Enrique Herrero

University of Alicante, Alicante, Valencia, Spain

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Publications (188)583.65 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A temperature dependent study on the formic acid oxidation reaction has been carried out in order to determine the activation energy of this reaction on different platinum single crystal electrodes, namely Pt(1 0 0), Pt(1 1 1), Pt(5 5 4) and Pt(5 4 4) surfaces. The chronoamperometric transients obtained with pulsed voltammetry have been analyzed to determine the current densities through the active intermediate and the CO formation rate. From the temperature dependency of those parameters, the activation energy for the direct reaction and the CO formation step have been calculated. For the active intermediate path, the activation energy are in the range of 50–60 kJ/mol. On the other hand, a large dependence on the electrode potential is found for the activation energy of the CO formation reaction on the Pt(1 0 0) electrode, and the activation energy values for this process range between 20 and 100 kJ/mol. These results have been explained using a reaction mechanism in which the oxidation of formic acid requires the presence of a pre-adsorbed anion on the electrode surface.
    Journal of electroanalytical chemistry 04/2015; 742. DOI:10.1016/j.jelechem.2015.02.003 · 2.87 Impact Factor
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    ABSTRACT: The borohydride oxidation reaction on platinum single-crystal electrodes has been studied in sodium hydroxide solution using static and rotating conditions. The results show that borohydride electro-oxidation is a structure sensitive process on Pt surfaces. Significant changes in the measured currents are observed at low potentials. In this region, the Pt(111) electrode exhibits the lowest activity, whereas the highest currents are measured for the Pt(110) electrode. The behavior of the different electrodes is discussed taking as reference the observed behavior on the blank electrolyte and the possible formation of weakly adsorbed intermediates.
    Electrochemistry Communications 02/2015; 51. DOI:10.1016/j.elecom.2014.12.024 · 4.29 Impact Factor
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    ABSTRACT: A collection of shape-controlled Pt nanoparticles has been prepared using two different and previously described methodologies, both using oleylamine/oleic acid as capping material/solvent. A new decontamination protocol is presented to effectively clean the surface of the different nanoparticles thus allowing a full exposure of their surface area and consequently to make the most of their surface structure dependent reactivity. Subsequently, the clean shape-controlled Pt nanoparticles have been electrochemically characterized and their electrocatalytic properties evaluated towards some surface structure reactions of interest. The results indicate that the full characterization of the surface structure cannot be done exclusively by the available microscopy techniques, since it is very difficult to determine the presence of surface defects. Additional surface characterization probes, such as those provided by electrochemical surface sensitive reactions, have been used to assess the surface structure of the samples.
    Electroanalysis 02/2015; 27(4). DOI:10.1002/elan.201400619 · 2.50 Impact Factor
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    Rosa M. Arán Ais, Enrique Herrero, Juan M. Feliu
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    ABSTRACT: Kinetic glycolic acid (GA) oxidation and thermodynamic glycolate adsorption have been studied on Pt single crystal electrodes. The voltammetric profiles of Pt(111), Pt(100), and Pt(110) in 0.1 M GA are shown, and the effect of the inclusion of steps on the Pt(111) surface has been studied by cyclic voltammetry. For Pt(111) electrode, different concentrations and sweep rates have been applied, revealing that both adsorption and oxidation processes take place. By establishing the appropriate conditions, a complete thermodynamic analysis has been performed by using the electrode potential and the charge as independent variables. Total charge density curves, surface pressure at total charge density and at constant electrode potential were determined to calculate the Gibbs excess and the charge number at constant electrode potential for glycolate adsorption on Pt(111). Maximum glycolate coverage on the surface reaches a value of ∼6.0× 1014 ions/cm2. Spectroscopic results show the formation of CO2 during the oxidation of glycolic acid, indicating that the cleavage of the C–C bond occurs during the oxidation process.
    Journal of Solid State Electrochemistry 01/2015; 19:13-21. DOI:10.1007/s10008-014-2646-1 · 2.23 Impact Factor
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    ABSTRACT: The determination of the potentials of zero total and free charge, pztc and pzfc respectively, were made in a wide pH range by using the CO displacement method and the same calculation assumptions used previously for Pt(1 1 1) electrodes in contact with non-specifically adsorbing anions. Calculation of the pzfc involves, in occasions, long extrapolations that lead us to the introduction of the concept of potential of zero extrapolated charge (pzec). It was observed that the pztc changes with pH but the pzec is independent of this parameter. It was observed that the pztc > pzec at pH > 3.4 but the opposite is true for pH > 3.4. At the latter pH both pzec and pztc coincide. This defines two different pH regions and means that adsorbed hydrogen has to be corrected in the “acidic” solutions at the pztc while adsorbed OH is the species to be corrected in the “alkaline” range. The comparison of the overall picture suggests that neutral conditions at the interface are attained at significantly acidic solutions than those at the bulk.
    Electrochimica Acta 01/2015; DOI:10.1016/j.electacta.2015.01.069 · 4.09 Impact Factor
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    ABSTRACT: In order to improve catalytic processes, elucidation of reac-tion mechanisms is essential. Here, supported by a combina-tion of experimental and computational results, the oxida-tion mechanism of formic acid on Pt(111) electrodes modified by the incorporation of bismuth adatoms is revealed. In the proposed model, formic acid is first physorbed, on bismuth, and then deprotonated and chemisorbed, also on bismuth, in formate form. From this configuration the C-H bond is cleaved, on a neighbor Pt site, yielding CO2. It was computa-tionally found that the activation energy for the C-H bond cleavage step is negligible, which was also verified experi-mentally.
    Journal of the American Chemical Society 09/2014; 136(38). DOI:10.1021/ja505943h · 11.44 Impact Factor
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    Rosa M. Arán-Ais, Enrique Herrero, Juan M. Feliu
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    ABSTRACT: Ethylene glycol (EG) oxidation has been studied on Pt(111) and its vicinal surfaces in acidic media by cyclic voltammetry and infrared spectroscopy. Even at Pt(111) the C 2
    Electrochemistry Communications 08/2014; 45:40–43. DOI:10.1016/j.elecom.2014.05.008 · 4.29 Impact Factor
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    ABSTRACT: Ethanol oxidation in 0.1 M NaOH on single-crystal electrodes has been studied using electrochemical and FTIR techniques. The results show that the activity order is the opposite of that found in acidic solutions. The Pt(111) electrode displays the highest currents and also the highest onset potential of all the electrodes. The onset potential for the oxidation of ethanol is linked to the adsorption of OH on the electrode surface. However, small (or even negligible) amounts of COads and carbonate are detected by FTIR, which implies that cleavage of the CC bond is not favored in this medium. The activity of the electrodes diminishes quickly upon cycling. The diminution of the activity is proportional to the measured currents and is linked to the formation and polymerization of acetaldehyde, which adsorbs onto the electrode surface and prevents further oxidation.
    ChemPhysChem 07/2014; 15(10). DOI:10.1002/cphc.201402044 · 3.36 Impact Factor
  • A. M. Gomez-Marin, R. Rizo, E. Herrero
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    ABSTRACT: Oxygen reduction reaction ORR is the main cathodic problem in electrochemistry and has a deep influence in the development of technologically relevant applications such as fuel cells. It is a complex reaction involving a nonpolar molecule with double bond breaking, 4 electron transfer and 4 O-H bond formation in different scenarios. In the reaction mechanism a possible important role can be played by intermediate peroxo species, after the exchange of only 2 electrons. To enhance reactivity, the understanding of the reaction mechanism at the Pt surfaces is necessary. Models can be used to simplify the complex reaction and from the experimental point of view such models are related to the use of single crystal surfaces with well defined orientations. For Pt(111) electrodes, the activation region is quite narrow despite the high overpotential and the process readily becomes transport controlled. Moreover, in the activation region the platinum electrode is covered by oxygenated species and it is well known the influence that these species can play in the electrode surface order, the surface stability being dependent a structure sensitive process. Possible influence of the surface oxygen-containing species, particularly as intermediates in the ORR is not clearly understood and only has been addressed at Pt(111), which likely is the most stable surface upon oxidation . On the other hand the ORR is structure sensitive, the Pt(111) being the most active in alkaline media [1] in contrast to that observed in acidic solution in which Pt(110) and Pt(hkl) surfaces with small two-dimensional domains are able to reduce oxygen at lower potentials. It is obvious that surface effects play an important role in the activation region as deduced from the marked anion effect that should be less important in alkaline solutions due to the shift in the surface charge on the metal. Another aspect that should be considered is the reactivity of hydrogen peroxide at these platinum surfaces, because its possible role as reaction intermediate [2]. In this respect if the ORR necessarily took place through the peroxo intermediate, a possible strategy would be based in the inhibition of peroxide oxidation while keeping constant ORR. Acknowledgements Financial support from MICINN (Spain) through project CTQ2010-16271 and Generalitat Valenciana (PROMETEO/2009/045, FEDER) are greatly acknowledged. References 1. Rizo R, Herrero E, Feliu JM (2013) Phys Chem Chem Phys 15:15416-15425 2. Gomez-Marin AM, Feliu JM (2013) Chemsuschem 6:1091-1100
    225th ECS Meeting; 05/2014
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    ABSTRACT: DFT studies on platinum stepped surfaces have been carried out in order to understand the differences in the electrochemical behavior between the surfaces with (111) and (100) terraces. Thus, adsorption energies of different species on selected surfaces have been computed. For the adsorption of Bi and Cu on the Pt(553) and Pt(711) surfaces, it has been found that the adsorption energy on the site corresponding to the step decoration for the Pt(553) surface is ca. 0.5 eV higher than that calculated on the (111) terrace sites. On the other hand, there is no preferential adsorption site for Cu or Bi on the Pt(711) surface, since the energy differences between the different sites on this stepped surface with (100) terraces are very small. CO and OH adsorption on the surfaces with (100) terraces, namely the Pt(100), the Pt(711) and the Pt(510) surfaces, has been also investigated. The energy differences between step sites and terrace sites for the surfaces are very small, ca. 0.2 eV for OH adsorption and <0.1 eV for CO adsorption. For OH, the preferred adsorption mode is a bridge mode, whereas the adsorption energy for the on top and bridge configurations of CO are similar on those surfaces. The comparison with previous DFT calculations indicates that the perturbation created by the step on the (100) terrace is significantly smaller than that created on the (111) terraces. Thus, the modification of the electrochemical properties produced by the presence of a step in the (100) terrace is minor, in agreement with the experimental results.
    Electrochimica Acta 04/2014; 125:666-673. DOI:10.1016/j.electacta.2014.01.138 · 4.09 Impact Factor
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    ABSTRACT: Thallium modified shape-controlled Pt nanoparticles were prepared and their electrocatalytic activity towards formic acid electrooxidation was evaluated in 0.5 M sulfuric acid. The electrochemical and in situ FTIR spectroscopic results show a remarkable improvement in the electrocatalytic activity, especially in the low potential region (around 0.1-0.2 V vs. RHE). Cubic Pt nanoparticles modified with Tl were found to be more active than the octahedral Pt ones in the entire range of Tl coverages and potential windows. In situ FTIR spectra indicate that the promotional effect produced by Tl results in the inhibition of the poisoning step leading to COads, thus improving the onset potential for the complete formic acid oxidation to CO2. Chronoamperometric experiments were also performed at 0.2 V to evaluate the stability of the electrocatalysts at constant potential. Finally, experiments with different concentrations of formic acid (0.05-1 M) were also carried out. In all cases, Tl-modified cubic Pt nanoparticles result to be the most active. All these facts reinforce the importance of controlling the surface structure of the electrocatalysts to optimize their electrocatalytic properties.
    Physical Chemistry Chemical Physics 03/2014; 16(27). DOI:10.1039/c4cp00304g · 4.20 Impact Factor
  • Journal of electroanalytical chemistry 03/2014; 716:16-22. DOI:10.1016/j.jelechem.2013.07.017 · 2.87 Impact Factor
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    ABSTRACT: The effect of the electrode potential in the reactivity of platinum stepped single crystal electrodes with (111) terraces toward CO oxidation has been studied. It is found that the CO adlayer is significantly affected by the potential at which the adlayer is formed. The electrochemical and FTIR experiments show that the adsorbed CO layer formed in acidic solution at 0.03 V vs SHE is different from that formed at −0.67 V vs SHE in alkaline solutions. The major effect of the electrode potential is a change in the long-range structure of CO adlayer. The adlayer formed in alkaline media presents a higher number of defects. These differences affect the onset and peak potential for CO stripping experiments. The stripping voltammogram for the adlayer formed at −0.67 V vs SHE always shows a prewave and the peak potential is more negative than that observed for the adlayer formed at 0.03 V vs SHE. This means that the apparent higher activity for CO oxidation observed in alkaline media is a consequence of the different CO adlayer structure on the (111) terrace, and not a true catalytic effect. The different behavior is discussed in terms of the different mobility of CO observed depending on the electrode potential. Also, the FTIR frequencies are used to estimate the pzc (potential of zero charge) for the Pt(111) electrode covered with a CO adlayer.
    The Journal of Physical Chemistry C 01/2014; 118(4):1925–1934. DOI:10.1021/jp408975t · 4.84 Impact Factor
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    ABSTRACT: Electrooxidation of CO at the Pt(hkl)-electrolyte interface in two different room temperature ionic liquids (RTILs) is probed to be surface-sensitive. Provided data reveal a specific surface structure, (110) sites, which selectively activate CO oxidation in RTILs. This new knowledge is crucial for designing the next generation of Pt nanosized electrocatalysts for the CO oxidation reaction by increasing that type of site on the catalyst surface.
    ACS Catalysis 11/2013; 3(12):2935–2938. DOI:10.1021/cs4007364 · 7.57 Impact Factor
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    ABSTRACT: The electrooxidation of ethanol on Au(111), Au(1 00), Au(110) and Au(210) single crystal electrodes as well as on Au polycrystalline electrode have been investigated in alkaline media using cyclic voltammetry (CV) and in situ Fourier transform infrared reflectance (FTIR) spectroscopy. It has been found that the catalytic activity for the electrooxidation of ethanol in the low potential region decreases in the following order: Au(110) > Au(210) > Au(100) > Au(poly) > Au(111). This suggests that the defect sites on the Au surface dominate the electrooxidation of ethanol. On the other hand, both the adsorbed OH and the potential of zero charge on the surface play an important role in the ethanol oxidation reaction. The FTIR spectroscopy measurements show that the main reaction product of ethanol oxidation reaction in the alkaline media is acetate. This result indicates that the reaction product on gold is independent of the electrode's orientation.
    Journal of electroanalytical chemistry 10/2013; 707:89-94. DOI:10.1016/j.jelechem.2013.08.034 · 2.87 Impact Factor
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    ABSTRACT: The electrochemical reactivity of catechol-derived adlayers is reported at platinum (Pt) single-crystal electrodes. Pt(111) and stepped vicinal surfaces are used as model surfaces possessing well-ordered nanometer-sized Pt(111) terraces ranging from 0.4 to 12 nm. The electrochemical experiments were designed to probe how the control of monatomic step-density and of atomic-level step structure can be used to modulate molecule-molecule interactions during self-assembly of aromatic-derived organic monolayers at metallic single-crystal electrode surfaces. A hard sphere model of surfaces and a simplified band formation model are used as a theoretical framework for interpretation of experimental results. The experimental results reveal (i) that supramolecular electrochemical effects may be confined, propagated, or modulated by the choice of atomic level crystallographic features (i.e.monatomic steps), deliberately introduced at metallic substrate surfaces, suggesting (ii) that substrate-defect engineering may be used to tune the macroscopic electronic properties of aromatic molecular adlayers and of smaller molecular aggregates.
    Langmuir 10/2013; 29(42). DOI:10.1021/la402627e · 4.38 Impact Factor
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    ABSTRACT: The co-adsorption of CO and OH on two Pt stepped surfaces vicinal to the (111) orientation has been evaluated by means of density functional theory (DFT) calculations. Focusing on Pt(533) and Pt(221), which contain (100) and (111)-steps, respectively, we find that (111)-steps should be more reactive towards CO oxidation than surfaces containing (100)-steps. The DFT results are compared with electrochemical experiments on the CO adsorption and oxidation on these vicinal surfaces.
    Physical Chemistry Chemical Physics 09/2013; 15(42). DOI:10.1039/c3cp53282h · 4.20 Impact Factor
  • Ruben Rizo, Enrique Herrero, Juan M Feliu
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    ABSTRACT: The oxygen reduction reaction (ORR) in 0.1 M NaOH on platinum single crystal electrodes has been studied using hanging meniscus rotating disk electrode configuration. Basal planes and stepped surfaces with (111) and (100) terraces have been employed. The results indicate that the Pt(111) electrode has the highest electrocatalytic activity among all the studied surfaces. The addition of steps on this electrode surface significantly diminishes the reactivity of the surface towards the ORR. In fact, the reactivity of the steps on the surfaces with wide terraces can be considered negligible with respect to that measured for the terrace. On the other hand, Pt(100) and Pt(110) electrodes have much lower activity than the Pt(111) electrode. These results have been compared with those obtained in acid media to understand the effect of the pH and the adsorbed OH on the mechanism. It is proposed that the surface covered by adsorbed OH is active for the reduction of the oxygen molecules.
    Physical Chemistry Chemical Physics 08/2013; 15(37). DOI:10.1039/c3cp51642c · 4.20 Impact Factor
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    ABSTRACT: Dream island: Monoatomic, high‐platinum islands deposited on a Rh(1 1 1) electrode have an electrocatalytic activity for ethanol oxidation that is 20 times higher than that measured on platinum electrodes. On these islands, CO2 and acetic acid are the final products.
    ChemCatChem 06/2013; 5(6). DOI:10.1002/cctc.201200687 · 5.04 Impact Factor
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    ABSTRACT: Ethanol oxidation on platinum nanoparticles with well-characterized surfaces is studied using cyclic voltammetry and FTIR techniques. Their behavior is compared with that obtained for platinum single crystal electrodes, in order to rationalize their performance and to understand the effects of the surface structure and anion adsorption on the reactivity. The results clearly demonstrate that there are strong effects of anion adsorption and surface structure on the measured current and oxidation mechanism. Thus, the main product of ethanol oxidation on (111) preferentially oriented Pt nanoparticles is acetic acid, and the amount of CO2 produced can be considered negligible. On the other hand, (100) preferentially oriented Pt nanoparticles are effective for the cleavage of the C–C bond yielding adsorbed CO, which eventually is oxidized to CO2. This nanoparticles electrode has the highest catalytic activity at high potentials, whereas (111) preferentially oriented Pt nanoparticles are more active at low potentials. In addition, no significant differences in the activity are reported by using different supporting electrolytes, which indicates that adsorbed acetate, which results from the adsorption of acetic acid, hinders ethanol oxidation.
    05/2013; 1(24):7068-7076. DOI:10.1039/C3TA10996H

Publication Stats

4k Citations
583.65 Total Impact Points

Institutions

  • 1993–2015
    • University of Alicante
      • Departamento de Química Física
      Alicante, Valencia, Spain
  • 1997–2010
    • Cornell University
      • • Department of Chemistry and Chemical Biology
      • • School of Applied and Engineering Physics
      Ithaca, New York, United States
  • 2008
    • Leiden University
      • Leiden Institute of Chemistry
      Leyden, South Holland, Netherlands
  • 2003
    • University of Chichester
      Chichester, England, United Kingdom
  • 2002
    • University of Illinois, Urbana-Champaign
      • Department of Chemistry
      Urbana, Illinois, United States