Unraveling Quinone Degradation Enables Stabilization Using Redox Helpers in Biological and Electrochemical Systems.

Quinones, known for their reversible redox properties, can serve as electron mediators in a wide range of contexts from electrochemical devices to biological electron transport chains. However, their practical use as redox components in aqueous environments can be significantly impaired by degradation issues. Here, we uncovered the molecular transformation mechanisms underpinning their degradation, the conditions that accelerate the degradation process, and simple strategies that can be applied to suppress their degradation. Specifically, the degradation of 2,6-dichlorobenzoquinone (DCBQ), a common electron mediator in photosynthesis and bioelectrochemistry research, was tracked under relevant operando conditions. The formation of semiquinone derivatives was identified as the key factor that drives side reactions with other molecules, including oxygen, generating deleterious radicals and decomposition pathways. These degradation pathways were accelerated under high pH conditions and in the presence of divalent cations. Guided by this mechanistic understanding, we demonstrate here that the addition of a redox helper, such as ferricyanide, establishes a redox equilibrium that effectively bypasses semiquinone buildup. This mechanism, explained by mathematical kinetics modeling, significantly prolongs the life of the quinone mediator across all tested conditions. This strategy unmasked the oxygen evolution rates of photosynthetic organisms and boosted the stability of mediated current outputs from a model living biophotoelectrochemical system, maintaining outputs at 73% higher levels over a 6 h operational period and increasing the effective half-life by 10-fold relative to control systems. These findings provide simple and effective strategies for rationally increasing the durability of quinone-based aqueous electrochemical systems, which form the essential foundation for many green energy technologies.