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... V. Slavov, I. Angelov, I. Slavova.....165 ... D.Sc. Eng. Nicola Nicolov Shoylev Profi. Dr. Eng. Alexander Draganov Stoyanov.....369 ...
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Research Interests: Engineering, Chemical Engineering, Materials Science, Electrochemistry, Cyclic Voltammetry, and 15 moreFuel Cell, Hydrogen Energy, Platinum, Surface Morphology, Magnetron Sputtering, Nafion, Steady state, CHEMICAL SCIENCES, Platinum Nanoparticles, Proton Exchange Membrane Fuel Cell, Electrode, Sputter Deposition, Electrochemical method, Electrolyte, and Catalytic Activity
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Here we present an easy and efficient procedure for the immobilization of proton-donating sulfo-groups in a polymer matrix. Sodium vinyl sulfonate was polymerized/cross-linked in a para-polybenzimidazole (p-PBI) matrix. After... more
Here we present an easy and efficient procedure for the immobilization of proton-donating sulfo-groups in a polymer matrix. Sodium vinyl sulfonate was polymerized/cross-linked in a para-polybenzimidazole (p-PBI) matrix. After acidification semi-interpenetrating networks, comprising p-PBI, containing cross-linked polyvinylsulfonic acid (cr-PVSA), have been obtained. Polymerization/crosslinking has been initiated either thermally or by UV irradiation. Two series of membranes, containing high concentrations of water insoluble acid groups, have been prepared. Proton conductivity was measured at 60, 80 and 95 °C and 100% relative humidity. The highest proton conductivity achieved was 63.2 mS.cm–1.
Like conventional superconductors, MgB 2 is a phonon-mediated superconductor with a relatively long coherence length. Its properties make the prospects for fabricating reproducible uniform Josephson junctions, the fundamental element of... more
Like conventional superconductors, MgB 2 is a phonon-mediated superconductor with a relatively long coherence length. Its properties make the prospects for fabricating reproducible uniform Josephson junctions, the fundamental element of superconducting circuits, much more favorable for MgB 2 than for high-temperature superconductors. Here, we report bulk superconductivity in nanophase MgB 2 , using a two-step technique of mechanically activated self-propagated high-temperature synthesis(MASHS). The conditions of synthesis and some properties of the product (structure, susceptibility, resistivity) were studied. It was shown that a single-phase product was obtained after 2 hours of intense mechanical treatment of reagents (Mg and B powders), and MASHS induced at 30 A.cm - 2 .
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Non-platinum electrode materials for hydrogen evolution: effect of catalyst support and metallic phase P. Paunović, D. Stoevska Gogovska, O. Popovski, I. Radev, E. Lefterova, E. Slavcheva, A. T. Dimitrov and S. Hadži Jordanov Faculty of... more
Non-platinum electrode materials for hydrogen evolution: effect of catalyst support and metallic phase P. Paunović, D. Stoevska Gogovska, O. Popovski, I. Radev, E. Lefterova, E. Slavcheva, A. T. Dimitrov and S. Hadži Jordanov Faculty of Technology and Metallurgy, University of Ss Cyril and Methodius, Skopje 1 Faculty of Technology and Metallurgy, University of Ss Cyril and Methodius, 16 Ruger Bošković St, 1000 Skopje 2 Military Academy, Mihajlo Apostolski Str., b.b., 1000 Skopje 3 Institute of Electrochemistry and Energy Systems, Bulgarian Academy of Sciences, Acad.G.Bonchev St., Building 10, 1113 Sofia, Bulgaria
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... D.Sc. Eng. Nicola Nicolov Shoylev Profi. Dr. Eng. Alexander Draganov Stoyanov.....369 Guide fior authors.....371 Issue 4 ...
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The paper describes an EasyTest cell developed for simple, safe and inexpensive to run testing and optimisation of the active materials (catalysts, catalytic supports, polymer membrane electrolytes) and electrode structures utilized in... more
The paper describes an EasyTest cell developed for simple, safe and inexpensive to run testing and optimisation of the active materials (catalysts, catalytic supports, polymer membrane electrolytes) and electrode structures utilized in PEM Fuel cells and Electrolysers. The main advantages of the new EasyTest technique are demonstrated by a comparative study on the performance of two types of membrane electrode assemblies for electrochemical energy conversion. Nafion and PBI-based polymer electrolyte membranes covered with catalytic layers containing 20 % Pt dispersed on carbon black (E-TEK, De Nora) are tested as hydrogen electrodes working in a fuel cell and an electrolyser mode at two characteristic temperatures, varying the total partial pressure in the cell. The PBI-based membrane electrode assembly (MEA) gives lower current densities compared to that containing Nafion, while its performance remains stable in a much broader potential range. At overpotentials of about η = 300-350...
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Antimony doped tin oxide (ATO) supported platinum nanoparticles are considered a more stable replacement for conventional carbon supported platinum materials for the oxygen reduction reaction. However, the interplay of antimony, tin and... more
Antimony doped tin oxide (ATO) supported platinum nanoparticles are considered a more stable replacement for conventional carbon supported platinum materials for the oxygen reduction reaction. However, the interplay of antimony, tin and platinum and its impact on the catalytic activity and durability has only received minor attention. This is partly due to difficulties in the preparation of morphology- and surface-area-controlled antimony-doped tin oxide materials. The presented study sheds light onto catalyst–support interaction on a fundamental level, specifically between platinum as a catalyst and ATO as a support material. By using a previously described hard-templating method, a series of morphology controlled ATO support materials for platinum nanoparticles with different antimony doping concentrations were prepared. Compositional and morphological changes before and during accelerated stress tests are monitored, and underlying principles of deactivation, dissolution and catalytic performance are elaborated. We demonstrate that mobilized antimony species and strong metal support interactions lead to Pt/Sb alloy formation as well as partially blocking of active sites. This has adverse consequences on the accessible platinum surface area, and affects negatively the catalytic performance of platinum. Operando time-resolved dissolution experiments uncover the potential boundary conditions at which antimony dissolution can be effectively suppressed and how platinum influences the dissolution behavior of the support.
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This experimental work deals with the preparation and investigation of PEM fuel cell electrodes, which are obtained using Graphene Related Material (GRM) serving as catalyst support material for platinum nanoparticles. The applied GRM... more
This experimental work deals with the preparation and investigation of PEM fuel cell electrodes, which are obtained using Graphene Related Material (GRM) serving as catalyst support material for platinum nanoparticles. The applied GRM belong to the group of carbon nanofibers and exhibits a helical-ribbon structure with dimensions of 50 nm in diameter and an average length up to a few µm. Furthermore, utilized GRM provide a superior graphitisation degree of about 100 %, which leads to both high corrosion resistance and low ohmic resistance. Material stability plays one of the main roles for long term fuel cell operation, whereby a great electrical catalyst contact combined with high specific surface area yields in high fuel cell performances. Prior to GRM dispersion and deposition onto a gas diffusion layer, the graphene structures are functionalized by oxygen plasma treatment. Through this step, functional oxygen groups are generated onto the GRM outer surface providing an improved hydrophilic behaviour and facilitating the GRM suspension preparation. In addition, the oxygen groups act as anchors for platinum nanoparticles which are subsequently deposited onto the GRM surface through a pulse electrodeposition process. Membrane electrode assemblies produced with the prepared electrodes are investigated in-situ in a PEM fuel cell test bench.
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A simple method for the preparation of nanostructured low loading Pt, PtNi and PtCo electrodes for application in PEM fuel cells is proposed. For high utilisation, the catalyst nanoparticles are directly deposited on the microporous layer... more
A simple method for the preparation of nanostructured low loading Pt, PtNi and PtCo electrodes for application in PEM fuel cells is proposed. For high utilisation, the catalyst nanoparticles are directly deposited on the microporous layer (MPL) of a commercially available gas diffusion layer by pulse electrodeposition. A special challenge for electrodeposition, in this study, was the hydrophobic character of the MPL. For a homogenous fine-grained electrodeposition, an activation treatment of the substrate surface was advantageous. Plasma etching of the surface, before electrodeposition, significantly improved fuel cell performance. Furthermore, the effects of electrolyte and electrodeposition parameters have been investigated in detail. For use as catalyst, nucleation should be predominant to enable a large surface area. Several electrochemical and optical techniques, including cyclic voltammetry, SEM, XRD, X-ray fluorescence analysis and IR spectroscopy, were used to investigate the catalytically relevant parameters of the deposited nanoparticles.
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Cost-efficiency, durability, and reliability of catalysts, as well as their operational lifetime, are the main challenges in chemical energy conversion. Here, we present a novel, one-step approach for the synthesis of Pt/C hybrid material... more
Cost-efficiency, durability, and reliability of catalysts, as well as their operational lifetime, are the main challenges in chemical energy conversion. Here, we present a novel, one-step approach for the synthesis of Pt/C hybrid material by plasma-enhanced chemical vapor deposition (PE-CVD). The platinum loading, degree of oxidation, and the very narrow particle size distribution are precisely adjusted in the Pt/C hybrid material due to the simultaneous deposition of platinum and carbon during the process. The as-synthesized Pt/C hybrid materials are promising electrocatalysts for use in fuel cell applications as they show significantly improved electrochemical long-term stability compared to the industrial standard HiSPEC 4000. The PE-CVD process is furthermore expected to be extendable to the general deposition of metal-containing carbon materials from other commercially available metal acetylacetonate precursors.
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ABSTRACT The paper presents the experimental validation of the “EasyTest Cell” operational principle via comparative electrochemical tests on MEAs carried out in three types of electrochemical hydrogen energy conversion (EHEC) testing... more
ABSTRACT The paper presents the experimental validation of the “EasyTest Cell” operational principle via comparative electrochemical tests on MEAs carried out in three types of electrochemical hydrogen energy conversion (EHEC) testing cells: conventional polymer electrolyte membrane fuel cells (PEMFC) and polymer electrolyte membrane water electrolyzers (PEMWE), properly equipped with all the required auxiliaries (products conditioning and supplying, reagents removal, etc.), and the simple, autonomous EasyTest Cell. Along with EasyTest Cell validation and demonstration of its advantages, the influence of argon pressure during sputtering on the electrode characteristics, including gas diffusion limitations was investigated. The electrodes under investigation were magnetron sputtered C/Ti/IrOx (IrOx loading in the range 0.12–0.4 mg cm−2), C/Ti/IrOx/Pt/IrOx (IrOx 0.08/Pt 0.06/IrOx 0.08 mg cm−2), sputtered at various argon pressure C/Ti/Pt (0.15 and 0.25 mg cm−2), and commercial ELAT electrode (V.21, Lot # MB030105-1, Pt loading 0.5 mg cm−2, E-TEK). The results obtained proved the reliability, simplicity (running-periphery-free) and broadened experimental possibilities of EasyTest Cell over PEMFC and PEMWE single cell testing. Thus, significant cost reduction and resource saving in R&D laboratory can be achieved. Moreover, validation of EasyTest Cell contributes not only to testing facilitations, but potentially to standardization of MEA testing since it gives possibilities for precise control and more uniform distribution of the working parameters applied to the testing object, which are both compulsory for performance comparison and qualifying.
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An EasyTest Cell concept is applied to study the performance characteristics of the electrochemical processor for polymer electrolyte membrane electrochemical hydrogen energy converters (PEM EHEC), broadly known as a membrane electrode... more
An EasyTest Cell concept is applied to study the performance characteristics of the electrochemical processor for polymer electrolyte membrane electrochemical hydrogen energy converters (PEM EHEC), broadly known as a membrane electrode assembly (MEA). A series of MEAs consisting of Nafion 117 polymer electrolyte and magnetron sputtered Pt, IrOx, and composite IrOx/Pt/IrOx catalysts with varying catalytic loadings were investigated. The partial electrode reactions proceeding in the real PEM EHEC, namely hydrogen oxidation (HOR), hydrogen evolution (HER), oxygen reduction (ORR), and oxygen evolution (OER), are simulated and studied in a recently developed test cell with a unitized gas compartment. The EasyTest Cell design gives possibilities for strict control of the experimental conditions by avoiding the usage of any auxilliary gas conditioning equipment. By varying the thickness of the sputtered Pt film, the catalyst loading is remarkably reduced (from 0.5 to 0.06mgcm−2 or about 8 times) for both HOR and HER without any sacrifice of the electrode performance. The electrode with 0.2mgcm−2 sputtered IrOx shows the best OER performance. The composite IrOx/Pt/IrOx electrode demonstrated a bi-functional catalytic activity toward both OER and ORR, as well as improved gas diffusion properties toward ORR compared to the single Pt layer with the same catalytic loading.A phenomenological criterion for evaluating the gas diffusion properties of the electrodes is proposed. The applied testing approach is validated via comparison of the results obtained in the EasyTestCell and the common laboratory PEM electrolytic cell.
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ABSTRACT The research reports on the electrocatalytic properties of IrOx, Pt, and composite IrOx–Pt–IrOx thin films prepared by physical vacuum deposition technique of dc magnetron sputtering. The efficiency toward the oxygen evolution in... more
ABSTRACT The research reports on the electrocatalytic properties of IrOx, Pt, and composite IrOx–Pt–IrOx thin films prepared by physical vacuum deposition technique of dc magnetron sputtering. The efficiency toward the oxygen evolution in aqueous solutions and in a laboratory electrolyser with polymer proton conductive electrolyte has been investigated using the conventional electrochemical methods of cyclic voltammetry and steady state polarisation curves. The sputtered films have demonstrated excellent catalytic properties, mechanical stability, and high corrosion resistance under intensive oxygen evolution. The best performance (anodic current density of 0.84Acm−2 at potential of 1.8V) has shown the IrOx film with loading of 0.2mgcm−2. Some data on the catalytic activity toward oxygen reduction reaction in aerated 0.5M H2SO4 solution and the possibility to use the method of magnetron sputtering for preparation of cost effective composite catalytic films with bifunctional properties are also presented and discussed.
Research Interests: Engineering, Cyclic Voltammetry, Energy Conversion, Thin Film, Physical sciences, and 11 moreCost effectiveness, Current Density, Magnetron Sputtering, Steady state, CHEMICAL SCIENCES, Oxygen Reduction Reaction, Aqueous Solution, Electrochemical method, Catalytic Activity, Corrosion Resistance, and Oxygen evolution reaction
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ABSTRACT In the present work, Pt3Cr/C alloy catalyst showed enhanced activity under half-cell and full-cell conditions as well as excellent corrosion stability compared to those of the 40 wt% Pt/CJM benchmark catalyst. At 2 mA cm-²,... more
ABSTRACT In the present work, Pt3Cr/C alloy catalyst showed enhanced activity under half-cell and full-cell conditions as well as excellent corrosion stability compared to those of the 40 wt% Pt/CJM benchmark catalyst. At 2 mA cm-², Pt3Cr/C catalyst exhibited 10 mV less over-potential and twofold higher specific and mass activity for ORR than Pt/CJM. The average particle size grew from 4.5 nm up to “only” 6-8 nm during accelerated degradation tests under half-cell conditions. For comparison, average particle size of Pt/CJM increased from 4.5 up to 15-20 nm. In full-cell experiments, MEA with Pt3Cr/C as cathode catalyst exhibits an excellent maximal power density retention of about 76% after 1000 degradation cycles compared to 55% for the MEA with the commercial catalyst.
This work reports on the influence of the geometric area ratio between identical electrodes in MEA on their electrochemical performance. The difficulties in obtaining half-cell electrochemical data of MEAs motivated this research. The... more
This work reports on the influence of the geometric area ratio between identical electrodes in MEA on their electrochemical performance. The difficulties in obtaining half-cell electrochemical data of MEAs motivated this research. The problem arises from the equality in geometric area of working electrode (WE) and counter electrode (CE), the thin distance between them (PEM thickness in the range 15–200 μm),
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The paper describes an EasyTest cell developed for simple, safe and inexpensive to run testing and optimisation of the active materials (catalysts, catalytic supports, polymer membrane electrolytes) and electrode structures utilized in... more
The paper describes an EasyTest cell developed for simple, safe and inexpensive to run testing and optimisation of the active materials (catalysts, catalytic supports, polymer membrane electrolytes) and electrode structures utilized in PEM Fuel cells and Electrolysers. The main advantages of the new EasyTest technique are demonstrated by a comparative study on the performance of two types of membrane electrode assemblies for electrochemical energy conversion. Nafion and PBI-based polymer electrolyte membranes covered with catalytic layers containing 20 % Pt dispersed on carbon black (E-TEK, De Nora) are tested as hydrogen electrodes working in a fuel cell and an electrolyser mode at two characteristic temperatures, varying the total partial pressure in the cell. The PBI-based membrane electrode assembly (MEA) gives lower current densities compared to that containing Nafion, while its performance remains stable in a much broader potential range. At overpotentials of about = 300–350 m...
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An easy and efficient procedure for reducing the doping level of phosphoric acid doped p-PBI membranes (p-PBI/PA) was developed. Starting from a membrane with very high doping level (PA/PBI per repeat unit), a series of membranes with... more
An easy and efficient procedure for reducing the doping level of phosphoric acid doped p-PBI membranes (p-PBI/PA) was developed. Starting from a membrane with very high doping level (PA/PBI per repeat unit), a series of membranes with reduced doping level was prepared. The effect of doping level on the mechanical parameters (E, tensile strength and Vickers microhardness-MHV) and proton conductivity was studied. Correlation between MHV and elastic modulus (E) is established. For p-PBI/PA membranes the reduction of the doping level from 42 to 17 moles PA per PBI results in drastic improvement of the mechanical parameters-the elastic modulus (E) goes up from 3.5 to 30.1 MPa, tensile strength-from 1.5 to 7.0 MPa and MHV-from 0.5 to 1.9 MPa. The proton conductivity measurements, performed at 160 °C and different relative humidity (RH), show that even the membrane with the lowest doping level (17 PA/PBI per r.u.) at RH 10% and 15% exhibits very high proton conductivity-over 150 mS·cm-1(co...
The management of multimedia information poses special requirements for multimedia information systems. Both representation and retrieval of the complex and multifaceted multimedia data are not easily handled with the flat relational... more
The management of multimedia information poses special requirements for multimedia information systems. Both representation and retrieval of the complex and multifaceted multimedia data are not easily handled with the flat relational model and require new data models. In the last several years, object-oriented and graph-based data models are actively pursued approaches for handling the multimedia information. In this paper the
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The paper presents an investigation on the electrocatalytic activity of co-sputtered PtIr thin films towards the ORR. The catalyst composition was controlled by varying the sputtering power of the Ir target in the range 20e100 W at... more
The paper presents an investigation on the electrocatalytic activity of co-sputtered PtIr thin films towards the ORR. The catalyst composition was controlled by varying the sputtering power of the Ir target in the range 20e100 W at constant power of 100 W for the Pt target. The films were analyzed applying SEM, XRD, EDX, XPS (physical characterization); stationary and quasi-stationary polarization curves, cyclic voltammetry and ac impedance (" in situ " tests performed in single PEMFC). The influence of the Pt/Ir ratio on the atomic interaction, morphology, and the resulting electrocatalytic activity was studied in detail. The contribution of the film content, morphology and the Pt/Ir electrocatalytic synergism to the electrode performance was evaluated. The optimal balance between the favourable effect of Ir addition and the lost of active surface sites due to substitution of Pt for Ir was established.