer rates by an order of magnitude. Replacement of a p-xylene bridge by a p-dimethoxybenzene spacer entails an acceleration of charge transfer rates by a factor of 3.5. In the dyads from this study, the relative order of importance of individual influences on electron transfer rates is therefore as follows: solvent polarity ≥ driving-force > donor-bridge energy gap.

Comparative genomic analysis of Geobacter sulfurreducens KN400, a strain with enhanced capacity for extracellular electron transfer and electricity production

BackgroundA new strain of Geobacter sulfurreducens, strain KN400, produces more electrical current in microbial fuel cells and reduces insoluble Fe(III) oxides much faster than the wildtype strain, PCA. The genome of KN400 was compared to wildtype with the goal of discovering how the network for extracellular electron transfer has changed and how these two strains evolved.ResultsBoth genomes were re-annotated, resulting in 14 fewer genes (net) in the PCA genome; 28 fewer (net) in the KN400 genome; and ca. 400 gene start and stop sites moved. 96% of genes in KN400 had clear orthologs with conserved synteny in PCA. Most of the remaining genes were in regions of genomic mobility and were strain-specific or conserved in other Geobacteraceae, indicating that the changes occurred post-divergence. There were 27,270 single nucleotide polymorphisms (SNP) between the genomes. There was significant enrichment for SNP locations in non-coding or synonymous amino acid sites, indicating significant selective pressure since the divergence. 25% of orthologs had sequence differences, and this set was enriched in phosphorylation and ATP-dependent enzymes. Substantial sequence differences (at least 12 non-synonymous SNP/kb) were found in 3.6% of the orthologs, and this set was enriched in cytochromes and integral membrane proteins. Genes known to be involved in electron transport, those used in the metabolic cell model, and those that exhibit changes in expression during growth in microbial fuel cells were examined in detail.ConclusionsThe improvement in external electron transfer in the KN400 strain does not appear to be due to novel gene acquisition, but rather to changes in the common metabolic network. The increase in electron transfer rate and yield in KN400 may be due to changes in carbon flux towards oxidation pathways and to changes in ATP metabolism, both of which indicate that the overall energy state of the cell may be different. The electrically conductive pili appear to be unchanged, but cytochrome folding, localization, and redox potentials may all be affected, which would alter the electrical connection between the cell and the substrate.

Correlated Single Quantum Dot Blinking and Interfacial Electron Transfer Dynamics.

The electron transfer (ET) dynamics from core/multi-shell (CdSe/CdS(3ML)ZnCdS(2ML)ZnS(2ML)) quantum dots (QDs) to adsorbed Fluorescein (F27) molecules have been studied by single particle spectroscopy to probe the relationship between single QD interfacial electron transfer and blinking dynamics. Electron transfer from the QD to F27 and the subsequent recombination were directly observed by ensemble-averaged transient absorption spectroscopy. Single QD-F27 complexes show correlated fluctuation of fluorescence intensity and lifetime, similar to those observed in free QDs. With increasing ET rate (controlled by F27-to-QD ratio), the lifetime of on states decreases and relative contribution of off states increases. It was shown that ET is active for QDs in on states, the excited state lifetime of which reflects the ET rate, whereas in the off state QD excitons decay by Auger relaxation and ET is not a competitive quenching pathway. Thus, the blinking dynamics of single QDs modulate their interfacial ET activity. Furthermore, interfacial ET provides an additional pathway for generating off states, leading to correlated single QD interfacial ET and blinking dynamics in QD-acceptor complexes. Because blinking is a general phenomenon of single QDs, it appears that the correlated interfacial ET and blinking and the resulting intermittent ET activity are general phenomena for single QDs.

Photosynthetic characteristics of C<sub>4</sub> trait in chlorina mutant of rice (Oryza sativa L.)

Biao 810S is a chlorina mutant of the thermosensitive genic male sterile (TGMS) rice. We compared photosynthetic characteristics of these two lines. The contents of chlorophylls and carotenoids in Biao 810S were approximately half of those in 810S. However, the net photosynthetic rate (P N) of Biao 810S was higher than that of 810S under high irradiance or low concentration of carbon dioxide, and the photon quantum efficiency was higher than that of 810S. The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in Biao 810S was only 69.80 % of that in 810S, but the activities of phosphoenolpyruvate carboxylase and NADP-malic enzyme were 79.50 and 69.06 % higher than those of 810S, respectively, suggesting that the efficiency of photon energy utilization in Biao 810S was enhanced by reduction of thermal dissipation and increase of electron transfer rate to generate sufficient assimilation power for the dark reactions. Consequently, the increased activities of C4 photosynthetic enzymes lead to more effective fixation of CO2 and the synergistic effect of light and dark reactions contributed to the higher P N of Biao 810S.

Local electron transfer rate measurements on modified and unmodified glassy carbon electrodes

A natural and artificial distribution of electron transfer activity on glassy carbon electrodes can be observed and quantified by the use of scanning electrochemical microscopy (SECM). A large (sevenfold) spread in rate constant is found for randomly sampled sites on polished, untreated glassy carbon surfaces. Direct-mode oxidation with the SECM tip was used to produce small regions of oxidized carbon on a polished surface. A large increase in electron transfer rate for the Fe(II/III) ion is observed on the locally oxidized carbon surface in comparison to the unoxidized region. Rate constant measurements made along a line profiles the transition from unoxidized to oxidized surfaces. SECM images of defect sites show reaction–rate variations. Rate constants measured at several locations of the defective surface allows discrimination between the kinetic and topographic components of the SECM image.

Mechanism of electron transfer in fusion protein cytochrome b 5—NADH-cytochrome b 5 reductase

In the present work we summarize results on construction of expression plasmid, heterologous expression in Escherichia coli, isolation and purification, as well as physicochemical characterization of chimeric protein consisting of hydrophilic domain of cytochrome b(5) and truncated from the N-terminal sequence (Delta(23)) form of NADH-cytochrome b(5) reductase. The kinetics and mechanism of electron transfer between NADH-cytochrome b(5) reductase and cytochrome b(5) in the frames of fusion protein consisting of cytochrome b(5) (94 amino acids) and truncated form of NADH-cytochrome b(5) reductase (277 amino acids) have been studied. It is shown that electron transfer takes place between redox partners belonging to two different molecules of the chimeric protein. Using computer modeling, we built the model of the tertiary structure of the fusion protein, which is in agreement with experimental data. By using Marcus theory of electron transfer in polar media, we demonstrate the inability of the hypothesis of electrostatic repulsions to explain the increase of electron transfer rate on increase of ion concentration in media due to elimination of the repulsion of similar charges. The real reason for the increase of the first order rate constant in some oxidation-reduction reactions between proteins, as shown in the present work, is a decrease of the media reorganization energy resulting in decrease of activation energy for oxidation-reduction reactions.

Modified carbon surfaces as "organic electrodes" that exhibit conductance switching.

Glassy carbon (GC) surfaces modified with monolayers of biphenyl and nitrobiphenyl molecules were examined as voltammetric electrodes for ferrocene, benzoquinone, and tetracyanoquinodimethane electrochemistry in acetonitrile. The modified electrodes exhibited slower electron transfer than unmodified GC, by factors that varied with the monolayer and redox system. However, after a negative potential excursion to approximately -2.0 V versus Ag+/Ag, the modified electrodes exhibited much faster electron-transfer kinetics, approaching those observed on unmodified GC. The effect is attributed to an apparently irreversible structural change in the biphenyl or nitrobiphenyl monolayer, which increases the rate of electron tunneling. The transition to the "ON" state is associated with electron injection into the monolayer similar to that observed in previous spectroscopic investigations and causes a significant decrease in the calculated HOMO-LUMO gap for the monolayer molecule. Once the monolayer is switched ON, it supports rapid electron exchange with outer-sphere redox systems, but not with dopamine, which requires adsorption to the GC surface. The increase in electron-transfer rate with electron injection is consistent with an increase in electron tunneling rate through the monolayer, caused by a significant decrease in tunneling barrier height. The ON electrode can reduce biphenyl- or nitrobiphenyldiazonium reagent in solution to permit formation of a second modification layer of biphenyl or nitrobiphenyl molecules. This "double derivatization" procedure was used to prepare tetraphenyl- and nitrotetraphenyl-modified electrodes, which exhibit significantly slower electron transfer than their biphenyl and nitrobiphenyl counterparts. A "switching" electrode may have useful properties for electroanalytical applications and possibly in electrocatalysis. In addition, the ON state represents an "organic electrode" in which electron transfer occurs at an interface between an organic conductor and a solution rather than an interface between a solution and a metal or carbon electrode.

Topological Effects in Electron Transfer: Applications to Dendrimers and Branched Molecules

Dendrimers belong to a class of complex hyperbranched structures through which electron transfer has been observed; in this work, we study the effect of the bridge topology on long-range transfer. Electron-transfer rates for bridge-mediated electron transfer are calculated by solving the steady-state Liouville equation with phenomenological corrections for solvent interaction. While the behavior of linear bridge groups is well-known, branched structures display interesting electron transport properties. Addition of a small side group with nodes equivalent to the bridge nodes increases the steady-state rate, and this effect is amplified by increasing the site−site couplings in the side group. The effect for a single side group is small, but increases with each additional side group producing a noticeable increase in electron transfer rates for structures with several side groups such as dendrimers. Addition of an electron withdrawing side group at the acceptor end of the bridge creates a structure that can...

Selective enhancement of resonance Raman spectra of separate bacteriopheophytins in Rb. sphaeroides reaction centers.

Tunable dye laser excitation of carefully prepared samples of Rb. sphaeroides reaction centers provides richly detailed resonance Raman (RR) spectra of the bacteriopheophytins, H, and the accessory bacteriochlorophylls, B. These spectra demonstrate selective enhancement of the separate bacteriopheophytins on the active (H(L)) and inactive (H(M)) sides of the reaction centers. The spectra are assigned with the aid of normal coordinate analyses using force fields previously developed for porphyrins and reduced porphyrins. Comparison of the H(L) and H(M) vibrational mode frequencies reveals evidence for greater polarization of the acetyl substituent in H(L) than H(M). This polarization is expected to make H(L) easier to reduce, thereby contributing to the directionality of electron transfer from the special pair, P. In addition, the acetyl polarization of H(L) is increased at low temperature (100 K), helping to account for the increase in electron transfer rate. The polarizing field is suggested to arise from the Mg(2+) of the neighboring accessory bacteriochlorophyll, which is 4.9 A from the acetyl O atom. The 100 K spectra show sharpening and intensification of a number of RR bands, suggesting a narrowing of the conformational distribution of chromophores, which is consistent with the reported narrowing of the distribution in electron transfer rates. Excitation at 800 nm produces high-quality RR spectra of the accessory bacteriochlorophylls, and the spectral pattern is unaltered on tuning the excitation to 810 nm in resonance with the upper exciton transition of P. Either the resonance enhancement of P is weak, or the bacteriochlorophyll RR spectra are indistinguishable for P and B.

Coupled activation of the donor and the acceptor side of photosystem II during photoactivation of the oxygen evolving cluster.

Photoactivation of photosystem II has been studied in the FUD 39 mutant of Chlamydomonas reinhardtii that lacks the 23 kDa extrinsic subunit of photosystem II. We have taken advantage of the slow photoactivation rate of FUD 39, earlier demonstrated in Rova, E. M., et al. [(1996) J. Biol. Chem. 271, 28918-28924], to study events in photosystem II during intermediate stages of the process. By measuring the EPR multiline signal, the decay of the variable fluorescence after single flashes, and electron transfer from water to the QB site, we found a good correlation between the building of a tetrameric Mn cluster, longer recombination times between QA- and the donor side of photosystem II, and the achievement of water splitting ability. An increased rate of electron transfer from QA- to the QB site on the acceptor side of photosystem II, mainly due to enhanced efficiency of binding of QB to its site, was found to precede the building of the Mn cluster. We also showed that TyrD was oxidized simultaneously with this increase in electron-transfer rate. Thus, it appears that photoactivation is sequential, with an increased rate of electron transfer on the acceptor side occurring together with the oxidation of TyrD in the first step, followed by the assembly of the Mn cluster. We suggest that a conformational change of photosystem II is induced early in the photoactivation process facilitating electron transfer from the primary donor to the acceptor side. As a consequence, TyrD, an auxiliary electron donor to P680+/TyrZ*, is oxidized. That this occurs before the Mn cluster is fully functional serves to protect photosystem II against donor side induced photodamage.

An integral equation approximation for the dynamics of reversible electron-transfer reactions

The solution to an integral equation [J. Zhu and J. C. Rasaiah, J. Chem. Phys. 96, 1435 (1992)] for the survival probabilities in the Sumi–Marcus model of reversible electron-transfer (ET) reactions, in which ligand vibrations and fluctuations in the solvent polarization play important roles, is obtained numerically using a simple computer program suitable for use on a PC. The solutions depend on the time correlation function Δ(t) of the reacting intermediates along the reaction coordinate which is shown to be equal to the time correlation function of the Born free energy of solvation of these intermediates even in discrete molecular solvents provided its response is linear. This enables Δ(t) to be determined accurately from time-delayed fluorescence Stokes shift experiments or from dynamical theories of ion solvation; it is usually an exponential (Debye solvent) function of time or a sum of such exponentials (non-Debye solvent). The solutions to the integral equation, which can be obtained numerically for any given Δ(t), are found to predict the electron-transfer dynamics successfully over a wide range of model parameters. They can also be approximated by single or multiexponential interpolation formulas in which the thermally equilibrated rate constants are modified by a factor which reflects the relative importance of ligand (or inner-sphere solvent) vibration and outer-sphere solvation dynamics. The use of an effective longitudinal relaxation time in calculations of ET rates in solution is shown to be a poor assumption in some solvents. The theory is compared with an experiment in the inversion region, and its extension to include high-frequency vibrational modes that lead to an increased ET rate in other experiments is discussed.

Iron-Induced Changes in Light Harvesting and Photochemical Energy Conversion Processes in Eukaryotic Marine Algae

The role of iron in regulating light harvesting and photochemical energy conversion processes was examined in the marine unicellular chlorophyte Dunaliella tertiolecta and the marine diatom Phaeodactylum tricornutum. In both species, iron limitation led to a reduction in cellular chlorophyll concentrations, but an increase in the in vivo, chlorophyll-specific, optical absorption cross-sections. Moreover, the absorption cross-section of photosystem II, a measure of the photon target area of the traps, was higher in iron-limited cells and decreased rapidly following iron addition. Iron-limited cells exhibited reduced variable/maximum fluorescence ratios and a reduced fluorescence per unit absorption at all wave-lengths between 400 and 575 nm. Following iron addition, variable/maximum fluorescence ratios increased rapidly, reaching 90% of the maximum within 18 to 25 h. Thus, although more light was absorbed per unit of chlorophyll, iron limitation reduced the transfer efficiency of excitation energy in photosystem II. The half-time for the oxidation of primary electron acceptor of photosystem II, calculated from the kinetics of decay of variable maximum fluorescence, increased 2-fold under iron limitation. Quantitative analysis of western blots revealed that cytochrome f and subunit IV (the plastoquinone-docking protein) of the cytochrome b(6)/f complex were also significantly reduced by lack of iron; recovery from iron limitation was completely inhibited by either cycloheximide or chloramphenicol. The recovery of maximum photosynthetic energy conversion efficiency occurs in three stages: (a) a rapid (3-5 h) increase in electron transfer rates on the acceptor side of photosystem II correlated with de novo synthesis of the cytochrome b(6)/f complex; (b) an increase (10-15 h) in the quantum efficiency correlated with an increase in D1 accumulation; and (c) a slow (>18 h) increase in chlorophyll levels accompanied by an increase in the efficiency of energy transfer from the light-harvesting chlorophyll proteins to the reaction centers.

Surface enhanced Raman examination of carbon electrodes: effects of laser activation and electrochemical pretreatment

Ag particles increase the Raman scattering intensity from the carbon substrate by 30-100 times, or larger for special cases. In the current report, the technique was used to characterize the surfaces of laser activated and electrochemically pretreated (ECP) glassy carbon (GC) and highly ordered pyrolytic graphite (HOPG). The SERS spectra were more surface selective than normal Raman and more closely correlated with electrochemical observations. For laser-activated HOPG, the SERS spectra revealed damage to the graphite lattice at lower power densities, and the disorder exhibited in SERS spectra more closely tracked the increase in electron transfer rate. For ECP of GC, HOPG, and pyrolytic graphite, the surface film examined with SERS was indistinguishable for the three substrates. Finally, the damage resulting from ECP of HOPG is consistent with a nucleation and growth mechanism. electrodeposition of 0.2 pmol/cm2 of metallic silver. As demonstrated previously, the resulting ca. 400w