Poly(acrylonitrile) films were deposited electrochemically onto vitreous carbon electrodes from air-saturated acrylonitrile. Electrodeposition on gold was investigated with the use of an electrochemical quartz crystal microbalance (EQCM). It was found that the onset of deposition coincided with the reduction of dissolved oxygen at the electrode surface, indicating that the polymerisation reaction is initiated by the nucleophilic superoxide anion. The chemical composition of the film was confirmed by Raman spectroscopy. Such electrodeposited polymer films may have applications as polymer electrolytes for 3D microbattery applications.