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Background Laccases and laccase-like multicopper oxidases (LMCOs) oxidize a vast array of phenolic compounds and amines, releasing water as a byproduct. Their low substrate specificity is responsible for their tremendous biotechnological interest, since they have been used for numerous applications. However, the laccases characterized so far correspond to only a small fraction of the laccase genes identified in fungal genomes. Therefore, the knowledge regarding the biochemistry and physiological role of minor laccase-like isoforms is still limited. Results In the present work, we describe the isolation, purification and characterization of two novel LMCOs, PcLac1 and PcLac2, from Pleurotus citrinopileatus. Both LMCOs were purified with ion-exchange chromatographic methods. PcLac2 was found to oxidize a broader substrate range than PcLac1, but both LMCOs showed similar formal potentials, lower than those reported previously for laccases from white-rot fungi. Proteomic analysis of both proteins revealed their similarity with other well-characterized laccases from Pleurotus strains. Both LMCOs were applied to the oxidation of ferulic and sinapic acid, yielding oligomers with possible antioxidant activity. Conclusions Overall, the findings of the present work can offer new insights regarding the biochemistry and variability of low-redox potential laccases of fungal origin. Low-redox potential biocatalysts could offer higher substrate selectivity than their high-redox counterparts, and thus, they could be of applied value in the field of biocatalysis.

Nanocellulose, either in the form of fibers or crystals, constitutes a renewable, biobased, biocompatible material with advantageous mechanical properties that can be isolated from lignocellulosic biomass. Enzyme-assisted isolation of nanocellulose is an attractive, environmentally friendly approach that leads to products of higher quality compared to their chemically prepared counterparts. Lytic polysaccharide monooxygenases (LPMOs) are enzymes that oxidatively cleave the β-1,4-glycosidic bond of polysaccharides upon activation of O

Lytic polysaccharide monooxygenases (LPMOs) consist of a class of enzymes that boost the release of oxidised products from plant biomass, in an approach that is more eco-friendly than the traditional ones, employing harsh chemicals. Since LPMOs are redox enzymes, they could possibly be exploited by immobilisation on electrode surfaces. Such an approach requires knowledge of kinetic and thermodynamic information for the interaction of the enzyme with the electrode surface. In this work, a novel methodology is applied for the determination of such parameters for an LPMO from the filamentous fungus Thermothelomyces thermophila, MtLPMO9H.

MtLPMO9 and FoLPMO9 are two lytic polysaccharide monooxygenases (LPMOs), from the filamentous fungi Thermothelomyces thermophila and Fusarium oxysporum, respectively. In the present study an attempt has been made to achieve direct electron transfer between these enzymes and a glassy carbon electrode by immobilization in Nafion polyelectrolyte. The method used to ascertain the feasibility of direct electron transfer was large amplitude Fourier transform alternating current voltammetry (FTacV) and the formal potentials of these enzymes were determined at different temperatures. The findings of this paper indicate that LPMOs can be studied by direct electron transfer, which could be exploited in the near future for their biochemical characterization.

Electrodeposition of the rare-earth metals La, Sm, Nd, and Dy from solution in the ionic liquids N-butyl-N-methylpyrrolidinium bistriflimide (BMPTFSI) and trimethyl butylammonium bistriflimide (Me3NBuTFSI) was studied in this work. Both ionic liquids are hydrophobic and present a wide electrochemical window as well as satisfactory ionic conductivity, rendering them promising electrolytes for electroreduction of rare-earth elements. Cyclic voltammetry (CV) performed using a Pt electrode in a three-electrode cell revealed that the rare-earth cations could indeed be reduced to the metallic state in the above-mentioned ionic liquids. Furthermore, electrodeposition of the rare earths was realized on copper substrate under potentiostatic conditions of − 3.1 V versus Ag/0.1 M AgNO3 in acetonitrile at 25 °C for 5 h. Analysis of the electrodeposits by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed that electrodeposition of the rare earths was feasible using these ionic liquids as the electrolytic medium. Finally, with the aim of identifying a sustainable metallurgical process for electrorecovery of rare earths, a two-compartment electrolytic cell was developed and tested for production of neodymium from a Nd(TFSI)3/BMPTFSI electrolyte.

In the present study, various representative models of finite length diffusion impedance were examined, in order to find the optimum description for dissolved oxygen diffusion, during corrosion of scribed coated steel in cyclic salt spray conditions, at 6, 8 and 12-week intervals. Modified restricted diffusion fitted the experimental data after 6 and 8 weeks and modified restricted or modified transmissive could fit the data after 12 weeks, accompanied by a decrease in corrosion resistance. Oxygen would diffuse through the porous corrosion layer and reduce on the magnetite layer, lying on top of the electrode surface.

Micro-nano structured super-hydrophobic coatings were successfully fabricated on biomimetic Au-film surfaces via a cathodic one-step electrodeposition method. The micro-structure of natural, hydrophobic plant surfaces was imprinted on cellulose acetate films and gold sputtered in order to create 70-100 nm thin, biomimetic Au-films. Two solutions for electrodeposition were studied: An ethanolic solution of myristic acid and lanthanum chloride, and an ethanolic solution of myristic acid and manganese chloride. The cathodic electrodeposition was performed in a two-electrode cell, with a biomimetic Au-film serving as the cathode, and a carbon electrode as the anode. After electrodeposition on the biomimetic Au substrates, the static contact angles of the coatings improved and were as high as 156° for the lanthanum myristate depositions, and 140° for the manganese myristate depositions. The sliding contact angles for both myristate coatings on the biomimetic substrates were less than 2°. The results indicate that a biomimetic substrate improves the hydrophobic properties of the surface. Deposition time and applied voltage were studied as variables, focusing on their influence on each coating’s contact angle, adhesion and substrate coverage. It was observed that tunable adhesion can be achieved for the manganese myristate depositions, showing a potential for future biomedical and lab-on-chip applications.

The enzyme MtPerII is a new peroxidase which has been isolated only recently from fungus Myceliophthora thermophila and has significant thermostability and stability at high H2O2 concentrations. In the present work, an electrochemical kinetic study, based on cyclic voltammetry, is performed for the first time for the catalytic decomposition of H2O2 by MtPerII, at 18°C. Leuco methylene blue (LMB) is used as a mediator and the catalytic and Michaelis constants are determined, assuming a Michaelis-Menten mechanism. Experimental evidence suggest the absence of inhibition by H2O2, for concentrations up to 16mM, and increasing catalytic activity for temperatures up to 50°C. Moreover, a modified electrode is constructed, by attempting the entrapment of MtPerII on a dodecanothiol self-assembled monolayer on gold. The modified electrode is studied chronoamperometrically in solutions containing methylene blue mediator and different concentrations of H2O2. It is shown that adsorbed MtPerII retains its activity and the modified electrode exhibits a considerably high linear region for the detection of H2O2. The experimental findings indicate that MtPerII is a new candidate for analytical and industrial applications.

In this work, a lytic polysaccharide monooxygenase (LPMO) belonging to the AA9 family from the filamentous fungus Thermothelomyces thermophilus, MtLPMO9H, is immobilized on cobalt functionalized multi-walled carbon nanotubes modified glassy carbon electrode. The step of the binding of phosphoric acid swollen cellulose on this LPMO is studied using large amplitude fast Fourier transform alternating current voltammetry (FTacV) at different temperatures, extracting the corresponding kinetic constants, based on a model developed for the interaction of immobilized enzyme with free, in the solution, species.

A newly developed, polyurethane-based, marine antifouling coating, containing 2% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was performed with XRD, Raman spectroscopy, SEM, and EDS methods. The absence of paint deformation during the experiment led to the formation of compact corrosion products, firmly adherent to the substrate, allowing transformation to more protective forms, such as oxides (hematite, maghemite, magnetite) and the least harmful of the oxyhydroxides (goethite, feroxyhyte), found in the mixture, ensuring sufficient corrosion protection. The unscratched part of the paint served as a barrier to corrosion product expansion beyond the scribed areas. An acrylic-based antifouling system was also examined for reasons of comparison. The experimental formulation exhibited superior anticorrosion performance overall, since the acrylic system presented extended material loss, blistering, checking, and extensive substrate rust coverage beneath the multilayer coat, implying unsatisfactory corrosion protection.

In the present study, hydrophobic surfaces have been fabricated in a one-step electrochemical process by anodic polarization of copper substrates in methanolic myristic acid solutions at relatively high applied potentials. These solutions have also been modified by the addition of tetraethylammonium tetrafluoroborate as a supporting electrolyte to improve their electric characteristics and enable the same fabrication in drastically milder working conditions. To elucidate the mechanism through which this fabrication occurs, various techniques, namely cyclic voltammetry, linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy, have been employed. The processes taking place during anodic oxidation of copper in methanol are electrodissolution and surface species formation depending on the presence of dissolved oxygen. Current oscillations resulting from the presence of these surface species have also been observed.

A newly developed, silicone-based, marine antifouling coating, containing 0.56% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was done with XRD, Raman spectroscopy, SEM and EDS methods. The observed paint swelling during the experiment caused the formation of large, coarse rust agglomerates without adherence, which detached frequently causing reinitiation of the corrosion process. This procedure was revealed by the oxyhydroxide nature of the corrosion products. The basic corrosion morphology observed was a mixture of akaganeite and goethite. A commercial, silicone-based, foul-release coating served as a reference. The experimental formulation exhibited superior anticorrosion performance overall, since the reference system presented higher enlargement of the scribed areas, increased substrate material loss, a highly inhomogeneous corrosion layer with voids and smaller (stable) goethite amounts in the rust areas containing mainly akaganeite/goethite mixture.

This study investigates the morphology, composition and corrosion resistance of hot dip galvanized (HDG) steel panels treated by immersion in NaCl solution in the presence of six protective compounds: 8-hydroxyquinoline, 2-mercaptobenzothiazole, 5-amino-1,3,4-thiadiazole-2-thiol, calcium phosphate, cerium nitrate and sodium molybdate. The results reveal that upon corrosion new compounds are formed onto the exposed areas of the treated panels. The presence of these compounds on the surface of the HDG steel panels hinders the corrosion process by reducing the rate of the anodic and cathodic reactions. Τhe conducted experiments provide new insights on the corrosion mechanisms of HDG steel.

The use of organic solvents in an electrolytic system for neodymium electrorecovery by electrolysis at low temperatures is studied in the current work. More specifically, an alternative route, that of the system of DMSO (Dimethyl sulfoxide) with dissolved NdCl3 has been researched and has given promising results. The study of this electrolytic system has been divided into two stages. Firstly, the characteristics of the electrolyte, the dissolution of NdCl3 in DMSO, the conductivity and the viscosity of NdCl3 solutions in DMSO at various temperatures, and the Nd complexation in the solution were studied and secondly, the electrolysis parameters and their impact on the Nd electrodeposition process were evaluated. Finally, the deposits were submitted to SEM-EDS (Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy) analysis and metallic Nd was confirmed to be electrodeposited by X-ray Photoelectron Spectroscopy (XPS) spectroscopy.

In the present work, the derivation of the standard rate constant k0, the transfer coefficient a and the standard (or formal) potential E0 of immobilized electroactive species, with the use of large amplitude Fourier transform alternating current cyclic voltammetry (FTacV) is examined. Both the kinetic equation of the coverage and the current integral equation are solved. The kinetic regions of the current response are distinguished, the chief observables in the case of both fast and slow kinetics are showcased and finally based on these, a methodology to extract k0, a and E0 is introduced.

Friction stir welding (FSW) is a viable technique for joining aluminium alloys that are difficult to fusion weld. However, the produced friction stir (FS) welded materials need to be improved in terms of their resistance to corrosion. The effect of nanoadditives as reinforcing materials on the corrosion behaviour of dissimilar metal/metal joints and compare with the parent metal alloys is demonstrated in the present study. Dissimilar FS welded materials were produced in plates of aluminium alloy (AA) 6082-T6 and AA5083-H111 using nanoadditives of titanium carbide (TiC) nanoparticles, multi walled carbon nanotubes (MWCNT) and cerium molybdate (CeMo) containers loaded with corrosion inhibitor 2-mercaptobenzothiazole (MBT), as reinforcing materials. The corrosion resistance of the samples with or without nanoadditives was studied by electrochemical methods. The results revealed that the incorporation of CeMo containers loaded with MBT during the FSW, enhances the corrosion resistance of the final material through the adsorption of MoO4−2 ions that come from the container shell onto the surface of both AA, as well as the formation of stable complexes between the thiol groups of MBT and the alloying metals, preventing chloride penetration. Keywords: Aluminium alloy 6082-T6, Aluminium alloy 5083-H111, Friction stir welding, Electrochemical impedance spectroscopy, Potentiodynamic polarization

The fundamental understanding of the behavior of various foods in environments that simulate the human organism is of crucial importance. The study of the release of various components in solutions simulating the human gastric fluid and saliva helps in understanding their availability in the human body. In the present study, disintegration of salt and sugar particulates contained in processed agricultural products was examined. Potatoes and bananas were osmotically dehydrated in salt and sucrose solutions, respectively, and then dried using two drying methods, air drying and freeze drying. The dried products were soaked in simulated saliva and gastric fluid at 37 °C. During immersion, salt release in saliva and gastric fluid was determined using three methods; electrochemical impedance spectroscopy, for measuring the resistance of the solution, titration with silver nitrate, for measuring the amount of salt in the solution and conductivity measurements, for measuring the conductivity of the solutions. Sugar release was determined by measuring degrees brix of the solutions at regular intervals. One Brix corresponds to 1 g of sugars/100 g of solution. The results indicated that different process conditions caused different impact on release kinetics of salt and sugar particulates in saliva and gastric fluid, influencing their taste perception and the bioavailability in the human body.

This study evaluates the corrosion inhibitive abilities of ammonium phosphate dibasic, 8-hydroxyquinoline, calcium fluoride, sodium fluoride, sodium dodecylbenzenesulfonate and zinc nitrate with respect to the protection of the magnesium ZK30 alloy to NaCl solution. A set of characterization assays addressing morphology, composition and structural aspects of the exposed alloys were conducted, along with electrochemical evaluations. The results reveal that upon corrosion new compounds are formed onto the exposed areas of the treated alloys. The conducted experiments shed light on the corrosion mechanisms for Mg ZK30, paving the way for future developments in this area.

Purpose – The purpose of this paper is to perform the evaluation of copper susceptibility to corrosion in industrial cooling systems. Microstructure and defects of copper are observed, while divergences from optimum structure are discussed. Design/methodology/approach – Various types of corrosion are examined. Electrochemical techniques such as electrochemical impedance spectroscopy and potentiodynamic polarisation are applied in these materials, using corrosion inhibitors. Microscopic observations and electrochemical measurements are interpreted according to possible mechanistic scenarios. Findings – It is evident that, under specific conditions (e.g. high pH), water cooling ingredients can enhance corrosion, leading to significant copper mass loss from the inner surface of the pipe and thus leading to failure. Originality/value – Evaluation of copper corrosion in cooling industrial systems was done, as well as studies of copper corrosion in sodium chloride.

In the present work, a kinetic analysis is made concerning the reaction of an electroactive immobilized enzyme with a free substrate, based on a Michaelis-Menten scheme. The proposed kinetic equations are investigated numerically for conditions describing large amplitude fast Fourier transform alternating current voltammetry (FTacV), under different reaction states (transient or steady state for the reaction intermediate as well as quasi or complete reversibility of the electrochemical step). The dependence of two chief observables that occur from the analysis of the results of the method, that is, the maximum of the harmonics and the potential shift of the corresponding dominant peaks, on substrate concentration is presented. The FTacV method is applied experimentally for an immobilized laccase-like multicopper oxidase from Thermothelomyces thermophila, TtLMCO1, and its reaction with epinephrine. From the experimental findings it is shown that the intrinsic characteristics of the system do not lead to the extraction of the desired kinetic data although indications on the relation between the kinetic constants is revealed. Finally, the response of the third harmonic for the first additions of epinephrine at subnanomolarity range can be exploited for the detection of epinephrine at rather low concentrations.

Background Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that oxidatively cleave recalcitrant lignocellulose in the presence of oxygen or hydrogen peroxide as co-substrate and a reducing agent as electron donor. One of the possible systems that provide electrons to the LPMOs active site and promote the polysaccharide degradation involves the mediation of phenolic agents, such as lignin, low-molecular-weight lignin-derived compounds and other plant phenols. In the present work, the interaction of the bulk insoluble lignin fraction extracted from pretreated biomass with LPMOs and the ability to provide electrons to the active site of the enzymes is studied. Results The catalytic efficiency of three LPMOs, namely MtLPMO9 with C1/C4 regioselectivity, PcLPMO9D which is a C1 active LPMO and NcLPMO9C which is a C4 LPMO, was evaluated in the presence of different lignins. It was correlated with the physicochemical and structural properties of lignins, such as the molecular weight and the composition of aromatic and aliphatic hydroxyl groups. Moreover, the redox potential of lignins was determined with the use of large amplitude Fourier Transform alternating current cyclic voltammetry method and compared to the formal potential of the Cu (II) center in the active site of the LPMOs, providing more information about the lignin-LPMO interaction. The results demonstrated the existence of low-molecular weight lignin-derived compounds that are diffused in the reaction medium, which are able to reduce the enzyme active site and subsequently utilize additional electrons from the insoluble lignin fraction to promote the LPMO oxidative activity. Regarding the bulk lignin fractions, those isolated from the organosolv pretreated materials served as the best candidates in supplying electrons to the soluble compounds and, finally, to the enzymes. This difference, based on biomass pretreatment, was also demonstrated by the activity of LPMOs on natural substrates in the presence and absence of ascorbic acid as additional reducing agent. Conclusions Lignins can support the action of LPMOs and serve indirectly as electron donors through low-molecular-weight soluble compounds. This ability depends on their physicochemical and structural properties and is related to the biomass source and pretreatment method. Electronic supplementary material The online version of this article (10.1186/s13068-018-1294-6) contains supplementary material, which is available to authorized users.

Composite nickel coatings, were produced under direct (DC) and pulse current (PC) from a Watt's type bath, containing 0.5 g/L hybrid MWCNT-Al2O3, in presence and absence of additive Sodium Dodecyl Sulfate - SDS. Surface morphology, crystallographic orientation, wear resistance and corrosion resistance were studied. Micro-Raman measurements revealed that MWCNT-Al2O3 particles are distributed at the whole depth of the cross-section profile analysis. The application of pulse current, favored a random crystallographic orientation of Ni crystallites with reduced grain sizes in comparison with pure Ni. The evaluation of the tribological data demonstrated that the composite coatings produced under pulse conditions in presence of additive, exhibited lower coefficient of friction, higher resistance to dry sliding accompanied by the presence of increased amounts of nickel oxide in wear tracks compared to pure Ni coatings. The behavior of pure and composite coatings in corrosive environment was evaluated by electrochemical impedance spectroscopy. It was found that composite coatings attained their corrosion resistance characteristics for 60 h in 0.6 M NaCl solution. Differences between pure nickel and composite coatings were attributed mainly to morphological differences rather than differences on corrosion performance.

The resonating properties of the electrochemical interface are studied under harmonic perturbations in galvanostatic control and under chaotic perturbations in potentiostatic control. The resonance conditions in galvanostatic control are derived analytically and explored numerically. The theoretical findings are confirmed experimentally for the Ni | 1 M H2SO4 system. The implementation of a Rossler and a Chua chaotic perturbation to an electrochemical resonator is explored numerically. It is shown that the electrochemical resonator acts effectively as a band pass filter thus enhancing the periodicity of the chaotic input.

The scope of the current research was to assess the feasibility of encapsulating three commercial antifouling compounds, Irgarol 1051, Econea and Zinc pyrithione, in biodegradable poly(lactic acid) (PLA) nanoparticles. The emulsification–solvent evaporation technique was herein utilized to manufacture nanoparticles with a biocide:polymer ratio of 40%. The loaded nanoparticles were analyzed for their size and size distribution, zeta potential, encapsulation efficiency and thermal properties, while the relevant physicochemical characteristics were correlated to biocide–polymer system. In addition, the encapsulation process was scaled up and the prepared nanoparticles were dispersed in a water-based antifouling paint in order to examine the viability of incorporating nanoparticles in such coatings. Metallic specimens were coated with the nanoparticles-containing paint and examined regarding surface morphology.

In the present work, the chief observables, i.e. peak height, peak width and peak potential of the principal peaks, are determined for the case of large amplitude ac-voltammetry (LA-FTacV) of a reversible reaction of free electroactive species. The values of the chief observables are derived from a semi-analytic solution as well as from the solution of the full initial-boundary value problem. A condition under which the large amplitude ac-voltammogram is independent of scan rate, up to the fifth harmonic, is introduced. The dependence of the chief observables on the parameters of the system is shown.

Corrosion protective sol–gel silica coatings were developed on AA2024-T3 alloy by in situ cross-linking with hyperbranched poly(ethylene imine). Coatings with or without corrosion inhibitors (2-mercaptobenzothiazole or 2-mercaptobenzimidazole) and of two different thicknesses (1–1.5 and 3–3.5 μm, respectively) were obtained. Potentiodynamic scans and electrochemical impedance spectroscopy (after immersion in Harrison's solution for up to 4 weeks) were employed to evaluate the anticorrosion performance of coatings, whereas their thickness, morphology and integrity were assessed by scanning electron microscopy and atomic force microscopy. Further the depth sensing nanoindentation technique was employed to measure the hardness and reduced modulus of coatings and the obtained data were analyzed to indicate their wear resistance, plastic deformation and mechanical integrity. In all cases, coatings of high quality with good barrier properties (impedance modulus reaching up to 10 6 Ω cm 2 at the very low frequency regime) and self-healing abilities (in case of the inclusion of an inhibitor) were obtained. The coating thickness was found to affect the anticorrosion performance, however, even thinner coatings demonstrate satisfactory protection and self-healing effect. Nanoindentation analysis revealed the flexible nature and viscous behavior of the coatings (with the theoretical transition of the elastic to plastic behavior appearing at 1000 μN applied load) demonstrating also an optimal integration of the organic inhibitors into the film. It also revealed an effect of thickness with thinner coatings exhibiting slightly superior behavior in terms of elasticity and wear resistance.

The ability of electrochemical interfaces to exhibit electric resonance and antiresonance is studied experimentally. The system under investigation is the electrodissolution of iron in sulfuric acid. The impedance of the system in the vicinity of a Hopf bifurcation is studied while the system rests on a steady state of a stable focus type. The frequency response is explored for different values of the solution concentration as well as different external ohmic resistance values. It is shown that the system undergoes electrical resonance and antiresonance at frequency values determined by the system parameters and thus acts as a resonator (band-pass filter) or wave trap (band-stop filter).

In this work, composite coatings were fabricated by electrolytic co-deposition of hybrid MWCNT-Al2O3 particles with Ni matrix from a Watts type bath, with and without the use of the sodium dodecyl sulfate additive, under both direct and pulse current conditions. The surface morphology and structural characteristics of the coatings were investigated for the different types of applied current mode, in the absence and presence of the additive. The mechanism of electrochemical co-deposition of Ni and hybrid particles was investigated by linear sweep voltammetry, electrochemical impedance spectroscopy and quartz crystal microbalance measurements in order to elucidate some aspects of the co-deposition mechanism. It was found that the presence of hybrid MWCNT-Al2O3 particles promotes direct proton discharge as well as hydrogen coverage, thus decreasing the deposition efficiency.

In this paper the available literature on the application of ionic liquids in rare earth metals electrodeposition, is briefly discussed and the main electrochemical properties of ionic liquids, in relation with such applications, are presented. In addition, the results of a preliminary investigation for the suitability of pyrrolidinium‐based ionic liquids on the electrodeposition of lanthanum are presented.

Resonating and antiresonating properties of electrochemical interfaces are explored. A general model for the electrochemical interface is employed in order to derive the conditions when the admittance exhibit a minimum (electrical antiresonance) or a maximum (electrical resonance) at a specific input frequency. The electrochemical interface functions as a band-pass filter under resonance and as a band-stop filter under antiresonance.

In the present work the modes of four-legged locomotion generated and controlled by a network of coupled electrochemical oscillatory electrode pairs are explored. Each pair, operating under constant potential conditions, consists of an iron disk (anode) and a copper coil (cathode) and all pairs are immersed in a common electrolytic bath (1 M H2SO4 and 0.4 M CuSO4). The electrochemistry of the system is studied and the conditions of oscillatory and synchronous firing are determined. The current response of each pair is determined by the geometry of the network: if the interactions are between the iron anodes then the oscillations are synchronized in-phase whereas if the interactions are between iron anodes and copper cathodes the oscillations are out-of-phase. The electric pulses produced by the network are supplied to a prototype, specially designed mechanical system where possible modes of four-legged locomotion are observed.

The dynamics of gas evolution during Kolbe electrolysis is studied. Trifluoroacetic acid is used as the organic fuel and platinum as a working electrode. The evolution of gas products is examined by potentiodynamic and potentiostatic experiments as well as by electrochemical impedance spectroscopy. It is found that for 0.5 mm or 1 mm electrode diameter the evolution of Kolbe gas products is accomplished by the nucleation, growth and release of a single gas bubble which is evolved periodically, depending on the surface roughness of the platinum electrode.

A generalized transfer function is introduced, defined as the ratio of the phasor of the electrode potential to the phasor of the applied potential. The occurrence of a maximum of this transfer function at a particular frequency is defined in this work as electrochemical resonance under potentiostatic control. The electrochemical resonance conditions are derived for an electrochemical system in steady state of a stable focus type, characterized by an eigenfrequency ω 0 . The resulting relations are explored and compared with the response of the electric parameters (impedance and admittance). The theoretical considerations are supported by experimental findings.

Corrosion protective sol–gel coatings were developed on AA2024-T3 through an aqueous sol–gel process (Modified Self-Assembled Nanophase Particle method) which includes in-situ formation of a dense silica network from hydrolyzed 3-glycidoxy-propyltri-methoxysilane and tetraethoxysilane by proper cross-linking. In the present study, hyperbranched poly(ethylene imine) of two different molecular weights was investigated as a cross-linking agent since this polymer is able to solubilize non-water-soluble organic molecules. In this respect, two organic corrosion inhibitors (2-mercaptobenzothiazole and 2-mercaptobenzimidazole) were combined with poly(ethylene imine) to induce self healing properties. The as developed coatings were also compared with Si/Zr containing coatings developed by a solvent based sol–gel technique. The potentiodynamic scan and the electrochemical impedance spectroscopy methods were employed to evaluate the corrosion protection performance, whereas the chemical structure, morphology and integrity of the coatings were evaluated by Fourier transformed infrared spectroscopy and scanning electron microscopy studies. Formulations that contain poly(ethylene imine) demonstrate better corrosion barrier properties compared to formulations cross-linked with the simple molecule of diethylenetriamine in all cases and especially when combined with the organic inhibitors.

The ability to produce bursting electrochemical oscillations via the slow external variation of the applied potential is investigated during the electrodissolution/passivation of iron in sulfuric acid. The results are compared with those concerning spontaneous electrochemical bursting in the presence of chloride ions. Moreover, an assembly of two electrochemical Fe/H 2 SO 4 bursters is studied experimentally. The effect of phase space topology on synchrony is explored by studying the coupled response for different types of electrochemical bursters.

In the present paper the non-linear time evolution of the electrodissolution/passivation of iron in sulfuric acid–sodium chloride solution is explored. The working electrode is an assembly of two iron disk electrodes, interacting through the electrolyte, and the time evolution of the electric current has the form of spontaneous bursting oscillations. The main aim of this work is to characterize the modes of synchrony and more specifically the synchronization of electric bursts and the synchronization of electric spikes. The characterization is based on the calculation of the firing rates from the experimental time series and the extraction of the slow dynamics by low-pass filtering. The analysis is performed both for elliptic and square wave electrochemical bursting and the results are compared with neural oscillations.

An experimental setup is designed in order to achieve unidirectional chemical coupling of an electrochemical oscillator and imitate neural synaptic transmission. The electrochemical oscillator is an iron electrode immersed in sulfuric acid solution and the chemical interaction is achieved via the flow of chloride ions towards the electrochemical interface, controlled by a peristaltic pump. The electrochemical interface responds to chemical pulses by producing periodic electric oscillations, electric bursts or electric spikes, depending on the interface potential. The type of electrical response to chemical interactions is determined by the topology of the phase space close to the bifurcation points.

The effect of halogen ions on the electrochemical oscillations of the Fe/H2SO4 system is studied experimentally. It is shown that the dynamic modification of the electrochemical interface transforms the periodic oscillator to a burster. The effect of the applied potential and the nature of halogen ions is investigated and bursting activity is classified according to the nonlinear characteristics of the oscillations. Different types of bursting are compared and interpreted according to the bifurcation characteristics of the periodic oscillator.