redoxactive

Redox-active (often written as redoxactive) describes substances capable of undergoing oxidation–reduction (redox) reactions by changing their oxidation state. Such species can either donate electrons (be oxidized) or accept electrons (be reduced) under appropriate conditions, and in many cases the redox couple is electrochemically reversible with a definable standard potential.

Examples span inorganic, organic, and biological chemistry. Transition metal ions such as Fe2+/Fe3+ or Cu+/Cu2+ are redox-active, as are organic compounds like quinones, catechols, ferrocene, and viologens. Redox-active ligands and biomolecules such as NAD+/NADH, cytochromes, and iron–sulfur clusters also participate in electron transfer.

Applications are widespread in electrochemistry, materials science, and energy storage. Redox-active species function as mediators or as the active components of devices and processes. Redox-flow batteries rely on soluble redox-active species in liquid electrolytes to store and release electrical energy. Redox-active polymers and organic molecules underpin electrochromic devices, sensors, catalysis, and various catalytic cycles.

Key properties include the chemical and electrochemical stability of both oxidized and reduced forms, reversibility or quasi-reversibility of the redox process, and the kinetics of electron transfer and diffusion in the medium. Practical usefulness depends on the potential window, compatibility with solvents and electrolytes, and resistance to side reactions. The term redox-active encompasses a broad range of substances across chemistry, materials science, and biology that engage in redox chemistry under accessible conditions.