Membrane electrochemical reactors (MER) for NADH regeneration in HLADH-catalysed synthesis: comparison of effectiveness

Two membrane electrochemical reactors(MER) were designed and applied to HLADH-catalysed reduction of cyclohexanone to cyclohexanol. The regeneration of the cofactor NADH was ensured electrochemically, using either methyl viologen or a rhodium complex as electrochemical mediator. A semipermeable membrane (dialysis or ultra-filtration) was integrated in the filter-press electrochemical reactor to confine the enzyme(s) as close as possible to the electrode surface. When methyl viologen was used, the transformation ratio of cyclohexanone varied from 0 to 65% depending on the internal arrangement of the reactor. Matching the reactor configuration to the reaction system was essential in this case. With the rhodium complex, the ultra-filtration MER was tested in continuous and recycling configurations. The best conditions led to 100% transformation of 0.1 L volume of 0.1 M cyclohexanone after 70 h with the recycling mode. Finally, the performances of the reactors are discussed with respect to different evaluations of the production yields

Electrochemical Reactivity at Free and Supported Gold Nanocatalysts Surface

This chapter presents an overview on size, structure, morphology, composition as well as the effect of the support on the electrocatalytic properties of gold nanoparticles (AuNPs). It was found that the electrocatalytic properties of unsupported AuNPs strongly depend on their size and shape. Consequently, the electrocatalytic properties of AuNPs can be tuned. Furthermore, to design high-performance electrocatalysts with minimal precious metal content and cost, the direct immobilization of metal NPs onto carbon-based substrates during their synthesis constitutes another elegant alternative and has been thoroughly examined. These “easy-to-use” supports as scaffolds for AuNPs, namely carbon black, carbon paper, etc., offer beneficial contributions. Indeed, thanks to their high available surface area, good electronic conductivity and synergistic effect between the chemical species present on their surface and the loaded NPs, carbon-based supports enable maximizing the efficient utilization of the catalysts toward drastic enhancement in both activity and durability. We also examined different judicious combinations of (electro)analytical techniques for the unambiguous determination of the reaction product(s) over the Au-based nanocatalysts, using glucose as model molecule given its importance in electrocatalysis. The performances of carbon-supported AuNPs as anode materials in direct glucose fuel cell in alkaline medium were also discussed

Préparation et caractérisation de nanoparticules à base d'or et de platine pour l'anode d'une biopile glucose-dioxygène

Les biopiles représentent une solution attractive et ambitieuse dans le développement des systèmes alternatifs de conversion d'énergie. Nous proposons de substituer la bioanode d'une pile glucose/O2 par un catalyseur abiotique constitué de nanomatériaux synthétisés à partir de la méthode w/o microemulsion . Une caractérisation physico-chimique de ces matériaux bimétalliques a permis de déterminer leur taille et de mettre en évidence leurs propriétés électroniques, les défauts cristallins en leur sein, les déformations dont ils font l'objet, leur composition de surface et leur caractère allié. Lors de l'étude de l'électrooxydation du glucose sur les nanostructures Au-Pt, le matériau bimétallique (Au70Pt30) a montré les meilleures performances catalytiques et ce, en raison d'un effet de synergie entre l'or et le platine, d'une modification des niveaux d'énergie de la bande de valence du platine et par la présence de défauts cristallins modifiant la surface catalytique. Le développement de bioélectrodes à base de GOD ou BOD a également été réalisé, soit par immobilisation dans une matrice de polymère, soit par greffage covalent. Les électrodes préparées ont permis de réaliser des tests en pile dans un système innovant, concentrique et sans membrane séparatrice. Une puissance de 42 W.cm-2 a été obtenue dans une biopile totalement enzymatique en présence de 10 mM de glucose. La substitution de la bioanode par un nanocatalyseur abiotique Au70Pt30 permet à la biopile de délivrer une densité de puisssance de 90 W.cm-2. Une augmentation de la concentration du combustible glucose (0,7 M) accroît ses performances électriques à 190 W.cm-2 pour une tension de cellule de 0,5 V.Biofuel cells represent an alternative and ambitious solution for the development of alternative power sources. In this study we propose to replace the bioanode of glucose/O2 biofuel cell by an abiotic nanocatalyst composed of gold and platinum nanoparticles synthesized by water-in-oil microemulsion method. A deep physico-chemical characterization of bimetallic materials allowed to determine their size and to bring to light their electronic properties, their surface composition, their alloyed properties, and both crystalline defects and strains in their structure. Glucose electrooxidation on Au70Pt30 nanocatalyst in physiological media, showed the best catalytic performances probably due to a synergistic effect between gold and platinum, a shift of the dband center of platinum, and the presence of numerous defects affecting the active surface of the catalyst. During this work, the development of glucose oxidase or bilirubin oxidase based bioelectrodes was also realized either by the enzyme entrapment in a polymeric matrix or by covalent grafting. The prepared bioelectrodes were tested in a novel and membrane-less cell which has a concentric design. A power density of 42 W cm-2 was delivered in the presence of 10 mM glucose. Under the same conditions, the replacement of the bioanode by an abiotic nanocatalyst (Au70Pt30) allowed to obtain a power density of 90 W cm-2. An increase of glucose concentration (0.7 M) leads to the rise of electrical performances of the biofuel cell which reach a power density of 190 W cm-2 for a cell voltage of 0.5 V.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Selective Nanomaterials for Glucose-to-Gluconate Oxidation in an Electrochemical Energy Converter: Cogenerating Organic Electrosynthesis

International audienceThe design of cogeneration devices is of paramount importance to cut down the overall utilization cost. For instance, the heat resulting from the operation of electrochemical technologies such as fuel cells can be concomitantly harvested and used in addition to the produced renewable, affordable, and relatively clean energy. There is another elegant alternative, which uses an organic molecule as a fuel for a simultaneous chemicals production from the selective operation at the anode material. Within this proceeding, we contribute by synthesizing nanomaterials to design and fabricate effective electrodes capable of a selective glucose-to-gluconate oxidation within an electrochemical energy converter, towards the ultimate goal of cogenerating organic electrosynthesis. Complementary methods of physical and (electro)analytical chemistry were integrated to interrogate the mysterious workings of anodic electrocatalysts. These interdisciplinary and preliminary results encourage researchers among the triple community of electrochemistry/electrocatalysis, material science and organic chemistry to move forward together

Probing the Surface of Noble Metals Electrochemically by Underpotential Deposition of Transition Metals

International audienceThe advances in material science have led to the development of novel and various materials as nanoparticles or thin films. Underpotential deposition (upd) of transition metals appears to be a very sensitive method for probing the surfaces of noble metals, which is a parameter that has an important effect on the activity in heterogeneous catalysis. Underpotential deposition as a surface characterization tool permits researchers to precisely determine the crystallographic orientations of nanoparticles or the real surface area of various surfaces. Among all the work dealing with upd, this review focuses specifically on the main upd systems used to probe surfaces of noble metals in electrocatalysis, from poly‒ and single-crystalline surfaces to nanoparticles. Cuupd is reported as a tool to determine the active surface area of gold‒ and platinum‒based bimetallic electrode materials. Pbupd is the most used system to assess the crystallographic orientations on nanoparticles’ surface. In the case of platinum, Bi and Ge adsorptions are singled out for probing (1 1 1) and (1 0 0) facets, respectively

Electrochemical Oxidation of Carbon Monoxide on Unsupported Gold Nanospheres in Alkaline Medium

International audienceCarbon monoxide (CO) is intensively studied as a model molecule for organics oxidation reaction or as a strong adsorbate on noble metal surfaces. In this work, quasi-spherical gold nanoparticles (AuNPs) prepared by a revisited Turkevich method were electrochemically characterized. Physical and electrochemical measurements demonstrated the presence of (111) and (110) facets. These unsupported NPs were used to study the effect of the upper potential limit and gold oxide formation on CO oxidation in alkaline medium. The results demonstrate that hydroxide species are crucial to oxidize CO, whereas the gold oxides species do not play a critical role

Electrochemical Energy Conversion from Direct Oxidation of Glucose on Active Electrode Materials

International audienceElectrochemical behavior of carbon supported platinum and gold-based catalysts towards glucose oxidation and oxygen reduction reaction were investigated separately in alkaline medium before implementing the glucose/O2 fuel cell with the best anode and cathode catalysts. These electrode materials, prepared from a surfactant-free synthesis approach, were then used in low metal loadings in a fuel cell operating in alkaline medium which can be easily removed on resin for analyzing all the reaction products, as any toxic compound has to be avoided for the interest of this specific application. Pt/rGO is the most active anode towards the glucose oxidation. For all tested catalysts, this oxidation reaction leads mainly to gluconate without chromatographically detectable reaction products resulted from CC bond cleavage

Synthèse et caractérisation de matériaux électrocatalytiques pour l'activation de la molécule d'eau (application dans une anode d'électrolyseur de type PEM)

Le stockage et la conversion d'énergie sont un défi scientifique majeur qui nécessite le développement de systèmes propres comme les piles à combustible. La production d'un combustible comme l'hydrogène par l'électrolyse de l'eau nécessite le développement de matériaux d'anode performants et efficaces pour diminuer les fortes surtensions observées et surtout les coûts liés à cette technologie. Ainsi des nanomatériaux d'anode à base d'oxydes de ruthénium, d'iridium et/ou d'un troisième métal non noble ont été synthétisés par deux méthodes qui sont, la méthode Pechini-Adams et la méthode polyol. Les caractérisations physico-chimiques prouvent l'existence d'oxydes métalliques et de grande surface spécifique, puis confirment la morphologie nanométrique et hétérogène des matériaux. Parmi les différentes compositions de nanomatériaux bimétalliques RuxIr1-xO2 synthétisées et étudiées, celle contenant x = 0,9 présente une bonne activité électrocatalytique pour l activation de la réaction d'oxydation de l eau. L'ajout d'un troisième métal comme le tantale, le titane, le niobium et l'étain a été bénéfique et montre que l'activité électrocatalytique peut être améliorée en diminuant la teneur en Ru et/ou en Ir. Ces nanomatériaux ont été optimisés et utilisés dans des électrolyseurs type PEM de 5 cm2 et de 25 cm2 de surface pour des tests de longue durée de plus de 1200 heures.The development of clean energy systems as fuel cells is one of the main challenges in the energy conversion and storage. The production of fuels as hydrogen by water electrolysis requires the development of efficient anode materials in order to decrease the high overpotential observed and the cost related to this technology. Anode oxide materials based on Ru, Ir and/or a third non noble metal are synthesized by Pechini-Adams and Polyol methods. The physico-chemical characterizations have confirmed the formation of oxide structure and their high specific surface area. Among the different compositions of bimetallic RuxIr1-xO2 materials studied, the sample Ru0.9Ir0.1 has presented the highest electrocatalytic activity with a long-term durability. The addition of the oxide of a third metal such as tantalum, titanium, tin and niobium has permitted to decrease the Ru and Ir contents but also to enhance the performance of the bimetallic electrocatalysts. The anode electrocatalysts synthesized to promote the water oxidation reaction were optimized and used for long-term durability tests in single 5 and 25 cm2 PEM electrolyzer cells over 1200 hours.POITIERS-BU Sciences (861942102) / SudocSudocFranceF