SwePub - sökning: WFRF:(Endrodi Balazs)

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1.	Bencsik, G., et al. (författare) Conducting polymer based multifunctional composite electrodes 2009 Ingår i: Reaction Kinetics and Catalysis Letters. - : Springer. - 0133-1736 .- 1588-2837. ; 96, s. 421-428 Tidskriftsartikel (refereegranskat)abstract In this paper, we report a novel pattern of composite electrocatalysts. PPy/iron-oxalate films exhibit photo-electrochemical activity. The PPy/B12 composite electrode on stainless steal (SS) support shows high catalytic activity in the electrochemical reduction of methylviologen. Thin polymer layers filled with magnetite particles can be applicable in magneto-selective electrochemical reactions.In this paper, we report a novel pattern of composite electrocatalysts. PPy/iron-oxalate films exhibit photo-electrochemical activity. The PPy/B12 composite electrode on stainless steal (SS) support shows high catalytic activity in the electrochemical reduction of methylviologen. Thin polymer layers filled with magnetite particles can be applicable in magneto-selective electrochemical reactions.
2.	Bencsik, Gábor, et al. (författare) Electrocatalytic properties of the polypyrrole/magnetite hybrid modified electrode towards the reduction of hydrogen peroxide in the presence of dissolved oxygen 2012 Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 73, s. 53-58 Tidskriftsartikel (refereegranskat)abstract In this study, we report on the electrocatalytic behaviour of a polypyrrole/magnetite hybrid electrode towards the reduction of hydrogen peroxide. The electrocatalytic activity of the composite electrode was demonstrated by cyclic voltammetric and chrono-amperometric measurements in comparison with the identically prepared neat polymer film. The stationary reduction currents, measured at an appropriately chosen potential (here at E = -0.3 V), plotted against the peroxide concentration gave a perfect linear correlation in nitrogen atmosphere in the micromolar concentration range. The performance of the composite electrode was not affected by the presence of sulphate, nitrate or chloride anions. In the presence of dissolved oxygen a complex electrocatalytic activity was observed, involving the reduction of both oxygen and H2O2. However, a linear dependence was found also in oxygen containing media, although with much higher currents, but with the same slope (even at different oxygen concentrations). This fact may trigger the development of such hybrid electrodes towards hydrogen peroxide sensors in different aqueous (including natural) samples.
3.	Bohner, B., et al. (författare) Flow-driven pattern formation in the calcium-oxalate system 2016 Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 144 Tidskriftsartikel (refereegranskat)abstract The precipitation reaction of calcium oxalate is studied experimentally in the presence of spatial gradients by controlled flow of calcium into oxalate solution. The density difference between the reactants leads to strong convection in the form of a gravity current that drives the spatiotemporal pattern formation. The phase diagram of the system is constructed, the evolving precipitate patterns are analyzed and quantitatively characterized by their diameters and the average height of the gravity flow. The compact structures of calcium oxalate monohydrate produced at low flow rates are replaced by the thermodynamically unstable calcium oxalate dihydrate favored in the presence of a strong gravity current.
4.	Endrodi, Balazs, et al. (författare) A review of chromium(VI) use in chlorate electrolysis : Functions, challenges and suggested alternatives 2017 Ingår i: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 234, s. 108-122 Forskningsöversikt (refereegranskat)abstract Sodium chlorate is industrially produced by electrolysis of an aqueous salt solution, in which chromium ( VI) constitutes an important excipient component. It is added to a concentration of a few grams Na2Cr2O7/ liter to the electrolyte and has several functions in the process, the most important being to increase the Faradaic efficiency for hydrogen evolution in the undivided electrochemical cells. A thin film of Cr(OH)(3) x nH(2)O formed by reductive deposition on the cathodes decreases the rate of unwanted side reactions, while still enabling hydrogen evolution to occur. In addition chromium(VI) buffers the electrolyte at the optimum pH for operation and promotes the desired homogeneous reactions in the electrolyte bulk. Chromium species also affect the rates of hydrogen and oxygen evolution at the electrodes and are said to protect the steel cathodes from corrosion. Although chromium(VI) stays in a closed loop during chlorate production, chromate is a highly toxic compound and new REACH legislation therefore intends to phase out its use in Europe from 2017. A production without chromium(VI), with no other process modifications is not possible, and today there are no commercially available alternatives to its addition. Thus, there is an urgent need for European chlorate producers to find solutions to this problem. It is expected that chromium-free production will be a requirement also in other parts of the world, following the European example. As the chromium(VI) addition affects the chlorate process in many ways its replacement might require a combination of solutions targeting each function separately. The aim of this paper is to explain the role and importance of chromium(VI) in the chlorate manufacturing process. Previous achievements in its replacement are summarized and critically evaluated to expose the current state of the field, and to highlight the most promising avenues to be followed. An attempt is also made to reveal connections with other research fields (e.g. photochemical water splitting, corrosion science) facing similar problems. Allied effort of these different communities is expected to open up research avenues to the mutual benefit of these fields.
5.	Endrődi, Balázs, 1987-, et al. (författare) Challenges and rewards of the electrosynthesis of macroscopic aligned carbon nanotube array/conducting polymer hybrid assemblies 2015 Ingår i: Journal of Polymer Science Part B. - : Wiley. - 0887-6266 .- 1099-0488. ; 53, s. 1507-1518 Tidskriftsartikel (refereegranskat)abstract Hybrid assemblies based on conducting polymers and carbon nanomaterials with organized nanoscale structure are excellent candidates for various application schemes ranging from thermal management to electrochemical energy conversion and storage. In the case of macroscopic samples, however, precise control of the nanoscale structure has remained a major challenge to be solved for the scientific community. In this study we demonstrate possible routes to homogeneously infiltrate poly(3-hexylthiophene), poly(3,4-ethylenedioxythiophene), and polyaniline into macroscopic arrays of vertically aligned multiwalled carbon nanotubes (MWCNTAs). Electron microscopic images and Raman spectroscopic analysis (performed along the longitudinal dimension of the hybrid samples) both confirmed that optimization of the electropolymerization circumstances allowed fine tuning of the hybrid structure towards the targeted application. In this vein, three different application avenues were tested. The remarkable anisotropy in both the electrical and thermal conductivity of the nanocomposites makes them eminently attractive candidates to be deployed in thermal management. Thermoelectric studies, aimed to understand the effect of organized nanoscale morphology on the important parameters (Seebeck coefficient, electrical-, and thermal conductivity) compared to their non-organized hybrid counterparts. Finally, extraordinary high charge storage capacity values were registered for the MWCNTA/PANI hybrids (500 F g−1 and 1–3 F cm−2).
6.	Endrodi, Balazs, et al. (författare) Continuous-flow electroreduction of carbon dioxide 2017 Ingår i: Progress in Energy and Combustion Science. - : Elsevier. - 0360-1285 .- 1873-216X. ; 62, s. 133-154 Tidskriftsartikel (refereegranskat)abstract Solar fuel generation through electrochemical CO2 conversion offers an attractive avenue to store the energy of sunlight in the form of chemical bonds, with the simultaneous remediation of a greenhouse gas. While impressive progress has been achieved in developing novel nanostructured catalysts and understanding the mechanistic details of this process, limited knowledge has been gathered on continuous-flow electrochemical reactors for CO2 electroreduction. This is indeed surprising considering that this might be the only way to scale-up this fledgling technology for future industrial application. In this review article, we discuss the parameters that influence the performance of flow CO2 electrolyzers. This analysis spans the overall design of the electrochemical cell (microfluidic or membrane-based), the employed materials (catalyst, support, etc.), and the operational conditions (electrolyte, pressure, temperature, etc.). We highlight R&D avenues offering particularly promising development opportunities together with the intrinsic limitations of the different approaches. By collecting the most relevant characterization methods (together with the relevant descriptive parameters), we also present an assessment framework for benchmarking CO2electrolyzers. Finally, we give a brief outlook on photoelectrochemical reactors where solar energy input is directly utilized.
7.	Endrődi, Balázs, 1987-, et al. (författare) Electrochemical synthesis and characterization of poly(3-hexylthiophene)/single-walled carbon nanotube array hybrid materials 2016 Ingår i: Journal of Solid State Electrochemistry. - : Springer. - 1432-8488 .- 1433-0768. ; 20:11, s. 3179-3187 Tidskriftsartikel (refereegranskat)abstract In this study, we demonstrate that by directly employing single-walled carbon nanotube arrays (SWCNT-arrays)-grown on conductive substrates-as working electrodes, selective and uniform electrodeposition of a conducting polymer, namely poly(3-hexylthiophene), can be achieved on the surface of the nanotubes. The overall kinetic pattern of the electrodeposition was studied by separating the deposition charge from the one related to the redox transformation of the polymer film deposited during the precedent cycles. Both the structure and the electrochemical properties of the hybrid materials were studied as a function of the electrodeposition cycles, thus the amount of the formed polymer. The hybrids were characterized by electron microscopic (SEM, TEM) and vibrational spectroscopic (Raman spectroscopy) means. The obtained results were compared and contrasted with those gathered on macroscopic-sized multi-walled carbon nanotube array-based composites in our group recently. Overall, we conclude that electrochemical polymerization is an attractive tool to synthesize conducting polymer/SWCNT hybrid materials with controlled composition and morphology.
8.	Endrődi, Balázs, 1987-, et al. (författare) Fixation of laccase enzyme into polypyrrole, assisted by chemical interaction with modified magnetite nanoparticles : A facile route to synthesize stable electroactive bionanocomposite catalysts 2014 Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 122, s. 282-288 Tidskriftsartikel (refereegranskat)abstract Effective bio-electrocatalysts require stable immobilization of sufficient amounts of the bioactive component. In this study, a novel and efficient method for specific binding of laccase enzyme onto magnetite nanoparticles (NPs) is presented. The interaction between the chemically modified magnetite NPs and the enzyme was evidenced by both infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Subsequently, the enzyme-coated magnetite NPs were successfully incorporated into polypyrrole (PPy) matrix during galvanostatic electropolymerization. The encapsulation of laccase covered NPs was proved by EQCN, TEM, and FT-IR spectroscopy; whereas the electrochemical behaviour of the formed bionanocomposite was characterized by cyclic voltammetiy. In oxygen saturated solution a cathodic charge surplus was observed, related to the electrochemical reduction of oxygen. This surplus was two times higher in the case of the laccase containing layer compared to its only magnetite containing counterpart. Kinetic aspects of the oxygen reduction reaction (ORR) on the laccase containing films were investigated by hydrodynamic voltammetry, and the four-electron route was found to be exclusive, which is promising from the fuel cell perspective. Such synergistic combination of inorganic NPs and enzymes may open new avenues in the application of these bio-nanocomposite materials.
9.	Endrodi, Balazs, et al. (författare) In situ formed vanadium-oxide cathode coatings for selective hydrogen production 2019 Ingår i: Applied Catalysis B. - : Elsevier. - 0926-3373 .- 1873-3883. ; 244, s. 233-239 Tidskriftsartikel (refereegranskat)abstract Electrode selectivity towards hydrogen production is essential in various conversion technologies for renewable energy, as well as in different industrial processes, such as the electrochemical production of sodium chlorate. In this study we present sodium metavanadate as a solution additive, inducing selective cathodic formation of hydrogen in the presence of various other reducible species such as hypochlorite, chlorate, oxygen, nitrate, hydrogen-peroxide and ferricyanide. During electrolysis a vanadium-oxide coating forms from the reduction of sodium metavanadate, explaining the observed enhanced selectivity. The hydrogen evolution reaction proceeds without significantly altered kinetics on such in situ modified electrode surfaces. This suggests that the reaction takes place at the interface between the electrode surface and the protective film, which acts as a diffusion barrier preventing the unwanted species to reach the electrode surface.
10.	Endrodi, Balazs, et al. (författare) Incorporation of cobalt-ferrite nanoparticles into a conducting polymer in aqueous micellar medium : Strategy to get photocatalytic composites 2014 Ingår i: Acta Chimica Slovenica. - 1318-0207. ; 61, s. 376-381 Tidskriftsartikel (refereegranskat)abstract In this study an easy strategy for conducting polymer based nanocomposite formation is presented through the deposition of cobalt-ferrite (CoFe 2O4) containing poly(3,4-ethylenedioxythiophene) (PEDOT) thin layers. The electrochemical polymerization has been performed galvanostatically in an aqueous micellar medium in the presence of the nanoparticlesand the surface active Triton X-100. The nanoparticles have been characterized by Transmission electron microscopy (TEM), the thin layers has been studied by applying Scanning electron microscopy (SEM), and X-ray diffraction (XRD), and the basic electrochemical properties have been also determined. Moreover, electrocatalytic activity of the composite was demonstrated in the electrooxidation reaction of dopamine (DA). The enhanced sensitivity - related to the cobalt-ferritecontent - and the experienced photocatalyitic activity are promising for future application.
11.	Endrődi, Balázs, 1987-, et al. (författare) Layer by layer growth of electroactive conducting polymer/magnetite hybrid assemblies 2013 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 171, s. 62-68 Tidskriftsartikel (refereegranskat)abstract Poly(thiophene-acetic-acid)/magnetite nanocomposite electrodes were fabricated from aqueous solutions on PDADMA (polydiallyldimethylammonium chloride) pre-treated ITO covered glass electrodes, employing layer by layer (LBL) technique. This approach was selected on the ground of the interaction between the surface OH-groups of the magnetite and the carboxylic group of the thiophene derivative. The gradual development of the hybrid assembly was followed by UV-vis spectroscopy, and was found to be continuous up to 30 bilayers. Moreover, the absorbance increase at the characteristic wavelengths was linear in the whole examined region. Importantly, the LBL-prepared composites proved to be electroactive, in aqueous phosphate buffer the Fe3+/Fe2+ redox transformation was observed. The electrocatalytic activity of the modified electrodes was demonstrated for electrooxidation of dopamine (DA), and the role of both components as well as their synergistic contribution was elucidated. Preliminary results indicate possible utilization of such hybrid assemblies in the amperometric detection of this analyte.
12.	Endrodi, Balazs, et al. (författare) Molecular and supramolecular parameters dictating the thermoelectric performance of conducting polymers: A case study using poly(3-alkylthiophene)s 2015 Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119, s. 8472-8479 Tidskriftsartikel (refereegranskat)abstract In this study, we investigated the impact of molecular and supramolecular structure of conducting polymers (CPs) on their thermoelectric properties. As a model system, poly(3-alkylthiophene)s (P3ATs) with different side-chain lengths were prepared through oxidative chemical polymerization and were recrystallized to a well-ordered lamellar structure, resulting in one-dimensional self-assembled nanofibers (evidenced by transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopic measurements). Thermoelectric characterization was performed at different doping levels (precisely tuned by doping in the redox reaction with Ag+ and Fe3+ cations), and the highly doped samples exhibited the best performance for all studied polymers. By varying the length of the alkyl side chain, the supramolecular structure and consequently the electronic properties were varied. The highest electrical conductivity was measured for poly(3-butylthiophene), rooted in its densely packed structure. The established structure-property relationships, concerning the monotonous decrease of the electrical conductivity with the alkyl side chain length, highlight the importance of the supramolecular structure (interchain distance in this case). These findings may contribute to the rational design of organic thermoelectric materials.
13.	Endrodi, Balazs, et al. (författare) One-Step Electrodeposition of Nanocrystalline TiO2 Films with Enhanced Photoelectrochemical Performance and Charge Storage 2018 Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:2, s. 851-858 Tidskriftsartikel (refereegranskat)abstract With the rapid development of renewable energy technologies there is an urgent need to find synthesis routes that address the needs of materials in a reproducible and affordable way. In this study, we present a one-step electrochemical method for the deposition of nanocrystalline titanium dioxide films on different carbon substrates. By optimizing the synthetic conditions, electrodeposition of nanocrystalline and porous titanium dioxide layers was achieved in only a few minutes. To deconvolute the complex effect of the solution pH and temperature, as well as the deposition potential, a set of systematic experiments was carried out on glassy carbon electrodes. The robustness and general applicability of this synthetic approach is demonstrated by extending it to graphene film electrodes. The phase composition of TiO2 was controlled by varying the solution composition. The photoelectrochemical performance of the electrodeposited titanium dioxide films was better than, or at least comparable to the benchmark P25 titanium dioxide films. Hydrogen-ion intercalation measurements for the TiO2/graphene electrodes indicated promising charge storage capacity, which might be exploited in the future in Li-ion batteries.
14.	Endrodi, Balazs, et al. (författare) Reasons behind the improved thermoelectric properties of poly(3-hexylthiophene) nanofiber networks 2014 Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 4:98, s. 55328-55333 Tidskriftsartikel (refereegranskat)abstract Enhanced thermoelectric properties of poly(3-hexylthiophene) nanofiber networks, doped in their reaction with silver cations, are presented. The role of charge carrier concentration and mobility (influenced by the supramolecular structure and nanoscale morphology) is discussed. The nanonet structure leads to a six fold increase in the ZT value compared to the bulk polymer counterpart.
15.	Endrodi, Balazs, et al. (författare) Selective electrochemical hydrogen evolution on cerium oxide protected catalyst surfaces 2020 Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 341 Tidskriftsartikel (refereegranskat)abstract To date the only known solution to avoid the unwanted electrochemical reduction of hypochlorite and chlorate in industrial chlorate production, performed in undivided cells, is the addition of dichromate to the chlorate electrolyte. Because of the toxicity of this compound its use is restricted within the European Union to time limited authorization by REACH. Therefore, an alternative to sodium dichromate is essential to maintain, or even increase the process efficiency. The addition of cerium (III) salts to a hypochlorite solution increases the cathodic selectivity towards hydrogen evolution (HER), the preferred cathode process in industrial chlorate production. This is attributed to the deposition of a thin cerium oxide/hydroxide coating on the cathode, induced by the increased local alkalinity during electrolysis. Performing the electrodeposition of such protective coating ex situ, well-controlled coating thickness can be achieved. Optimizing the deposition conditions (time, current density), a coherent and stable coating is formed on the electrode surface. On this protected electrode surface the electrochemical reduction of hypochlorite is suppressed by ca. 90% compared to the bare Pt electrode, while the HER proceeds with high selectivity and unchanged kinetics. Interestingly, other electrochemical reactions (O-2 reduction, H2O2 reduction and oxidation) are also suppressed by the protective coating, suggesting that the deposited layer acts as an inorganic membrane on the electrode surface.
16.	Endrodi, Balazs, et al. (författare) Selective Hydrogen Evolution on Manganese Oxide Coated Electrodes : New Cathodes for Sodium Chlorate Production 2019 Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:14, s. 12170-12178 Tidskriftsartikel (refereegranskat)abstract The safety and feasibility of industrial electrochemical production of sodium chlorate, an important chemical in the pulp and paper industry, depend on the selectivity of the electrode processes. The cathodic reduction of anodic products is sufficiently suppressed in the current technology by the addition of chromium(VI) to the electrolyte, but due to the high toxicity of these compounds, alternative pathways are required to maintain high process efficiency. In this paper, we evaluate the electrochemical hydrogen evolution reaction kinetics and selectivity on thermally formed manganese oxide-coated titanium electrodes in hypochlorite and chlorate solutions. The morphology and phase composition of manganese oxide layers were varied via alteration of the annealing temperature during synthesis, as confirmed by scanning electron microscopy, X-ray diffraction, synchrotron radiation X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy measurements. As shown in mass spectroscopy coupled electrochemical measurements, the hydrogen evolution selectivity in hypochlorite and chlorate solutions is dictated by the phase composition of the coating. Importantly, a hydrogen evolution efficiency of above 95% was achieved with electrodes of optimized composition (annealing temperature, thickness) in hypochlorite solutions. Further, these electrode coatings are nontoxic and Earth-abundant, offering the possibility of a more sustainable chlorate production.
17.	Endrodi, Balázs, et al. (författare) Suppressed oxygen evolution during chlorateformation from hypochlorite in the presenceof chromium(VI) 2019 Ingår i: Journal of chemical technology and biotechnology (1986). - : Wiley. - 0268-2575 .- 1097-4660. ; 94:5, s. 1520-1527 Tidskriftsartikel (refereegranskat)abstract BACKGROUND: Chromium(VI) is a crucial electrolyte component in industrial chlorate production. Due to its toxicity, iturgently needs to be abandoned and its functions fulfilled by new solutions. In the industrial production of sodium chlorate,homogeneous decomposition of the hypochlorite intermediate to chlorate is a key step. As a competing loss reaction,hypochlorite can decompose to oxygen. How chromium(VI) affects these reactions is not well understood.RESULTS: This work shows, for the first time, that chromium(VI) selectively accelerates the chlorate formation from hypochloriteboth in dilute and concentrated, industrially relevant solutions. The effect of the ionic strength and the specific contributionof different electrolyte components were systematically studied. By simultaneously measuring the concentration decayof hypochlorite (UV–vis spectroscopy) and the oxygen formation (mass spectrometry), both the rate and the selectivity of thereactions were evaluated.CONCLUSION: In the presence of chromium(VI) the hypochlorite decomposition is described by the sum of an uncatalyzedand a parallel catalyzed reaction, where oxygen only forms in the uncatalyzed reaction. When removing chromium(VI),the homogeneous oxygen formation increases, causing economic and safety concerns. The need for a catalyst selectivefor chlorate formation is emphasized.
18.	Endrődi, Balázs, et al. (författare) Towards sustainable chlorate production : The effect of permanganate addition on current efficiency 2018 Ingår i: Journal of Cleaner Production. - : Elsevier. - 0959-6526 .- 1879-1786. ; 182, s. 529-537 Tidskriftsartikel (refereegranskat)abstract Sodium dichromate is an essential solution additive for the electrocatalytic production of sodium chlorate, assuring selective hydrogen evolution. Unfortunately, the serious environmental and health concerns related to hexavalent chromium mean there is an urgent need to find an alternative solution to achieve the required selectivity. In this study sodium permanganate is evaluated as a possible alternative to chromate, with positive results. The permanganate additive is stable in hypochlorite-containing solutions, and during electrolysis a thin film is reductively deposited on the cathode. The deposit is identified as amorphous manganese oxide by Raman spectroscopic and X-ray diffraction studies. Using different electrochemical techniques (potentiodynamic measurements, galvanostatic polarization curves) we demonstrate that the reduction of hypochlorite is suppressed, while the hydrogen evolution reaction can still proceed. In addition, the formed manganese oxide film acts as a barrier for the reduction of dissolved oxygen. The extent of hydrogen evolution selectivity in hypochlorite solutions was quantified in an undivided electrochemical cell using mass spectrometry. The cathodic current efficiency is significantly enhanced after the addition of permanganate, while the effect on the anodic selectivity and the decomposition of hypochlorite in solution is negligible. Importantly, similar results were obtained using electrodes with manganese oxide films formed ex situ. In conclusion, manganese oxides show great promise in inducing selective hydrogen evolution, and may open new research avenues to the rational design of selective cathodes, both for the chlorate process and for related processes such as photocatalytic water splitting.
19.	Janáky, C., et al. (författare) Chemical synthesis of poly(3-thiophene-acetic-acid)/magnetite nanocomposites with tunable magnetic behaviour 2010 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 160:1-2, s. 65-71 Tidskriftsartikel (refereegranskat)abstract Conducting polymer-based magnetic composites with controlled magnetic behaviour have been synthesized by chemical polymerization in nanoparticle containing organic media. Poly(3-thiophene-acetic-acid)–Fe3O4 hybrids have been prepared with five different iron-oxide contents, up to 20 m/m%, according to the results obtained by thermogravimetric analysis (TGA) and inductively coupled plasma atomic emission spectroscopic (ICP-AES) measurements. X-ray diffraction (XRD) and Mössbauer spectroscopic results gave direct evidences for the incorporation of both maghemite and magnetite. Photoacoustic Fourier transform infrared spectroscopic (PAS-FT-IR) measurements showed a chemical interaction between the polymer and the iron-oxide particles. SQUID investigations indicated a typical superparamagnetic behaviour for all samples, where saturation magnetization values proved to be tunable by the Fe3O4 content. After coating them onto electrode surfaces, basic electrochemical activity of the composite samples was demonstrated by cyclic voltammetry.
20.	Janáky, C., et al. (författare) Electro- and Photoreduction of Carbon Dioxide: The Twain Shall Meet at Copper Oxide/Copper Interfaces 2016 Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 1, s. 332-338 Tidskriftsartikel (refereegranskat)abstract Of the myriad electrode materials that have been used for electrochemical (EC) and photoelectrochemical (PEC) reduction of carbon dioxide in aqueous media, copper oxide/copper interfaces have shown a remarkable range of hydrocarbon and oxygenated products including acids, aldehydes, ketones, and alcohols. This Perspective highlights experimental evidence for the fact that both EC and PEC reduction scenarios have similar chemical and morphological underpinnings in the in situ formation of copper nano- or microcubes on the (photo)cathode surface. Recent rapid developments in our fundamental understanding of these interfaces and areas requiring further studies are discussed in light of recent studies in the authors' laboratories and elsewhere.
21.	Janaky, C., et al. (författare) Synthesis and characterization of polypyrrole-magnetite-vitamin B12 hybrid composite electrodes 2010 Ingår i: Journal of Solid State Electrochemistry. - : Springer. - 1432-8488 .- 1433-0768. ; 14, s. 339-346 Tidskriftsartikel (refereegranskat)abstract In this study vitamin B12 covered magnetite nanoparticles have been incorporated into a conducting polypyrrole. This polymer was electrochemically synthesized in the presence of the B12-coated magnetite. The adsorption of B12 was demonstrated by the decrease in absorbance of the vitamin in the supernatant liquid after B12 has been in contact with magnetite sol overnight. The composition of the layers was studied by the electrochemical quartz crystal microbalance technique during the polymerization. The slope of the mass change–charge curves indicate the incorporation of 27 m/m% magnetite and 15 m/m% B12. The redox transformation of the film in monomer- and nanoparticle-free solutions was also investigated by this method and the difference in the virtual molar masses of the moving species was evidenced. The morphology and the composition of the layers were characterized by scanning electron microscopy combined with energy dispersive X-ray microanalysis measurements, which latter proved the successful incorporation of the magnetic and bio-active components. The electrochemical behavior of the films unambiguously showed the complex redox activity of the composites and the current surplus were quantified by the redox capacity of the layers. These data show the doubling of the redox capacity in case of the hybrid material compared to the neat polymer. The successful enrichment of B12 can be exploited in the recently evidenced redox mediation process performed by a PPy/B12 film.
22.	Janáky, C., et al. (författare) Visible-light-enhanced electrocatalytic activity of a polypyrrole/magnetite hybrid electrode toward the reduction of dissolved dioxygen 2010 Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114, s. 19338-19344 Tidskriftsartikel (refereegranskat)abstract Conducting polymers are getting more and more interest as both supporting matrixes and electrocatalysts in the oxygen reduction reaction (ORR). A polypyrrole-magnetite nanocomposite layer has been synthesized by using potassium tetraoxalate as the conducting electrolyte. FT-IR measurements proved that chemical modification of the iron oxide by a reaction between the nanoparticles and the salt-leading to an iron oxalate layer on their surface-endows a negative charge to the particles, which leads to their penetration into the polymeric film as a part of the charge compensation. The new hybrid material showed significant photoelectrocatalytic behavior in the ORR. The ratio observed between the stabilized stationary currents under and without illumination is 2.0 for this hybrid. Separate studies on the electrochemical decomposition of H(2)O(2) also indicated an enhanced catalytic activity of the polypyrrole/magnetite hybrid compared with the neat polymer. The results may open new opportunities in the next generation of solar fuel cell applications.
23.	Kecsenovity, E., et al. (författare) Decoration of ultra-long carbon nanotubes with Cu2O nanocrystals: A hybrid platform for enhanced photoelectrochemical CO2 reduction 2016 Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 4, s. 3139-3147 Tidskriftsartikel (refereegranskat)abstract Photoelectrochemical reduction of CO2 to form useful chemicals is an increasingly studied avenue for harnessing and storing solar energy. In the quest for efficient and stable photocathode materials, nanostructured hybrid assemblies are eminently attractive candidates, because they exhibit multiple favorable properties that cannot be expected from a single material. One possible direction is to combine p-type inorganic semiconductors with highly conductive large surface area electrodes such as carbon nanotube networks. In this work, the controlled synthesis and photoelectrochemical behavior of CNT/Cu2O films was reported for the first time for CO2 reduction applications. A carefully designed, multiple-step electrodeposition protocol was developed that ensured homogeneous coating of CNTs with Cu2O nanocrystals. The hybrid materials were characterized by electron microscopy, X-ray diffraction, Raman spectroscopy, electrochemical impedance spectroscopy, and photoelectrochemical methods. The hybrid films had five-fold higher electrical conductivity compared to their pure Cu2O counterparts. This enhanced charge transport property resulted in a drastic increase in the photocurrents measured for CO2 reduction. In addition to this superior performance, long term photoelectrolysis measurements proved that the CNT/Cu2O hybrids were more stable than the oxide alone. These observations, together with the established structure/property relationships, may contribute to the rational design of nanocarbon/inorganic semiconductor hybrid photocathodes for deployment in photoelectrochemical cells.
24.	Kecsenovity, E., et al. (författare) Enhanced Photoelectrochemical Performance of Cuprous Oxide/Graphene Nanohybrids 2017 Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 139:19, s. 6682-6692 Tidskriftsartikel (refereegranskat)abstract Combination of an oxide semiconductor with a highly conductive nanocarbon framework (such as graphene or carbon nanotubes) is an attractive avenue to assemble efficient photo electrodes for solar fuel generation. To fully-exploit the possible synergies of the hybrid formation, however, precise knowledge of these systems is required to allow rational design and morphological engineering. In this paper, we present the controlled electrochemical deposition of nanocrystalline p-Cu2O on the surface of different graphene substrates. The developed synthetic protocol allowed tuning of the-morphological features of the hybrids as, deduced from electron microscopy. (Photo)electrochemical measurements (including photovoltammetry, electrochemical impedance spectroscopy, photocurrent transient analysis) demonstrated better performance for the 2D graphene containing photoelectrodes, compared to the bare Cu2O films, the enhanced performance being rooted in suppressed charge carrier recombination. To elucidate the precise role of graphene, comparative studies were performed with carbon nanotube (CNT) films and 3D graphene foams. These studies revealed, after allowing for the effect of increased surface area, that the 3D graphene substrate outperformed the other two nanocarbons. Its interconnected structure facilitated effective charge separation and transport, leading to better harvesting of the generated photoelectrons. These hybrid assemblies are shown to be potentially attractive candidates in photoelectrochemical energy conversion schemes, namely CO2 reduction.
25.	Kim, Hyeyun, 1986-, et al. (författare) One-step electro-precipitation of nanocellulose hydrogels on conducting substrates and its possible applications : coatings, composites, and energy devices 2019 Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:24, s. 19415-19425 Tidskriftsartikel (refereegranskat)abstract TEMPO-oxidized cellulose nanofibrils (TOCN) are pH-responsive biopolymers which undergo sol–gel transition at acidic conditions (pH < 4) due to charge neutralization. Electronically conducting materials can be coated by such gels during aqueous electrolysis, when an electrochemical reaction generates a local pH decrease at the electrode surface. In this work, electro-precipitation of different TOCN gels has been performed on oxygen evolving anodes. We demonstrate that TOCN hydrogels can be electrochemically coated on the surface of any conductive material with even complex 3D shape. Further, not only TOCN but also micro- or nanosized particles containing TOCN composites can be coated on the electrode surface, and coatings containing multiple layers of different composites can be also produced. We demonstrate that this simple and facile electrocoating technique can be subject to various applications, such as coatings making electrodes selective for the hydrogen evolution reaction, as well as a new eco-friendly aqueous-based synthesis of Li-ion battery electrodes.
26.	Kormányos, A., et al. (författare) Controlled photocatalytic synthesis of core-shell SiC/polyaniline hybrid nanostructures 2016 Ingår i: Materials. - : MDPI. - 1996-1944. ; 9:3 Tidskriftsartikel (refereegranskat)abstract Hybrid materials of electrically conducting polymers and inorganic semiconductors form an exciting class of functional materials. To fully exploit the potential synergies of the hybrid formation, however, sophisticated synthetic methods are required that allow for the fine-tuning of the nanoscale structure of the organic/inorganic interface. Here we present the photocatalytic deposition of a conducting polymer (polyaniline) on the surface of silicon carbide (SiC) nanoparticles. The polymerization is facilitated on the SiC surface, via the oxidation of the monomer molecules by ultraviolet-visible (UV-vis) light irradiation through the photogenerated holes. The synthesized core-shell nanostructures were characterized by UV-vis, Raman, and Fourier Transformed Infrared (FT-IR) Spectroscopy, thermogravimetric analysis, transmission and scanning electron microscopy, and electrochemical methods. It was found that the composition of the hybrids can be varied by simply changing the irradiation time. In addition, we proved the crucial importance of the irradiation wavelength in forming conductive polyaniline, instead of its overoxidized, insulating counterpart. Overall, we conclude that photocatalytic deposition is a promising and versatile approach for the synthesis of conducting polymers with controlled properties on semiconductor surfaces. The presented findings may trigger further studies using photocatalysis as a synthetic strategy to obtain nanoscale hybrid architectures of different semiconductors.
27.	Lindberg, Jonas, et al. (författare) Li Salt Anion Effect on O-2 Solubility in an Li-O-2 Battery 2018 Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:4, s. 1913-1920 Tidskriftsartikel (refereegranskat)abstract For the promising Li-O-2 battery to be commercialized, further understanding of its constituents is needed. This study deals with the role of O-2 in Li-O-2 batteries, both its influence on electrochemical performance and its solubility in lithium-salt-containing dimethyl sulfoxide (DMSO) electrolytes. Experimentally, the electrochemical performance was evaluated using cylindrical ultramicroelectrodes. Two independent techniques, using a mass spectrometer and an optical sensor, were used to evaluate the O-2 solubility, expressed as Henry's constant. Furthermore, the ionic conductivity, dynamic viscosity, and density were also measured. Density functional theory calculations were made of the interaction energy between O-2 and the different species in the electrolytes. When varying O-2 partial pressure, the current was larger at high pressures confirming that the O-2 concentration is of key importance when studying the kinetics of this system. Compared with neat DMSO, the O-2 solubility increased with addition of LiTFSI and decreased with addition of LiClO4, indicating that the salt influences the solubility. This solubility trend is best explained in terms of apparent molar volume and interaction energy between O-2 and the salt anion. In conclusion, this study shows the importance of O-2 concentration, not just its partial pressure, and that the choice of Li salt can make this concentration increase or decrease.
28.	Magyar, M., et al. (författare) Sensing hydrogen peroxide by carbon nanotube/horseradish peroxidase bio-nanocomposite 2013 Ingår i: Physica Status Solidi (B) Basic Research. - : John Wiley & Sons. - 0370-1972. ; 250, s. 2559-2563 Tidskriftsartikel (refereegranskat)
29.	Samu, G. F., et al. (författare) Bandgap-engineered quaternary MxBi2-xTi2O7 (M: Fe, Mn) semiconductor nanoparticles : Solution combustion synthesis, characterization, and photocatalysis 2017 Ingår i: Applied Catalysis B. - : Elsevier. - 0926-3373 .- 1873-3883. ; 208, s. 148-160 Tidskriftsartikel (refereegranskat)abstract Ternary and quaternary metal oxides form a rapidly emerging class of new functional materials tackling the grand challenge of efficient solar energy harvesting. Currently the main interest is devoted to the characteristics of these materials and little consideration has been given to their preparation. Solution combustion synthesis (SCS) is considered a green and sustainable alternative to the widely employed energy-and/or time-consuming synthesis methods. In this study, SCS was employed to prepare Bi2Ti2O7 and to perform bandgap engineering through foreign ion (Fe, Mn) incorporation. The synthesized materials were characterized by powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray microanalysis, diffuse reflectance UV-vis and Raman spectroscopy, and surface area determination via N-2 adsorption. We found that nanocrystalline materials were formed during the SCS synthesis. Further, the phase composition of these materials and the amount of the foreign metal ions incorporated in the parent structure, could be effectively controlled. Consequently, the SCS technique provided a simple and reliable tool for bandgap engineering. The photocatalytic activity of the materials was tested through methyl orange degradation, and the intrinsic photocatalytic activity of the various samples were compared after deconvoluting the effect of their vastly different specific surface areas.
30.	Szabó, T., et al. (författare) Charge stabilization by reaction center protein immobilized to carbon nanotubes functionalized by amine groups and poly(3-thiophene acetic acid) conducting polymer 2012 Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 249:12, s. 2386-2389 Tidskriftsartikel (refereegranskat)abstract A large number of studies have indicated recently that photosynthetic reaction center proteins (RC) bind successfully to nanostructures and their functional activity is largely retained. The major goal of current research is to find the most efficient systems and conditions for the photoelectric energy conversion and for the stability of this bio-nanocomposite. In our studies, we immobilized the RC protein on multiwalled carbon nanotubes (MWNT) through specific chemical binding to amine functional groups and through conducting polymer (poly(3-thiophene acetic acid), PTAA). Both structural (TEM, AFM) and functional (absorption change and conductivity) measurements has shown that RCs could be bound effectively to functionalized CNTs. The kinetics of the light induced absorption change indicated that RCs were still active in the composite and there was an interaction between the protein cofactors and the CNTs. The light generated photocurrent was measured in an electrochemical cell with transparent CNT electrode designed specially for this experiment.
31.	Szabó, T., et al. (författare) Generating photocurrent by nanocomposites based on photosynthetic reaction centre protein 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 252:11, s. 2614-2619 Tidskriftsartikel (refereegranskat)abstract An optoelectronic device, which converts light energy to electric potential, was designed and fabricated by using photosynthetic reaction centre (RC) proteins of purple bacterium Rhodobacter sphaeroides R-26, based on the structure and function of the dye sensitised organic solar cells. First, an electrochemical cell with three electrodes was created especially for this measurement. ITO covered by the MWCNT-RC containing sample served as the working electrode and the counter and the reference electrodes were platinum and Ag\AgCl, respectively. Water soluble ubiquinone-0 and ferrocene, in some experiments were used as mediators. In another experiment, the presence of the RCs in the active layer under dried conditions assured tuneable wavelength sensitivity, in general in the visible, but specially, in the near infrared (700-1000 nm) spectral range. The lifetime of the primary charge separation is in the ps time scale and that of the charge stabilisation can be modulated (at least theoretically) between ps and seconds. A successful combination of RC protein with a light energy converter device in spectroelectrochemical cell (wet conditions in buffered electrolyte) and in dried multilayer structure will be presented here.
32.	Tóth, P. S., et al. (författare) Development of polymer-dopant interactions during electropolymerization, a key factor in determining the redox behaviour of conducting polymers 2015 Ingår i: Journal of Solid State Electrochemistry. - : Springer-Verlag New York. - 1432-8488 .- 1433-0768. ; 19:9, s. 2891-2896 Tidskriftsartikel (refereegranskat)abstract Investigation of ionic motion in connection with the redox transformation of conjugated polymers (CP) has always been at the leading edge of research. Motivated by recent proofs for the chemical bond formation between chloride ion and alpha-positioned carbon in poly (3,4-ethylenedioxythiophene) (PEDOT), comprehensive studies have been extended to another strongly electronegative halide (F-) and to another CP, polypyrrole (PPy). As the electrochemical quartz crystal nanobalance (EQCN) results proved, the movement of the bulky Bu4N+ cations has been exclusively experienced during the redox processes of both systems. Moreover, the decisive role of the anions being present in the polymerization solution in determining the redox capacity and, consequently, the maximum doping level of the films was evidenced. On the grounds of the systematic experiments, the strong and permanent chemical interaction of highly electronegative anions and the polymer has been demonstrated as a general phenomenon. Importantly, this observation requires the necessary reconsideration of specific polymer-dopant interactions and calls attention to the necessity of careful design of the polymerization procedure.
33.	Tóth, P. S., et al. (författare) Hyphenated in situ conductance and spectroelectrochemical studies of polyaniline films in strongly acidic solutions 2013 Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 110, s. 446-451 Tidskriftsartikel (refereegranskat)abstract The redox transformations of polyaniline (PANI) have been studied in acidic solutions of pH <1 by in situ optical electrochemistry and in situ ac conductance technique applied both separately and by using them in a hyphenated mode. For the combination of the two in situ electrochemical techniques, thin layers have been deposited on a special double-band ITO electrode (dbITO), with a gap of 15 p,m. The structure of the dbITO printed circuit electrode made possible to monitor simultaneously the electrochemical, the optical and the conductance changes during the redox processes, occurring in the self-same film. Spectral features confirmed the existence of protonated segments in the reduced film, formed in these strongly acidic media, assumingly via the proton partition at the reduced film/solution interface, coupled also with anion uptake to fulfil electroneutrality. The simultaneous in situ spectral and ac conductance data gave evidence that the development of the conducting state starts only with the oxidative transformation of emeraldine type radical cations coupled with anion entry, leading to the increase in the quinoid/benzonoid ratio in the charge carriers.
34.	Varga, A., et al. (författare) Controlled Photocatalytic Deposition of CdS Nanoparticles on Poly(3-hexylthiophene) Nanofibers: A Versatile Approach to Obtain Organic/Inorganic Hybrid Semiconductor Assemblies 2015 Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119, s. 28020-28027 Tidskriftsartikel (refereegranskat)abstract To efficiently harness the possible synergies, stemming from the combination of organic conducting polymers and inorganic semiconductors; sophisticated assembling methods are required to control the composition and morphology at the nanoscale. In this proof-of-concept study, we demonstrate the in situ photocatalytic deposition of CdS nanoparticles on poly(3-hexylthiophene) (P3HT) nanofibers, exploiting the semiconducting nature of this polymer. The formation of the hybrid assembly was monitored by UV-vis and Raman spectroscopy, Energydispersive X-ray microanalysis, and X-ray diffraction (XRD). Transmission electron microscopic studies and AFM images confirmed that both the particle size and the loading can be tuned by the deposition time. Photoelectro chemical studies revealed the facile transfer of photogenerated electrons from P3HT to CdS, as well as that of the holes from CdS to P3HT. It is believed that ensuring intimate contact between the components in these nanohybrids will open new avenues in various application schemes, e.g., solar energy conversion.
35.	Visy, C., et al. (författare) In situ techniques used in hyphenated mode for studying the properties of electroactive materials 2016 Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 215, s. 187-191 Forskningsöversikt (refereegranskat)abstract In situ electrochemical techniques are widely applied to study the synthesis and properties of redox active materials. These combined methods enable the in-depth understanding of the complex processes, since they are able to furnish extra information about the given process from some additional aspect. Thus, detection of spectral modifications, changes in mass, structure, volume and conductivity, occurring in parallel with the redox transformations, complete the knowledge by enlightening secondary effects of the electrochemical perturbation. Various combinations of two in situ electrochemical methods extend further the understanding of the behaviour of electroactive materials by furnishing information from several aspects at the same time from the self-same layer. In this work these advantageous hyphenations are summarized, which combinations enable to correlate additive or secondary effects, provoked by the same background: the electrochemical process. The presented methods can be implemented and used ubiquitously in studies of divers modified electrodes.

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