Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil mic... more Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil microemulsion method and examined for formic acid and methanol oxidation. Prepared catalyst powder was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). These techniques revealed that the catalyst contains rather agglomerated quasi-spherical particles, ∼4 nm diameter, composed of a solid solution of Pt and Au with only ∼4 at% of Au. In spite of such low Au content, both onset and peak potentials for CO oxidation are shifted some 150 mV to more positive values in comparison to Pt synthesized in the same manner due to stronger binding of CO as a result of notable electronic effect. It is important that this small quantity of Au also significantly influences oxidation of formic acid promoting direct path and suppressing indirect path in formic acid oxidation in a degree as expected by a much larger quantity of Au. Such improvement could be due exclusively by ensemble effect of high number of small Pt domains which formation could be possible only by very fine dispersion of such low Au quantity. High number of small Pt domains is corroborated by lower activity for methanol oxidation in comparison to Pt catalyst synthesized by the same procedure. These results emphasize the importance of the Au dispersion on the surface of Pt over its quantity in PtAu catalyst with regards to both, the ensemble and the electronic effects.
Metallic zirconium has a broad range of potential applications in engineering and in industries t... more Metallic zirconium has a broad range of potential applications in engineering and in industries that are operating under harsh corrosive environments, such as nuclear and chemical industry. Compared to other metals like aluminum, its behavior in electrochemical reactions is poorly understood and so far, there are no larger-scale electrochemical approaches to process zirconium. Ionic liquids are a suitable reaction medium for electrochemical reactions of zirconium. To better understand the electrochemical reactivity of zirconium, different combinations of ionic liquids and zirconium precursors are investigated. It was found that interactions between the Zr precursor and the ionic liquids can have significant influence on the diffusion properties of Zr. Furthermore, mixtures of ionic liquids with other solvents were explored and it could be determined that most of the electrochemical properties of Zr are retained also in solvent mixtures. This could potentially save costs for industrial applications, as lower amounts of the ionic liquids can be used, to obtain similar electrochemical properties.
Abstract Corrosion of metals is producing huge costs by the depreciation of corroded structures w... more Abstract Corrosion of metals is producing huge costs by the depreciation of corroded structures with major impact on environment and human safety. It requires the proper selection of a specific protecting coating material. Innovative ways of counteracting corrosion by use of electrospun polymeric nanofibers will be reviewed. The use and benefits of single-component nanofibers for improving the mechanical properties of organic coatings are described. A further approach is the incorporation of corrosion inhibitors within the nanofiber structure in order to increase corrosion coatings performance. Attention is given to core-shell nanofibers using coaxial electrospinning setups for providing self-healing capabilities. The self-healing performance of various composite coatings reinforced with core-shell nanofibers is discussed. Literature results of improved corrosion resistance by nanofiber introduction into coatings are summarized. An outlook is provided for future potential ideas and possible applications of this emerging field. The commercial viability of those innovative processes is discussed and evaluated.
Abstract The use of smart nanocontainers as carriers of corrosion inhibitors offers good alternat... more Abstract The use of smart nanocontainers as carriers of corrosion inhibitors offers good alternatives to the classical corrosion protection methods. This chapter aims to give a concise review on the most important recent achievements in the field of development and fabrication of protective coatings based on corrosion inhibitor loaded–smart nanocontainers, as well as explanation of the different corrosion inhibition mechanisms. The most significant types of smart nanocontainers have been demonstrated from polymer nanocapsules, nanofibers, nanotubes, and nanolayers to the porous nanoparticles. The commercial viability of those innovative materials and processes, as well as the advantages and limitations associated with their practical applications are discussed and evaluated in the chapter.
Journal of energy and power engineering, Nov 28, 2015
The most critical disadvantages of the Zn-air flow battery system are corrosion of the zinc, whic... more The most critical disadvantages of the Zn-air flow battery system are corrosion of the zinc, which appears as a high self-discharge current density and a short cycle life due to the non-uniform, dendritic, zinc electrodeposition that can lead to internal short-circuit. In our efforts to find a dendrite-free Zn electrodeposition which can be utilized in the Zn-air flow battery, the surface morphology of the electrolytic Zn deposits on a polished polymer carbon composite anode in alkaline, additive-free solutions was studied. Experiments were carried out with 0.1 M, 0.2 M and 0.5 M zincate concentrations in 8 M KOH. The effects of different working conditions such as: elevated temperatures, different current densities and different flow velocities, on current efficiency and dendrite formation were investigated. Specially designed test flow-cell with a central transparent window was employed. The highest Coulombic efficiencies of 80%-93% were found for 0.5 M ZnO in 8 M KOH, at increased temperatures (50-70 °C), current densities of up to 100 mA•cm-2 and linear electrolyte flow velocities higher than 6.7 cm•s-1 .
Glassy metallic Hf thin films were obtained using electron beam deposition at room temperature du... more Glassy metallic Hf thin films were obtained using electron beam deposition at room temperature due to the low energy received by Hf atoms during the film formation process. The amorphous nature of the Hf films suggested by XRD was confirmed by low temperature electrical conductivity measurements where a negative temperature coefficient of resistivity was identified. Anodic oxidations using a scanning droplet cell microscopy were performed on a typical crystalline (hexagonal) Hf film obtained by sputtering and on the glassy Hf. A decrease of the oxide formation factor by 30% (from 2.4 to 1.7 nm V −1) was evidenced on the amorphous Hf. Electrochemical impedance spectroscopy on both samples revealed almost identical capacitances while the electrical permittivities were found to differ by 40%. The dielectric constant of the HfO 2 decreased from 33.5 on the crystalline parent metal sample to 19.8 on the amorphous one. The unexpected 10% deviation was attributed to a smoother defect-free oxide/metal interface in the case of HfO 2 grown on glassy Hf film.
PtAu systems are recognized as good catalysts for the oxidation of formic acid electrooxidation, ... more PtAu systems are recognized as good catalysts for the oxidation of formic acid electrooxidation, which is investigated as a possible anodic reaction in low-temperature fuel cells. In this research, bimetallic PtAu nanoparticles, supported on high area carbon Vulcan XC-72R, were synthesized by water in oil microemulsion method. The precursor reduction process took place in a single microemulsion, simultaneously, in the presence of 35% of HCl in the water phase, as a capping agent. Electrochemical behavior of the PtAu/C catalyst was investigated at as prepared electrodes by cyclic voltammetry in 0.5M H 2 SO 4 as a supporting electrolyte, and also in the oxidation of adsorbed CO. The results were compared to the Pt/C catalyst prepared by the same synthesis procedure. PtAu/C catalyst powder was also characterized by X-Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Average particle diameter, of 2nm, was calculated from XRD data, which is close to the value of 2.82 nm obtained from TEM images. Compared to identically synthesized Pt nanoparticles, the bimetallic ones are significantly smaller. EDS maps of PtAu/C sample confirm the presence of both elements, and indicate a very fine distribution of Au in the sample. Elemental composition of about 20% Au and 80% Pt was also determined from these maps. Prepared catalyst was tested for formic acid electro-oxidation in terms of its activity and stability over the long term cycling. The voltammograms recorded indicate the change of reaction mechanism and better utilization of the catalyst surface in comparison to Pt/C.
In this research, a water-in-oil microemulsion method with HCl as a capping agent was applied to ... more In this research, a water-in-oil microemulsion method with HCl as a capping agent was applied to synthesize carbon supported Pt catalysts. Varying the concentration of HCl caused changes in the shape of obtained nanoparticles, i.e. preferential growth of certain facets. Addition of catalyst support in the synthesis process facilitated the cleaning procedures necessary to remove the surfactant residues. Prepared catalyst powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis indicated the influence of HCl addition on the crystallite size and crystal habit. TEM revealed that addition of higher amounts of the capping agent led to the formation of a noticable amount of particles with concave cubic or branched-like structures. Influence of the catalyst particles shape on its electrochemical properties was tested in the oxidations of CO ads , ammonia and formic acid. The latter one was examined in terms of both activity and stability of as prepared and oxide-annealed (electrochemically treated) catalysts. The results clearly demonstrate that even small changes in the nanoparticle surface structure give rise to distinct modifications in their properties. Concave cubic particles, in comparison to other catalysts, show improved catalytic properties and the contribution of their preferentially oriented {100} facets is electrochemically detectable.
Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticl... more Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticles modified with a sub-monolayer of underpotentially deposited Cu (Cu@Pd/C) and Pd-Cu alloy nanoparticles (Pd-Cu/C), and examined for the ethanol oxidation reaction (EOR) in alkaline solution. The catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, as well as cyclic voltammetry. As reference catalysts, Pd/C and Pt/C were used. The electrochemically active surface area of all samples was determined from CO ads and Cu upd desorption and Pd oxide reduction, and used to assess their intrinsic activity for EOR. Intimate contact of Pd with Cu atoms enhanced its activity, regardless of the type of bimetal catalyst. The atomic Pd:Cu ratio between 2:1 and 4:1 appears to be optimal for high activity. The most active catalyst under the potentiodynamic conditions was Cu@Pd/C with θ(Cu) = 0.21,although Pd-Cu/C was superior during the potentiostatic test. All bimetallic catalysts surpassed Pd/C in mass activity. The EOR activity of Pt/C was higher compared to Pd-based catalysts at low potentials, both in terms of specific and mass activity, but with a significant decline over a 30-min potentiostatic stability test.
Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticl... more Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticles modified with a sub-monolayer of underpotentially deposited Cu (Cu@Pd/C) and Pd-Cu alloy nanoparticles (Pd-Cu/C), and examined for the ethanol oxidation reaction (EOR) in alkaline solution. The catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, as well as cyclic voltammetry. As reference catalysts, Pd/C and Pt/C were used. The electrochemically active surface area of all samples was determined from CO ads and Cu upd desorption and Pd oxide reduction, and used to assess their intrinsic activity for EOR. Intimate contact of Pd with Cu atoms enhanced its activity, regardless of the type of bimetal catalyst. The atomic Pd:Cu ratio between 2:1 and 4:1 appears to be optimal for high activity. The most active catalyst under the potentiodynamic conditions was Cu@Pd/C with θ(Cu) = 0.21,although Pd-Cu/C was superior during the potentiostatic test. All bimetallic catalysts surpassed Pd/C in mass activity. The EOR activity of Pt/C was higher compared to Pd-based catalysts at low potentials, both in terms of specific and mass activity, but with a significant decline over a 30-min potentiostatic stability test.
Metallic zirconium has a broad range of potential applications in engineering and in industries t... more Metallic zirconium has a broad range of potential applications in engineering and in industries that are operating under harsh corrosive environments, such as nuclear and chemical industry. Compared to other metals like aluminum, its behavior in electrochemical reactions is poorly understood and so far, there are no larger-scale electrochemical approaches to process zirconium. Ionic liquids are a suitable reaction medium for electrochemical reactions of zirconium. To better understand the electrochemical reactivity of zirconium, different combinations of ionic liquids and zirconium precursors are investigated. It was found that interactions between the Zr precursor and the ionic liquids can have significant influence on the diffusion properties of Zr. Furthermore, mixtures of ionic liquids with other solvents were explored and it could be determined that most of the electrochemical properties of Zr are retained also in solvent mixtures. This could potentially save costs for industri...
AbstractIn our previous paper, we described in detail studies of Sn influence on electrocatalytic... more AbstractIn our previous paper, we described in detail studies of Sn influence on electrocatalytic activity of PtSn catalyst for CO and formic acid oxidation (Stevanović et al., J. Phys. Chem. C, 118 (2014) 278–289). The catalyst was composed of a Pt phase, Pt3Sn alloy and very small SnO2 particles. Different electrochemical treatment enabled studies of PtSn/C having Sn both in surface and subsurface layers and skeleton structure of this catalyst with Sn only in subsurface layers. The results obtained revealed the promotional effect of surface Sn whether alloyed or as oxide above all in preventing accumulation of CO and blocking the surface Pt atoms. As a consequence, in formic acid oxidation, the currents are not entering the plateau but increasing constantly until reaching a maximum. It was concluded that at lower potentials the effect of Sn on formic acid oxidation was predominantly electronic but with increasing the potential bi-functional mechanism prevailed due to the leading role of SnO2. This role of SnO2 is restated in the present study. Therefore, CO and formic acid oxidation were examined at PtSnO2/C catalyst. The catalyst was synthesised by the same microwave-assisted polyol procedure. According to XRD analysis, the catalyst is composed of a Pt phase and SnO2 phase. The reactions were examined on PtSnO2/C catalyst treated on the same way as PtSn/C. Comparing the results obtained, the role of SnO2 is confirmed and at the same time the significance of alloyed Sn and its electronic effect is revealed. Graphical Abstract
Abstract Pd-Ni/C catalyst was synthesized employing a borohydride reduction method. The high area... more Abstract Pd-Ni/C catalyst was synthesized employing a borohydride reduction method. The high area Ni was first dispersed on the carbon support and then modified by Pd nanoparticles. Transmission electron microscopy confirmed relatively even distribution of Ni across the carbon support with discrete palladium particles of about 3.3 nm mean diameter on it. Cyclic voltammetry confirmed the presence of Ni on the catalyst surface. The activity of the Pd-Ni/C catalysts for ethanol oxidation reaction (EOR) in alkaline solution was tested under the potentiodynamic and potentiostatic conditions and the results were compared to those obtained on the Pd/C catalyst. It was found that Pd-Ni/C is more active for the EOR compared to Pd/C by a factor up to 3, depending on the type of experiments and whether specific activity or mass activity are considered. During the potentiodynamic stability test an interesting phenomenon of activation of Pd-Ni/C catalyst was observed. It was found that maximum activity is attained after fifty cycles with the positive potential limit of 1.2 V, regardless of whether they were performed in the electrolyte with or without ethanol. It was postulated that potential cycling of the Pd-Ni surface causes reorganization of the catalyst surface bringing Pd and Ni sites to a more suitable arrangement for the efficient ethanol oxidation.
The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B ... more The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B 13 C 2 alloy after thermal treatment at different temperatures from 298 K to 973 K (25 °C to 700 °C) was studied. The as-prepared alloy ribbon containing a small amount of crystalline phases, as well as domains of short-range crystalline ordering embedded in the amorphous matrix, exhibits unexpectedly high microhardness, mostly due to its composition. After thermal treatment above 723 K (450 °C), the alloy samples begin to crystallize, creating a nanocomposite structure involving nanocrystals embedded in an amorphous matrix, leading to an increase in microhardness. Further growth of the nanocrystals, as the heating temperature was increased to 973 K (700 °C), caused the change from nanocomposite structure into a more granulated and porous structure, with a dominant type of interface changing from amorphous/ crystal to crystal/crystal, leading to a decrease in microhardness.
Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil mic... more Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil microemulsion method and examined for formic acid and methanol oxidation. Prepared catalyst powder was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). These techniques revealed that the catalyst contains rather agglomerated quasi-spherical particles, ∼4 nm diameter, composed of a solid solution of Pt and Au with only ∼4 at% of Au. In spite of such low Au content, both onset and peak potentials for CO oxidation are shifted some 150 mV to more positive values in comparison to Pt synthesized in the same manner due to stronger binding of CO as a result of notable electronic effect. It is important that this small quantity of Au also significantly influences oxidation of formic acid promoting direct path and suppressing indirect path in formic acid oxidation in a degree as expected by a much larger quantity of Au. Such improvement could be due exclusively by ensemble effect of high number of small Pt domains which formation could be possible only by very fine dispersion of such low Au quantity. High number of small Pt domains is corroborated by lower activity for methanol oxidation in comparison to Pt catalyst synthesized by the same procedure. These results emphasize the importance of the Au dispersion on the surface of Pt over its quantity in PtAu catalyst with regards to both, the ensemble and the electronic effects.
Metallic zirconium has a broad range of potential applications in engineering and in industries t... more Metallic zirconium has a broad range of potential applications in engineering and in industries that are operating under harsh corrosive environments, such as nuclear and chemical industry. Compared to other metals like aluminum, its behavior in electrochemical reactions is poorly understood and so far, there are no larger-scale electrochemical approaches to process zirconium. Ionic liquids are a suitable reaction medium for electrochemical reactions of zirconium. To better understand the electrochemical reactivity of zirconium, different combinations of ionic liquids and zirconium precursors are investigated. It was found that interactions between the Zr precursor and the ionic liquids can have significant influence on the diffusion properties of Zr. Furthermore, mixtures of ionic liquids with other solvents were explored and it could be determined that most of the electrochemical properties of Zr are retained also in solvent mixtures. This could potentially save costs for industrial applications, as lower amounts of the ionic liquids can be used, to obtain similar electrochemical properties.
Abstract Corrosion of metals is producing huge costs by the depreciation of corroded structures w... more Abstract Corrosion of metals is producing huge costs by the depreciation of corroded structures with major impact on environment and human safety. It requires the proper selection of a specific protecting coating material. Innovative ways of counteracting corrosion by use of electrospun polymeric nanofibers will be reviewed. The use and benefits of single-component nanofibers for improving the mechanical properties of organic coatings are described. A further approach is the incorporation of corrosion inhibitors within the nanofiber structure in order to increase corrosion coatings performance. Attention is given to core-shell nanofibers using coaxial electrospinning setups for providing self-healing capabilities. The self-healing performance of various composite coatings reinforced with core-shell nanofibers is discussed. Literature results of improved corrosion resistance by nanofiber introduction into coatings are summarized. An outlook is provided for future potential ideas and possible applications of this emerging field. The commercial viability of those innovative processes is discussed and evaluated.
Abstract The use of smart nanocontainers as carriers of corrosion inhibitors offers good alternat... more Abstract The use of smart nanocontainers as carriers of corrosion inhibitors offers good alternatives to the classical corrosion protection methods. This chapter aims to give a concise review on the most important recent achievements in the field of development and fabrication of protective coatings based on corrosion inhibitor loaded–smart nanocontainers, as well as explanation of the different corrosion inhibition mechanisms. The most significant types of smart nanocontainers have been demonstrated from polymer nanocapsules, nanofibers, nanotubes, and nanolayers to the porous nanoparticles. The commercial viability of those innovative materials and processes, as well as the advantages and limitations associated with their practical applications are discussed and evaluated in the chapter.
Journal of energy and power engineering, Nov 28, 2015
The most critical disadvantages of the Zn-air flow battery system are corrosion of the zinc, whic... more The most critical disadvantages of the Zn-air flow battery system are corrosion of the zinc, which appears as a high self-discharge current density and a short cycle life due to the non-uniform, dendritic, zinc electrodeposition that can lead to internal short-circuit. In our efforts to find a dendrite-free Zn electrodeposition which can be utilized in the Zn-air flow battery, the surface morphology of the electrolytic Zn deposits on a polished polymer carbon composite anode in alkaline, additive-free solutions was studied. Experiments were carried out with 0.1 M, 0.2 M and 0.5 M zincate concentrations in 8 M KOH. The effects of different working conditions such as: elevated temperatures, different current densities and different flow velocities, on current efficiency and dendrite formation were investigated. Specially designed test flow-cell with a central transparent window was employed. The highest Coulombic efficiencies of 80%-93% were found for 0.5 M ZnO in 8 M KOH, at increased temperatures (50-70 °C), current densities of up to 100 mA•cm-2 and linear electrolyte flow velocities higher than 6.7 cm•s-1 .
Glassy metallic Hf thin films were obtained using electron beam deposition at room temperature du... more Glassy metallic Hf thin films were obtained using electron beam deposition at room temperature due to the low energy received by Hf atoms during the film formation process. The amorphous nature of the Hf films suggested by XRD was confirmed by low temperature electrical conductivity measurements where a negative temperature coefficient of resistivity was identified. Anodic oxidations using a scanning droplet cell microscopy were performed on a typical crystalline (hexagonal) Hf film obtained by sputtering and on the glassy Hf. A decrease of the oxide formation factor by 30% (from 2.4 to 1.7 nm V −1) was evidenced on the amorphous Hf. Electrochemical impedance spectroscopy on both samples revealed almost identical capacitances while the electrical permittivities were found to differ by 40%. The dielectric constant of the HfO 2 decreased from 33.5 on the crystalline parent metal sample to 19.8 on the amorphous one. The unexpected 10% deviation was attributed to a smoother defect-free oxide/metal interface in the case of HfO 2 grown on glassy Hf film.
PtAu systems are recognized as good catalysts for the oxidation of formic acid electrooxidation, ... more PtAu systems are recognized as good catalysts for the oxidation of formic acid electrooxidation, which is investigated as a possible anodic reaction in low-temperature fuel cells. In this research, bimetallic PtAu nanoparticles, supported on high area carbon Vulcan XC-72R, were synthesized by water in oil microemulsion method. The precursor reduction process took place in a single microemulsion, simultaneously, in the presence of 35% of HCl in the water phase, as a capping agent. Electrochemical behavior of the PtAu/C catalyst was investigated at as prepared electrodes by cyclic voltammetry in 0.5M H 2 SO 4 as a supporting electrolyte, and also in the oxidation of adsorbed CO. The results were compared to the Pt/C catalyst prepared by the same synthesis procedure. PtAu/C catalyst powder was also characterized by X-Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Average particle diameter, of 2nm, was calculated from XRD data, which is close to the value of 2.82 nm obtained from TEM images. Compared to identically synthesized Pt nanoparticles, the bimetallic ones are significantly smaller. EDS maps of PtAu/C sample confirm the presence of both elements, and indicate a very fine distribution of Au in the sample. Elemental composition of about 20% Au and 80% Pt was also determined from these maps. Prepared catalyst was tested for formic acid electro-oxidation in terms of its activity and stability over the long term cycling. The voltammograms recorded indicate the change of reaction mechanism and better utilization of the catalyst surface in comparison to Pt/C.
In this research, a water-in-oil microemulsion method with HCl as a capping agent was applied to ... more In this research, a water-in-oil microemulsion method with HCl as a capping agent was applied to synthesize carbon supported Pt catalysts. Varying the concentration of HCl caused changes in the shape of obtained nanoparticles, i.e. preferential growth of certain facets. Addition of catalyst support in the synthesis process facilitated the cleaning procedures necessary to remove the surfactant residues. Prepared catalyst powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis indicated the influence of HCl addition on the crystallite size and crystal habit. TEM revealed that addition of higher amounts of the capping agent led to the formation of a noticable amount of particles with concave cubic or branched-like structures. Influence of the catalyst particles shape on its electrochemical properties was tested in the oxidations of CO ads , ammonia and formic acid. The latter one was examined in terms of both activity and stability of as prepared and oxide-annealed (electrochemically treated) catalysts. The results clearly demonstrate that even small changes in the nanoparticle surface structure give rise to distinct modifications in their properties. Concave cubic particles, in comparison to other catalysts, show improved catalytic properties and the contribution of their preferentially oriented {100} facets is electrochemically detectable.
Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticl... more Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticles modified with a sub-monolayer of underpotentially deposited Cu (Cu@Pd/C) and Pd-Cu alloy nanoparticles (Pd-Cu/C), and examined for the ethanol oxidation reaction (EOR) in alkaline solution. The catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, as well as cyclic voltammetry. As reference catalysts, Pd/C and Pt/C were used. The electrochemically active surface area of all samples was determined from CO ads and Cu upd desorption and Pd oxide reduction, and used to assess their intrinsic activity for EOR. Intimate contact of Pd with Cu atoms enhanced its activity, regardless of the type of bimetal catalyst. The atomic Pd:Cu ratio between 2:1 and 4:1 appears to be optimal for high activity. The most active catalyst under the potentiodynamic conditions was Cu@Pd/C with θ(Cu) = 0.21,although Pd-Cu/C was superior during the potentiostatic test. All bimetallic catalysts surpassed Pd/C in mass activity. The EOR activity of Pt/C was higher compared to Pd-based catalysts at low potentials, both in terms of specific and mass activity, but with a significant decline over a 30-min potentiostatic stability test.
Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticl... more Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticles modified with a sub-monolayer of underpotentially deposited Cu (Cu@Pd/C) and Pd-Cu alloy nanoparticles (Pd-Cu/C), and examined for the ethanol oxidation reaction (EOR) in alkaline solution. The catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, as well as cyclic voltammetry. As reference catalysts, Pd/C and Pt/C were used. The electrochemically active surface area of all samples was determined from CO ads and Cu upd desorption and Pd oxide reduction, and used to assess their intrinsic activity for EOR. Intimate contact of Pd with Cu atoms enhanced its activity, regardless of the type of bimetal catalyst. The atomic Pd:Cu ratio between 2:1 and 4:1 appears to be optimal for high activity. The most active catalyst under the potentiodynamic conditions was Cu@Pd/C with θ(Cu) = 0.21,although Pd-Cu/C was superior during the potentiostatic test. All bimetallic catalysts surpassed Pd/C in mass activity. The EOR activity of Pt/C was higher compared to Pd-based catalysts at low potentials, both in terms of specific and mass activity, but with a significant decline over a 30-min potentiostatic stability test.
Metallic zirconium has a broad range of potential applications in engineering and in industries t... more Metallic zirconium has a broad range of potential applications in engineering and in industries that are operating under harsh corrosive environments, such as nuclear and chemical industry. Compared to other metals like aluminum, its behavior in electrochemical reactions is poorly understood and so far, there are no larger-scale electrochemical approaches to process zirconium. Ionic liquids are a suitable reaction medium for electrochemical reactions of zirconium. To better understand the electrochemical reactivity of zirconium, different combinations of ionic liquids and zirconium precursors are investigated. It was found that interactions between the Zr precursor and the ionic liquids can have significant influence on the diffusion properties of Zr. Furthermore, mixtures of ionic liquids with other solvents were explored and it could be determined that most of the electrochemical properties of Zr are retained also in solvent mixtures. This could potentially save costs for industri...
AbstractIn our previous paper, we described in detail studies of Sn influence on electrocatalytic... more AbstractIn our previous paper, we described in detail studies of Sn influence on electrocatalytic activity of PtSn catalyst for CO and formic acid oxidation (Stevanović et al., J. Phys. Chem. C, 118 (2014) 278–289). The catalyst was composed of a Pt phase, Pt3Sn alloy and very small SnO2 particles. Different electrochemical treatment enabled studies of PtSn/C having Sn both in surface and subsurface layers and skeleton structure of this catalyst with Sn only in subsurface layers. The results obtained revealed the promotional effect of surface Sn whether alloyed or as oxide above all in preventing accumulation of CO and blocking the surface Pt atoms. As a consequence, in formic acid oxidation, the currents are not entering the plateau but increasing constantly until reaching a maximum. It was concluded that at lower potentials the effect of Sn on formic acid oxidation was predominantly electronic but with increasing the potential bi-functional mechanism prevailed due to the leading role of SnO2. This role of SnO2 is restated in the present study. Therefore, CO and formic acid oxidation were examined at PtSnO2/C catalyst. The catalyst was synthesised by the same microwave-assisted polyol procedure. According to XRD analysis, the catalyst is composed of a Pt phase and SnO2 phase. The reactions were examined on PtSnO2/C catalyst treated on the same way as PtSn/C. Comparing the results obtained, the role of SnO2 is confirmed and at the same time the significance of alloyed Sn and its electronic effect is revealed. Graphical Abstract
Abstract Pd-Ni/C catalyst was synthesized employing a borohydride reduction method. The high area... more Abstract Pd-Ni/C catalyst was synthesized employing a borohydride reduction method. The high area Ni was first dispersed on the carbon support and then modified by Pd nanoparticles. Transmission electron microscopy confirmed relatively even distribution of Ni across the carbon support with discrete palladium particles of about 3.3 nm mean diameter on it. Cyclic voltammetry confirmed the presence of Ni on the catalyst surface. The activity of the Pd-Ni/C catalysts for ethanol oxidation reaction (EOR) in alkaline solution was tested under the potentiodynamic and potentiostatic conditions and the results were compared to those obtained on the Pd/C catalyst. It was found that Pd-Ni/C is more active for the EOR compared to Pd/C by a factor up to 3, depending on the type of experiments and whether specific activity or mass activity are considered. During the potentiodynamic stability test an interesting phenomenon of activation of Pd-Ni/C catalyst was observed. It was found that maximum activity is attained after fifty cycles with the positive potential limit of 1.2 V, regardless of whether they were performed in the electrolyte with or without ethanol. It was postulated that potential cycling of the Pd-Ni surface causes reorganization of the catalyst surface bringing Pd and Ni sites to a more suitable arrangement for the efficient ethanol oxidation.
The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B ... more The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B 13 C 2 alloy after thermal treatment at different temperatures from 298 K to 973 K (25 °C to 700 °C) was studied. The as-prepared alloy ribbon containing a small amount of crystalline phases, as well as domains of short-range crystalline ordering embedded in the amorphous matrix, exhibits unexpectedly high microhardness, mostly due to its composition. After thermal treatment above 723 K (450 °C), the alloy samples begin to crystallize, creating a nanocomposite structure involving nanocrystals embedded in an amorphous matrix, leading to an increase in microhardness. Further growth of the nanocrystals, as the heating temperature was increased to 973 K (700 °C), caused the change from nanocomposite structure into a more granulated and porous structure, with a dominant type of interface changing from amorphous/ crystal to crystal/crystal, leading to a decrease in microhardness.
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Papers by Aleksandra Gavrilovic-Wohlmuther