Antonio Berná

C-Type Cytochromes Wire Electricity-Producing Bacteria to Electrodes†

Fil: Busalmen, Juan Pablo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina

Surface structure effects on the electrochemical oxidation of ethanol on platinum single crystal electrodes

Ethanol oxidation has been studied on Pt(111), Pt(100) and Pt(110) electrodes in order to investigate the effect of the surface structure and adsorbing anions using electrochemical and FTIR techniques. The results indicate that the surface structure and anion adsorption affect significantly the reactivity of the electrode. Thus, the main product of the oxidation of ethanol on the Pt(111) electrode is acetic acid, and acetaldehyde is formed as secondary product. Moreover, the amount of CO formed is very small, and probably associated with the defects present on the electrode surface. For that reason, the amount of CO2 is also small. This electrode has the highest catalytic activity for the formation of acetic acid in perchloric acid. However, the formation of acetic acid is inhibited by the presence of specifically adsorbed anions, such as (bi)sulfate or acetate, which is the result of the formation of acetic acid. On the other hand, CO is readily formed at low potentials on the Pt(100) electrode, blocking completely the surface. Between 0.65 and 0.80 V, the CO layer is oxidized and the production of acetaldehyde and acetic acid is detected. The Pt(110) electrode displays the highest catalytic activity for the splitting of the C-C bond. Reactions giving rise to CO formation, from either ethanol or acetaldehyde, occur at high rate at any potential. On the other hand, the oxidation of acetaldehyde to acetic acid has probably the lower reaction rate of the three basal planes.

The role of the steps in the cleavage of the C–C bond during ethanol oxidation on platinum electrodes

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.

ATR-SEIRAs characterization of surface redox processes in G. sulfurreducens.

In this work we report on the occurrence of at least two different redox pairs on the cell surface of the electrogenic bacteria Geobacter sulfurreducens adsorbed on gold that are expressed in response to the polarization potential. As previously reported on graphite (Environ. Sci. Technol. 42 (2008) 2445) a typical low potential redox pair is found centered at around -0.06 V when cells are polarized for a few hours at 0.2 V, while a new pair centered at around 0.38 V is expressed upon polarization at 0.6 V. Reversible changes in the IR band pattern of whole cells where obtained by Attenuated Total Reflection-Surface Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS) upon potential cycling around both redox pairs. Changes clearly resemble the electrochemical turnover of oxidized/reduced states in c-type cytochromes, thus evidencing the nature of the involved molecules. 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.

Silica Colloid Formation Enhances Performance of Sediment Microbial Fuel Cells in a Low Conductivity Soil

The performance of sediment microbial fuel cells (SMFCs) is usually limited by the structure, moisture, and salt content of the soil where they are allocated. Despite the influence of soil, so far most of efforts to improve SMFCs have been limited to the hardware design of the bioelectrochemical device. Our main objective was to enhance performance of SMFCs by stimulating the in situ formation of silica colloids in a low conductivity rice paddy soil. Our results have revealed that the presence of a silica colloid network, described by cryo-SEM analysis, reduced soil resistivity, enhanced ion mobility and consequently enhanced the power production by a factor of 10. Furthermore, our silica-supplemented soil showed better utilization of the electron donor, either acetate or natural rice root exudates, by electrogenic microbial populations. Sustainable manipulation of soil micromorphology using environmentally friendly reagents such as silica offers a novel approach for enhancing the performance of in situ microbial electrochemical applications in low conductivity soils, thus silica colloid geoengineering should be considered as part of future applications of SMFCs.

Opportunities behind the unusual ability of geobacter sulfurreducens for exocellular respiration and electricity production

The possibility to improve the connection of cells to the electrode is significant for microbial fuel cell technology. In this communication we demonstrate that an improved connection can be made by controlling the physiological state of electricity-harvesting bacteria as Geobacter sulfurreducens.

Role of axially coordinated surface sites for electrochemically controlled carbon monoxide adsorption on single crystal copper electrodes

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.

The Planktonic Relationship Between Fluid-Like Electrodes and Bacteria: Wiring in Motion

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.

Model system for the study of 2D phase transitions and supramolecular interactions at electrified interfaces: hydrogen-assisted reductive desorption of catechol-derived adlayers from Pt(111) single-crystal electrodes.

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(upsilon-->0)) 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-nucleation-growth 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. Donor-acceptor (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.

Chapter 1 – In-situ FTIR Studies on the Acid–Base Equilibria of Adsorbed Species on Well-Defined Metal Electrode Surfaces

Publisher Summary This chapter illustrates the in-situ Fourier transform infrared spectroscopy (FTIR) studies on the acid–base equilibria of adsorbed species on well-defined metal electrode surfaces. Infrared spectroscopy is one of the most useful techniques mainly used for the in-situ characterization of interfaces at a molecular level. The infrared window is used as the substrate for the deposition of a thin metal film which acts as the working electrode. Adsorbates on metallic thin film electrodes exhibit enhanced infrared absorption. The external reflection configuration can be used to study the structural aspects of the adsorption processes. It can also be used to probe the reflecting surface of any bulk electrode material. The specific adsorption of anions plays a pivotal role in the understanding of electrochemical reactions. In-situ infrared spectroscopy has been used in an external reflection configuration. Cyclic voltammetry and in-situ infrared experiments were performed in perchloric acid solutions in the presence of carbon dioxide. The role of surface site distribution on the surface acid–base equilibria of oxalic acid are explored for the platinum electrodes.