Reoxidize

Reoxidize is a verb meaning to oxidize again or to restore a substance to a higher oxidation state after it has been reduced. In redox chemistry, reoxidation occurs when a reduced species loses electrons or reacts with an oxidant, returning to a more oxidized form. The term is used across chemistry, materials science, and biology to describe the regeneration of oxidized species or the formation of oxide from lower oxidation states.

In catalytic and industrial contexts, reoxidation is a key step in many cycles. Reduced metal centers are reoxidized by an oxidant to regenerate the active form of a catalyst, enabling continuous turnover. Common oxidants include molecular oxygen, hydrogen peroxide, and other oxidizing agents. Reoxidation helps sustain processes such as oxidation–reduction cycles in metal catalysts and in fuel cells where the catalyst must be restored to its higher oxidation state after electron transfer.

In materials science and semiconductor processing, reoxidation refers to forming or restoring an oxide layer. For example, reoxidation of silicon surfaces forms silicon dioxide (SiO2) layers used for surface passivation or as gate oxides in microelectronics. This can be performed by high-temperature dry or wet oxidation, with oxide thickness and quality controlled by temperature, time, and gas composition.

In biology, reoxidation describes the regeneration of oxidized cofactors. NADH is reoxidized to NAD+ during cellular respiration by the electron transport chain, allowing glycolysis and the Krebs cycle to continue. Similarly, FADH2 is reoxidized in closely coupled respiratory pathways.

See also oxidation state, redox, oxidation, oxide, and catalytic cycle.