Publications

  • Applied Catalysis B Environmental 09/2014; s 156–157:301–306. · 6.01 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; · 3.36 Impact Factor
  • 224th ECS Meeting; 10/2013
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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.
    Electrochimica Acta 09/2013; 106(1):453-459. · 4.09 Impact Factor
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    ABSTRACT: In the present paper we investigated the effect of adsorbed PVA on Pt electrodes on classic electrochemical processes such as hydrogen UPD, oxygen reduction and CO electro-oxidation. Upon adsorption PVA blocks roughly 50% of the hydrogen sites and can not be removed from the Pt surface through cycling in the potential range of 0.05–1.0 V vs. RHE. Potentiodynamic experiments under controlled hydrodynamic conditions provided by rotating disk electrode experiments showed a negative impact of the adsorbed PVA on the oxygen reduction reaction (ORR). Cyclic-voltammetry results revealed that not even CO was able to remove PVA from the Pt surface. Regarding the oxidation of CO, the adsorbed polymer positively shifted the CO oxidation peak potential, therefore higher potentials are required to free the Pt surface from CO poisoning. In situ Fourier transform infrared spectroscopy evidenced that the presence of PVA shifted the linearly bound CO frequency toward higher wavenumbers, a process found to be independent of the Pt surface orientation. In situ electrochemical X-ray absorption spectroscopy results showed that PVA also impacted the electronic properties of platinum by decreasing the occupancy of the Pt conducting 5d band. Our findings clearly support the efforts toward understanding the nature of the interaction between polymers and metallic surfaces as well as the impact on technological applications (e.g. in PEMFCs).
    Electrochimica Acta 08/2013; 104:358–366. · 4.09 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 07/2013; 17(7). · 2.23 Impact Factor
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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. · 2.93 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
  • 223th ECS Meeting; 05/2013
  • 223th ECS Meeting; 05/2013
  • Sydney F. Santos, José Fernando R. de Castro, Edson Antonio Ticianelli
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    ABSTRACT: Magnesium and several of its alloys can absorb large amounts of hydrogen. This feature is desirable for several technological applications such as solid state hydrogen storage tanks and anodes of nickel-metal hydride (Ni-MH) batteries. For the latter, Mg-Ni alloys are considered very promising due to their high discharge capacities. Conversely, the low stability of Mg-Ni alloys in alkaline electrolytes have hindered their practical use. In the present manuscript, the effects of palladium black addition on the structure and electrochemical properties of the Mg50Ni50 (in at.%) alloy were investigated. The studied ternary alloys have general composition of Mg50Ni(50-x)Pdx, with 0 ≤ x ≤ 5 (in at.%). These alloys were synthesized by mechanical alloying from pure elements. The alloy powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) while their electrode performances were evaluated by galvanostatic cycles of charge and discharge. The investigated alloys have multi-phase structures composed of amorphous and nanocrystalline phases, with nano-grain sizes of nearly 5 nm. Concerning the electrode performance, the best results were attained by the Mg50Ni47.5Pd2.5 alloy, which kept a high discharge capacity and improved the cycling stability.
    Central European Journal of Chemistry 04/2013; 11(4). · 1.33 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 02/2013; 89:607-615. · 4.09 Impact Factor
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    ABSTRACT: A non-noble oxygen reduction catalyst based on nickel−manganese oxide supported on high-surface area carbon has been synthesized by a mild hydrothermal treatment, resulting in nanocrystalline needles. Cyclic voltammetry showed the electrochemical redox characteristics of this material, evidencing the appearance of peaks associated to consecutive reversible transitions involving Mn(IV)/Mn(III) and Mn(III)/Mn(II). The catalyst displayed a high activity for the oxygen reduction, despite that the complete reduction was not achieved, consuming less than three electrons of the four available in the oxygen molecule. More importantly, this activity did not decay under the presence of ethanol, revealing the high ethanol tolerance of this material. Finally, single-cell results have demonstrated the suitability of this material as cathode catalysts for alkaline DEFC: The open circuit voltage and the maximum power densities are close to those obtained by a standard Pt/C catalyst.
    Electrocatalysis. 01/2013; 5(1):41-49.
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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. · 5.21 Impact Factor
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    ABSTRACT: The performance of proton exchange membrane fuel cells (PEMFC) with Pt/C and PtMo/C anodes has been investigated using single cell polarization and on line mass spectrometry (OLMS) measurements in a wide range of temperature (70–105 °C) for the system supplied with hydrogen containing different amounts of CO. As expected a higher CO tolerance is observed at higher temperatures for both catalysts. The anode exit gas analysis revealed that CO2 is produced already at the cell open circuit potential, and it increases with the increase of the anode overpotential. The CO tolerance phenomena are assigned to different processes depending on the catalyst nature. For the Pt/C containing anodes, at temperatures above 80 °C, thermal desorption, reduced CO oxidation potential and CO oxidation by O2 crossover are responsible for enhanced tolerance, whilst PtMo/C shows greater tolerance due the occurrence of a MoOx-mediated water gas shift reaction (WGS), which is activated at high temperatures. Although the occurrence of WGS leads to the anode poisoning in the presence of CO2, the polarization results show that only small additive contamination effect occurs by the combined presence of CO + CO2 in the hydrogen stream.
    Electrochimica Acta 01/2013; 88:217–224. · 4.09 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 12/2012; 84:202-212. · 4.09 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; · 8.60 Impact Factor
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    ABSTRACT: In this paper we report the electrosynthesis of PVA-protected PtCo films (PVA = poly(vinylalcohol)) and their activities towards the oxygen reduction reaction (ORR). PtCo electrodeposits were potentiostatically obtained in the presence and absence of PVA at distinct potentials. The film morphology and composition were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), which revealed that the use of PVA in the electrodeposition of PtCo films was decisive to achieve better film composition control. Cyclic voltammetry for PVA-protected PtCo films showed that the electrochemical surface area is dependent on the electrodeposition potentials and suggested different adsorption strengths of oxygen-containing species. Films produced in the presence of PVA presented the following activity order towards ORR as a function of the electrodeposition potential (vs. Ag/AgCl): −0.9 V > −0.8 V > −1.0 V > −0.7 V. In contrast, PtCo films electrodeposited in the absence of PVA displayed very similar activities regardless of the electrodeposition potential. The simplicity of the electrodeposition method combined with its effectiveness enabled the production of “model electrodes” for investigating the fundamental aspects of the reactions taking place in the fuel cell cathodes.
    Journal of Power Sources 01/2012; 197:97–101. · 5.21 Impact Factor

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