[en] Highlights: • VO²⁺ electro-oxidation in ‘Liquid-Solid’ suspensions for vanadium redox batteries. • Effect of the stirring of a V^(IV) sulphate suspension on the oxidation of the VO²⁺. • Influence of inert glass beads on the mass transfer of the VO²⁺in the posolyte. • Effect of VOSO₄ solid particles on the current of its oxidation. • Electronic percolation by ketjen black as an enhancer for the VO²⁺ oxidation. -- Abstract: This study considers the effect of mechanical stirring of V^(IV) solutions and of the presence of solid suspensions on the $V{O}_{\left(aq\right)}^{2+}$ oxidation current measured on a graphite electrode, with the objective of a better understanding of the electrochemical reactions taking place in a vanadium redox flow battery (VRFB). Our research question was to determine whether the presence of different kind of solid particles (inert glass spheres, VOSO₄ powder and nanometric ketjen black (KB)) could be beneficial to the electrochemical performances of the VRFB. The experimental method consisted in measuring the anodic limiting current of a VOSO₄-H₂SO₄-H₂O solution on a rotating graphite cylinder, by linear sweep voltammetry. In the absence of solid particles, we show that the mass transfer coefficient dependence against the angular velocity of both the electrode and an additional stirrer obey to a power law (k = f(ω^γ)) with an exponent γ found to be lower than the theoretical value. The beneficial effect on the mass transfer of VO²⁺ at the interface observed with low fraction of inert glass particles dramatically disappears as the spheres fraction increases. This is attributed to the decrease of the available free volume for the diffusion. When the solid consists of VOSO₄ particles, the anodic current decreases as the mass fraction of the solid increases, which demonstrates the absence of any significant beneficial effect of the dissolution of the VOSO₄ grains in the diffusion layer. Conversely, an important increase (~ 40%) of the oxidation current is observed when KB particles were introduced at low fractions (0.15%) in the bulk, thanks to the electronic percolation created by the KB. However, this beneficial effect disappears for higher mass fraction of both vanadium or KB solid particles, because of the destruction of the aggregates enabling the electron to be driven into the bulk.

[en] This work focuses on kinetic studies of anisole and triethylamine trihydrofluoride (fluorinating agent) on platinum electrode and acetonitrile as solvent, in order to get a better understanding of their anodic behavior. Results show that both compounds can be oxidized and some kinetic parameters are calculated: the diffusion coefficient within the working media, the anodic electronic transfer coefficient and the apparent intrinsic heterogeneous electronic transfer constant. An unusual variation of these parameters occurs within the chosen reaction conditions, particularly by varying the triethylamine trihydrofluoride concentration. Preliminary experiments for anodic fluorination of dimethoxy ethane (DME) and anisole were carried out and even if results show a possible electrofluorination for the DME (classically used as solvent), there is no fluorination of anisole when electrochemical microreactor was used.

[en] Highlights: • Sonoelectrochemical production of metallic iron (micro/nano)particles. • Effect of ultrasound on mass transport and iron electrodeposit dispersion. • Electrodes characterization by contact angle and roughness measurements. • Effect of adhesion and interfacial tension on morphology of electrodeposited iron. - Abstract: This study relates the sonoelectrochemical production of metallic particles and nanoparticles. The emphasis is on the influence of electrode material and roughness on the morphology of iron electrodeposits and their dispersion from the electrode by ultrasonification. Ultrasonification is either applied during cyclic voltammetries with solution stirring or after galvanostatic iron electrodeposition; no dispersion was observed when using a gold electrode, whereas dispersion was always observed when using vitreous carbon (VC) substrates. Scanning Electron Microscopy (SEM) imaging of the electrodeposits shows higher iron coverage on gold than on VC electrodes. Iron spreads more on gold than on VC. The values of both the interfacial energy of the iron/electrode interface and the work of adhesion of iron on the electrode are in agreement with the previous observations. Dispersion kinetics on VC were found to be dependent on the electrode surface roughness. Results suggest that dispersion follows a first order kinetics, which is coherent with the constant action of cavitation bubbles in the vicinity of the electrode surface. Enhancement of mass-transfer by ultrasound has also been observed.