Selective insulation with poly(tetrafluoroethylene) of substrate electrodes for electrochemical background reduction in scanning electrochemical microscopy

We describe a wet process for the fabrication of poly-(tetrafluoroethylene) (PTFE)-covered electrodes in which arrays of holes (∼200 μm) are formed. The PTFE coating provides electrical insulation of most of the electrode surface with selected regions exposed for electrochemical experiments. The arrays of microholes can be controllably patterned and filled with precursor solutions using a piezoelectric dispenser. A micrometer spot of electrocatalyst is produced after reduction of the precursor. The application is tested for scanning electrochemical microscopy (SECM) in the tip generation-substrate collection (TG-SC) studies of electrocatalysts. The method is shown to reduce the substrate background currents that are included in the electrochemical signal read from the local perturbation induced with the SECM tip to the substrate in the TG-SC mode of SECM. This background current reduction is consistent with the decrease in the exposed area of the electrode. The general methodology for the fabrication of the substrate electrodes and two proof-of-concept applications in the TG-SC SECM modality are described.