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Papers by marta Figueiredo
Journal of the American Chemical Society, Jun 27, 2011
Electrochemistry Communications, 2009
This work presents the effect of Bi modification of Pt(1 1 1) electrodes on the electroreduction ... more This work presents the effect of Bi modification of Pt(1 1 1) electrodes on the electroreduction of nitrate anions by using voltammetric and FTIR experiments. On Pt(1 1 1) nitrate consumption occurs at potentials lower than 0.35 V, but with Pt(1 1 1)/Bi this process is shifted to significantly higher potentials (0.6-0.7 V). In the latter surface N 2 O was observed as the main product in solution. Different forms of adsorbed NO were detected on the adatom covered surfaces as well as on clean Pt(1 1 1).
I would like to acknowledge to all that contributed for the successful ending of this thesis:
Applied Catalysis B Environmental, 2014
ALD is solvent-free, controlled method suitable for preparing bimetallic particles.Metal location... more ALD is solvent-free, controlled method suitable for preparing bimetallic particles.Metal location and particle size effecting catalyst activity was modified by ALD.Synthetized nanoparticles have well defined surface structure.The catalysts show enhanced activity for important fuel cell reactions MOR and ORR.Catalyst durability in MOR is adjusted by suitable catalyst preparation parameters.Atomic layer deposition (ALD) is a thin layer synthesis method applied in this study for preparing carbon-supported mono-metallic Pt- and bi-metallic PtCo catalysts. The catalyst characterization confirmed that small metal particles with a narrow particle size distribution and high metal dispersion were obtained. The location of the metals on the surface was controlled by alternating the ALD cycles, and the formation of bi-metallic PtCo particles on the support was observed. The prepared catalysts proved to be active for methanol oxidation and oxygen reduction in an acidic media. In addition, the durability of the catalysts in electrochemical oxidation was enhanced by varying the metal cycle order in the catalyst preparation. After the deposition of Co on the catalyst, one ALD cycle of Pt favored the catalyst durability in the methanol oxidation reaction.
Journal of Catalysis, 2014
Recent developments on anion-exchange membranes for fuel cell application renewed the interest in... more Recent developments on anion-exchange membranes for fuel cell application renewed the interest in the study of alcohol oxidation at high pHs for applications in anion-exchange membrane direct alcohol fuel cells (AEM-DAFC). Although platinum is still the most studied catalyst for oxidation of alcohols in alkaline media, the introduction of one or more metals in order to increase the oxophilicity of the catalyst is a common approach in the development of improved materials for these reactions. In this manuscript, we report the enhancement of the catalytic activity of Pt/C toward ethanol, methanol, and propanol oxidation in alkaline media by simple adsorption of Bi surface. The activity was checked by cyclic voltammetry, and the reaction products and intermediates were analyzed by ''in situ'' infrared spectroscopy. The presence of Bi was shown to increase the activity of Pt toward the oxidation of the referred alcohols by acting as a third body (impeding surface poisoning) and also by an electronic effect (on water adsorption at the surface).
Journal of Catalysis, 2015
ABSTRACT In this work, PtRu/C–Sb materials prepared by adding a Sb salt to the ink of commercial ... more ABSTRACT In this work, PtRu/C–Sb materials prepared by adding a Sb salt to the ink of commercial PtRu/C were studied as catalysts for ethanol oxidation. The prepared trimetallic catalysts showed enhanced properties for ethanol oxidation through a wide range of surface coverages. However, coverage higher than 0.7 of Sb on PtRu/C causes the decrease of the catalytic activity suggesting that specific sites composed of 3 metals are necessary to achieve the highest performance. In situ Fourier Transform Infrared Spectroscopy experiments were also performed to compare the reaction products of the bimetallic and trimetallic catalysts. The catalysts were also tested under fuel cell conditions. Also in this case, higher power densities, higher open-circuit voltages and better stability than the bimetallic substrate were found. With this catalyst preparation method, the catalysts showed 2 times higher current densities than for the PtRu catalysts and 6 times better than for pure Pt anodes.
Electrochemistry Communications, 2015
The demand for power sources alternative to fossil fuels makes urgent the development of more eff... more The demand for power sources alternative to fossil fuels makes urgent the development of more efficient electrocatalysts for fuel cells applications and the maximization of the performances of the existent ones. This work reports, for the first time, the use of carbon-supported shape-controlled Pt nanoparticles as anode catalysts in direct ethanol fuel cells. By using cubic Pt nanoparticles, on which (100) surface sites are predominant, the performance of the fuel cell can be increased from 14 to 24 mW per mg of Pt when compared with cuboctahedral nanoparticles. Moreover, the open circuit potential shifts about 50 mV toward more positive potentials. In comparison with commercially available Pt catalysts, the performance for the (100) preferentially oriented nanoparticles is about three times higher. The reported results evidence that, from an applied point of view, the effect of the surface structure/shape of the electrocatalysts can be also considered to improve the performance of real fuel cell systems.
Electrochimica Acta, 2015
Electrocatalysis, 2011
In this paper, the electrocatalytic enhancement of the Pt(111) surface modified with Bi adatoms t... more In this paper, the electrocatalytic enhancement of the Pt(111) surface modified with Bi adatoms towards nitrite reduction and the quantification of the catalytic effect of different adatom coverages are reported. The results were obtained in acidic and neutral media using cyclic voltammetry and in situ infrared spectroscopy measurements and show that the presence of irreversible adsorbed bismuth on Pt(111) electrodes catalyzes nitrite reduction. The presence of the foreign adatom shifts nitrite reduction to potentials as high as 0.80-0.60 V vs RHE, coinciding with the potential at which Bi undergoes its redox surface reaction. Different coverages of Bi on the surface were prepared, revealing that the activity increases with the amount of Bi until its coverage approaches half the saturation of the maximum surface blockage. For higher coverages, the activity decreases steeply, resulting in a volcano-like curve. The spectroelectrochemical experiments show that the main product of nitrite reduction at these high potentials is N 2 O.
The Journal of Physical Chemistry C, 2014
Langmuir, 2012
The first part of this report studies the electrochemical properties of single-crystal platinum e... more The first part of this report studies the electrochemical properties of single-crystal platinum electrodes in acetonitrile electrolytes by means of cyclic voltammetry. Potential difference infrared spectroscopy in conjunction with linear voltammetry was used to obtain a molecular-level picture of this interface. The second part of this report studies the hydrogen evolution and the hydrogen oxidation reactions on the three low-index faces of Pt electrodes in acetonitrile electrolytes. The data (CVs and IR spectra) strongly suggest that acetonitrile and CN(-) molecules are adsorbed on single-crystal platinum electrodes in the range of -1.5 to 0.3 V versus Ag/AgCl. Those species block part of the adsorption sites for hydrogen adatoms, and they decompose on the surface in the presence of water. The nature of the cation and the presence of water strongly affect the onset of acetonitrile electrolysis and the kinetics and stability of the adsorbed species on the electrode. Finally, the hydrogen evolution and the hydrogen oxidation reactions on platinum single-crystal surfaces in acetonitrile electrolytes are strongly affected by the surface-energy state of Pt electrodes.
Journal of the American Chemical Society, 2011
![Research paper thumbnail of The electrical double layer at the [BMIM][PF6] ionic liquid/electrode interface – Effect of temperature on the differential capacitance](https://attachments.academia-assets.com/48883676/thumbnails/1.jpg)
](Journal of Electroanalytical Chemistry, 2008
Impedance spectra (50 kHz-1 Hz) were acquired and used to obtain the differential capacitance at ... more Impedance spectra (50 kHz-1 Hz) were acquired and used to obtain the differential capacitance at the interfaces between 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6] ionic liquid and three different electrode materials (Hg, Pt, and glassy carbon (GC)) as a function of the applied potential. The electrocapillary curve for the Hg/[BMIM][PF6] interface was obtained from drop time measurements, from which the potential of zero charge was calculated to be À0.39 V (Ag wire). The potential of zero charge is 0.30 V less negative than the potential of differential capacitance minimum. This disagreement suggests that the differential capacitance minimum is not related to a classical diffuse layer minimum. Additional support to this conclusion was obtained from positive temperature coefficient for the differential capacitance in contrast to the negative temperature predicted by the classic Gouy-Chapman model. The results do not support the recent model predictions of bell shaped capacitance curves for room temperature ionic liquids, RTILs.
Journal of Catalysis, 2014
Recent developments on anion-exchange membranes for fuel cell application renewed the interest in... more Recent developments on anion-exchange membranes for fuel cell application renewed the interest in the study of alcohol oxidation at high pHs for applications in anion-exchange membrane direct alcohol fuel cells (AEM-DAFC). Although platinum is still the most studied catalyst for oxidation of alcohols in alkaline media, the introduction of one or more metals in order to increase the oxophilicity of the catalyst is a common approach in the development of improved materials for these reactions. In this manuscript, we report the enhancement of the catalytic activity of Pt/C toward ethanol, methanol, and propanol oxidation in alkaline media by simple adsorption of Bi surface. The activity was checked by cyclic voltammetry, and the reaction products and intermediates were analyzed by ''in situ'' infrared spectroscopy. The presence of Bi was shown to increase the activity of Pt toward the oxidation of the referred alcohols by acting as a third body (impeding surface poisoning) and also by an electronic effect (on water adsorption at the surface).
Journal of Catalysis, 2014
Recent developments on anion-exchange membranes for fuel cell application renewed the interest in... more Recent developments on anion-exchange membranes for fuel cell application renewed the interest in the study of alcohol oxidation at high pHs for applications in anion-exchange membrane direct alcohol fuel cells (AEM-DAFC). Although platinum is still the most studied catalyst for oxidation of alcohols in alkaline media, the introduction of one or more metals in order to increase the oxophilicity of the catalyst is a common approach in the development of improved materials for these reactions. In this manuscript, we report the enhancement of the catalytic activity of Pt/C toward ethanol, methanol, and propanol oxidation in alkaline media by simple adsorption of Bi surface. The activity was checked by cyclic voltammetry, and the reaction products and intermediates were analyzed by ''in situ'' infrared spectroscopy. The presence of Bi was shown to increase the activity of Pt toward the oxidation of the referred alcohols by acting as a third body (impeding surface poisoning) and also by an electronic effect (on water adsorption at the surface).
Zeitschrift für Physikalische Chemie, 2012
Electrochimica Acta, 2013
Journal of the American Chemical Society, Jun 27, 2011
Electrochemistry Communications, 2009
This work presents the effect of Bi modification of Pt(1 1 1) electrodes on the electroreduction ... more This work presents the effect of Bi modification of Pt(1 1 1) electrodes on the electroreduction of nitrate anions by using voltammetric and FTIR experiments. On Pt(1 1 1) nitrate consumption occurs at potentials lower than 0.35 V, but with Pt(1 1 1)/Bi this process is shifted to significantly higher potentials (0.6-0.7 V). In the latter surface N 2 O was observed as the main product in solution. Different forms of adsorbed NO were detected on the adatom covered surfaces as well as on clean Pt(1 1 1).
I would like to acknowledge to all that contributed for the successful ending of this thesis:
Applied Catalysis B Environmental, 2014
ALD is solvent-free, controlled method suitable for preparing bimetallic particles.Metal location... more ALD is solvent-free, controlled method suitable for preparing bimetallic particles.Metal location and particle size effecting catalyst activity was modified by ALD.Synthetized nanoparticles have well defined surface structure.The catalysts show enhanced activity for important fuel cell reactions MOR and ORR.Catalyst durability in MOR is adjusted by suitable catalyst preparation parameters.Atomic layer deposition (ALD) is a thin layer synthesis method applied in this study for preparing carbon-supported mono-metallic Pt- and bi-metallic PtCo catalysts. The catalyst characterization confirmed that small metal particles with a narrow particle size distribution and high metal dispersion were obtained. The location of the metals on the surface was controlled by alternating the ALD cycles, and the formation of bi-metallic PtCo particles on the support was observed. The prepared catalysts proved to be active for methanol oxidation and oxygen reduction in an acidic media. In addition, the durability of the catalysts in electrochemical oxidation was enhanced by varying the metal cycle order in the catalyst preparation. After the deposition of Co on the catalyst, one ALD cycle of Pt favored the catalyst durability in the methanol oxidation reaction.
Journal of Catalysis, 2014
Recent developments on anion-exchange membranes for fuel cell application renewed the interest in... more Recent developments on anion-exchange membranes for fuel cell application renewed the interest in the study of alcohol oxidation at high pHs for applications in anion-exchange membrane direct alcohol fuel cells (AEM-DAFC). Although platinum is still the most studied catalyst for oxidation of alcohols in alkaline media, the introduction of one or more metals in order to increase the oxophilicity of the catalyst is a common approach in the development of improved materials for these reactions. In this manuscript, we report the enhancement of the catalytic activity of Pt/C toward ethanol, methanol, and propanol oxidation in alkaline media by simple adsorption of Bi surface. The activity was checked by cyclic voltammetry, and the reaction products and intermediates were analyzed by ''in situ'' infrared spectroscopy. The presence of Bi was shown to increase the activity of Pt toward the oxidation of the referred alcohols by acting as a third body (impeding surface poisoning) and also by an electronic effect (on water adsorption at the surface).
Journal of Catalysis, 2015
ABSTRACT In this work, PtRu/C–Sb materials prepared by adding a Sb salt to the ink of commercial ... more ABSTRACT In this work, PtRu/C–Sb materials prepared by adding a Sb salt to the ink of commercial PtRu/C were studied as catalysts for ethanol oxidation. The prepared trimetallic catalysts showed enhanced properties for ethanol oxidation through a wide range of surface coverages. However, coverage higher than 0.7 of Sb on PtRu/C causes the decrease of the catalytic activity suggesting that specific sites composed of 3 metals are necessary to achieve the highest performance. In situ Fourier Transform Infrared Spectroscopy experiments were also performed to compare the reaction products of the bimetallic and trimetallic catalysts. The catalysts were also tested under fuel cell conditions. Also in this case, higher power densities, higher open-circuit voltages and better stability than the bimetallic substrate were found. With this catalyst preparation method, the catalysts showed 2 times higher current densities than for the PtRu catalysts and 6 times better than for pure Pt anodes.
Electrochemistry Communications, 2015
The demand for power sources alternative to fossil fuels makes urgent the development of more eff... more The demand for power sources alternative to fossil fuels makes urgent the development of more efficient electrocatalysts for fuel cells applications and the maximization of the performances of the existent ones. This work reports, for the first time, the use of carbon-supported shape-controlled Pt nanoparticles as anode catalysts in direct ethanol fuel cells. By using cubic Pt nanoparticles, on which (100) surface sites are predominant, the performance of the fuel cell can be increased from 14 to 24 mW per mg of Pt when compared with cuboctahedral nanoparticles. Moreover, the open circuit potential shifts about 50 mV toward more positive potentials. In comparison with commercially available Pt catalysts, the performance for the (100) preferentially oriented nanoparticles is about three times higher. The reported results evidence that, from an applied point of view, the effect of the surface structure/shape of the electrocatalysts can be also considered to improve the performance of real fuel cell systems.
Electrochimica Acta, 2015
Electrocatalysis, 2011
In this paper, the electrocatalytic enhancement of the Pt(111) surface modified with Bi adatoms t... more In this paper, the electrocatalytic enhancement of the Pt(111) surface modified with Bi adatoms towards nitrite reduction and the quantification of the catalytic effect of different adatom coverages are reported. The results were obtained in acidic and neutral media using cyclic voltammetry and in situ infrared spectroscopy measurements and show that the presence of irreversible adsorbed bismuth on Pt(111) electrodes catalyzes nitrite reduction. The presence of the foreign adatom shifts nitrite reduction to potentials as high as 0.80-0.60 V vs RHE, coinciding with the potential at which Bi undergoes its redox surface reaction. Different coverages of Bi on the surface were prepared, revealing that the activity increases with the amount of Bi until its coverage approaches half the saturation of the maximum surface blockage. For higher coverages, the activity decreases steeply, resulting in a volcano-like curve. The spectroelectrochemical experiments show that the main product of nitrite reduction at these high potentials is N 2 O.
The Journal of Physical Chemistry C, 2014
Langmuir, 2012
The first part of this report studies the electrochemical properties of single-crystal platinum e... more The first part of this report studies the electrochemical properties of single-crystal platinum electrodes in acetonitrile electrolytes by means of cyclic voltammetry. Potential difference infrared spectroscopy in conjunction with linear voltammetry was used to obtain a molecular-level picture of this interface. The second part of this report studies the hydrogen evolution and the hydrogen oxidation reactions on the three low-index faces of Pt electrodes in acetonitrile electrolytes. The data (CVs and IR spectra) strongly suggest that acetonitrile and CN(-) molecules are adsorbed on single-crystal platinum electrodes in the range of -1.5 to 0.3 V versus Ag/AgCl. Those species block part of the adsorption sites for hydrogen adatoms, and they decompose on the surface in the presence of water. The nature of the cation and the presence of water strongly affect the onset of acetonitrile electrolysis and the kinetics and stability of the adsorbed species on the electrode. Finally, the hydrogen evolution and the hydrogen oxidation reactions on platinum single-crystal surfaces in acetonitrile electrolytes are strongly affected by the surface-energy state of Pt electrodes.
Journal of the American Chemical Society, 2011
Journal of Electroanalytical Chemistry, 2008
Impedance spectra (50 kHz-1 Hz) were acquired and used to obtain the differential capacitance at ... more Impedance spectra (50 kHz-1 Hz) were acquired and used to obtain the differential capacitance at the interfaces between 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6] ionic liquid and three different electrode materials (Hg, Pt, and glassy carbon (GC)) as a function of the applied potential. The electrocapillary curve for the Hg/[BMIM][PF6] interface was obtained from drop time measurements, from which the potential of zero charge was calculated to be À0.39 V (Ag wire). The potential of zero charge is 0.30 V less negative than the potential of differential capacitance minimum. This disagreement suggests that the differential capacitance minimum is not related to a classical diffuse layer minimum. Additional support to this conclusion was obtained from positive temperature coefficient for the differential capacitance in contrast to the negative temperature predicted by the classic Gouy-Chapman model. The results do not support the recent model predictions of bell shaped capacitance curves for room temperature ionic liquids, RTILs.
Journal of Catalysis, 2014
Recent developments on anion-exchange membranes for fuel cell application renewed the interest in... more Recent developments on anion-exchange membranes for fuel cell application renewed the interest in the study of alcohol oxidation at high pHs for applications in anion-exchange membrane direct alcohol fuel cells (AEM-DAFC). Although platinum is still the most studied catalyst for oxidation of alcohols in alkaline media, the introduction of one or more metals in order to increase the oxophilicity of the catalyst is a common approach in the development of improved materials for these reactions. In this manuscript, we report the enhancement of the catalytic activity of Pt/C toward ethanol, methanol, and propanol oxidation in alkaline media by simple adsorption of Bi surface. The activity was checked by cyclic voltammetry, and the reaction products and intermediates were analyzed by ''in situ'' infrared spectroscopy. The presence of Bi was shown to increase the activity of Pt toward the oxidation of the referred alcohols by acting as a third body (impeding surface poisoning) and also by an electronic effect (on water adsorption at the surface).
Journal of Catalysis, 2014
Recent developments on anion-exchange membranes for fuel cell application renewed the interest in... more Recent developments on anion-exchange membranes for fuel cell application renewed the interest in the study of alcohol oxidation at high pHs for applications in anion-exchange membrane direct alcohol fuel cells (AEM-DAFC). Although platinum is still the most studied catalyst for oxidation of alcohols in alkaline media, the introduction of one or more metals in order to increase the oxophilicity of the catalyst is a common approach in the development of improved materials for these reactions. In this manuscript, we report the enhancement of the catalytic activity of Pt/C toward ethanol, methanol, and propanol oxidation in alkaline media by simple adsorption of Bi surface. The activity was checked by cyclic voltammetry, and the reaction products and intermediates were analyzed by ''in situ'' infrared spectroscopy. The presence of Bi was shown to increase the activity of Pt toward the oxidation of the referred alcohols by acting as a third body (impeding surface poisoning) and also by an electronic effect (on water adsorption at the surface).
Zeitschrift für Physikalische Chemie, 2012
Electrochimica Acta, 2013