H2/O2 Biofuel cells : nanostructuration of the electrochemical interface for the immobilisation of redox enzymes

Dans la nature, la réduction de l'oxygène et l'oxydation de l'hydrogène sont catalysées par des enzymes oxydoréductases. Ces catalyseurs spécifiques, efficaces, renouvelables et biodégradables constituent une alternative séduisante au platine dans les piles à combustible. L'immobilisation à des interfaces nanostructurées de l'hydrogénase membranaire tolérante à l'oxygène de la bactérie hyperthermophile Aquifex aeolicus, et de la bilirubine oxydase thermostable de la bactérie Bacillus pumilus, a été étudiée dans ce sens.L'électrochimie et la dynamique moléculaire ont permis d'affiner le modèle d'orientation de l'hydrogénase sur les surfaces planes. L'efficacité de l'immobilisation de l'hydrogénase sur différents nanomatériaux carbonés (nano-particules, tubes et fibres de carbone) structurant la surface de l'électrode a été évaluée. Les nanofibres de carbone (CNFs) ont permis de former une bioanode efficace pour l'oxydation de l'H2 en l'absence de médiateurs redox. L'étude a souligné l'importance d'un transport efficace du substrat dans le film carboné mésoporeux. Les CNFs ont également été utilisées comme matériau d'électrode pour réaliser la 1ère connexion directe de la bilirubine oxydase. L'existence d'une forme resting alternative de l'enzyme, influencée par les ions chlorures, le pH et la température, a été mise en évidence. Une biocathode efficace pour la réduction de l'oxygène a été développée.Les deux électrodes thermostables ont permis le développement de la 1ère biopile H2/O2 qui délivre des densités de puissance supérieures au mW.cm-2 sur une large gamme de température. Ce résultat ouvre la voie à l'alimentation électrique de dispositifs de faibles puissances.The oxygen reduction and the hydrogen oxidation reactions are realized in nature by oxidoreductase enzymes. These highly efficient, specific, renewable and biodegradable catalysts appear as a seducing alternative to platinum in fuel cell devices. The immobilization at nanostructured interfaces of the membrane-bound oxygen-tolerant hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus, and of the thermostable bilirubin oxidase from Bacillus pumilus, has been studied within this objective.Electrochemistry and molecular dynamics have been used to validate the orientation model of the hydrogenase at planar electrodes. Hydrogenase immobilisation in 3D-networks based on various carbon materials (nanoparticles, nanotubes and nanofibers) has been especially studied. Fishbone carbon nanofibers were demonstrated to provide an efficient platform for mediatorless H2 oxidation. Mass transport inside the carbon mesoporous film has been especially studied and demonstrated to be one of the limitations of the catalytic efficiency. Direct electrical connection of bilirubin oxidase has also been realized for the first time thanks to its immobilization on carbon nanofiber films. An alternative resting form of the enzyme, influenced by chlorides, pH and temperature, has been evidenced. An efficient biocathode for the oxygen reduction reaction has been developed. Thanks to the two thermostable electrodes, the first H2-O2 bio fuel cell able to deliver power densities over 1 mW.cm-2 over a large temperature range has been developed. This result paves the way for the electrical alimentation of low-power devices

O2 Reduction in Enzymatic Biofuel Cells

International audienceCatalytic four-electron reduction of O2 to water is one of the most extensively studied electrochemical reactions due to O2 exceptional availability and high O2/H2O redox potential, which may in particular allow highly energetic reactions in fuel cells. To circumvent the use of expensive and inefficient Pt catalysts, multicopper oxidases (MCOs) have been envisioned because they provide efficient O2 reduction with almost no overpotential. MCOs have been used to elaborate enzymatic biofuel cells (EBFCs), a subclass of fuel cells in which enzymes replace the conventional catalysts. A glucose/O2 EBFC, with a glucose oxidizing anode and a O2 reducing MCO cathode, could become the in vivo source of electricity that would power sometimes in the future integrated medical devices. This review covers the challenges and advances in the electrochemistry of MCOs and their use in EBFCs with a particular emphasis on the last 6 years. First basic features of MCOs and EBFCs are presented. Clues provided by electrochemistry to understand these enzymes and how they behave once connected at electrodes are described. Progresses realized in the development of efficient biocathodes for O2 reduction relying both on direct and mediated electron transfer mechanism are then discussed. Some implementations in EBFCs are finally presented

Electrode Nanopatterning for Bioelectroanalysis and Bioelectrocatalysis

Although intensive research in the bioelectroanalysis domain in the last twenty years led to great improvements in protein-based electrode and device performances, their large application remains limited by their stability overtime under operational and resting conditions. One under-studied issue is the role played by the spatial distribution of enzymes on electrocatalysis. Actually, high fluxes in metabolic pathways involve compartmentalization and spatial organization of active biomolecules. In a mimicking way, it can be expected that controlled localization of proteins on electrode surfaces may play a role in the overall electron transfer processes and bioelectrocatalysis performances. In this short review, we will discuss recent developments in surface patterning allowing to tune in a controlled manner the localization and density of enzymes on the electrode surface. We will investigate how mixed functional layers, electrode and biological materials can serve as protein platforms to provide such electrode patterning

Wireless Electronic Light Emission: An Introduction to Bipolar Electrochemistry

International audienceElectrochemistry is taught in most undergraduate chemistry programs. Although this topic is important for students due to its broad interest in industry (energy, diagnostics, car industry, etc.), they often find it difficult, because it is based on a combination of various physical concepts such as electric fields, interfacial processes or charge and mass transports. Among electrochemical concepts, bipolar electrochemistry is of special interest and might be easier to teach due to a very simple general setup. In this case, an oxidation and a reduction reactions occur at the two ends of a single conductive object exposed to an electric field in solution. Such an object is therefore called a bipolar electrode. The nature of the electrochemical reactions and their amplitude can be tuned by playing with the electric field. The fundamental concepts of bipolar electrochemistry are introduced here with a series of basic experiments designed to be carried out in a standard teaching laboratory. These simple and affordable experiments illustrate the key-parameters driving electrochemical reactions at a bipolar electrode. Their influence can be readily visualized using a cheap, commercially available light emitting diode (LED) acting as the bipolar electrode, which illuminates when the current generated by the electrochemical reactions flows through it. The concept of bipolar electrochemistry with eye-catching experiments enables a good introduction to genera

High electrolyte concentration effect on enzymatic oxygen reduction

International audienceThe nature, the composition and the concentration of electrolytes is essential for electrocatalysis involving redox enzymes. Here, we discuss the effect of various electrolyte compositions with increasing ionic strengths on the stability and activity towards O2 reduction of the bilirubin oxidase from Myrothecium verrucaria (Mv BOD). Different salts, Na2SO4, (NH4)2SO4, NaCl, NaClO4, added to a phosphate buffer (PB) were evaluated with concentrations ranging from 100 mM up to 1.7 M. On functionalized carbon nanotube-modified electrodes, it was shown that the catalytic current progressively decreased with increasing salt concentrations. The process was reversible suggesting it was not related to enzyme leakage. The enzyme was then immobilized on gold electrodes modified by self-assembling of thiols. When the enzyme was simply adsorbed, the catalytic current decreased in a reversible way, thus behaving similarly as on carbon nanotubes. Enzyme mobility at the interface induced by a modification in the interactions between the protein and the electrode upon salt addition may account for this behavior. When the enzyme was covalently attached, the catalytic current increased. Enzyme compaction is proposed to be at the origin of such catalytic current increase because of shorter distances between the first copper site electron acceptor and the electrode

Molecular Modeling of Hydrogenase Enzymes for Biofuel Cell Design

International audienc

From Enzyme Stability to Enzymatic Bioelectrode Stabilization Processes

International audienceBioelectrocatalysis using redox enzymes appears as a sustainable way for biosensing, electricity production, or biosynthesis of fine products. Despite advances in the knowledge of parameters that drive the efficiency of enzymatic electrocatalysis, the weak stability of bioelectrodes prevents large scale development of bioelectrocatalysis. In this review, starting from the understanding of the parameters that drive protein instability, we will discuss the main strategies available to improve all enzyme stability, including use of chemicals, protein engineering and immobilization. Considering in a second step the additional requirements for use of redox enzymes, we will evaluate how far these general strategies can be applied to bioelectrocatalysis

A snapshot of the electrochemical reaction layer by using 3 dimensionally resolved fluorescence mapping

The coupling between electrochemistry and fluorescence confocal laser scanning microscopy (FCLSM)allows deciphering the electrochemical and/or redox reactivity of electroactive fluorophores. This isdemonstrated with phenoxazine electrofluorogenic species frequently used in bioassays by mapping thevariation of fluorescence intensity with respect to the distance from the electrode. The electrochemicalconversion of resorufin dye (RF) to non-fluorescent dihydroresorufin (DH) leads to a sharp decrease ofthe fluorescence signal in the vicinity of the electrode. In contrast, the direct reduction of resazurin (RZ)to DH leads to an unexpected maximum fluorescence intensity localized further away from the surface.This observation indicates that the initial electron transfer (heterogeneous) is followed by a chemicalcomproportionation step (homogeneous), leading to the formation of RF within the diffusion layer witha characteristic concentration profile. Therefore, in situ FCLSM affords a direct way to monitor suchchemical reactivity in space and to decipher a new redox pathway that cannot be resolved solely byelectrochemical means.SCOPUS: ar.jinfo:eu-repo/semantics/publishe