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Liquid anhydrous hydrogen fluoride (aHF) is a widely used solvent for the anodic fluorination of organic and inorganic molecules, electrosynthesis of fluorine containing compounds and electrolytic generation of fluorine. Anhydrous hydrogen fluoride is also used on the industrial scale for the production of most fluorine compounds. In this research we intended to use aHF in electrosynthesis of divalent silver fluoride, AgIIF2, which is the most stable and commonly used divalent silver compound. Currently, the chemical methods of AgIIF2 synthesis involve several steps performed in aHF leading to the formation of a fine graded powders contaminated with amorphous impurities. Strongly aggressive nature and high toxicity of aHF makes this synthesis difficult and time consuming, however by using electrochemical methods one may reduce the number of necessary steps and complexity of the synthesis. It should be noted that in general electrosynthesis is inexpensive, safe and effective method of high purity chemicals preparation. Electrochemical methods usually lead also to the formation of more crystalline products as we have recently observed for silver(II) sulfate obtained in the form of compact crystallites with a few tens of micrometers in size [1]. Electrochemical studies in aHF are seldom reported, Hackerman et al. reported kinetic measurements of anodic dissolution of 24 different materials in aHF [2]. All investigated electrodes have undergone corrosion in aHF particularly during anodic polarization. To date no stable working electrode material has been reported for electrochemical studies in aHF. The most promising materials with the slowest anodic dissolution are platinum and nickel [2]. Here we report the mechanistic studies of platinum and nickel corrosion during anodic polarization in aHF carried out by using Electrochemical Impedance Spectroscopy (EIS). It should be noted that although this method is the most suitable for mechanistic studies it has not been previously reported for electrochemical processes in anhydrous HF. The stability of individual electrodes during anode polarization in aHF was determined. Based on the impedance analysis we report strong passivation of nickel electrode and we discuss the mechanism of platinum oxidation. Pt undergo anodic dissolution with the formation of adsorbed intermediates, furthermore the electrode processes are coupled with chemical reactions leading to the fluorine evolution. The electrosynthesis of AgIIF2 in aHF containing AgF was attempted and possible reaction mechanism will be also discussed. [1] P. Połczyński, T.E. Gilewski, J. Gawraczyński, M. Derzsi, P.J. Leszczyński, W. Gadomski, Z. Mazej, R. Jurczakowski, W. Grochala, Efficient Electrosynthesis of AgIISO4: A Powerful Oxidizer and Narrow Band Gap Semiconductor, European Journal of Inorganic Chemistry, 2016 (2016) 5401-5404. [2] N. Hackerman, E. Snavely, L. Fiel, The anodic polarization behaviour of metals in hydrogen fluoride, Corrosion Science, 7 (1967) 39-50.

Electrochemical conversion of carbon dioxide into eligible fuels has become the subject of particular fundamental interest. Recently, we have reported electrochemical studies on CO2 electroreduction at multilayered catalyst composed of the monatomic layer of copper covering palladium overlayers (0.8-10 monolayers) deposited on the well-defined Au(111) surface [1]. In this study Carbon dioxide electroreduction has been studied at ultrathin palladium layers deposited on copper electrode. The Pd deposits have been prepared by using chemical methods. The spontaneous galvanic displacement and resulting uncontrolled deposition of the palladium on copper has been entirely eliminated by the use of palladium(II). This method allowed us for controlled and precise deposition of palladium layers by electrochemical methods. The deposits coverage was changed within the range 0.5 to 5 atomic monolayers. The effectiveness of the method and the durability of the obtained ultrathin palladium layers have been confirmed by X-ray photoelectron spectroscopy (XPS). XPS has been also used for detailed analysis of the electronic properties of the Pd/Cu systems. Significant chemical interactions of both elements resulted in a partial shift of the electron density from palladium to copper and in the changes in the symmetry of 3d palladium signals characteristic for two-dimensional palladium structures (Pd monolayers). A detailed analysis of the valence band structure of Pd/Cu was correlated to the catalytic activity of the studied systems. The unique properties of the valence band structure cannot be attributed to the simple superposition of pure metal bands (Pd and Cu). It has been shown that the increase in the electron density near the Fermi level results in a significant decrease in the overpotential of the carbon dioxide electroreduction. Analysis of the gaseous products obtained in the CO2 electroreduction was performed by gas chromatography. Adsorption of carbon dioxide on Pd/Cu layers was demonstrated by XPS measurements in the presence of 1 mbar CO2 in XPS measurements under near ambient pressure XPS (NAP-XPS). [1] A. Januszewska, R. Jurczakowski, P. Kulesza, Langmuir 30(2014)14314-14321

There is general agreement that catalytic activity is correlated to electronic properties of the catalyst’s surface. For selected molecules and simple surfaces it was shown by Norskov and co-workers that the strength of adsorption of such molecule and the kinetics of the respective catalytic reaction can be correlated to theoretically predicted electronic properties of the surface, i.e. catalyst d-band center (in relation to Fermi edge). However the calculated energy of the d-band center cannot be always correlated to catalytic activity, and the calculated electronic structure (DOS) is not always representative of the experimentally determined electronic structure, especially for non-uniform systems. This is the major drawback of the theoretical approaches currently being used to predict or explain the observed catalytic activity. Thus for assessing the factors responsive for catalytic activity, experimental determination of surface electronic structure is imperative. X-ray Photoelectron Spectroscopy (XPS) and UV Photoelectron Spectroscopy (UPS) experiments are often used to study the electronic properties of materials. In particular core-level electron’s binding energy and valence band (VB) electron’s density of state can be determined using XPS and UPS. Due to interactions of ejected photoelectrons with matter those experiments are in general limited to the Ultra-High Vacuum (UHV) conditions (ca. 10-9 mbar). In the recent years however the Near Ambient Pressure X-ray Photoelectron Spectroscopy/UV Photoelectron Spectroscopy techniques (NAP XPS/UPS) were developed, allowing for local (at the sample surface) increase in pressure up to tenths of millibars, bridging the gap between UHV adsorption studies and real-life systems. Using of the NAP methods presents unique opportunity to study the electronic properties (and changes of electronic properties) of surface during the adsorption from gas phase. This is of paramount importance as insight can be gained on electron-level interactions between the surface and adsorbing molecule, bond breaking/bond forming and similar phenomena, which was not possible before. Investigating the electronic properties of catalysts, in particular valence band DOS, in both – Ultra-High Vacuum (UHV) and Near Ambient Pressure (NAP) conditions allows for experimental determination of electronic-level properties of surface in absence and presence of CO2 molecule, the electronic-level changes induced by CO2 adsorption and experimental verification of CO2 adsorption theories. It can be expected that utilizing NAP XPS will results in better understanding of CO2 adsorption processes, fine-tuning the theoretical models and advance the science and technology of catalytic CO2 reduction.

Impedance spectroscopy, unlike any other electrochemical method, can provide a full insight into the mechanism and kinetics of electrode processes. However, the interpretation of impedance spectra is possible only for systems having a meaningful mathematical description leading to a proper equivalent circuit. Recently, we have provided, for the first time, an exact analytical solution in linear diffusion regime for impedance of catalytic processes involving redox mediators [1]. In this process the electrochemical step (E) is followed by a homogeneous chemical reaction regenerating depolarizer (C’). In such systems various electroinactive and quite inert molecules can be catalytically oxidized or reduced by means of redox mediators that carry electrons from or to the electrode surface. Introduced model obtained for general case provide a powerful research tool that can be used in studies of many important catalytic processes. However, in many cases microelectrodes are used and spherical diffusion needs to be taken into account. In this work, we present an analytical solution for faradaic impedance of the catalytic EC’ processes in spherical diffusion geometry. We provide the range of electrode radius, for which spherical model should be applied. We deliver an equivalent circuit together with potential dependence of all impedance parameters, which allows to rapid and precise determination of all kinetic and thermodynamic parameters of EC’ type reactions on microelectrodes. Similarly as for the solution in linear geometry the resistance of the charge transfer, R ct tends to a constant value at high overpotentials. The applicability of the model in characterization of the catalytic processes was confirmed experimentally. It has been shown that all key parameters of catalytic systems may be readily obtained even from a single impedance spectrum. References: [1] R. Jurczakowski, P. Połczyński, J. Phys. Chem. 118 (2014) 7980–7988

Alcohols might be a promising alternative to gaseous hydrogen in fuel cells technologies. In this study ethanol electrooxidation and oxygen electroreduction were studied by using classical electrochemical methods and electrochemical impedance spectroscopy (EIS). Studies have been carried out for both Pt and Pt-Ru catalysts for the cathode and anode separately in 0.5 M sulfuric acid solutions and for the assembled fuel cells with Nafion membranes. EIS investigations for anodes were carried out in the potentiodynamic conditions because otherwise a stationary state necessary for impedance measurements does not occur [1]. Impedance of the ethanol electrooxidation was recorded in voltammetric experiments with a sinusoidal perturbation of single frequency and small amplitude additionally applied at the electrode. After several voltammetric runs impedance spectra were built for selected electrode potentials. Thus obtained time and potential resolved impedance spectra were characterised by good reproducibility and their validity was confirmed in Kramers–Kronig transformations. The impedance spectra were qualitatively similar to those reported earlier and obtained by using Dynamic EIS (DEIS) experiments [1]. Complex mechanism of ethanol oxidation manifest itself as a negative resistance of the charge transfer, which is related to decrease in the rate of ethanol electrooxidation with increasing anodic potential. This effect is also accompanied by a significant drop in the capacity of the double layer and can be ascribed to the accumulation of carbon monoxide at the electrode surface. Impedance measurements were also performed for assembled fuel cells under different loads with current perturbation equal to 5% of the overall current density. Since the stationary state was assured by a constant flow of the reactants, in this configuration impedance was recorded in a broader frequency range and for much lower frequencies than in ex situ experiments. Equivalent circuit were proposed to model experimentally recoded spectra. The resistance of the charge transfer and the capacity of the double layer at the cathode were virtually independent from the oxygen partial pressure within studied range. This effect, observed particularly for current densities greater than 4 mA cm-2, suggest nearly constant potential of the cathode. Ethanol concentration largely affects impedance of the anode. For higher ethanol concentration a decrease in the double layer capacity accompanied by an increase in the absolute values of the negative resistance were observed. These effects reflect a strong poisoning of the electrode surface. Results points out that the current efficiency is strongly limited by the electrooxidation process at the anode. The influence of other experimental conditions such as temperature and fuel to oxygen stoichiometry on the impedance of direct ethanol fuel cells will be also discussed. [1] E.Desilets, A. Lasia, Electrochimica Acta 78 (2012) 286-293

Ethanol, due to its low toxicity and relatively high energy density, is a promising candidate to be used in fuel cells. It is mainly obtained from biomass, thus its oxidation does not influence the total CO2 amount in the biosphere. However incomplete and slow electrooxidation of ethanol impedes the commercialization of low-temperature ethanol fuel cells. Electrocatalytic oxidation of ethanol is a complex, multi-step process with not completely understood mechanism. Factors influencing the catalytic activity of many systems towards ethanol electrooxidation are still unclear, and effective catalyst for ethanol electrooxidation has not been discovered yet. Most systems used for electrocatalytic oxidation of ethanol contain platinum-group metals in the form of nanoparticles, but even for those systems high overpotentials and incomplete oxidation of ethanol is observed. Another factor influencing the catalytic activity towards ethanol oxidation is poisoning of catalysts’ surface by products of incomplete oxidation. In particular for Pt, a quick decrease in surface activity during ethanol electrooxidation has been observed, which is related to surface poisoning by strongly adsorbed CO, a by-product of ethanol electrooxidation reaction. Adsorption of CO inhibits further electrooxidation of ethanol, and as a result high electrode potential is required to oxidize ethanol, as the surface CO must be oxidized first. To overcome the problem of surface poisoning by CO, bi-metallic surfaces, such as Pt-Ru and Pt-Sn were proposed, due to the fact, that the second metal provides adsorbed OH groups, required to oxidize the adsorbed CO, at lower potential than Pt. This so-called “bifunctional mechanism” was firstly described for methanol electrooxidation on Pt-Ru by Watanabe and Motoo in 1975. However in the case of ethanol electrooxidation the presence of Ru or Sn on Pt surface, despite yielding higher current density, leads to even further decrease in CO2 yield, increase the amount of acetic acid produced. This shift in product distribution significantly decrease the maximum amount of energy, which can be obtained from ethanol electrooxidation in conditions relevant to fuel cells on Pt-Sn or Pt-Ru, as it is impossible to oxidize acetic acid in those conditions, making oxidation of ethanol effectively a 4-electron process. It is thus imperative to develop new catalysts more active towards C-C bond scission, which is impossible without good understanding of the factors influencing catalytic activity in general. It is postulated, that electronic properties are in part responsible for catalytic activity of a given material. Theoretical DFT calculations suggest that chemisorption energy, activation barrier and energy of dissociation of small molecules on metal surface can be correlated to the d-band center of gravity of that metal (so called d-band center theory). This holds true for many systems and reactions it is possible that for more complex system other factors, not included in the d-band center theory, can play a significant role. For instance for more complex reactions, such as oxidation of simple alcohols, the relation between electronic and electrocatalytic properties are much more complicated, because those reactions are multi-step processes and the change of electronic properties may influence the elementary reactions to a different degree. One of the model systems allowing for studying the relation between catalytic and electronic properties of transition metals are pseudomorphic layers. Such systems consist of one metal (substrate) on which another metal is deposited forming a thin layer, usually a monolayer. It has been discovered, that in those systems the top atom layer mimics the crystallographic structure and lattice parameter of the substrate. Possible examples of such systems are monocrystal substrate with a monolayer of other metal or core-shell nanoparticles. Pseudomorphic layers allow to introduce and study changes in electronic properties due to modification of lattice parameter of the topmost layer and changes resulting from possible partial charge transfer between topmost layer and substrate material. At the same time, if pseudomorphic layer provides full coverage of the substrate’s surface, non-electronic effects, such as above mentioned bi-functional mechanism, can be eliminated. We focused on correspondence between electronic properties of noble metals (especially Pt and Pd) and their pseudomorphic layers observed using X-ray Photoelectron Spectroscopy (XPS) and UV Photoelectron Spectroscopy (UPS) and catalytic activity towards CO, formic acid and ethanol electrooxidation reactions. Catalytic activity was investigated using electrochemical methods. Oxidation of formic acid was selected as a model electrode reaction while oxidation of CO is a crucial step in electrooxidation of ethanol on noble metals. This project was funded from Polish National Science Centre budget based on decision number DEC-2013/09/B/ST4/00099

Persistent Organic Pollutants (POP) are hazardous environmental contaminants of mainly synthetic origin, highly toxic and chemically inert. They accumulate in the environment and in living organisms. Most POPs do not ignite themselves and they cannot be combusted. Therefore it is very important to find an alternative processes of POP neutralization. Mediated Electrochemical Oxidation has been proven to be an efficient approach, in which those dangerous substances are electrochemically combusted under ambient conditions. Mediated electrochemical oxidation is an indirect electrolysis, where pollutants are oxidized through the mediation of some electrochemically generated redox reagents, which act as an intermediary for electrons shuttling between the electrode and the target molecule. This technique enables the possibility to oxidize an (electro)inactive compounds.1 Recently, we have derived the exact analytical solution for impedance of catalytic processes involving redox mediators. The results obtained for general case in the rigorous treatment provide a powerful research tool that can be used in studies of many important catalytic processes.2 Unusual impedance characteristics have been found for systems having unequal diffusivities of the oxidized and reduced forms of the redox mediator. Depending on the ratio of diffusion coefficients the spectra are either markedly deformed at low frequency range or an inductive loop appears at the complex plane. It is impossible to fit these spectra in the whole frequency range, neither with the Gerischer impedance nor with any other known transfer function.2 We show that the key parameters of the studied systems, such as both heterogeneous and homogeneous rate constants, which are limiting factors for the electrochemical combustion efficiency, can be readily obtained even from a single impedance spectrum.2 In this research, silver(II) compounds were used as redox mediators for electrochemical combustion of organic molecules.3 As reported by us previously, the redox potential of the system Ag(II)/Ag(I) can reach up to 2.9V in sulfuric acid media.4 Moreover the average lifetime of the produced radical oxidant was estimated to be in order of seconds.5 Initially, investigations were carried out for a model organic molecule - acetic acid, which is known to be difficult to oxidize, and next for 1,2-dichlorobenzene an organic compound from POP group. The catalytic activity of Ag(II) was characterized mainly by using electrochemical methods with a particular emphasis placed on Electrochemical Impedance Spectroscopy (EIS). We have also performed analysis of volatile products by using mass spectrometry coupled with electrochemical measurements DEMS (Differential Electrochemical Mass Spectroscopy). This technique allows to detect in situ volatile electrooxidation products and/or intermediates. The latter were monitored for catalytic electrooxidation of acetic acid and 1,2-dichlorobenzene in function of electrode potential, for both compounds a large amount of CO2 was detected. 1. M. Panizza and G. Cerisola, Chemical Reviews, 2009, 109, 6541-6569. 2. R. Jurczakowski and P. Polczynski, J Phys Chem C, 2014, 118, 7980-7988. 3. M. Fleischmann and D. Pletcher, Tetrahedron Letters, 1968, 9, 6255-6258. 4. P. Polczynski, R. Jurczakowski and W. Grochala, Chem Commun, 2013, 49, 7480-7482. 5. P. Polczynski, R. Jurczakowski and W. Grochala, J Phys Chem C, 2013, 117, 20689-20696.

Atmospheric carbon dioxide levels have risen rapidly over the last few decades. Electrochemical conversion of carbon dioxide into eligible fuels has potential as a technology that may prevent from a serious environmental problems. Electroreduction of carbon dioxide to hydrocarbons is a complex process that usually involves adsorbed carbon monoxide as an intermediate. The overall electroreduction path is determined to a large extent by the catalyst’s surface affinity to carbon monoxide and hydrogen. Strongly bounded CO inhibits further reduction while weakly bounded CO easily desorbs as a final product [1]. One of primary step is CO2 adsorption followed by its reduction to absorbed carbon monoxide. The presences of adsorbed atomic hydrogen at the catalyst surface can significantly facilitate the formation of hydrocarbons. However, within the potential range of CO2 reduction in the aqueous solution a competitive reaction of hydrogen evolution (HER) takes place, which can even dominate in the electroreduction processes. Our result points out the possibility of tuning catalyst’s affinities to both hydrogen and CO by designing multilayered structures obtained by sequential UPD strategies [2]. Results show that catalytic activity can be finely tuned by using the multilayered near-surface-alloy approach [3]. Our results clearly demonstrate that the Pd-layer thickness and location significantly changes the surface catalytic activity of palladium toward CO2 electroreduction. Interestingly, multilayered films covered with the silver monolayer largely reflect the properties of palladium deposits existing under the Ag surface. Differential Electrochemical Mass Spectrometry method (DEMS) was used to analyze and determine gaseous products of carbon dioxide electroreduction together with evolved hydrogen. Individual molecules are recognized by ionic current mass signals. DEMS method allows to identify reduction products during faradaic reduction [4]. This technique is particularly useful for investigations of electroinactive molecules such as methane or ethylene. Ion current changes are related to applied potential, and were presented as MS-CV (mass spectrum cyclic voltammograms). MS-CV provide useful information on the formation potentials of each products. Electroactive products and intermediates, such as carbon monoxide and formic acid were also detected by using classical electrochemical methods. For this purpose a palladium electrode was used for detection of CO2 electroreduction products obtained in macroelectrolysis. [1]Jitaru, M., et al., Journal of Applied Electrochemistry, 1997. 27(8): p. 875-889. [2]Januszewska, A., R. Jurczakowski, and P.J. Kulesza, Langmuir, 2014. 30(47): p. 14314-14321. [3]Greeley, J. and M. Mavrikakis. Journal of Physical Chemistry B, 2005. 109(8): p. 3460-3471. [4]Baltruschat, H., Journal of the American Society for Mass Spectrometry, 2004. 15(12): p. 1693-1706.

The difficulty of the kinetics determination for very fast electrochemical reaction by using impedance spectroscopy (EIS) is related to the fact that the charge transfer resistance for this process is much smaller than the solution resistance. Moreover, for very fast reactions only a low frequency part of the spectra can be observed when potentiostat is coupled with frequency response analyzer in a classical three electrode arrangement. In such case, the high frequency part of the spectra is very often entirely covered by artifacts related to a relatively low time constant of the potentiostat. A special experimental setup is needed for such experiments, in which impedance is measured in stand-alone mode of the frequency response analyzer. The solution resistance can be minimized by using twin electrode arrangement, in which two identical electrodes are facing each other [1]. However, at high frequency part of the impedance spectra a distinct frequency dispersion occurs due to an unequal and frequency dependent current distribution. Therefore a special attention has to be devoted to control the geometry of the electrode arrangement. Unequal current distribution can be eliminated by using recessed electrodes [2]. However, even for recessed electrodes, a distinct frequency dispersion can be observed at kHz region. This effect is more pronounced in the presence of specific adsorption [3]. To date its origin has not been fully understood. In this study high frequency impedance measurements (up to 1 MHz) have been carried out in a twin electrode and hanging meniscus configurations. Recessed electrodes have been used for the first time to study the kinetics of hydrogen electrosorption at Pt(111) at high frequency range. Hydrogen absorption in palladium thin layers (50 nm) covered by platinum monolayers (1ML/Pd) have also been investigated as model systems involving diffusion processes related to hydrogen absorption. In the 1ML/Pd system, the hydrogen insertion is particularly fast [4], the resistance of the charge transfer, related to this process, is in the order of 0.02 Ωcm2. For these model electrochemical processes the frequency dispersion at high frequency rage will be discussed. Literature: [1] B. Losiewicz, R. Jurczakowski, A. Lasia, Electrochim. Acta, 80 (2012) 292-301 [2] Frateur, I.; Huang, V. M. W.; Orazem, M. E.; Pebere, N.; Tribolletd, B.; Vivier, V., Electrochim. Acta 53 (2008) 7386-7395. [3] T. Pajkossy, Z. Phys. Chem.,226 (2012) 935-943 [3] P. Połczyński, R. Jurczakowski, J. Power Sources, 2016 in press

Persistent Organic Pollutants (POP) are hazardous environmental contaminants of mainly synthetic origin, highly toxic and chemically inert. They accumulate in the environment and in living organisms. The highest concentrations are found in animals at the top of the food chains. The most commonly human health effects related to POPs are skin conditions, liver damage, impaired fetal growth1 and further dysfunctions in intellectual development of the child.2 Most POPs do not ignite themselves and they cannot be combusted. Incineration process result in incomplete combustion despite a large excess of fuels and oxygen. This lead to the formation of dioxins, furans and PCBs, which are known human carcinogens. Therefore it is very important to find an alternative processes of POP neutralization. Mediated Electrochemical Oxidation has been proven to be an efficient approach, in which those dangerous substances are electrochemically combusted under ambient conditions. Mediated electrochemical oxidation is an indirect electrolysis, where pollutants are oxidized through the mediation of some electrochemically generated redox reagents, which act as an intermediary for electrons shuttling between the electrode and the target molecule. This technique enables the possibility to oxidize an (electro)inactive compounds.3 In this research, for mediated electrochemical oxidation, we have chosen silver(II) compounds as redox mediators.4 As reported by us previously, the redox potential of the system Ag(II)/Ag(I) can reach up to 2.9V in sulfuric acid media.5 Moreover the average lifetime of the produced radical oxidant was estimated to be in order of seconds.6 The catalytic activity of Ag(II) was characterized mainly by using electrochemical methods with a particular emphasis placed on Electrochemical Impedance Spectroscopy (EIS). Recently, we have derived the exact solution for the analysis of catalytic systems. Kinetics of the pseudo-first order chemical reaction with depolarizer reproducing was included in the model using the proposed element.7 Here we show that the key parameters of the studied systems, such as both heterogeneous and homogeneous rate constants, which are limiting factors for the electrochemical combustion efficiency, can be readily obtained even from a single impedance spectrum.7 Exemplary results for electrocatalytic oxidation of 1,2-dichlorobenzene are shown in Figure 1. Before the addition of the pesticide, two semicircles are observed on the Niquist plot of impedance registered in sulfuric acid containing silver(I) (-○-). The first semicircle, related to the coupling of the charge transfer resistance with the double layer capacitance, is followed by the second skewed semicircle characteristic for the Gerischer Impedance and related to catalytic oxidation of the acid.6 The determined homogenous reaction rate constant for the latter is equal to k=0.0100±0.0003 dm3∙mol-1∙s-1. The nonzero value is related to a finite half-life time of the electrogenerated oxidizer. After addition of the pesticide (-●-), the second semicircle decreases markedly. According to our theoretical model, this is related to a higher rate constant of the chemical homogeneous step.7 First semicircle is also smaller because the resistance of the charge transfer is inversely proportional to the square root of the homogeneous reaction rate constant.7 The homogenous reaction rate constant of pesticide oxidation is equal to 120±5 dm3∙mol-1∙s-1, which is four order of magnitude higher than that observed in pure sulfuric acid. This result indicates that electrogenerated Ag(II) effectively oxidize 1,2-dichlorobenzene. Products and possible mechanism of this reaction will be discussed. 1. C. Koopman-Esseboom, D. C. Morse, N. Weisglas-Kuperus, I. J. Lutkeschipholt, C. G. Van Der Paauw, L. G. Tuinstra, A. Brouwer and P. J. Sauer, Pediatric res, 1994, 36, 468-473. 2. J. L. Jacobson, S. W. Jacobson and H. E. Humphrey, J pediatrics, 1990, 116, 38-45. 3. M. Panizza and G. Cerisola, Chem Rev, 2009, 109, 6541-6569. 4. M. Fleischmann and D. Pletcher, Tetrahedron Letters, 1968, 9, 6255-6258. 5. P. Polczynski, R. Jurczakowski and W. Grochala, Chem. Commun., 2013, 49, 7480-7482. 6. P. Polczynski, R. Jurczakowski and W. Grochala, J Phys. Chem. C, 2013, 117, 20689-20696. 7. R. Jurczakowski and P. Polczynski, J Phys. Chem. C, 2014, 118, 7980-7988. Figure 1

Impedance is a powerful technique that provides a deep insight into the mechanism, kinetics, and thermodynamics of various physicochemical processes. Impedance of electrochemical systems coupled with homogeneous chemical reactions is seldom reported. Catalytic processes governed by the EC′ mechanism are of particular relevance since these processes are widely employed for mediated electrochemical oxidation of persistent environmental pollutants, gas sensing, catalytic hydrogen evolution, carbon dioxide electroreduction, enzyme oxidation, electrochemistry of nucleic acids, amino acids, as well as for numerous other bioanalytical applications. These system has been investigated almost exclusively by using classical transient electrochemical methods. Recently we have developed an analytical expressions describing the faradaic impedance of the catalytic processes governed by (pseudo) first-order chemical kinetics. The solution was obtained in the rigorous treatment and it is applicable to the analysis of the experimental EC’ systems regardless the kinetics of the homogeneous and electrochemical steps.1 We have found that unequal diffusivities of the oxidized and reduced forms of the redox mediator have a strong effect on the impedance characteristics of the catalytic EC’ systems. This behavior is related to the novel impedance element, which reduces to the Gerischer impedance when both diffusion coefficients are equal.1 In this study we demonstrate how to fully characterize EC’ type processes by using impedance spectroscopy and our model. Provided equivalent circuit together with potential dependence of all impedance parameters allow for a rapid and precise determination of all kinetic and thermodynamic parameters of EC’ type reactions. For Fenton reaction, the formal potential, E 0’, heterogeneous, k 0, and homogeneous, k, rate constants, electron transfer coefficients, α, β, and both diffusion coefficient of the redox mediator D ox, D red were precisely determined. Greater part of these parameters have been determined here for the first time while the other are in good agreement with the previous literature reports. [1] R. Jurczakowski and P. Polczynski, J Phys. Chem. C, 2014, 118, 7980-7988.