Showing papers by "Juan M. Feliu published in 2010"
TL;DR: In this paper, the potentials of zero total charge (pztc) were determined by using the CO displacement approach, both in sulphuric and perchloric media.
170 citations
TL;DR: It is shown that the achievable maximum current density for mature wastewater-based microbial biofilms is strongly dependent on the electrode material and the operation temperature, and the real surface area values measured by BET surface area technique cannot provide a reasonable explanation for suitability of an electrode material for the formation of electrochemically active biofilm.
163 citations
TL;DR: In this article, the authors compared the behavior of unsupported platinum nanoparticles and 2.5-nm nanoparticles on carbon with different platinum loadings (from 10% to 50%) and showed that the nanoparticles retain most of their individual physical identity and significant loss of active surface area does not take place.
128 citations
TL;DR: In this paper, the influence of the surface structure and shape of the Pt nanoparticles on the formic acid electrooxidation was analyzed using pulsed voltammetry. And the results pointed out that, in agreement with fundamental studies with Pt single crystal electrodes, surface structure of the electrodes plays an important role on the reactivity and kinetics of Formic acid oxidation, thus the electrocatalytic properties for this reaction strongly depend on the dominant structure on the surface of the nanoparticles.
Abstract: Pulsed voltammetry was used to study formic acid electrooxidation on Pt nanoparticles with well-characterized surfaces. Polyoriented and preferential (100), (100−111), and (111) Pt nanoparticles were characterized and employed to evaluate the influence of the surface structure and shape of the Pt nanoparticles on this model electrochemical reaction. The results pointed out that, in agreement with fundamental studies with Pt single crystal electrodes, the surface structure of the electrodes plays an important role on the reactivity and kinetics of formic acid oxidation. Thus the electrocatalytic properties for this reaction strongly depend on the dominant structure on the surface of the nanoparticles, in particular on the presence of domains with (100) and (111) symmetry. Among the Pt nanoparticles studied, those containing (100) domains are clearly the most active toward formic acid electrooxidation via the active intermediate path, but also exhibit the highest poisoning rate. (111) Pt nanoparticles show ...
102 citations
TL;DR: The extrapolation of the results obtained with stepped surfaces with (111) terraces to zero step density indicates that CO formation should not occur on an ideal Pt(111) electrode, and the analysis of the Tafel slopes obtained for the different electrodes suggests that the oxidation of formic acid is strongly affected by the presence of adsorbed anions, hydrogen and water.
Abstract: Pulsed voltammetry has been used to study formic acid oxidation on platinum stepped surfaces to determine the kinetics of the reaction and the role of the surface structure in the reactivity. From the current transients at different potentials, the intrinsic activity of the electrode through the active intermediate reaction path (jθ = 0), as well as the rate constant for the CO formation (kads) have been calculated. The kinetics for formic acid oxidation through the active intermediate reaction path is strongly dependent on the surface structure of the electrode, with the highest activity found for the Pt(100) surface. The presence of steps, both on (100) and (111) terraces, does not increase the activity of these surfaces. CO formation only takes place in a narrow potential window very close to the local potential of zero total charge. The extrapolation of the results obtained with stepped surfaces with (111) terraces to zero step density indicates that CO formation should not occur on an ideal Pt(111) electrode. Additionally, the analysis of the Tafel slopes obtained for the different electrodes suggests that the oxidation of formic acid is strongly affected by the presence of adsorbed anions, hydrogen and water.
100 citations
87 citations
77 citations
TL;DR: In this paper, the kinetics of O2 reduction on novel electrocatalyst materials deposited on carbon substrates were studied in 0.5 m H2SO4 and 0.1 m NaOH solutions using the rotating disk electrode (RDE) technique.
74 citations
TL;DR: In this article, the Gibbs thermodynamics in the presence of charge transfer processes has been applied to characterize temperature effects on Pt(1, 1, 1), Pt( 1, 0, 0), Pt (1, 0, 0), and Pt(0, 1, 1, 0) electrodes in 0.1 M HClO 4 solutions.
59 citations
TL;DR: The expression of external cytochromes in response to the potential of the electron acceptor suggests the existence of alternative pathways of electron transport with different energy yield, though it remains to be demonstrated.
56 citations
TL;DR: It is concluded that sulfate rather than bisulfate adsorption takes place at potentials higher than the potential of zero charge, which agrees with the fact that similar FTIRRAS bands for adsorbed sulfate species are observed for pH 0.8-3.5.
Abstract: The nature of the adsorbed species for Pt(111) in sulfuric acid solutions has been elucidated by a careful thermodynamic analysis of the effect of pH on charge density data. This analysis takes advantage of the fact that, for solutions of constant total sulfate + bisulfate concentration, an increase of pH would increase the sulfate concentration, at the expense of decreasing the bisulfate concentration. As a result, sulfate adsorption would be shifted toward lower potentials, while bisulfate adsorption would follow the opposite trend. In the present work, coulostatic data for Pt(111) in (0.2 − x) M Me2SO4 + x M H2SO4 (Me: Li, Na; x: 10−4 − 0.2) and (0.1 − x) M KClO4 + x M HClO4 + 10−3 M K2SO4 (x: 10−4 − 0.1) solutions are carefully analyzed. It is concluded that sulfate rather than bisulfate adsorption takes place at potentials higher than the potential of zero charge. This result agrees with the fact that similar FTIRRAS bands for adsorbed sulfate species are observed for pH 0.8−3.5 in (0.2 − x) M K2SO4 ...
TL;DR: In this article, the authors used potential cycling between 0.05 and 0.3 to estimate actual coverage of Pt surface with 3D-Cu adatoms and found that the steady-state currents are higher at the potentials of 0.12 and 1.3 compared to pure platinum.
TL;DR: In this paper, the first oxidation of the electrode reflects independent contributions from terrace and step sites, the latter being structure sensitive, and oxygen adsorption charges amount to a mean value of one electron per step site.
TL;DR: In this article, the electrocatalytic activity of different shape-controlled gold nanoparticles and nanorods has been studied by scanning electrochemical microscopy (SECM), where TEM images and lead underpotential deposition (UPD) voltammetric profiles were used to physically and electrochemically characterize all gold particles studied here.
TL;DR: In this work, surface modification at an atomic level, coupled with CO as molecular probe, was applied to study the step-site reactivity of platinum single crystals to investigate the reactivity changes before and after modification of the electrode surfaces.
Abstract: In this work, surface modification at an atomic level, coupled with CO as molecular probe, was applied to study the step-site reactivity of platinum single crystals. Stepped platinum single crystal electrodes with (111) terraces and step sites of different symmetry were modified by irreversible adsorption of Bi and Te adatoms selectively deposited on steps, and characterized in 0.1 M HClO4 solution. CO charge-displacement and oxidative stripping were employed to investigate the reactivity changes before and after modification of the electrode surfaces. The values of potential of zero total charge (pztc) determined from CO displacement experiments were found to shift positively on all decorated electrodes. The CO oxidation peaks also shifted to higher potential once the step sites were blocked by the adatoms, indicating a catalytic effect of the step sites for this reaction. The CO coverage values on the step sites were determined by comparing the stripping charges and the change in the hydrogen de/adsorption charge, using the pztc's for double layer correction. The CO coverage was determined to be ca. 0.7 for (110) step sites while only 0.4 for (100) step sites, which suggests a different bond of CO adsorbed on the different step sites. This was confirmed by in situ infrared reflection–absorption spectroscopy (IRAS) studies, showing that the (110) step sites are dominated by atop CO while bridged bonded CO are prevalent on (100) step sites. The comparison of CO stripping and hydrogen adsorption charges before and after adatom modification allows the separation of step and terrace contributions to the overall CO coverage.
TL;DR: The results suggest that sulfate is the most likely candidate for this adsorbate in solutions of variable pH and the same species is predominantly adsorbed on the metal surface for this broad range of pH values.
Abstract: Subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) was applied to study (bi)sulfate adsorption on a Pt(111) surface in solutions of variable pH while maintaining a constant total bisulfate/sulfate ((bi)sulfate) concentration without the addition of an inert supporting electrolyte. The spectra were recorded for both the p- and s-polarizations of the IR radiation in order to differentiate between the IR bands of the (bi)sulfate species adsorbed on the electrode surface from those species located in the thin layer of electrolyte. The spectra recorded with p-polarized light consist of the IR bands from both the species adsorbed at the electrode surface and those present in the thin layer of electrolyte between the electrode surface and ZnSe window whereas the s-polarized spectra contain only the IR bands from the species located in the thin layer of electrolyte. A new procedure was developed to calculate the angle of incidence and thickness of the electrolyte between the Pt(111) electrode surface and the ZnSe IR transparent window. By combining these values with the knowledge of the optical constants for Pt, H(2)O and ZnSe, the mean square electric field strength (MSEFS) at the Pt(111) electrode surface and for thin layer of solution were accurately calculated. The spectra recorded using s-polarization were multiplied by the ratio of the average MSEFS for p- and s-polarizations and subtracted from the spectra recorded using p-polarization in order to remove the IR bands that arise from the species present within the thin layer cavity. In this manner, the resulting IR spectra contain only the IR bands for the anions adsorbed on the Pt(111) electrode surface. The spectra of adsorbed anions show little change with respect to the pH ranging from 1 to 5.6. This behavior indicates that the same species is predominantly adsorbed on the metal surface for this broad range of pH values and the results suggest that sulfate is the most likely candidate for this adsorbate.
TL;DR: In this article, the Pt(111)/Nafion model interface in HClO4 acid solutions is studied by IRRAS and cyclic voltammetry, and it was found that the presence of an electric field mainly promotes deprotonation of sulfonic groups and structuring of water inside the membrane (polar molecules), especially near the electrode surface, with a sudden change of system optical properties at the Pt (111)/membrane interface at 0.9 V, possibly due to clustering within the polymer.
Abstract: Understanding the structure and molecular processes at the electrode/membrane interfaces constitutes an important topic in PEFC as well as in electrochemistry. In this work, the Pt(111)/Nafion model interface in HClO4 acid solutions is studied by IRRAS and cyclic voltammetry. It was found that the presence of an electric field mainly promotes deprotonation of sulfonic groups and structuring of water inside the membrane (polar molecules), especially near the electrode surface, with a sudden change of system optical properties at the Pt(111)/membrane interface at 0.9 V, possibly due to clustering within the polymer. Furthermore, the performance of the Pt(111)/Nafion in a typical electrochemical reaction as CO oxidation has been also analyzed. It is shown that there are notable differences between the characteristics of CO adsorption and oxidation at Pt(111) with and without polymer electrolyte membrane, like a continual wavenumber increase with the potential for the on-top CO band, even during CO oxidation,...
TL;DR: In this paper, a mean field Langmuir−Hinselwood mechanism was used to simulate the CO oxidation curves on the Pt(111) electrode in the presence and absence of CO. The rate constants of the different steps in the mechanism were determined.
Abstract: CO oxidation curves on the Pt(111) electrode in the presence and the absence of CO are simulated using a mean field Langmuir−Hinselwood mechanism, in which the rate-determining step is an electrochemical reaction between adsorbed CO and adsorbed OH. The OH adsorption process has been modeled using a Frumkin isotherm that reproduces the experimental OH adsorption behavior on the clean Pt(111) electrode. From the results of the simulation, the rate constants of the different steps in the mechanism are determined. Although the model reproduces quite well the main characteristics of the chronoamperometric and voltammetric curves, some deviations are observed due to factors that cannot be included in the model. These factors are the existence of a nonhomogeneous distribution of defects on the surface of a real Pt(111) electrode, the CO−CO and OH−CO interactions in the adsorbed adlayer, and the nonhomogeneous flux of the CO from the bulk to the electrode surface. Using the model, the effective Tafel slope that ...
TL;DR: The results demonstrate the technical feasibility of performing domain-selective decapping of nanoparticles by handle of an externally controlled parameter, i.e., the applied potential.
Abstract: This manuscript compares the electrochemically controlled adsorption of hydroquinone-derived adlayers and their reductive desorption from nanometer-sized Pt(111) domains present on the surface (i) ...
TL;DR: Results of the formal partial charge numbers corroborate that potassium adsorption involves sulfate cooperative coadsorption, in such a way that the effective adsorbing species is anionic, rather than cationic.
Abstract: This work contributes to the understanding of cation specific effects on platinum electrochemistry by means of a thorough thermodynamic analysis of potassium adsorption on Pt(111) in sulfuric acid solutions. It is concluded that potassium specific adsorption is better described as the adsorption of the K(+)-SO ion pair. From the evaluation of the potassium sulfate concentration, it is found that potassium specific adsorption only takes place in the presence of coadsorbed sulfate species. Within the main sulfate adsorption state, for ∼0.3 V 0.1 M. Then, at higher potentials, E > 0.55 V (vs. SHE), a second potassium adsorption process takes place, concomitant with the second sulfate adsorption process (associated to the small voltammetric feature called "the hump"). This last process involves the adsorption of an equal amount of potassium and sulfate species, leading to the adsorption of ∼0.5 × 10(14) ion pair species per cm(2) (∼0.03 ion pair species per platinum surface atom). Furthermore, the results of the formal partial charge numbers corroborate that potassium adsorption involves sulfate cooperative coadsorption, in such a way that the effective adsorbing species is anionic, rather than cationic. In conclusion, this work evidences that cation specific effects may originate from the formation of surface ion pairs, which is probably related to the presence of ion pairs in solution.
25 Nov 2010-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: Debye Function Analysis (DFA) and Whole Powder Pattern Modelling (WPPM) of the measured X-ray diffraction pattern were carried out to obtain statistical information on the particle size and shape present in the sample.
Abstract: Platinum nanoparticles with a mean size of 8.7 nm were synthesized by a salt reduction reaction having polyhedron shapes with preferential (1 1 1) surfaces. In situ electrochemical characterization of nanoparticles was performed which confirmed the existence of mostly (1 1 1) surface sites in the sample. The effect of this surface in the electrooxidation of CO was measured. Debye Function Analysis (DFA) and Whole Powder Pattern Modelling (WPPM) of the measured X-ray diffraction pattern were carried out to obtain statistical information on the particle size and shape present in the sample. Both analyses determined that the octahedron particle shape was the most abundant which was also consistent with TEM observations. The existence of a small percentage of single twinned particles was determined by DFA, WPPM, as well as analysis of HRTEM images.
15 Dec 2010
TL;DR: In this article, the behavior of the adatoms on different platinum surfaces is discussed and a model for the actuation of the Adatoms is given, where a modification of the surface with adatom has been used to increase catalytic activity and/or diminish the poisoning of the platinum surfaces.
Abstract: Formic acid oxidation on platinum is a structure-sensitive reaction that takes place via a mechanism with two paths. One of the paths leads to the formation of CO (poison intermediate), which adsorbs strongly on to the surface and hinders the oxidation of formic acid through the active intermediate. Both paths are structure sensitive. Activities for both paths are parallel; a high activity for the path through the active intermediate is usually associated with a high activity for poison formation. The modification of the surface with adatoms has been used to increase catalytic activity and/or diminish the poisoning of the platinum surfaces. The behavior of the adatoms on the different platinum surfaces is discussed and a model for the actuation of the adatoms is given.
Keywords:
polycrystalline platinum electrodes;
platinum single crystals;
formic acid;
adatoms;
CO
TL;DR: PtCo nanoparticles with homogeneous size (around 3-4 nm) have been synthesized in a water-in-oil microemulsion of water/polyethylenglycol-dodecylether (BRIJ®30)/n-heptane as discussed by the authors.
Abstract: PtCo nanoparticles with homogeneous size (around 3–4 nm) have been synthesized in a water-in-oil microemulsion of water/polyethylenglycol–dodecylether (BRIJ®30)/n-heptane. X-ray diffraction study revealed the formation of a cubic phase with a gradual decrease of the cell parameter with increasing cobalt incorporation in the crystalline lattice of platinum. In relation to their magnetic properties, the PtCo nanoparticles present a superparamagnetic behaviour even after annealing, although higher permeability was induced by the thermal treatment. Finally, the electrocatalytic activity of the particles towards oxalic acid oxidation in H2SO4 was evaluated. The Pt74Co26 nanoparticles showed the highest reactivity for this reaction.
TL;DR: In this paper, the frequency dispersion of the impedance at potentials of the adsorption region has been analyzed according to the Frumkin-Melik-Gaykazyan (FML) theory without any a priori assumption about the potential dependence of the adorption rate constant.
TL;DR: In this article, the behavior of tretrafluoroborate anion (BF 4 - ) at Pt single crystal electrodes was investigated based on voltammetric experiments, and it was shown that the BF 4 - anion chemisorb on the Pt(1 1/1/1) surface with enough strength to suppress part of the characteristics of the voltammogram recorded in perchloric acid.
TL;DR: For the three cases studied, the results suggest that reductive desorption of the adlayers can be accomplished in aqueous 0.5 M H(2)SO(4) solutions within the time frame of a single cathodic scan, i.e. the first half of asingle CV experiment.
Abstract: The electrochemical reactivity of hydroquinone-derived, catechol-derived and benzene-derived adlayers is compared at Pt(111) single-crystal surfaces (i) under stagnant hanging meniscus (HM) configu...
TL;DR: In this article, the authors discuss the effect of the topology of a terrasse on the performance of the electroquimica of the terrasse, i.e., the ability of the electrodes of the amplies terrasse to be revisited.
Abstract: Els pilars fonamentals de l'electroquimica de la superficie
dels electrodes de plati son revisats. Aquests pilars es relacionen
primerament amb la topografia de la superficie perque
les correctes respostes electroquimiques de les amplies terrasses
i l'efecte dels esglaons de simetria diferent i dels setis
ondulats son importants per a la caracteritzacio in situ. L'adsorcio
d'anions te tambe un paper clau en les caracteristiques
selectives associades a la topografia de la superficie. Addicionalment,
l'adsorcio competitiva d'anions i d'altres especies en
solucio te unes consequencies importants en la reactivitat. De
la mateixa manera, l'adsorcio d'adatoms es un proces sensible
a l'estructura que afecta la composicio de la superficie de
l'electrode. Es poden considerar dos casos segons si l'adatom
pot formar una capa estable o mes en la regio de potencial
usualment enregistrada. En el cas de mes d'una capa, els resultats
es poden comparar amb els electrodes monocristal·lins
corresponents, i s'obre aixi la possibilitat de relacionar el comportament
caracteristic d'ambdos sistemes.
15 Oct 2010
TL;DR: In this article, the effect of adsorption from very diluted solutions on the electrochemical response of actual systems was explored by applying Nernstian equilibrium expressions to the high quality data.