Heterogeneous Electron Transfer Process Research Articles

Electrogenerated Chemiluminescence Imaging of Single‐Atom Nanocatalysts

AbstractSingle‐atom catalysts (SACs), distinguished by their maximum atom efficiency and precise control over the coordination and electronic properties of individual atoms, show great promise in electrocatalysis. Gaining a comprehensive understanding of the electrochemical performance of SACs requires the screening of electron transfer process at micro/nano scale. This research pioneers the use of electrogenerated chemiluminescence microscopy (ECLM) to observe the electrocatalytic reactions at individual SACs. It boasts sensitivity at the single photon level and temporal resolution down to 100 ms, enabling real‐time capture of the electrochemical behavior of individual SACs during potential sweeping. Leveraging the direct correlation between ECL emission and heterogeneous electron transfer processes, we introduced photon flux density for quantitative analysis, unveiling the electrocatalytic efficiency of individual SACs. This approach systematically reveals the relationship between SACs based on different metal atoms and their peroxidase (POD)‐like activity. The outcomes contribute to a fundamental understanding of SACs and pave the way for designing SACs with diverse technological and industrial applications.

Electrogenerated Chemiluminescence Imaging of Single-Atom Nanocatalysts.

Single-atom catalysts (SACs), distinguished by their maximum atom efficiency and precise control over the coordination and electronic properties of individual atoms, show great promise in electrocatalysis. Gaining a comprehensive understanding of the electrochemical performance of SACs requires the screening of electron transfer process at micro/nano scale. This research pioneers the use of electrogenerated chemiluminescence microscopy (ECLM) to observe the electrocatalytic reactions at individual SACs. It boasts sensitivity at the single photon level and temporal resolution down to 100 ms, enabling real-time capture of the electrochemical behavior of individual SACs during potential sweeping. Leveraging the direct correlation between ECL emission and heterogeneous electron transfer processes, we introduced photon flux density for quantitative analysis, unveiling the electrocatalytic efficiency of individual SACs. This approach systematically reveals the relationship between SACs based on different metal atoms and their peroxidase (POD)-like activity. The outcomes contribute to a fundamental understanding of SACs and pave the way for designing SACs with diverse technological and industrial applications.

Electrosynthesis of Au nanocluster embedded conductive polymer films at soft interfaces using dithiafulvenyl-functionalized pyrene.

Nanoparticle (NP) embedded conductive polymer films are desirable platforms for electrocatalysis as well as biomedical and analytical applications. Increased catalytic and analytical performance is accompanied by concomitant decreases in NP size. Herein, highly reproducible electrogeneration of low dispersity Au nanocluster embedded ultra-thin (∼2 nm) conductive polymer films at a micro liquid|liquid interface is demonstrated. Confinement at a micropipette tip facilitates a heterogeneous electron transfer process across the interface between two immiscible electrolyte solutions (ITIES), between KAuCl4(aq) and a dithiafulvenyl-substituted pyrene monomer, 4,5-didecoxy-1,8-bis(dithiafulven-6-yl)pyrene (bis(DTF)pyrene), in oil, i.e., a w|o interface. At a large ITIES the reaction is spontaneous, rapid, and proceeds via transfer of AuCl4- to the oil phase, followed by homogeneous electron transfer generating uncontrolled polymer growth with larger (∼50 nm) Au nanoparticles (NPs). Thus, miniaturization facilitates external, potential control and limits the reaction pathway. Atomic (AFM) and Kelvin probe force microscopies (KPFM) imaged the topography and work function distribution of the as-prepared films. The latter was linked to nanocluster distribution.

Recent advances in electroanalytical methods for electroorganic synthesis

Electroorganic synthesis is a sustainable technique that effectively combines electrochemistry and organic synthesis. However, the investigation of its mechanism remains a challenge owing to the complexity of the heterogeneous electron transfer process. Electroanalytical methods can offer valuable insights into its mechanism through simple and rapid procedures. In this short review, we highlight the advancements achieved in the last two years in electroanalytical methods used for the mechanistic investigation of electroorganic synthesis, from widely used cyclic voltammetry to other advanced electroanalytical techniques. Finally, we discuss our perspective on these methods.

A Critical Reassessment of the Mechanism of the Oxygen Reduction Reaction on Au(poly) in Aqueous Alkaline Electrolytes

The oxygen reduction reaction, ORR, in aqueous electrolytes, may rank among the most studied heterogeneous electron transfer processes. Despite the extraordinary efforts of numerous research groups worldwide, critical questions still remain unanswered regarding critical aspects of this technologically important reaction and the dependence of its mechanism and rates on the nature of the electrode material. In their pioneering studies, Zurilla et al.1 examined the ORR on polycrystalline gold, Au(poly), in alkaline solutions, using rotating ring-disk electrode, RRDE, techniques. According to these authors, the experimental evidence collected was consistent with a mechanism involving an initial one-electron transfer to yield adsorbed superoxide ion, O2 -(ads), which, subsequently, underwent a second order heterogeneous dismutation generating solution phase peroxide and oxygen, O2(aq) and HO2 -(aq). The same mechanism was later invoked by Adzic et al.2 for the ORR on Au(100), a surface that displayed extraordinary activity compared to other low index faces of Au. More recently, Ignaczak et al.3 put forward theoretical arguments that support the view that the initial RDS is actually of the outer sphere type, yielding a solvated species, i.e. O2 -(aq), which is then followed by a subsequent, fast, outer sphere one electron-transfer, generating solution phase peroxide, HO2 -(aq), and not by a second order dismutation of as was postulated earlier in the literature. This is shown as the ‘outer sphere pathway’ in Scheme 1. Scheme 1: Proposed inner and outer sphere pathways for ORR on Au in basic solution.This presentation will describe the use of RRDE methods to examine the kinetics of the ORR on Au(poly) in 0.1 M NaOH + 0.9 M NaClO4 aqueous electrolytes containing oxygen in one case and peroxide in the other. The results obtained were found to be consistent with Ignaczak et al.’s mechanism, or equivalently an inner sphere pathway (Scheme 1) which includes a fast equilibrium between O2 -(aq), HO2 -(aq) and their corresponding adsorbed counterparts, O2 -(ads) i.e. and HO2 -(ads) however, a critical assessment of in situ vibrational spectroscopy data published in the literature has raised questions regarding the assignment of the spectral features reported for these adsorbed species. Also considered in this model is the direct reduction of HO2 -(aq) and O2(aq) to generate OH-(aq). Quantitative analyses of data collected in O2-saturated and Ar-purged containing solutions made it possible to determine a unique set of kinetic rate constants for the various steps in the proposed mechanism over a wide potential range.

Dual Role of MoS2 Quantum Dots in a Cross-Dehydrogenative Coupling Reaction.

Modern day research focuses on the development of greener and eco-friendlier protocols to fabricate biologically relevant targets with minimal waste generation. C-C bond formation reactions are of prime importance in this regard. In a typical photocatalytic hydrogen evolution reaction, three components are used, viz, catalyst, photosensitizer, and sacrificial amine donor. Among these, the photosensitizer and sacrificial amine donors are wasted at the end of the reaction. Considering these drawbacks, in this work, we have developed a methodology targeted at the utilization of sacrificial amine donors for C-H functionalization with MoS2 quantum dots (QDs) as the catalyst as well as the photosensitizer. QDs indeed emerged to be an active participant in the heterogeneous electron transfer process. This concept opens up new possibilities in the field of nanomaterial-based photomediated organic transformations without the aid of any external photosensitizers via a clean and sustainable protocol with no side product.

Cu@Pd Core–Shell Nanostructures on Pencil Graphite Substrates as Disposable Electrochemical Sensors for the Detection of Biological Amines

Adsorption of molecules at the electrode/solution interface is of great significance in understanding heterogeneous electron transfer processes. Herein, we study the interfacial properties of coppe...

Redox activity of single bacteria revealed by electrochemical collision technique

This paper reports on an innovative strategy based on the electrochemical collision technique to quantify the redox activity of two bacterial species: the Gram-negative Escherichia coli and the Gram-positive Bacillus subtilis. Thionine (TH), as a redox mediator, was electrostatically adsorbed on bacterial surface and formed the bacterium-TH complexes. TH can receive electrons from bacterial metabolic pathways and be reduced. When a single bacterium-TH complex collides on the ultramicroelectrode, the reduced TH will be re-oxidized at certain potential and generate current spike. The frequency of the spikes is linearly proportional to the living bacteria concentration, and the redox activity of individual bacterium can be quantified by the charges enclosed in the current spike. The redox ability of Gram-negative E.coli to the TH mediator was 6.79 ± 0.26 × 10−18 mol per bacterial cell in 30 min, which is relatively more reactive than B. subtilis (3.52 ± 0.31 × 10−18 mol per cell). The spike signals, fitted by 3D COMSOL Multiphysics simulation, revealed that there is inherent redox ability difference of two bacterial strains besides the difference in bacterial size and collision position. This work successfully quantified the bacterial redox activity to mediator in single cells level, which is of great significance to improve understanding of heterogeneous electron transfer process and build foundations to the microorganism selection in the design of microbial electrochemical devices.

Urea-induced denaturation of immobilized yeast iso-1 cytochrome c: Role of Met80 and Tyr67 in the thermodynamics of unfolding and promotion of pseudoperoxidase and nitrite reductase activities

The Met80Ala and Met80Ala/Tyr67Ala variants of S. cerevisiae iso-1 cytochrome c (ycc) immobilized on a decane-1-thiol coated gold electrode subjected to the denaturing action of urea were studied through variable temperature cyclic voltammetry and Surface-Enhanced Resonance Raman spectroscopy (SERRS). We found that the His/OH− axial heme iron coordination in both variants is unaffected by urea up to 7 M, although some conformational changes occur that increase exposure of the heme center to solvent. The thermodynamics of the unfolding process were determined with an unprecedented approach, which can be of general use for electroactive proteins. The free energy of unfolding for both variants includes relevant entropic contributions and is lower than that for the species carrying an intact Met/His coordination, consistent with the role of the axial Fe-(S)Met bond and the H-bond network involving Tyr67 in stabilizing the polypeptide matrix in the heme crevice. Their lower conformational stability results in a different interaction with the MUA/MU SAM compared to the His/Met ycc forms. Denaturation invariably slows down the heterogeneous electron transfer process, but its effect on the activation enthalpy and pre-exponential factor differs for the species with and without His/Met axial heme ligation. In particular, urea unfolding of the M80A and M80A/Y67A mutants lowers the structural restraint to the heterogeneous ET. Here we show that removal of the Met ligand and an increased accessibility of the heme center to solvent through partial protein unfolding– which mimic the molecular stress experienced by mammalian cytochromes c upon binding to cardiolipin in the early events of apoptosis - add up to transform cytochrome c into an efficient electrocatalyst toward the reduction of hydrogen peroxide and nitrite.

Linkage between Fluorescence and Electrochemical Properties of Imidazolium Compounds in Acetonitrile Solution.

The fluorescence properties of some imidazolium derivatives are relevant in photosensing and therefore, the structural analysis of them is a key point for its rational design, which would be useful to prepare new systems with novel applications. Herein we report a multidisciplinary study of the fluorescence and voltammetric properties of three imidazolium compounds {1,3-bis[(R,R)-1'-chloro-1'-phenylpropan-2'-yl]-imidazolium chloride (1), 1,3-bis[(Z)-1'-phenylprop-1'-en-2'-yl]imidazolium chloride (2) 1,3-bis[(R)-1'-chlorobutan-2'-yl]-imidazolium chloride (3)}. Electronic structure calculations and Bader analyses were used to correlate both fluorescence and the capability of the molecules to be reduced through a heterogeneous electron transfer process. Both properties are strongly dependent on the proton in position two of the imidazolium ring, where the electron transfer as well as the excitation of the electrons are carried out. The reactivity in this position is controlled by the N-substituents on the imidazolium ring and is due to single contacts H⋅⋅⋅Cl- , tricentric contacts Cl⋅⋅⋅Cl- ⋅⋅⋅Cl, π-electronic delocalization and π-stacking interactions.

(Invited) Thin Layer Sonoelectrochemistry: Impacts on Slow Electron Transfer Kinetics without Visible Cavitation

Sonochemistry and sonoelectrochemistry are typically undertaken in a bulk fluid with sonication of sufficient intensity to generate visible cavitation. Sonoelectrochemistry was undertaken in a thin layer of fluid with a quartz crystal oscillator. In the thin layer configuration, no cavitation is visible and mass transport is not impacted, but impacts on electron transfer kinetics are observed. Because there is no visible cavitation, cyclic voltammetric responses typical of a quiescent electrolyte are observed. From the voltammograms for species that undergo rapid heterogeneous electron transfer such as outer sphere Ru(bpy)₃²⁺⇌Ru(bpy)₃³⁺+e, voltammetric morphology is unchanged on sonication of a thin layer of fluid. For Fe³+e⇌ Fe² that undergoes quasireversible (slower) electron transfer under cyclic voltammetric perturbation, sonication in a thin layer is found to increase the rate of heterogeneous electron transfer by roughly an order of magnitude. Sonoelectrochemical catalysis for inherently slow heterogeneous electron transfer processes is generated and observed in a thin layer of electrolyte. In the experiments reported here, the fluid layer was less than the wavelength of sonication. The aqueous electrolyte contains redox species and acid. Experiments were undertaken at a platinum wire electrode using a 41 kHz quartz crystal oscillator. For the same experimental conditions, no impact on the electron transfer reversible Ru(bpy)₃²⁺ was observed. All data were collected at a fixed frequency; impacts varied with oscillator intensity. As with many sonoelectrochemical experiments, subtle variation in experimental parameters complicate generation of reproducible results. Here, data generated by two different experimentalists yield similar outcomes. Best operating conditions differed slightly for the two experimentalists but the pattern of increased interfacial electron transfer rates for iron on sonication was found by both. Reference [1] Johna Leddy, Chester G. Duda, Jacob Lyon, and William J. Leddy III, "Thin Layer Sonoelectrochemistry and Sonoelectrochemistry Devices and Methods," published 28 May 2015 as US Patent Application 20150147594 A1.

Electron transfer controlled by solvent and counter-anion dynamics in electrochemistry of viologen-type ionic liquid

Temperature-dependent diffusion coefficients (DO) and heterogeneous electron transfer rate constants (k0) were measured for the viologen dication (V2+) in 1-butyl-1′-heptyl-4,4′-bipyridinium bis[(trifluoromethane)sulfonyl]imide [C4VC7][Tf2N]2 redox-active ionic liquid (RAIL) and its solution. The measurements were made in three systems: (1) 10 mM of [C4VC7][Tf2N]2 dissolved in 0.1 M K[Tf2N]/acetonitrile (an organic electrolyte), (2) 10 mM [C4VC7][Tf2N]2 dissolved in a 1-n-hexyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate, [HMIm][FEP] ionic liquid (IL) (an ionic liquid (IL) electrolyte), and (3) the undiluted RAIL of 1.68 M [C4VC7][Tf2N]2 with no additional solvents or supporting electrolytes. At 25 °C, the DO values in systems (1), (2), and (3) were 8.2 × 10−6, 6.7 × 10−8, and 1.3 × 10−9 cm2 s−1, and the k0 values were 1.1 × 10−2, 3.6 × 10−3, and 2.0 × 10−5 cm s−1, respectively. Temperature-dependent DO and k0 values were further interrelated to investigate heterogeneous interfacial electron transfer processes in systems (2) and (3). Solvent dynamics and counter-ion relaxation processes were used to describe the results. In system (3), k0 values were proportional to both DO and counter-ion diffusion coefficients (DCIon) but inversely proportional to the viscosity (η). Moreover, almost the same magnitude of thermal activation barrier (∼64 kJ mol−1) was found for k0, DO, DCIon, and η−1 in the system (3). In system (2), k0 values showed a non-linear relationship with DO, DCIon and η−1, and a thermal activation barrier was found to be 22.2 kJ mol−1. These results enabled us to conclude that the V+/V2+ heterogeneous electron transfer in system (3) is controlled concurrently by solvent dynamics (segmental motion of alkyl chains attached to viologen centers) and electro-inactive counter anion motion. This work reveals an inherent dependency of heterogeneous electron transfer kinetics on the solvent and counter-ion dynamics in viologen IL systems.

Dynamical simulation of electron transfer processes in self-assembled monolayers at metal surfaces using a density matrix approach

A single-particle density matrix approach is introduced to simulate the dynamics of heterogeneous electron transfer (ET) processes at interfaces. The characterization of the systems is based on a model Hamiltonian parametrized by electronic structure calculations and a partitioning method. The method is applied to investigate ET in a series of nitrile-substituted (poly)(p-phenylene)thiolate self-assembled monolayers adsorbed at the Au(111) surface. The results show a significant dependence of the ET on the orbital symmetry of the donor state and on the molecular and electronic structure of the spacer.

Local electrochemical reactivity of single layer graphene deposited on flexible and transparent plastic film using scanning electrochemical microscopy

The local electrochemical reactivity of single layer graphene/ethylene vinyl acetate/polyethylene terephthalate (EVA/PET) plastic film was investigated using scanning electrochemical microscopy (SECM). Interestingly, depending on the reducing or oxidizing power of the selected redox mediator, the SECM response changes from slow (case of electron donor) to fast (case of electron acceptor) electron transfer rate. Furthermore, the as-prepared graphene was modified through the electrochemical reduction of p-nitrophenyl diazonium leading to the attachment of thin organic layer. The SECM investigations demonstrate that the attached nitrophenyl layer accelerates the heterogeneous electron transfer process when using electron donor as redox probe. The overpotential transition from slow to fast electron transfer was shifted by 400 mV, when compared to the un-modified graphene, suggesting the increase of the work function of the modified graphene. However, further functionalization with a Pt nanoparticles selectively makes the substrate as “insulating-like” layer toward electron acceptor species. Overall, depending on the deposited material and the used redox probe (electron donor or acceptor) the SECM investigations reveals that the properties of the graphene change from p to n type doping. This technique can be applied to the electrochemical investigations of graphene supported insulating, flexible and transparent material.

Efficient Photoluminescence of Mn2+-Doped ZnS Quantum Dots Sensitized by Hypocrellin A

Mn2+-doped ZnS semiconductor quantum dots reveal remarkably intense photoluminescence with the4T1(4G) f6A1(6S) transition. In this study, following growth doping technique, Mn2+-doped ZnS quantum dots (ZnS:Mn2+QDs) with high-quality optical properties and narrow size distribution were synthesized successfully. The dopant emission has been optimized with various reaction parameters, and it has been found that the percentage of introduced dopant, reaction temperature, and time as well as the pH of a reaction mixture are key factors for controlling the intensity. Photoluminescence emission (PL) measurements of ZnS:Mn2+QDs show Mn2+d-d orange luminescence along with band-edge blue luminescence. Moreover, the electron transfer from singlet states of hypocrellin A (HA) to colloidal ZnS:Mn2+QDs has been examined by absorption spectra and fluorescence quenching. The absorption spectrum gave an evidence of the increases in the extinction coefficient and the red-shift of the absorption maxima in the absorption spectra of HA in the presence of ZnS:Mn2+QDs, demonstrating the occurrence of surface interactions between the sensitizer and the particle surface. Fluorescence quenching by ZnS:Mn2+QDs also suggested that there were a complex association between HA and ZnS:Mn2+QDs, which was necessary for observing the heterogeneous electron-transfer process at the interface of sensitizer-semiconductor.

Kinetic Control of Electron Transfer at Doped Zinc Oxide/Redox-active Molecule Interface for Photocurrent Rectification

Abstract Reactivity of redox-active molecules for heterogeneous electron-transfer processes at the surface of doped zinc oxide substrates depended on their energy levels. The redox-active molecules with negative redox potentials displayed a reversible electrochemical response but those with positive redox potentials were characterized by slow electrode kinetics, which was attributed to more than three times larger heterogeneous electron-transfer rate constant for the former redox-active molecules. A photovoltaic cell using methyl viologen as an acceptor molecule, TEMPOL as a donor molecule, and the doped ZnO as the transparent conducting substrate gave high photovoltage, which was ascribed to the reactivity of the redox-active molecules at the doped ZnO surface.

Modulating indium doped tin oxide electrode properties for laccase electron transfer enhancement

Indium doped tin oxide (ITO) electrodes were functionalized with gold nanoparticles (GNPs) and cysteamine monolayer to enhance the heterogeneous electron transfer process of laccase from Trametes versicolor. The assembly of GNP on ITO support was performed through generation of H+ species at the electrode surface by hydroquinone electrooxidation at 0.9V vs Ag/AgCl. Uniform distribution of gold nanoparticle aggregates on electrode surfaces was confirmed by atomic force microscopy. The size of GNP aggregates was in the range of 200–500nm. The enhanced charge transfer at the GNP functionalized ITO electrodes was observed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy. Electrocatalytic behavior of laccase immobilized on ITO modified electrode toward oxygen reduction reaction was evaluated using CV in the presence of 2,2′-azino-bis 3-ethylbenzothiazoline-6-sulfuric acid (ABTS). The obtained sigmoidal-shaped voltammograms for ABTS reduction in oxygen saturated buffer solution are characteristic for a catalytic process. The intensity of catalytic current increased linearly with mediator concentration up to 6.2×10−4M. The registered voltammogram in the absence of ABTS mediator clearly showed a significant faradaic current which is the evidence of the interfacial oxygen reduction.

Heterogeneous electron transfer at nanoscopic electrodes: importance of electronic structures and electric double layers.

Heterogeneous electron-transfer (ET) processes at solid electrodes play key roles in molecular electronics and electrochemical energy conversion and sensing. Electrode nanosization and/or nanostructurization are among the major current strategies for performance promotion in these fields. Besides, nano-sized/structured electrodes offer great opportunities to characterize electrochemical structures and processes with high spatial and temporal resolution. This review presents recent insights into the nanoscopic size and structure effects of electrodes and electrode materials on heterogeneous ET kinetics, by emphasizing the importance of the electric double-layer (EDL) at the electrode/electrolyte interface and the electronic structure of electrode materials. It is shown, by general conceptual analysis and recent example demonstrations of representative electrode systems including electrodes of nanometer sizes and gaps and of nanomaterials such as sp(2) hybridized nanocarbons and semiconductor quantum dots, how the heterogeneous ET kinetics, the electronic structures of electrodes, the EDL structures at the electrode/electrolyte interface and the nanoscopic electrode sizes and structures may be related.

Nitrite Reactivity with Magnetite

Under Fe(3+)-reducing conditions, soil Fe(2+) oxidation has been shown to be coupled with nitrate (NO3(-)) reduction. One possible secondary reaction is the involvement of NO3(-) and nitrite (NO2(-)) with magnetite, a mixed valence Fe(2+)/Fe(3+) mineral found in many natural environments. Currently, little information exists on NO3(-) and NO2(-) reactivity with magnetite. This study investigates NO3(-) and NO2(-) reactivity with magnetite under anoxic conditions using batch kinetic experiments across a range of pH values (5.5-7.5) and in the presence of added dissolved Fe(2+). Solid phase products were characterized using X-ray diffraction (XRD), Mössbauer spectroscopy, and scanning electron microscopy (SEM). Nitrate removal by magnetite was much slower when compared with NO2(-). There was a pH-dependence in the reduction of NO2(-) by magnetite; the initial rate of NO2(-) removal was two times faster at pH 5.5 than at pH 7.5. The influence of pH was explained by the binding of NO2(-) to positively charged sites on magnetite (≡ S-OH2(+)) and to neutral sites (≡ S-OH(0)). As NO2(-) was removed from solution, nitric oxide (NO) and nitrous oxide (N2O) were identified as products confirming that nitrite was reduced. Structural Fe(2+) in magnetite was determined to be the reductant of NO2(-) based on the lack of measurable dissolved Fe(2+) release to solution coupled with Mössbauer spectra and XRD analysis of solid phase products. Addition of dissolved Fe(2+) to magnetite slurries resulted in adsorption and an acceleration in the rate of nitrite reduction at a given pH value. In summary, findings reported in this study demonstrate that if magnetite is present in Fe(3+)-reducing soil and NO2(-) is available, it can remove NO2(-) from solution and reduce a portion of it abiotically to NO and subsequently to N2O by a heterogeneous electron transfer process.

Giving physical insight into the Butler–Volmer model of electrode kinetics: Part 2 – Nonlinear solvation effects on the voltammetry of heterogeneous electron transfer processes

Electrochemical and spectroscopic experiments have shown the weaknesses of the symmetric Marcus–Hush model to model electrode processes, which is likely related to “asymmetric” oxidation and reduction processes. In a previous paper (M.C. Henstridge, E. Laborda, Y. Wang, D. Suwatchara, N. Rees, A. Molina, F. Martínez-Ortiz, R.G. Compton, J. Electroanal. Chem. 672 (2012) 45) the effects arising from different vibrational force constants have been considered, and in the present work we focus on those associated with solvent reorganization.The effects of different solvent frequencies in the oxidized and reduced forms are analyzed for the Gibbs energy surface, the oxidation/reduction rate constants and the voltammetry of solution-phase and surface-bound redox systems. Criteria to assess these effects by electrochemical experiments are given based on the analysis of the value of the Butler–Volmer transfer coefficient.