Antonio Berna - Academia.edu (original) (raw)

Papers by Antonio Berna

Book of abstracts, 2008

Oxidation of ethanol on ruthenium-modified Pt(775) and Pt(332) stepped electrodes has been studie... more Oxidation of ethanol on ruthenium-modified Pt(775) and Pt(332) stepped electrodes has been studied using electrochemical and FTIR techniques. It has been found that the oxidation of ethanol on these electrodes takes place preferentially on the step sites yielding CO(2) as the major final product. The cleavage of the C-C bond, which is the required step to yield CO(2), occurs only on this type of site. The presence of low ruthenium coverages on the step sites promotes the complete oxidation of ethanol since it facilitates the oxidation of CO formed on the step from the cleavage of the C-C bond. However, high ruthenium coverages have an important inhibiting effect since the adatoms block the step sites, which are required for the cleavage of the C-C bond. Under these conditions, the oxidation current diminishes and the major product in the oxidation process is acetic acid, which is the product formed preferentially on the (111) terrace sites.

Elsevier eBooks, 2007

... Page 18. A. Berna et al. 4 (N48, L'Air Liquide) or oxalic acid (pro analysi from Merck).... more ... Page 18. A. Berna et al. 4 (N48, L'Air Liquide) or oxalic acid (pro analysi from Merck). Perchloric acid solutions were prepared from the concentrated acid (Suprapur from Merck) and ultrapure water (Elga-Vivendi). Potassium ...

Electrochimica Acta, Mar 1, 2004

... 22]. Experiments were carried out at room temperature. Test solutions were made of 0.1 M perc... more ... 22]. Experiments were carried out at room temperature. Test solutions were made of 0.1 M perchloric acid (Merck Suprapur ® ) in Purelab Ultra ® (Elga-Vivendi) water. Oxalic acid (Merck Suprapur) up to 10 −2 M was added. ...

Journal of Physical Chemistry C, Mar 29, 2016

Carbonate and bicarbonate adsorption on Pt(111) electrodes from CO 2 saturated acidic solutions i... more Carbonate and bicarbonate adsorption on Pt(111) electrodes from CO 2 saturated acidic solutions is investigated by cyclic voltammetry and Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS). Spectroscopic results show carbonate and bicarbonate adsorption even at pH=1, where bulk concentration of these anions is negligible. Moreover, analysis of the potential dependence of band intensities corresponding to adsorbed carbonate and bicarbonate reveals an effect of the electrode potential on the surface acid-base equilibrium. In this regards, increasing potentials favor bicarbonate deprotonation, leading to carbonate formation. A tentative thermodynamic analysis is given to rationalize these trends. 1. Introduction. The understanding of interfacial properties is a challenging topic in physical electrochemistry and requires careful experiments combining different techniques. One of the classical subjects in this field deals with the specific adsorption of anions. This topic has already been addressed on mercury electrodes 1 and extended later to coinage 2-4 and platinum group metal electrodes 5-8 to explore the validity of double layer models. These investigations have important implications in practical electrochemistry, since anion adsorption competes with other molecular species, either reagents or intermediates, in electrocatalytic reactions, thus hindering the reaction rate. As an example, oxygen reduction shifts to lower potentials in

Journal of Physical Chemistry C, Jun 15, 2007

Supporting information Cyclic voltammograms for Au(100), Au(111), Au(110) and an electrochemicall... more Supporting information Cyclic voltammograms for Au(100), Au(111), Au(110) and an electrochemically annealed thin-film gold electrode in 0.1 M HClO 4 (a, dashed line) and 0.01 M H 4 C 3 O 4 + 0.1 M HClO 4 (b and c, solid lines, correspond to the first and second voltammetric cycle, respectively). Sweep rate: 50 mV s-1. Dotted curves (d) correspond to the charge density vs potential curves calculated by integrating the difference between voltammetric curves c and a.

Electrochimica Acta, 2008

Acetate adsorption at gold electrodes is studied in perchloric acid solutions by cyclic voltammet... more Acetate adsorption at gold electrodes is studied in perchloric acid solutions by cyclic voltammetry and in-situ infrared spectroscopy. External reflection measurements, performed with gold single crystal electrodes, are combined with Surface Enhanced Infrared Reflection Absorption Spectroscopy experiments under attenuated total reflection conditions (ATR-SEIRAS) carried out with sputtered gold thin-film electrodes. Theoretical harmonic IR frequencies of acetate species adsorbed with different geometries on Au clusters with (1 1 1), (1 0 0) and (1 1 0) orientations have been obtained from B3LYP/LANL2DZ, 6-31 + G* calculations. The theoretical and experimental results confirm that, irrespective of the surface crystallographic orientation, bonding of acetate to the surface involves the two oxygen atoms of the carboxylate group, with the OCO plane perpendicular to the metal surface. DFT calculations reveal also that the total charge of the metal cluster-acetate supermolecule has small effect on the vibrational frequencies of adsorbed acetate species. Both the external and the internal reflection measurements show the co-adsorption of acetate and perchlorate anions. Step-scan measurements carried out with the gold thin-film electrodes have allowed the monitoring of the time-dependent behaviour of perchlorate, acetate and water bands in potential step experiments. Acetate adsorption under those conditions is shown to involve perchlorate desorption and to follow a Langmuir-type kinetics. The step-scan spectra also show the rise and decay of transient water structures with parallel time-dependent shifts of the background intensity in the infrared spectra.

Physical Chemistry Chemical Physics, 2008

Electrochemistry Communications, Dec 1, 2007

The adsorption of hydroxyl on Pt(1 1 1) single crystal electrodes from aqueous acidic solutions i... more The adsorption of hydroxyl on Pt(1 1 1) single crystal electrodes from aqueous acidic solutions is carefully reinvestigated. The effect of small additions (10 À8-10 À5 M) of chloride and bisulphate anions on the OH adsorption region in perchloric acid solution has been studied. Two regions can be differentiated in the voltammetric profile, that behave differently after the addition of the foreign anion. The initial broad adsorption process is unaffected until the highest concentration is attained. However, the sharper peak at higher potentials is affected even at the lower anion concentration. Since mass transport limitations allow to discard the anion adsorption as the main process giving this peak, we propose that the two processes are due to the dissociative adsorption of two different kinds of water, that are affected by the anion in a different way. From this idea, a new model, based on the Frumkin adsorption isotherm, is proposed, which gives an excellent fit of the experimental results.

Langmuir, Feb 27, 2008

Classical electroanalytical techniques and in situ FTIR are used to study the oxidative chemisorp... more Classical electroanalytical techniques and in situ FTIR are used to study the oxidative chemisorption of catechol (o-H 2 Q) and the hydrogen-assisted reductive desorption of catechol-derived adlayers (o-Q (ads)) at nearly defect-free Pt(111) single-crystal electrodes in 0.5 M H 2 SO 4. At near equilibrium conditions (lim υf0) the cyclic voltammetric response does not conform to the behavior expected from classical models of molecular adsorption at electrochemical interfaces. Instead, attractive interactions play a controlling role, i.e., hydrogen-assisted displacement of o-Q (ads) takes place as an electrochemically reversible two-dimensional (2D) phase transition controlled by collision-nucleationgrowth phenomena in the presence of 2 mM o-H 2 Q (aq). In contrast, different desorption dynamics are observed when the reductive desorption of the adlayers is carried out in clean (0 mM o-H 2 Q (aq)) supporting electrolyte. Donoracceptor (DA) interactions between the Pt(111)/o-Q (ads) surface adduct and o-H 2 Q (aq) are postulated as a possible intervening mechanism leading to the observed differences in the macroscopic electrochemical responses. The results also demonstrate that in aqueous solutions it is thermodynamically feasible to shift the formal oxidation potential of catechol-metal adducts to potentials near those of molecular hydrogen via chemically reversible, nondissociative interactions, taking place as a 2D phase transition.

Surface Science, 2008

Ethylene adsorption and oxidation on platinum electrodes have been investigated in acidic solutio... more Ethylene adsorption and oxidation on platinum electrodes have been investigated in acidic solution by means of cyclic voltammetry and in situ infrared spectroscopy. Ethylene oxidation is a surface structure-sensitive reaction being Pt(1 1 1) the only active electrode surface at potentials below surface oxidation. In situ infrared reflection absorption spectroscopy (IRRAS) allows to identify the products formed during the adsorption and oxidation of ethylene. Vinylidene species were detected as oxidized adsorbates coming from ethylene and the only oxygen-containing species observed were on-top adsorbed CO and dissolved CO 2 that is the final oxidation product. A potential dependent equilibrium for transformation between two different adsorption configurations of adsorbed vinylidene, l 3-g 2-C@CH 2 and l-C@CH 2 , has been observed.

Energy and Environmental Science, 2011

Physical Chemistry Chemical Physics, 2009

Ethanol oxidation has been studied on stepped platinum single crystal electrodes in acid media us... more Ethanol oxidation has been studied on stepped platinum single crystal electrodes in acid media using electrochemical and Fourier transform infrared (FTIR) techniques. The electrodes used belong to two different series of stepped surfaces: those having (111) terraces with (100) monoatomic steps and those with (111) terraces with (110) monoatomic steps. The behaviors of the two series of stepped surfaces for the oxidation of ethanol are very different. On the one hand, the presence of (100) steps on the (111) terraces provides no significant enhancement of the activity of the surfaces. On the other hand, (110) steps have a double effect on the ethanol oxidation reaction. At potentials below 0.7 V, the step catalyzes the C-C bond cleavage and also the oxidation of the adsorbed CO species formed. At higher potentials, the step is not only able to break the C-C bond, but also to catalyze the oxidation of ethanol to acetic acid and acetaldehyde. The highest catalytic activity from voltammetry for ethanol oxidation was obtained with the Pt(554) electrode.

Electrochimica Acta, Sep 1, 2015

Rh modified Au(111-25 nm) electrodes, prepared by electron beam evaporation and galvanostatic dep... more Rh modified Au(111-25 nm) electrodes, prepared by electron beam evaporation and galvanostatic deposition, were employed to study adsorption and electro-oxidation of CO This is a previous version of the article published by Elsevier in

Surface Science, Dec 1, 2004

The formation of submonolayers of palladium on well-defined Pt(1 0 0) electrodes is described. It... more The formation of submonolayers of palladium on well-defined Pt(1 0 0) electrodes is described. It has been found that the adsorption of NO at open circuit and its further reductive stripping enable the possibility to prepare Pt(1 0 0) electrodes fully covered by the first palladium layer, without contributions coming from palladium in the subsequent layers. This method enables a better characterization of the palladium islands formed in the submonolayer range. The CO displacement method points out that hydrogen and anion adsorption play a role in the charge transfer processes involved in the voltammetric profile. The analysis of the charge-potential curves is used to determine the values of the potentials of zero total charge (pztc) of the different adelectrodes. The pztc diminishes almost linearly with palladium coverage, this shift being related to increasing anion adsorption at low potentials. Adsorbed palladium does not electrocatalyze the oxidation of adsorbed CO.

Physical Chemistry Chemical Physics, 2011

The adsorption of CO on low index copper single crystals in electrochemical environments has been... more The adsorption of CO on low index copper single crystals in electrochemical environments has been investigated. The results, analysed through a combination of in situ infrared spectroscopy, DFT and cyclic voltammetry, reveal a unique adsorption behaviour when compared to previous studies on copper and the more widely studied noble metal surfaces. By employing small, weakly specifically adsorbed electrolytes, it is shown that carbon monoxide is adsorbed over a much wider electrode potential range than previously reported. The electrochemical Stark shift (δν/δE) observed is similar for the three Cu(hkl) surfaces examined despite different surface coverages. Most notably, however, is an electrochemical feature observed at ca. -1.0 V (vs. Ag/AgCl) on the (110) surface. It is proposed that this voltammetric feature arises from the reduction/oxidation of Cu(δ+) surface sites involved in the binding of carbon monoxide with the participation of the electrolyte anion. This provides additional specific sites for CO adsorption. DFT calculations support the proposed presence of low-coordination copper sites stabilised by electrolyte anions. An experimental electron transfer rate constant of 4.2 s(-1) to the Cu(δ+) surface sites formed was found. These new observations concerning the surface electrochemistry of CO on Cu indicate that the electrocatalytic behaviour of Cu electrodes in processes such as CO(2) reduction need to be re-evaluated to take account of the rich adsorption behaviour of CO, including the co-adsorption of the electrolyte anion to these sites.

Angewandte Chemie, Jun 16, 2008

Langmuir, Apr 21, 2007

The interaction between bacterial cells of Pseudomonas fluorescens (ATCC 17552) and gold electrod... more The interaction between bacterial cells of Pseudomonas fluorescens (ATCC 17552) and gold electrodes was analyzed by cyclic voltammetry (CV) and attenuated total reflection-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The voltammetric evaluation of cell adsorption showed a decrease in the double-layer capacitance of polyoriented single-crystal gold electrodes with cell adhesion. As followed by IR spectroscopy in the ATR configuration, the adsorption of bacterial cells onto thin-film gold electrodes was mainly indicated by the increase in intensity with time of amide I and amide II protein-related bands at 1664 and 1549 cm-1 , respectively. Bands at 1448 and 2900 cm-1 corresponding to the scissoring and the stretching bands of CH 2 were also detected, together with a minor peak at 1407 cm-1 due to the V s COOstretching. Weak signals at 1237 cm-1 were due to amide III, and a broad band between 1100 and 1200 cm-1 indicated the presence of alcohol groups. Bacteria were found to displace water molecules and anions coadsorbed on the surface in order to interact with the electrode intimately. This fact was evidenced in the SEIRAS spectra by the negative features appearing at 3450 and 3575 cm-1 , corresponding to interfacial water directly interacting with the electrode and water associated with chloride ions adsorbed on the electrode, respectively. Experiments in deuterated water confirmed these assignments and allowed a better estimation of amide absorption bands. In CV experiments, an oxidation process was observed at potentials higher than 0.4 V that was dependent on the exposure time of electrodes in concentrated bacterial suspensions. Adsorbed bacterial cells were found to get closer to the gold surface during oxidation, as indicated by the concomitant increment in the main IR bacterial signals including amide I, a sharp band at 1240 cm-1 , and a broad one at 1120 cm-1 related to phosphate groups in the bacterial membranes. It is proposed to be due to the oxidation of lipopolysaccharides on the outermost bacterial surface.

Journal of Electroanalytical Chemistry, Feb 1, 2004

Oxalic acid adsorption and oxidation processes have been studied at platinum single crystal elect... more Oxalic acid adsorption and oxidation processes have been studied at platinum single crystal electrodes with basal orientations. Cyclic voltammetry and charge displacement experiments have been combined with in situ external reflection infrared experiments for the study of oxalic acid adsorption at potentials below 0.70 V. Whereas reversible anion-like adsorption is observed for Pt(100) and Pt(111) electrodes, oxalic acid is reduced at Pt(110) leading to the formation of an irreversibly bonded adsorbate which has been identified as adsorbed CO from the infrared spectra. Spectroscopic data confirm the potential dependent behaviour of oxalic acid adsorption on Pt(111) and Pt(100) electrodes derived from electrochemical data. At the same time, the infrared spectra show distinct CO stretching bands for adsorbates on Pt(100) and P(111). In acidic solutions (pH ¼ 1), for which oxalic acid and bioxalate anions predominate as solution species, oxalate anions are adsorbed at the Pt(100) electrode surface whereas bioxalate anions seem to be the adsorbed species at Pt(111). In neutral solutions, oxalate anions are adsorbed on both Pt(111) and Pt(100) surfaces. No intermediates coming from oxalic acid other than adsorbed CO for Pt(110) and adsorbed (bi)oxalate anions for Pt(111) and Pt(100) are detected during the oxidation of oxalic acid. Adsorbate bands are observed between 1400 and 1600 cm À1 for the Pt(111) electrode for potentials between 0.85 and 1.0 V. These bands are related to adsorbed carbonate anions formed in the presence of carbon dioxide molecules generated from oxalic acid oxidation.

Chemsuschem, Jan 3, 2017

We have explored a new concept in bacteria‐electrode interaction based on the use of fluid‐like e... more We have explored a new concept in bacteria‐electrode interaction based on the use of fluid‐like electrodes and planktonic living cells. We show for the first time that living in a biofilm is not a strict requirement for Geobacter sulfurreducens to exchange electrons with an electrode. The growth of planktonic electroactive G. sulfurreducens could be supported by a fluid‐like anode as soluble electron acceptors and with electron transfer rates similar to those reported for electroactive biofilms. This growth was maintained by uncoupling the charge (catabolism) and discharge (extracellular respiration) processes of the cells. Our results reveal a novel method to culture electroactive bacteria in which every single cell in the medium could be instantaneously wired to a fluid‐like electrode. Direct extracellular electron transfer is occurring but with a new paradigm behind the bacteria–electrode interaction.

Energies, Nov 19, 2015

Microbial electrochemical technologies (METs) have a number of potential technological applicatio... more Microbial electrochemical technologies (METs) have a number of potential technological applications. In this work, we report the use of screen-printed electrodes (SPEs) as a tool to analyze the microbial electroactivity by using Geobacter sulfurreducens as a model microorganism. We took advantage of the small volume required for the assays (75 µL) and the disposable nature of the manufactured strips to explore short-term responses of microbial extracellular electron transfer to conductive materials under different scenarios. The system proved to be robust for identifying the bioelectrochemical response, while avoiding complex electrochemical setups, not available in standard biotechnology laboratories. We successfully validated the system for characterizing the response of Geobacter sulfurreducens in different physiological states (exponential phase, stationary phase, and steady state under continuous culture conditions) revealing different electron transfer responses. Moreover, a combination of SPE and G. sulfurreducens resulted to be a promising biosensor for quantifying the levels of acetate, as well as for performing studies in real wastewater. In addition, the potential of the technology for identifying electroactive consortia was tested, as an example, with a mixed population with nitrate-reducing capacity. We therefore present SPEs as a novel low-cost platform for assessing microbial electrochemical activity at the microscale level.