Analytical performances of a flow electrochemical sensor for preconcentration and stripping voltammetry of metal ions

International audienc

Development of a novel flow sensor for copper trace analysis by electrochemical reduction of 4-methoxybenzene diazonium salt

Due to the rapidity and the effectiveness of the method, the reduction of diazonium salts has been widely used to functionalize electrodes for sensor applications. However, the resulting organic film usually designed to provide complexing capabilities for the species to be determined could affect the sensor properties. The electrochemical reduction of 4-methoxybenzene diazonium salt on graphite felt that leads to the formation of an organic film with unexpected high affinity for copper ions is presented. This property combined with a flow electrochemical system led us to achieve a sensitive sensor for copper detection, with good selectivity towards some common interferent ions. Keywords: Sensor, Graphite felt, Diazonium salts, Copper, Flo

Addition of weak acids in electrolytes to prevent osmosis in aqueous organic redox flow batteries

International audienceWater transfer issues related to unbalanced ionic strengths in aqueous organic redox flow batteries (AORFBs) are often overlooked. In this work, a simple strategy based on the addition of a weak acid in the negolyte was studied to prevent osmosis in AORFBs. Ferrocyanide [Fe(CN)6]4- and anthraquinone-2,7-disulfonic acid disodium salt (AQDS) were used as positive and negative active materials, respectively, and aspartic acid was chosen as a weak acid. The addition of acid aspartic as well as strong bases such as KOH, NaOH or LiOH to reach the complete deprotonation of the acid and the desired pH contributes to balancing the cations total concentration of both compartments. Battery cycling experiments were carried out with 0.2 – 0.3 M AQDS and 0.4 – 0.6 M [Fe(CN)6]4−. When no weak acid was used, osmosis quickly leading to a shortage of negative electrolyte was observed, while in presence of aspartic acid both electrolyte volumes remained unchanged during the time of experiment. © 202

Feasibility of combined electrochemical and biological treatment for tylosin removal

The purpose of this work was to examine biodegradability improvement of tylosin - containing solutions after an electrochemical pre-treatment, since about 70% of the applied drugs are not metabolized and hence can be found in wastewaters.  Cyclic voltammetry with nickel electrode revealed a significant electrochemical activity of tylosin, on nickel electrode. Electrochemical treatment was, therefore, performed in a home-made flow cell. Optimal conditions led to more than 95% conversion yield of tylosine, in oxidation, using alkaline media as supporting electrolyte. TOC analyses of the electrolyzed solution revealed that the level of mineralization remained low, underlying the interest of a combined electrochemical and biological treatment. The biodegradability, based on the BOD5 on COD ratio, increased from 0, for untreated tylosin, to 0.43 for electrolyzed tylosin at 0.55 V/ESC

A new hydroxyanthraquinone derivative with a low and reversible capacity fading process as negolyte in alkaline aqueous redox flow batteries

International audience2,3-dihydroxylated anthraquinone (2,3-DHAQ) is evaluated for the first time in a redox flow battery. This compound exhibits a good solubility in alkaline media (0.7 M in KOH at pH andgt; 13.5) and a suitable potential (−0.85 V vs Ag/AgCl) leading to a 1.11 V theoretical open circuit voltage at 50% state of charge with potassium ferrocyanide as posolyte. It is implemented in a 25 cm2 cell during 180 cycles with a capacity fading of 0.022% per cycle and a current efficiency higher than 99.7%. Owing to its high solubility, an initial energy density up to 17 Wh L−1 (7.7 Wh L−1 when both posolyte and negolyte are considered) is obtained. 2,3-DHAQ exhibits a good chemical stability compared with other dihydroxyanthraquinone (around 0.1% per cycle). After more than 3000 cycles, 2,3-DHAQ is observed as the main product, showing its high chemical stability. Moreover, the capacity fading process is reversible since changing the discharge conditions allows a full recovery of the initial capacity. This opens up new perspectives as the capacity loss is often used to evaluate the relevance of new molecules. A wider range of active materials in AORFB can be considered if the capacity fading they exhibit can be reversible. © 2022 Elsevier B.V

New porous bismuth electrode material with high surface area

International audienceBismuth electrodes are particularly interesting owing to their high hydrogen evolution overpotential and electrocatalytic activity. In this work, a novel porous bismuth electrode was prepared via an electrochemical deposition of bismuth on a porous graphite felt of high specific surface area, employing bismuth(III) oxide as reactant and a flow electrochemical cell as reactor. A solubility up to 1 mol L −1 of bismuth was obtained in basic medium using a suitable complexing agent. We solved the problems linked to the heterogeneous potential distribution in the 3D porous structure and to the formation of dendritic excrescences that led to mechanically fragile material by using a suitable flow electrochemical cell, a periodically changing current with short on-pulses and long off-pulses and by limiting the electrodeposition of Bi on the external surfaces of the felt due to diffusion. A Bi-modified electrode with high specific surface area and low bulk density was achieved using this method