An exoelectrogen normally refers to a bacterium or prokaryote that has the ability to transfer electrons extracellularly. This normally occurs via an external electron acceptor such as strong oxidizing agent in aqueous solution or a solid conductor/electron acceptor.
The electrons are thought to be transferred along pili (external cell structures used in conjugation and adhesion).
Cells are able to do this strictly in the absence of oxygen as during aerobic respiration a cell converts an energy source into ATP, carbon dioxide and water via glycolysis, the Krebs cycle and oxidative phosphorylation whereas in the absence of oxygen, water is not created and in its place electrons and hydrogen ions are formed.