The local electrochemical activity of polytetrafluorethylene (PTFE) membranes coated with diamond-like carbon (DLC) was investigated using scanning electrochemical microscopy (SECM) During z-approach curves in the feedback mode of SECM unexpected local variations in the electron-transfer rate of [Fe(CN)(6)](3-/4-) and [Ru(NH3)(6)](3+/2+) were observed This local heterogeneity of the electrochemical activity was further evaluated in a system adapted from SO2 gas sensors In this case the Cu2+/+ couple is used as dissolved reversible redox system Reaction of SO2 with Cu2+ yields Cu which is re-oxidized at the DLC-coated PTFE membrane Gas permeation/tip-collection mode SECM experiments allowed visualizing the local pore distribution as sites where the SO2 is permeating through the membrane and hence formation of Cu+ takes place (C) 2010 Elsevier Ltd All rights reserved