Zero-Resistance Ammeter as a Tool To Study Redox-Mediated Reactions at Composite Interfaces

Redox-mediated systems may unlock new opportunities for electrochemical technologies, but the factors governing the performance of the off-electrode redox reactions are not well-understood, particularly for solid materials with multiple components. Motivated by its conventional use in the study of corrosion, we employ zero-resistance ammeter (ZRA) to quantify how the rate and potential of heterogeneous redox-mediated reactions are influenced by the presence of conductive additives or supports. Specifically, we study how a quinone-mediated oxidation of zinc (Zn) metal is influenced when a chemically inert disk electrode (e.g., glassy carbon) is electronically connected to a Zn disk. Using ZRA, we find that the pairing can undergo rapid transitions in potential and current as a function of the mediator concentration and mass transport to the electrically connected inert electrode. These dynamics are found to be consistent with mixed potential theory when comparing the ZRA responses to the characteristic behavior of the individual electrochemical half-reactions. The theory suggests that such transitions arise when the mediator flux outpaces the maximum Zn oxidation rate, forcing the mixed potential into a passivated regime with low reactivity. Overall, this work illustrates a combination of experimental apparatus and theoretical insights that enable insights into redox-mediated reactions occurring at multicomponent interfaces.