Scanning Electrochemical Cell Microscopy (SECCM) on Porous Electrode Materials: A Study on an Electrochemically Deposited Conducting Polymer Film

• SECCM is applied to porous conducting polymer electrodes • Electrolyte viscosity controls droplet wetting during SECCM measurements • Glycerol addition enables stable, spatially resolved electrochemical imaging • Micron- to millimetre-scale heterogeneities in polymer activity are revealed • Practical guidance is provided for SECCM on non-ideal porous electrodes High-resolution electrochemical imaging is critical for understanding structure–function relationships in porous electrode materials, where spatial heterogeneity strongly influences performance in applications such as catalysis, sensing, and energy storage. Scanning electrochemical cell microscopy (SECCM) offers unique advantages for probing such heterogeneities at the micro- to nanoscale, yet its application to porous electrode materials is often complicated by uncontrolled droplet cell wetting and transient electrolyte ingress into the porous structure during measurement. Herein, electrodeposited PEDOT:ClO₄ films are employed as a model porous conducting polymer (CP) electrode to systematically investigate wetting phenomena and strategies for their mitigation. By tuning electrolyte viscosity with glycerol as an additive, droplet cell ingress into the porous matrix of the CP can be suppressed, enabling more stable and reproducible SECCM mapping. This reveals a trade-off: while higher viscosity minimises droplet cell ingress, it also slows mass-transport, exemplified through investigating the oxidation of 1,1-ferrocenedimethanol in water/glycerol mixtures. Under optimised conditions (i.e., glycerol concentration, probe approach rate, potential and feedback threshold), SECCM uncovers pronounced heterogeneities in PEDOT:ClO₄ activity across both µm- and mm-length scales, which correlate with variations in film thickness, porosity, and/or morphology. These findings highlight the critical role of droplet cell dynamics in SECCM and demonstrate how careful optimisation of measurement parameters enables high-fidelity electrochemical mapping of highly porous materials. More broadly, this work provides a practical framework for applying SECCM to complex, non-ideal electrode surfaces, opening new opportunities to correlate local electrochemical activity with structural and chemical features across a wide range of porous functional materials.