The corrosion protection mechanism by polyaniline based coatings on metals is widely suggested to be due to the formation of an improved interfacial passive layer. However, it is argued against this that just an improved passive layer is not sufficient on metals such as iron and zinc for providing significant delay of cathodic delamination. Instead a significant inhibition of oxygen reduction is required, e.g. by an electronically insulating oxide. In this work results are presented providing proof for the formation of a highly electronically insulating and stable zinc oxide layer underneath an emeraldine base composite coating. It is shown how the Scanning Kelvin Probe (SKP) can be used to screen for such highly insulating oxide layers underneath coatings containing conducting polymer. (C) 2015 Elsevier Ltd. All rights reserved.