FADH2 and NADH Defined. Flavin adenine dinucleotide, or FADH2, is a redox cofactor that is created during the Krebs cycle and utilized during the last part of respiration (the electron transport chain).Nicotinamide adenine dinucleotide, or NADH, is a similar compound and used more actively in the electron transport chain as well.asically, the NADH and FADH2 molecules are affixed with electrons and are transferred to the inner membrane of the mitochondria. They travel down the electron transport chain, releasing the electrons that they once had.