pH sensing in aqueous solutions using a MnO2 thin film electrodeposited on a glassy carbon electrode

International audienceAn electrolysis technique at a constant potential was used to develop a highly reproducible and fast elaboration method of adherent manganese dioxide thin films on a glassy carbon electrode from aqueous solutions containing sulfuric acid and manganese sulfate. The resulting films were found to have a nanostructured character presumably due rather to birnessite (delta-MnO2) than to gamma-MnO2, as suggested by their Raman and XRD signatures. They lead to modified electrodes that present an obvious although complex pH dependent potentiometric response. This sensor indeed showed a single slope non-Nernstian linear behaviour over the 1.5-12 pH range for increasing pH direction ("trace"), whereas a Nernstian two slopes linear behaviour was observed for decreasing pH direction ("re-trace"). Preliminary EIS experiments carried out at a pH value of 1.8 seem to reveal a sensitivity mechanism based on proton insertion process at least at highly acidic pH values

Synthèse électrochimique et caractérisation du dioxyde de manganèse nanostructuré (application au stockage d'énergie et comme capteur pH)

En premier lieu, la synthèse de poudres de MnO2 a été réalisée par CP à 80C sur Ti dans une solution aqueuse contenant MnSO4 et H2SO4. Les poudres de -MnO2 obtenues sont nanostructurées. Leur comportement électrochimique en milieu alcalin KOH (1 M) a été étudié par SIE après vieillissement par CV en utilisant une MEC. Les résultats ont montré i) que la réduction de MnO2 dans ce milieu se déroule en parallèle avec la réduction de O2 dissout et ii) que sa réactivité est influencée par le processus de vieillissement produit par CV ou fonction du temps d immersion. Dans une seconde partie, un procédé d'électrosynthèse par CA a été utilisé pour développer une méthode d'élaboration hautement reproductible et rapide de films minces de MnO2 adhérents sur une électrode de carbone vitreux à partir de solutions aqueuses contenant MnSO4 et H2SO4. Les films obtenus ont un caractère nanostructuré résultant plutôt de la birnessite ( -MnO2) que de -MnO2 révélé par Raman et DRX. En circuit ouvert, ils présentent une réponse potentiométrique dépendante du pH de façon évidente mais complexe. Le capteur pH ainsi produit a en effet montré un comportement non-Nernstien à une seule pente sur toute la gamme de pH 1,5-12 parcourue dans le sens croissant du pH ("trace"). En revanche, un comportement Nernstien à deux pentes a été observé pour une gamme de pH parcourue dans le sens décroissant ("re-trace"). Des expériences de SIE effectuées à une valeur de pH de 1,8 révèlent un mécanisme de sensibilité basé sur l'insertion de protons au moins aux valeurs de pH fortement acides. Ce mécanisme n est pas altéré par la présence des interférents étudiés (K+, Ca2+, Cl- et Li+) à l exception de Fe2+.In a first part, the synthesis of MnO2 powders was carried out by CP at 80 C on a titanium electrode in an aqueous solution containing MnSO4 and H2SO4. The -MnO2 powders obtained are nanostructured. The electrochemical behavior of such MnO2 powders in alkaline KOH (1 M) was investigated by EIS after aging of these powders by CV and EIS using the CME. The results showed that i) the reduction of MnO2 in this medium occurs in parallel with the reduction of dissolved oxygen and ii) that its reactivity is influenced by the aging of these powders produced by CV or function of immersion time. In a second part, an electrodeposition method based on chronoamperometry was used to develop a highly reproducible and fast elaboration method of adherent manganese dioxide thin films on a glassy carbon electrode from aqueous solutions containing MnSO4 and H2SO4. The resulting films were found to have a nanostructured character presumably due rather to birnessite ( -MnO2) than to -MnO2, as suggested by their Raman and XRD signatures. They lead to modified electrodes that present an obvious although complex pH dependent potentiometric response when used in open circuit conditions. This sensor indeed showed a single slope non-Nernstian behaviour over the 1.5-12 pH range for increasing pH direction ( trace ) whereas a two slope Nernstian behaviour was observed for decreasing pH direction ( re-trace ). EIS experiments carried out at a pH value of 1.8 reveal a sensitivity mechanism based on a proton insertion process at least at highly acidic pH values. This mechanism is not altered by the presence of the studied interferents (K+, Ca2+, Cl- and Li+) with the exception of Fe2+.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Chemical synthesis of hollow sea urchin like nanostructured polypyrrole particles through a core-shell redox mechanism using a MnO2 powder as oxidizing agent and sacrificial nanostructured template

International audienceHollow sea urchin shaped nanostructured polypyrrole powder was successfully synthesized chemically in an acidic medium through a core-shell redox mechanism by using a nanostructured MnO2 powder as oxidizing agent and sacrificial template simultaneously. The morphology and the structure of MnO2 powder based reactant and produced polypyrrole powder were characterized respectively by using FEG-SEM, TEM, EDX and XRD techniques, which led us to demonstrate clearly the formation of hollow and open microparticles of polypyrrole with the presence of nanotubes on their surface. Nanostructured polypyrrole powder was found to be rather amorphous even though the shape of the polypyrrole particles was induced by the crystalline and nanostructured sea urchin shaped MnO2 powder on which they grew. In addition, neither MnO2 nor any manganese based species were found within the produced polypyrrole powder, which ruled out the production of composite materials. Moreover, Raman technique showed that the synthesized PPy powder was produced in the oxidized and thus conducting state. It actually possesses a 0.31 doping level and a 0.05 S cm−1 conductivity, as shown by XPS and impedance spectroscopy measurements respectively. Cyclic voltammetry and UV-vis spectroscopy studies allowed us to identify the oxidation mechanism of pyrrole by our MnO2 powder through the detection of soluble Mn2+ cations as reaction products isolated after filtration of the reaction medium