• Applied Catalysis B Environmental 09/2014; s 156–157:301–306. · 5.83 Impact Factor
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    ABSTRACT: A nickel–copper alloy is prepared by using the oxalate method and subsequent in situ reduction. The bimetallic alloy is mixed with gadolinium-doped ceria (CGO) to obtain a composite material with mixed electronic–ionic conductivity. The catalytic and electrocatalytic properties of the composite material for ethanol conversion are described. Different conditions to simulate bio-ethanol feed operation are selected. Electrochemical tests are performed by utilizing the NiCu/CGO cermet as a barrier layer in a conventional anode-supported solid-oxide fuel cell (AS-SOFC). A comparative study between the modified cell and a conventional AS-SOFC without the protective layer is made. A maximum power density of 277 mW cm−2@0.63 V is recorded in the presence of a mixture of ethanol–water for a cell containing the protective anodic layer compared with 231 mW cm−2@0.64 V for a bare cell under the same conditions. This corresponds to a 20 % increase in performance.
    ChemElectroChem. 05/2014;
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    ABSTRACT: This work provides insights into the processes involved in the borohydride oxidation reaction (BOR) in alkaline media on metal hydride alloys formed by LaNi4.7 Sn0.2 Cu0.1 and LaNi4.78 Al0.22 with and without deposited Pt, Pd, and Au. The results confirm the occurrence of hydrolysis of the borohydride ions when the materials are exposed to BH4 (-) and a continuous hydriding of the alloys during BH4 (-) oxidation measurements at low current densities. The activity for the direct BOR is low in both bare metal hydride alloys, but the rate of the BH4 (-) hydrolysis and the hydrogen-storage capacity are higher, while the rate of H diffusion is slower for bare LaNi4.78 Al0.22 . The addition of Pt and Pd to both alloys results in an increase of the BH4 (-) hydrolysis, but the H2 formed is rapidly oxidized at the Pt-modified catalysts. In the case of Au modification, a small increase in the BH4 (-) hydrolysis is observed as compared to the bare alloys. The presence of Au and Pd also leads to a reduction of the rates of alloy hydriding/de-hydriding.
    ChemPhysChem 04/2014; · 3.35 Impact Factor
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    Amanda Cristina Garcia, Edson A. Ticianelli
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    ABSTRACT: he activity of Pt catalysts dispersed on tungsten carbide (WC) prepared with a high surface area carbon with two different WC/C ratios is investigated for the oxygen reduction reaction (ORR) in alkaline electrolyte. The electrochemical methods employed are cyclic voltammetry (CV) and steady-state polarization carried out on an ultrathin catalyst layer deposited on the disk of a rotating ring-disk electrode. The PtWC-based catalysts show higher activity for the ORR compared to Pt/C, also involving a transfer of 4 electrons per oxygen molecule. CV and X-ray absorption near edge structure spectroscopy (XANES) results for the PtWC-based materials indicate weaker Pt–OHx interaction in these materials, resulting in a lower Pt-oxide coverage and explaining the increased rate of the ORR, as compared to Pt/C.
    09/2013; 106(1):453-459.
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    Waldemir J. Paschoalino, Edson A. Ticianelli
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    ABSTRACT: In this study, LaNi4.7Sn0.2Cu0.1 metal hydride alloys, with and without surface deposits of Pt, are investigated as electrocatalysts for the borohydride oxidation reaction (BOR) in alkaline media. Results obtained for LaNi4.78Al0.22 and LaNi4.78Mn0.22 are used for comparison. It is observed that wet exposition to hydrogen or sodium borohydride lead to some hydriding of the metal hydride alloy particles, particularly that with a coating of Pt. In the presence of borohydride ions, the hydrided charged alloys present more negative potentials for the (boro)hydride oxidation process, and these enhancements are significantly larger for the Pt-coated material. In the potential range of interest, the results demonstrate considerable activity for the BOR, but just for the alloy with Pt. In the presence of borohydride ions in the solution there is a continuous hydriding the alloy during the discharge of the metal hydride electrode. Differential electrochemical mass spectrometry (DEMS) measurements showed that there is formation of H2, either by hydrolysis or by partial oxidation of the borohydride ions, but in the absence of Pt the hydrolysis process is quite slow.
    International Journal of Hydrogen Energy 06/2013; 38(18):7344–7352. · 3.55 Impact Factor
  • F.R. Nikkuni, S.F. Santos, E.A. Ticianelli
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    ABSTRACT: SUMMARY Magnesium – nickel alloys have been considered an alternative for AB5 and AB2-type alloys in nickel–metal hydride batteries due to their larger maximum discharge capacities, but their low stability in alkaline solution has hindered their use in commercial cells. Aiming to improve the electrode performance of the Mg55Ni45 alloy, we investigated the simultaneous addition of Ti and a noble metal (Pd and Pt) as alloying elements. The investigated system has general composition Mg49Ti6Ni(45-x)Mx, where M is Pd or Pt, and x assumed values of 0, 2.0 and 4.0 at.%. The electrochemical measurements showed that the Mg49Ti6Ni41Pd4 alloy has the best electrode performance among the studied alloys, reaching 431 mA h g−1 of maximum discharge capacity at the first cycle of charge/discharge. After 10 and 20 cycles, this alloy presented relative discharge capacities of 84 and 77% of the initial one, respectively. The electrode performance of the investigated alloys is discussed in light of results of structural characterization by transmission electron microscopy and X-ray diffraction. Copyright © 2013 John Wiley & Sons, Ltd.
    International Journal of Energy Research 06/2013; 37(7). · 2.74 Impact Factor
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    ABSTRACT: The ammonia borane (NH3BH3) oxidation reaction (ABOR) was studied on gold electrodes using the rotating disk electrode (RDE) setup and coupled physical techniques: on-line differential electrochemical mass spectrometry (DEMS) and in situ Fourier Transform Infrared spectroscopy (FTIR). Non-negligible heterogeneous hydrolysis in the low-potential region was asserted via molecular H2 detection. As a consequence, the number of electron exchanged per BH3OH- species is ca. 3 at low potential, and only reaches ca. 6 above 0.6 V vs. RHE. These figures were confirmed by Levich and Koutecki-Levich calculations using the RDE experiments data. The nature of the ABOR intermediates and products was determined using in situ FTIR. While BH2 species were detected during the ABOR, it seems that its adsorption onto the Au electrode proceeds via the O atom, in opposition to what happens during the borohydride oxidation reaction (BOR). Therefore, it is likely that the mechanism of the ABOR differs from that of the BOR. From the whole set of data (RDE, DEMS, FTIR), a relevant reaction pathway was proposed, including competition between the BH3OH- heterogeneous hydrolysis and oxidation at low potential, and preponderant oxidation at higher potential. Finally, a simplified kinetic modeling accounting with this reaction pathway was proposed, which nicely fit the stationary (i vs. E) ABOR plot.
    Electrochimica Acta. 01/2013; 89:607-615.
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    ABSTRACT: The electrocatalytic activity for the oxygen reduction reaction of nickel-doped MnOx nanoparticles, dispersed onto different carbon powders (M1000, MM225 and E350) is studied in alkaline media in the presence of borohydride ions. Differential electrochemical mass spectrometry (DEMS) is used to quantify the H2 yields coming from the borohydride hydrolysis as a function of the electrode potential. The polarization results show that materials containing Ni segregate phases present significant Faradaic currents for the borohydride oxidation, while the on-line DEMS results clearly evidence the production of H2. For these electrocatalysts, the presence of BH4− induces a decrease of the overall ORR activity, and this is assigned, into a large extent, to a superposition of the ORR reduction currents with the currents related to the direct borohydride oxidation. This effect is far more pronounced for the electrocatalyst dispersed onto the E350 carbon. On the contrary, materials dispersed onto M1000 carbon and without Ni segregated phases seem tolerant to the presence of BH4− ions. Therefore, these materials may be an alternative to be used as cathode electrocatalysts of direct borohydride fuel cells.
    Journal of Power Sources 01/2013; 222:305-312. · 5.26 Impact Factor
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    ABSTRACT: A number of fuel cell relevant reactions are known to undergo kinetic instabilities under certain conditions. The majority of the experiments in such systems have been performed in liquid electrolyte systems on half-cell setups. Results for proton exchange membrane fuel cells fed with H2/CO mixtures at the anode show that there can be a range of gas flow rate and current density where spontaneous potential oscillations take place. Despite the recent developments in this area, there are still many mechanistic aspects underlying the emergence of electrochemical oscillations that remain unknown. In the present contribution, we report results on the CO2 production during the oxidation of carbon monoxide-containing hydrogen in a proton exchange membrane fuel cell, as measured by online mass spectrometry. By extensive fitting and careful consideration of the proposed mechanism, we were able to estimate the coverage of hydrogen and CO during the oscillations. As no other approach seems capable to probe the adsorbate coverage in an operando fuel cell, our analyses access experimental hidden information that can be of high value for fuel cell research.
    Journal of Solid State Electrochemistry 01/2013; 17(7). · 2.28 Impact Factor
  • Ernesto R. Gonzalez, Edson A. Ticianelli, Ermete Antolini
    ChemInform 06/2012; 43(23).
  • J. Souza-Garcia, E. A. Ticianelli, V. Climent, J. M. Feliu
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    ABSTRACT: Reduction of nitrate on palladium-modified platinum single-crystal electrodes has been investigated both voltammetrically and spectroscopically in acidic media (pH = 1). Results obtained in H2O and D2O solvents are compared for the three crystallographic orientations. FTIR and differential electrochemical mass spectrometry (DEMS) results clearly indicate that the isotopic substitution of the solvent has a large effect in the mechanism of the reaction, changing the nature of the detected products. For Pt(111)/Pd and Pt(100)/Pd, N2O is detected as the main product of nitrate reduction when D2O is used as solvent, while no N2O is detected when the reaction is performed in H2O. For Pt(110)/Pd, N2O is detected in both solvents, although the use of D2O clearly favours the preferential formation of this product. The magnitude of voltammetric currents is also affected by the nature of the solvent. This has been analysed considering, in addition to the different product distribution, the existence of different transport numbers and optical constants of the solvent.
    Chemical Science 01/2012; · 8.31 Impact Factor
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    ABSTRACT: The lack of a highly efficient electrocatalyst for the borohydride oxidation reaction has been a major factor limiting the performance of direct borohydride fuel cells (DBFC). In considering this issue, this work presents recent advances in the knowledge of the BOR pathways on polycrystalline (bulk) Au and Pt electrocatalysts. It presents the studies of the BOR reaction on Au and Pt electrodes using in situ Fourier transform infrared spectroscopy (FTIR), and on-line Differential Electrochemical Mass Spectrometry (DEMS). The spectroscopic and spectrometric data provided physical evidence of intermediate species and the formation of H2 in the course of the BOR as a function of the electrode potential. These results enabled to advance in the knowledge about the BOR pathways on Au and Pt electrocatalysts.
    Electrochimica Acta. 01/2012; 84:202-212.
  • Ernesto R. González, Edson A. Ticianelli, Ermete Antolini
    10/2011: pages 453 - 485; , ISBN: 9780470929421
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    ABSTRACT: Palladium deposition on Pt(1 1 0) electrodes was studied. Differently from Pt(1 1 1) and Pt(1 0 0), first and further layers cannot be distinguished in this case only through the voltammetric behavior of hydrogen and anion adsorption. The potential of zero total charge (pztc) was determined as a function of the amount of deposited Pd using CO charge displacement experiments and voltammetric curves. The variation of the voltammetric charge due to hydrogen and anion adsorption has been followed during Pd deposition. The voltammetric charge between 0.06 and 0.4 V first decreases to a minimum, then increases and finally becomes stable, suggesting that the surface is finally covered with a Pd multilayer. The pztc and CO oxidation charge show similar behavior. CO oxidation, NO reduction and Cu UPD were used as probes to monitor Pd coverage. The potential of CO oxidation increases with Pd coverage while the potential of NO reduction decreases. Using the information obtained from Cu UDP and FTIR experiments it
    Journal of electroanalytical chemistry 09/2011; 660(2):276-284. · 2.67 Impact Factor
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    ABSTRACT: Physical and electrochemical properties of nanostructured Ni-doped manganese oxides (MnOx) catalysts supported on different carbon powder substrates were investigated so as to characterize any carbon substrate effect toward the oxygen reduction reaction (ORR) kinetics in alkaline medium. These NiMnOx/C materials were characterized using physicochemical analyses. Small insertion of Ni atoms in the MnOx lattice was observed, which consists of a true doping of the manganese oxide phase. The corresponding NiMnOx phase is present in the form of needles or agglomerates, with crystallite sizes in the order of 1.5–6.7 nm (from x-ray diffraction analyses). Layered manganite (MnOOH) phase has been detected for the Monarch1000-supported NiMnOx material, while different species of MnOx phases are present at the E350G and MM225 carbons. Electrochemical studies in thin porous coating active layers in the rotating ring-disk electrode setup revealed that the MnOx catalysts present better ORR kinetics and electrochemical stability upon Ni doping. The ORR follows the so-called peroxide mechanism on MnOx/C catalysts, with the occurrence of minority HO<sub>2</sub><sup>-</sup> disproportionation reaction. The HO<sub>2</sub><sup>-</sup> disproportionation reaction progressively increases with the Ni content in NiMnOx materials. The catalysts supported on the MM225 and E350G carbons promote faster disproportionation reaction, thus leading to an overall four-electron ORR pathway.
    Journal of The Electrochemical Society 01/2011; 158(3):B290-B296. · 2.59 Impact Factor
  • Pietro P. Lopes, Edson A. Ticianelli, Hamilton Varela
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    ABSTRACT: We report in this paper the occurrence of potential oscillations in a proton exchange membrane fuel cell (PEMFC) with a Pd–Pt/C anode, fed with H2/100 ppm CO, and operated at 30 °C. We demonstrate that the use of Pd–Pt/C anode enables the emergence of dynamic instabilities in a PEMFC. Oscillations are characterized by the presence of very high oscillation amplitude, ca. 0.8 V, which is almost twice that observed in a PEMFC with a Pt–Ru/C anode under similar conditions. The effects of the H2/CO flow rate and cell current density on the oscillatory dynamics were investigated and the mechanism rationalized in terms of the CO oxidation and adsorption processes. We also discuss the fundamental aspects concerning the operation of a PEMFC under oscillatory regime in terms of the benefit resulting from the higher average power output.
    Journal of Power Sources. 01/2011;
  • Eduardo G. Ciapina, Edson A. Ticianelli
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    ABSTRACT: This paper describes a modification of the surface properties of a carbon-supported Pt3Co catalyst resulting from an electrochemical cycling treatment in a 0.1M HClO4 and in a CO-saturated 0.1M HClO4 solution (electrochemical CO-annealing). The procedure generated a Pt-rich surface with electrochemical properties different from that presented by the as-received (untreated) sample. This was evidenced by a shift in the CO stripping peak to more positive potentials in the CO stripping voltammetry, and by an increased charge of Hupd region and a modification of the oxide reduction peak observed in the base cyclic voltammogram. In situ X-ray absorption spectroscopy experiments conducted in the dispersive mode revealed differences in the electronic 5d band occupancy after the CO annealing, whereas the behavior of the intensity of the white-line as function of the potential for this material approached that found for pure Pt/C nanoparticles, in contrast to the small potential dependence profile exhibited by the as-received Pt3Co nanoparticles. Mass activities towards the oxygen reduction reaction measured by rotating disk experiments carried out at 1600rpm in a O2-saturated solution at 25°C increased from 0.10A/mg of Pt to 0.19A/mg of Pt, evidencing the higher Pt utilization in the CO-annealed Pt3Co/C electrocatalyst. The origin of the different electrochemical behavior is discussed.
    Electrochimica Acta - ELECTROCHIM ACTA. 01/2011;
  • 01/2011: pages 103-135;
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    ABSTRACT: The borohydride oxidation reaction (BOR) was studied on Pt and Au electrodes by cyclic voltammetry in dilute alkaline borohydride solutions (0.1 M NaOH + 10-3 mol L-1 NaBH4). More specifically, the electrodes were considered as either Vulcan XC72-supported Pt or Au (noted as Pt/C and Au/C, respectively) active layers or smooth Pt or Au surfaces, the latter possibly being covered by a layer of (non-metalized) Vulcan XC72 carbon powder. The BOR onset potential and the number of electrons (ne-) exchanged per BH4- anion (faradaic efficiency) were investigated for these electrodes, to determine whether the residence time of reaction intermediates (at the electrode surface or inside the porous layer) does influence the overall reaction pathway/completion. For the carbon-supported platinum, ne- strongly depends on the thickness of the active layer. While thin (ca. 0.5 [mu]m-thick) Pt/C active layers yield ne- < 4, thick layers (approximately 3 [mu]m) yield ne- [approximate] 8, which can be ascribed to the sufficient residence time of the molecules formed within the active layer (H2, by heterogeneous hydrolysis, or BOR intermediates) enabling further (near-complete) oxidation. This puts into evidence that not only the nature of the electrocatalyst is important to reach high BOR efficiency, but also the structure/thickness of the active layer. The same trend applies for Au/C active layers and for smooth Pt or Au surfaces covered with a layer of (inactive) Vulcan XC72. In addition, the BOR onset usually shifts negative when the reaction intermediates are trapped, which suggests that some of the intermediates are more easily oxidized than BH4- itself; based on literature data, BH3OH- species is a likely candidate.
    Catalysis Today 01/2011; 170(1):110-119. · 3.31 Impact Factor
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    ABSTRACT: Early reports stated that Au was a catalyst of choice for the BOR because it would yield a near complete faradaic efficiency. However, it has recently been suggested that gold could yield to some extent the heterogeneous hydrolysis of BH, therefore lowering the electron count per BH, especially at low potential. Actually, the blur will exist regarding the BOR mechanism on Au as long as no physical proof regarding the reaction intermediates is not put forward. In that frame, in situ physical techniques like FTIR exhibit some interest to study the BOR. Consequently, in situ infrared reflectance spectroscopy measurements (SPAIRS technique) have been performed in 1 M NaOH/1 M NaBH(4) on a gold electrode with the aim to detect the intermediate species. We monitored several bands in B-H (nu ∼ 1180, 1080 and 972 cm(-1)) and B-O bond regions (nu = 1325 and ∼1425 cm(-1)), which appear sequentially as a function of the electrode polarization. These absorption bands are assigned to BH(3), BH(2) and BO species. At the light of the experimental results, possible initial elementary steps of the BOR on gold electrode have been proposed and discussed according to the relevant literature data.
    Physical Chemistry Chemical Physics 10/2010; 12(37):11507-16. · 4.20 Impact Factor

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