Abstract
In this study we report the exceptional potentiometric properties of pH microprobes made with nanostructured palladium hydride microelectrodes and demonstrate their application by monitoring pH variations resulting from a reaction confined in a porous medium. Their potentiometric response was found to be reproducible and stable over several hours but primarily Nernstian over a remarkably wide pH range, including alkaline conditions up to pH 14. Continuous operation was demonstrated by reloading hydrogen at regular intervals to maintain the correct hydride composition thereby alleviating the need for calibration. These properties were validated by detecting pH transients during the carbonation of Ca(OH)2 within a fibrous mesh. Experimental pHs recorded in situ were in excellent agreement with theoretical calculations for the CO2 partial pressures considered. Results also showed that the electrodes were sufficiently sensitive to differentiate between the formation of vaterite and calcite, two polymorphs of CaCO3. These nanostructured microelectrodes are uniquely suited to the determination of pH in highly alkaline solutions, particularly those arising from interfacial reactions at solid and porous surfaces and are thus highly appropriate as pH sensing tips in scanning electrochemical microscopy.
Highlights
Article with a proton specific ionophore.[28,29] Oesch et al.[30] proposed 11 neutral hydrogen ionophores to produce ion-selective electrodes for distinct pH ranges
The Pd must be loaded with hydrogen to a H to Pd ratio corresponding to the β to α phase transition of the Pd hydride (PdH).[32]
We have shown that the presence of oxygen affects the potentiometric response where, instead of delivering a potential proportional to pH, the electrodes produce a mixed potential related to pH and to the flux of oxygen toward the electrode as it reduces on the nanostructured Pd film.[39]
Summary
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