Recent advances in the application of electron shuttles for improved electrochemical characterization of redox active species.

Kocur, C.

Dans les comptes rendus d’articles de la conférence: GeoNiagara 2021: 74th Canadian Geotechnical Conference; 14th joint with IAH-CNC

ABSTRACT: Electron shuttles are redox-active molecules that can reversibly undergo oxidation and reduction, allowing them to effectively transfer electrons between neighboring redox couples. Single and double electron transfer shuttles play an important role in cycling energy and aid in the efficiency of living systems. Numerous examples of naturally occurring and synthetically created shuttles have been described and characterized to date, including many interesting model systems. It has been recently demonstrated that potentiometric measurement (i.e., reduction potential or ORP) can be significantly improved in terms of electrode response by adding an electron shuttle compound to aqueous systems. In a geochemical system the electron shuttle acts as an intermediate redox couple, facilitating transfer from electron donors (i.e. minerals) to acceptors (i.e. electrode). This advancement has significant implications in the characterization of geochemical systems where reduction potential is difficult to interpret, leading to the assumption that reduction potential results are unreliable due to their variability. The novel application of mediated electrode techniques is necessary and shown to be effective when measuring reactive solid phases in aqueous systems that are sensitive to oxidation. This potentiometric technique has attracted interest for applications in the environmental remediation industry where reductive mineral phases can break down recalcitrant compounds abiotically through surface-mediated reactions. Although this abiotic breakdown process can be slow the contribution to natural attenuation is significant. The assumed relationship between reduction potential and contaminant degradation rate has been the rationale for making millions of field ORP measurements over the last 50 years. A growing body of experimental work - including the work presented here - is providing a more-quantitative understanding of that relationship and allowing for the study of groundwater and environmental systems with a new clarity.

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