A corrosion and electrodeposition study of a Zn electrode in 5.3 M KOH, used as a model system for the anode of a secondary Zn–air battery, was performed by means of electrochemical and spectroelectrochemical techniques. The formation of a zinc oxide passive film and its cathodic removal were monitored by electroreflectance spectroscopy, spectroellipsometry and optical second harmonic generation. A dynamic optical model of the growth pathway, morphology and failure modes of the interfacial Zn oxide films was proposed to rationalise the electrokinetics of the secondary battery anode. Some experiments were performed in the absence and in the presence of polyethylene glycol. In situ spectroscopy confirmed and placed on a molecular basis the well-known formation of more compact and uniform electrodeposits crucial for secondary batteries.