Recent Developments in Advanced Materials and Processes

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Authors: Obrad S. Aleksić, S.M. Savić, Mica D. Luković, K.T. Radulović, L.S. Lukić
Abstract: An investigation path starting from (Mn,Ni,Co,Fe)3O4 nanometric powder preparation, NTC thick-film characterization, realization and optimization of new planar thermistor geometries to custom design thermistors and their application for temperature and volume airflow sensors was recently determined. The aim was to make custom designed segmented NTC thermistors printed and sintered on alumina. Two types of volume airflow sensors were formed: indirectly heated and self-heated. A pair of segmented thermistors was placed in an air guide and connected to differential branches of the Wheatstone bridge. A heater was placed in the middle between the thermistors for the indirectly heated type, while for the self-heated type the same thermistors were self-heated by a constant current source. First the thermistor responses vs. the airflow (calibration curves) were measured, and then thermistor responses in time (inertia) to fast airflow changes from the minimum to the maxi
Authors: Lj.M. Vračar, N. Krstajić, N. Elezović
Abstract: The underpotential deposition of hydrogen was studied in 0.5 mol dm-3 HClO4 solution on an electrode based on Ebonex-supported platinum electrocatalyst spread on rotation Au disk electrode (Ebonex/Pt). Pt catalyst was prepared by the impregnation method from 2-propanol solution of Pt(NH3)2(NO2)2 and Ebonex powder. Ebonex support (nonstoichiometric mixture of titanium oxides) was characterized by: X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and BET techniques. The synthesized catalyst was analyzed by TEM technique. Voltammetric profiles at the Ebonex/Pt catalyst surface in 0.5 mol dm-3 HClO4 aqueous solution obtained at different temperatures with the evaluation of the temperature effect on the reversible adsorption of the Hupd state are presented and the thermodynamic state functions for H adatom adsorption process are calculated. The chemisorptive energy strength of the Ebonex/Pt-H state is estimated in order to establish the relationship between the surface structure and the electrocatalytic activity of Ebonex/Pt electrode and compare it to the one for smooth polycrystalline Pt.
Authors: J.D. Lović, S.Lj. Gojković, K.Dj. Popović, D.V. Tripković, A.V. Tripković
Abstract: Formic acid oxidation was studied at low-index Pt single crystals (model systems) as well as at the platinum catalyst supported on high area carbon (real catalyst) in HClO4. The Pt single crystals were characterized by LEED. The LEED patterns obtained after a mild heating of flame-annealed crystals have shown clean, well ordered unreconstructured surfaces. Pt-C supported catalyst was analyzed by AFM and STM in air and by XRD. AFM and STM images revealed the presence of Pt-C agglomerates of several tenth of nm consisting of Pt particles ranged from 2 nm to 6 nm. The electrocatalytic activity of these catalysts in formic acid oxidation increased in a sequence: Pt(100) < Pt(110) < Pt-C/GC < Pt(111).
Authors: S. Mentus, Ivan Krstić, Ž. Tešić, Amelia Montone
Abstract: Potentiodynamic polarization of a mechanically polished titanium electrode in a diluted solution of Rhodium(III) chloride in 0.1 M perchloric acid was performed, resulting in simultaneous formation of both Rh and TiO2 films. The morphology of obtained Rh/TiO2 composite film followed the morphology of titanium support, as evidenced by SEM technique. This composite surface was examined by cyclic voltammetry in both acidic and alkaline solutions, in the potential region of both hydrogen and oxygen underpotential deposition. The charge related to hydrogen underpotential deposition corresponded to a surface roughness of 43. As a consequence of high surface roughness, the diffusion current of oxygen reduction in an oxygen saturated 0.1 M NaOH solution, measured by voltammetry on rotating disc electrode, was found to be comparable to the current of hydrogen underpotential deposition.
Authors: A. Kowal, P. Olszewski, D.V. Tripković, R. Stevanović
Abstract: Electrodes, assigned as GC/Pt-C and GC/Pt-Ru-C, were formed by deposition of Ptbased catalysts (47.5 wt % Pt + high surface area carbon) and (54 wt. % Pt-Ru alloy + high surface area carbon) on glassy carbon (GC) discs. X-ray diffraction measurements were used for the determination of the average crystallite size and phase composition of both catalysts. Crystallite size for Pt-C catalyst was 2.9 nm for Pt-fcc. In the diffraction pattern of the Pt-Ru-C catalyst two phases, e.g. Pt-Ru-fcc and Ru-hcp were refined using the Rietveld method. Crystallite sizes were 3.9 nm for Pt-Ru-fcc and 2.8 nm for Ru-hcp. STM observations of the surface of GC/Pt-C and GC/Pt-Ru-C electrodes revealed the presence of metal particles of the size in the range 2-6 nm and Pt-C or Pt- Ru-C agglomerates in the range of several tenth of nm. The thickness of the Nafion covering layer determined by AFM is ca. 100 nm. A simplified scheme of the investigated electrodes was created.
Authors: M. Macherzynski, A. Kowal, B. Macherzynska, J. Gołas
Abstract: Glassy carbon (GC) discs and platinum microcylindrical electrodes were modified with a layer of nickel(II) tetrakis 3-methoxy-4 hydroxyphenyl porphyrin (poly-TMHPP-Ni) of different loadings (Γ) between 0.6 and 10 nmol/cm2, and subsequently with a Nafion layer. The topography and in some cases the thickness of films were measured by means of contact mode AFM. SEM and optical microscopy observations were used for the comparative studies on a larger scale. The useful range of the coverage with modifying polymer was investigated. The optimal value of loading for the sensor was found to be in the range of 6-8 nmole of poly-TMHPP-Ni per cm2. We observed the Nafion layer uniformity in nanometric scale.
Authors: B. Babić, Velimir Radmilović, N. Krstajić, B. Kaludjerović
Abstract: Mesoporous carbon cryogel synthesized by sol-gel polycondensation and freeze-drying with specific surface area (BET) of 517 m2 g-1 was used as a catalyst support. Pt/C catalysts were prepared by a modified ethylene glycol method (EG). Transmission electron microscopy (TEM) images show that the dispersion of the catalyst is very uniform with a mean particle size of about 2.65 nm. Hydrogen oxidation reaction (HOR) was studied on Pt/C catalyst in 0.5 mol dm-3 HClO4 acid solution. It has been found that HOR appears as a reversible two-electron direct discharged reaction (Tafel slope for this reaction is ≈30mV dec-1) and that Pt/C catalyst exhibits a very high catalytic activity. However, the corresponding value of the exchange current density obtained by dividing the exchange current by the active surface area of Pt particles has the same order of magnitude as those for the HOR in acidic solution at single crystal and polycrystalline Pt.
Authors: Lj.M. Gajić-Krstajić, T.Lj. Trišović, B. Babić, Lj.M. Vračar
Abstract: The kinetics of oxygen reduction (ORR) on carbon cryogel supported Pt nanoparticles (Pt / C) in acid solution was studied using the rotating disk electrode technique. This electrocatalyst was prepared by a modified polyol synthesis method and characterized by transmission electron microscopies. The kinetics of ORR shows a significant enhancement at Pt nanoparticle surfaces as compared with the same reaction on polycrystalline Pt surface. The four-electron reduction, with a first-charge transfer-rate determining step, has been found to be operative. However, the specific activity of the Pt / C is similar to that of the polycrystalline Pt electrocatalyst.
Authors: M. Stanković, P. Banković, B. Marković, Z. Vuković, D. Jovanović
Abstract: Silver promoted nickel catalysts supported on diatomite were prepared by precipitation method. Characterization of the catalysts prepared with different silver contents (0.1-4.0 wt%) included AAS, XRD, Hg porosimetry, BET and H2 chemisorption measurements. The catalytic activity and selectivity were tested by soybean oil (SBO) hydrogenation under pressure of hydrogen of 0.16 MPa at 160 °C. Fatty acids (FA) contained in hydrogenated SBO were analysed by gas chromatography. Trans fatty acid (TFA) content in hydrogenated SBO varied considerably depending of the silver content in prepared catalysts.
Authors: N. Potkonjak, Lj. Kolar-Anić, T. Potkonjak, S. Nikola Blagojević, S. Anić
Abstract: This work presents the current oscillation phenomena observed in an electrochemical Cu/0.5 M CF3COOH system. The dynamical response of this new oscillator was followed by both current density-potential (j-E) and current density-time (j-t) curves. The current oscillation phenomena of the investigated system were monitored over various potential scan rates and constant applied potentials as control parameters. The increase of potential scan rate significantly decreases both the potential range of current oscillations and the frequency of oscillations. At the j-t curves both the simple and the complex (period adding) oscillations were found. Moreover, with the increase of applied potential, the increase of period of oscillations and current oscillation amplitudes were observed. It appears that the period of current oscillations exponentially grows with applied potential.

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