Local reactivity of diamond-like carbon modified PTFE membranes used in SO2 sensors

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.