Reductive dehalogenation of 1,3-dichloropropane by a [Ni(tetramethylcyclam)]Br2-Nafion modified electrode

International audienceDechlorination reaction of 1,3-dichloropropane, a contaminant solvent, was investigated by electrochemical reduction in aqueous medium using a Ni(tmc)Br2 complex, known as effective catalyst in dehalogenation reactions. The catalytic activity of the complex was first investigated by cyclic voltammetry and flow homogeneous redox catalysis using a graphite felt as working electrode. A total degradation of 1,3-dichloropropane was obtained after 5 h of electrolysis with a substrate/catalyst ratio of 2.3. The concentration of chloride ions determined by ion chromatography analysis showed a dechlorination yield of 98%. The complex was then immobilized on the graphite felt electrode in a Nafion® film. Flow heterogeneous catalytic reduction of 1,3-dichloropropane was then carried out with the [Ni(tmc)]Br2-modified Nafion® electrode. GC analyses underlined the total degradation of the substrate in only 3.5 h with a substrate/catalyst ratio of 100. A dechlorination yield of 80% was obtained, as seen with ion chromatography analyses of chloride ion. Comparison of both homogeneous and heterogeneous reactions highlighted the interest of the [Ni(tmc)]Br2-modified Nafion® electrode that led to a higher stability of the catalyst with a turnover number of 180 and a higher current efficiency

Direct electrochemical oxidation of a pesticide, 2,4-dichlorophenoxyacetic acid, at the surface of a graphite felt electrode: Biodegradability improvement

International audiencePesticides' biorecalcitrance can be related to the presence of a complex aromatic chains or of specific bonds, such as halogenated bonds, which are the most widespread. In order to treat this pollution at its source, namely in the case of highly concentrated solutions, selective processes, such as electrochemical processes, can appear especially relevant to avoid the possible generation of toxic degradation products and to improve biodegradability in view of a subsequent biological mineralization. 2,4-D was found to be electroactive in oxidation, but not in reduction, and the absence of hydroxyl radicals formation during the electrochemical step was demonstrated, showing that the pretreatment can be considered as a "direct" electrochemical process instead of an advanced electrochemical oxidation process. The presence of several degradation products in the oxidized effluent showed that the pretreatment was not as selective as expected. However, the relevance of the proposed combined process was confirmed since the overall mineralization yield was close to 93%

Combined process for 2,4-Dichlorophenoxyacetic acid treatment-Coupling of an electrochemical system with a biological treatment

International audienceA coupled process was studied for the removal of a chlorinated pesticide: 2,4-Dichlorophenoxyacetic acid (2,4-D). A home-made electrochemical flow cell was used for the pre-treatment and a biological treatment was then carried out using activated sludge supplied by a local wastewater treatment plant. 2,4-D was used as a target compound for the study. Several parameters were monitored during the biological treatment, like dissolved organic carbon (DOC), the target compound and the major by-product. Pretreatment led to a quick decrease of DOC during the biological process, since a 66% mineralization yield was measured after the second day, and 79% after the seventh day of culture. After two days of treatment, HPLC results revealed a total degradation of Chlorohydroquinone, the major by-product. The electrochemical pretreatment shortened the length of the biological treatment, since DOC measurements showed that in the case of non-pretreated 2,4-D, no mineralization was observed before day 7. These promising results should be subsequently confirmed on commercial 2,4-D-containing solutions and then on real effluents

Combined electrochemical treatment/biological process for the removal of a commercial herbicide solution, U46D

International audienceThe removal of a commercial solution of 2,4-D, U46D , was carried out by coupling an electrochemical oxidation and a biological process involving activated sludge. The similar electrochemical behavior of 2,4-D and U46D highlighted their oxidation around 1.6 V/SCE and the feasibility of an electrochemical pretreatment. It was based on a home-made flow cell involving bare graphite felt electrode. To propose a consistent mechanism for 2,4-D oxidation, the indirect determination of OH has been performed and the absence of radicals formation during 2,4-D electrolysis was confirmed. Consequently, the proposed pretreatment can be considered as a 'direct' electrochemical process instead of an advanced electrochemical oxidation process. The impact of the flow rate on the pretreatment showed that 3 mL min 1 was a good compromise between the pretreatment time and the electrolysis efficiency, since it led to an almost total degradation of the pollutant while its mineralization remained limited. At this flow rate and for 500 mg L 1 of 2,4-D, the energy cost was estimated at 5 kWh m 3. The biodegradability of U46D solution was not significantly modified after electrolysis, most likely due to the presence of dimethylamine salt in U46D . Owing to the significant BOD5/COD ratio measured, a biological treatment of the commercial U46D solution was however considered. The electrochemical pretreatment shortened the duration of the biodegradation. For non-pretreated U46D (100 mg L 1 2,4-D), mineralization remained limited until 6 days of culture (33.7% DOC removal), and total removal of the DOC was observed after 8 days. For pretreated U46D , 63.7% decrease until the fifth day of culture was observed but total mineralization was not reached at the end of culture (72.1%). An overall mineralization yield during the coupled process of 82.1% was therefore reached. The presence of refractory compounds generated during the electrochemical pretreatment in small concentration was therefore show

How to go beyond C1 products with electrochemical reduction of CO2

The electrochemical reduction of CO2 to produce fuels and value-added organic chemicals is of great potential, providing a mechanism to convert and store renewable energy within a carbon-neutral energy circle. Currently the majority of studies report C1 products such as carbon monoxide and formate as the major CO2 reduction products. A particularly challenging goal within CO2 electrochemical reduction is the pursuit of multi-carbon (C2+) products which have been proposed to enable a more economically viable value chain. This review summaries recent development across electro-, photoelectro- and bioelectro-catalyst developments. It also explores the role of device design and operating conditions in enabling C–C bond generation

Low cost and efficient alloy electrocatalysts for CO2 reduction to formate

Oxide-derived (OD) Sn and Sn−Pb−Sb composite electrocatalysts were prepared by electrochemical oxidation treatment at various potentials for electrochemical reduction of CO2 (eCO2R) for formate (HCOO−) production. The morphology, elemental mapping, phase identification, surface characteristics and electrochemical performance of the electrocatalysts were probed systematically. The surface of OD-Sn and OD-Sn-Pb-Sb shows polycrystalline electrodes with porous morphology and XPS results confirm the formation of composite metal/metal oxide surface related to Sn, Pb and Sb. The EDX mapping analysis shows two distant regions of Pb and Sn rich areas in the alloy. The electrochemical results demonstrate that pristine Sn electrodes show higher CO2 Faradaic Efficiency (FE) to formate compared to pristine Sn-Pb-Sb alloy electrode (80% vs. 66%) at −1.4 V vs. RHE. Upon oxidation treatment of pristine Sn at 4 V, the FEHCOO− improves to 84% at the expense of decreased current density. On the contrary, upon oxidation treatment of Sn-Pb-Sb alloy at 5 V, the FEHCOO− improved remarkably from 68% to 91% without any reduction in current density. The improved eCO2R performance of OD-Sn and OD-Sn-Pb-Sb electrodes relative to their pristine electrodes could be attributed to the presence of composite metal/metal oxide structure which leads to local geometric and electronic structural changes

Influence of temperature and other system parameters on microbial fuel cell performance: numerical and experimental investigation

This study presents a steady state, two dimensional mathematical model of microbial fuel cells (MFCs) developed by coupling mass, charge and energy balance with the bioelectrochemical reactions. The model parameters are estimated and validated using experimental results obtained from ve aircathode MFCs operated at different temperatures. Model analysis correctly predicts the nonlinear performance trend of MFCs with temperatures ranging between 20 oC - 40 oC. The two dimensional distribution allows the computation of local current density and reaction rates in the biolm, helping to correctly capture the interdependence of system variables and predict the drop in power density at higher temperatures. Model applicability for parametric analysis and process optimization is further highlighted by studying the effect of electrode spacing and ionic strength on MFC performance

How anthraquinones can enable aqueous organic redox flow batteries to meet the needs of industrialization

International audienceOwing to the importance of storage and its hybridization with renewable energy technologies for the energy transition, a high attention has been paid towards the development of redox flow batteries. Among all different emerging technologies, aqueous organic redox flow batteries (AORFBs) are particularly attractive since the objectives in terms of sustainability, cost and safety issues can be achieved owing to the high possibilities offered by molecular engineering, organometallic and coordination chemistry. Thus, AORFBs based on anthraquinones paired with ferrocyanide in basic medium have been widely developed and are close to reach the performances required for industrial processes. This review aims to focus on the main parameters making possible the integration of anthraquinone derivatives as negolyte in AORFB with a special attention for their implementation in industrial process. © 2022 Elsevier Lt

Electrochemical oxidation of 2,4-Dichlorophenoxyacetic acid: Analysis of by-products and improvement of the biodegradability

International audienceThe relevance of an electrochemical pre-treatment of 2,4-D prior to a biological process with the aim of increasing the biodegradability of a 2,4-D effluent was examined. A homemade flow-cell was used and electrolysis were performed at 1.6 V/SCE on a bare graphite felt. After a single pass through the cell, 96% elimination yield was obtained. After electrolysis, 34% of the initial dissolved organic carbon was mineralized, and COD decreased by 41%. The results were promising as the biodegradability of the effluent, evaluated through the BOD5/COD ratio, was improved from 0.04 to 0.25. In a second part, main degradation by-products were identified and quantified. Results showed that Chlorohydroquinone and 4-Chlorocatechol represented 35% and 10% of the fate of the initial 2,4-D, respectively. Other by-products such as 2,4-Dichlorophenol and glycolic acid were also detected. Finally, a mechanism scheme was proposed for the two main by-products

Nouveaux électrolytes pour les batteries aqueuses et organiques en flux

International audienceRôle des Batteries à flux : - stockage grande capacité et stabilité réseaux- répond aux variations journalières voire semi-hebdomadaire de la consommation électrique- limitation du parc de production électrique en répondant aux pics de consommationsEnjeux : dans la Stratégie Nationale Bas Carbone 2050, les scenarios d’électrification avec ou sans nucléaire nécessitent l’augmentation de la part de renouvelable et des moyens de stockage accrus. Principes : la capacité de la batterie est assurée par des électrolytes stockés dans des réservoirs, et qui sont amenés au niveau des électrodes par un système de pompage (flux).Objectifs : afin de substituer le vanadium utilisé dans les batteries à flux actuelles, il faut trouver des molécules organiques ayant : - un potentiel redox adapté pour délivrer une tension suffisante- une bonne stabilité électrochimique - solubles dans l’eau afin de pouvoir l’utiliser comme solvant électrolytique (coûts et risques incendies)- solubles à forte concentration pour densifier l’énergie stockée.Résultats : de nouveaux négolytes ont été synthétisés à partir de synthons biosourcés, leur diagramme électrochimique de Pourbaix modélisés, puis testés en système batterie. Valorisation : un brevet en cours d’écriture