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Photosystem‐II (PSII) is a multi‐subunit protein complex that harvests sunlight to perform oxygenic photosynthesis. Initial light‐activated charge separation takes place at a reaction centre consisting of four chlorophylls and two pheophytins. Understanding the processes following light excitation remains elusive due to spectral congestion, the ultrafast nature, and multi‐component behaviour of the charge‐separation process. Here, using advanced computational multiscale approaches which take into account the large‐scale configurational flexibility of the system, we identify two possible primary pathways to radical‐pair formation that differ by three orders of magnitude in their kinetics. The fast (short‐range) pathway is dominant, but the existence of an alternative slow (long‐range) charge‐separation pathway hints at the evolution of redundancy that may serve other purposes, adaptive or protective, related to formation of the unique oxidative species that drives water oxidation in PSII. [ABSTRACT FROM AUTHOR]

The curves for charge and discharge experiments demonstrate specific temperature and current behaviour for the 26650-type battery cell. For that reason, it is extremely important the heat impact on electrochemical reactions and on transfer actions. The base for model parameterization is built by isothermal simulations at different temperatures. In this article, there are presented modifications of thermodynamics and kinetics to accomplish a good connection with the results of the processes concerning charge and discharge curves for different C-rates and various background heat. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of Sm-MOF@GCN composite via simple ultrasonication method. • The as-synthesized Sm-MOF@GCN composite-modified GCE probe was utilized for selective determination of PG. • The fabricated Sm-MOF@GCN@GCE showed a linear range from 0.02-60 µM with 2.05 nM limit of detection. • Additionally, the proposed sensor exhibited good recovery results in detecting PG on real-world food samples. A novel electrochemical sensor has been developed using the sonochemically synthesized samarium metal–organic framework (Sm-MOF) and the graphitic carbon nitride (GCN) composite for the selective determination of propyl gallate (PG). The as-synthesized Sm-MOF@GCN composite was characterized by XRD, XPS, and FESEM. The morphological studies of the prepared Sm-MOF@GCN composite revealed the bar-shaped Sm-MOF and porous sheet-like morphology of GCN. The combined effect of the Sm-MOF and GCN enhance the current density response and lowers the oxidation potential, which was beneficial for the electrochemical sensing of PG. Moreover, the high electrochemical active surface area (EASA) (0.0649 cm2) and the rate constant value (K o) of 1.44x10-5 cm s−1 confirm the faster electron transfer kinetics at the interface of Sm-MOF@GCN composite. However, the developed Sm-MOF@GCN composite possesses linear range from 0.02 to 60 µM with a nanomolar detection level (2.05 nM), high sensitivity (0.1914 μA μM−1 cm−2), excellent reproducibility, repeatability, and stability for up to 30 days towards the PG detection. Finally, the Sm-MOF@GCN composite-modified electrocatalyst was utilized for the quantification of PG in foodstuffs such as instant noodles, cookies, cakes, and oils. The result of the study, the Sm-MOF@GCN composite displayed good recovery results, making it a promising candidate for detecting PG in real-world samples in view of its binder-free approach and facile fabrication process. [ABSTRACT FROM AUTHOR]

The synergism of phosphomolybdic acid hydrate (POM) decorated with silver-iron (III) oxide (Ag-Fe2O3) nanoparticles and anchored on reduced graphene oxide (RGO) have been demonstrated to be effective as a nonenzymatic H2O2 sensor platform. The assembly of the sensor components and their interactions were probed morphologically, spectroscopically and electrochemically. The Ag-Fe2O3/POM/RGO nanocomposite sensor provided an enhanced electroactive surface area, electrical conductivity and sensitivity for hydrogen peroxide compared to an unmodified glassy carbon electrode (GCE) at –0.55 V versus a saturated calomel electrode. The developed sensor amperometric response was linear across the concentration range from 0.3 mM to 3.3 mM (R2 = 0.992) with a detection limit and sensitivity of 0.2 μM and 271 μA·mM‒1·cm−2 respectively. Concomitantly, a short response time of T90 < 5 sec at a signal-to-noise ratio of 4 was achieved. The sensor was shown to determine hydrogen in the presence of interfering species, and exhibited high selectivity with relative standard deviation values less than 4.2%. The results indicate that the use of RGO to anchor and photochemically reduce POM also improved the reduction properties due to the irregular size distribution and catalytic activity of Ag-Fe2O3 stimulated by its adhesion to the distinctive POM/RGO matrix. [ABSTRACT FROM AUTHOR]

This work demonstrates the applicability of red-mud-reduced graphene oxide (RM-rGO) nanocomposites (NCs) for the reliable and selective electrochemical (EC) detection of arsenic. The new NC material shows excellent anti-interference activity toward arsenic (As3+) ions with the cooccurrence of other common cations (Cd2+, Cr2+, Zn2+, Pb2+, and Hg2+). Especially, the NC is exceptionally selective for As3+ ions in the presence of Cu2+ ions, which is stated to be the main interfering agent in the EC detection of As3+. Under optimal experimental conditions, the new NC displays a high sensitivity (2.49 μA ppb–1) as well as a very low detection limit (0.07 ppb) toward As3+ detection. This excellent EC performance of the composite is accounted for by the high adsorption proficiency of hematite (Fe2O3)-phase-rich red mud nanoparticles and enhanced electron-transfer kinetics due to the presence of rGO. [ABSTRACT FROM AUTHOR]

• A new strategy for fabricating hierarchical nanoporous electrodes by self-assembly of edge-truncated, monodisperse ITO nanocubes as building blocks. • Small self-assembled clusters of nanocubes created small uniform pores between edges. • Random aggregation of the clusters created larger pores. • Nanoporous ITO exhibited enhanced electron-transfer kinetics and electrocatalytic activity. The enhanced catalytic activity of the nanoporous electrodes with small and uniform pores is caused by structural effects and represents a significant breakthrough in catalysis research. Herein, a new strategy for fabricating hierarchical nanoporous electrodes is presented. Nanoporous electrodes were constructed by self-assembly using indium tin oxide (ITO) nanocube as building blocks. The self-assembly of nanocubes created small and uniform pores between edges, and random aggregation of the small self-assembled clusters readily created a multimodal structure. It was observed that the simple one electron-transfer reaction of Fe ions was greatly improved at the ITO nanoporous electrodes when compared with the flat ITO electrode. Such enhancement is a result of improved reactivity through small pores and rapid mass transfer through large pores. Furthermore, it was confirmed that the catalytic activity of the ascorbic acid reaction increased when using these nanoporous electrodes. These findings provide insight into the fabrication of nanoporous electrodes and their potential use as catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • In-doped SnO 2 cathodes bearing Ag, Cu and bimetal Ag/Cu nanoparticulate arrays were prepared by potentiostatic double-pulse technique. • These cathode systems were employed for studying the multi-step charge-transfer kinetics of CO 2 electrochemical reduction in propylene carbonate solutions. • Current exchange density of CO 2 electrochemical reduction at rate-determining step depends in large part on the values achieved by the outer-Helmholtz plane potential for the three cathode systems that we explored. • Individual electrocatalytic properties of Ag and Cu were successfully coupled when deposited in a bimetallic array to intentionally tune the CO 2 electrochemical reduction rate in propylene carbonate. Abstract In-doped SnO 2 (ITO) cathodes bearing Ag, Cu and bimetallic Ag/Cu nanoparticulate arrays (cathode systems ITO//Ag, ITO//Cu and ITO//Ag/Cu, respectively) were prepared by a potentiostatic double-pulse technique and employed for studying the multi-step charge-transfer kinetics of CO 2 electrochemical reduction (CO 2 ER) in propylene carbonate solution. Our results demonstrated, on one hand, that the current exchange density of the rate-determining step (rds) for the CO 2 electrochemical reduction (i o,rds) depends, predominantly, on the values achieved by the outer-Helmholtz plane (OHP) potential (Δψ OHP, rds) on the three cathode systems here explored. Furthermore, these results showed that a large Δψ OHP, rds (−647 mV) promoted a large i o,rds (1.09 × 10−2 A⋅ cm−2) for CO 2 reduction at the cathode system ITO//Cu, whereas a small Δψ OHP, rds (−168 mV) produced a small i o,rds (2.05 × 10−4 A⋅ cm−2) for CO 2 reduction at the cathode system ITO//Ag. In contrast, intermediate values of Δψ OHP, rds and i o,rds (−333 mV, 1.09 × 10−3 A⋅ cm−2) were found for CO 2 reduction on the cathode system ITO//Ag/Cu, demonstrating that the individual electrocatalytic properties of Ag and Cu can be coupled in a bimetallic array to intentionally tune the CO 2 ER rate in nonaqueous solvents having low proton availability. [ABSTRACT FROM AUTHOR]

We investigate the product selectivity of CO 2 reduction using NiO photocathodes decorated with CdSe quantum dots (QDs) of varying size in a photoelectrochemical (PEC) cell. Size-tunable and quantized energy states of conduction band in CdSe QDs enable systematic control of electron transfer kinetics from CdSe QDs to NiO. It turns out that different size of CdSe QDs results in variation in product selectivity for CO 2 reduction. The energy gap between conduction band edge and redox potential of each reduction product ( e.g. , CO and CH 4 ) correlates with their production rate. The size dependence of the electron transfer rate estimated from the energy gap is in agreement with the selectivity of CO 2 reduction products for all reduction products but CO. The deviation in the case of CO is attributed to sequential conversion of CO into CH 4 with CO adsorbed on electrode surface. Based on a premise that the CdSe QDs would exhibit similar surface configuration regardless of QD size, it is concluded that the electron transfer kinetics proves to alter the selectivity of CO 2 reduction. [ABSTRACT FROM AUTHOR]

Maquettes are man-made cofactor-binding oxidoreductases designed from first principles with minimal reference to natural protein sequences. Here we focus on water-soluble maquettes designed and engineered to perform diffusive electron transport of the kind typically carried out by cytochromes, ferredoxins and flavodoxins and other small proteins in photosynthetic and respiratory energy conversion and oxido-reductive metabolism. Our designs were tested by analysis of electron transfer between heme maquettes and the well-known natural electron transporter, cytochrome c . Electron-transfer kinetics were measured from seconds to milliseconds by stopped-flow, while sub-millisecond resolution was achieved through laser photolysis of the carbon monoxide maquette heme complex. These measurements demonstrate electron transfer from the maquette to cytochrome c , reproducing the timescales and charge complementarity modulation observed in natural systems. The ionic strength dependence of inter-protein electron transfer from 9.7 × 10 6 M − 1 s − 1 to 1.2 × 10 9 M − 1 s − 1 follows a simple Debye–Hückel model for attraction between + 8 net charged oxidized cytochrome c and − 19 net charged heme maquette, with no indication of significant protein dipole moment steering. Successfully recreating essential components of energy conversion and downstream metabolism in man-made proteins holds promise for in vivo clinical intervention and for the production of fuel or other industrial products. This article is part of a Special Issue entitled Biodesign for Bioenergetics — the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson. [ABSTRACT FROM AUTHOR]

This work focused on the morphology-controlled electrochemical impedance spectroscopic (EIS) studies of polycarbazole (PCz) in two different electrolytes. PCz is synthesized through controlled interfacial polymerization by using two different oxidizing agents, (NH4)2S2O8 (APS) and KMnO4. Voltammetric and EIS studies were carried out to explore charge-transfer properties in the vicinity of modified PCz/glassy carbon (GC) and PCz/Pt electrodes with different electrolytes that have different-sized anions. It has been observed that PCz-APS exhibits enhanced electron-transfer kinetics compared to PCz-KMnO4 at either electrode (GC or Pt) in a supporting electrolyte with a smaller anion size. This is attributed to its favorable diffusion inside the porous polymer film, resulting in easy ion exchange at the electrode surface. The morphology-controlled synthesis approach presented herein is extremely significant for chemical sensors, biosensors, and catalytic applications, owing to its high electroactivity. [ABSTRACT FROM AUTHOR]

Molecular wires consisting of RuII bis(σ-arylacetylide) organometallics functionalized with different anchoring groups (thiol, isocyanide) connected with different bridges [Ø, −CH2−, −O−(CH2)6−] were self-assembled onto gold surfaces. The materials were characterized through wettability, ellipsometric, infrared absorption reflection, and electrochemical measurements. The dynamics of the electron transfers within the monolayers were examined with high-speed voltammetry. Similar fast electron-transfer dynamics (104 s−1) associated with discrete oxidation events (up to four distinct oxidation states) at remarkably low potentials (≤0.7 V vs. SCE) were observed for all complexes. Neither the extension of the molecular wires, nor the variation in the anchoring/bridging units, led to the decrease in electron-transfer kinetics. These results highlight the potential of RuII bis(σ-arylacetylide) complexes as a charge-storage medium for processing information in multibit devices with low power consumption. [ABSTRACT FROM AUTHOR]

The redox and interactive behaviour of flavin adenine dinucleotide (FAD) with a ruthenium (Ru)-modified glassy carbon electrode (GCE) was investigated. The electron-transfer kinetics on the Ru-modified GCE gives an apparent electron-transfer coefficient, αapp of 0.56, and an apparent heterogeneous electron transfer rate constant, kapp of 2.32 s-1, respectively. The cyclic voltammetry (CV) complemented by alternating cyclic voltammetry (ACV) shows reduction of FAD to be a quasi-reversible reaction involving FAD adsorption. The adsorption of FAD on the Ru-modified GCE fits a Langmuir adsorption isotherm. The large apparent negative Gibbs energy of adsorption ΔGads (-38.2 kJ mol-1) of FAD onto the Ru-modified GCE confirmed a strong chemical adsorption of FAD on the surface. The deposited Ru islands block surface sites for FAD adsorption and the electron-transfer communication between FAD and the electrode surface does not significantly improve with a deposited Ru monolayer. [ABSTRACT FROM AUTHOR]

Abstract: We report our electrochemical studies in a W/O microemulsion phase consisting of a ternary mixture of water, Triton X-100, and toluene. The microemulsion phase plays the dual role of a template in the electrodeposition of nickel and as an electrolytic medium in the study of electron-transfer kinetics. The nickel electrodeposits obtained using this microemulsion phase as a template were characterized by surface analysis techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies while cyclic voltammetry (CV) was used to determine the electro-active true surface area of the template-deposited nickel. For electron-transfer studies, CV and electrochemical impedance spectroscopy were employed using potassium ferro/ferricyanide as a redox probe. In contrast to the diffusion-controlled process of the redox probe in aqueous medium, a charge-transfer control was observed in the W/O microemulsion phase. We found that the rate constant value for this particular redox reaction in the microemulsion phase is decreased by about four orders of magnitude when compared to the corresponding value in aqueous medium. The observed phenomenon has been correlated to the structure of the W/O microemulsion phase at the interface, exhibiting a microelectrode array behavior. [Copyright &y& Elsevier]

Abstract: The adsorption of 4-nitrobenzenediazonium tetrafluoroborate (NBD) in acidic aqueous solution was investigated by scanning electrochemical microscopy (SECM) on polycrystalline gold and glassy carbon (GC) substrates. The feedback mode of SECM was used to study the local properties of each substrate before and after immersion in the aryldiazonium solution, by performing approach curves with two redox mediators, and . The fitting of the approach curves with analytical approximate equation was used to evaluate the apparent heterogeneous rate constant k for redox system at NBD-adsorbed GC (k =2.6×10−4 cms−1). [Copyright &y& Elsevier]

Abstract: Pyrroloquinoline quinone (PQQ) was covalently attached to a gold electrode surface via the self-assembled monolayers of aminoalkanethiols (NH2(CH2) n SH) with different alkyl chain lengths (n =2, 6, 8, and 11). The voltammetric behaviors of PQQ-SAMs both at full and at partial monolayers were examined. It was found that the redox response of PQQ became more reversible with increasing dilution by alkanethiols owing to the less lateral interaction between PQQ heads. Voltammograms were transformed from quasi-reversibility to irreversibility as the alkyl chain spacer became longer. The electron tunneling barrier constant (β) and distance dependence of the long range electron-transfer parameters have been studied in acidic solution using cyclic voltammetry. A logarithmic dependence of the heterogeneous electron-transfer rate constant on the alkyl chain length was found for full and partial PQQ monolayers. The β value was close to 1.0 per CH2 unit regardless of dilution effect. [Copyright &y& Elsevier]

Abstract: A new type of carbon film electrode, composed of a thin layer of tightly packed carbon black (CB) nanoparticles deposited onto a gelatin-covered indium tin oxide/glass support using the surface-induced deposition (SID) approach, is presented. Some parameters of the novel SID method were optimized and the surface image and functionalization of the investigated carbon black film electrode (CBFE) was inspected by employing scanning electron microscopy and infrared spectroscopy. A cyclic voltammetry (CV) study was conducted in which the electron-transfer kinetics and CBFE interfacial characteristics were evaluated employing several selected reference redox systems, such as [Ru(NH3)6]3+/2+, [Fe(CN)6]3−/4− and Fe3+/2+ in aqueous, and ferrocene/ferrocenium in acetonitrile media. CV recordings were also performed in order to compare the electrochemical behavior of the CBFE with that of some well-known and established bare carbon-based electrodes. In order to confirm the validity of the CB film preparation method, the electroanalytical performance of the proposed CBFE was examined by carrying out linear sweep voltammetry of ascorbic acid (AA), anodic stripping square-wave voltammetry of Cu(II) in acidic medium, and amperometric measurements of hydrogen peroxide under flow injection conditions. The sensing characteristics of the novel carbon film electrode, demonstrated in this preliminary study, comprise: (i) a wide working potential window ranging from +1.0 to −1.3V (depending on the solution pH), (ii) a wide applicable pH range (at least from 2 to 12), (iii) low voltammetric background (<5μAcm−2), (iv) a satisfactory linear voltammetric and amperometric response (r 2 >0.99) to various analytes, (v) good reproducibility (for example, r.s.d. of 2% in amperometric detection of H2O2 and r.s.d. of 8.5% for electrode-to-electrode CV runs), and (vi) stable and fast current response (at least 100 CV runs with negligible change in CV response). The main advantages of the proposed CBFE originate from the unique CB film formation procedure that enables fast, simple, inexpensive and non-toxic CBFE preparation, which can find application in advanced electrochemical devices and is suitable for mass production. [Copyright &y& Elsevier]

Abstract: This paper examines the role of reactant mass transfer in the preparation of monolayers derived by the chemisorption of thiols on gold and related systems. As a starting point, equations are derived that relate the total impingement of thiol molecules, specifically n-hexanethiol, onto a gold surface for two substrate/deposition vessel geometries. The first model is based on a construct that delivers the reactant to the surface by linear diffusion. The second geometry mimics the case in which hemispherical mass transport is a critical component in the diffusional delivery of reactants. The relationships describe the effects of thiol concentration and immersion time solely on the impingement of the reactant on the gold surface with respect to both deposition geometries. With these predictive equations as guides, adlayer formation is followed by using infrared reflection-absorption spectroscopy, contact angle measurements, and assessments of heterogeneous electron-transfer kinetics. This work demonstrates that, in addition to pretreatment protocols of the substrate surface, the mode of reactant mass transport must be carefully considered and controlled in order to repetitively yield adlayers with comparable structures and, therefore, interfacial properties. Both the total impingement and the rate of impingement of the reactant are found to be major contributors, which implicates the role of nucleation and growth in ultimately dictating subtle, but important differences in the interfacial properties of the adlayer. [Copyright &y& Elsevier]

Abstract: Boron-doped diamond (BDD) thin film surfaces were modified by brief plasma treatment using various source gases such as Cl2, CF4, Ar and CH4, and the electrochemical properties of the surfaces were subsequently investigated. From X-ray photoelectron spectroscopy analysis, Cl and F atoms were detected on the BDD surfaces after 3min of Cl2 and CF4 plasma treatments, respectively. From the results of cyclic voltammetry and electrochemical AC impedance measurements, the electron-transfer rate for Fe(CN)6 3−/4− and Fe2+/3+ at the BDD electrodes was found to decrease after Cl2 and CF4 plasma treatments. However, the electron-transfer rate for Ru(NH3)6 2+/3+ showed almost no change after these treatments. This may have been related to the specific interactions of surface halogen (C–Cl and C–F) moieties with the redox species because no electrical passivation was observed after the treatments. In addition, Raman spectroscopy showed that CH4 plasma treatment of diamond surfaces formed an insulating diamond-like carbon thin layer on the surfaces. Thus, by an appropriate choice of plasma source, short-duration plasma treatments can be an effective way to functionalize diamond surfaces in various ways while maintaining a wide potential window and a low background current. [Copyright &y& Elsevier]

Abstract: The direct electron transfer of surface-confined horse heart cytochrome c (Cyt c) was achieved using COOH-terminated alkanethiolate-modified gold electrode. Later DNA was immobilized on the two-layer modified electrode. The quantitative determination of DNA was explored and the interaction between cytochrome c and DNA was studied. The binding site sizes were determined to be 15bp per Cyt c molecule with double-stranded (ds) DNA and 30 nucleotides binding one Cyt c molecule with single-stranded (ss) DNA. At the dsDNA/Cyt c/MUA/Au electrode, the rate constant of oxidation electron transfer ks,ox=1.59×10−3cms−1 was obtained, at the ssDNA/Cyt c/MUA/Au electrode, the value was 2.43×10−3ms−1 when the scan rate was 1.0V/s. The different electrodes were characterized with electrochemical quartz crystal microbalance and atomic force microscope. [Copyright &y& Elsevier]

The oxidation of the CrIII hydroxy complex, TptBu,MeCr(pz′)(OH), 1, (TptBu,Me=hydrotris(3-tert-butyl-5-methylpyrazolyl)borate; pz′=3-tert-butyl-5-methylpyrazolyl anion) was studied in methylene chloride at a glassy carbon electrode. There are two oxidation peaks, Ia and IIa, that are totally irreversible and CrIV oxo complex 2 is the product at both peaks. Peak Ia grows with respect to IIa as the scan rate is reduced and the voltammograms were quantitatively accounted for by a CEirr mechanism involving two interconverting forms of 1, 1a giving peak Ia and 1b giving peak IIa. The reduction of 2 is detected on the return scan along with a small amount of 3 that arises from hydrogen-atom abstraction by 2 from hydrogen-atom donors in the medium. The processes giving rise to peaks Ia and IIa have the characteristics of dissociative electron- transfer reactions. It is suggested that they may be concerted electron-proton transfer reactions. It is speculated that the postulated minor form of 1, 1a, may be an isomer having axial OH rather than the equatorial OH found in the favored isomer, 1b. [Copyright &y& Elsevier]

Electrochemical impedance spectroscopy has been used to determine the heterogeneous electron-transfer kinetic parameters for the reduction of the following nitrobenzene derivatives in acetonitrile containing 0.10 M tetrabutylammonium hexafluorophosphate at a mercury working electrode: 2-methylnitrobenzene(1), 2,6-dimethylnitrobenzene(2), 2,4,6-trimethylnitrobenzene(3), 2,3,5,6-tetramethylnitrobenzene (4), pentamethylnitrobenzene (5), 2,4,6-triisopropylnitrobenzene (6) and 2,4,6-tri-tert-butylnitrobenzene (7). The results are discussed together with previously published results for nitromethane (8), nitroethane (9), 2-nitropropane (10) and 2-methyl-2-nitropropane (11). In general, a decrease in the standard electron-transfer rate constant, ks, is seen on going from 1 to 7 and this trend continues for 8–11. Double layer effects are shown to be of minor importance. A previous explanation, based on increasing outer reorganization energies on going from 1 to 11 is called into question by the fact that the Gibbs energies of solvation of the radical anions of 1, 3 and 8 have been found to be almost identical. Arguments are presented supporting the idea that the outer reorganization energy should scale linearly with the Gibbs energy of solvation. A previously presented model, used to explain the effect of electrolyte cation size on the values of ks, has been extended to include the effect of reactant size. It is inferred that the decrease in ks on going from 8 (CH3NO2) to 11 ((CH3)3CNO2) results at least partly from the increased size of the alkyl group, which causes the average distance of closest approach to increase from 8 to 11 resulting in an increased tunneling distance and smaller rate constants. This suggests that the “true” values of ks for 8–11, corrected for this distance effect, are roughly constant. Finally, semi-empirical molecular orbital methods (AM1; 6 and 7) and density functional theory (B3LYP; 1–5; 8–11) were used to estimate the contributions of the inner reorganization energy for 1–11. These contributions are small for 1 but steadily increase on going to 5. The inner reorganization contribution for 8–11 is quite substantial, ca. 4–5 kcal/mol (1 kcal/mol = 4.184 kJ/mol). This suggests that the inner reorganization term is a very significant factor underlying the sharp decrease in ks on going from 1 to 11. The principal structural change causing the calculated larger values of inner reorganization energy for 1–5 is the significant turning of the nitro group out of the plane of the ring in the neutral, a feature that is resisted in the radical anion. For 8–11, pyramidalization at nitrogen in the radical anion is the most significant structural change. [Copyright &y& Elsevier]

Aqueous-soluble monolayer-protected palladium nanoparticles were synthesized by hydrogen reduction of Pd(II) in a water solution. The particles were then further functionalized by incorporating multiple copies of mercapto derivatives of viologen into the particle protecting monolayers. The electrochemistry of the viologen moieties with the particles dissolved in solution or immobilized onto electrode surfaces was carefully studied using various electrochemical techniques. The particle molecular capacitance was evaluated by rotating-disk-electrode voltammetry and the electron-transfer rate constant of the particle-bound viologen moieties was estimated by impedance measurements. [ABSTRACT FROM AUTHOR]

• Theoretical models of heterogeneous electron transfer can predict electrochemical responses at low temperature. • Kinetic and thermodynamic data can be extracted from various electrochemical methods at low temperature. • Chemically-coupled electron-transfer reactions can be better investigated by using low-temperature electrochemistry. This paper aims at providing theoretical basis on electrochemical processes performed at low temperature (T) according to three different aspects. First, the effect of T -decrease is treated in terms of thermodynamics, mass-transfer, and kinetics of electron transfer (ET) heterogeneous reactions. In particular, predictions of ET kinetics at low temperature are discussed in the frame of Marcus-Hush's model. The second part is focused on the changes associated to temperature decrease for different electrochemical methods including cyclic voltammetry (CV), chronoamperometry (CA), AC Impedance (ACI) and AC voltammetry (ACV). This section gives keys to extract electrochemical data from low- T experimental curves. In the third part, theoretical aspects of low- T cyclic voltammetry for multiple or chemically-coupled electron-transfer reactions are discussed. CVs of typical molecular mechanisms (EE, EC, ECE...) are provided in order to better visualize the impact of temperature on the redox behavior. [ABSTRACT FROM AUTHOR]

Tungsten oxide (WO 3 ) electrochromic devices have attracted a lot of interest in the energy conservation field and have shown a preliminary application potential in the market. However, it is difficult to quantitatively direct experiments with the existing electrochromic theoretical models, which can restrict the further development of electrochromism. Here, an electrochromic physical simulation model of WO 3 films was built to solve the above problem. Experimentally, the actual electrochromic kinetics of WO 3 in the LiClO 4 /propylene carbonate electrolyte was determined as a continuous electron-transfer process by cyclic voltammetry measurement and X-ray photoelectron spectroscopy analysis. Theoretically, the continuous electron-transfer process, Li + -ion diffusion process, and the transmittance change process were described by a modified Butler-Volmer equation, Fick's law, and charge versus coloration efficiency/bleaching efficiency coupling equation, respectively. The comparisons between theoretical and experimental data were conducted to verify this model. The shape of the simulated current curves was basically consistent with that of experiments. Besides, the difference of transmittance between the simulation and experiments was less than 8%. The difference between theory and experiment was attributed to the influence of the electric double layer and the actual reaction interface. The success of the simulation was attributed to the accurate description of the electrochromic process by continuous electron-transfer kinetics. This model can be applied in the research of electrochromic mechanisms, experimental result prediction, and novel device development due to its clear physical nature.

Conductive polymers are exceptionally promising for modular electrochemical applications including chemical sensors, bioelectronics, redox-flow batteries, and photoelectrochemical systems due to considerable synthetic tunability and ease of processing. Despite well-established structural heterogeneity in these systems, conventional macroscopic electroanalytical methods-specifically cyclic voltammetry-are typically used as the primary tool for structure-property elucidation. This work presents an alternative correlative multimicroscopy strategy. Data from laboratory and synchrotron-based microspectroscopies, including conducting-atomic force microscopy and synchrotron nanoscale infrared spectroscopy, are combined with potentiodynamic movies of electrochemical fluxes from scanning electrochemical cell microscopy (SECCM) to reveal the relationship between electrode structure and activity. A model conductive polymer electrode system of tailored heterogeneity is investigated, consisting of phase-segregated domains of poly(3-hexylthiophene) (P3HT) surrounded by contiguous regions of insulating poly(methyl methacrylate) (PMMA), representing an ultramicroelectrode array. Isolated domains of P3HT are shown to retain bulk-like chemical and electronic structure when blended with PMMA and possess approximately equivalent electron-transfer rate constants compared to pure P3HT electrodes. The nanoscale electrochemical data are used to model and predict multiscale electrochemical behavior, revealing that macroscopic cyclic voltammograms should be much more kinetically facile than observed experimentally. This indicates that parasitic resistances rather than redox kinetics play a dominant role in macroscopic measurements in these conductive polymer systems. SECCM further demonstrates that the ambient degradation of the P3HT electroactivity within P3HT/PMMA blends is spatially heterogeneous. This work serves as a roadmap for benchmarking the quality of conductive polymer films as electrodes, emphasizing the importance of nanoscale electrochemical measurements in understanding macroscopic properties.

The efficiency of charge collection at the organic/transparent conducting oxide (TCO) interface in organic photovoltaic (OPV) devices affects overall device efficiency. Modifying the TCO with an electrochemically active molecule may enhance OPV efficiency by providing a charge-transfer pathway between the electrode and the organic active layer, and may also mitigate surface recombination. The synthesis and characterization of phosphonic acid-ruthenium phthalocyanine (RuPcPA) monolayer films on indium tin oxide (ITO), designed to facilitate charge harvesting at ITO electrodes, is presented in this work. The PA group was installed axially relative to the Pc plane so that upon deposition, RuPcPA molecules were preferentially aligned with the ITO surface plane. The tilt angle of 22° between the normal axes to the Pc plane and the ITO surface plane, measured by attenuated total reflectance (ATR) spectroscopy, is consistent with a predominately in-plane orientation. The effect of surface roughness on RuPcPA orientation was modeled, and a correlation was obtained between experimental and theoretical mean tilt angles. Based on electrochemical and spectroelectrochemical studies, RuPcPA monolayers are composed predominately of monomers. Electrochemical impedance spectroscopy (EIS) and potential modulated-ATR (PM-ATR) spectroscopy were used to characterize the electron-transfer (ET) kinetics of these monolayers. A rate constant of 4.0 × 10 3 s -1 was measured using EIS, consistent with a short tunneling distance between the chromophore and the electrode surface. Using PM-ATR, k s,opt values of 2.2 × 10 3 and 2.4 × 10 3 s -1 were measured using TE and TM polarized light, respectively; the similarity of these values is consistent with a narrow molecular orientation distribution and narrow range of tunneling distances. The ionization potential of RuPcPA-modified ITO was measured using ultraviolet photoelectron spectroscopy and the results indicate favorable energetics for hole collection at the RuPcPA/ITO interface, indicating that this type of TCO modification may be useful for enhancing charge collection efficiency in OPV devices.

A low-spin cobalt(II) complex, cobalt bis(trithiacyclononane), [Co(ttcn)2](3+/2+), was investigated for use as a redox shuttle in dye-sensitized solar cells, DSSCs. This unique cobalt complex redox shuttle is stable, transparent, and easy to synthesize from commercial ligands and has attractive energetic and kinetic features for use in DSSCs. Initial results indicate that the overall performance is limited by recombination. Variation of the sensitizer and deposition of an ultrathin coating of alumina on nanoparticle-based TiO2 DSSC photoanodes reduced recombination, which resulted in significantly improved quantum yields. The photovoltaic behavior was compared to the current record efficiency cobalt tris-bipyridine, [Co(bpy)3](3+/2+), redox shuttle and produced similar results. Further use of high extinction organic sensitizers with only ∼200 mV of driving force for regeneration was examined, which produced efficiencies of over 2%; importantly, regeneration is not rate-limiting in this system, thus demonstrating the promise of using such fast redox shuttles.

Using a monolayer of zinc phthalocyanine (ZnPcPA) tethered to indium tin oxide (ITO) as a model for the donor/transparent conducting oxide (TCO) interface in organic photovoltaics (OPVs), we demonstrate the relationship between molecular orientation and charge-transfer rates using spectroscopic, electrochemical, and spectroelectrochemical methods. Both monomeric and aggregated forms of the phthalocyanine (Pc) are observed in ZnPcPA monolayers. Potential-modulated attenuated total reflectance (PM-ATR) measurements show that the monomeric subpopulation undergoes oxidation/reduction with ks,app = 2 × 10(2) s(-1), independent of Pc orientation. For the aggregated ZnPcPA, faster orientation-dependent charge-transfer rates are observed. For in-plane-oriented Pc aggregates, ks,app = 2 × 10(3) s(-1), whereas for upright Pc aggregates, ks,app = 7 × 10(2) s(-1). The rates for the aggregates are comparable to those required for redox-active interlayer films at the hole-collection contact in organic solar cells.