Redox-active antioxidants enable highly stable bio-electrochemical systems.

Efficient interfacial electron transfer between electroactive microorganisms and electrodes underpins bio-electrochemical systems for energy, environmental, biosensors, and bioelectronic applications. Yet oxygen infiltration, unavoidable under practical conditions, and severely impairs performance. Here, we propose a strategy where plant-sourced antioxidants, such as fraxetin, with high thermodynamic stability are employed as electron shuttles. Electrochemical analysis and density functional theory revealed that fraxetin, unlike flavin mononucleotide, resists oxygen oxidation and sustains electron transfer under saturated dissolved oxygen conditions. Additionally, oxygen infiltration caused a 75% decrease in the current generated by Shewanella oneidensis MR-1 mediated by flavin mononucleotide, whereas the current mediated by fraxetin only decreased by 18%. This approach provided a fundamentally different and more practical solution than physical oxygen-exclusion methods, oxygen-tolerant ESs as a robust and versatile avenue to maintain efficient interfacial electron transfer in bio-electrochemical systems under actual environments.