Abderrezak Hammouche

Study of a pH sensor with MnO2 and montmorillonite-based solid-state internal reference

Abstract The MnO 2 –montmorillonite composite mass has been investigated as an all-solid internal reference for pH sensors. Owing to its protonic conducting and cationic exchange features, protonated montmorillonite ensures a reversible cationic exchange (H + /Na + ) between the internal active mass and the glass membrane. The effect of the mixture composition and that of relative humidity inside the electrode have been studied. The electrode consisting of MnO 2 (75%), H-montmorillonite (20%) and acetylene black (5%) displays proper behavior at relative humidities greater than 0.8. The performances of such a sensor are comparable to those of a conventional glass electrode.

Investigation of hydration and protonic conductivity of H-montmorillonite

Abstract In this work, the hydration and protonic conductivity of H-montmorillonite were investigated. The hydration water state was characterized by DTA, TGA and XRD at different environmental relative humidities (RH). The results, showing good reproducibility and consistency, mark two distinguishable categories of hydration water: molecular H 2 O and H 3 O + species, those coordinated with the proton. The proportion of each was quantitatively analyzed. The electrical conductivity measured by impedance spectroscopy increases with RH from 10 −7 Ω −1 cm −1 at 0.2 RH up to 0.6×10 −2 Ω −1 cm −1 at 0.9 RH, at 20 °C. The mechanism of protonic conduction involved in H-montmorillonite is also discussed.

On the impedance of the gassing reactions in lead-acid batteries

Oxygen and hydrogen evolution reactions in flooded lead-acid batteries during float charging were studied by galvanostatic steady-state polarization and impedance spectroscopy techniques. Given the very low relaxation frequencies of such processes (between 2 and 0.05 mHz), impedance measurements needed to be extended to the ultra-low frequency domain. Investigation of their dynamic behavior provided a complete description of the porous character of the active zone. The steps involved in the reaction mechanisms are also discussed.