Redox Potential Distribution Research Articles

Sebaran Tingkat Kemasaman Tanah dan Potensial Redoks serta Kedalaman Pirit (FeS2) pada Lahan Sulfat Masam di Kecamatan Alalak

Acid sulfate soil has a layer of pyrite, when it is oxidized, can acidify the soil. The presence of pyrite in acid sulfate soils is very diverse and must be known. Not knowing the depth of pyrite can have fatal consequences, because layers of pyrite can be lifted to the surface due to tillage so that it oxidizes. This study aims to determine and map the distribution of pyrite depth, soil pH, and redox potential. Soil samples were determined with an exploratory descriptive method through land surveys and supported by laboratory analysis of pH, Eh and FeS2. The results showed that acidity of acid sulphate soil at all sample points was classified as very acid, Eh was classified as low reduction till oxidation. Based on the results of observations of pyrite depth, 3,492.15 ha (78.1%) was actual acid sulfate soil and 979.13 ha (21.9) was potential acid sulfate soil. So proper management is needed when turning over the soil so that the pyrite is not exposed, applying lime, organic material and regulating the water level so that the groundwater level is not below the depth of the pyrite

Mitochondrial network: electric cable and more

Mitochondria in a cell can unite and organize complex extended structures that extend over the entire cellular volume, ensuring a uniform supply of energy to cellular compartments with ATP synthesized in the mitochondria. In accordance with the chemiosmotic concept, the energy of oxidation of respiratory substrates is largely stored in the form of an electrical potential difference on the inner membrane of mitochondria. The theory of the functioning of extended mitochondrial structures as intracellular electrical wires suggests that mitochondria provide the fast delivery of electrical energy through the cellular volume, with following use of this energy for ATP synthesis, thereby speeding up the process of ATP delivery compared to the rather slow diffusion of ATP in the cell. The analytical review gives the history of the cable theory, solved and unsolved critical problems, the lability of the mitochondrial network and the role of oxidative stress in this process. In addition to the already proven functioning of extended mitochondrial structures as electrical cables, a few of additional functions are proposed, in particular, the hypothesis is put forward that mitochondrial networks provide a uniform distribution of redox potential throughout the cell, which can change in pathological conditions during fragmentation of the mitochondrial reticulum. A few of pathologies accompanied by a violation of the redox status and the participation of mitochondria in them are considered.

Biohydrogen production from brown algae fermentation: Relationship between substrate reduction degree and hydrogen production

In this study, mannitol and mannitol-rich seaweed were fermented to investigate the relationship between substrate reduction degree and hydrogen production performance. The results showed that acetate was required in mannitol fermentation with an optimum acetate/mannitol mass ratio of 1:5. Hydrogen production and yield of mannitol fermentation reached 123.76 mL and 2.12 mol/mol-mannitol, respectively, 42.02 % and 26.95 % higher than that of glucose, respectively. The acetate was fully assimilated and the butyrate selectivity reached 100 % in the effluent. Redox potential and electron distribution showed that mannitol increased the overall electron input from mannitol and acetate, leading to the increase in hydrogen and butyrate generation. Hydrogen yield reached 2.33 mol/mol-mannitol with brown algae hydrolysate, which was the highest ever reported. This study demonstrated that substrate with a higher reduction degree could yield higher hydrogen and showed the great application potential of brown algae fermentation for the co-production of hydrogen and butyrate.

Manipulating saltmarsh microtopography modulates the effects of elevation on sediment redox potential and halophyte distribution

Abstract Halophyte distributions on saltmarshes are strongly related to elevation in the tidal frame. However, collinearity between elevation, the consequent inundation regime, and sediment waterlogging/redox potential obscures the proximate causes of distribution patterns. We sought to distinguish the effects of elevation per se from those of waterlogging by manipulating microtopography. We experimentally manipulated elevation by ±15 cm at locations that spanned the elevation ranges of three saltmarshes recently reactivated by managed coastal realignment. Experimental plots were initially cleared of any vegetation. Elevation and sediment redox potential were determined for each plot. We planted five perennial species (Armeria maritima, Atriplex portulacoides, Limonium vulgare, Plantago maritima and Triglochin maritima) in half of the plots, recording survival over 4 years, and monitored natural colonization of the other plots. Overall, redox potential increased with elevation. Sediments were more oxidizing in raised plots and more reducing in lowered plots. Redox reductions in lowered plots were in line with those that would be predicted from the overall redox/elevation relationship, but increases in raised plots were greater than predicted from elevation alone. Plant colonization and survival was poorer in lowered plots and, for most species, improved in raised plots. This poorer colonization and survival can, in part, be attributed to the concomitant alterations in redox potential and elevation in the tidal frame, but microtopographic manipulation also had substantial independent effects on plant performance, including on the survival of all planted species and the colonization of Puccinellia maritima, Salicornia europaea agg. and Tripolium pannonicum. Synthesis. Microtopography can have effects on sediment chemistry and plant performance similar in magnitude to those of overall tidal elevation. Understanding how its effects modulate the relationship between tidal elevation, redox and other environmental conditions helps clarify the abiotic factors that fundamentally determine halophyte colonization and survival. These results support the use of topographic manipulation to enhance the diversity of created saltmarshes.

Surface Recognition and Electron Transfer in Electroactive Bacterial Biofilms: Principal Component Analysis

Bacterial electroactive biofilms attract researchers’ attention due to their ability for generation of electric current when electrons travel for very long, up to several tens microns, distance. It was demonstrated that this electron transfer ability correlates with the accumulation in the BF a c-type cytochrome (Cyt), but molecular nature of this Cyt, its spatial localization, interaction with the environment, regulation and the controlling factors are not understood. Bacterial cell polarity is an internal cell asymmetry that correlates with the cell ability to sense energy and metabolite sources, chemical signals, quorum signals, toxins, and movement in the desired directions. This ability also plays central role in cell attachment to various surfaces and biofilm formation. In the present work, we develop a new experimental approach for analyzing redox potential spatial distribution within individual bacterial cells and use this approach for identification how attachment to inorganic mineral, mica affects redox state inside individual G. sulfurreducens cells. The approach is based on confocal Raman microscopy allowing for precise estimation of redox state and localization of subcellular cytochromes. Applying Gaussian deconvolution and principal component analysis we are able to identify spectral signatures of cytochromes in different redox states and intracellular locations. Our results give a new tool for quick identification of internal and surface exposed cytochromes and their localization at bacterial cell sides facing the substrate and the solution. They open up the possibility for analyzing electrochemical potentials inside individual bacterial cells and indicate that Cyt redox state might be a driving force switching cell metabolic activity that leads to irreversible cell attachment to electrode, cell-to-cell association, and biofilm formation. Nikolai Lebedev, Matthew Yates, Igor Griva, and Leonard M Tender: Internal Polarity of G. Sulfurreducens Bacterial Cells attached to an Inorganic Substrate. ChemPhysChem 19:1–11, 2018 Nikolai Lebedev, Igor Griva, Anders Blom and Leonard M. Tender Effect of iron doping on protein molecular conductance. - Physical Chemistry Chemical Physics 20: 14072-14081, 2018

Surface Recognition and Electron Transfer in Electroactive Bacterial Biofilms: Principal Component Analysis

Bacterial electroactive biofilms attract researchers’ attention due to their ability for generation of electric current when electrons travel for very long, up to several tens microns, distance. It was demonstrated that this electron transfer (ET) ability correlates with the accumulation in the BF huge amounts of a c-type cytochrome (Cyt), but molecular nature of this Cyt, its spatial localization, interaction with the environment, regulation and the controlling factors are not completely understood. Bacterial cell polarity is an internal cell asymmetry that correlates with the cell ability to sense energy and metabolite sources, chemical signals, quorum signals, toxins, and movement in the desired directions. This ability also plays central role in cell attachment to various surfaces and biofilm formation. Biochemical analysis and molecular imaging demonstrate that sensing of energy and nutrients by the cell correlates with asymmetric protein, lipid and other molecule distributions within the cell. In the present work, we develop a new experimental approach for analyzing redox potential spatial distribution within individual bacterial cells and use this approach for identification how attachment to inorganic mineral, mica affects redox state inside individual G. sulfurreducens cells. The approach is based on confocal Raman microscopy allowing for precise estimation of redox state and localization of subcellular cytochromes. Applying Gaussian deconvolution and principal component analysis we are able to identify spectral signatures of cytochromes in different redox states and intracellular locations. Our results give a new tool for quick identification of internal and surface exposed cytochromes and their localization at bacterial cell sides facing the substrate and the solution. They open up the possibility for analyzing electrochemical potentials inside individual bacterial cells and indicate that Cyt redox state might be a driving force switching cell metabolic activity that leads to irreversible cell attachment to electrode, cell-to-cell association, and biofilm formation.

Dark Field Scattering Spectroelectrochemistry of Single Au Nanoparticles at Transparent Planar and Micro-Sized Electrodes

Boron dipyrromethene (BODIPY) molecules with donor-acceptor configurations are of great interests for harvesting and converting solar energy in a solar cell. Au nanoparticles have been applied to enhance solar energy harvesting and conversion efficiency of organic solar cells because of their surface plasmon properties for increasing light absorption cross-section of an organic dye. Electrochemical properties of single BODIPY dyes and plasmonic Au nanoparticles (NPs) are studied using combined optical and electrochemical methods to reveal their structure-function relationship at the nanometer scale. Our study shows a heterogeneous half redox potential distribution for the BODIPY molecules embedded in polystyrene film because of the heterogeneity in their charge transfer rates. Single molecules adsorbed onto a TiO2 surface with ordered nanostructures show surprising fluorescence blinking activity with the shortest ON duration time in comparison to bare glass and indium-doped tin oxide (ITO) surfaces. Dark field scattering (DFS), photoluminescence (PL), and electrogenerated chemiluminescence (ECL) are used to probe local redox reactions of single Au nanoparticles at transparent planar and micro-sized electrode. Our study shows that these optical responses at individual plasmonic NPs are strongly dependent on particle size, and are affected by the local chemical and charge transfer environment of the NPs.

Redox potential distribution of an organic-rich contaminated site obtained by the inversion of self-potential data

Mapping the redox potential of shallow aquifers impacted by hydrocarbon contaminant plumes is important for the characterization and remediation of such contaminated sites. The redox potential of groundwater is indicative of the biodegradation of hydrocarbons and is important in delineating the shapes of contaminant plumes. The self-potential method was used to reconstruct the redox potential of groundwater associated with an organic-rich contaminant plume in northern France. The self-potential technique is a passive technique consisting in recording the electrical potential distribution at the surface of the Earth. A self-potential map is essentially the sum of two contributions, one associated with groundwater flow referred to as the electrokinetic component, and one associated with redox potential anomalies referred to as the electroredox component (thermoelectric and diffusion potentials are generally negligible). A groundwater flow model was first used to remove the electrokinetic component from the observed self-potential data. Then, a residual self-potential map was obtained. The source current density generating the residual self-potential signals is assumed to be associated with the position of the water table, an interface characterized by a change in both the electrical conductivity and the redox potential. The source current density was obtained through an inverse problem by minimizing a cost function including a data misfit contribution and a regularizer. This inversion algorithm allows the determination of the vertical and horizontal components of the source current density taking into account the electrical conductivity distribution of the saturated and non-saturated zones obtained independently by electrical resistivity tomography. The redox potential distribution was finally determined from the inverted residual source current density. A redox map was successfully built and the estimated redox potential values correlated well with in-situ measurements.

Coral recruits settlement in Gulf of Mannar Marine Biosphere Reserve, India

Coral recruitment is one of the critical processes, leading to the recovery of coral reefs in the marine system. Density of coral recruits and their settlement sites in relation to the distribution of sediment hydrogen ion concentration (pH) and redox potential (Eh) was investigated in the selected islands of the Gulf of Mannar Marine Biosphere Reserve (GOMMBR). Among the island groups, the Mandapam group recorded the highest coral recruitment density (7.37±4.45m−2) followed by Vembar (4.26±4.64m−2), Keezhakarai (3.47±5.43m−2) and the Tuticorin group (1.79±2.55m−2). Among the groups of islands Bray-Curtis dissimilarity found 58.94 %, while the individual islands dissimilarity was 30.19 %. ANCOVA (ANalysis of COVAraians) results suggested that among the settlement sites, DRS (p>0.0001), SR (p>0.0001), NNR (p>0.011) and CCA (p>0.033) possessed suitable pH. Similarly, high coral recruit density on DRS (p>0.0001) SR (p>0.0001) and CCA (0.037) were found with suitable Eh for coral recruits. Non-New Recruitment sites (NNR) and coral rubble (CR) were not statistically significant. Overall average, settlement of coral recruits with prevailing sediment pH, observed with 7.21 to 7.49 and redox potential (Eh) 23.90 to 39.2 mV. Among different sites studied for the settlement of coral recruits, higher density of coral recruits found on dead reefs (DR) (22.08±14.71m−2) than crustose coralline algae (CCA) site (12.72±12.12m−2). Further studies are required to confirm the prevalence of these effects in recruits, which will enhance our understanding of settlement sites and improve the estimation of reproductive performance in relation to the phase shift and acidification in shallow water corals sediment–water flux.

Molecular modeling and spectroscopic study of quinone–protein adducts: insight into toxicity, selectivity, and reversibility

The toxicity, reversibility and selectivity of quinone–protein adducts were studied using molecular modeling and molecular spectroscopy. Adduction of quinones with proteins could affect their redox potential, bioavailability, and intracellular distribution.

Electron Transfer from Humic Substances to Biogenic and Abiogenic Fe(III) Oxyhydroxide Minerals

Microbial humic substance (HS) reduction and subsequent abiotic electron transfer from reduced HS to poorly soluble Fe(III) (oxyhydr)oxides, a process named electron shuttling, significantly increases microbial Fe(III) mineral reduction rates. However, the importance of electron shuttling in nature and notably the electron transfer from HS to biogenic Fe(III) (oxyhydr)oxides have thus far not been determined. In this study, we have quantified the rate and extent of electron transfer from reduced and nonreduced Pahokee Peat humic acids (PPHA) and fresh soil organic matter (SOM) extracts to both synthetic and environmentally relevant biogenic Fe(III) (oxyhydr)oxides. We found that biogenic Fe(III) minerals were reduced faster and to an equal or higher degree than their abiogenic counterparts. Differences were attributed to differences in crystallinity and the association of bacterial biomass with biogenic minerals. Compared to purified PPHA, SOM extract transferred fewer electrons per milligram of carbon and electron transfer was observed only to poorly crystalline ferrihydrite but not to more crystalline goethite. This indicates a difference in redox potential distribution of the redox-active functional groups in extracted SOM relative to the purified PPHA. Our results suggest that HS electron shuttling can also contribute to iron redox processes in environments where biogenic Fe(III) minerals are present.

Interfacial charge transfer events of BODIPY molecules: single molecule spectroelectrochemistry and substrate effects.

We present single molecule fluorescence and spectroelectrochemistry characteristics of 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) bearing two carboxylic acid groups at its 2 and 6 positions. Our study shows a heterogeneous half redox potential distribution for the BODIPY molecules embedded in polystyrene film because of the heterogeneity in their charge transfer rates. Single molecules adsorbed onto a TiO2 surface with ordered nanostructures show surprising fluorescence blinking activity with the shortest ON duration time in comparison to bare glass and indium-tin oxide (ITO) surfaces. Single molecule stability tests show longer ON duration time and a stable fluorescence feature when dispersed in polystyrene thin film than molecules exposed to air. Shorter ON times are observed for molecules. In intimate contact with ITO in comparison to glass substrates. Such a decrease in their fluorescence stability or intensity is explained by charge transfer activities from the dye molecules to the metal oxide surface. Electron transfer and back transfer rates are calculated to illustrate the substrate effects by using a well-established model.

Field Study of the Chemical and Physical Stability of Highly Sulphide-Rich Tailings Stored Under a Shallow Water Cover

Highly sulfide-rich (approximately 83 % pyrite), potentially acid-generating mine tailings were sub-aqueously deposited in the Don Rouyn old quarry pit from 1997 to 2000. The site covers approximately 7 ha near Rouyn-Noranda, Quebec. Various in situ measurements and laboratory tests were performed during the summer and autumn of 2008, 2009, and 2010 to: characterize tailings samples; monitor water quality in the final effluent, shallow water cover, and groundwater around the pit, and; study tailings erosion and resuspension. In situ measurements included the vertical profile and spatial distribution of pH, temperature, dissolved oxygen, electric conductivity, and redox potential. Suspended tailings, wind speed, and direction were monitored. Groundwater, cover water, and final effluent water samples were chemically analyzed and suspended sediment concentrations (SSCs) was determined. Physical, mineralogical, and chemical tailings properties were also determined. Results show that the quality of the groundwater, cover, and effluent waters complied with Canadian and Quebec regulations. SSCs were also within regulation limits. No association was found between SSC and hydrodynamic conditions (wind speed, fetch, etc.). Although theoretical calculations indicated a critical wind speed of at least 10 m/s for tailings resuspension, suspended sediment was observed for wind speeds at <10 m/s.

Effect of the potential on the electrochemically induced ageing of polyaniline films

The electrochemically induced ageing of polyaniline films, as a function of the ageing potential, was investigated employing films of different thicknesses in 3.7M H2SO4 solutions. The ageing process was monitored by the change of the voltammetric response in a subsequent positive going potential scan after the ageing. It is observed that the ageing process, at more positive potentials, involves increasing amounts of non-reduced polymer. Also, it is observed that the rate of ageing decreases as the ageing potential increases. The changes in the voltammetric response after ageing is interpreted through a model for the voltammetric response, previously developed, that includes capacitive currents and interactions between the redox centers. The analysis shows that neither the capacitive parameters nor the total faradaic charge change during the ageing. On the other hand, only the interaction energy between the reduced centers change during the ageing. This fact leads to a narrowing of the formal redox potential distribution that can be characterized by the apparent number of exchanged electrons. The decrease of the interaction energy between reduced centers is consistent with the reduction of the free energy of the polymer during the ageing. The kinetics of ageing is analyzed through an Elovich type of equation from which k0, the pseudo zero order rate constant and β, a parameter that indicates how fast the activation free energy changes with the extent of the process, can be obtained.

Influence of soil type and natural Zn chelates on flax response, tensile properties and soil Zn availability

A greenhouse experiment was conducted on weakly acidic and calcareous soils to evaluate the relative efficiencies of three natural Zn chelates [Zn-aminelignosulphonate (Zn-AML), Zn-polyhydroxyphenylcarboxylate (Zn-PHP) and Zn-S,S-ethylenediaminedisuccinate (Zn-S,S-EDDS)] applied to a crop textile flax (Linum ussitatisimum L.) at application rates of 0, 5 and 10 mg Zn kg−1. In the flax plant, the following parameters were determined: dry matter yield, soluble and total Zn concentrations in leaf and stem, chlorophyll, crude fibre, and tensile properties. For the different soil samples, the following parameters were determined: available Zn (DTPA-AB and Mehlich-3 extractable Zn), easily leachable Zn (BaCl2-extractable Zn), the distribution of Zn fractions, pH and redox potential. On the basis of the use of added Zn by flax, or Zn utilization, it would seem recommendable to apply Zn-S,S-EDDS at the low Zn rate in both soils. In contrast, adding the high Zn rate of this chelate to the weakly acidic soil produced an excessive Zn concentration in the plant, which caused a significant decrease in both dry matter yield and chlorophyll content. Furthermore, assessing available Zn with the DTPA-AB method proved the best way of estimating the level of excess Zn in flax plants. The soluble Zn concentration, which was established with 2-(N-morpholino)ethanesulfonic acid reagent (MES), of plant fresh and dry matter could be used as an alternative way of diagnosing the nutritional status of Zn in flax plants. In this experiment, the highest soil pHs were associated with the lowest redox potentials, which coincided with the smallest amounts of available Zn and water soluble Zn in soil, and the lowest levels of Zn uptake by flax plants.

Redox potential distribution inferred from self‐potential measurements associated with the corrosion of a burden metallic body

ABSTRACTNegative self‐potential anomalies can be generated at the ground surface by ore bodies and ground water contaminated with organic compounds. These anomalies are connected to the distribution of the redox potential of the ground water. To study the relationship between redox and self‐potential anomalies, a controlled sandbox experiment was performed. We used a metallic iron bar inserted in the left‐hand side of a thin Plexiglas sandbox filled with a calibrated sand infiltrated by an electrolyte. The self‐potential signals were measured at the surface of the tank (at different time lapses) using a pair of non‐polarizing electrodes. The self‐potential, the redox potential, and the pH were also measured inside the tank on a regular grid at the end of the experiment. The self‐potential distribution sampled after six weeks presents a strong negative anomaly in the vicinity of the top part of the iron bar with a peak amplitude of −82 mV. The resulting distributions of the pH, redox, and self‐potentials were interpreted in terms of a geobattery model combined with a description of the electrochemical mechanisms and reactions occurring at the surface of the iron bar. The corrosion of iron yields the formation of a resistive crust of fougerite at the surface of the bar. The corrosion modifies both the pH and the redox potential in the vicinity of the iron bar. The distribution of the self‐potential is solved with Poisson's equation with a source term given by the divergence of a source current density at the surface of the bar. In turn, this current density is related to the distribution of the redox potential and electrical resistivity in the vicinity of the iron bar. A least‐squares inversion method of the self‐potential data, using a 2D finite difference simulation of the forward problem, was developed to retrieve the distribution of the redox potential.

Enhanced electrokinetic remediation of contaminated manufactured gas plant soil

This paper evaluates different flushing agents to enhance the efficiency of electrokinetic remediation of a manufactured gas plant (MGP) soil contaminated with polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Because of high concentrations, PAHs were of environmental concern and required to be removed to acceptable levels. Four flushing agents, which included two surfactants (3% Tween 80, and 5% Igepal CA-720), one cosolvent (20% n-Butylamine) and one cyclodextrin (10% hydroxypropyl-β-cyclodextrin or HPCD), were examined to enhance the solubilization of PAHs in the soil. Four electrokinetic experiments were conducted at 2.0 VDC/cm voltage gradient and 1.4 hydraulic gradient in order to assess the effectiveness of these flushing solutions for the removal of PAHs. Variables measured during the application of electric potential were electric current, electroosmotic flow, and contaminant removal from the soil. After the completion of each test, the soil was further examined for moisture content, pH, redox potential, electrical conductivity, and residual contaminant distribution. It is found that cosolvent increased the soil pH, while the surfactants and HPCD did not induce substantial change in the soil pH. The current densities fluctuated with time for all tests and remained less than 1 mA/cm 2. The current density for the test conducted with cosolvent was higher as compared to the tests conducted with surfactants and HPCD. Electroosmotic flow was the maximum with the cosolvent, while the lowest flow was observed with Tween 80 surfactant. Overall, Igepal CA-720 surfactant yielded the highest removal efficiency due to partial solubilization of PAHs, causing some PAHs to migrate towards the cathode. Heavy metals are found to be strongly adsorbed/ precipitated and showed negligible migration behavior in all the tests. Based on the contaminant mass remaining in the soil, it is apparent that further optimization of the electrokinetic system is required to improve PAH removal efficiency for the MGP soil.

Vertical and Horizontal Distribution of Redox Potential of Soil in Wetland Forests in Lahei, Central Kalimantan, Indonesia

Vertical and horizontal profiles of redox potential were studied in two wetland forest ecosystems in Lahei, Central Kalimantan, Indonesia. Eh of the soil surface showed a clear correspondence to the surface micro-topography of a 40 cm difference in relative elevation. The lower inundated soil showed the low values of Eh (0-300 mV) and the higher emerged area showed the high values of Eh (>500 mV). The values of Eh changed clearly at the boundary between inundated and emerged soil. A vertical profile of Eh showed the difference between the plot in a peat swamp forest on well-developed peat, accumulated up to 7.5 m and the plot in a temporal wetland shrub community on 15-30 cm of peat layer, The Eh in the shrub community decreased from the top to a depth of 45 cm. However, the Eh in the peat swamp forest showed constant values from the top to a depth of 50 cm, and the values were > 400 mV. Constantly high values of Eh in the peat swamp forest would be due to aeration by aerenchyma of plants and to the low activity of microorganisms in the peat.

Apparent formal redox potential distribution in electroactive arylamine-derived polymers

The concept of distributed formal redox potentials is employed to analyse and study the i/ E response of different arylamine-derived polymers, poly- o-aminophenol (POAP), poly- o-phenylenediamine (POPD) and polybenzidine (PBZ), and a conducting polymer, poly- o-toluidine (POT), in different electrolytic media. The analysis of the experimental data allows determining the formal redox potential distribution. The experimental formal redox potential distributions are interpreted on the basis of a simple statistical thermodynamic model that considers the possibility of expansions and contractions during the oxidation–reduction cycles applied to the polymer. It is considered that units having several redox centres constitute the polymers and that these units change in size during the oxidation–reduction cycles. The analysis of the experimental formal redox potential distribution allows obtaining the number of redox centres per polymer unit, the ratio of the internal partition function of the units and the formal redox potential of the centres. These results are in agreement with the previous studies on the electrochemical behaviour of these polymers.

Redox Potential Distribution in the Presence of Mechanical Stress. The Case of Electroactive Polymers

The current/potential response during the redox switching of electroactive polymers derived from substituted arylamines is analyzed in terms of a sigmoidal distribution of apparent formal potentials. This kind of polymers shows expansion and contraction during the redox switching. A thermodynamic analysis of these systems, including mechanical stresses developed during the oxidation and reduction cycles, leads to a distribution of apparent formal potentials. It is shown that the concept of electron binding can be applied to describe the redox switching of an electroactive polymer. On the basis of this concept, simple statistical thermodynamic models can be applied to describe the distribution of apparent formal potentials during the redox switching of this kind of polymers. In particular, a simple model based on the mean field approximation, including interaction between near neighbors, leads to a linear distribution of the apparent formal potential. On the other hand, a statistical thermodynamical model, including the development of strains during the redox switching, successfully describes the experimental sigmoidal distribution of apparent formal potentials.